Work

304 Unselected self-reactivity in neoantigen-specific CD8 T cell clones primes for dysfunction and impairs immunotherapy efficacy

Year: 2026

Type: conference-abstract

Abstract: Background Accumulated mutations within tumor cells generate neoantigens capable of inducing anti-tumor CD8 T cell responses. While neoantigen diversity can lead to a polyclonal intratumoral T cell population, a single neoantigenic peptide may induce the priming of a variety of T cell clonotypes with unique T cell receptors (TCR). Determining how differences between T cell clones against the same target influence tumor killing capacity may inform the development of optimal adoptive cell therapies (ACT) and improve response to immune checkpoint therapies (ICT).Methods Using our well-characterized mouse sarcoma model (T3), we performed single-cell TCR sequencing of T cells specific for the dominant H2-K b restricted neoantigen epitope (G1254V mLama4) during tumor progression and ICT-induced rejection. We identified two major mLama4 clonal families (TCR A and C) that expanded during ICT and one (TCR B) that decreased in frequency after treatment. Transgenic mice were generated expressing TCRs from each clonal family to study their anti-tumor capacity during ACT, and their T cells were analyzed by bulk RNA-seq and ATAC-seq to study their unique transcriptional and epigenetic phenotypes.Results The three mLama4-specific CD8 T cell clonal families showed similar peptide:MHCI affinity but differential reactivity to the mLama4 epitope. TCR A and C developed a cytotoxic profile after activation and mediated rejection of T3 following ACT. In contrast, TCR B had poor peptide reactivity, lower cytokine production, and failed to mount an optimal anti-tumor response. TCR B showed evidence of self-reactivity at the naïve state, with higher expression of CD5 and genetic changes associated with exposure to type I interferons. Prior to stimulation, TCR B had closed loci associated with activation associated transcription factors and enabled the binding of dysfunction-associated transcription factors such as Helios, priming them for exhaustion after chronic stimulation and leading to their diminished anti-tumor efficacy.Conclusions This study shows that TCR-driven heterogeneity in naïve neoantigen specific CD8 T cells determines the ability of individual clonotypes to react to antigen and differentiate into cytotoxic effectors. We propose that weak T cell receptor signaling against self-peptides can establish a CD5 hi state, inducing transcriptional and epigenetic reprogramming that impairs T cell activation, promotes an exhausted state, and limits antitumor efficacy during immunotherapy. Identifying dysfunctional clonotypes and their associated signatures within the neoantigen-specific CD8 T cell pool may inform T cell receptor choices for engineered T cell therapies and identify populations of T cells in patients that will respond to ICT.

Source: Journal for ImmunoTherapy of Cancer

DOI: 10.1136/jitc-2026-sitc2026.0304