Reversal of tumour immune evasion via enhanced MHC-Class-I antigen presentation by a dual-functional RNA regulated system.

BACKGROUND: Motivating the immune system to target tumour cells plays an increasingly prominent role in the treatment of hepatocellular carcinoma (HCC), but challenges such as low overall response rates persist in current clinical practice. Tumour cell MHC-Class-I (MHC-I) downregulation and antigen loss are typical mechanisms of immune evasion. To this end, a dual-functional RNA-based strategy was conceived for HCC immunotherapy.

METHODS: MHC-I expression on HCC and paratumour tissues from patients was assessed, and the correlations between MHC-I regulators and HCC prognosis were analyzed. Small interfering RNA (siRNA) targeting proprotein convertase subtilisin/kexin type 9 (PCSK9) and mRNA encoding tumour antigens were encapsulated in a fluorinated lipid nanoparticle (LNP), which direct nucleic acids primarily to the liver, making it ideal for HCC treatment. Anti-tumour efficacy was investigated in an orthotopic HCC model, with single-cell RNA sequencing used for in-depth analysis of the tumour microenvironment (TME).

RESULTS: A marked downregulation of MHC-I expression was observed in HCC tumour cells from a cohort of patients, with this MHC-I suppression correlating with poor prognosis and diminished responsiveness to immunotherapy. Among the various MHC-I regulators, PCSK9 is the only one that shows a significant correlation with the prognosis of HCC patients. Knockdown of PCSK9 inhibited MHC-I degradation and thus increased the efficiency of antigen presentation by up to sixfold compared to untreated tumour cells. The hybrid RNA LNPs (h-LNP) enhanced Th1-mediated immune responses, reinvigorating and expanding anti-tumour immunity within the TME. Following treatment with h-LNPs, the TME showed a pronounced infiltration of CD8+ T cells and NK cells, coupled with a significant reduction in immune-suppressive populations, such as M2-like macrophages, in contrast to the controls. These changes in the immune landscape were accompanied by a marked inhibition of tumour growth in an orthotopic HCC model as well as melanoma, where this dual-functional RNA-regulated system outperformed the control groups.

CONCLUSIONS: The present study successfully engineered a dual-functional RNA-regulated system that augments tumour cell antigen presentation and reconfigures the immune landscape within the TME, thereby potentiating the anti-tumour efficacy of the mRNA vaccine.