Immune checkpoint blockade in the treatment of malignant tumor: current statue and future strategies.

Background

Immunotherapy with immune checkpoint inhibitors (ICIs) has modified the therapeutic strategy to malignant tumors and emerge as a rapidly developing area of research. It primarily changes the body’s immune system and enhances anti-tumor immunity, inhibiting and killing tumor cells. In the late nineteenth century, people first tried to use the immune system to treat cancer [ 1 ]. However, even after nearly a hundred years of research, the mechanism of the immune system to identify and fight cancer is still very controversial [ 2 ]. Today, after almost 120 years of basic research in immunology, molecular biology, virology, cell biology, and structural biology, we have further understood the role of the immune system in the regulation of tumors and the strategy of tumor cells to avoid monitoring, and subsequently decided to use immunotherapy as a promising technique to deal with the dynamic and complicated interplay between cancers and immunity [ 3 , 4 ]. To defend the host from any potential threats, the immune system can do considerable damage to harmful invaders and effectively eliminate most pathological microorganisms and toxic substances. Still, the immune system must accomplish this task by weakening the checkpoint pathway of the immune response based on maintaining healthy cells and preserving its own tolerance [ 5 ].

Currently, with continuous in-depth research on the mechanism of tumor immune escape, ICIs have proven better clinical effects in the treatment of a variety of solid tumors and have become a landmark event in the history of cancer treatment. The mechanism of action of PD-1/PD-L1 in tumor immune escape and its application in tumor immunotherapy are a hot topic in current oncology research. In traditional organisms, the PD-1/PD-L1 signaling pathway plays a pivotal role in maintaining immune tolerance. In the tumorigenesis, the PD-1/PD-L1 signaling pathway can inhibit the immune response of T cells and promote the occurrence of tumor immune escape. Anti-PD-1/PD-L1 therapy has significant clinical effects, preventing the progression of advanced metastatic tumors and improving the progression the survival rate of patients to a certain extent. By the end of December 2018, the FDA-approved tumor immunotherapeutics are pembrolizumab, nivolumab, atezolizumab, avelumab, and durvalumab. Simultaneously, a range of malignant tumors has benefited from anti-PD-1/PD-L1 therapy, such as melanoma, non-small-cell lung cancer (NSCLC), small cell lung cancer (SCLC), renal cell carcinoma (RCC), classical Hodgkin lymphoma (cHL), head and neck squamous cell carcinoma (HNSCC), colorectal cancer (CRC), hepatocellular carcinoma (HCC), primary mediastinal large B-cell lymphoma (PMLBCL), Merkel cell carcinoma (MCC), etc.

However, studies [ 6 ] found that the inhibition rate of PD-1/PD-L1 inhibitors on solid tumors is solely 10–40%, which indicates that a large portion of patients can not benefit from immunotherapy. Hence, exploring accurate biomarkers for therapeutic efficacy and screening patients who benefit from PD-1/PD-L1 inhibitor therapy have become first-rate problems in the field of immunotherapy for malignant tumors. This article reviews the mechanism of action of PD-1/PD-L1 inhibitors, the application of PD-1/PD-L1 inhibitors in various malignancies and their efficacy biomarkers, as well as predictive markers of irAEs.

Rationale of anti-PD-1/PD-L1 antibody therapy

PD-1 is a crucial immunosuppressive molecule obtained in apoptotic T-cell hybridomas. It is a type I transmembrane glycoprotein consisting of 268 amino acids with a relative molecular mass of 55,000–60,000. Its extracellular domain shares 21–33% sequence homology with CTLA-4, CD28, and ICOS [ 7 , 8 ]. In the early 1990s, the American biologist Ishida et al. first discovered PD-1 when separating the transiently expressed genes involved in the programmed cell death process in apoptosis-induced mouse T cells. In typical organisms, PD-L1, on the surface of cells, can inhibit the function of lymphocytes and induce the apoptosis of activated lymphocytes after being combined with PD-1 on the surface of lymphocytes. The activation of the PD-1/PD-L1 signaling pathway can reduce immune response damage to the surrounding tissues and avoid autoimmune diseases [ 9 ]. Additionally, activation of this pathway leads to the binding of PD-L1 expressed by tumor cells to PD-1 on the surface of tumor-infiltrating lymphocytes (TILs), weakening the immune role of T cells in the local tumor microenvironment. This mediates the occurrence of tumor immune escape and promotes tumor progression [ 10 ].

Studies [ 11 ] have showed that PD-L1 can be selectively and highly expressed on the surface of cancer cells, activating the PD-1/PD-L1 downstream pathway by binding specifically to PD-1 and delivering negative regulatory signals, leading to apoptosis of activated T cells and loss of immunologic activity (illustrated in Fig. 1 ). Therefore, the PD-1/PD-L1 pathway is a key molecule that mediates immune escape in the tumor microenvironment [ 12 ]. Targeted blockade of the PD-1/PD-L1 signaling pathway can relieve the inhibition of T lymphocytes by tumor cells, and enhance the recognition and killing effect of the immune system on foreign tumor cells. It is believed that with the deepening of research, scientists will thoroughly clarify the role and mechanism of PD-1 in the body’s immune regulation and tumor immunotherapy. Fig. 1 Tumor cells inhibit T cell activation by expressing PD-L1 on their cell surface, and PD-1/PD-L1 inhibitors reactivate T cells by specifically binding to PD-1/PD-L1

Current clinical practice: immunotherapy approaches and checkpoint inhibition

ICIs therapy exerts antitumor effects by inhibiting the activity of immune checkpoints, releasing the “immune brake” in the tumor microenvironment and reactivating the immune response of T cells to tumors. Currently, there are two main categories of ICIs that block the PD-1/PD-L1 pathway: monoclonal antibodies against PD-1, such as nivolumab (Opdivo) and pembrolizumab (Keytruda), and monoclonal antibodies against PD-L1, such as atezolizumab (Tecentri), avelumab (Bavencio), and durvalumab (Imfinzi). Here, we review the registration trials that have successfully led to FDA approval and the commercialization of PD-1 and PD-L1 inhibitors.

Pembrolizumab (Keytruda)

Pembrolizumab is a potent, highly selective, human-derived IgG4-kappa monoclonal antibody with potential immune checkpoint inhibitory activity and anti-tumor activity. By blocking the interaction between PD-1 and PD-L1, it helps tumors get away the immune system. It is approved for use in metastatic or unresectable melanoma, metastatic NSCLC, advanced UC, recurrent or metastatic HNSCC, cHL, HCC, CRC, malignant pleural mesothelioma (PM), MCC, MSI-H/d-MMR adult and pediatric solid tumors, advanced cervical cancer (CC), gastric or gastroesophageal junction adenocarcinoma (GEJA), and PMBCL. Table 1 lists all clinical trials of pembrolizumab for the treatment of patients with malignant tumors. Table 1 Summary of pembrolizumab trials in malignant cancer Pathology Trial Phase No of. patients Treatment mPFS (months) mOS (months) ORR (%) Other outcomes Melanoma KEYNOTE-006 III 834 Pembrolizumab vs. Ipilimumab 5.5 vs. 2.8 – 34 vs. 12 – NSCLC KEYNOTE-010 II – Pembrolizumab vs. Docetaxel 5.2 vs. 4.1 17.3 vs. 8.2 – KEYNOTE-189 III 616 Pembrolizumab + Pemetrexed and platinum vs. Placebo 8.8 vs. 4.9 – 62.9 vs. 49.4 – HNSCC KEYNOTE-012 Ib 60 Pembrolizumab – – 18 – UC KEYNOTE-052 II 370 Pembrolizumab 2.0 – 24 CR: 5%; DCR: 47% KEYNOTE-045 III 542 Pembrolizumab vs. Paclitaxel and vinflunine – 10.3 vs. 7.4 21.1 vs. 11.4 – cHL KEYNOTE-087 II 210 Pembrolizumab 72.4%* 99.5%* 69 CR: 22.4% PMBCL KEYNOTE-170 II 49 Pembrolizumab – 62%* 41 CR: 14%; PR: 28% DLBCL Frigault et al II 29 pembrolizumab 59%* 73%* – MM Badros et al II 48 Pembrolizumab + Pomalidomide and Dexamethasone – – 60 CR: 8%; PR: 19% CC KEYNOTE-028 Ib 24 Pembrolizumab 2.0 11.0 17 DCR: 30% KEYNOTE-158 II 98 Pembrolizumab 2.1 9.4 13.3 DCR: 30.6% Ovarian cancer KEYNOTE-028 II 26 Pembrolizumab 1.9 13.8 11.5 SD: 26.9% Endometrial cancer Makker et al II 23 Pembrolizumab + lenvatinib – – 39.6 DCR: 86.8% TNBC KEYNOTE-086 II – Pembrolizumab 2.0 9.0 5.3 DCR: 7.6% MSI-H and dMMR S KEYNOTE-164 II 63 Pembrolizumab – – 26.2 – PM Cedrés et al Ib 25 Pembrolizumab – – 28 SD: 48%; DCR: 76% GEJA KEYNOTE-059 II 143 Pembrolizumab – – 13.3 DOR: 16.3 months CRC Ribas et al Ib – Pembrolizumab + Oncolytic virus – – 62 CR: 33% HCC KEYNOTE-224 II 104 Pembrolizumab – 12.9 17 CR: 1%; PR: 16%; DCR: 60% NSCLC: non-small cell lung cancer; HNSCC: head and neck squamous cell carcinoma; UC: urothelium carcinoma; cHL: classic Hodgkin lymphoma; PMBCL: primary mediastinal large B-cell lymphoma; DLBCL: diffuse large B cell lymphoma; MM: multiple myeloma; CC: cervical cancer; TNBC: triple-negative breast cancer; MSI-H and dMMRS: unresectable or metastatic solid tumors, including colorectal, endometrial and other gastrointestinal cancers; PM: pleural mesothelioma; GEJA: gastric or gastroesophageal junction adenocarcinoma; CRC: colorectal cancer; HCC: hepatocellular carcinoma; mPFS: median progression-free survival; mOS: median overall survival; ORR: objective response rate; CRR: complete response; PRR: partial remission; DCR: disease control rate; DOR: duration of response; SD: stable disease; *: PFS or OS rate. –: Not available

