Abstract 4: Identifying novel patient-derived T cell receptors targeting TP53 public neoantigens
Authors: Gormally Michael V. , Chandran Smita S. , Etxebarria Inaki , Klebanoff Christopher 
Published: March 2024

Abstract
Adoptive cell transfer (ACT) is a promising immunotherapeutic strategy to bolster reactivity against immunologically cold tumors through infusion of T cells that can recognize and eliminate cancer cells bearing mutation-derived neoantigens (NeoAgs). T cell receptors (TCRs) that confer recognition of public NeoAgs–an elite subset of Human leukocyte antigen (HLA)-restricted epitopes arising from recurrent hotspot mutations in driver genes that enhance cancer cell fitness and are clonally conserved–are highly desirable and would be effective against many tumors sharing the common hotspot mutation. Tumor suppressor TP53 is a supreme target for this approach: it is the most frequently mutated gene in cancer yet remains untargetable with FDA-approved therapies. The most common TP53 alteration (R175H) generates a public NeoAg in the context of HLA-A*02, an allele expressed by ~40% of the North American and Western European populations. Earlier work established the immunogenicity of this public NeoAg by isolating a TP53(R175H)-specific clone from a colorectal cancer patient. ACT of this TCR in a single patient produced an objective anti-tumor response, but also resulted in multisystem organ failure indicating this receptor might possess off-target reactivity to unrelated proteins in healthy tissue. To discover safe and effective TP53(R175H)-specific TCRs, we assembled a unique biorepository of peripheral blood mononuclear cells (PBMCs) from n=26 cancer patients with diverse tumors that co-express HLA-A*02/TP53(R175H) and applied a novel high-throughput screening technique to retrieve candidate TCRs. These efforts resulted in a panel of n=9 genetically distinct and functionally validated receptors, each with NeoAg-specific anti-tumor activity against a panel of cancer cell lines. To define the cross-reactivity profile of these novel TCRs and the benchmark TCR that caused toxicity, we performed amino acid scanning mutagenesis (X-Scan) to identify potential off-targets. Importantly, we identified significant off-target reactivity to normal human proteins for the benchmark TCR, which may explain the lung and kidney toxicities observed in the trial patient. By contrast, a subset of the novel TCRs exhibited exquisite specificity for the TP53 public NeoAg with no predicted off-targets. Finally, we performed ACT of all TCRs in a mouse xenograft model and identified several novel TCRs that potently eliminated TP53(R175H)+/HLA*A02+ tumors in vivo. Based on these data, we are now proceeding with the clinical development of a best-in-class TCR. This work is poised to bring an important new class of precision immunotherapeutics to patients with TP53-mutant tumors that presently lack effective molecularly targeted agents.
Citation Format: Michael V. Gormally, Smita S. Chandran, Inaki Etxebarria, Christopher Klebanoff. Identifying novel patient-derived T cell receptors targeting TP53 public neoantigens [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 4.