HIV-1 broadly neutralizing antibodies (bNAbs) are currently under clinical evaluation for their ability to prevent
transmission. Until a conventional vaccine is realized, repetitive dosing of a bNAb would be necessary to
maintain protective antibody concentrations. An alternative to passive infusion of bNAbs is to use adeno-
associated virus (AAV) vectors that can turn muscles into antibody production factories. This one-time
treatment would have clear cost advantages over the continuous production, purification, and administration of
recombinant monoclonal antibodies. However, host immune responses limit the efficacy of AAV vectors.
CD8+ T cell clearance of AAV transduced muscle cells limits the total number of cells producing the antibody,
and pre-existing immunity to AAV capsids limit the number of possible individuals that can receive AAV
vectors. We and others have previously shown that host immune responses are detrimental to AAV-delivered
HIV-1 antibodies resulting in low to no detectable serum concentrations. Thus, overcoming the host immune
response to the AAV vector and expressed transgene is critical for future evaluation of AAV-delivered antibody
studies in non-human primates. One area of investigation for limiting a host immune response would be to
utilize immune checkpoints that regulate immune system pathways. To this end, in a pilot study, we have
observed about a 21-fold increase in concentrations of an HIV-1 antibody in rhesus macaques when
macaques were co-inoculated with an AAV vector encoding rhesus macaque PD-L1. PD-L1 functions in
binding T cell expressed PD-1 to inhibit the cytolytic and degranulation functions. It also helps in the
development of regulatory T cells. Thus, we hypothesize that expression of PD-L1 on muscle cells transduced
by AAV vectors to express antibodies will avoid T cell clearance and maintain expression of the antibody.
Here we seek to demonstrate that co-inoculation of vectors encoding PD-L1 will result in serum concentrations
of a bNAb that will protect rhesus macaques from repetitive, low-dose SHIV challenges. Additionally, we will
develop this system by evaluating strategies to reduce the dose of AAV vector. Furthermore, we will engineer
AAV transgene cassettes and assess novel a novel AAV capsid for increasing expression from intramuscular
inoculation. Together, the results from these studies will provide a foundation for AAV gene therapy studies in
non-human primates as well as lead to the development of novel AAV vectors for expressing HIV-1 bNAbs.