Background: CD32 has been identified as a marker of a substantially enriched HIV reservoir. Here we explore the relationship of CD32 expression on CD4 T cells with other correlates of reservoir size including time to viral rebound after treatment interruption.
Methods: CD32 expression was measured by flow cytometry on PBMCs (n=39) and tonsillar tissue (n=1) from individuals who initiated ART during primary HIV infection (PHI), and uninfected controls (n=10). Co-expression with immune checkpoint receptors (ICRs), lineage, memory and T follicular helper (Tfh) markers was measured. HIV DNA was quantified in bulk and sorted CD32+ and CD32- populations.
Results: One-year post-ART initiation, the frequency of CD32+ CD4 T cells was 1.5% (range 0.2-6.4), and did not differ from controls. CD32+ CD4 T cells were found predominantly within differentiated memory subsets (transitional, effector memory, and TEMRA) compared with CD32- CD4 T cells (all p< 0.001) for HIV+ (n=20) and controls. CD32+ CD4 T cells were highly enriched for HIV DNA compared with CD32- cells (average 103-fold, n=6, p=0.03), although CD32 percentage did not correlate with reservoir size (n=29). In a subset of individuals (n=19) who interrupted ART after 48 weeks, CD32+ CD4% did not predict viral load rebound, although all three individuals with persistently undetectable viraemia had CD32+ CD4% below the median.
CD32+ CD4 T cells from blood had higher expression of PD-1, Tim-3 and TIGIT (all p< 0.0001) and a higher density of CD2 (p=0.001) than CD32- cells in HIV+ participants (n=20) and controls. Tonsil CD32+ CD4 T cells (n=1) showed a similar pattern of memory distribution and ICR expression as the periphery. Although tonsillar CD32+ CD4 T cells had higher individual expression of Bcl-6, ICOS and CXCR5 than CD32- cells, the co-expression pattern was not consistent with a Tfh phenotype.
Conclusions: We confirm the role of CD32 as a marker of the HIV reservoir, and show that this may occur early during PHI on more differentiated CD4 T cells and is highly co-expressed with ICRs. That expression is similar between HIV+ and HIV- individuals suggests that preferential infection or survival of CD32+ cells, rather than CD32 up-regulation, is responsible for the observed enrichment.