In the current setting, data from a single-center, open-label, phase III trial [ 13 , 14 ] (KEYNOTE-006) of pembrolizumab or ipilimumab monotherapy in the treatment of advanced or unresectable melanoma was recently published. The primary endpoint of median progression-free survival (mPFS) and objective response rate (ORR) was met and favored of the pembrolizumab group: 5.5 vs. 2.8 months, 34% vs. 12%. The benefit of combination ICI with chemotherapy in the first-line setting of NSCLC is well established and has been studied in phase III trials [ 15 ] (KEYNOTE-189). KEYNOTE-189 investigated the addition of pembrolizumab to pemetrexed and platinum as first-line treatment of NSCLC. Eligible patients received chemotherapy plus either pembrolizumab or placebo, followed by maintenance. The addition of pembrolizumab improved mPFS and ORR: 8.8 vs. 4.9 months, 69.2% vs. 49.4%. A phase Ib, placebo-controlled, randomized KEYNOTE-012 [ 16 ], tested the safety and efficacy of pembrolizumab treatment with any level of PD-L1 expression (at least 1% of tumor cells or stroma positive by immunohistochemistry for PD-L1) in the HNSCC. The results showed an acceptable safety profile for the drug, with an ORR of 18% for all patients and 25% vs. 14% for HPV-positive and negative patients. This suggests that patients can benefit regardless of HPV infection status. The efficacy of combining pembrolizumab with or without paclitaxel and vincristine with chemotherapy was investigated in the phase II trial KEYNOTE-052 [ 17 ] and phase III KEYNOTE-045 [ 18 ] in the treatment of UC. During the phase II trial KEYNOTE-052, the mPFS and ORR in the total population were 2.0 months and 29%. During the phase II trial KEYNOTE-052, the total mPFS and ORR were 2.0 months and 29%. The disease control rate (DCR) was 47% among the responding patients and the complete response (CR) rate was 5%. Additionally, in the phase III KEYNOTE-045, the median overall survival (mOS) was 10.3 months in the pembrolizumab group and 7.4 months in the chemotherapy group, with ORRs of 21.1% and 11.4% in the two arms, respectively. Based on these results, FDA’s accelerated approval was granted.

Information from a single-arm, open-label, phase II trial (KEYNOTE-087) [ 19 ] of pembrolizumab monotherapy for cHL was recently published. This trial was divided into three cohort groups: cohort 1 was formed by cHL patients who progressed after autologous stem cell transplantation (ASCT) and subsequent medication of brentuximab vedotin (BV) treatment, cohort 2 consisted of cHL patients who progressed after chemotherapy and BV treatment, and cohort 3 was cHL patients who had received ASCT but without BV. All adult patients received pembrolizumab. The total ORR was 69% (73.9%, 64.2% and 70.0%, respectively). The PFS and OS rates were 72.4% and 99.5%. Moreover, the benefit of combination pembrolizumab with chemotherapy in the first-line setting of non-Hodgkin lymphoma (NHL) is well established and has been studied in three phase II trials. In study KEYNOTE-170 [ 20 ], PMBCL patients were treated with pembrolizumab monotherapy and the OS rate had been met and was in favor of the pembrolizumab group (62%). Notedly, pembrolizumab delivered a high response rate with an ORR of 41%, including 14% CR and 28% PR. Frigault et al. ( NCT02362997 ) [ 21 ] evaluated the efficacy and safety of consolidation remedy with pembrolizumab in sufferers with relapsed or refractory DLBCL. The results in the 29 patients indicated that the PFS and OS had been met (59% and 73%). Similarly, Badros et al. also assessed the phase II trial ( NCT02289222 ) [ 22 ], where 48 patients with relapsed or refractory MM were treated with pembrolizumab combination with pomalidomide and dexamethasone. The primary endpoints of ORR validated statistical significance in favor of the pembrolizumab plus chemotherapy cohort (60%) with CR in 8% and PR in 19% of the patients. These results prompted the solely approval of pembrolizumab for hematological malignancy.

Furthermore, the safety and effectiveness of pembrolizumab in gynecologic oncology have also been demonstrated. The efficacy of pembrolizumab alone for first-line treatment of CC was presented from the randomized phase II KEYNOTE-158 trial [ 23 ] and phase Ib KEYNOTE-028 trial [ 24 ]. In phase II KEYNOTE-158 trial, pembrolizumab was approved for the treatment of patients with relapsed or metastatic CC whose disease progressed during or after chemotherapy, with 83% of patients positive for PD-L1 expression. Similarly, significant differences in mPFS, mOS, ORR, and DCR were observed (2.1 months, 9.4 months, 13.3%, and 30.6%, respectively). In the phase Ib KEYNOTE-028 trial, a total of 24 patients were treated with pembrolizumab: mPFS was 2.0 months, mOS was 11.0 months, ORR reached 17%, and DCR was 30%. A phase II KEYNOTE-028 trial [ 25 ] demonstrated pembrolizumab improved both mPFS (1.9 months) and mOS (13.8 months) in the therapy of ovarian cancer. Simultaneously, 26.9% of patients reached stable disease (SD) and the ORR reached 11.5%. Makker et al. ( NCT02501096 ) [ 26 ] explored the efficacy of pembrolizumab in aggregate with lenvatinib in advanced endometrial cancer. The principal endpoint of ORR and DCR had been met: 39.6% and 86.8%. Besides, the phase II KEYNOTE-086 trial [ 27 ] confirmed that pembrolizumab could benefit TNBC patients more without other treatment, with an ORR of 5.3%, DCR of 7.6%, mPFS of 2 months, and mOS of 9 months, respectively.

In May 2017, FDA authorized the use of pembrolizumab for patients with unresectable or metastatic solid tumors bearing either of these two biomarkers referred to as microsatellite instability-high (MSI-H) or mismatch repair deficient (d-MMR) based on the phase II KEYNOTE-158 trial ( https://clinicaltrials.gov/ct2/show/NCT02628067 ). The ORR was reported as 42.9%. In June 2015, pembrolizumab was accredited to treat patients with malignant PM based on the phase Ib trial [ 28 ]. The ORR reached 28%, with 48% of SD and 76% of DCR. A phase II KEYNOTE-059 trial [ 29 ] available to date in patients with advanced GEJA indicates the positive effects of pembrolizumab. The ORR reached 13.3% and DOR was 16.3 months. As of now, a single-arm, phase Ib trial [ 30 ] demonstrated the safety of presurgical and postsurgical pembrolizumab plus oncolytic virus in a set of advanced CRC patients. The ORR reached 62%, including 33% CR. Also, an increase in CD8 + T cell density and upregulation of PD-L1 expression was observed after treatment, suggesting that lysing viruses can improve the tumor microenvironment and have a synergistic effect with ICIs. At last, in November 2018, the FDA approved pembrolizumab for patients with sorafenib or sorafenib-intolerant HCC based on the single-arm multicenter phase II KEYNOTE-224 trial [ 31 ]. The results confirmed an ORR of 17%, DCR of 60%, mOS of 12.9 months, CR rate of approximately 1%, and PR rate of 16%.

Nivolumab (Opdivo)

The humanized monoclonal IgG4 anti-PD-1 antibody nivolumab is approved for the treatment of metastatic melanoma, metastatic NSCLC, UC, advanced RCC, HNSCC, cHL, CRC, ovarian cancer, FL (follicular lymphoma), AML (acute myeloid leukemia), CLL (chronic lymphocytic leukemia), DLBCL, and HCC. Nivolumab works by binding to the PD-1 receptor and blocking its interaction with PD-L1 and PD-L2, thereby releasing the PD-1 pathway-mediated immunosuppressive effects on tumor cells. Completed trials using nivolumab to target malignant tumors are listed in Table 2 . Table 2 Summary of nivolumab trials in malignant cancer Pathology Trial Phase No of. patients Treatment mPFS (months) mOS (months) ORR (%) Other outcomes Melanoma CheckMate-037 III 370 Nivolumab vs. ICC – – 31.7 vs. 10.6 – CheckMate-067 III 945 Nivolumab + ipilimumab vs. Monotherapy (Ipilimumab or Nivolumab) 11.5 vs. 6.9 vs. 2.9 – 50 vs. 40 vs. 14 – NSCLC CheckMate-017 III 272 Nivolumab vs. Docetaxel – 9.2 vs. 6.0 – HNSCC CheckMate-141 III 361 Nivolumab vs. ICC – 7.5 vs. 5.1 13.3 vs. 5.8 – UC CheckMate-275 II 270 Nivolumab 2.0 – 19.6 – cHL CheckMate-205 II 243 Nivolumab 14.7 – 69 CR: 16%; DOR: 16.6 months FL Lesokhin et al Ib – Nivolumab – – 40 – DLBCL Cao et al – 11 Nivolumab + Anti-CD19 CAR-T cell therapy – – 81.81 CR: 45.45% AML Daver et al II 70 Nivolumab + Azacitidine vs. Demethylation medication – 6.3 vs. 4.6 33 vs. 20 CR: 8%; PR: 19% CLL Jain et al II – Nivolumab + Ibrutinib – – 43 – Ovarian cancer Hamanishi et al II 20 Nivolumab 3.5 20.0 15 DCR: 45% RCC CheckMate-214 III 847 Nivolumab + Ipilimumab vs. Sunitinib 11.6 vs. 8.4 75%* vs. 60%* 42 vs. 27 CR: 9% vs. 1% NSCLC: non-small cell lung cancer; HNSCC: head and neck squamous cell carcinoma; UC: urothelium carcinoma; cHL: classic Hodgkin lymphoma; FL: follicular lymphoma; DLBCL: diffuse large B cell lymphoma; AML: acute myeloid leukemia; CLL: chronic lymphocytic leukemia; RCC: renal cell carcinoma; HCC: hepatocellular carcinoma; mPFS: median progression-free survival; mOS: median overall survival; ORR: objective response rate; CR: complete response; PR: partial remission; DCR: disease control rate; DOR: duration of response; ICC: Investigator's choice of chemotherapy; *: PFS or OS rate. –: Not available

