ALTERED CLONOGENIC CAPABILITY AND STROMAL CELL FUNCTION CHARACTERIZE BONE MARROW OF HIV-1 INFECTED SUBJECTES WITH LOW CD4+ T-CELL COUNT DESPITE VIRAL SUPPRESSION DURING HAART

Background. Inflammatory cytokines in bone marrow may impair hematolymphopoiesis in human immunodeficiency virus (HIV)–infected subjects who do not experience reconstitution of CD4+ T cells despite suppression of virus replication while receiving highly active antiretroviral therapy (HAART) (immunological nonresponders). Methods. Bone marrow samples from 12 immunological nonresponders receiving HAART were studied and compared with samples from 11 immunological responders. The mean CD4+ T cell count ( standard deviation) was 17468 cells/mm3 and plasma HIV RNA levels had been !50 copies/mL for at least 1 year for individuals enrolled in the study. The clonogenic capability of bone marrow samples was evaluated using the colony forming cell assay and the long-term culture-initiating cell assay. CD34+ cells from the colony forming cell assay were pooled for real-time polymerase chain reaction analysis of Fas and Fas ligand. Bone marrow cytokine production (interleukin-2 and tumor necrosis factor–a) and stromal interleukin-7 levels were analyzed by enzyme-linked immunosorbent assay in both groups. Flow cytometric analysis of CD4+ and CD8+ T cell subsets was performed. Results. A reduced clonogenic capability and a decrease in the level of more primitive progenitor cells were observed in parallel with lower production of interleukin-2 and increased tumor necrosis factor–a levels. A significant upregulation of Fas and Fas ligand on CD34+ cells and a higher stromal interleukin-7 production were observed. Impairment of the naive T cell compartment and persistent T cell activation were observed in peripheral blood. Conclusions. Samples from immunological nonresponders show reduced growth of in vitro colonies and an altered cytokine production in bone marrow. The cytokine pattern observed and the altered Fas and Fas ligand pathway may determine stem cell apoptosis and low CD4+ cell recovery. These features, which are similar to those observed in HIV-infected subjects before starting therapy, persist despite treatment.