Abstract CT170: Trial in progress: A phase 1, first in human clinical trial for T-Plex, a multiplexed, enhanced T cell receptor-engineered T cell therapy (TCR-T) for solid tumors

Abstract Checkpoint immunotherapies have revolutionized solid tumor treatment yet durably benefit a minority of patients, as they rely on endogenous anti-tumor T cells. A potential solution for patients lacking functional endogenous anti-tumor T cells is engineering their T cells with exogenous T cell receptors (TCRs) to target and kill tumor cells. Initial clinical trials with TCR engineered T cell therapies (TCR-Ts) targeted single tumor antigens on single HLA and produced partial, short-lasting responses. Solid tumors are notoriously heterogenous with highly variable antigen expression. Recent discoveries also identified HLA loss of heterozygosity in up to 40% of solid tumors, allowing tumor cells to evade T cell attack. To overcome this heterogeneity, TScan has developed T-Plex, a multiplexed cell therapy comprising 2-3 different TCR-Ts, chosen from a collection of TCR-Ts called the ImmunoBank, to target different tumor antigens on different HLA types with confirmed tumor expression. To deepen clinical responses, TCR-T cells are engineered to express CD8α/β co-receptors that, in preclinical experiments, enable CD4+ helper T cells to have 100-fold improved cytotoxicity and cytokine secretion over CD4+ cells expressing the TCR alone. Finally, to allow T cell persistence despite immunosuppressive TGF-β in the solid tumor microenvironment, TCR-T cells also express the dominant negative TGF-βreceptor, enabling ~10-fold improved proliferation in the presence of TGF- β compared to T cells expressing the TCR and CD8α/β co-receptors alone. A proprietary transposon vector with larger cargo limit enables the inclusion of these additional genes. The Phase 1 study utilizes a separate screening protocol to pre-identify patients with head and neck, cervical, anogenital cancers, NSCLC, and melanoma, any time during standard clinical care, enabling rapid enrollment into the treatment protocol upon disease progression. Screening comprises germline HLA testing, and archival tumor testing for antigen expression and exclusion of HLA loss. Treatment includes standard non-myeloablative lymphodepletion followed by one or 2 doses of T-Plex infused 28 days apart. Dose escalation under the interval 3+3 design starts with testing single TCR-Ts in dose levels 1 and 2. Thereafter, TCR-Ts are combined and escalated in dose levels 3 and 4. TCR-Ts currently in the master protocol target PRAME, MAGE-A1 or HPV16 on HLA-A*02: 01 or MAGE-A1 on HLA-C*07: 02. Additional TCR-Ts added to the ImmunoBank and master protocol go through dose levels 1 and 2 as single therapies before becoming available for multiplexed dose levels 3 and 4. Primary endpoints include safety, feasibility and identifying the recommended Phase 2 dose. Secondary endpoints are rates and durations of response and exploratory endpoints measure T cell activation and persistence. Two additional TCR-Ts are on track to be added to the ImmunoBank, which could allow 50-80% of common solid tumor patients to qualify for multiplexed TCR-T therapy. Citation Format: Justin Moser, Brian Pico, Brian Henick, Rom Leidner, Jared Weiss, James Isaacs, Jaspreet Grewal, Michael Hurwitz, Jim Murray, Marlyane Motta, Yun Wang, Shrikanta Chattopadhyay, Debora Barton, Gavin MacBeath, Sajeve Thomas. Trial in progress: A phase 1, first in human clinical trial for T-Plex, a multiplexed, enhanced T cell receptor-engineered T cell therapy (TCR-T) for solid tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT170.