PROJECT SUMMARY/ABSTRACT Human immunodeficiency virus type-1 (HIV-1) is a retrovirus that infects CD4+ T cells of the immune system. If left untreated, people living with HIV-1 (PLWH) will progress to AIDS and may ultimately die as a result. Combination antiretroviral therapy (ART) with small-molecule drugs is extremely effective at stopping the replication of HIV-1 in infected individuals but requires daily dosing often with considerable side effects. Importantly, despite the success of this approach at suppressing HIV-1 replication to clinically undetectable levels, antiretroviral therapy is not curative. This is due to the persistence of HIV-1 in a silent, or latent, state within long-lived CD4+ T cells at extremely low frequencies. These latently infected cells are not targeted by current small-molecule ART regimens. As a result, PLWH must remain on lifelong antiretroviral therapy. Broadly neutralizing antibodies targeting critical epitopes in HIV-1 Env (HIV-1 bNAbs) are currently being developed as a potential approach to eliminate latent HIV-1 and/or as an alternative to small-molecule ART. HIV-1 bNAbs offer several advantages over traditional small-molecule ART, including the potential for long-acting formulations, reduced side effects, and the potential to eliminate latently infected cells over time. However, a major challenge to the implementation of HIV-1 bNAbs in treatment and cure is pre-existing variation or resistance in the bNAb-targeted epitopes. Scalable clinical tests are needed to determine (1) whether people who will receive HIV-1 bNAbs have pre-existing resistance, and (2) personalize HIV-1 bNAb combinations to each individual. To address this critical unmet need, AccelevirDx is developing the HIV-1 EnvLRS assay as the first scalable sequence-based test to assess HIV-1 bNAb resistance and predict antibody efficacy by in-depth env sequence analysis. Broadly, this proposal aims to (1) analytically qualify AccelevirDx’s novel, proprietary HiFi-dePCR approach for env amplification underlying HIV-1 EnvLRS, (2) determine the reproducibility of the HIV-1 EnvLRS assay of samples from PLWH, and (3) apply the assay to a recently completed ACTG A5340 clinical trial of the HIV-1 bNAb VRC01 in PLWH to assess assay performance and utility.