Background:  HIV-1 replication in the brain results in AIDS dementia complex in about 30% of AIDS patients. The mechanisms that lead to neuropathogenesis are unclear. Also it is not known whether neurotropic or neurovirulent HIV-1 variants are involved. Others reported HIV-1 isolates with enhanced tropism and fusigenicity for macrophages. Here we used PCR to recover complete envelope (env) genes from brain tissue of 5 patients with AIDS dementia complex. These env have not been altered by culture during isolation. The biological properties of these env were then investigated.

Methods:  Complete env genes were amplified from autopsy brain tissue of the 5 patients and lymph node tissue of 2 of these patients. All env were cloned into the pSVIIIenv expression vector; 293T cells were co-transfected with env⁺ pSVIIIenv and env^- NL43 and pseudotype virus harvested. Single-round infectivity assays were conducted on co-receptor⁺ indicator cells and on macrophages. Sensitivities to CCR5 inhibitor TAK779 and CD4 specific antibody Q4120 were tested on GHOST/CCR5. The effects of receptor density were assessed by single-round infectivity assays on HeLa clones expressing various amounts of CD4 and CCR5.

Results:  From the 5 patients, 19 env had distinct V1V2 sequences. Of these, 13 env were functional and conferred infectivity for CD4⁺ CCR5⁺ cells. Infectivity and cell:cell fusion assays showed that most env used both CCR5 and CCR3. One env used a broad range of co-receptors, while several were restricted to CCR5. There was no correlation between tissue of origin and co-receptor use. Env that were highly fusigenic and tropic for macrophages were identified in brain tissue from 4 of 5 patients. These env were at the top limit of macrophage tropism when compared to a panel of well-characterized macrophage tropic control env. The enhanced macrophage-tropism correlated with sensitivity to inhibition by the CD4-specific antibody Q4120 but not with sensitivity to the CCR5 inhibitor TAK779. The highly macrophage-tropic env were able to infect cells expressing low levels of CD4 or CCR5.

Conclusions:  Our data show the presence of env that are highly fusigenic and tropic for macrophages in the brains of patients with neurological complications. These env are able to infect cells that express low levels of CD4 or CCR5 and may have adapted for replication in brain macrophages and microglia that express limited amounts of CD4.

Keywords: Envelope; Tropism; Macrophage