Enhancing neoadjuvant immunotherapy for locally advanced rectal cancer via an injectable thermosensitive hydrogel system with multipathway macrophage immunomodulation.

Conventional surgery for locally advanced rectal cancer (LARC) faces challenges including difficult sphincter preservation and high recurrence rates. Neoadjuvant immunotherapy holds promise for addressing this clinical challenge by reducing the preoperative tumor burden and activating immune memory. However, the benefit remains limited for most patients, who present with the pMMR/MSS subtype, a so-called "immunosuppressive tumor". Therefore, we developed an injectable thermosensitive hydrogel (OXA/αCD47/CpG@PLEL) that, upon transanal minimally invasive injection, achieves precise location and in situ sustained release of oxaliplatin (OXA), anti-CD47 antibody (αCD47), and CpG oligodeoxynucleotides (CpG) at the tumor site for neoadjuvant immunotherapy of LARC. Released OXA induced cancer cell immunogenic cell death, accompanied by exposure of the calreticulin "eat me" signal to macrophages, while αCD47 blocked the CD47-SIRPα "don't eat me" pathway between cancer cells and macrophages, and CpG further activated macrophages. These effects synergistically enhanced phagocytosis by macrophages, while the combination of αCD47 and CpG promoted M1-type polarization of macrophages. In an orthotopic mid-low LARC mouse model, a single preoperative dose of this hydrogel effectively enhanced macrophage antitumor activity. In addition, it promoted dendritic cell maturation and the subsequent systemic CD8+ T-cell response. This triple-action approach significantly reduced the tumor burden and in turn facilitated surgical resection, minimized organ damage, and suppressed postoperative recurrence, culminating in markedly prolonged survival. More importantly, tumor-free mice after initial treatment resisted tumor re-exposure, which was accompanied by increased effector memory T cells. This injectable thermosensitive hydrogel with multipathway macrophage immunomodulation may enhance innate and adaptive immune responses through minimally invasive intervention, precise drug delivery, and long-term regulation, representing a potential synergistic neoadjuvant immunotherapy strategy for LARC.