Cellular Tropism and Viral Genetics in Appendix Tissue Reservoirs of Subtype C HIV-1-Infected Aviremic Persons

Abstract

Background: Although antiretroviral therapy (ART) can suppress plasma viral loads in people living with human immunodeficiency virus (HIV), it cannot eliminate HIV-1 proviruses persisting in various tissue reservoirs, and HIV-1 will rebound after ART cessation. We have identified the appendix as a novel HIV tissue reservoir, but nothing is known about the provirus and the cellular tropism in this tissue.

Methods: We used single-genome analysis of HIV-1 env DNA and compared the viral sequences from appendix tissues and lymph nodes of the same people living with HIV-1. Sequential multiplex immunofluorescence labeling and RNAscope in situ hybridization on formalin-fixed, paraffin-embedded appendix sections were performed to identify cell types harboring HIV-1 proviral DNA in the appendix, by visualizing viral and cellular biomarkers colocalization.

Results: The viral populations from the appendix were less heterogeneous than those from the lymph nodes in aviremic individuals, suggesting there is reduced ART selective pressure or the presence of appendix tropic HIV-1. Furthermore, we demonstrated that follicular dendritic cell (FDCs), rather than CD4+ T cells within the appendix, are the major cell type harboring subtype C HIV-1. Notably, although some subtype C HIV-1 signals could be remaining virions captured by FDCs even in aviremic individuals, HIV-1 proviral DNA was detected in some FDCs in the appendix tissues of aviremic individuals, indicating the presence of infected FDCs.

Conclusions: These results highlight the importance of analyzing all potential tissue and cellular tropism across different HIV-1 subtypes, to inform tailored therapeutic strategies for the diverse reservoirs that may differ across subtypes.

Keywords: Follicular dendritic cells; HIV-1 reservoir; Human appendix; Subtype C HIV-1; Viral genetics.