Abstract 778: Cellular and molecular requirements for rejection of B16 melanoma in the setting of regulatory T cell depletion and homeostatic proliferation
Authors: Kline Justin P. , Zhang Long , Cohen Kenneth , Gajewski Thomas F. 
Published: June 2012

Abstract
We have recently demonstrated that adoptive transfer of regulatory T cell (Treg) -depleted polyclonal T cells into lymphopenic mice can result in rejection of B16 melanoma. In the current work, we investigated the cellular and molecular requirements for tumor rejection by CD25-depleted T cells in RAG−/− or irradiated C57BL/6 recipient mice. Consistent with the robust expansion of antigen-specific CD8+ T cells observed in this model, tumor antigen cross-presentation and B7 costimulation of T cells by host cells was required, as tumor rejection did not occur in irradiated Kb−/− bone marrow chimeric mice or B71/2−/− mice following CD25-depleted T cell transfer. Using donor T cells from CD4−/− or CD8−/− mice, we observed that both CD4+ and CD8+ T cells were necessary for B16.SIY rejection. The contribution of conventional CD4+ T cells led us to investigate mechanisms of T cell help. Interestingly, tumor rejection occurred in irradiated CD40−/− hosts, and with transfer of IL2−/− CD4+CD25− T cells along with wildtype CD8+ T cells into RAG2−/− hosts. These results indicate that the role of CD4+ T cells was not to license antigen-presenting cells (APC) through CD40L, and not through provision of IL-2 to CD8+ T cells, and may be to directly recognize and kill B16 cells. At the effector phase, IFN-γ production by adoptively-transferred CD8+ or CD4+ T cells was sufficient for B16 elimination. Tumor rejection was lost when both host and B16 cells were incapable of signaling through IFN-γ. In a host environment completely devoid of IFN-γ, we found decreased intra-tumoral expression of CXCL-10 and increased tumor vascularity, suggesting that IFN-γ produced by adoptively-transferred T cells induced CXCL-10 expression by tumor and/or stromal cells which in turn, inhibited tumor angiogenesis, resulting in IFN-γ-dependent tumor rejection. Finally, production of TNF-α, perforin and expression of FasL by adoptively-transferred CD25-depleted T cells was dispensable, though B16 melanomas grew progressively in mice receiving CD25-depleted T cells deficient in perforin and FasL, arguing that B16 cells can be killed either through granule mediated lysis or apoptosis-induction. Collectively, these results support a model in which host tumor antigen cross-presentation and B7 costimulation to CD8+ T cells, along with an as yet undefined role of CD4+ T cells, generate effector cells that depend at least upon IFN-γ for tumor control. The elimination of Tregs and homeostatic proliferation maintain persistent T cell function in the context of a growing tumor. This straightforward adoptive transfer strategy has strong potential for translation to the clinic.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 778. doi:10.1158/1538-7445.AM2011-778