Background
While current antiretroviral treatment regimens can reliably prevent new infection events in people living with HIV (PLWH), they cannot actively eliminate the persistent population of CD4 T cells harboring intact provirus that can give rise to viral rebound if treatment is interrupted. Various approaches to HIV cure rely on the elimination of this reservoir through cytotoxic T lymphocytes (CTLs). However, some studies have suggested that HIV-infection might confer some level of intrinsic resistance to CTL-mediated lysis through various mechanisms such as the upregulation of anti-apoptotic factors. Here, we show that the rate of lysis did not differ between primary CD4 T cells that are uninfected, harboring intact HIV provirus, or actively expressing an HIV reporter construct.
Methods
We performed co-culture killing assays using either primary CD4+ T cells of 7 aviremic PLWH or healthy donor CD4+ T cells that were spinoculated with different NL4-3 HIV GFP-reporter constructs, with autologous CD8+ T cells and CTL-engaging single-chain diabodies specific for a exogenous peptides in the context of HLA-A2 or HLA-E. CD4+ T cells were converted into target cells by pulsing them with saturating concentrations of the respective peptides. Following the co-culture, killing was assessed via flow cytometry. The frequency of HIV-infected cells before and after the co-culture was determined using the intact proviral DNA assay in the case of primary cells from PLWH, or by quantifying the frequency of GFP+ reporter cells for spinoculated CD4 T cells.
Results
In 6 of the 7 study participants, we did not see any enrichment for cells harboring intact provirus over the course of the co-culture. When testing healthy donor cells expressing NL4-3 reporter virus using an HLA-A2 antigen, we saw nef-dependent enrichment for actively infected cells. Surface HLA staining showed that in cells infected with nef-sufficient virus, HLA-A2, but not HLA-E, is downregulated. When we repeated the assay using an HLA-E antigen, GFP+ and GFP- cells were eliminated at the same rate for all three viral reporter constructs.
Conclusions
Our findings indicate that HIV-infection does not generally render CD4 T cells more resistant to CTL-mediated lysis. While some immune escape mechanisms, such as the downregulation of classical MHC class I molecules, can lower the antigen availability and therefore limit recognition by specific CTL clones, this does not affect their susceptibility to cell death.
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