In the adjuvant setting, data from a multi-Center, open-label, phase III trial (CheckMate-037) [ 11 ] of nivolumab or investigator’s choice of chemotherapy in the treatment of advanced or unresectable melanoma was recently published. The primary endpoint of ORR had been met and favored the pembrolizumab group: 31.7% vs. 10.6%. Notably, the efficacy of combining nivolumab with ipilimumab or monotherapy was investigated in the phase III trial CheckMate-067 [ 32 ] which included 945 patients in total. The primary endpoint of mPFS and ORR was met and favored of combining nivolumab with ipilimumab group: 11.5 vs. 6.9 vs. 2.9 months, 50% vs. 40% vs. 14%. In March 2015, nivolumab was approved for the treatment of NSCLC based on the phase III CheckMate-017 trial [ 33 ], whose patients were randomly assigned to the nivolumab arm and the docetaxel arm. The primary endpoint of mOS was safety and favor of the nivolumab group: 9.2 vs. 6.0 months. In November 2016, nivolumab became the first FDA-approved immunotherapy for the treatment of relapsed or metastatic HNSCC based on phase III randomized trial (CheckMate-141) [ 34 ]. The nivolumab group had a 30% lower risk of death than the control group (investigator’s choice of chemotherapy). The mOS and ORR in the two arms had been met and nivolumab was more beneficial to patients (7.5 vs. 5.1 months, 13.3% vs. 5.8%, respectively). In February 2017, The FDA approved nivolumab for locally advanced or metastatic UC following the results from CheckMate-275 [ 35 ]. The overall ORR was 19.6% in patients with high PD-L1 expression (28.4% for PD-L1 ≥ 5%, 23.8% for PD-L1 ≥ 1%, and 16.1% for PD-L1 ˂ 1%) whereas mPFS was also higher (2.0 months).

In May 2016, nivolumab received the first approval for the treatment of patients with cHL who have relapsed or progressed after autologous hematopoietic stem cell transplantation and post-transplantation brentuximab vedotin (BV), based totally on the single-arm, phase II, multicenter trials (CheckMate-205) [ 36 ]. Nivolumab delivered a high response rate with an ORR of 69% and mPFS of 14.7 months, including 16% CR. Among responders, the DOR was maintained over time for a median of 16.6 months. Additionally, the benefit of combining nivolumab with chemotherapy in the first-line setting of non-Hodgkin lymphoma (NHL) is well established and studied in four trials. A study [ 37 ] evaluated the efficacy and safety of anti-CD19 CAR-T cell therapy in combination with nivolumab for relapsed or refractory DLBCL. The total ORR was 81.81%, including 45.45% CR. In 2016, a phase Ib trial [ 38 ] evaluated the efficacy of nivolumab in hematologic tumors, in which FL had the highest efficiency with an ORR of 40%. Also, in the phase II trial [ 39 ], patients with relapsed or refractory AML were randomized to treat with nivolumab combined with azacitidine vs. demethylation medication. The results showed that the combination therapy could benefit the patients more, where the mOS was 6.3 months vs. 4.6 months and the ORR was 33% vs. 20% in two arms, including 8% CR and 19% PR. In 2018, a phase II clinical study [ 40 ] evaluated the efficacy of nivolumab in combination with ibrutinib for relapsed or refractory CLL, with an ORR of 43%. In summary, nivolumab offers a new strategy for the treatment of hematologic malignancies.

Following platinum-based chemotherapy, a phase II trial [ 41 ] was carried out with advanced or metastatic ovarian cancer patients. The ORR of 15% was demonstrated, including 45% DCR. The mPFS was 3.5 months, and the mOS was 20.0 months. CheckMate-214 [ 42 ] investigated the addition of nivolumab to ipilimumab as the first-line treatment of RCC. Eligible patients received nivolumab plus ipilimumab vs. sunitinib monotherapy, followed by maintenance. The results proved that the addition of nivolumab improved PFS (11.6 months vs. 8.4 months), a statistically significant difference in OS rate was narrowly missed (75% vs. 60%). Nivolumab arms delivered a high response rate with ORR (42% vs. 27%), including higher CR (9% vs. 1%).

Atezolizumab (Tecentriq)

Atezolizumab is a human anti-PD-L1 IgG1 monoclonal antibody that activates T cells and the adaptive immune system primarily by inhibiting the action of PD-L1, which in turn induces antibody-dependent cell-mediated cytotoxicity. It has been approved to treat melanoma, metastatic NSCLC, UC, CRC, and other diseases. Completed trials using atezolizumab to target malignant tumors are listed in Table 3 . Table 3 Approved therapies based on PD-1/PD-L1 blockade Pathology Trial Phase No of. patients Treatment mPFS (months) mOS (months) ORR (%) Other outcomes Atezolizumab Melanoma IMspire150 III – Atezolizumab + Cobitinib + Verofini vs. Placebo + Cobitinib + Verofini 15.1 vs. 10.6 – – DOR: 21.0 vs. 12.6 months NSCLC POPLAR II 287 Atezolizumab vs. Docetaxel – 12.6 vs. 9.7 15 – OAK III 1125 Atezolizumab vs. Docetaxel – 13.8 vs. 9.6 – UC IMvigor210 II 310 Atezolizumab 2.1 7.9 15 – IMvigor211 III 931 Atezolizumab vs. ICC – 11.1 vs. 10.6 23 vs. 22 DOR: 15.9 vs. 8.3 months CRC Bendell et al I 23 Atezolizumab + Cobitinib – 72%* PR: 17% Avelumab MCC JAVELIN II 88 Avelumab – – 31.8 CR: 9.1%; PR: 22.7% UC Patel et al Ib – Avelumab 1.5 7.4 17 CR: 6%; PR: 11% Ovarian cancer Disis et al I – Avelumab – – 9.7 DCR: 54% Durvalumab NSCLC PACIFIC III 713 Durvalumab vs. Placebo 16.8 vs. 5.6 – – DOR: 72.8% vs. 46.8% UC Powles et al I/II 191 Durvalumab 1.5 18.2 17.8 CR: 4.7% Ovarian cancer MEDIOLOA II 32 Durvalumab + Olaparib – – 63 – NSCLC: non-small cell lung cancer; UC: urothelium carcinoma; CRC: colorectal cancer; MCC: merkle cell carcinoma; mPFS: median progression-free survival; mOS: median overall survival; ORR: objective response rate; PR: partial remission; CR: complete remission; DOR: duration of response; DCR: disease control rate; ICC: Investigator's choice of chemotherapy; *: PFS or OS rate. –: Not available

In July 2020, the FDA approved atezolizumab or placebo in combination with cobimetinib and verofinil for the treatment of patients with advanced melanoma based on the Phase III IMspire150 trial [ 43 ]. The two primary endpoints of the trial, PFS and DOR, demonstrated statistical significance in favor of the atezolizumab plus chemotherapy cohort: PFS 15.1 months vs. 10.6 months and DOR 21.0 months vs. 12.6 months. In October 2016, based on the results of the phase II POPLAR [ 44 ] and phase III OAK [ 45 ] trials, atezolizumab was approved for the treatment of metastatic NSCLC with disease progression during or after platinum-containing chemotherapy. In the phase II POPLAR trial, an overall ORR of 15% was achieved, with an ORR of 26% for PD-L1 ≥ 5% and 18% for PD-L1 ≥ 1%. At a minimum follow-up of 13 months, atezolizumab significantly improved OS compared with Docetaxel (12.6 months vs. 9.7 months). In the OAK trial, OS was significantly improved in the atezolizumab arm compared with the polygalactin arm (13.8 months vs. 9.6 months). Atezolizumab also improved OS in the subgroup of patients with low or undetectable PD-L1 expression (12.6 months vs. 8.9 months). In brief, atezoluzimab achieved a significant OS benefit, with greater advantage in patients with higher PD-L1 expression in two trials.

In May 2016, an open, multicenter, single-arm phase II IMvigor210 trial (n = 310) evaluated the clinical efficacy of atezolizumab in patients with platinum-resistant locally advanced or metastatic UC. Rosenberg et al. [ 46 ] reported data from cohort 2 with an ORR of 15%, mOS of 7.9 months, and mPFS of 2.1 months. Also, on this basis, the phase III IMvigor211 trial ( NCT02302807 ) [ 47 ] (n = 931) reported the clinical efficacy and safety of atezolizumab compared with ICC in UC patients. Results showed no significant improvement in mOS with atezolizumab compared to the chemotherapy arm (11.1 months vs. 10.6 months), and ORR was similar (23% vs. 22%). Still, DOR was longer with atezolizumab than with chemotherapy (15.9 months vs. 8.3 months). Bendell et al. [ 48 ] reported the results of a study of the atezolizumab combined with cobitinib in patients with CRC, in which 17% of patients achieved PR and the OS rate was 72%. It is unclear whether these results differ from those of chemotherapy alone.

