Interleukin-7-dependent expansion and persistence of melanoma-specific T cells in lymphodepleted mice lead to tumor regression and editing.

Active-specific immunotherapy with dendritic cells loaded with peptide derived from the melanoma antigen, gp100, failed to mediate regression of established B16F10 melanoma in normal mice. Dendritic cell vaccination induced activation and subsequent deletion of adoptively transferred naive CD8+ T-cell receptor transgenic (pmel-1) T cells specific for gp100 in normal mice. In lymphodepleted mice, dendritic cell vaccination produced greater T-cell expansion, long-term persistence of memory T cells, and tumor regression. Most tumors that persisted in the presence of functional memory T cells had either lost or exhibited reduced expression of MHC class I or gp100 proteins. In contrast to other naive T cells, pmel-1 T cells adoptively transferred to lymphodepleted mice exhibited faster proliferation and a more differentiated phenotype after exposure to peptide-pulsed dendritic cells. Proliferation and persistence of pmel-1 T cells was highly dependent on interleukin-7 (IL-7) in irradiated mice, and IL-15 when IL-7 was neutralized, two critical homeostatic cytokines produced in response to the irradiation-induced lymphodepletion.