Improvement of immune response after radiofrequency ablation in colorectal cancer.

Abstract

102 Background: Radiofrequency ablation (RFA) efficiency of liver tumors is compromised by high rates of relapse. Death of cancer cells by hyperthermia induced tumor antigen releasing, expression of danger signals that activate a specific T-cell response. This effect is ineffective to avoid recurrence. We propose to combine RFA with priming of a strong immune antitumor response as curative treatment of an aggressive colorectal cancer (CRC) in immunocompetent mouse. Methods: RFA was used to treat a CT26- luc tumor as primary lesion. In two distinct clinical situations, macroscopic or microscopic distant tumors were established as secondary lesions. The immune response was modulated by the injection, in the treated area, of a thermo-reversible hydrogel loaded by GM-CSF and BCG, targeting recruitment and maturation of dendritic cells. In mice with far large lesions, this strategy was combined with PD1checkpoint inhibition. The efficiency was assessed on survival, evolution of distant lesions, characterization of tumoral lymphocyte infiltration TNF-α and IFN-y expression in peripheral T lymphocytes. Results: The in situ immunogel injection after RFA resulted in prolonged survival of mice. Regression of distant lesions was related to the induction of a strong systemic antitumor immune response and a great improvement of tumor infiltration by CD3+ T lymphocytes. In adjuvant situation, the use of immunogel induced a complete cure of microscopic secondary lesions without another treatment. Immune escape of large secondary lesions was reversed by association of the RFA-immunogel vaccination with a systemic immune checkpoint inhibition, separately ineffective. Conclusions: Validation of this strategy, combining RFA of macroscopic lesions and activation of a strong immune response controlling the residual disease, could result in the design of a clinical assay including this approach within a standard treatment of colorectal liver metastases. The synergy between in situ immunomodulation as priming process and checkpoint blockade, ineffective alone in metastatic microsatellite stable CRC or after single RFA, allows reconsidering the use of checkpoint inhibitors in CRC.