Gut tissue and lymph nodes (LN) harbor HIV DNA and RNA during antiretroviral therapy (ART)–mediated viral suppression, but less is known about HIV protein expression. The goal of this study is to apply a sensitive immunoassay for detecting HIV p24 antigen in lymphoid tissues during ART and to assess the relationships between immune phenotypes and HIV control to inform on HIV cure strategies.
HIV gag p24 protein was measured by an in house optimized digital ELISA in cells isolated from either rectal tissue, LN biopsies, or LN fine needle aspirates from HIV participants in the UCSF and University of Minnesota cohorts. HIV gag protein was assessed from study participants with variable levels of plasma viremia levels, ranging from fully suppressed to viremic, either naturally controlling or on ART.
HIV gag p24 protein persists in lymph node and rectal biopsies in well-suppressed participants. HIV p24 levels in rectal and peripheral blood CD4+ T cells were moderately correlated among all participants (r: 0.54, P=0.0169); Rectal p24 levels discriminated between viremic, ART-suppressed, and HIV-uninfected participants much better than peripheral blood p24 levels. Furthermore, ART-suppressed immunological non-responders (INR) had significantly higher median rectal p24 levels than immunological responders (IR (0.024 vs 0.009 pg p24 per million rectal CD4+ T cells, P=0.009). Rectal tissue from viremic and elite controllers also had measurable p24 pre-ART that declined significantly following ART. Among all ART-suppressed participants, higher rectal p24 levels were associated with lower CD4 counts and among the controllers, rectal p24 levels are better predictors of HIV-specific CD107a+ CD8 response than HIV RNA. p24 was also detected in aviremic FNA LN samples and early data suggests associations with PD1, CXCR5+ PD1 and Tfh CD4+ cells.
HIV gag p24 was detected in most rectal and lymph node biopsies from ART-suppressed donors and controllers suggesting a higher burden of p24 in tissues than blood. The capacity to measure and characterize HIV reservoir at the level of viral protein and assess the relationship between immune phenotype revealed p24 correlates with immune function and will be important for immune-based clearance strategies.