In vitro generation of HIV type 1 subtype C isolates resistant to enfuvirtide

Short Communication: A Recombinant Variant with Increased Envelope Entry Efficiency Emerged During Early Infection of an HIV-1 Subtype C Dual Infected Rapid Progressor

Mutations in functionally constrained sites of the HIV envelope (Env) can affect entry efficiency and are potential targets for vaccine and drug design. We investigated Du151, a dual-infected individual with rapid disease progression. At her death 19 months postinfection (mpi), she was infected with a recombinant variant, which outgrew both parental viruses. We aimed to determine whether the recombinant virus had enhanced Env entry efficiency compared to the parental viruses and to identify the functional determinant. We generated 15 env clones at 1, 2, 8, and 19 mpi. Pseudovirus carrying a recombinant Env clone (PSV clone), C18 (19 mpi), had significantly higher entry efficiency compared to the parents, suggesting that the recombinant virus had enhanced fitness. To identify the functional determinant, we compared two recombinant PSV clones (C18 and C63)-differing in entry efficiency (2-fold) and by four and three amino acids in gp120 and gp41, respectively. The increased entry efficiency of a C18-gp41 PSV chimera indicated that the three amino acids in the C18 gp41 region were involved (K658, G671, and F717). Site-directed mutagenesis of the three amino acids of C63 showed that a single amino acid mutation, R658K, increased pseudovirion entry efficiency. The introduction of R658 into two PSV clones (C1 and C18) decreased their entry efficiency, suggesting that R658 carries a fitness cost. Thus, our data suggest that a recombinant virus emerged at 19 mpi with enhanced Env entry efficiency. Therefore, K658 in gp41 could in part be a contributing factor to the increased viral load and rapid disease progression of Du151.

Current perspectives on HIV-1 antiretroviral drug resistance

Current advancements in antiretroviral therapy (ART) have turned HIV-1 infection into a chronic and manageable disease. However, treatment is only effective until HIV-1 develops resistance against the administered drugs. The most recent antiretroviral drugs have become superior at delaying the evolution of acquired drug resistance. In this review, the viral fitness and its correlation to HIV-1 mutation rates and drug resistance are discussed while emphasizing the concept of lethal mutagenesis as an alternative therapy. The development of resistance to the different classes of approved drugs and the importance of monitoring antiretroviral drug resistance are also summarized briefly.

Escape from human immunodeficiency virus type 1 (HIV-1) entry inhibitors

The human immunodeficiency virus (HIV) enters cells through a series of molecular interactions between the HIV envelope protein and cellular receptors, thus providing many opportunities to block infection. Entry inhibitors are currently being used in the clinic, and many more are under development. Unfortunately, as is the case for other classes of antiretroviral drugs that target later steps in the viral life cycle, HIV can become resistant to entry inhibitors. In contrast to inhibitors that block viral enzymes in intracellular compartments, entry inhibitors interfere with the function of the highly variable envelope glycoprotein as it continuously adapts to changing immune pressure and available target cells in the extracellular environment. Consequently, pathways and mechanisms of resistance for entry inhibitors are varied and often involve mutations across the envelope gene. This review provides a broad overview of entry inhibitor resistance mechanisms that inform our understanding of HIV entry and the design of new inhibitors and vaccines.

4E10-resistant variants in a human immunodeficiency virus type 1 subtype C-infected individual with an anti-membrane-proximal external region-neutralizing antibody response

The broadly neutralizing monoclonal antibody (MAb) 4E10 recognizes a linear epitope in the C terminus of the membrane-proximal external region (MPER) of gp41. This epitope is particularly attractive for vaccine design because it is highly conserved among human immunodeficiency virus type 1 (HIV-1) strains and neutralization escape in vivo has not been observed. Multiple env genes were cloned from an HIV-1 subtype C virus isolated from a 7-year-old perinatally infected child who had anti-MPER neutralizing antibodies. One clone (TM20.13) was resistant to 4E10 neutralization as a result of an F673L substitution in the MPER. Frequency analysis showed that F673L was present in 33% of the viral variants and in all cases was linked to the presence of an intact 2F5 epitope. Two other envelope clones were sensitive to 4E10 neutralization, but TM20.5 was 10-fold less sensitive than TM20.6. Substitutions at positions 674 and 677 within the MPER rendered TM20.5 more sensitive to 4E10 but had no effect on TM20.6. Using chimeric and mutant constructs of these two variants, we further demonstrated that the lentivirus lytic peptide-2 domain in the cytoplasmic tail affected the accessibility of the 4E10 epitope, as well as virus infectivity. Collectively, these genetic changes in the face of a neutralizing antibody response to the MPER strongly suggested immune escape from antibody responses targeting this region.

