Reactivation of low avidity tumor-specific CD8⁺T cells associates with immunotherapeutic efficacy of anti-PD-1

Abstract

BackgroundCD8+T cells are a highly diverse population of cells with distinct phenotypic functions that can influence immunotherapy outcomes. Further insights on the roles of CD8+specificities and TCR avidity of naturally arising tumor-specific T cells, where both high and low avidity T cells recognizing the same peptide-major histocompatibility complex (pMHC) coexist in the same tumor, are crucial for understanding T cell exhaustion and resistance to PD-1 immunotherapy.MethodsCT26 models were treated with anti-PD-1 on days 3, 6 and 9 following subcutaneous tumor implantation generating variable responses during early tumor development. Tetramer staining was performed to determine the frequency and avidity of CD8+T cells targeting the tumor-specific epitope GSW11 and confirmed with tetramer competition assays. Functional characterization of high and low avidity GSW11-specific CD8+T cells was conducted using flow cytometry and bulk RNA-seq. In vitro cytotoxicity assays and in vivo adoptive transfer experiments were performed to determine the cytotoxicity of high and low avidity populations.ResultsTreatment success with anti-PD-1 was associated with the preferential expansion of low avidity (Tetlo) GSW11-specific CD8+T cells with Vβ TCR expressing clonotypes. High avidity T cells (Tethi), if present, were only found in progressing PD-1 refractory tumors. Tetlodemonstrated precursor exhausted or progenitor T cell phenotypes marked by higher expression of Tcf-1 and T-bet, and lower expression of the exhaustion markers CD39, PD-1 and Eomes compared with Tethi, whereas Tethicells were terminally exhausted. Transcriptomics analyses showed pathways related to TCR signaling, cytotoxicity and oxidative phosphorylation were significantly enriched in Tetlofound in both regressing and progressing tumors compared with Tethi, whereas genes related to DNA damage, apoptosis and autophagy were downregulated. In vitro studies showed that Tetloexhibits higher cytotoxicity than Tethi. Adoptive transfer of Tetloshowed more effective tumor control than Tethi, and curative responses were achieved when Tetlowas combined with two doses of anti-PD-1.ConclusionsTargeting subdominant T cell responses with lower avidity against pMHC affinity neoepitopes showed potential for improving PD-1 immunotherapy. Future interventions may consider expanding low avidity populations via vaccination or adoptive transfer.

Interferon-γ driven differentiation of monocytes into PD-L1+and MHC II+macrophages and the frequency of Tim-3+tumor-reactive CD8+T cells within the tumor microenvironment predict a positive response to anti-PD-1-based therapy in tumor-bearing mice

“…Similarly, CAR-T cells expressing high affinity TCRs may be more prone to terminal exhaustion (57), while lower affinity CAR T cells display increased proliferation and in vivo antitumor activity (58,59). Accordingly, PD-1 appears to preferentially inhibit the activation of low-affinity T cells (60), which is in line with several observations indicating that the immunotherapeutic efficacy of anti-PD-1-based ICB is associated with the reactivation of low avidity, tumor-specific lymphocytes (61,62). Although we cannot evaluate the overall avidity of P1A vs P1E-specific lymphocytes in our model (these tumor antigens are presented by distinct MHC molecules whose tumor-cell surface MHC-peptide complex density remains to be established), it is noteworthy that neoantigen specific T cells (P1E-reactive) display a reduced TCR expression in the draining lymph nodes (a privileged site of anti-tumor response generation, (63)), compatible with a sustained, and possibly high avidity interaction of these cells with their cognate Ag/MHC complex.…”

Identification and Structural Characterization of a mutant KRAS-G12V specific TCR restricted by HLA-A3

“…Our recent work on KRAS-G12D specific TCRs suggests that TCRs with affinities in the high nM to low μM range are most effective for anti-tumour function, in line with a 'goldilocks' zone for TCR affinities [2,7,27,28]. However, other models have suggested that low avidity TCRs are superior to higher avidity [29]. More investigations into the affinities of effective anti-tumour TCRs are required to understand the desired biophysical properties of TCRs to be used in the clinic.…”

Cancer neoepitopes viewed through negative selection and peripheral tolerance: a new path to cancer vaccines

“…In case of a high pMHC affinity and a high pMHC-TCR affinity, the overall avidity shall be high. It is posited that, for the small proportion of the neoepitopes that mediate tumor control in vivo and have a high affinity for MHC I (see Table 1 , and some in Table 2 ), the pMHC-TCR affinity would, of necessity, be low, so that the pMHC-TCR avidity is also low: as recently observed ( 121 – 124 ), only CD8 + T cells with low to intermediate avidity, but not those with high avidity are able to mediate tumor control.…”