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Activation of CD4$^+$ T lymphocytes from human immunodeficiency virus-type 1 (HIV-1)-infected donors with immobilized antibodies to CD3 and CD28 induces a virus-resistant state. This effect is specific for macrophage-tropic HIV-1. Transcripts encoding CXCR4/Fusin, the fusion cofactor used by T cell line-tropic isolates, were abundant in CD3/CD28-stimulated cells, but transcripts encoding CCR5, the fusion cofactor used by macrophage-tropic viruses, were not detectable. Thus, CD3/CD28 costimulation induces an HIV-1-resistant phenotype similar to that seen in some highly exposed and HIV-uninfected individuals.

Because stimulation of CD4$^+$ lymphocytes leads to activation of human immunodeficiency virus-type 1 (HIV-1) replication, viral spread, and cell death, adoptive CD4$^+$ T cell therapy has not been possible. When antigen and CD28 receptors on cultured T cells were stimulated by monoclonal antibodies (mAbs) to CD3 and CD28 that had been immobilized, there was an increase in the number of polyclonal CD4$^+$ T cells from HIV-infected donors. Activated cells predominantly secreted cytokines associated with T helper cell type 1 function. The HIV-1 viral load declined in the absence of antiretroviral agents. Moreover, CD28 stimulation of CD4$^+$ T cells from uninfected donors rendered these cells highly resistant to HIV-1 infection. Immobilization of CD28 mAb was crucial to the development of HIV resistance, as cells stimulated with soluble CD28 mAb were highly susceptible to HIV infection. The CD28-mediated antiviral effect occurred early in the viral life cycle, before HIV-1 DNA integration. These data may facilitate immune reconstitution and gene therapy approaches in persons with HIV infection.

Phase I studies of volunteers not infected with human immunodeficiency virus type 1 HIV-1) have shown that immunization with envelope subunit vaccine products elicits antibodies that neutralize laboratory-adapted (prototype) HIV-1 strains in vitro. Prototype strains are adapted to grow in continuous (neoplastic) cell lines and are more susceptible to neutralization than are primary isolates cultured in human peripheral blood mononuclear cells. In this study, 50 sera from nine phase I vaccine trials and 16 from HIV-1-infected persons were evaluated for neutralizing antibody activity against 3 laboratory-adapted and 5 primary HIV-1 isolates. Of 50 sera, 49 neutralized at least 1 of the prototype strains; however, none displayed neutralizing activity against primary isolatesof HIV-1. Serum from most HIV-1-infected persons neutralized both laboratory-adapted and primary HIV-1 isolates. These data demonstrate a qualitative, or large quantitative, differencein the neutralizing antibody response induced by envelope subunit vaccination and natural HIV-1 infection.

The pathogenesis of progressive spastic paraparesis [HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP)], a serious consequence of human T-cell leukemia virus type I (HTLV-I) infection, is unclear. T and B lymphocytes can be naturally infected by HTLV-I, but the susceptibility to HTLV-I infection of other cell types that could contribute to the pathogenesis of HAM/TSP has not been determined. We found that a human monocyte cell line (THP-1), primary human peripheral blood monocytes, and isolated microglial cells but not astrocytes or oligodendroglial cells derived from adult human brain were infected by HTLV-I in vitro. Infection with HTLV-I enhanced the secretion of interleukin 6 in human microglial cell-enriched cultures but did not stimulate the release of interleukin 1 from monocytes or microglial cells. Tumor necrosis factor α production was stimulated by HTLV-I infection of monocytes and microglial cells and could be enhanced by suboptimal amounts of lipopolysaccharide. Since both tumor necrosis factor α and interleukin 6 have been implicated in inflammatory demyelination and gliosis, our findings suggest that human microglial cells and monocytes infected with and activated by HTLV-I could play a role in the pathogenesis of HAM/TSP.

To prevent mother-to-child human immunodeficiency virus type 1 (HIV-1) transmission, it is important to identify its determinants. Because HIV-1 RNA levels can be reduced by antiviral therapy, we examined the role of maternal plasma HIV-1 RNA level in mother-to-child transmission. We used quantitative competitive PCR to measure HIV-1 RNA in 30 infected pregnant women and then followed their infants prospectively; 27% of the women transmitted HIV-1 to their infants and maternal plasma HIV-1 RNA level correlated strikingly with transmission. Eight of the 10 women with the highest HIV-1 RNA levels at delivery (190,400-1,664,100 copies per ml of plasma) transmitted, while none of the 20 women with lower levels (500-155,800 copies per ml) did (P = 0.0002). Statistical analysis of the distribution of HIV-1 RNA loads in these 30 women projected a threshold for mother-to-child transmission in a larger population; the probability of a woman with a viral RNA level of ≤100,000 copies per ml not transmitting is predicted to be 97%. Examination of serial HIV-1 RNA levels during pregnancy showed that viral load was stable in women who did not initiate or change antiviral therapy. These data identify maternal plasma HIV-1 RNA level as a major determinant of mother-to-child transmission and suggest that quantitation of HIV-1 RNA may predict the risk of transmission.

Primary resistance of HIV to zidovudine was first described in 1992 and has since been identified in up to 10% of antiretroviral-naive patients in some centers. Primary resistance to nevirapine has also been reported, but the prevalence of primary resistance to other agents in widespread use in clinical practice in unknown. We now report two cases of primary lamivudine resistance in two antiretroviral-naive patients who presented with acute HIV infection.

Genotypes that confer drug resistance were evaluated in human immunodeficiency virus (HIV) proviral DNA obtained from peripheral blood mononuclear cells (PBMC) and lymphoid tissue at baseline and after 8 weeks of therapy with zidovudine alone or in combination with didanosine from 22 patients (8 zidovudine-naive and 14 zidovudine-experienced). There was evidence of zidovudine resistance at codon 215 in 27.3% (6/22) of patients. All 20 patients evaluable for codon 74 (site of didanosine resistance) had virus that remained wild type during the 8-week study period. When HIV proviral DNA from PBMC was compared with that from lymphoid tissue, 94.7% (18/19) of evaluable samples were concordant at codon 215 at baseline, while 85.7% (12/14) were concordant at week 8. Resistance in PBMC (but not in lymphoid tissue) developed in 1 of 8 zidovudine-naive patients; an increased proportion of resistant strains in PBMC (but not in lymphoid tissue) was observed in 2 of 14 zidovudine-experienced patients. These results suggest high concordance for drug resistance mutations in HIV proviral DNA from blood and lymph node tissue.