Anti-tumor immunological response induced by cryoablation and anti-CTLA-4 antibody in an in vivo RM-1 cell prostate cancer murine model

Cryoablation combination therapy with blockade of the T-cell inhibitory receptor CTL-associated antigen-4 (CTLA-4) may augment the anti-tumor immune response (ATIR). It is crucial to determine the duration of ATIR after cryoablation and anti-CTLA-4 antibody therapy to determine the most appropriate treatment interval of therapy. To investigate the characteristics of ATIR induced by cryoablation and anti-CTLA-4 antibody therapy, we developed a prostate cancer model system to test the capacity of cryoablation and anti-CTLA-4 antibody to generate ATIR. Mice were randomly assigned to receive no treatment (group A), cryoablation only (group B), cryoablation plus anti-CTLA-4 antibody (group C), or anti-CTLA-4 antibody only (group D). We collected specimens on days 0, 7, 14 and 21 to study the ATIR through different techniques. Our results indicated that cryoablation induced ATIR and further enhanced this effect and reduced the number of distant metastases through combination with anti-CTLA-4 antibody. ATIR induced by cryoablation was achieved through decreasing regulatory T cell (Treg) number. The number of Tregs induced by cryoablation was lowest on day 14 but then returned to preoperative levels on day 21, indicating that ATIR induced by cryoablation was time-dependent. However, ATIR induced by anti-CTLA-4 antibody might be mainly achieved through influencing Treg function, which was exactly not by decreasing Treg number and still maintain its ATIR effect on day 21 after therapy. In conclusion, ATIR induced by cryoablation was achieved through decreasing Treg number and is time-dependent, whereas ATIR caused by anti-CTLA-4 antibody was achieved exactly not by decreasing Treg number and not time-dependent in the first 21 days after therapy.