In vitro HIV-1 infection in Macaca nemestrina PBMCs is blocked at a step beyond reverse transcription

A variant macaque-tropic human immunodeficiency virus type 1 is resistant to alpha interferon-induced restriction in pig-tailed macaque CD4+ T cells

Human immunodeficiency virus type 1 (HIV-1) antagonizes innate restriction factors in order to infect and persistently replicate in a host. In a previous study, we demonstrated that HIV-1 NL4-3 with a simian immunodeficiency virus mne (SIVmne) vif gene substitution (HSIV-vif-NL4-3) could infect and replicate in pig-tailed macaques (PTM), indicating that APOBEC3 proteins are primary barriers to transmission. Because viral replication was persistent but low, we hypothesized that HSIV-vif-NL4-3 may be suppressed by type I interferons (IFN-I), which are known to upregulate the expression of innate restriction factors. Here, we demonstrate that IFN-α more potently suppresses HSIV-vif-NL4-3 in PTM CD4(+) T cells than it does pathogenic SIVmne027. Importantly, we identify a variant (HSIV-vif-Yu2) that is resistant to IFN-α, indicating that the IFN-α-induced barrier can be overcome by HSIV-vif chimeras in PTM CD4(+) T cells. Interestingly, HSIV-vif-Yu2 and HSIV-vif-NL4-3 are similarly restricted by PTM BST2/Tetherin, and neither virus downregulates it from the surface of infected PTM CD4(+) T cells. Resistance to IFN-α-induced restriction appears to be conferred by a determinant in HSIV-vif-Yu2 that includes env su. Finally, we show that the Yu-2 env su allele may overcome an IFN-α-induced barrier to entry. Together, our data demonstrate that the prototype macaque-tropic HIV-1 clones based on NL4-3 may not sufficiently antagonize innate restriction in PTM cells. However, variants with resistance to IFN-α-induced restriction factors in PTM CD4(+) T cells may enhance viral replication by overcoming a barrier early in the viral replication cycle.

Vif substitution enables persistent infection of pig-tailed macaques by human immunodeficiency virus type 1

Among Old World monkeys, pig-tailed macaques (Pt) are uniquely susceptible to human immunodeficiency virus type 1 (HIV-1), although the infection does not persist. We demonstrate that the susceptibility of Pt T cells to HIV-1 infection is due to the absence of postentry inhibition by a TRIM5 isoform. Notably, substitution of the viral infectivity factor protein, Vif, with that from pathogenic SIVmne enabled replication of HIV-1 in Pt T cells in vitro. When inoculated into juvenile pig-tailed macaques, the Pt-tropic HIV-1 persistently replicated for more than 1.5 to 2 years, producing low but measurable plasma viral loads and persistent proviral DNA in peripheral blood mononuclear cells. It also elicited strong antibody responses. However, there was no decline in CD4(+) T cells or evidence of disease. Surprisingly, the Pt-tropic HIV-1 was rapidly controlled when inoculated into newborn Pt macaques, although it transiently rebounded after 6 months. We identified two notable differences between the Pt-tropic HIV-1 and SIVmne. First, SIV Vif does not associate with Pt-tropic HIV-1 viral particles. Second, while Pt-tropic HIV-1 degrades both Pt APOBEC3G and APOBEC3F, it prevents their inclusion in virions to a lesser extent than pathogenic SIVmne. Thus, while SIV Vif is necessary for persistent infection by Pt-tropic HIV-1, improved expression and inhibition of APOBEC3 proteins may be required for robust viral replication in vivo. Additional adaptation of the virus may also be necessary to enhance viral replication. Nevertheless, our data suggest the potential for the pig-tailed macaque to be developed as an animal model of HIV-1 infection and disease.