Avelumab (Bavencio)

Avelumab is also an IgG1 antibody directed against PD-L1, which was approved in 2017 for the treatment of patients with metastatic MCC, ovarian cancer, or metastatic UC etc. (Table 3 ).

In March 2017, avelumab was approved to treat patients with metastatic MCC based on the phase II JAVELIN trial [ 49 ]. In this multicenter, international, prospective, single-arm, open-label phase II trial, an ORR of 31.8% was achieved in patients with stage IV chemotherapy-refractory, histologically confirmed MCC, including 9.1% CR and 22.7% PR of the patients. As a result, the accelerated approval of Avelumab allows it to address unmet medical needs using clinical trial data that are believed to predict clinical benefit for patients. In an open, multicenter, single-arm phase Ib trial ( NCT01772004 ) [ 50 ], avelumab demonstrated clinical efficacy and safety in patients with platinum-refractory UC. The results indicated that the PFS and OS had been met (1.5 months and 7.4 months). The ORR of 17% was demonstrated with CR in 6% and PR in 11% of the patients. A phase I trial [ 51 ] was carried out with advanced or metastatic ovarian cancer patients, following platinum-based chemotherapy. An ORR of 9.7% was demonstrated with DCR in 54% of the patients.

Durvalumab (Imfinzi)

Durvalumab is a monoclonal IgG1k antibody approved only by the FDA in 2017 for the treatment of NSCLC, UC, and ovarian cancer (Table 3 ).

In February 2018, durvalumab was approved for the treatment of patients with stage III NSCLC based on the phase III PACIFIC trial [ 52 ]. The primary endpoint of mPFS and DOR had been met and favored the durvalumab arm: 16.8 vs. 5.6 months, 72.8% vs. 46.8%. Lately, Powles et al. [ 53 ] have confirmed the effectiveness of durvalumab in UC patients: ORR of 17.8% in 191 patients and CR of 4.7%. Besides, the primary endpoint of PFS and OS had been met and was in favor of the durvalumab arm: 1.5 months and 18.2 months. In 2018, durvalumab was used in combination with olaparib for the treatment of platinum-sensitive ovarian cancer patients in an open-label, single-arm, phase II study (MEDIOLOA) [ 54 ]. The results of the study showed an ORR of 63% in 32 patients treated with the combination. The combination therapy has fewer adverse reactions and no dose-limiting toxicity has been reported.

Toxicities of PD-1/PD-L1 signal blocking

Although ICIs enhance the antitumor t-cell response, they may still lead to the development of various immune-related adverse events (irAEs) that are usually considered well-tolerated and manageable, such as interstitial pneumonia, colitis with gastrointestinal perforation, immune platelets after steroid therapy reduction, neutropenia, and sepsis [ 55 ]. A recent meta-analysis evaluated the safety and tolerability of PD-1/PD-L1 inhibitors in 3450 patients with advanced cancer from seven randomized controlled studies [ 56 ]. Compared with chemotherapy, PD-1/PD-L1 inhibitors significantly reduced the risk of fatigue, diarrhea, anorexia, nausea, and constipation. Among them, the proportions of grade 1–4 AEs, ≥ 3 AEs and discontinuation of treatment were 67.6% vs. 82.9%, 11.4% vs. 35.7% and 4.5% vs. 11.1%, respectively. While most irAEs are manageable and can be managed by clinicians, some can seriously endanger patients' lives, such as cardiac arrest, heart failure, and myocardial infarction.

In July 2017, the FDA has placed an emergency hold on several clinical trials of nivolumab, pembrolizumab, and durvalumab-containing regimens for various hematologic malignancies based on safety concerns from KEYNOTE-183 [ 57 ]. Therefore, early prevention, early recognition of grade 1 and 2 adverse reactions, and timely intervention are critical and can significantly reduce patient morbidity and mortality [ 58 ]. Notably, the use of drugs such as steroids to manage side effects does not seem to affect the efficacy of immune checkpoint inhibitors [ 59 ], which opens new paths for future research on how to reduce adverse drug reactions. Furthermore, optimization of relevant guidelines and specific care approaches facilitate early intervention and management of irAEs.

In a nutshell, the clinical manifestations of irAEs are complex and affect the quality of life of patients, and severe irAEs even require discontinuation of ICIs, which delays patient treatment. Therefore, it is particularly important to find biomarkers that predict irAEs in tumor patients treated with ICIs.

Predictive biomarkers to assess the efficacy of ICIs

Tumor mutation burden (TMB)

Tumor mutation burden (TMB) is defined as the total number of base substitutions (including synonymous mutations) per megabase in the coding region of the target gene. In short, it is the total number of somatic mutations in the tumor genome after removing germline mutations. The CheckMate 026 study demonstrated significantly improved PFS and OS in patients with high TMB (≥ 243 missense mutations) treated with nivolumab compared with conventional chemotherapeutic agents [ 60 ]. The POPLAR study analyzed the relationship between blood TMB (bTMB) and clinical benefit. Among patients with bTMB ≥ 10, ≥ 16, and ≥ 20, atezolizumab treated patients had an increased benefit in PFS and OS, with the greatest benefit in patients with bTMB ≥ 16 [ 61 ]. In addition, the results of the CheckMate 227 study [ 62 ] showed that nivolumab plus low-dose ipilimumab treatment significantly prolonged patients’ 1-year PFS (7.2 months vs. 5.4 months) compared with platinum-based doublet chemotherapy in patients with advanced NSCLC with TMB ≥ 10. Although TMB is considered to be a good predictor of immunotherapy, there are limitations in clinical practice. Immune nonresponse occurs in patients with high TMB, while patients with low TMB produce good immune effects. In the future, we need many prospective trials to investigate how TMB can be effectively combined with PD-L1 expression levels to predict the efficacy of ICIs jointly. Furthermore, how HLA genotypes and other germline variants affect the effect of TMB and the response to ICIs needs to be further explored.

PD-L1 expression status

Currently, the detection of PD-L1 mainly relies on immunohistochemistry (IHC) in clinical practice. The results of KEYNOTE 024 [ 63 ] showed that patients with advanced NSCLC with high PD-L1 expression (≥ 50%) had better OS, PFS with pembrolizumab compared to conventional chemotherapeutic agents. Nevertheless, the efficacy of immunotherapy was comparable to that of conventional drug chemotherapy when PD-L1 expression was ˂ 50%. Therefore, the higher the expression level of PD-L1, the better the immunotherapy effect of NSCLC. CheckMate 012 study [ 64 ] illustrated that nivolumab in combination with ipilimumab in advanced NSCLC was more than 90% effective in patients with PD-L1 ≥ 50%. Nevertheless, CheckMate 017 and OAK trials manifested that the expression level of PD-L1 in tumor cells might not be an appropriate biomarker to predict the effectiveness of immunotherapy [ 33 , 45 ]. This may be because specific signaling pathways promote malignant behavior of cancer cells, such as EGFR, mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase protein kinase (PI3K AKT). The current PD-L1 detection platforms are DAKO and Ventana, and it is recommended to detect antibodies 22C3 and 28-8 using the DAKO detection platform and SP142 and SP263 using the Ventana detection platform. Whereas, due to the different antibodies used by different companies’ testing platforms, the different thresholds set for positivity, and the subjective nature of the interpretation, this leaves a great deal of uncertainty in the test results [ 65 ]. In brief, concerning patients with low or absent PD-L1 expression capacity, or patients with high PD-L1 expression capacity who urgently need cell induction, we prefer combination regimens containing ICIs and histologically selected platinum double chemotherapy to achieve higher clinical benefit.

Tumor-infiltrating lymphocytes (TILs)

Tumor-infiltrating lymphocytes (TILs) are mononuclear immune cells distributed in tumor cell clusters and mesenchyme and are usually stained with hematoxylin–eosin (HE) and evaluated semi-quantitatively under light microscopy [ 66 ]. Since the action of PD-1/PD-L1 inhibitors requires the involvement of lymphocytes in the vicinity of the tumor, the degree of TILs infiltration can also be used as a biomarker to predict the efficacy of PD-1/PD-L1 inhibitors. In cancer tissues, TILs consist mainly of CD8 + and CD4 + T cells, followed by regulatory T cells and B cells [ 67 ]. Infiltration of TILs, especially CD8 + T cells, often indicates good immunotherapy response and prognosis [ 68 ]. In TNBC patients, high infiltration of CD8 + TILs is associated with high response rates to immune checkpoint inhibitors [ 69 ]. Previous studies have shown [ 70 ] that patients with metastatic melanoma infiltrated with high CD8 + TILs in the tumor tissue and tumor margins respond more significantly to immunotherapy compared to conventional cytotoxic chemotherapy. It was found [ 71 ] that NSCLC patients effectively treated with pembrolizumab had a much higher number of CD8 + and cut edge infiltrates in baseline biopsy specimens than patients with progressive disease. It is believed that as the study progresses, the comprehensive prediction model combining TILs with PD-L1 or TMB expression status will eventually become the most accurate biomarker for tumor immunotherapy.

