Leveraging prenatal tolerance to improve AAV/bNAb therapy outcomes in infancy - PROJECT SUMMARY Despite significant progress in HIV testing and vertical transmission prevention programs, over 100,000 children are still infected annually, predominantly in sub-Saharan Africa. Several factors contribute to this high burden of pediatric HIV infections in the region, including inadequate healthcare infrastructure, limited access to clinics, maternal infections during pregnancy, and stigma. Additionally, high rates of unplanned pregnancies among women living with HIV, many of whom struggle with antiretroviral therapy adherence, complicate efforts to eliminate pediatric HIV. While breastfeeding is a major route of vertical HIV transmission, it is also a pillar of child survival in Africa, so a key challenge in developing pediatric HIV interventions is ensuring safer breastfeeding for at-risk infants in a way that is practical, discreet, and does not require strict adherence to treatment. Passive immunization with broadly neutralizing antibodies (bNAbs) offers promise for preventing pediatric HIV infections. However, the current approach, which relies on repeated infusions of recombinant bNAb proteins, is both expensive and difficult to implement in resource-limited settings. A potentially transformative alternative is adeno-associated virus (AAV)-mediated gene transfer, which enables continuous in vivo production of bNAbs by host cells, thereby eliminating the need for repeated dosing. This strategy is particularly attractive due to the excellent safety profile of AAV vectors and their ability to transduce long-lived cells, such as myocytes, allowing for durable bNAb expression. Consistent with the phenomenon of neonatal tolerance, we recently identified the first four weeks after birth as an optimal window for achieving high and sustained bNAb expression in infant rhesus macaques (RhMs) following AAV/bNAb therapy. Beyond this period, the effectiveness of the therapy diminishes significantly as infants develop the ability to mount humoral immune responses against the AAV-delivered bNAb (also known as anti-drug antibodies, or ADAs) that reduce or shut down transgene expression. To extend the 4-week window for effective AAV/bNAb therapy, we sought ways to prevent ADAs in infants treated beyond the neonatal stage. We discovered that RhMs exposed in utero to a recombinant form of the same bNAb delivered by AAV did not mount ADAs after postnatal AAV/bNAb treatment, even when the vector was given at 3 months of age. However, this effect waned by 8 months, at which point treatment outcomes became indistinguishable between prenatally exposed and bNAb-naïve RhMs. Thus, the immunological program responsible for prenatally induced tolerance to the AAV-delivered bNAb appears to be “switched off” at some point between 3 and 8 months of age. Based on these data, this project seeks to elucidate the mechanism of in utero bNAb tolerization in primates (Aim 1) and prolong bNAb tolerance throughout infancy (Aim 2). Ultimately, our goal is for a one-time administration of AAV/bNAb vectors to generate long-lasting (possibly lifelong) HIV immunity in children of all ages.
