143 Background: The aim is to characterize the effect of Radiofrequency Ablation (RFA) with anti-CTLA-4 and anti-PD1 checkpoint inhibitors, on tumor growth and immune responses against B16-OVA melanoma tumors implanted in a syngeneic mouse model. Methods: Adult c57BL/6J female mice were distributed among a non-tumor placebo group (n=5) and four experimental tumor groups: no RFA (n=10); RFA alone (n=5); CPI post-RFA (n=5); and CPI pre-and-post-RFA (n=5). On day 0, mice were inoculated SQ with 2.5x105 B16-OVA cells. RFA was performed at day 15. Three doses of anti-mouse CTLA-4 and anti-mouse PD-1 (200 µg/dose each, every 24 h) were given IP to the appropriate groups. To evaluate the effect of the therapy on a distant tumor, each tumor group was re-inoculated SQ at day 20 with 2.5x105 B16-OVA cells. Serum samples were collected to measure concentration of cytokines. Mice were euthanized at day 36. T-cell and non-T cell fractions were collected from splenocytes for co-culture and evaluation of killing in vitro. Results: Mice that received RFA alone or RFA plus CPI showed significantly smaller primary tumors and minimal growth of secondary tumors compared to untreated mice, suggesting that these therapies may have an abscopal effect. Based on the cytokine profile in serum, mice treated with CPI pre-and-post-RFA showed balanced and sustained concentrations of IFNγ and IL-2 (T cell activation) and controlled inflammatory responses. In vitro experiments showed that T cells from mice treated with CPI pre-and-post-RFA produced significantly more IFNγ when co-cultured with B16-OVA cells. However, these T cells did not demonstrate a high killing activity on the tumor cells. The killing capacity of T cells from mice treated with RFA alone or with CPI pre-and-post-RFA increased significantly when the non-T cell fraction (dendritic cells, macrophages, NK cells, and B cells) was added to the co-culture. Conclusions: RFA therapy combined with CPI given to mice bearing B16-OVA tumors may induce systemic immune responses capable of improving control of distant tumor growth. In culture, primed T cells are not able to kill B16-OVA by themselves, but the addition of the non-T cell fraction may improve T cell killing capacity.
Further observations on the inhibition of tumor growth byC. parvum with cyclophosphamide.VII. Effect of treatment prior to primary tumor removal on the growth of distant tumor