Inhibitors of the human immunodeficiency virus type 1 (HIV-1) protease have entered clinical study as potential therapeutic agents for HIV-1 infection. The clinical efficacy of HIV-1 reverse transcriptase inhibitors has been limited by the emergence of resistant viral variants. Similarly, variants expressing resistance to protease inhibitors have been derived in cell culture. We now report the characterization of resistant variants isolated from patients undergoing therapy with the protease inhibitor MK-639 (formerly designated L-735,524). Five of these variants, isolated from four patients, exhibited cross-resistance to all members of a panel of six structurally diverse protease inhibitors. This suggests that combination therapy with multiple protease inhibitors may not prevent loss of antiviral activity resulting from resistance selection. In addition, previous therapy with one compound may abrogate the benefit of subsequent treatment with a second inhibitor.

Indinavir (IDV) (also called CRIXIVAN, MK-639, or L-735,524) is a potent and selective inhibitor of the human immunodeficiency virus type 1 (HIV-1) protease. During early clinical trials, in which patients initiated therapy with suboptimal dosages of IDV, we monitored the emergence of viral resistance to the inhibitor by genotypic and phenotypic characterization of primary HIV-1 isolates. Development of resistance coincided with variable patterns of multiple substitutions among at least 11 protease amino acid residues. No single substitution was present in all resistant isolates, indicating that resistance evolves through multiple genetic pathways. Despite this complexity, all of 29 resistant isolates tested exhibited alteration of residues M-46 (to I or L) and/or V-82 (to A, F, or T), suggesting that screening of these residues may be useful in predicting the emergence of resistance. We also extended our previous finding that IDV-resistant viral variants exhibit various patterns of cross-resistance to a diverse panel of HIV-1 protease inhibitors. Finally, we noted an association between the number of protease amino acid substitutions and the observed level of IDV resistance. No single substitution or pair of substitutions tested gave rise to measurable viral resistance to IDV. The evolution of this resistance was found to be cumulative, indicating the need for ongoing viral replication in this process. These observations strongly suggest that therapy should be initiated with the most efficacious regimen available, both to suppress viral spread and to inhibit the replication that is required for the evolution of resistance.

To characterize the role of CD4 in human immunodeficiency virus type 1 (HIV-1) infection of macrophages, we examined the expression of CD4 by primary human monocyte-derived macrophages and studied the effect of recombinant soluble CD4 and anti-CD4 monoclonal antibodies on HIV-1 infection of these cells. Immunofluorescence and Western blot (immunoblot) studies demonstrated that both monocytes and macrophages display low levels of surface CD4, which is identical in mobility to CD4 in lymphocytes. Recombinant soluble CD4 and the anti-CD4 monoclonal antibody Leu3a blocked infection of macrophages by three different macrophage-tropic HIV isolates, and the cytopathic effects of HIV-1 infection were similarly prevented. Dose-response experiments using a prototype isolate which replicates in both macrophages and T lymphocytes showed that recombinant soluble CD4 inhibited infection of macrophages more efficiently than in lymphocytes. These results indicate that CD4 is the dominant entry pathway for HIV-1 infection of macrophages. In addition, recombinant soluble CD4 effectively blocks HIV-1 infection by a variety of macrophage-tropic strains and thus has the potential for therapeutic use in macrophage-dependent pathogenesis in HIV disease.

Aedes aegypti were infected with chikungunya virus by being fed on a blood–virus suspension poured over a sugar cube. The virus infection in the salivary glands was then studied with the electron microscope. In the proximal portion of the lateral lobes, 250–310 Å virus precursor particles were seen in the nucleus, in the cytoplasm, and on the membranes of cytoplasmic vesicles. Enveloped 500–580 Å virus particles with a 250–310 Å core were seen within the vesicles, in intercellular spaces, and in large numbers in the apical cavity and periductal space. In the distal portions of the lateral and median lobes precursor particles were present in the nucleus and cytoplasm, but no cytoplasmic vesicles were seen. Numerous enveloped virus particles were seen in the apical cavity and periductal space, and in the median lobe within the duct lumen as well. No evidence of virus replication was seen in the intermediate portion of the median lobe.In the distal portions, virus particles were frequently associated with a concentration of the secretory material. No other microscopically visible pathological changes were seen in the infected salivary glands.