Improving Tumor Immunotherapy by Using Distinct Subpopulations of the γδT Cell Repertoire with High Anti-Tumor Reactivity.

Currently innate immune cells such as γ9δ2T cells are explored in tumor immunotherapy e.g. by adoptive transfer of in vitro expanded bulk γ9δ2T cells.

We speculated that γ9δ2T cells are highly variable in function and specificity due to differences in γ9δ2TCR, NKG2D and KIR expression and that efficacy of adoptively transferred γ9δ2T cells can be increased by transfer of defined subpopulations or clones rather than bulk γ9δ2T cells.

A variety of γ9δ2T cell clones, derived from a healthy donor, were tested for expression levels of γ9δ2TCR, NKG2D and KIRs by flow cytometry analysis. The sequence of the γ9δ2TCR of different clones was further analyzed. Reactivity of γ9δ2T cell clones to a panel of tumor and normal cell lines was tested and these functional analyses were correlated to receptor expression levels and compared with bulk γ9δ2T cells of the same donor.

Functional analyses revealed a high interclonal variability in recognizing leukemia or solid tumor cell lines. Consequently, γ9δ2T cell clones with high anti-tumor reactivity were superior in killing tumor cells when compared to bulk γ9δ2T cells. Different variable regions of γ9δ2-chains and different expression levels of NKG2D and KIRs were detected in multiple clones. No correlations could be found between TCR, NKG2D, and KIR expression on γ9δ2T cell clones and their response to different tumor cell lines when clones expressed different γ9δ2TCRs. However, analysis of γ9δ2T-cell clones with identical γ9δ2TCRs revealed that a clone with higher reactivity against cancer cells expresses higher amounts of NKG2D and lower inhibitory KIRs when compared to a clone with lower reactivity.

γ9δ2TCR, NKG2D and KIR expression in γ9δ2T cells is highly variable and cannot be directly correlated to an effective anti-tumor response. Only, when T-cells express one defined γ9δ2TCR, a modulating activity of NKG2D and KIRs can be observed. Thus, we conclude that anti-tumor reactivity is fine tuned by all three receptors and thereby we speculate that the γ9δ2TCR defines tumor-specificity and activity is further modulated by NKG2D and KIRs. These results support the application of distinct subpopulations or of genetically engineered γδT cells with defined receptors rather than bulk γ9δ2T cells in the context of anti-tumor immunotherapies.

No relevant conflicts of interest to declare.