TCRVγ9 γδ T Cell Response to IL-33: A CD4 T Cell-Dependent Mechanism

The availability of specific stimuli to induce the anticancer cytotoxicity of human TCRV gamma 9-expressing T lymphocytes has allowed the development of gamma delta T cell based cancer immunotherapies. However, the stringent dependence of such strategies on the inherently toxic IL-2 has raised safety concerns for patients, justifying a search for alternative methods for inducing gamma delta T cell stimulation. IL-33 is a gamma-chain receptor-independent cytokine of the IL-1 superfamily that is expressed by endothelial cells from a tumor microenvironment and can sustain Th1 and Th2 immune responses. Therefore, we investigated its ability to support the stimulation of human TCRV gamma 9(+) gamma delta T cells. In this study, we report that IL-33 efficiently sustained the in vitro activation of V gamma 9 T lymphocytes by synthetic phosphoantigens, zoledronate, and a BTN3A1 Ab in the absence of an exogenous supply of IL-2. IL-33 was as potent as IL-2 in allowing the proliferative amplification of V gamma 9 T cells isolated from PBMC following activation by the synthetic phosphoantigen bromohydrin pyrophosphate. IL-33 also induced an identical maturation into TNF-alpha- and IFN-gamma-producing Thl effector memory cells, and IL-33 stimulated cells showed an equivalent cytotoxicity for various tumor cells in vitro. Finally, we found that the bioactivity of IL-33 on the V gamma 9 T cell was indirectly mediated through contact with CD4 T cells and IL-2 production by CD4 T cells and V gamma 9 T cells themselves. These data posit IL-33 as an alternative to IL-2 for V gamma 9 T cell based cancer immunotherapies.