Boosting class II HLA epitope presentation to T cells with endoplasmic reticulum transmembrane domain fusion proteins

Antigen processing and presentation are crucial for T-cell receptor engagement and potent adaptive immune responses. While establishing an antigen presentation system to identify TCR-epitope pairs from large libraries of genetically templated, ectopically expressed antigens, we observed a longitudinal suppression of antigen processing in B cells, which we call antigen processing attenuation (APA). Beyond its potential role in regulating B cell-enforced peripheral tolerance, APA represents a bottleneck to sustained antigen presentation in screening and vaccination approaches. To overcome APA we screened several pathways which might enhance processing. Notably, we identified several sequences derived from transmembrane domains (TM) of endoplasmic reticulum-resident proteins which promote sustained minigene-encoded antigen presentation. In particular, the first TM domain of SYT6, a protein associated with synaptic vesicles, greatly enhances processing and ameliorates APA. These findings suggest a new entry point into antigen processing pathways, enabling the discovery of novel immune epitopes and improving T-cell based immunization strategies.