Complex Determinants in Human Immunodeficiency Virus Type 1 Envelope gp120 Mediate CXCR4-Dependent Infection of Macrophages

Abstract

Host cell range, or tropism, combined with coreceptor usage defines viral phenotypes as macrophage tropic using CCR5 (M-R5), T-cell-line tropic using CXCR4 (T-X4), or dually lymphocyte and macrophage tropic using CXCR4 alone or in combination with CCR5 (D-X4 or D-R5X4). Although envelope gp120 V3 is necessary and sufficient for M-R5 and T-X4 phenotypes, the clarity of V3 as a dominant phenotypic determinant diminishes in the case of dualtropic viruses. We evaluated D-X4 phenotype, pathogenesis, and emergence of D-X4 viruses in vivo and mapped genetic determinants in gp120 that mediate use of CXCR4 on macrophages ex vivo. Viral quasispecies with D-X4 phenotypes were associated significantly with advanced CD4؉ -T-cell attrition and commingled with M-R5 or T-X4 viruses in postmortem thymic tissue and peripheral blood. A D-X4 phenotype required complex discontinuous genetic determinants in gp120, including charged and uncharged amino acids in V3, the V5 hypervariable domain, and novel V1/V2 regions distinct from prototypic M-R5 or T-X4 viruses. The D-X4 phenotype was associated with efficient use of CXCR4 and CD4 for fusion and entry but unrelated to levels of virion-associated gp120, indicating that gp120 conformation contributes to cell-specific tropism. The D-X4 phenotype describes a complex and heterogeneous class of envelopes that accumulate multiple amino acid changes along an evolutionary continuum. Unique gp120 determinants required for the use of CXCR4 on macrophages, in contrast to cells of lymphocytic lineage, can provide targets for development of novel strategies to block emergence of X4 quasispecies of human immunodeficiency virus type 1.

Alternative Coreceptor Requirements for Efficient CCR5- and CXCR4-Mediated HIV-1 Entry into Macrophages

“…The results of our mutagenesis studies confirmed that Ile326 is critically important for efficient HIV-1 entry into macrophages by both SG3 and Macs1-Spln Envs. Our results support and extend the findings of Ghaffari et al (28), where, in a reciprocally designed experiment, replacement of Met for Ile at position 326 in two non-M-tropic CXCR4-using Envs enhanced macrophage entry via CXCR4. Together, these studies provide independent evidence that affirms a critical role for Ile326 in promoting efficient CXCR4-mediated HIV-1 entry into macrophages.…”

“…In addition, little is known about gp120-coreceptor interactions that may contribute to efficient CXCR4-mediated HIV-1 entry into macrophages. Although one previous study identified Ile326 in the gp120 V3 loop as being important for CXCR4-mediated HIV-1 entry into macrophages (28), the mechanism by which this amino acid variant permits macrophage entry is unknown. Here, we identified and characterized alternative mechanisms of coreceptor engagement by HIV-1 Envs that have efficient CCR5-and CXCR4-mediated entry into macrophages.…”

Genetic and Functional Analysis of R5X4 Human Immunodeficiency Virus Type 1 Envelope Glycoproteins Derived from Two Individuals Homozygous for the CCR5Δ32 Allele

“…2A). Consistent with previous studies, ADA and 89.6 Envs entered PBMC and MDM, whereas HXB2 Env entered PBMC but not MDM (18,19,34,42,43,(49)(50)(51). All C2 and DR Envs entered PBMC, but only C2-16 and DR-17 Envs entered MDM.…”

Baseline Resistance of Primary Human Immunodeficiency Virus Type 1 Strains to the CXCR4 Inhibitor AMD3100

“…While many HIV-1 strains can use either CCR5 or CXCR4 (R5X4 viruses) to infect cell lines, the efficiency with which a given virus uses each coreceptor for infection can vary widely and does not always predict the mechanism of entry into human T cells or macrophages (18). Thus, some R5X4 viruses use only CXCR4 to infect certain primary cells, others use only CCR5, and some viruses use both coreceptors to infect multiple cell types (16,17,26,36,(59)(60)(61). The use of specific and potent coreceptor antagonists can be utilized to prevent entry via one coreceptor, revealing the efficiency with which the alternative coreceptor can support virus infection.…”