Perspectives for applying Alphaviruses in antitumor therapy

Oncolytic viral therapy is a promising approach for treating tumors. Oncolytic viruses can directly lyse tumor cells and indirectly activate antitumor immunity. Alphaviruses, as oncolytic viruses, are particularly promising agents because they can selectively infect and lyse tumor cells, modulate microtumor environment, elicit immune-mediated lysis of tumor cells, and serve as a platform for transgene delivery. To ensure safety, attenuated strains of Alphaviruses are typically used for genetic engineering, and immunogenic tumor-associated antigens or cytokines are commonly chosen as transgenes. Studies evaluating both in vitro and in vivo oncolytic and immunomodulatory effects of Alphaviruses and vectors based on them have been growing exponentially. Animal models of various tumor types were used to examine the effectiveness of Alphaviruses, including Sindbis, Semliki Forest virus, Geta (strain M1), Venezuelan equine encephalitis virus, and vectors based on them. Additionally, Alphaviruses revealed enhanced antitumor activity while used in combination therapies with other oncolytic viruses. Alphavirus-like replicon particles based on attenuated Venezuelan equine encephalitis virus may serve for transgene delivery to express heterologous proteins at high levels, and induce both humoral and cellular immune responses. An alphaviral vector-based vaccine, encoding the HER2 extracellular and transmembrane domains, has demonstrated safety and efficacy in preclinical mouse models, as well as in phase I clinical trials for advanced breast cancer patients with HER2 overexpression. This vaccine is known to be safe, effective, and capable of inducing T-cell immunity. In this review, we discuss the current progress in preclinical and clinical investigations, as well as the future potential of Alphaviruses for oncolytic virotherapy.