Harnessing nucleic acid sensors in tumor cells to reprogram biogenesis and RNA cargo of extracellular vesicles for T-cell-mediated cancer immunotherapy
Background Due to their intrinsic immunomodulatory properties, tumor-derived extracellular vesicles (EVs) have sparked great interest in T-cell cancer immunotherapy. However, clinical development is hampered by a limited understanding of signaling pathways that regulate their biogenesis and function. We here show that the nucleic acid sensor RIGI (but not cGAS/STING) in tumor cells governs biogenesis, RNA cargo and thus T-cell immunomodulation by EVs. Methods EVs were enriched from murine and human tumor cell cultures with varying RIG-I pathway activity, utilizing selective receptor ligands and genetically engineered cell lines. EV cargo and immunostimulatory function were assessed in vitro and in murine cancer models.  Findings  Cancer cell-intrinsic RIG-I activation releases EVs, which mediate dendritic cell maturation and T-cell antitumor immunity, synergizing with immune checkpoint blockade. Intact RIG-I, autocrine Interferon-I-signaling and the GTPase Rab27a in tumor cells are required for biogenesis of immunostimulatory EVs. Active intrinsic RIG-I signaling governs composition of the EV RNA cargo including endogenous triphosphate-RNAs, small nuclear and nucleolar RNAs, as well as other stimulatory RNAs. In patient melanoma samples, high transcriptional activity of EV pathway genes and RIG-I associate with prolonged survival and beneficial response to anti-CTLA-4/-PD-1 immunotherapy. EVs generated from human melanoma after RIG-I stimulation induced potent antigen-specific T-cell responses. Conclusions We here define a specific molecular pathway that can be targeted in human tumors to govern EV cargo constituents, favorably altering their immunomodulatory function. We propose “reprogramming” of patient-autologous tumor EVs as a personalized strategy for T-cell cancer immunotherapy.