Adaptive immune responses elicited by baculovirus and impacts on subsequent transgene expression in vivo

Baculovirus (BV) is a promising gene therapy vector and typically requires readministration because BV mediates transient expression. However, how the prime-boost regimen triggers BV-specific adaptive responses and their impacts on BV readministration, transgene expression, and therapeutic/vaccine efficacy remain unknown. Here we unraveled that BV injection into BALB/c mice induced the production of BV-specific antibodies, including IgG1 and IgG2a, which could neutralize BV by antagonizing the envelope protein gp64 and impede BV-mediated transgene expression. Moreover, humans did not possess preexisting anti-BV antibodies. BV injection also elicited BV-specific Th1 and Th2 responses as well as CD4(+) and CD8(+) T cell responses. gp64 was a primary immunogen to activate the antibody and CD8(+) T cell response, with its peptide at positions 457 to 465 (peptide 457-465) being the major histocompatibility complex (MHC) class I epitope to stimulate CD8(+) T cell and cytotoxic responses. Nonetheless, a hybrid Sleeping Beauty-based BV enabled long-term expression for >1 year by a single injection, indicating that the T cell responses did not completely eradicate BV-transduced cells and implicating the potential of this hybrid BV vector for gene therapy. These data unveil that BV injection triggers adaptive immunity and benefit rational design of BV administration schemes for gene therapy and vaccination.