Changes in simian immunodeficiency virus reverse transcriptase alleles that appear during infection of macaques enhance infectivity and replication in CD4+ T cells

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.

Relative replication capacity of phenotypic SIV variants during primary infections differs with route of inoculation

Background

Previous studies of human and simian immunodeficiency virus (HIV and SIV) have demonstrated that adaptive mutations selected during the course of infection alter viral replicative fitness, persistence, and pathogenicity. What is unclear from those studies is the impact of transmission on the replication and pathogenicity of the founding virus population. Using the SIV-macaque model, we examined whether the route of infection would affect the establishment and replication of two SIVmne variants of distinct in vitro and in vivo biological characteristics. For these studies, we performed dual-virus inoculations of pig-tailed macaques via intrarectal or intravenous routes with SIVmneCl8, a miminally pathogenic virus, and SIVmne027, a highly pathogenic variant that replicates more robustly in CD4⁺ T cells.

Results

The data demonstrate that SIVmne027 is the dominant virus regardless of the route of infection, indicating that the capacity to replicate efficiently in CD4⁺ T cells is important for fitness. Interestingly, in comparison to intravenous co-infection, intrarectal inoculation enabled greater relative replication of the less pathogenic virus, SIVmneCl8. Moreover, a higher level of SIVmneCl8 replication during primary infection of the intrarectally inoculated macaques was associated with lower overall plasma viral load and slower decline in CD4⁺ T cells, even though SIVmne027 eventually became the dominant virus.

Conclusions

These results suggest that the capacity to replicate in CD4⁺ T cells is a significant determinant of SIV fitness and pathogenicity. Furthermore, the data also suggest that mucosal transmission may support early replication of phenotypically diverse variants, while slowing the rate of CD4⁺ T cell decline during the initial stages of infection.

Dendritic cell-mediated HIV-1 infection of T cells demonstrates a direct relationship to plasma viral RNA levels

OBJECTIVE

To examine the relationship between infectivity of HIV-1 variants in dendritic cell (DC)-mediated in trans infection of T cells and plasma viral RNA levels in infected subjects.

METHODS

HIV-1 was isolated from peripheral blood mononuclear cells of chronically infected individuals, typed for coreceptor usage, and viral replication were examined in monocyte-derived DCs-peripheral blood lymphocytes cocultures. The rate of p24 antigen production during the logarithmic phase of viral replication was determined by enzyme-linked immunosorbent assay. Additionally, nef variants were cloned and expressed in trans with a HIV luciferase vector and CCR5-tropic HIV-1 envelope, and infectivity was measured in DC-mediated capture-transfer assays.

RESULTS

Replication capacity of HIV-1 viral CCR5-tropic isolates in monocyte-derived dendritic cells-peripheral blood lymphocytes cocultures was linearly associated with the plasma viral RNA levels in a cohort of HIV-1-infected individuals exhibiting an inverse relationship between plasma viral RNA and CD4 cell count. Furthermore, infectivity activity of nef variants in context of DC-mediated enhanced infection of T cells also showed a linear relationship to plasma viral RNA levels.

CONCLUSIONS

These results illustrate that replication capacity of HIV-1 in DC T-cell cultures is a significant determinant of plasma viral RNA level. The data suggest that adaptation of HIV-1 to DC interactions with T cells influences the level of viral replication in the host.

A decrease in albumin in early SIV infection is related to viral pathogenicity

A decrease in circulating albumin levels after seroconversion has been reported as a predictor of disease progression in HIV-infected adults. We hypothesized that a similar decrease would be seen in pig-tailed macaques in early SIV infection, and that the degree of this decrease would be related to the pathogenicity of the infecting viral strain. Ten juvenile pig-tailed macaques were previously inoculated with virus derived from molecular clones representing different stages of infection: early (SIVMneCL8, n = 2), intermediate (SIVMne35wkSU, n = 2), late blood (SIVMne170, n = 3), or late lymph node (SIVMne027, n = 3). Albumin was measured in stored samples. Changes from baseline were evaluated by paired sample t tests and by linear regression with generalized estimating equations (GEE). Albumin levels decreased in the week after SIV inoculation (p = 0.02), increased above baseline at week 5, then fell, returning below baseline by week 16 (p = 0.03). In GEE modeling, albumin decreased significantly in both early and chronic infection (weeks 0-3, p < 0.001; weeks 5-16, p = 0.004) and this change differed significantly between infections caused by late versus early or intermediate virus variants (weeks 0-3, p = 0.002; weeks 5-16, p = 0.001). A decrease in albumin levels occurs in both early and chronic SIV infection, and is more marked in macaques infected with more pathogenic virus variants. These results suggest that both early and late events in SIV pathogenesis are influenced by properties of the infecting viral strain.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4(+) T cell population, despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics with different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.