During HIV-1 infection most blood dendritic cells are not productively infected and can induce allogeneic CD4+ T cells clonal expansion.

We have considered the possibility that antigen-presenting cells of the dendritic cell lineage may be infected in vivo and spread HIV-1 at the time dendritic cells initiate the clonal expansion of antigen-specific T cells. Dendritic cells were isolated from 25 HIV-1-infected subjects (CDC stages II-IV). Fewer dendritic cells were recovered from most infected subjects. Reduced numbers of total non-T cells were also found in these patients, so that preferential loss of dendritic cells did not occur. Dendritic cell function was assessed by stimulatory capacity for allogeneic CD4+ T cells in the mixed leucocyte reaction (MLR). Potent MLR stimulator activity was retained in the dendritic cell-enriched populations from HIV-infected patients. Seven out of nine patients without AIDS (asymptomatic, lymphadenopathy or ARC) and three out of six patients with AIDS had proliferative responses equivalent to those induced by dendritic cells from controls. Dendritic cells from HIV+ subjects were able to initiate the expansion of allogeneic CD4+ T cell clones with cloning efficiency not different from controls and without evidence of cytopathic effect in the expanding CD4+ clones. In situ hybridization of the different mononuclear cell populations with a gag-specific riboprobe demonstrated positive cells in the T cell fractions of 12 of the 15 patients tested. None of the asymptomatic or ARC patients had riboprobe-positive cells in the dendritic cell-enriched populations. Four out of nine patients with AIDS had cells positive for HIV-1 expression in the dendritic cell-enriched fraction. However, the positive cells had the nuclear profile of lymphocytes, and by cytofluorography some residual low-density T cells were present. By limiting dilution and polymerase chain reaction (PCR), CD4+ lymphocytes carried HIV provirus in inocula of 500-5000 cells, while provirus could only be detected in 50,000 cells from the dendritic cell-enriched fraction. The latter signal may be due to the demonstrated levels of T cell contamination. Our data indicate that productive or latent HIV-1 infection of blood dendritic cells in vivo is rare, certainly no greater than in T lymphocytes, and that in vitro dendritic cell preparations from patients can expand CD4+ T cells efficiently and therefore may be able to expand T cells with immunotherapeutic activity.