Abstract
Cell-based immunotherapy strategies target tumors directly (via cytolytic effector cells) or aim at mobilizing endogenous anti-tumor immunity. The latter approach includes dendritic cells (DC) most frequently in the form of in vitro cultured peripheral blood monocytes-derived DC. Human blood gamma delta T cells are selective for a single class of non-peptide agonists ("phosphoantigens") and develop into potent antigen-presenting cells (ARC), termed ("phosphoantigens") and develop into potent antigen-presenting cells (ARC), termed gamma delta T-ARC within 1-3 days of in vitro culture. Availability of large numbers of gamma delta T-APC would be advantageous for use as a novel cellular vaccine. We here report optimal gamma delta T cell expansion (>10(7) cells/ml blood) when peripheral blood mononuclear cells (PBMC) from healthy individuals and melanoma patients were stimulated with zoledronate and then cultured for 14 days in the presence of IL-2 and IL-15, yielding gamma delta T cell cultures of variable purity (77 +/- 21 and 56 +/- 26%, respectively). They resembled effector memory alpha beta T (TEO cells and retained full functionality as assessed by in vitro tumor cell killing as well as secretion of pro-inflammatory cytokines (IFN gamma,TNF alpha) and cell proliferation in response to stimulation with phosphoantigens. Importantly, day 14 gamma delta T cells expressed numerous ARC-related cell surface markers and, in agreement, displayed potent in vitro ARC functions. Day 14 gamma delta T cells from PBMC of patients with cancer were equally effective as their counterparts derived from blood of healthy individuals and triggered potent CD8(+) alpha beta T cell responses following processing and cross-presentation of simple (influenza M1) and complex (tuberculin purified protein derivative) protein antigens. Of note, and in clear contrast to peripheral blood gamma delta T cells, the ability of day 14 gamma delta T cells to trigger antigen-specific alpha beta T cell responses did not depend on re-stimulation. We conclude that day 14 gamma delta T cell cultures provide a convenient source of autologous ARC for use in immunotherapy of patients with various cancers.