The cell surface receptor protein CD32a has recently been postulated as a marker of a CD4+ T-cell HIV reservoir harboring replication-competent proviruses in ART-suppressed subjects. The expression of CD32 in different CD4+ T-cell subsets in HIV-infected patients and expression in persistent infected cells retained within lymphoid tissue after ART are important questions that still need to be evaluated.
The expression of CD32 in different CD4+ T-cell subpopulations was measured in 9 ART-treated patients by fluorescence activated cell sorting (FACS) immunophenotyping using antibodies that recognized CD3, CD4, CD27, CD45RO, CD32 and HLA-DR. HIV and CD32a RNA expression in tissue was measured by fluorescent in situ hybridization (FISH) in lymph node sections from 2 aviremic and 4 viremic HIV-infected patients. Ex vivo HIV-1 infection kinetics was measured by the RNA/flow technique during 6 days after the initial infection of healthy donor unstimulated PBMCs, and in a cervico-vaginal tissue explant model of HIV infection. Wilcoxon signed rank and spearman’s rank correlation tests were used for statistical analysis.
Terminally-differentiated CD4+ T cells expressed significantly higher proportions of CD32 receptor compared to other CD4+ T subpopulations (p<0.05 for all comparisons). The majority of CD4+CD32+ cells had a naïve phenotype (CD45RO–CD27+) followed by central memory (CD45RO+CD27+) and terminally-differentiated phenotype (CD45RO–CD27–). In vivo, the vast majority of productively infected cells in lymph node tissues from HIV aviremic and viremic patients also co-expressed the CD32a marker (90% of all infected cells), while most of CD32a single positive cells were absent from the B cell follicle, one of the major reservoirs for HIV. HIV infection of unstimulated PBMCs and cervico-vaginal histocultures upregulated the expression of CD32 in approximately 10-20% of all infected cells. CD32+ infected cells expressed more frequently the activation marker HLA-DR compared to CD32- infected cells (92% vs 77%) and the immune check-point PD-1 (46% vs 25%).
CD32 is preferentially detected in HIV transcriptionally active cells in tissues after ART and was identified to be co-expressed with activation markers in in vitro infected cells suggesting its expression is also associate with active HIV-infected cells