Tumor microenvironment (TME)

Many cytokines and tumor-derived exosomes in the tumor microenvironment (TME) can induce PD-L1 expression and promote tumor immune escape. TME is mainly composed of the vascular system, extracellular matrix (ECM), other non-malignant cells surrounding the tumor, and a complex network of signaling molecules that maintain the connections within the microenvironment [ 72 ]. These components promote the growth and multiplication of malignant cells, and induce their invasion and metastasis. In addition, exosomes carrying non-coding RNA are another vital component of the tumor microenvironment, contributing to tumor cell growth and migration [ 73 ]. For instance, IL-12 and IL-6 can induce PD-1 upon TCR activation by altering the chromatin structure of the PD-1 gene and enhancing PD-1 transcription through activation of STAT3/STAT4. This process that requires the proximal cis-element of the PD-1 promoter as well as the transcription factors FOXO1 and NF-κB [ 74 ]. In macrophages, IFN-α can also regulate PD-1 expression by activating the JAK/STAT signaling pathway, which enhances PD-1 transcription by forming a p48/STAT1/STAT2 complex that binds to the ISRE binding site on the PD-1 promoter [ 75 ]. TNF-α upregulates PD-L1 mRNA and protein levels, mainly through activation of NF-κB and ERK1/2 signaling pathways [ 76 ]. Tumor-derived exosomes also promote the polarization of monocytes to M2 macrophages and the expression of PD-L1 in M2-polarized macrophages via STAT3 phosphorylation, further enhancing the immunosuppressive effect [ 77 ]. In conclusion, high expression of inflammatory factors in the tumor microenvironment may be an essential factor in the poor outcome of immunotherapy. The combination of anti-inflammatory drugs and PD-1/PD-L1 inhibitors may lead to better treatment outcomes for cancer patients.

Gut microbiome

The diversity and composition of the intestinal flora have recently been found to significantly influence the efficacy of treatment with ICIs in oncology patients [ 78 ]. It has been shown that the efficacy of treatment with ICIs decreases with the use of antibiotics and is better in certain specific intestinal microorganisms, such as Bifidobacterium spp., Eckermannia spp. and Bacteroidetes spp. Based on the results of a retrospective multivariate analysis, receipt of antibiotics before immunotherapy was a negative predictor of long-term patient survival. Routy et al. [ 79 ] found that the relative abundance of Ekmania spp. was significantly associated with good clinical outcomes in patients with advanced NSCLC and UC. Immunoassays showed higher densities of melanoma-infiltrating CD8 + T cells and higher frequencies of circulating CD8 + and CD4 + T cells in responding patients with a good gut microbiome [ 80 ]. All these findings suggest that the gut microbiome of oncology patients can significantly influence the efficacy of anti-PD-1 therapy. It has been reported that if antibiotics are used within 30 days prior to the start of treatment with ICIs, then patients have significantly lower PFS and OS [ 81 ]. Therefore, in future studies, perhaps we can use phages as highly selective tools to specifically eliminate negative bacteria as potential intervention tools to enhance the efficacy of immunotherapy.

Microsatellite instability-high (MSI-H) or mismatch repair deficient (d-MMR) status

Mismatch repair deficient (d-MMR) is an important mechanism for avoiding gene replication errors, which prevents mutations and repairs polymerase errors during replication and is essential for genetic gene stability. Several clinical studies have shown that MSI-H/dMMR patients are more likely to benefit from immunotherapy [ 82 ]. In addition, the FDA has approved pembrolizumab for the treatment of MSI-H/dMMR-expressing positive solid tumors, which presented that 39.6% of patients achieved complete or partial remission and 78% of patients had a duration of drug response of 6 months or longer [ 83 ]. CheckMate142 demonstrated that compared to nivolumab monotherapy, the combination of nivolumab and pembrolizumab in patients with MSI-H/dMMR metastases was more effective than nivolumab [ 84 ]. A recent clinical trial supports this view even more [ 85 ]. The study pointed out that the pembrolizumab group had a significantly higher PFS and OS (16.5 months, 43.8%) than the chemotherapy group (8.2 months, 33.1%), at a median follow-up time of 32.34 months.

Lymphocyte and monocyte ratio (LMR)

In 2020, a retrospective analysis investigated the predictive value of LMR in patients with advanced tumors using PD-1 inhibitors to identify patients who might have a better response to PD-1 inhibitors [ 86 ]. The optimal cut-off values for LMR were delineated using the working characteristic curves of the subjects, and patients were divided into high and low LMR groups. The results of the study showed that the ORR of the high and low LMR 6-week groups were 32.7% and 7.6%, respectively. LMR-6 weeks was significantly associated with the effect of anti-PD-1 antibody therapy; therefore, LMR-6 weeks can be used as an early predictor for stratification of patients with better response to anti-PD-1 drugs. Currently, studies on such trials are relatively scarce and need to be further confirmed by a large number of high-quality prospective studies.

Human leukocyte antigen class I (HLA-I) molecules

Host genetics-related biomarkers are mainly associated with host immune gene polymorphisms, including HLA-I diversity and FcγR single nucleotide polymorphisms, which are positively correlated with the efficacy of ICIs. Correale et al. [ 87 ] reported that class I HLA allele characterization has vital implications in predicting nivolumab efficacy in mNSCLC. The study demonstrated that a poor outcome in patients negative for the expression of the two most frequent HLA-A alleles was detected (HLA: HLA-A*01 and or A*02; PFS: 7.5 vs. 15.9 months). In particular, HLA-A*01-positive patients showed a prolonged PFS of 22.6 and OS of 30.8 months, respectively. Simultaneously, several studies [ 88 , 89 ] have already shown that HLA-I diversity was mainly expressed at the HLA-B and HLA-C loci: HLA-B-encoded MHCs could bind to a greater diversity TCRs, and HLA-C in APCs expression was higher than that of other cells. Moreover, HLA-I diversity could also promote the efficacy of ICIs from the perspective of TMBs and TCRs. It was shown that the increased affinity of FcγR encoded by allele CD16AV158F with IgG immunoglobulin was positively correlated with CTLA antibody efficacy in melanoma.

Predictive biomarkers of irAEs

Chemokines and cytokines

A study of chemokine changes in patients with irAEs found that CXCL9, CXCL10, CXCL11, and CXCL19, among the CXC subfamily of chemokines, were lower at baseline levels before treatment than in patients without irAEs. In contrast, only CXCL9 and CXCL10 showed significant increases after treatment [ 90 ]. In another study, patients with irAEs showed only an increase in chemokine CCL5 after treatment with ICIs [ 91 ]. CXCL9 and CXCL10 had functions in the tumor microenvironment, such as regulating T cell differentiation and directing the migration of immune cells to tumor tissues, while CCL5 was thought to be associated with graft-versus-host disease. In other words, these chemokines have different regulatory effects on the immune system, and monitoring their changes has a significant impact on irAEs.

Soluble CD163

Soluble CD163 was derived from macrophages and was significantly elevated in a variety of autoimmune diseases, such as rheumatoid arthritis and common aspergillosis. CD163-positive macrophages secrete the chemokine CXCL5. Fujimura et al. [ 92 ] measured the concentrations of soluble CD163 and CXCL5 before and after 42 days of nivolumab treatment, and both CD163 and CXCL5 appeared significantly elevated in patients with irAEs compared to those without irAEs.

HLA alleles

The development of autoimmune diseases was closely related to genetic factors, and similarly, genetic factors were associated with the development of irAEs. A study showed that the HLA-DRB1*11:01 haplotype was related to pneumonitis irAEs [ 93 ]. HLA-DRB1*03:01 was about colitis irAEs [ 94 ]. HLA-B* 52:01 and HLA-C* 12:02 were associated with arthritis irAEs [ 95 ]. HLA-B* 4002 was concerned with nivolumab for Hodgkin’s lymphoma type 1 diabetes mellitus that emerged from Bartholin’s tumor [ 96 ]. HLA-DRB1* 09:01-DQB1* 03:03 was related to nivolumab in treating of thyroiditis in renal cancer [ 97 ]. In short, accurate and real-world evidence-based multimodal definition of baseline tumor immunogenicity, as well as HLA haplotype characterization, can help identify not only patients with responders but patients at high risk for fatal irAEs [ 98 ].

Conclusions and future prospectus

In summary, PD-1/PD-L1 inhibitors alone or in combination with other regimens are of great importance in the treatment of malignancies. And the emergence of biomarkers provides a direction for precision therapy of tumor immunity. Future prospective studies are still needed to evaluate the integration of these biomarkers with other potential factors (e.g., TILs with PD-L1 or TMB) and, in turn, to explore more precise biomarkers of efficacy for tumor immunotherapy using standardized methods and thresholds, such as liquid biopsy-based analysis. Despite the significant advances in immunotherapy, today’s studies demonstrate that most patients eventually relapse and develop severe adverse effects such that patient prognosis is compromised. Therefore, there is an urgent need to address how to find more effective biomarkers of efficacy and how to reduce the adverse effects of drugs.

In addition, targeting the innate immune system may also be an essential therapeutic tool in the future. Innate immune cells, such as macrophages, NK cells, neutrophils, and other myeloid cells, play an important role in complementing the effector activity of T cells. Various combination treatments are being investigated. In short, there is an increasing emphasis on the potential contribution of innate immune effectors against tumor immunity, and the integration of multiple means of targeting the adaptive immune system into PD-1/PD-L1 inhibitor-based therapies may be a fundamental combination approach in immunotherapy in the future. Clinical research in cancer immunotherapy is outpacing its basic research advances, creating an opportunity to combine emerging scientific and clinical insights to deepen our understanding of cancer immunity, and present a significant challenge to establish future cancer immunotherapies. It is believed that as the research progresses, immunotherapy for malignant tumors will eventually enter the era of individualized and precise treatment.

