Analysis of nonhuman primate peripheral blood mononuclear cells for susceptibility to HIV-1 infection and HIV coreceptor expression

Cross-Linking of a CD4-Mimetic Miniprotein with HIV-1 Env gp140 Alters Kinetics and Specificities of Antibody Responses against HIV-1 Env in Macaques

Evaluation of the epitope specificities, locations (systemic or mucosal), and effector functions of antibodies elicited by novel HIV-1 immunogens engineered to improve exposure of specific epitopes is critical for HIV-1 vaccine development. Utilizing an array of humoral assays, we evaluated the magnitudes, epitope specificities, avidities, and functions of systemic and mucosal immune responses elicited by a vaccine regimen containing Env cross-linked to a CD4-mimetic miniprotein (gp140-M64U1) in rhesus macaques. Cross-linking of gp140 Env to M64U1 resulted in earlier increases of both the magnitude and avidity of the IgG binding response than those with Env protein alone. Notably, IgG binding responses at an early time point correlated with antibody-dependent cellular cytotoxicity (ADCC) function at the peak immunity time point, which was higher for the cross-linked Env group than for the Env group. In addition, the cross-linked Env group developed higher IgG responses against a linear epitope in the gp120 C1 region of the HIV-1 envelope glycoprotein. These data demonstrate that structural modification of the HIV-1 envelope immunogen by cross-linking of gp140 with the CD4-mimetic M64U1 elicited an earlier increase of binding antibody responses and altered the specificity of the IgG responses, correlating with the rise of subsequent antibody-mediated antiviral functions.IMPORTANCE The development of an efficacious HIV-1 vaccine remains a global priority to prevent new cases of HIV-1 infection. Of the six HIV-1 efficacy trials to date, only one has demonstrated partial efficacy, and immune correlate analysis of that trial revealed a role for binding antibodies and antibody Fc-mediated effector functions. New HIV-1 envelope immunogens are being engineered to selectively expose the most vulnerable and conserved sites on the HIV-1 envelope, with the goal of eliciting antiviral antibodies. Evaluation of the humoral responses elicited by these novel immunogen designs in nonhuman primates is critical for understanding how to improve upon immunogen design to inform further testing in human clinical trials. Our results demonstrate that structural modifications of Env that aim to mimic the CD4-bound conformation can result in earlier antibody elicitation, altered epitope specificity, and increased antiviral function postimmunization.

Effective activation alleviates the replication block of CCR5-tropic HIV-1 in chimpanzee CD4+ lymphocytes

Human immunodeficiency virus type 1 (HIV-1) originated in chimpanzees; yet, several previous studies have shown that primary HIV-1 isolates replicate poorly in chimpanzee CD4+ T lymphocytes in vitro and in vivo. The reasons for this apparent restriction are not understood. Here, we describe a new activation protocol that led to a reproducible expansion and activation of chimpanzee CD4+ T lymphocytes in vitro. Using this protocol, we uncovered species-specific differences in the activation profiles of human and chimpanzee CD4+ T-cells, including HLA-DR and CD62L. Moreover, we found that improved activation facilitated the replication of both CXCR4 and CCR5-tropic HIV-1 in CD4+ T-cell cultures from over 30 different chimpanzees. Thus, the previously reported "replication block" of CCR5-tropic HIV-1 in chimpanzee lymphocytes appears to be due, at least in large part, to suboptimal T-cell activation.

A dominant block to HIV-1 replication at reverse transcription in simian cells

Although nonhuman primates are genetically close to humans, their T cells do not support productive replication of HIV-1. In contrast, HIV-1 replicates in activated human CD4(+) T cells, monocytes, and metabolically active human cells of a variety of cell types become permissive for HIV-1 replication when transduced to express CD4 and CCR5 or CXCR4. The molecular basis of this species restriction to HIV-1 replication was investigated by using African green monkey and rhesus macaque cell lines that were stably transduced to express human CD4 and CCR5. The cells supported replication of cognate viruses [simian immunodeficiency virus from African green monkeys (SIV-AGM) and macaques (SIVmac239)] but did not support replication of an R5-tropic cytopathic HIV-1. A beta-lactamase-based HIV-1 entry assay was used to show that the virus efficiently entered the nonhuman primate cells. Provirus formation was reduced 50-fold compared with similarly infected human cells. Real-time PCR quantitation demonstrated that reverse transcription failed to initiate efficiently in the simian cells. The block to reverse transcription was overridden at multiplicity of infection >1 or by preincubation of the nonhuman primate cells with virus, a feature reminiscent of the Friend virus resistance gene-1 (FV-1), restriction to murine leukemia virus replication in mouse cells. Heterokaryon analysis in which human and simian cells were fused demonstrated that the block was dominant. These findings suggested that the primate cells contain a dominant inhibitor that prevents HIV-1 reverse transcription.

