Insights into the Mechanism of Action of Phosphoantigen Prodrugs on Vγ9Vδ2 T Cell Activation

The activation of Vγ9Vδ2 T cells has emerged as a promising modality in cancer immunotherapy. Phosphate and phosphonate prodrugs of Vγ9Vδ2 T cell phosphoantigens have been developed as potent activators of Vγ9Vδ2 T cells that are capable of effectively facilitating lysis of a range of cancer cells in vitro. In this work, we show that phosphonate prodrugs of the phosphoantigen derivative, HMBP, enter cells in an energy-independent manner and produce their pharmacological activity independently of the mevalonate pathway, a target of the widely used bisphosphonate and Vγ9Vδ2 T cell activator, zoledronate. Interestingly, these prodrugs, termed HMBP ProPAgens, induced an enhanced and more universal Vγ9Vδ2 T cell cytotoxicity against diverse cancer cell lines in vitro compared to zoledronate, an effect also observed in patient-derived colorectal cancer organoids. Together, the data presented in this work further support the development of HMBP ProPAgens as a novel class of cancer immunotherapeutic agents.