Abbreviations

Immune checkpoint inhibitors

Immune-related adverse events

Programmed death-1

Cytotoxic T-lymphocyte associated protein 4

Programmed cell death ligand-1

Non-small-cell lung cancer

Small cell lung cancer

Renal cell carcinoma

Classical Hodgkin lymphoma

Head and neck squamous cell carcinoma

Colorectal cancer

Hepatocellular carcinoma

Primary mediastinal large B-cell lymphoma

Merkel cell carcinoma

Microsatellite instability-high or DNA mismatch repair deficient

Pleural mesothelioma

Cervical cancer

Gastric or gastroesophageal junction adenocarcinoma

Median progression-free survival

Objective response rate

Disease control rate

Complete response

Autologous stem cell transplantation

Brentuximab vedotin

Median overall survival

Non-Hodgkin lymphoma

Combined positive score

Stable disease

Follicular lymphoma

Acute myeloid leukemia

Chronic lymphocytic leukemia

Tumor mutation burden

Tumor microenvironment

Tumor-infiltrating lymphocytes

Lymphocyte to monocyte ratio

Human leukocyte antigen

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Wenwen Yang, Caining Lei and Shaoming Song contributed equally to this work

Wenwen Yang, Caining Lei and Shaoming Song are first authors

Acknowledgements

We are grateful to all of the reviewers for their comments.

Authors’ contributions

Conceived and designed the study: HWT, TKG. Data collection and analysis: WWY, CNL, SMS. Generated figures: WTJ, CWJ, SYG. Wrote the manuscript: WWY, CNL, SMS. Revised and edited the manuscript: HWT, TKG. All authors read and approved the final manuscript.

Authors’ information

Hongwei Tian is the co-corrresponding author of this paper. Hongwei Tian was the director of two foundation programs and revised and edited the revised manuscript (Fundamental Research Funds for the Central Public Welfare research Institutes of the Chinese Academy of Medical Sciences 2019PT320005, Natural Science Foundation of Gansu Province 20JR10RA403). In addition, He also provided ideas for writing this study and made improvements in the English language as the second person in charge of the paper.

Funding

This work was supported by Grants from the Key Laboratory of Molecular Diagnostics and Precision Medicine for Surgical Oncology in Gansu Province (18JR2RA033), the Fundamental Research Funds for the Central Public Welfare research Institutes of the Chinese Academy of Medical Sciences (2019PT320005) and Natural Science Foundation of Gansu Province (20JR10RA403).

Availability of data and materials

Not applicable.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

We assure that the material is original and it has not been published elsewhere yet.

Competing interests

The authors declare that they have no competing interests.

References

1. Coley WB II Contribution to the knowledge of sarcoma Ann Surg 1891 14 3 199 220 10.1097/00000658-189112000-00015 17859590 PMC1428624

2. Parish CR Cancer immunotherapy: the past, the present and the future Immunol Cell Biol 2003 81 2 106 113 10.1046/j.0818-9641.2003.01151.x 12631233

3. Wu X Xing X Dowlut D Integrating phosphoproteomics into kinase-targeted cancer therapies in precision medicine J Proteomics 2019 191 68 79 10.1016/j.jprot.2018.03.033 29621648

4. Chen DS Mellman I Elements of cancer immunity and the cancer-immune set point Nature 2017 541 7637 321 330 10.1038/nature21349 28102259

5. Ianchecchi E Delfino DV Fierabracci A Recent insights into the role of the PD-1/PD-L1 pathway in immunological tolerance and autoimmunity Autoimmun Rev 2013 12 11 1091 1100 10.1016/j.autrev.2013.05.003 23792703

6. Zou W Wolchok JD Chen L PD-L1 (B7–H1) and PD-1 pathway blockade for cancer therapy: mechanisms, response biomarkers, and combinations Sci Transl Med. 2016 8 328 328rv4 10.1126/scitranslmed.aad7118 26936508 PMC4859220

7. Okazaki T Honjo T PD-1 and PD-1 ligands: from discovery to clinical application Int Immunol 2007 19 7 813 824 10.1093/intimm/dxm057 17606980

8. Ishida Y Agata Y Shibahara K Induced expression of PD-1, a novel member of the immunoglobulin gene superfamily, upon programmed cell death EMBO J 1992 11 11 3887 3895 10.1002/j.1460-2075.1992.tb05481.x 1396582 PMC556898

9. Elhag OA Hu XJ Wen-Ying Z Reconstructed adeno-associated virus with the extracellular domain of murine PD-1 induces antitumor immunity Asian Pac J Cancer Prev 2012 13 8 4031 4036 10.7314/APJCP.2012.13.8.4031 23098512

10. Topalian SL Hodi FS Brahmer JR Safety, activity, and immune correlates of anti-PD-1 antibody in cancer N Engl J Med 2012 366 26 2443 2454 10.1056/NEJMoa1200690 22658127 PMC3544539

11. Weber JS D'Angelo SP Minor D Nivolumab versus chemotherapy in patients with advanced melanoma who progressed after anti-CTLA-4 treatment (CheckMate 037): a randomised, controlled, open-label, phase 3 trial Lancet Oncol 2015 16 4 375 384 10.1016/S1470-2045(15)70076-8 25795410

12. Motzer RJ Rini BI McDermott DF Nivolumab for metastatic renal cell carcinoma: results of a randomized phase II trial J Clin Oncol 2015 33 13 1430 1437 10.1200/JCO.2014.59.0703 25452452 PMC4806782

13. Schachter J Ribas A Long GV Pembrolizumab versus ipilimumab for advanced melanoma: final overall survival results of a multicentre, randomised, open-label phase 3 study (KEYNOTE-006) Lancet 2017 390 10105 1853 1862 10.1016/S0140-6736(17)31601-X 28822576

14. Robert C Schachter J Long GV Pembrolizumab versus ipilimumab in advanced melanoma N Engl J Med 2015 372 26 2521 2532 10.1056/NEJMoa1503093 25891173

15. Gandhi L Rodríguez-Abreu D Gadgeel S Pembrolizumab plus chemotherapy in metastatic non-small-cell lung cancer N Engl J Med 2018 378 22 2078 2092 10.1056/NEJMoa1801005 29658856

16. Seiwert TY Burtness B Mehra R Safety and clinical activity of pembrolizumab for treatment of recurrent or metastatic squamous cell carcinoma of the head and neck (KEYNOTE-012): an open-label, multicentre, phase 1b trial Lancet Oncol 2016 17 7 956 965 10.1016/S1470-2045(16)30066-3 27247226

17. Balar AV Castellano D O'Donnell PH First-line pembrolizumab in cisplatin-ineligible patients with locally advanced and unresectable or metastatic urothelial cancer (KEYNOTE-052): a multicentre, single-arm, phase 2 study Lancet Oncol 2017 18 11 1483 1492 10.1016/S1470-2045(17)30616-2 28967485

18. Bellmunt J de Wit R Vaughn DJ Pembrolizumab as second-line therapy for advanced urothelial carcinoma N Engl J Med 2017 376 11 1015 1026 10.1056/NEJMoa1613683 28212060 PMC5635424

19. Chen R Zinzani PL Fanale MA Phase II study of the efficacy and safety of pembrolizumab for relapsed/refractory classic hodgkin lymphoma J Clin Oncol 2017 35 19 2125 2132 10.1200/JCO.2016.72.1316 28441111 PMC5791843

20. Armand P Rodig S Melnichenko V Pembrolizumab in relapsed or refractory primary mediastinal large B-cell lymphoma J Clin Oncol 2019 37 34 3291 3299 10.1200/JCO.19.01389 31609651 PMC6881098

21. Frigault MJ Armand P Redd RA PD-1 blockade for diffuse large B-cell lymphoma after autologous stem cell transplantation Blood Adv 2020 4 1 122 126 10.1182/bloodadvances.2019000784 31917843 PMC6960482

22. Badros A Hyjek E Ma N Pembrolizumab, pomalidomide, and low-dose dexamethasone for relapsed/refractory multiple myeloma Blood 2017 130 10 1189 1197 10.1182/blood-2017-03-775122 28461396

23. Chung HC Ros W Delord JP Efficacy and safety of pembrolizumab in previously treated advanced cervical cancer: results from the phase II KEYNOTE-158 study J Clin Oncol 2019 37 17 1470 1478 10.1200/JCO.18.01265 30943124

24. Frenel JS Le Tourneau C O'Neil B Safety and efficacy of pembrolizumab in advanced, programmed death ligand 1-positive cervical cancer: results from the phase Ib KEYNOTE-028 trial J Clin Oncol 2017 35 36 4035 4041 10.1200/JCO.2017.74.5471 29095678

25. Varga A Piha-Paul S Ott PA Pembrolizumab in patients with programmed death ligand 1-positive advanced ovarian cancer: analysis of KEYNOTE-028 Gynecol Oncol 2019 152 2 243 250 10.1016/j.ygyno.2018.11.017 30522700

26. Makker V Rasco D Vogelzang NJ Lenvatinib plus pembrolizumab in patients with advanced endometrial cancer: an interim analysis of a multicentre, open-label, single-arm, phase 2 trial Lancet Oncol 2019 20 5 711 718 10.1016/S1470-2045(19)30020-8 30922731 PMC11686814

27. Adams S Schmid P Rugo HS Pembrolizumab monotherapy for previously treated metastatic triple-negative breast cancer: cohort A of the phase II KEYNOTE-086 study Ann Oncol 2019 30 3 397 404 10.1093/annonc/mdy517 30475950