Enhancing exposure of HIV-1 neutralization epitopes through mutations in gp41

BACKGROUND

The generation of broadly neutralizing antibodies is a priority in the design of vaccines against HIV-1. Unfortunately, most antibodies to HIV-1 are narrow in their specificity, and a basic understanding of how to develop antibodies with broad neutralizing activity is needed. Designing methods to target antibodies to conserved HIV-1 epitopes may allow for the generation of broadly neutralizing antibodies and aid the global fight against AIDS by providing new approaches to block HIV-1 infection. Using a naturally occurring HIV-1 Envelope (Env) variant as a template, we sought to identify features of Env that would enhance exposure of conserved HIV-1 epitopes.

METHODS AND FINDINGS

Within a cohort study of high-risk women in Mombasa, Kenya, we previously identified a subtype A HIV-1 Env variant in one participant that was unusually sensitive to neutralization. Using site-directed mutagenesis, the unusual neutralization sensitivity of this variant was mapped to two amino acid mutations within conserved sites in the transmembrane subunit (gp41) of the HIV-1 Env protein. These two mutations, when introduced into a neutralization-resistant variant from the same participant, resulted in 3- to >360-fold enhanced neutralization by monoclonal antibodies specific for conserved regions of both gp41 and the Env surface subunit, gp120, >780-fold enhanced neutralization by soluble CD4, and >35-fold enhanced neutralization by the antibodies found within a pool of plasmas from unrelated individuals. Enhanced neutralization sensitivity was not explained by differences in Env infectivity, Env concentration, Env shedding, or apparent differences in fusion kinetics. Furthermore, introduction of these mutations into unrelated viral Env sequences, including those from both another subtype A variant and a subtype B variant, resulted in enhanced neutralization susceptibility to gp41- and gp120-specific antibodies, and to plasma antibodies. This enhanced neutralization sensitivity exceeded 1,000-fold in several cases.

CONCLUSIONS

Two amino acid mutations within gp41 were identified that expose multiple discontinuous neutralization epitopes on diverse HIV-1 Env proteins. These exposed epitopes were shielded on the unmodified viral Env proteins, and several of the exposed epitopes encompass desired target regions for protective antibodies. Env proteins containing these modifications could act as a scaffold for presentation of such conserved domains, and may aid in developing methods to target antibodies to such regions.

Impact of HIV-1 pol diversity on drug resistance and its clinical implications

PURPOSE OF REVIEW

HIV knowledge is based on subtype B, common in resource-rich settings, whereas globally non-B subtypes predominate. Inter-subtype pol diversity encompasses multiple genotypic differences among HIV variants, the consequence of which is unknown. This review summarizes publications from the past year relevant to the impact of HIV diversity on drug resistance evolution and its potential clinical implications.

RECENT FINDINGS

The benefit of antiretroviral therapy in non-B infected patients is ongoing, though subtype heterogeneity in rates of disease progression is observed. Pol inter-subtype diversity is high, and known subtype B drug resistance mutations occur in non-B subtypes. New mutations and subtype-specific mutation rates are identified, however, unexplained drug susceptibilities are seen, and additional insight is offered on structural pathogenic mechanisms of resistance in non-B subtypes. These differences may affect genotypic interpretation and our ability to apply drug resistance to patient care.

SUMMARY

Current evidence suggests good treatment response and comparable drug resistance evolution in HIV-1 B and non-B infected patients, with increasingly emerging differences. Impact of inter-subtype diversity on drug susceptibility and on evolution of drug resistance should continue to be a major research focus to increase our understanding and ability to improve global patient care.