Dendritic cells, exposed to primary, mixed phenotype HIV-1 isolates preferentially, but not exclusively, replicate CCR5-using clones

HIV-1 Gag-virus-like particles inhibit HIV-1 replication in dendritic cells and T cells through IFN-α-dependent upregulation of APOBEC3G and 3F

Human immunodeficiency virus-1 (HIV-1) infection and the acquired immune deficiency syndrome (AIDS) pandemic remain global threats in the absence of a protective or a therapeutic vaccine. HIV-1 replication is reportedly inhibited by some cellular factors, including APOBEC3G (A3G) and APOBEC3F (A3F), which are well known inhibitors of HIV-1. Recently, HIV-1 Gag-virus-like particles (Gag-VLPs) have been shown to be safe and potent HIV-1 vaccine candidates that can elicit strong cellular and humoral immunity without need of any adjuvant. In this report, we stimulated human monocyte-derived dendritic cells (DCs) with Gag-VLPs and we demonstrated that Gag-VLP-treated DCs (VLP-DCs) produced interferon alpha (IFN-α), along with an increase in mRNA and protein expression of A3G and A3F. Gag-VLPs inhibited HIV-1 replication not only in DCs themselves, but also in cocultured T cells in an IFN-α-dependent manner. In addition, A3G/3F content in HIV virions released from VLP-DCs increased. Both the increase in A3G/3F expression and the inhibition of HIV-1 replication were reversed by anti-IFN-α or anti-IFNAR antibodies. Our findings in this study provide insight into the mechanism of Gag-VLP-induced inhibition of HIV-1 replication in DCs and T cells.

Differential susceptibility of naïve, central memory and effector memory T cells to dendritic cell-mediated HIV-1 transmission

Background

Dendritic cells (DC) have been proposed to facilitate sexual transmission of HIV-1 by capture of the virus in the mucosa and subsequent transmission to CD4⁺ T cells. Several T cell subsets can be identified in humans: naïve T cells (T_N) that initiate an immune response to new antigens, and memory T cells that respond to previously encountered pathogens. The memory T cell pool comprises central memory (T_CM) and effector memory cells (T_EM), which are characterized by distinct homing and effector functions. The T_EM cell subset, which can be further divided into effector Th1 and Th2 cells, has been shown to be the prime target for viral replication after HIV-1 infection, and is abundantly present in mucosal tissues.

Results

We determined the susceptibility of T_N, T_CM and T_EM cells to DC-mediated HIV-1 transmission and found that co-receptor expression on the respective T cell subsets is a decisive factor for transmission. Accordingly, CCR5-using (R5) HIV-1 was most efficiently transmitted to T_EM cells, and CXCR4-using (X4) HIV-1 was preferentially transmitted to T_N cells.

Conclusion

The highly efficient R5 transfer to T_EM cells suggests that mucosal T cells are an important target for DC-mediated transmission. This may contribute to the initial burst of virus replication that is observed in these cells. T_N cells, which are the prime target for DC-mediated X4 virus transmission in our study, are considered to inefficiently support HIV-1 replication. Our results thus indicate that DC may play a decisive role in the susceptibility of T_N cells to X4 tropic HIV-1.

Human immunodeficiency virus fusion to dendritic cells declines as cells mature

The maturation of dendritic cells (DCs) is associated with a diminished ability to support human immunodeficiency virus (HIV) replication; however, the precise step in the HIV life cycle impaired by DC maturation remains uncertain. Using an HIV virion-based fusion assay, we now show that HIV fusion to monocyte-derived DCs (MDDCs) both decreases and kinetically slows when DCs are induced to mature with poly(I:C) and tumor necrosis factor alpha. Specifically, laboratory-adapted CCR5-tropic 81A virions fused with markedly lower efficiency to mature MDDCs than immature DCs. In contrast, fusion of NL4-3, the isogenic CXCR4-tropic counterpart of 81A, was low in both immature and mature MDDCs. Fusion mediated by primary HIV envelopes, including seven CCR5- and four CXCR4-tropic envelopes, also decreased with DC maturation. The kinetics of virion fusion were also altered by both the state of DC maturation and the coreceptor utilized. Fusion of 81A and NL4-3 virions was delayed in mature compared to immature MDDCs, and NL4-3 fused more slowly than 81A in both mature and immature MDDCs. Surprisingly, primary envelopes with CXCR4 tropism mediated fusion to immature MDDCs with efficiencies similar to those of primary CCR5-tropic envelopes. This result contrasted with the marked preferential fusion of the laboratory-adapted 81A over NL4-3 in immature MDDCs and in ex vivo Langerhans cells, indicating that these laboratory-adapted HIV strains do not fully recapitulate all of the properties of primary HIV isolates. In conclusion, our results demonstrate that the defect in HIV replication observed in mature MDDCs stems at least in part from a decline in viral fusion.

