Anti-BTN3A 20.1 Agonist Monoclonal Antibody Enhances Autologous Vγ9Vδ2 T Cells Cytotoxicity Against Primary Acute Myeloid Blasts

Introduction: Vγ9Vδ2 T cells immunotherapy is an emerging strategy in acute myeloid leukemia (AML). Partial effects of phosphoantigens like zoledronate, prompted us to investigate other molecules. Using Vγ9Vδ2 T cells expanded from healthy volunteers, recent works of our team demonstrate that anti-BTN3A 20.1 agonist monoclonal antibody (mAb) improves Vγ9Vδ2 T cells cytotoxicity in vitro and in vivo, including in zoledronate resistant blasts. Efficacy of anti-BTN3A 20.1 agonist mAb remains undetermined using autologous Vγ9Vδ2 T cells and mechanism of its action on AML blasts is understudied. Material and methods: Expression of co-stimulatory molecules on surface of AML blasts and Vγ9Vδ2 T cells, from 37 PBMC of AML patients, was assessed by flow cytometry. Vγ9Vδ2 T cells expansion was realized from the same samples with zoledronate, and administrations of Il-2 and Il-15. Purity was assessed by flow cytometry at day 13. Degranulation assay was performed at day 14. Results: 20 degranulation assays were realized on successfully expanded Vγ9Vδ2 T cells (69% of analyzable samples). Degranulation with anti-BTN3A 20.1 agonist mAb was enhanced compared to zoledronate condition (p=0.0085) or negative control (p<0.0001). We also show a positive correlation between level of degranulation and expression of DNAM-1 on Vγ9Vδ2 T cells surface, exclusively under anti-BTN3A 20.1 agonist mAb treatment (rS=0.54; p=0.0134). Conversely, under zoledronate treatment, Vγ9Vδ2 T cells degranulation was positively correlated with expression of NKG2D on Vγ9Vδ2 T cells surface (rS=0.62; p=0.0099) and was inversely associated to their expression of PD-1 (p=0.0482). Conclusion: Efficacy of anti-BTN3A 20.1 agonist mAb on primary AML blasts is confirmed in an autologous setting. Degranulation seems to play a major role in enhancement of Vγ9Vδ2 T cells cytotoxicity under anti-BTN3A 20.1 agonist mAb treatment, where DNAM-1 could play a determinant role. An autologous strategy for Vγ9Vδ2 T cells may be studied and considered in AML patients, with potent extrapolation to γδ T cell therapy protocols in targeting strategies. Disclosures Vey: Novartis: Consultancy, Honoraria; Janssen: Honoraria. Olive:ImCheck Therapeutics: Consultancy, Equity Ownership, Patents & Royalties; GlaxoSmithKline: Patents & Royalties.