Analysis of human lung endothelial cells for susceptibility to HIV type 1 infection, coreceptor expression, and cytotoxicity of gp120 protein

The lung represents a potential target during HIV infection, and the onset of AIDS is associated with severe pulmonary complications in many patients. T-lymphocytes and alveolar macrophages form the majority of HIV-infected cells in the lung. However, other cell types in the lung could participate in HIV-mediated lung pathology and their role has not been investigated. The aims of this study were to determine if human lung microvascular endothelial cells (HLMEC) express HIV receptor and coreceptors, and if HIV can directly infect HLMEC. Specifically, we wished to determine if these cells constitute a viral reservoir in the lung, and if HIV-1 envelope proteins induce cytotoxic effects on HLMEC. Our results showed that by flow cytometry, HLMEC failed to express any CXCR4 or CCR5 on their surface. In contrast, RT-PCR revealed the presence of CXCR4 and CCR5 mRNA, but not CD4 in HLMEC. Two dual-tropic HIV-1 isolates failed to infect HLMEC in vitro, as determined by (1) p24 antigen capture ELISA, (2) reverse transcriptase assay, RT-PCR, and (3) DNA PCR. However, a recombinant HIV-1 gp120 preparation induced apoptotic cell death of HLMEC. These data support the hypothesis that no productive HIV-1 infection of HLMEC occurs in vitro. This suggests that in vivo, HLMEC may not be a major reservoir of HIV in the lung and the primary route for HIV invasion of the lung. Thus, while other mechanisms must play a role in HIV invasion and subsequent dissemination in the lung, lung endothelial cells do represent potential targets for the lethal effects of HIV viral proteins.

CXCR4 homologues of gibbon ape, African green monkey, squirrel monkey, and cotton-top marmoset

CXCR4 gene homologues were isolated from an ape (gibbon), an Old World monkey (African green monkey), and two New World monkeys (squirrel monkey and cotton-top marmoset), and their DNA sequences determined. The squirrel monkey and cotton-top marmoset CXCR4 sequences more closely resemble homologues from apes than Old World monkeys, a pattern not seen for the related chemokine receptor CCR5. The African green monkey CXCR4 gene is similar to its homologue in baboon, a pattern that has also been seen among CCR5 homologues. The gibbon CXCR4 contains the first polymorphisms recognized in ape homologues, the human and chimpanzee CXCR4 proteins being identical, and two of these three differences are also observed in one or more Old World monkey homologues. While 18 positions within CXCR4 are now known to be polymorphic in primates, 7 of these polymorphisms have been observed in multiple examples and 11 have been observed only once.

Idiotype cascades associated with the CD4-HIV glycoprotein 120 interaction: immunization with anti-idiotypic antibodies induces anti-anti-idiotypic responses with anti-CD4 specificity and in vitro neutralizing activity

Anti-idiotypic antibodies (Ab-2), which were generated in baboons against a mouse monoclonal antibody specific for the CD4 molecule expressed on human T cells, were used to produce anti-anti-idiotypic antibodies (Ab-3) in mice. This response induced by Ab-2 immunization of BALB/c mice was classified as anti-anti-idiotype (Ab-3) on the basis of the ability of the mouse Ab-3 to (1) specifically bind the baboon Ab-2 preparation, but not irrelevant baboon IgG preparations, (2) inhibit the binding of the anti-CD4 Ab-1 preparation to the baboon Ab-2, and (3) recognize a second baboon Ab-2, along with a rabbit Ab-2 specific for the monoclonal anti-CD4 Ab-1 preparation. The murine Ab-3 response also recognizes the CD4 molecule expressed on a human CD4+ T cell line, as determined by flow cytometry; recognizes the same epitopes on the CD4 molecule as the Ab-1; inhibits HIV-1 syncytium formation; and neutralizes HIV-1 primary isolates in vitro. These studies suggest that Ab-3 responses can be induced by anti-Id immunization, which serologically mimicks the antigen and Id specificities of the monoclonal anti-CD4 preparation used to generate the anti-Id. Thus, the Ab-3 response exhibits the characteristics of a population that represents the internal image of the Ab-1.