Multi-virus specific T cells to enhance the activity of bispecific antibodies in lymphoma.

7004 Background: Although Bispecific Antibodies (BsAbs) have the advantage of an “off the shelf” immune approach, their clinical activity relies on the patients’ native T-cell population that is impaired by prior chemotherapy and tumor-induced T cell exhaustion. T-cell dysfunction within the TME is one potential mechanism of BsAb resistance (Falchi, L. et. al. Blood), while continuous exposure to bispecific molecules also induces T-cell exhaustion (Phillipp, N. et. al. Blood). A higher frequency of regulatory T cells and increased markers of T cell exhaustion were seen in BsAb non-responders (Cortes-Selva, D. et. al. Blood). Banks of multi-virus specific T cells (MVSTs) have safely controlled viral infections in allogeneic hematopoietic stem-cell transplantation recipients (Tzannou, et. al JCO). Expanded MVSTs have a differentiated phenotype, exhibit immediate effector functions (cytotoxicity and cytokine secretion) and have not produced severe graft versus host disease in hundreds of recipients. We hypothesized that MVSTs would enhance the antitumor activity of BsAbs. Methods: To compare the anti-tumor activity of PBMCs and MVSTs, we cocultured GFP-labeled CD20+ BJAB lymphoma cells alone or with healthy donor PBMCs or MVST at a 1:1 ratio, in the presence or absence of CD3xCD20 BsAb. We evaluated T-cell activation using CD69 and CD25 antibodies using quantitative flow cytometry and tumor cell killing by assessing tumor survival at 24 and 48 hours. Results: While the addition of both MVSTs and PBMCs alone reduced tumor cell numbers, PBMCs + BsAbs reduced tumor cells to less than 50% of the cultures at 24 hours but the subsequent increase tumor cell numbers indicated lack of effective control. By contrast, MVSTs reduced the frequency of tumor cells from 42.5% at 24 hours and less than 2% by 48 hours. The number of T-cells in PBMCs decreased by 0.88-fold after 48-hours, while MVSTs increased by 2.16-fold in the presence of 1ng/ml BsAb. The number of T cells expressing CD25 increased 6.25-fold with PBMCs and 456.68-fold with MVST in the presence of BsAb. Conclusions: We have demonstrated that in combination with BsAb, MVSTs exhibit more rapid effector function and expansion than similarly cultured PBMCs, suggesting they could enhance tumor response depth. Despite using healthy donor PBMCs, which showed a 6-fold increase in activated T cells with BsAb, MVSTs induced 456-fold increase. This significant boost in T cell activation highlights MVSTs’ potential to overcome endogenous T cell exhaustion and enhance BsAb therapy. Tumor cell and T cell numbers after co-culture with PBMC or MVST +/- BsAb. Tumor cell numbers CD3+ T-cell numbers CD25+ Activated T-cells 24 hours 48 hours 48 hours 48 hours BJAB Alone 104,345 101,992 + PBMC 104,632 57,094 30,458 5,058 + PBMC + BsAb 1ng 17,350 37,621 26,665 31,621 BJAB Alone 51,633 69,183 + MVST 52,815 19,858 86,545 419 + MVST + BsAb 1ng 28,259 1,584 186,737 191,348