Isolation of neoantigen-specific T cell receptors for T cell receptor gene therapy

Abstract

In recent years, adoptive T cell therapy has brought a revolutionary change in the treatment for B-cell leukemias, lymphomas and multiple myeloma. Along with T cells modified with chimeric antigen receptors (CARs), there is ongoing development of T cells modified with T cell receptors (TCRs). TCR-T cells are not restricted to recognizing surface antigens but can also recognize targets derived from intracellular antigens and specifically mutated antigens, including neoantigens. This increases the number of target antigens for developing precision immunotherapies with high tumor specificity and a favorable safety profile. Challenges in the development include identifying suitable tumor epitopes, isolating high-affinity TCRs, and expanding patient TCR-T cells in sufficient quantities with the preferred phenotype. To tackle these questions, the first objective was to isolate neoepitope-specific TCRs from different repertoires in a side-by-side investigation. These repertoires included patients’ peripheral blood lymphocytes (PBLs) and tumor-infiltrating lymphocytes (TILs), PBLs of healthy donors, and a humanized mouse model. Results of the study show the advantage and feasibility of stimulating healthy donor repertoires and humanized mice TCR repertoires to generate mutation-specific TCRs with different specificities, especially when patient material is sparse. It was also shown that no specific TCR was isolated for neoepitope used in this study from the patients’ own repertoire. Furthermore, it is desirable to target recurrent mutations. A high-affinity TCR specific to the HLA-B*07:02-restricted epitope of the common lymphoma-specific driver mutation MyD88 L265P was successfully isolated from the healthy donor repertoire. However, screening 24 donors was necessary to identify one high-avidity TCR that could recognize tumor cells endogenously expressing L265P. This highlights the influence of the individual TCR repertoire of the T cell donor, along with inherent immunogenicity of the epitope. Lastly, the expansion of gene-modified T cells is a crucial part of the TCR-T cell manufacturing process. This is especially true for patients with insufficient numbers of T cells, or for T cells with insufficient expansion during the standard culture process. The feasibility of prolonging the T cell culture processes with minimal alteration to the standard process was demonstrated in the last presented study. These findings need to be confirmed on a GMP-compliant manufacturing platform but hold the promise to increase accessibility of adoptive T cell therapy (ATT) for certain patients.