Enhanced efficacy of a next-generation EEEV self-replicating RNA platform for combination cancer immunotherapies.

Self-replicating RNA (srRNA) technology has received its first approval with Kostaive and Emergency Use Authorization for GEMCOVAC COVID-19 vaccines. The effective doses for srRNA vaccines are far lower than for conventional mRNA, as srRNA drives greater protein expression and has attributes of viral vectors that can potentiate immunogenicity. Importantly, srRNA encodes for a viral replicase, frequently derived from non-structural proteins (nsP) from Venezuelan equine encephalitis virus (VEEV), that helps amplify the encoded transgene. nsPs also influence critical cellular processes, including protein translation and processing, inflammation, and autophagy, that can impact downstream performance. Here, we show that a next-generation srRNA vector derived from Eastern equine encephalitis virus, identified from a wider screen of alphaviruses, has high potency in two immunotherapeutic applications, RBI-1000 and RBI-2000. RBI-1000, a multigenic vaccine targeting acquired resistance mutations in breast cancer, was able to elicit antigen-specific immune responses to tumor-associated antigens and neoantigens. In addition, RBI-2000, a combination interleukin-12 and IL-1 receptor antagonist biotherapeutic, resulted in therapeutic levels of protein expression that bolstered anti-tumor immune responses in vivo. Both RBI-1000 and RBI-2000 successfully demonstrated efficacy in preclinical tumor models. These data show the importance of empirically evaluating new srRNA vectors for the development of fit-for-purpose therapies.