28. Cedrés S Ponce-Aix S Zugazagoitia J Analysis of expression of programmed cell death 1 ligand 1 (PD-L1) in malignant pleural mesothelioma (MPM) PLoS ONE 2015 10 3 e0121071 10.1371/journal.pone.0121071 25774992 PMC4361537

29. Fuchs CS Doi T Jang RW Safety and efficacy of pembrolizumab monotherapy in patients with previously treated advanced gastric and gastroesophageal junction cancer: phase 2 clinical KEYNOTE-059 trial JAMA Oncol 2018 4 5 e180013 10.1001/jamaoncol.2018.0013 29543932 PMC5885175

30. Ribas A Dummer R Puzanov I Oncolytic virotherapy promotes intratumoral t cell infiltration and improves anti-PD-1 immunotherapy Cell 2017 170 6 1109 1119.e10 10.1016/j.cell.2017.08.027 28886381 PMC8034392

31. Zhu AX Finn RS Edeline J Pembrolizumab in patients with advanced hepatocellular carcinoma previously treated with sorafenib (KEYNOTE-224): a non-randomised, open-label phase 2 trial Lancet Oncol 2018 19 7 940 952 10.1016/S1470-2045(18)30351-6 29875066

32. Larkin J Chiarion-Sileni V Gonzalez R Combined nivolumab and ipilimumab or monotherapy in untreated melanoma N Engl J Med 2015 373 1 23 34 10.1056/NEJMoa1504030 26027431 PMC5698905

33. Brahmer J Reckamp KL Baas P Nivolumab versus docetaxel in advanced squamous-cell non-small-cell lung cancer N Engl J Med 2015 373 2 123 135 10.1056/NEJMoa1504627 26028407 PMC4681400

34. Ferris RL Blumenschein G Jr Fayette J Nivolumab vs investigator's choice in recurrent or metastatic squamous cell carcinoma of the head and neck: 2-year long-term survival update of CheckMate 141 with analyses by tumor PD-L1 expression Oral Oncol 2018 81 45 51 10.1016/j.oraloncology.2018.04.008 29884413 PMC6563923

35. Sharma P Retz M Siefker-Radtke A Nivolumab in metastatic urothelial carcinoma after platinum therapy (CheckMate 275): a multicentre, single-arm, phase 2 trial Lancet Oncol 2017 18 3 312 322 10.1016/S1470-2045(17)30065-7 28131785

36. Armand P Engert A Younes A Nivolumab for relapsed/refractory classic hodgkin lymphoma after failure of autologous hematopoietic cell transplantation: extended follow-up of the multicohort single-arm phase II CheckMate 205 Trial J Clin Oncol 2018 36 14 1428 1439 10.1200/JCO.2017.76.0793 29584546 PMC6075855

37. Cao Y Lu W Sun R Anti-CD19 chimeric antigen receptor T cells in combination with nivolumab are safe and effective against relapsed/refractory B-cell non-hodgkin lymphoma Front Oncol 2019 9 767 10.3389/fonc.2019.00767 31482064 PMC6709654

38. Lesokhin AM Ansell SM Armand P Nivolumab in patients with relapsed or refractory hematologic malignancy: preliminary results of a phase Ib study J Clin Oncol 2016 34 23 2698 2704 10.1200/JCO.2015.65.9789 27269947 PMC5019749

39. Daver N Garcia-Manero G Basu S Efficacy, safety, and biomarkers of response to azacitidine and nivolumab in relapsed/refractory acute myeloid leukemia: a nonrandomized, open-label, phase II study Cancer Discov 2019 9 3 370 383 10.1158/2159-8290.CD-18-0774 30409776 PMC6397669

40. Younes A Brody J Carpio C Safety and activity of ibrutinib in combination with nivolumab in patients with relapsed non-Hodgkin lymphoma or chronic lymphocytic leukaemia: a phase 1/2a study Lancet Haematol 2019 6 2 e67 e78 10.1016/S2352-3026(18)30217-5 30642819

41. Hamanishi J Mandai M Ikeda T Safety and antitumor activity of anti-PD-1 antibody, nivolumab, in patients with platinum-resistant ovarian cancer J Clin Oncol 2015 33 34 4015 4022 10.1200/JCO.2015.62.3397 26351349

42. Motzer RJ Tannir NM McDermott DF Nivolumab plus ipilimumab versus sunitinib in advanced renal-cell carcinoma N Engl J Med 2018 378 14 1277 1290 10.1056/NEJMoa1712126 29562145 PMC5972549

43. Sullivan RJ Hamid O Gonzalez R Atezolizumab plus cobimetinib and vemurafenib in BRAF-mutated melanoma patients Nat Med 2019 25 6 929 935 10.1038/s41591-019-0474-7 31171876

44. Fehrenbacher L Spira A Ballinger M Atezolizumab versus docetaxel for patients with previously treated non-small-cell lung cancer (POPLAR): a multicentre, open-label, phase 2 randomised controlled trial Lancet 2016 387 10030 1837 1846 10.1016/S0140-6736(16)00587-0 26970723

45. Rittmeyer A Barlesi F Waterkamp D Atezolizumab versus docetaxel in patients with previously treated non-small-cell lung cancer (OAK): a phase 3, open-label, multicentre randomised controlled trial Lancet 2017 389 10066 255 265 10.1016/S0140-6736(16)32517-X 27979383 PMC6886121

46. Rosenberg JE Hoffman-Censits J Powles T Atezolizumab in patients with locally advanced and metastatic urothelial carcinoma who have progressed following treatment with platinum-based chemotherapy: a single-arm, multicentre, phase 2 trial Lancet 2016 387 10031 1909 1920 10.1016/S0140-6736(16)00561-4 26952546 PMC5480242

47. Powles T Durán I van der Heijden MS Atezolizumab versus chemotherapy in patients with platinum-treated locally advanced or metastatic urothelial carcinoma (IMvigor211): a multicentre, open-label, phase 3 randomised controlled trial Lancet 2018 391 10122 748 757 10.1016/S0140-6736(17)33297-X 29268948

48. Eng C Kim TW Bendell J Atezolizumab with or without cobimetinib versus regorafenib in previously treated metastatic colorectal cancer (IMblaze370): a multicentre, open-label, phase 3, randomised, controlled trial Lancet Oncol 2019 20 6 849 861 10.1016/S1470-2045(19)30027-0 31003911

49. Kaufman HL Russell J Hamid O Avelumab in patients with chemotherapy-refractory metastatic Merkel cell carcinoma: a multicentre, single-group, open-label, phase 2 trial Lancet Oncol 2016 17 10 1374 1385 10.1016/S1470-2045(16)30364-3 27592805 PMC5587154

50. Patel MR Ellerton J Infante JR Avelumab in metastatic urothelial carcinoma after platinum failure (JAVELIN Solid Tumor): pooled results from two expansion cohorts of an open-label, phase 1 trial Lancet Oncol 2018 19 1 51 64 10.1016/S1470-2045(17)30900-2 29217288 PMC7984727

51. Disis ML Taylor MH Kelly K Efficacy and safety of avelumab for patients with recurrent or refractory ovarian cancer: phase 1b results from the JAVELIN solid tumor trial JAMA Oncol 2019 5 3 393 401 10.1001/jamaoncol.2018.6258 30676622 PMC6439837

52. Antonia SJ Villegas A Daniel D Durvalumab after chemoradiotherapy in stage III non-small-cell lung cancer N Engl J Med 2017 377 20 1919 1929 10.1056/NEJMoa1709937 28885881

53. Powles T O’Donnell PH Massard C Efficacy and safety of durvalumab in locally advanced or metastatic urothelial carcinoma: updated results from a phase 1/2 open-label study JAMA Oncol 2017 3 9 e172411 10.1001/jamaoncol.2017.2411 28817753 PMC5824288

54. Domchek SM Postel-Vinay S Im SA Olaparib and durvalumab in patients with germline BRCA-mutated metastatic breast cancer (MEDIOLA): an open-label, multicentre, phase 1/2, basket study Lancet Oncol 2020 21 9 1155 1164 10.1016/S1470-2045(20)30324-7 32771088

55. Iwai Y Hamanishi J Chamoto K Cancer immunotherapies targeting the PD-1 signaling pathway J Biomed Sci 2017 24 1 26 10.1186/s12929-017-0329-9 28376884 PMC5381059

56. Nishijima TF Shachar SS Nyrop KA Safety and tolerability of PD-1/PD-L1 inhibitors compared with chemotherapy in patients with advanced cancer: a meta-analysis Oncologist 2017 22 4 470 479 10.1634/theoncologist.2016-0419 28275115 PMC5388381

57. Gong J Chehrazi-Raffle A Reddi S Development of PD-1 and PD-L1 inhibitors as a form of cancer immunotherapy: a comprehensive review of registration trials and future considerations J Immunother Cancer 2018 6 1 8 10.1186/s40425-018-0316-z 29357948 PMC5778665

58. Hu YB Zhang Q Li HJ Evaluation of rare but severe immune related adverse effects in PD-1 and PD-L1 inhibitors in non-small cell lung cancer: a meta-analysis Transl Lung Cancer Res 2017 6 Suppl 1 S8 S20 10.21037/tlcr.2017.12.10 29299404 PMC5750164

59. Friedman CF Proverbs-Singh TA Postow MA Treatment of the immune-related adverse effects of immune checkpoint inhibitors: a review JAMA Oncol 2016 2 10 1346 1353 10.1001/jamaoncol.2016.1051 27367787

