Low TCR Binding Strength Results in Increased Progenitor-like CD8+ Tumor-Infiltrating Lymphocytes

Abstract

T cell receptor (TCR) binding strength to peptide-MHC antigen complex influences numerous T cell functions. However, the vast diversity of a polyclonal T cell repertoire for even a single antigen greatly increases the complexity of studying the impact TCR affinity has on T cell function. Here, we determined how TCR binding strength affected the protein and transcriptional profile of an endogenous, polyclonal T cell response to a known tumor-associated antigen (TAA) within the tumor microenvironment (TME). We confirmed that flow and CITE-Seq counts of MHC-tetramer labeling were reliable surrogates for the TCR-peptide-MHC steady-state binding affinity. We further demonstrated by single-cell RNA sequencing that tumor-infiltrating lymphocytes (TILs) with high and low binding affinity for a TAA can differentiate into cells with many antigen-specific transcriptional profiles within an established TME. However, more progenitor-like phenotypes were significantly biased towards lower affinity T cells, and proliferating phenotypes showed significant bias towards high-affinity TILs. Additionally, we found in a progressing TME that higher affinity T cells advanced more rapidly to terminal phases of T cell exhaustion and exhibited better tumor control. We confirmed the polyclonal TIL results using a TCR transgenic mouse possessing a single low-affinity TCR targeting the same TAA. These T cells maintained a progenitor-exhausted phenotype and exhibited impaired tumor control. We propose that high-affinity TCR interactions drive T cell fate decisions more rapidly than low-affinity interactions and that these cells differentiate faster. These findings illustrate divergent forms of T cell dysfunction based on TCR affinity which may impact TIL therapies and antitumor responses.

PD-1 controls differentiation, survival, and TCR affinity evolution of stem-like CD8+ T cells

“…Importantly, the latter enables high affinity clones to be preserved as TSL. The prolonged association of high affinity TSL with cDC1 also helps explain prior observations that lower affinity antigen-specific clones egressed from lymphoid tissues earlier than their high affinity counterparts 41,42 . A recent study found that tumor antigen-specific T cells remained highly enriched in the tdLN as TSL and differentiate into effectors upon migrating to the TME 43 .…”

“…Such changes may compromise subsequent treatment efficacy, as higher TCR affinity/avidity CD8+ TILs are associated with better tumor clearance in anti-PD-1-treated patients [54][55][56] , as well as superior tumor infiltration and improved tumor control in adoptive cell therapy 57,58 . As high affinity CD8+ TILs can rapidly become dysfunctional upon exposure to persistent antigen in the TME, these cells may only have a narrow time window to facilitate effective tumor killing before losing functional cytotoxicity 42,59 . The capacity of non-metastatic tdLNs to act as an ongoing source of TCF-1+ TSL, as recently reported 7-9 , could become dysregulated by PD-1 checkpoint immunotherapy, leading to impaired long-term maintenance of high affinity TSL clones in the tdLNs, the loss of which could be permanent due to reduced naïve T cell output from the adult thymus 60,61 .…”

Insights into anti-tumor immunity via the polyomavirus shared across human Merkel cell carcinomas

“…Along the same lines, several groups have discovered that a specific subset of PD-1+ cancer-specific T cells (expressing stem cell markers, TCF1 and CXCR5) do expand in response to anti-PD-1 therapy and are largely responsible for controlling the tumor ( 64 – 70 ). It is postulated that these progenitor exhausted cancer-specific T cells recognize antigens that may be expressed at lower levels or do not bind class I MHC as avidly, allowing these T cells to receive fewer activation signals and avoid a more irreversible dysfunctional phenotype ( 69 , 71 ). It would be pertinent to determine whether this subset of cells could serve as a biomarker of response to immunotherapy in MCC.…”

Low avidity T cells drive endogenous tumor immunity in mice and humans

“…These pioneering studies have typically analyzed monoclonal T cell populations adoptively transferred into mice or humans. Not surprisingly in view of the heterogeneity of the antigens studied and the models used, they have resulted in every possible conclusion: (i) high avidity responses are more effective (3,7,8,11,12), (ii) low as well as high avidity TCRs can be effective and sometimes, equally so (2,5,6), (iii) high avidity responses can risk autoimmunity while low avidity responses are less likely to do so (4,5,13) and (iv) low and intermediate avidity responses are more effective at tumor control (9).…”