Reduced replication capacity of NL4-3 recombinant viruses encoding reverse transcriptase-integrase sequences from HIV-1 elite controllers

CD4+ T cells from elite suppressors are more susceptible to HIV-1 but produce fewer virions than cells from chronic progressors

Elite suppressors/controllers (ES) are HIV-1-infected individuals who maintain stable CD4(+) T-cell counts and viral loads of <50 copies/mL without antiretroviral therapy. Research has predominantly focused on immune factors contributing to the control of viral replication in these patients. A more fundamental question, however, is whether there are differences in the nature of CD4(+) T-cell infection in ES compared with viremic patients. Here, we compare chronic progressor (CP), ES, and uninfected donors in terms of three aspects of CD4(+) T-cell infection: cellular susceptibility to infection, death of infected cells, and production of virus from infected cells. Using multiple methods of infection and both single-cycle and replication-competent virus, we show that unmanipulated CD4(+) T-cell populations from ES are actually more susceptible to HIV-1 infection than those populations from CP. Depletion of highly susceptible cells in CP may contribute to this difference. Using 7AAD and AnnexinV staining, we show that infected cells die more rapidly than uninfected cells, but the increased death of infected cells from CP and ES is proportional. Finally, using an assay for measuring virus production, we show that virus production by cells from CP is high compared with virus production by cells from ES or uninfected donors. This higher virus production is linked to cellular activation levels. These data identify fundamental differences in chronic infection of ES and CP that likely contribute to differential HIV-1 disease progression.

Immune-mediated attenuation of HIV-1

Immune escape mutations selected by human leukocyte antigen class I-restricted CD8(+) cytotoxic T lymphocytes (CTLs) can result in biologically and clinically relevant costs to HIV-1 replicative fitness. This phenomenon may be exploited to design an HIV-1 vaccine capable of stimulating effective CTL responses against highly conserved, mutationally constrained viral regions, where immune escape could occur only at substantial functional costs. Such a vaccine might 'channel' HIV-1 evolution towards a less-fit state, thus lowering viral load set points, attenuating the infection course and potentially reducing the risk of transmission. A major barrier to this approach, however, is the accumulation of immune escape variants at the population level, possibly leading to the loss of immunogenic CTL epitopes and diminished vaccine-induced cellular immune responses as the epidemic progresses. Here, we review the evidence supporting CTL-driven replicative defects in HIV-1 and consider the implications of this work for CTL-based vaccines designed to attenuate the infection course.

HIV-1 replicative fitness in elite controllers

PURPOSE OF REVIEW

Differential rates of disease progression are obviously multifactorial, but the virulence of the actual infecting virus is most frequently ignored as potential source of slow or rapid disease progression. In this review, the argument will be made that nearly all elite suppressors are infected by weak HIV-1 strain (in terms of replicative capacity). Whether this poor virus replication is the cause of elite suppression or the consequence of a strong immune response remains a leading question in the field.

RECENT FINDINGS

Although numerous research studies have related HIV-1 replicative capacity/fitness in tissue culture to virulence within patients, this review will focus on several recent and key discoveries on the important role of HIV-1 fitness in elite suppression. First, elite suppressors appear to harbor HIV-1 variants that encode Gag, Pol, and Env proteins that are less efficient than their counterparts of HIV-1 in typical/chronic progressors. Second, the actual HIV-1 clone(s) that establish acute infection may be less fit in patients who become elite controllers as compared with typical progressors. Finally, the fitness costs of cytotoxic T lymphocyte escape in HIV-1 may be easily compensated by secondary mutations if the infecting strain is capable of high replication kinetics and rapid evolution. A strain with weak replicative capacity might not compensate for fitness loss or even generate the initial escape mutations.

SUMMARY

A combination of good, anti-HIV-1 host genetics (e.g. HLA-B*57) along with infection by a 'whimpy' HIV-1 strain may be necessary for elite suppression, whereas only one of these may lead to slow progression and viremia.

HIV cure and eradication: how will we get from the laboratory to effective clinical trials?

Combination antiretroviral therapy (cART) has led to a major reduction in HIV-related mortality and morbidity; however, HIV can still not be cured. Achieving either a functional cure (long-term control of HIV in the absence of cART) or a sterilizing cure (elimination of all HIV-infected cells) remains a major challenge. The most significant barrier to cure is the establishment of a latent or 'silent' infection in resting CD4 T cells. Several randomized clinical trials have demonstrated that treatment intensification with additional antiretrovirals has little impact on latent reservoirs. Some potential other approaches that may reduce the latent reservoir include very early initiation of cART and the use of agents that could reverse latent infection. Drugs such as histone deacetylase inhibitors, currently used and licensed for the treatment of some cancers; methylation inhibitors; cytokines such as IL-7 or activators of nuclear factor kappa B (NF-κB) such as prostratin, show promising activity in reversing latency in vitro when used either alone or in combination. Alternate strategies include using gene therapy to modify expression of CCR5 and therefore make cells resistant to HIV. This review will primarily focus on the advantages and disadvantages of methods currently being used to quantify persistent virus ex vivo in patients receiving cART and strategies aimed at cure that are being tested in vitro or in early clinical development. In addition, we discuss key issues that need to be addressed to successfully move laboratory research to clinical trials aimed at curing HIV.