Human γδ T cells expressing Vγ2Vδ2 TCRs monitor self- and foreign-isoprenoid metabolites to mediate immunity to tumors and microbes. Bisphosphonate treatment of tumors increases isopentenyl pyrophosphate that is sensed by butyrophilin 3A1, allowing Vγ2Vδ2 cells to kill tumors independent of MHC expression or tumor mutational burden. In clinical trials, adoptive immunotherapy with Vγ2Vδ2 cells has few side effects but has resulted in only a few partial and complete remissions. Direct immunization of cancer patients with either a bisphosphonate or bromohydrin pyrophosphate and IL-2, expands Vγ2Vδ2 cells but they rapidly contract, terminally differentiate, and lose responsiveness. Similarly, we find that monkeys immunized with zoledronic acid and IL-2 lose Vγ2Vδ2 cell responsiveness with terminal differentiation. To identify a live bacterial vaccine for Vγ2Vδ2 cells, we tested Listeria monocytogenes (Lm) attenuated by actA deletion with a mutant PrfA protein (G155S) that increases their virulence. Immunization with these attenuated Lm expanded Vγ2Vδ2 cells on secondary immunization that persisted after a third immunization. Vγ2Vδ2 cells retained central memory phenotypes, expressed inflammatory chemokine receptors, and produced IFN-γ without induction of anergy. Expression of PrfA (G155S) was critical because immunization with ΔactA Lm with wild-type PrfA resulted in minimal Vγ2Vδ2 T cell expansions. Similarly, despite high HMBPP levels, immunization with ΔlytB ΔactA prfAwt Lm resulted in minimal expansions. Thus, Lm stimulation of Vγ2Vδ2 T cells is dependent on their virulence rather than their HMBPP levels. Unlike zoledronic acid, immunization with ΔactA prfAG155S Lm induces large expansions of Vγ2Vδ2 T cells that retain central memory phenotypes and responsiveness.
Craig Morita– Professor, University of Iowa/VA Health Care System
Mohanad Nada– Assistant Professor, American University of Iraq, Sulaimani
Grefachew Workalemahu– Research Associate, University of Iowa College of Medicine
Hong Wang– Research Scientist, University of Iowa College of Medicine