Development of Lentiviral Vectors for HIV-1 Gene Therapy with Vif-Resistant APOBEC3G

Strategies to control HIV-1 replication without antiviral therapy are needed to achieve a functional cure. To exploit the innate antiviral function of restriction factor cytidine deaminase APOBEC3G (A3G), we developed self-activating lentiviral vectors that efficiently deliver HIV-1 Vif-resistant mutant A3G-D128K to target cells. To circumvent APOBEC3 expression in virus-producing cells, which diminishes virus infectivity, a vector containing two overlapping fragments of A3G-D128K was designed that maintained the gene in an inactive form in the virus-producer cells. However, during transduction of target cells, retroviral recombination between the direct repeats reconstituted an active A3G-D128K in 89%-98% of transduced cells. Lentiviral vectors that expressed A3G-D128K transduced CD34+ hematopoietic stem and progenitor cells with a high efficiency (>30%). A3G-D128K expression in T cell lines CEM, CEMSS, and PM1 potently inhibited spreading infection of several HIV-1 subtypes by C-to-U deamination leading to lethal G-to-A hypermutation and inhibition of reverse transcription. SIVmac239 and HIV-2 were not inhibited, since their Vifs degraded A3G-D128K. A3G-D128K expression in CEM cells potently suppressed HIV-1 replication for >3.5 months without detectable resistant virus, suggesting a high genetic barrier for the emergence of A3G-D128K resistance. Because of this, A3G-D128K expression in HIV-1 target cells is a potential anti-HIV gene therapy approach that could be combined with other therapies for the treatment and functional cure of HIV-1 infection.

Retroviral restriction: nature's own solution

PURPOSE OF REVIEW

The present review will discuss recent advances in the development of anti-HIV therapies inspired by studies of the mechanisms of host restriction factor-mediated resistance to HIV infection.

RECENT FINDINGS

Manipulating the interplay between host cell restriction factors and viral accessory factors that overcome them can potentially be therapeutically useful. Preliminarily successful therapies - some of which are entering clinical trials - either inhibit the ability of virus to evade restriction factor-mediated immunity, or promote intracellular levels of restriction factors. These aims are achieved by multiple means, which are discussed.

SUMMARY

Many restriction factors appear to provide potentially useful targets for anti-HIV therapies, so time and interest should be invested in investigating ways to successfully therapeutically manipulate restriction factor-mediated immunity.

Persistent HIV-1 replication during antiretroviral therapy

Purpose of review

The present review will highlight some of the recent findings regarding the capacity of HIV-1 to replicate during antiretroviral therapy (ART).

Recent findings

Although ART is highly effective at inhibiting HIV replication, it is not curative. Several mechanisms contribute to HIV persistence during ART, including HIV latency, immune dysfunction, and perhaps persistent low-level spread of the virus to uninfected cells (replication). The success in curing HIV will depend on efficiently targeting these three aspects. The degree to which HIV replicates during ART remains controversial. Most studies have failed to find any evidence of HIV evolution in blood, even with samples collected over many years, although a recent very intensive study of three individuals suggested that the virus population does shift, at least during the first few months of therapy. Stronger but still not definitive evidence for replication comes from a series of studies in which standard regimens were intensified with an integration inhibitor, resulting in changes in episomal DNA (blood) and cell-associated RNA (tissue). Limited drug penetration within tissues and the presence of immune sanctuaries have been argued as potential mechanisms allowing HIV to spread during ART. Mathematical models suggest that HIV replication and evolution is possible even without the selection of fully drug-resistant variants. As persistent HIV replication could have clinical consequences and might limit the efficacy of curative interventions, determining if HIV replicates during ART and why, should remain a key focus of the HIV research community.

Summary

Residual viral replication likely persists in lymphoid tissues, at least in a subset of individuals. Abnormal levels of immune activation might contribute to sustain virus replication.

Anti-HIV Drug Discovery and Development: Current Innovations and Future Trends

The early effectiveness of combinatorial antiretroviral therapy (cART) in the treatment of HIV infection has been compromised to some extent by rapid development of multidrug-resistant HIV strains, poor bioavailability, and cumulative toxicities, and so there is a need for alternative strategies of antiretroviral drug discovery and additional therapeutic agents with novel action modes or targets. From this perspective, we first review current strategies of antiretroviral drug discovery and optimization, with the aid of selected examples from the recent literature. We highlight the development of phosphate ester-based prodrugs as a means to improve the aqueous solubility of HIV inhibitors, and the introduction of the substrate envelope hypothesis as a new approach for overcoming HIV drug resistance. Finally, we discuss future directions for research, including opportunities for exploitation of novel antiretroviral targets, and the strategy of activation of latent HIV reservoirs as a means to eradicate the virus.

African green monkey TRIM5α restriction in simian immunodeficiency virus-specific rhesus macaque effector CD4 T cells enhances their survival and antiviral function

The expression of xenogeneic TRIM5α proteins can restrict infection in various retrovirus/host cell pairings. Previously, we have shown that African green monkey TRIM5α (AgmTRIM5α) potently restricts both human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus mac239 (SIV(mac239)) replication in a transformed human T-cell line (L. V. Coren, et al., Retrovirology 12:11, 2015, http://dx.doi.org/10.1186/s12977-015-0137-9). To assess AgmTRIM5α restriction in primary cells, we transduced AgmTRIM5α into primary rhesus macaque CD4 T cells and infected them with SIV(mac239). Experiments with T-cell clones revealed that AgmTRIM5α could reproducibly restrict SIV(mac239) replication, and that this restriction synergizes with an intrinsic resistance to infection present in some CD4 T-cell clones. AgmTRIM5α transduction of virus-specific CD4 T-cell clones increased and prolonged their ability to suppress SIV spread in CD4 target cells. This increased antiviral function was strongly linked to decreased viral replication in the AgmTRIM5α-expressing effectors, consistent with restriction preventing the virus-induced cytopathogenicity that disables effector function. Taken together, our data show that AgmTRIM5α restriction, although not absolute, reduces SIV replication in primary rhesus CD4 T cells which, in turn, increases their antiviral function. These results support prior in vivo data indicating that the contribution of virus-specific CD4 T-cell effectors to viral control is limited due to infection.

