Abstract 895: Tumor-wide neoantigen-specific T-cells infiltrating mutant IDH1 low-grade gliomas and persisting in peripheral blood allow for personalized TCR-based immunotherapies
Authors: Kwok Darwin W. , Zhang Michael Y. , Wang Cliff , Stevers Nicholas , Borrman Tyler , Pan Zheng , Yuen Benjamin , Peng Songming , Nguyen Diana , Martin Michael , Hong Chibo , Hilz Stephanie , Phillips Joanna , Shai Anny , Bush Nancy Ann Oberheim , Hervey-Jumper Shawn , McDermott Michael , Mandl Stefanie , Okada Hideho , Costello Joseph 
Published: April 2023

Abstract
BACKGROUND: The low mutational burden and immunologically “cold” microenvironment of mutant IDH1 low-grade gliomas (LGG) are considerable challenges facing immunotherapy against these tumor types. However, we hypothesize that LGG-targeting T-cells may exist at low frequency and with limited regional infiltration within the tumor. Multi-region tumor sampling coupled with high-throughput T-cell receptor (TCR) profiling across the LGG landscape detected neoantigen-specific T-cells that persisted in peripheral blood. TCR-engineered T-cells transduced with these TCRs demonstrated neoantigen-specific immunogenicity.
METHODS: Maximal-anatomical sampling of at least 10 distinct tumor regions were collected at the initial resection for three WHO Grade II diffuse astrocytoma patients for exome-based prediction of clonally and subclonally expressed neoantigens, RNAseq analysis of regional immune cell composition, and TCR beta deep sequencing. We used these predictions to generate a barcoded library of patient-specific peptide-HLA multimers loaded with predicted neoepitopes. With this library, neoantigen-specific CD8+ T-cells were captured and isolated from patient peripheral blood. Single cell TCR sequencing allowed us to identify the neoantigen-reactive TCR clonotypes which were transduced subsequently into Jurkat76 cell lines for functional validation.
RESULTS: We screened patient-derived peripheral blood drawn two years after initial resection in 3 mutant IDH1 LGG patients and detected a total of 20 TCR clonotypes recognizing neoepitopes derived from truncal, tumor-wide mutations in CNTNAP1 (n=8), TP53 (n=3), and MRPL46 (n=2) as well as subclonal mutations in PRMT5 (n=1) and ZDHHC5 (n=6). Multi-sampling RNAseq analysis indicated varying degrees of interpatient and intratumoral immune infiltration as well as distally located populations of neoantigen-reactive T-cells within the tumor, suggesting widespread migration of neoantigen-specific T-cells across the glioma landscape. We proceeded with TCR functional analysis for one patient (P375) with 5 detected TCR clonotypes recognizing neoantigens derived from mutations in PRMT5, MRPL46, and TP53. Jurkat76 cells transduced with the mutant-PRMT5-specific TCR demonstrated a neoantigen-specific immune response when co-cultured with mutant-PRMT5 pulsed-antigen presenting cells expressing HLA-A*0201 (T2 cells).
CONCLUSION: Our study demonstrates the existence and persistence of neoantigen-targeting T-cells within the blood and tumor of mutant IDH1 LGG patients. We identified a TCR clonotype that successfully recognizes and induces an immune response against mutant-PRMT5. These findings suggest a feasible methodology to develop personalized T-cell-based immunotherapies for patients with mutant IDH1 LGGs.
Citation Format: Darwin W. Kwok, Michael Y. Zhang, Cliff Wang, Nicholas Stevers, Tyler Borrman, Zheng Pan, Benjamin Yuen, Songming Peng, Diana Nguyen, Michael Martin, Chibo Hong, Stephanie Hilz, Joanna Phillips, Anny Shai, Nancy Ann Oberheim Bush, Shawn Hervey-Jumper, Michael McDermott, Stefanie Mandl, Hideho Okada, Joseph Costello. Tumor-wide neoantigen-specific T-cells infiltrating mutant IDH1 low-grade gliomas and persisting in peripheral blood allow for personalized TCR-based immunotherapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 895.