γ9 and δ2CDR3 domains regulate functional avidity of T cells harboring γ9δ2TCRs

Immunotherapy with innate immune cells has recently evoked broad interest as a novel treatment option for cancer patients. γ9δ2T-cells in particular are emerging as an innate cell population with high frequency and strong anti-tumor reactivity, which makes γ9δ2T-cells and their receptors promising candidates for immune-interventions. However, clinical trials have so far reported only limited tumor control by adoptively transferred γ9δ2T-cells. As a potential explanation for this lack of efficacy, we found unexpectedly high variability in tumor recognition within the physiological human γ9δ2T-cell repertoire, which is substantially regulated by the CDR3 domains of individual γ9δ2T-cell receptors (TCR). We demonstrate that here reported molecular requirements of CDR3 domains to interact with a target-cell shape the physiological γ9δ2T-cell repertoire and most likely limit protective and therapeutic anti-tumor efficacy of γ9δ2T-cells. Based on these findings, we propose combinatorial-γδTCR-chain-exchange (CTE) as an efficient method for designing high-affinity γ9δ2TCRs that mediate improved anti-tumor responses when expressed in αβT-cells, both in vitro and in vivo in a humanized mouse model.