Abstract 6722: A CD33 antigen targeted Gamma Delta T-cell engager in combination with zoledronate promotes Vg9Vd2+ T cell proliferation and cytotoxicity against acute myeloid leukemia

Abstract

Abstract Vγ9Vδ2+ T cell (GDT) targeted immunotherapy is of interest to harness its MHC-independent cytotoxic potential to promote anti-tumor immunity. However, it remains unclear whether GDT (1-5% of total T cells) are present at sufficient numbers to be therapeutically relevant. Accumulation of intracellular phosphoantigens promotes heterodimerization of butyrophilin (BTN) 2A1 and BTN3A1 on the cell surface, leading to TCR-mediated activation of GDT. To date, clinical trials in cancer patients have failed to demonstrate monotherapy activity using a variety of GDT activating agents, including aminobisphosphonates such as zoledronic acid (ZA), Vδ2+ targeted T cell engagers and BTN3A1 targeted antibodies. These data leave fundamental questions regarding the therapeutic potential of GDT unanswered, including whether they are present in sufficient numbers, whether the agents in question are providing adequate GDT activation, and whether GDT are being directed to tumor cell targets. The studies herein were thus designed to further understand the role of phosphoantigens, butyrophilins and antigen presenting cells (APCs) in activating GDT. Specifically, APC mediated GDT activation was studied in an in vitro co-culture system in the presence and absence of ZA or a CD33-directed GDT engager incorporating a heterodimer of BTN2A1 and BTN3A1 to dissect the contribution of phosphoantigens, butyrophilins and other costimulatory molecules on GDT proliferation and activation. To this end, while BTN2A1/3A1-Fc-CD33scFv treatment alone in T and monocyte-derived dendritic cell (mDC) co-cultures or in unfractionated PBMCs increased the frequency of GDT by 2 to 10-fold after 7-12 days, the combination with low dose ZA (0.5 to 2 μM) synergistically increased GDT proliferation by 40 to 100-fold. These results indicate that GDT proliferation relies both on the abundance of BTN2A1/3A1 heterodimers and other costimulatory signals activated by ZA. Synergistic effects of ZA and BTN2A1/3A1-Fc-CD33scFv in GDT proliferation was similarly observed in human PBMC-engrafted NSG-IL-15tg mice 12 days after treatment. Importantly, the addition of BTN2A1/3A1-Fc-CD33scFv to T (or PBMC) and CD33+ AML co-cultures enhanced both GDT proliferation and anti-leukemic activity while sparing healthy CD33+ immune cells. Collectively, these results demonstrate that GDT proliferation and effector function is dependent both upon the abundance of butyrophilin heterodimers, and other cell surface molecules which are modulated by intracellular phosphoantigen accumulation. Citation Format: Anne Y. Lai, Chunyan Wang, Dana C. Baiu, Kelsey Smith, Arpita Patel, Kinsley Evans, Noah Murr, Derek Franklin, Mahmud Hussain, Joseph Pate, Nathan Oien, Vishruti Makani, Abhinav Shukla, Keith Wilson, George Fromm, Taylor H. Schreiber, Jenny E. Gumperz, Suresh De Silva. A CD33 antigen targeted Gamma Delta T-cell engager in combination with zoledronate promotes Vg9Vd2+ T cell proliferation and cytotoxicity against acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6722.