Immunological effects of heated intraperitoneal chemotherapy can be augmented by thymosin α1

Background: Peritoneal metastases of colorectal carcinoma origin (PM-CRC) are treated by cytoreductive surgery and heated intraperitoneal chemotherapy (HIPEC). However, the majority of patients recur, calling for novel treatments. We explored the immunogenic changes induced by HIPEC and the possibility to use thymosin α1 (Tα1) as an immune-stimulatory agent. Methods: We used an experimental murine model of PM-CRC combined with mitomycin (MMC)-based HIPEC. We determined immune cell infiltration into tumor metastases after HIPEC administration by means of immunohistochemistry, and determined immunogenic cell death signals in tumor cells by real-time polymerase chain reaction. Results: Mice with PM-CRC treated by HIPEC had increased overall survival (OS) compared to sham-treated mice (median OS 22.8 vs 18.9 days, respectively; P < 0.001). HIPEC induced increased infiltration of CD4+, CD8+, CD68 + and CD20 + cells into omental and visceral metastases at a magnitude of 40–100 %. We searched for potential immune signals induced by HIPEC by determining its effects on known immunogenic cell death proteins (heat-shock protein [HSP]-70, HSP-90 and calreticulin). HIPEC significantly increased HSP-90 mRNA expression (2.37 ± 1.5 vs 1-fold change, P < 0.05). The OS of Tα1 treated mice significantly improved compared to HIPEC-treated mice (16.3 ± 0.8 vs 14.1 ± 0.6 days, respectively, P = 0.02) and vs sham (11.8 ± 0.8 days, P = 0.007). Conclusions: HIPEC induced immunogenic changes that led to increased immune cell infiltration. These changes were further augmented by Tα1 treatment. Future studies aimed at optimizing Tα1 treatment should focus upon the immune response it evokes.