Purpose Radiofrequency ablation (RFA) has been shown to elicit tumor-specific T cell immune responses but is not sufficient to prevent cancer progression. Here we investigated immune suppressive mechanisms limiting the efficacy of RFA. Experimental design We performed a retrospective case-controlled study on patients with synchronous colorectal cancer liver metastases who had received primary tumor resection with or without pre-operative RFA for liver metastases. Tumor infiltrating T cells and tumoral PD-L1 expression in human colorectal cancer tissues were analyzed by immunohistochemistry. T cell immune responses and PD-1/PD-L1 expression were also characterized in a RFA mouse model. In addition, the combined effect of RAF and PD-1 blockade was evaluated in the mouse RFA model. Results We found that RFA treatment of liver metastases increased not only T cell infiltration but also PD-L1 expression in primary human colorectal tumors. Using mouse tumor models, we demonstrated that RFA treatment of one tumor initially enhanced a strong T cell-mediated immune response in tumor. Nevertheless, tumor quickly overcame the immune responses by inhibiting the function of CD8+ and CD4+T cells, driving a shift to higher Treg to Teff ratio, and up-regulating of PD-L1/PD-1 expression. Furthermore, we established that the combined therapy of RFA and anti-PD-1 antibodies significantly enhanced T cell immune responses, resulting in stronger antitumor immunity and prolonged survival. Conclusions The PD-L1/PD-1 axis plays a critical role in dampening RFA-induced antitumor immune responses. And this study provides a strong rationale for combining RFA and the PD-L1/PD-1 blockade in the clinical setting.

Radiofrequency ablation (RFA) promotes tumor antigen-specific T cell responses and enhances the effect of immunotherapy in preclinical settings. Here we report that the existence of remnant tumor masses due to incomplete RFA (iRFA) is associated with earlier new metastases and poor survival in patients with colorectal cancer liver metastases (CRCLM). Using mouse models, we demonstrate that iRFA promotes tumor progression and hinders the efficacy of anti-PD-1 therapy. Immune analysis reveals that iRFA induces sustained local inflammation with predominant myeloid suppressor cells, which inhibit T cell function in tumors. Mechanistically, tumor cell-derived CCL2 is critical for the accumulation of monocytes and tumor-associated macrophages (TAMs). The crosstalk between TAMs and tumor cells enhances the CCL2 production by tumor cells. Furthermore, we find that administration of a CCR2 antagonist or the loss of CCL2 expression in tumor cells enhances the antitumor activity of PD-1 blockade, providing a salvage alternative for residual tumors after iRFA.

ObjectiveIt remains controversial whether tumour mutational burden (TMB) or neoantigens are prognostic markers in hepatocellular carcinoma (HCC). This study aimed to define the function of TMB or neoantigens in antitumour immunotherapy.DesignNeoantigens of patients (n=56) were analysed by pVAC tools with major histocompatibility complex-1 (MHC-I) algorithms based on whole exome sequencing and neoantigens with mutant type IC50 <50 nM were defined as high-affinity neoantigens (HANs). Patients were segregated into HAN-high/low groups by median of HAN value, and overall survival (OS) was analysed. Autologous organoid killing model was developed to clarify the antitumour activity of HANs.ResultsThe value of HAN showed a better correlation with OS (p=0.0199) than TMB (p=0.7505) or neoantigens (p=0.2297) in patients with HCC and positively correlated with the frequency of CD39+CD8+ tumour infiltrating lymphocytes (TILs). Furthermore, HAN-specific CD8+ T cells were identified in CD39+CD8+ TILs, which showed better antitumour activity in HAN-high versus HAN-low group. In addition, more effective HAN peptides were identified in HAN-high versus HAN-low group. Besides, flow cytometry data showed that in fresh tumour, CD39+PD-1intCD8+ TILs displayed an effector phenotype and stronger antitumour activity in HAN-high versus HAN-low group. More importantly, patients in HAN-high versus HAN-low group showed a better prognosis after anti-PD-1 therapy.ConclusionsOur study first demonstrates that HAN value positively correlates with better OS in patients with HCC. HANs trigger antitumour activity by activating tumour-reactive CD39+CD8+ T cells, and patients in HAN-high group benefited more from anti-PD-1 therapy than HAN-low group. These findings may provide a novel strategy for personalised antitumour therapies for HCC.