PD-1 Predicts CD4 Loss Rate in Chronic HIV-1 Infection Better Than HIV RNA and CD38 But Not in Cryopreserved Samples

The immunopathogenic factor programmed cell death 1 (PD-1) was compared to CD38 and HIV RNA in predicting actual CD4+ T cell loss rate indicative for clinical progression. This cross sectional exploratory study included 50 consecutive, healthy HIV-infected patients off antiretroviral therapy (ART); 43 had the required observation times > 12 months. PD-1 and CD38 were determined on various T cell subsets by FACS analyses in fresh and later in parallel cryopreserved samples. Here more rapid progressors were relatively defined by having CD4 loss rates <median at -45.7/μl/year. PD-1 and CD38 densities in fresh blood were lower (p<0.001) in patients on ART (n=14) and seronegative controls (n=8). CD4 loss rates correlated significantly to current HIV RNA (R=-0.30), CD38 (R=-0.33) and PD-1 densities (R=-0.38) on CD8+ T cells, and best to ΔCD38, i.e. the difference in CD38 between the PD-1+CD8+ and CD8+ subsets (R=-0.51). PD- 1 was highest on the CD27+CD28-CD8+ subset with best correlation to progression (R=-0.54) in rapid progressors. Logistic regression models from HIV RNA, CD38 and PD-1 predicting rapid progression included PD-1 as best independent variable in combination with ΔCD38 or CD38, supported by similar results from multiple regression analyses. PD-1 did not correlate with any of the other candidate variables. Cryopreservation reduced the CD38+ and PD-1+ fractions but corresponding densities became more suppressed through a non-linear loss most pronounced in CD38hi/PD-1hi cells with loss of predictive power. In conclusion, PD-1 was the best independent predictor for CD4 loss rates in fresh blood compared with CD38 and HIV RNA.