60. Chan TA Yarchoan M Jaffee E Development of tumor mutation burden as an immunotherapy biomarker: utility for the oncology clinic Ann Oncol 2019 30 1 44 56 10.1093/annonc/mdy495 30395155 PMC6336005

61. Gandara DR Paul SM Kowanetz M Blood-based tumor mutational burden as a predictor of clinical benefit in non-small-cell lung cancer patients treated with atezolizumab Nat Med 2018 24 9 1441 1448 10.1038/s41591-018-0134-3 30082870

62. Hu H She L Liao M Cost-effectiveness analysis of nivolumab plus ipilimumab vs. chemotherapy as first-line therapy in advanced non-small cell lung cancer Front Oncol 2020 10 1649 10.3389/fonc.2020.01649 33014826 PMC7507990

63. Reck M Rodríguez-Abreu D Robinson AG Pembrolizumab versus chemotherapy for PD-L1-positive non-small-cell lung cancer N Engl J Med 2016 375 19 1823 1833 10.1056/NEJMoa1606774 27718847

64. Hellmann MD Rizvi NA Goldman JW Nivolumab plus ipilimumab as first-line treatment for advanced non-small-cell lung cancer (CheckMate 012): results of an open-label, phase 1, multicohort study Lancet Oncol 2017 18 1 31 41 10.1016/S1470-2045(16)30624-6 27932067 PMC5476941

65. Capalbo C Scafetta G Filetti M Predictive biomarkers for checkpoint inhibitor-based immunotherapy: the Galectin-3 signature in NSCLCs Int J Mol Sci 2019 20 7 1607 10.3390/ijms20071607 30935099 PMC6479404

66. Criscitiello C Esposito A Trapani D Prognostic and predictive value of tumor infiltrating lymphocytes in early breast cancer Cancer Treat Rev 2016 50 205 207 10.1016/j.ctrv.2016.09.019 27744144

67. Burugu S Asleh-Aburaya K Nielsen TO Immune infiltrates in the breast cancer microenvironment: detection, characterization and clinical implication Breast Cancer 2017 24 1 3 15 10.1007/s12282-016-0698-z 27138387

68. Dong ZY Wu SP Liao RQ Potential biomarker for checkpoint blockade immunotherapy and treatment strategy Tumour Biol 2016 37 4 4251 4261 10.1007/s13277-016-4812-9 26779629

69. Gu-Trantien C Loi S Garaud S CD4 + follicular helper T cell infiltration predicts breast cancer survival J Clin Invest 2013 123 7 2873 2892 10.1172/JCI67428 23778140 PMC3696556

70. Di Giacomo AM Danielli R Guidoboni M Therapeutic efficacy of ipilimumab, an anti-CTLA-4 monoclonal antibody, in patients with metastatic melanoma unresponsive to prior systemic treatments: clinical and immunological evidence from three patient cases Cancer Immunol Immunother 2009 58 8 1297 1306 10.1007/s00262-008-0642-y 19139884 PMC11030873

71. Garon EB Rizvi NA Hui R Pembrolizumab for the treatment of non-small-cell lung cancer N Engl J Med 2015 372 21 2018 2028 10.1056/NEJMoa1501824 25891174

72. Wang JP Tang YY Fan CM The role of exosomal non-coding RNAs in cancer metastasis Oncotarget 2017 9 15 12487 12502 10.18632/oncotarget.23552 29552328 PMC5844764

73. Shao C Yang F Miao S Role of hypoxia-induced exosomes in tumor biology Mol Cancer 2018 17 1 120 10.1186/s12943-018-0869-y 30098600 PMC6087002

74. Bally AP Tang Y Lee JT Conserved region C functions to regulate PD-1 expression and subsequent CD8 T cell memory J Immunol 2017 198 1 205 217 10.4049/jimmunol.1601464 27895178 PMC5173413

75. Cho HY Lee SW Seo SK Interferon-sensitive response element (ISRE) is mainly responsible for IFN-alpha-induced upregulation of programmed death-1 (PD-1) in macrophages Biochim Biophys Acta 2008 1779 12 811 819 10.1016/j.bbagrm.2008.08.003 18771758

76. Seto T Sam D Pan M Mechanisms of primary and secondary resistance to immune checkpoint inhibitors in cancer Med Sci (Basel) 2019 7 2 14 10.3390/medsci7020014 PMC6410194 30678257

77. Gabrusiewicz K Li X Wei J Glioblastoma stem cell-derived exosomes induce M2 macrophages and PD-L1 expression on human monocytes Oncoimmunology 2018 7 4 e1412909 10.1080/2162402X.2017.1412909 29632728 PMC5889290

78. Zitvogel L Ma Y Raoult D The microbiome in cancer immunotherapy: diagnostic tools and therapeutic strategies Science 2018 359 6382 1366 1370 10.1126/science.aar6918 29567708

79. Routy B Le Chatelier E Derosa L Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors Science 2018 359 6371 91 97 10.1126/science.aan3706 29097494

80. Gopalakrishnan V Spencer CN Nezi L Gut microbiome modulates response to anti-PD-1 immunotherapy in melanoma patients Science 2018 359 6371 97 103 10.1126/science.aan4236 29097493 PMC5827966

81. Elkrief A El Raichani L Richard C Antibiotics are associated with decreased progression-free survival of advanced melanoma patients treated with immune checkpoint inhibitors Oncoimmunology 2019 8 4 e1568812 10.1080/2162402X.2019.1568812 30906663 PMC6422373

82. Nebot-Bral L Coutzac C Kannouche PL Why is immunotherapy effective (or not) in patients with MSI/MMRD tumors? Bull Cancer 2019 106 2 105 113 10.1016/j.bulcan.2018.08.007 30342749

83. Le DT Durham JN Smith KN Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade Science 2017 357 6349 409 413 10.1126/science.aan6733 28596308 PMC5576142

84. Overman MJ McDermott R Leach JL Nivolumab in patients with metastatic DNA mismatch repair-deficient or microsatellite instability-high colorectal cancer (CheckMate 142): an open-label, multicentre, phase 2 study Lancet Oncol 2017 18 9 1182 1191 10.1016/S1470-2045(17)30422-9 28734759 PMC6207072

85. André T Shiu KK Kim TW Pembrolizumab in microsatellite-instability-high advanced colorectal cancer N Engl J Med 2020 383 23 2207 2218 10.1056/NEJMoa2017699 33264544

86. Xiao L Li L Chen G The lymphocyte-to-monocyte ratio could predict the efficacy of PD-1 inhibitors in patients with advanced cancer Transl Cancer Res 2020 9 7 4111 4120 10.21037/tcr-20-1451 PMC8799307 35117780

87. Correale P Saladino RE Giannarelli D Distinctive germline expression of class I human leukocyte antigen (HLA) alleles and DRB1 heterozygosis predict the outcome of patients with non-small cell lung cancer receiving PD-1/PD-L1 immune checkpoint blockade J Immunother Cancer 2020 8 1 e000733 10.1136/jitc-2020-000733 32554614 PMC7304840

88. Krijgsman D Roelands J Hendrickx W HLA-G: a new immune checkpoint in cancer? Int J Mol Sci 2020 21 12 4528 10.3390/ijms21124528 32630545 PMC7350262

89. Chowell D Morris LGT Grigg CM Patient HLA class I genotype influences cancer response to checkpoint blockade immunotherapy Science 2018 359 6375 582 587 10.1126/science.aao4572 29217585 PMC6057471

90. Khan S Khan SA Luo X Immune dysregulation in cancer patients developing immune-related adverse events Br J Cancer 2019 120 1 63 68 10.1038/s41416-018-0155-1 30377338 PMC6325132

91. Oyanagi J Koh Y Sato K Predictive value of serum protein levels in patients with advanced non-small cell lung cancer treated with nivolumab Lung Cancer 2019 132 107 113 10.1016/j.lungcan.2019.03.020 31097082

92. Fujimura T Sato Y Tanita K Serum levels of soluble CD163 and CXCL5 may be predictive markers for immune-related adverse events in patients with advanced melanoma treated with nivolumab: a pilot study Oncotarget 2018 9 21 15542 15551 10.18632/oncotarget.24509 29643991 PMC5884646

93. Correale P Saladino RE Giannarelli D HLA expression correlates to the risk of immune checkpoint inhibitor-induced pneumonitis Cells 2020 9 9 1964 10.3390/cells9091964 32854442 PMC7564884

94. Hasan Ali O Berner F Bomze D Human leukocyte antigen variation is associated with adverse events of checkpoint inhibitors Eur J Cancer 2019 107 8 14 10.1016/j.ejca.2018.11.009 30529903

95. Cappelli LC Dorak MT Bettinotti MP Association of HLA-DRB1 shared epitope alleles and immune checkpoint inhibitor-induced inflammatory arthritis Rheumatology (Oxford) 2019 58 3 476 480 10.1093/rheumatology/key358 30508191 PMC6821338

96. Munakata W Ohashi K Yamauchi N Fulminant type I diabetes mellitus associated with nivolumab in a patient with relapsed classical Hodgkin lymphoma Int J Hematol 2017 105 3 383 386 10.1007/s12185-016-2101-4 27696192

97. Sakurai K Niitsuma S Sato R Painless thyroiditis and fulminant type 1 diabetes mellitus in a patient treated with an immune checkpoint inhibitor, nivolumab Tohoku J Exp Med 2018 244 1 33 40 10.1620/tjem.244.33 29343652

98. Correale P Saladino RE Nardone V Could PD-1/PDL1 immune checkpoints be linked to HLA signature? Immunotherapy 2019 11 18 1523 1526 10.2217/imt-2019-0160 31865873