Novel MVA Vector Expressing Anti-apoptotic gene, B13R, Delays Apoptosis and Enhances Humoral Responses

Modified vaccinia virus Ankara (MVA) has been explored as a vaccine vector for use against infectious diseases and cancer. MVA is an immunogenic, attenuated poxvirus capable of eliciting robust cellular and humoral responses in pre-clinical animal models and in patients. However, upon infection with MVA, cells undergo rapid apoptosis leading to faster clearance of recombinant antigens. The fragmentation of the anti-apoptotic gene B13R in MVA could contribute to this effect. Here, we replaced the fragmented B13R with a functional version and observed that MVA-B13R infected HeLa cells and muscle cell lines delayed caspase 3 activation compared to MVA indicating slower progression of apoptosis. For immunogenicity studies, mice were intramuscularly immunized with recombinant MVA or MVA-B13R expressing SIV Gag, Pol and HIV Env (SHIV). We observed higher Env-specific humoral responses from MVA-B13R SHIV compared to MVA SHIV mice. To determine differences in the innate immune response that may have contributed to the augmented humoral response, we performed RNA-Seq analysis on draining lymph node cells after immunization. Gene set enrichment analysis from day 1 after immunization showed that MVA-B13R SHIV immunizations were associated with a negative enrichment for type I and II interferon responses compared to MVA SHIV mice indicating MVA-B13R SHIV induces a delayed anti-viral interferon response that may lead to the enhanced humoral response observed. Taken together, these results demonstrate that restoring B13R functionality in MVA significantly delays MVA-induced apoptosis, augments Env-specific antibody responses, and is associated with reduced interferon-alpha and interferon-gamma responses induced after vaccination. Female BALB/c mice were intramuscularly immunized at 10^7 pfu/dose with MVA expressing SHIV antigens or MVA-B13R expressing SHIV. At days 1, 2, and 6 post immunization, draining inguinal lymph node cells were harvested for RNA extraction. 5 animals per group per time point including 5 naive mice as a control group.