Type: Oral
Session: 622. Lymphomas: Translational – Non-Genetic: Elucidating Biomarkers and Mechanisms of Therapy in Lymphoma
Hematology Disease Topics & Pathways:
Research, Biological therapies, Translational Research, Lymphomas, B Cell lymphoma, Chimeric Antigen Receptor (CAR)-T Cell Therapies, Combination therapy, Diseases, Therapies, Lymphoid Malignancies
Strikingly, treating EZB cells with EZH2 inhibitor tazemetostat (taz) ex vivo reprogrammed them to re-express the full spectrum of T cell engagement genes such as ICOSL, ITGB7, 4-1BBL, and OX40L and rendered them highly immunogenic. For example, mixing endogenous T cells with taz pre-treated EZB cells yielded markedly enhanced killing (p<0.001). Taz pre-treated EZB cells failed to engraft in syngeneic mice due to immunological rejection, but caused fatal DLBCL in Rag1-/- mice. EZB cell lines did not undergo proliferation arrest after taz ex vivo, but showed a significant reduction in tumor burden (p<0.05) when treated in vivo, along with a 3-fold increase in tumor CD4 and CD8 cells (p<0.05), and 50% reduction in Tregs (p<0.01). Taz also increased the proportion of naïve/memory CD8 and reduced effector CD8 cells. EZH2 inhibitors therefore mediate their effects at least in part through immunological mechanisms.
We next examined whether taz had any deleterious effect on CART cells. Pre-treating donor mice with taz prior to harvesting T cells yielded significant increase in memory CD8 CART cells after transduction (p<0.05). Taz pre-treated CART cells displayed superior killing of EZB cells (p<0.001) and proliferative capacity ex vivo (p<0.001). Infusing taz pre-treated CART cells in EZB mice resulted in significantly reduced tumor burden in vivo (p<0.001) and reduction in PD1+CD38+ exhausted CD8 CART cells (p<0.001).
On the other hand, pre-treatment of EZB cells (but not CART cells) with taz ex vivo enhanced CART cell killing by 3-fold (p<0.001). Administering CART cells in vivo in EZB mice after taz treatment significantly prolonged their survival (100% vs 30%, p<0.01) and was associated with significant reduction in tumor burden assessed by IVIS and post-mortem examination. Therefore, EZH2 inhibition enhances CART cell activity through direct effects on CART cells, in addition to making EZB immunogenic.
Finally, to directly demonstrate the functional consequence of rendering EZB lymphomas immunogenic on CART performance in vivo, we performed intravital 2-photon imaging of popliteal lymph nodes using dTomato labeled CART cells and GFP+ EZB lymphomas. Remarkably, pre-treatment of EZB cells with taz, doubled the recruitment of CART cells into lymphomas (p<0.001) and significantly enhanced the CART to EZB lymphoma cell surface engagement index (strength and duration of binding, p<0.001). This was associated with increased killing, and CART-engaged lymphoma cells were observed to be ingested/engulfed or phagocyted by tumor resident macrophages.
Collectively, EZH2 inhibitors yield a potent boost to CART mediated anti-lymphoma effects by enhancing CART cell functions and B cell immunogenicity, which would likely yield a significant clinical benefit for these patients where CART cells are less active. These results prompted us to initiate a clinical trial evaluating the safety and efficacy of this combination in B cell lymphomas (NCT05934838).
Disclosures: Melnick: Ipsen: Consultancy, Research Funding; Janssen: Research Funding; Treeline Biosciences: Consultancy; Daiichi Sankyo: Consultancy, Research Funding. Ruella: AbClon: Consultancy, Research Funding; NanoString: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; Bayer: Consultancy; GlaxoSmithKline: Consultancy; viTToria biotherapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Scientific Founder, Research Funding; Beckman Coulter: Research Funding.
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