Influence of sickle cell disease on susceptibility to HIV infection

Abstract

People with sickle cell disease (SCD) are reported to have low rates of HIV infection, slower progression to AIDS and lower HIV-associated mortality compared to the general population. Mechanisms of potential resistance to HIV in SCD are incompletely understood. We retrospectively reviewed the Transfusion Safety Study to compare HIV status between people with SCD and other congenital anemias who were routinely exposed to blood products during the high-risk period before HIV screening implementation. Non-SCD congenital anemia diagnosis was associated with a higher risk of HIV acquisition compared to SCD (OR 13.1 95%CI 1.6-108.9). In addition, we prospectively enrolled 30 SCD cases and 30 non-SCD controls to investigate potential mechanisms of resistance to HIV in SCD. CCR5 and CCR7 expression was lower and CD4 expression was higher on CD4+ T cells from SCD cases compared to controls. Surface expression of CD4+ T cell CXCR4, CD38 and HLA-DR did not differ between the groups. SCD CD4+ T cells were not less susceptible to HIV infection than controls. Levels of multiple cytokines were elevated in the SCD plasma, but SCD plasma compared to control plasma did not inhibit HIV infection of target cells. In conclusion, our epidemiological data support people with SCD being resistant to HIV infection. Potential mechanisms include lower CD4+ T cell expression of CCR5 and CCR7, balanced by increased CD4 expression and cytokine levels, which did not result in in vitro resistance to HIV infection. Further study is needed to define the risk and pathophysiology of HIV in persons with SCD.

Fig 1. Comparison of HIV co-receptors, CD4+ T cell activation markers, CD4+ MFI and Percent of CD4+ Cells Among Total T Cells between SCD patients and non-SCD controls.

Twenty four-hour old whole blood samples from SCD patient and non-SCD controls were labeled for CD4 T cells and incubated with antibodies to detect markers associated with HIV or cellular activation. Following incubation, surface expression of the HIV co-receptors CCR5 and CXCR4 and T cell trafficking molecule CCR7 were measured by flow cytometry (Panel A). MFI, mean fluorescence intensity between SCD patients and non-SCD controls were compared. Percent of CD4⁺ T cells expressing the activation markers CD38 or HLA-DR were measured and compared between SCD patients and non-SCD controls (Panel B). The intensity of expression of CD4+ amongst T cells (Panel C) and the percent of CD4+ T cells among total T cells (Panel D) was significantly higher in SCD patients compared to non-SCD controls. Mean and standard errors of the means for 30 SCD patients and 30 non-SCD controls are shown, *p<0.05.

Fig 2. HIV Infectivity of PBMCs from SCD Patients and non-SCD Controls.

CD8-depleted PBMC from SCD patients and non-SCD controls were infected with HIV NL4-3 (CXCR4-tropic) and 81-A (CCR5-tropic) at increasing MOI for six days. Following incubation, supernatants and cells were harvested for detection of HIV p24 (Panel A) and pro-viral load (Panel B) respectively. Mean and standard errors of the means for 30 SCD patients and 30 non-SCD controls are shown. Samples from four SCD patients and two non-SCD controls spanning a range of proviral load were assayed for integrated HIV DNA (Panel C). Five samples showed undetectable HIV DNA on both assays and are not graphed. The linear regression line of the log₁₀ values is shown.

Fig 3. Cytokines and Chemokines Compared between SCD Patients (treated or not treated with HU) and non-SCD Controls.

Biomarkers tested are grouped into anti-inflammatory (AI), chemoattractant (CA), coagulation (CO), growth factor (GF) and pro-inflammatory (PI) functional categories. Relative increases in concentration are shown in red and decreases in blue. * significantly different between SCD patients and non-SCD controls (p<0.05 after FDR correction).

Fig 4. HIV Infectivity of Target MT-2 cells in the Presence of Plasma from SCD Patients or Plasma from Non-SCD Controls.

MT-2 cells maintained at log phase growth were infected with either HIV NL4-3 (Panel A) or 81-A virus (Panel B) at MOI of 10⁻² in cultures spiked with 20% plasma from SCD patients or non-SCD controls. Following 7-day infections supernatants were measured for p24 by ELISA. Mean and SEM are shown. * p<0.05.