Neoantigens (NeoAg) offer the potential to directtherapeutic T cell responses to immunogenic mutations exclusively expressed bytumors. Most strategies for their identification select potentialligands for CD8+ T cells rather than for CD4+ T cells,despite the extensive literature showing functional cooperation between thesesubsets. To better understand CD4-CD8synergy in anti-tumor immunity, we have applied a novel functional approach toidentify the subset of expressed mutations targeted as NeoAg by natural CD4+and CD8+ T cell responses to a poorly-immunogenic spontaneoussquamous cell tumor, SCC VII. We demonstrate that a single mutation (Cltc H129>Q) that is recognized byboth subsets is capable of eradicating large established SCCVII tumors in thesetting of therapeutic vaccination provided the relevant epitopes whenphysically linked. Single-cell TCR analysis revealed that the endogenous CD4+T cell response against this epitope comprises both low-affinity CD4+-dependentand high-affinity CD4+-independent receptors, with the latterdisplaying superior capacity in promoting prophylactic and therapeutic CD8+T cell-mediated immunity against the MHC class I+ class IItumors in the setting of adoptive cellular therapy. These findings demonstratethat linked CD4+ T cell help enables potent therapeuticNeoAg-specific vaccination and provides instructive insights into the qualityof TCRs mediating this effect.

Citation Format: Stephen P. Schoenberger. Targeting natural ligands for TCR engineering [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr SY26-01.