Graduate student UConn Health (University of Connecticut Health Center) Farmington, Connecticut, United States
Disclosure(s):
Stabonia Maji, MSc: No financial relationships to disclose
Introduction/Rationale: The binding affinities of tumor-controlling neoepitopes for MHCI span a broad range (8 nM–40,000 nM), with the overwhelming majority of them exhibiting low to ultra-low affinities (see Srivastava 2024 J. Clinical Investigation for review). Since low-affinity neoepitope–MHCI complexes are unstable, conventional MHCI tetramers cannot be generated. Here, we have engineered single-chain trimers (SCT) in which the neoepitope is linked to the MHCI α-chain and β2-microglobulin via peptide linkers within a single genetic construct and examined the functional activity of tetramer-reactive CD8 T cells.
Methods: SCT-based tetramers were generated and CD8 T cells recognizing them were adoptively transferred of into mice with pre-existing tumors.
Results: CD8 T cells from un-immunized mice or mice immunized with the ccdc85cMUT neoepitope, were stained with the SCT-tetramer described. Unexpectedly, we detected ccdc85cMUT-Kd specific CD8 T cells in both groups of mice although the number of tetramer-reactive cells was statistically significantly higher in mice immunized with ccdc85cMUT-pulsed BMDCs than in mice immunized with un-pulsed BMDCs in independent experiments. The efficacy of tetramer-reactive cells was tested by adoptively transferring the cells into mice bearing ~5mm diameter Meth A tumors. Tetramer-reactive CD8 T cells from immunized mice mediated excellent tumor control while those from un-immunized mice did not, except in mice treated with CTLA4 blockade.
Conclusion: We report here the first identification of antigen-specific CD8 T cells recognising a neoepitope with low affinity for MHCI. Our observations also suggest the existence of two populations of ccdc85cMUT-reactive CD8 T cells, one that exists even in un-immunized mice where it is under Treg control, and the other that exists only in immunized mice where it is not under such control. These findings have implications for the intersection between neoepitope-elicited cancer immunity and autoimmunity.