IMPORTANCE

The potential of effector CD4 T cells to immunologically modulate SIV/HIV infection likely is limited by their susceptibility to infection and subsequent inactivation or elimination. Here, we show that AgmTRIM5α expression inhibits SIV spread in primary effector CD4 T cells in vitro. Importantly, protection of effector CD4 T cells by AgmTRIM5α markedly enhanced their antiviral function by delaying SIV infection, thereby extending their viability despite the presence of virus. Our in vitro data support prior in vivo HIV-1 studies suggesting that the antiviral CD4 effector response is impaired due to infection and subsequent cytopathogenicity. The ability of AgmTRIM5α expression to restrict SIV infection in primary rhesus effector CD4 T cells now opens an opportunity to use the SIV/rhesus macaque model to further elucidate the potential and scope of anti-AIDS virus effector CD4 T-cell function.

Potent restriction of HIV-1 and SIVmac239 replication by African green monkey TRIM5α

BACKGROUND

The TRIM5α protein is a principal restriction factor that contributes to an HIV-1 replication block in rhesus macaque CD4+ T cells by preventing reverse transcription. HIV-1 restriction is induced in human CD4+ T cells by expression of rhesus TRIM5α as well as those of other old world monkeys. While TRIM5α restriction has been extensively studied in single-round infection assays, fewer studies have examined restriction after extended viral replication.

RESULTS

To examine TRIM5α restriction of replication, we studied the ability of TRIM5α proteins from African green monkey (AgmTRIM5α) and gorilla (gorTRIM5α) to restrict HIV-1 and SIVmac239 replication. These xenogeneic TRIM5α genes were transduced into human Jurkat-CCR5 cells (JR5), which were then exposed to HIV-1 or SIVmac239. In our single-round infection assays, AgmTRIM5α showed a relatively modest 4- to 10-fold restriction of HIV-1 and SIVmac239, while gorTRIM5α produced a 2- and 3-fold restriction of HIV-1 and SIVmac239, respectively, consistent with the majority of previously published single-round studies. To assess the impact of these modest effects on infection, we tested restriction in replication systems initiated with either cell-free or cell-to-cell challenges. AgmTRIM5α powerfully restricted both HIV-1 and SIVmac239 replication 14 days after cell-free infection, with a ≥ 3-log effect. Moreover, expression of AgmTRIM5α restricted HIV-1 and SIVmac239 replication by 2-logs when co-cultured with infected JR5 cells for 12 days. In contrast, neither expression of gorTRIM5α nor rhesus TRIM5α induced significant resistance when co-cultured with infected cells. Follow up experiments showed that the observed differences between replication and infection were not due to assembly defects as xenogeneic TRIM5α expression had no effect on either virion production or specific infectivity.

CONCLUSIONS

Our results indicate that AgmTRIM5α has a much greater effect on extended replication than on any single infection event, suggesting that AgmTRIM5α restriction acts cumulatively, building up over many rounds of replication. Furthermore, AgmTRIM5α was able to potently restrict both HIV-1 and SIV replication in a cell-to-cell infection challenge. Thus, AgmTRIM5α is unique among the TRIM5α species tested to date, being able to restrict even at the high multiplicities of infection presented by mixed culture with nonrestrictive infected cells.

Establishing Restricted Expression of Caveolin-1 in HIV Infected Cells and Inhibition of Virus Replication

Background:

Caveolin-1 (Cav-1) is the major protein of the caveolae and plays a role in multiple cellular functions and implicated to have anti-HIV activity. Regulated expression of Cav-1 is important for safe and effective use in order to exploit Cav-1 for HIV therapeutic applications.

Methods:

A series of Cav-1 and GFP expression vectors were constructed under the control of the HIV LTR for conditional expression or CMV promoter and the expression of Cav-1 was monitored in the presence or absence of Tat or HIV infection in order to establish the restricted expression of Cav-1 to HIV infected cells.

Results:

Cav-1 expression was evident under the control of the HIV LTR in the absence of Tat or HIV infection as demonstrated by immunoblot. Placing two internal ribosomal entry sequences (IRES) and a Rev response element, RRE (5’~ LTR-IRES-GFP-RRE-IRES-Cav-1~3’) resulted in no expression of Cav-1 in the absence of Tat with effective expression in the presence of Tat. Transduction of HIV permissive cells with this construct using a foamy virus vector show that Cav-1 was able to inhibit HIV replication by 82%. Cells that received LTR-IRES-GFP-RRE-IRES-Cav-1 remain healthy in the absence of Tat or HIV infection.

Conclusion:

These results taken together reveal the inclusion of two IRES establishes a significant reduction of leak through expression of Cav-1 in the absence of Tat or HIV infection. Such regulated expression will have therapeutic application of Cav-1 for HIV infection as well as broad applications which can be beneficial for other host-targeted interventions as therapeutics.