Abstract Body

Background: HIV infection is associated with diminished protective responses against opportunistic infections including cytomegalovirus (CMV). In this study, we examined the effect of HIV expanded myeloid derived suppressor cells (MDSCs) on CMV specific effector cells. Methodology: Peripheral blood mononuclear cells (PBMCs) obtained from HIV seronegative, CMV seropositive healthy donors were cultured in presence of heat inactive HIVBaL. After 5 days, cells were stained with anti-CD11b, anti-CD33, anti-CD14 and anti-HLA DR. CD11b+CD33+CD14+HLA DRhi (DRhi monocytes) and CD11b+CD33+CD14+HLA DR-/lo (MDSCs) cell subsets were sorted using flow cytometry. Sorted cell fractions were cultured with freshly isolated autologous PBMCs in presence or absence of a peptide pool of CMV pp65 antigen (1 μg/ml). IFNγ and IL-10 were determined by ELISPOT and expressed as spot forming units (SFU). Sorted cell fractions were cultured in presence of LPS (100 ng/ml) and IFNγ (2 ng/ml). IL-12p70 was determined in culture supernatants by ELISA and surface expression of HLA DR and CD83 (maturation markers) by flow cytometry. CD150 and B7H4 (leukocyte activation markers) expression on sorted cell fractions was determined by flow cytometry. Data were analyzed using two-tailed, paired Student’s t test. Results: Culture of PBMCs with heat inactivated HIV resulted in a significant expansion of MDSCs as compared to control PBMCs (p=0.003). Expansion of MDSC and DRhi monocyte cell populations were comparable in the presence of HIV (p=0.74). PBMCs stimulated with the CMV pp65 peptide pool and cultured with sorted autologous MDSCs had fewer IFNγ SFU compared to PBMCs without MDSCs (p=0.03); however, PBMCs cultured with DRhi monocytes did not significantly differ (p=0.37). Furthermore, pp65 stimulated PBMCs produced increased IL-10 SFU when cultured with MDSCs compared to cultures with the DRhi monocyte subset. The MDSC subset exhibited a 2-fold increase in expression of surface CD150 and 1.3-fold increased expression of B7H4 as compared to the expression on the DRhi monocyte subset (p=0.03). HIV MDSCs maintained HLA DRlo and CD83lo expression as compared to the DRhi monocytes, even when cultured with LPS and IFNγ. Furthermore, these cells produced 4-fold less of the TH1 polarizing cytokine IL12p70 as compared to DRhi monocytes (p=0.02). Conclusions: These findings suggest that HIV infection results in a significant expansion of MDSCs and that MDSCs are involved in suppression of the immune response directed against CMV. Understanding the mechanism(s) responsible for the suppressed immune response against CMV will assist in the development of treatment strategies designed to improve the immunity to CMV and other opportunistic infections associated with advanced HIV infection.