Replicative fitness of CCR5-using and CXCR4-using human immunodeficiency virus type 1 biological clones

CCR5-tropic viruses cause the vast majority of new HIV-1 infections while about half of the individuals infected with HIV-1 manifest a co-receptor switch (CCR5 (R5) to CXCR4 (X4)) prior to accelerated disease progression. The underlying biological mechanisms of X4 outgrowth in AIDS patients are still poorly understood. Although X4 viruses have been associated with increased "virulence" in vivo, in vitro replication and cytopathicity studies of X4 and R5 viruses have led to conflicting conclusions. We studied the replicative fitness of HIV-1 biological clones with different co-receptor tropism, isolated from four AIDS patients. On average, R5 and X4 clones replicated equally well in mitogen-activated T cells. In contrast, X4 variants were transferred more efficiently from dendritic cells to autologous CD4+ T cells. These observations suggest that interaction between X4 viruses, DC and T cells might contribute to the preferential outgrowth of X4 viruses in AIDS patients.

Differential effects of R5 and X4 human immunodeficiency virus type 1 infection on CD4+ cell proliferation and activation

Human immunodeficiency virus type 1 (HIV-1) isolates can be distinguished by their chemokine coreceptor usage. Non-syncytium-inducing (NSI), macrophage-tropic viruses utilize CCR5 and are called R5 viruses; syncytium-inducing (SI) isolates use CXCR4 and are known as X4 viruses. R5 and X4 HIV isolates are both transmitted but, in most cases, R5 viruses predominate in the blood prior to the development of AIDS-related pathogenesis. The reason for the selective growth of the R5 strain is not known, but could reflect a replication advantage of R5 viruses over X4 viruses in CD4+ cells. To explore this possibility, eight phenotypically distinct viruses were used to infect CD4+ cells and cellular proliferation and activation were evaluated. In unstimulated CD4+ cells, R5 virus isolates increased the level of cell activation compared with X4 virus isolates and uninfected control cells. In CD4+ cells that were stimulated with interleukin 2, both R5 and X4 viruses were found to decrease the level of cell proliferation and reduce the majority of the activation markers studied when compared with uninfected control CD4+ cells from the same donors. However, although equal amounts of CD4+ cells were infected, R5 virus-infected CD4+ cells showed a two- to fourfold increase in cellular proliferation over X4 viruses, as measured by [3H]thymidine incorporation (P=0.001) and nuclear expression of Ki67 (P=0.001). In addition, a larger proportion of CD4+ T cells infected with R5 viruses had significantly higher levels of activation-marker expression (e.g. CD25, CD71 and HLA-DR) than CD4+ T lymphocytes infected with X4 viruses (P<0.02). Taken together, these results indicate that CD4+ cells infected with R5 virus isolates may have a selective advantage over X4 virus-infected CD4+ T cells for survival and, hence, virus spread.

Pre-Incubation of Cell-Free HIV-1 Group M Isolates with Non-Nucleoside Reverse Transcriptase Inhibitors Blocks Subsequent Viral Replication in Co-Cultures of Dendritic Cells and T Cells

In order to study the inhibitory effect of various reverse transcriptase inhibitors (RTIs) on cell-free HIV, we adapted a recently described in vitro system, based on co-cultures of dendritic cells and resting CD4 T cells, modelling early target cells during sexual transmission. The compounds tested included the second-generation non-nucleoside RTI (NNRTI) TMC-120 (R147681, dapivirine) and TMC-125 (R165335, travertine), as well as the reference nucleoside RTI AZT (zidovudine), the nucleotide RTI PMPA (tenofovir) and the NNRTI UC-781. The virus strains included the reference strain HIV-1Ba-L and six primary isolates, representative of the HIV-1 group M pandemic. They all display the non-syncytium-inducing and CCR5 receptor-using (NSI/R5) phenotype, important in transmission. Cell-free virus was immobilized on a poly-L-lysine (PLL)-treated microwell plate and incubated with compound for 1h. Afterwards, the compound was thoroughly washed away; target cells were added and cultured for 2 weeks, followed by an extended culture with highly susceptible mitogen-activated T cells. Viral production in the cultures was measured on supernatant with HIV antigen ELISA. Negative results were confirmed by showing absence of proviral DNA in the cells.

