Abstract 2313: Enhanced activity of second-generation MAGE-A4 SPEAR T-cells through co-expression of a CD8α homodimer

Abstract Affinity enhanced T-cell receptors (TCRs) have shown promise in the clinic. Second-generation strategies that enhance T-cell function alongside the TCR may improve the depth and durability of anti-tumor responses. In this second-generation TCR study, we added a CD8α homodimer to our MAGE-A4c1032TCR, a first-generation TCR currently being tested in a clinical trial (NCT03132922). Transduction of HLA class I-restricted, specific peptide enhanced affinity receptor (SPEAR) TCRs into peripheral blood lymphocytes creates both cytotoxic (CD8+) and helper (CD4+) T-cells of the same specificity; however, the lack of CD8 co-receptors on CD4+ T-cells may affect binding avidity of the engineered TCR. The addition of CD8α co-receptor into CD4+ T-cells alongside the engineered TCR (CD8α_MAGE-A4c1032) is anticipated to increase TCR binding avidity and enhance the polyfunctional response of CD4+ T-cells against tumor antigens, thereby widening the immune response to the tumor through dendritic cell (DC) activation and enhanced cytotoxicity. The effect of co-expressing the CD8α co-receptor on the MAGE-A4c1032TCR was assessed by in vitro assays addressing proof of concept for increased potency, focusing on CD4+ function, in parallel with assessment of potential safety issues. In assays involving antigen-positive tumor cell lines co-cultured with T-cells, we demonstrated improved T-cell engagement, as measured by increased CD40L on the T-cell surface in response to antigen. There were modest improvements in T-cell proliferation and cytokine production in response to tumor cells, particularly when isolated CD4+ cells were analyzed. However, when immature DCs were added to the co-culture, a more marked improvement with the second-generation T-cells was seen. DCs and T-cells in conditions containing CD8α_MAGE-A4c1032T-cells produced higher levels of cytokines and chemokines (e.g. IL-12, MIG for DCs, IFNγ, IL-2 for T-cells) than in conditions that contained MAGE-A4c1032T-cells without the CD8α co-receptor. Flow cytometry analyses illustrated T-cell-driven maturation of the DCs during the course of the co-culture. We also saw that second-generation CD4+ T-cells expressing the CD8α homodimer were able to kill antigen-expressing 3D tumor line microspheres, an additional benefit to the improvement of CD4+ helper functions. No changes in TCR specificity, sensitivity, or aberrant cytokine release arose from co-expressing the CD8α co-receptor in T-cells transduced with the MAGE-A4c1032TCR, suggesting no change to the existing safety profile. These data illustrate improved engagement and function in the CD4+ T-cells transduced with CD8α_MAGE-A4c1032, without additional off-target reactivity. The second generation CD8α_MAGE-A4 SPEAR T-cells are expected to improve long term T-cell functions as well as immediate anti-tumor activity in vivo. Citation Format: Victoria E. Anderson, Anika M. Weber, Guy E. Wiedermann, Anette Pachnio, Sumaya Dauleh, Tina Ahmed, Roslin Y. Docta, Adriano Quattrini, George Pope, Laura Quinn, Thomas M. Ashton, Helen M. Tunbridge, Joseph P. Sanderson, Andrew B. Gerry. Enhanced activity of second-generation MAGE-A4 SPEAR T-cells through co-expression of a CD8α homodimer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2313.