40P - The role of low avidity tumour-specific CD8+ T cells in immunotherapeutic response to anti-PD-1

Background

T cell avidity plays a crucial role in antigen presentation and influences the quality of TCR signaling and T cell metabolic fitness. It is crucial in chronic inflammation e.g. cancer where persistent antigen exposure and chronic T cell stimulation may lead to exhaustion. Thus, mechanistic insights on the roles of CD8⁺ specificities and T cell avidity of naturally arising tumour-specific T cells where both high (Tet^hi) and low (Tet^lo) avidity T cells recognising the same pMHC co-exist in the same tumour, are crucial for understanding resistance to PD-1 immunotherapy.

Methods

CT26 models were treated with anti-PD-1 on days 3, 6 and 9 following tumour implantation generating variable responses during early tumour development. Tetramer staining and T cell avidity measurement using acoustic force spectroscopy were conducted to determine the frequency and avidity of CD8⁺ T cells targeting the tumour-specific epitope GSW11. Tet^hi and Tet^lo were functionally characterised using flow cytometry, RNA-seq, in vitro and in vivo cytotoxicity experiments.

Results

Treatment success with anti-PD-1 was associated with the preferential expansion of Tet^lo. Tet^lo were precursor exhausted with higher expression of Tcf-1 and T-bet, and lower expression of CD39, PD-1 and Eomes compared to Tet^hi. Pathways related to TCR signaling, cytotoxicity and oxidative phosphorylation were significantly upregulated in Tet^lo found in both responding and non-responding tumours compared to Tet^hi. Interestingly, a small percentage of Tet^lo found in the non-responding tumours were functional but metabolically challenged. In vitro studies showed that Tet^lo exhibited higher cytotoxicity than Tet^hi. Curative response was achieved when Te^tlo were adoptively transferred and in combination with anti-PD-1.

Conclusions

Targeting 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 adoptive transfer or drugs targeting immunometabolism. These approaches may be combined with non-invasive tumour metabolism imaging and T cell tracking to understand the impact of immunometabolism on T cell dynamics at a system level.

Legal entity responsible for the study

The authors.

Funding

Worldwide Cancer Research Fund (20-0229), Cancer Research UK Programme Grant (A28279).

Disclosure

All authors have declared no conflicts of interest.