TMC-120 and TMC-125 inhibited replication of HIV-1Ba-L with average EC50 values of 38 nM and 117 nM, respectively, whereas the EC50 of UC-781 was 517 nM. Complete suppression of virus and provirus was observed at compound concentrations of 100, 300 and 1000 nM, respectively. Inhibition of all primary isolates followed the same pattern as HIV-1Ba-L. In contrast, pre-treating the virus with the nucleotide RTI PMPA and AZT failed to inhibit infection even at a concentration of 100000 nM. These data clearly suggest that NNRTIs inactivate RT enzymatic activity of different viral clades (predominant in the epidemic) and might be proposed for further testing as a sterilizing microbicide worldwide.

A series of diaryltriazines and diarylpyrimidines are highly potent nonnucleoside reverse transcriptase inhibitors with possible applications as microbicides

An in vitro model of monocyte-derived dendritic cells (MO-DC) and CD4(+) T cells, representing the primary targets of sexual human immunodeficiency virus (HIV) transmission, was used to evaluate the antiviral and immune suppressive activity of new classes of nonnucleoside reverse transcriptase inhibitors, diaryltriazines (DATAs) and diarylpyrimidines (DAPYs), compared to the reference compounds UC-781 and PMPA. Antiviral activity (as reflected by the 50% effective concentration [EC(50)]) was determined by treating HIV-infected MO-DC/CD4(+)-T-cell cocultures with a dose range of a compound during 14 days, followed by analysis of supernatants in HIV p24 antigen enzyme-linked immunosorbent assay. A limited, 24-h treatment evaluated the compounds as microbicides. Viral rescue was evaluated in a PCR by monitoring proviral DNA in secondary cultures with phytohemagglutinin-interleukin-2 blasts. We determined 50% immunosuppressive concentrations in mixed leukocyte cultures of MO-DC and allogeneic T cells, with compound either continuously present or present only during the first 24 h. The EC(50) values of DATA and DAPY compounds ranged from 0.05 to 3 nM compared to 50 nM for UC-781 and 89 nM for PMPA. When evaluated in the "microbicide" setting, the most potent compounds completely blocked HIV infection at 10 to 100 nM. The immunosuppressive concentrations were well above the EC(50), resulting in favorable therapeutic indices for all compounds tested. The DATA and DAPY compounds described here are more potent than earlier reverse transcriptase inhibitors and show favorable pharmacological profiles in vitro. They could strengthen the antiretroviral armamentarium and might be useful as microbicides.

Activity of reverse transcriptase inhibitors in monocyte-derived dendritic cells: a possible in vitro model for postexposure prophylaxis of sexual HIV transmission

Because prevention of heterosexual HIV transmission is not always possible, it is important to develop effective strategies of postexposure prophylaxis (PEP). Since in vivo comparison of drug potency is difficult, we developed an in vitro model with cells resembling primary targets during sexual transmission: monocyte-derived dendritic cells (MO-DCs), Langerhans cells (MO-LCs), and resting autologous CD4(+) T cells. Nucleoside and nonnucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs, respectively) were evaluated for their antiviral activity, when added immediately after infection or at a later time point. In parallel, their immune-suppressive effect was examined by measuring inhibition of mixed MO-DC/allogeneic CD4(+) T cell cultures. Most RTIs potently inhibited HIV replication, even if added 24 hr after infection (representing PEP). The sensitivity to antiretroviral drugs was similar in HIV-infected MO-DCs and MO-LCs, but decreased in cocultures with resting autologous CD4(+) T cells. The NNRTIs efavirenz and UC-781 as well as the NRTIs AZT, 3TC, and d4T showed a similar high potency in MO-DC plus autologous CD4(+) T cell cocultures as compared with CEM T cells, whereas their activity in phytohemagglutinin/interleukin 2 (PHA/IL-2)-activated CD4(+) T cells was lower. The dideoxynucleoside RTI abacavir as well as the phosphonates (R)-PMPA and PMEA were more active in infected MO-DCs as compared with either CEM T cells or PHA/IL-2 activated CD4(+) T cells. Infection in cocultures of MO-DCs and autologous CD4(+) T cells could be aborted in a proportion of the cultures, with high concentrations of PMEA and/or efavirenz, but not with AZT. Suppressive activity in mixed leukocyte cultures was observed only at very high concentrations of RTI. Our data suggest that cocultures of MO-DCs and autologous CD4(+) T cells can be used as a possible in vitro model to explore protocols for PEP after sexual HIV transmission.