Abrogation of postentry restriction of HIV-1-based lentiviral vector transduction in simian cells

HIV-1 replication in simian cells is restricted at an early postentry step because of the presence of an inhibitory cellular factor. This block reduces the usefulness of HIV-1-based lentiviral vectors in primate animal models. Here, we demonstrate that substitution of the cyclophilin A (CyPA) binding region in the capsid of an HIV-1-based lentiviral vector (LV) with that of the macrophage tropic HIV-1 Ba-L resulted in a vector that was resistant to the inhibitory effect and efficiently transduced simian cells. Notably, the chimeric gag LV efficiently transduced primary simian hematopoietic progenitor cells, a critical cellular target in gene therapy. The alterations in the CyPA binding region did not affect CyPA incorporation; however, transduction by the gag chimeric LV seemed to be relatively insensitive to cyclosporin A, indicating that it does not require CyPA for early postentry steps. In dual infection experiments, the gag chimeric LV failed to remove the block to transduction of the WT LV, suggesting that the gag chimeric LV did not saturate the inhibitory simian cellular factor. These data suggest that the CyPA binding region of capsid contains a viral determinant involved in the postentry restriction of HIV-1-based lentiviral vectors. Overall, the findings demonstrate that the host range of HIV-1-based LV can be altered by modifications in the packaging construct.

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.

Evolution of a human immunodeficiency virus type 1 variant with enhanced replication in pig-tailed macaque cells by DNA shuffling

DNA shuffling facilitated the evolution of a human immunodeficiency virus type 1 (HIV-1) variant with enhanced replication in pig-tailed macaque peripheral blood mononuclear cells (pt mPBMC). This variant consists exclusively of HIV-1-derived sequences with the exception of simian immunodeficiency virus (SIV) nef. Sequences spanning the gag-protease-reverse transcriptase (gag-pro-RT) region from several HIV-1 isolates were shuffled and cloned into a parental HIV-1 backbone containing SIV nef. Neither this full-length parent nor any of the unshuffled HIV-1 isolates replicated appreciably or sustainably in pt mPBMC. Upon selection of the shuffled viral libraries by serial passaging in pt mPBMC, a species emerged which replicated at substantially higher levels (50 to 100 ng/ml p24) than any of the HIV-1 parents and most importantly, could be continuously passaged in pt mPBMC. The parental HIV-1 isolates, when selected similarly, became extinct. Analyses of full-length improved proviral clones indicate that multiple recombination events in the shuffled region and adaptive changes in the rest of the genome contributed synergistically to the improved phenotype. This improved variant may prove useful in establishing a pig-tailed macaque model of HIV-1 infection.

Conserved CXCR4 usage and enhanced replicative capacity of HIV-2/287, an isolate highly pathogenic in Macaca nemestrina

OBJECTIVE

To investigate viral properties that contribute to the pathogenic potential of HIV-2 in macaques.

DESIGN

We compared HIV-2/287, a virus highly pathogenic in Macaca nemestrina, with its non-pathogenic progenitor HIV-2 EHO, for coreceptor usage and ability to infect human and macaque peripheral blood mononuclear cells (PBMC).

METHODS

Coreceptor usage was determined in GHOST cells expressing known coreceptors, and in PBMC with coreceptor-specific inhibitors. Infectivity in PBMC was determined by virus titration and p27 antigen production. Early and late products of reverse transcription were measured by PCR with primers specific for the long terminal repeat (LTR), or the gag region, respectively.

RESULTS

Both viruses preferentially infect HOS-CD4 cells expressing CXCR4. Inhibition by CXCR4-specific peptide TW70 and monoclonal antibody 12G5 indicated that both viruses use predominantly CXCR4 to infect macaque and human PBMC. HIV-2/287 showed greater infectivity than HIV-2 EHO in macaque cells, but the situation was reversed in human cells. Kinetic analysis of reverse transcription products revealed no restriction in reverse transcription following HIV-2 EHO infection of macaque PBMC. However, comparison of the level of newly initiated HIV-2 EHO DNA in macaque and human PBMC indicated that there is an early restriction, prior to the initiation of reverse transcription.

CONCLUSIONS

Results indicate that the adaptation of HIV-2 EHO in M. nemestrina to a highly pathogenic virus HIV-2/287 is not correlated with a shift in or an expansion of coreceptor usage, but with the acquisition of an ability to overcome restrictions for growth in macaque PBMC.