Neoantigen‐based cancer vaccination using chimeric RNA‐loaded dendritic cell‐derived extracellular vesicles

Cancer vaccines critically rely on the availability of targetable immunogenic cancer-specific neoepitopes. However, mutation-based immunogenic neoantigens are rare or even non-existent in subgroups of cancer types. To address this issue, we exploited a cancer-specific aberrant transcription-induced chimeric RNA, designated A-P(as)chiRNA, as a possible source of clinically relevant and targetable neoantigens. A-P(as)chiRNA encodes a recently discovered cancer-specific chimeric protein that comprises full-length astrotactin-2 (ASTN2) C-terminally fused in-frame to the antisense sequence of the 18(th) intron of pregnancy-associated plasma protein-A (PAPPA). We used extracellular vesicles (EVs) from A-P(as)chiRNA-transfected dendritic cells (DCs) to produce the cell-free anticancer vaccine DEXA-P. Treatment of immunocompetent cancer-bearing mice with DEXA-P inhibited tumour growth and prolonged animal survival. In summary, we demonstrate for the first time that cancer-specific transcription-induced chimeric RNAs can be exploited to produce a cell-free cancer vaccine that induces potent CD8(+) T cell-mediated anticancer immunity. Our novel approach may be particularly useful for developing cancer vaccines to treat malignancies with low mutational burden or without mutation-based antigens. Moreover, this cell-free anticancer vaccine approach may offer several practical advantages over cell-based vaccines, such as ease of scalability and genetic modifiability as well as enhanced shelf life.