Rapid assessment of phenotypic resistance to protease inhibitors in human immunodeficiency virus type 1 group O

HIV-1 Group O Genotypes and Phenotypes: Relationship to Fitness and Susceptibility to Antiretroviral Drugs

Despite only 30,000 group O HIV-1 infections, a similar genetic diversity is observed among the O subgroups H (head) and T (tail) (previously described as subtypes A, B) as in the 9 group M subtypes (A-K). Group O isolates bearing a cysteine at reverse transcriptase (RT) position 181, predominantly the H strains are intrinsically resistant to non-nucleoside reverse transcriptase inhibitors (NNRTIs). However, their susceptibility to newer antiretroviral drugs such as etravirine, maraviroc, raltegravir (RAL), and elvitegravir (EVG) remains relatively unknown. We tested a large collection of HIV-1 group O strains for their susceptibility to four classes of antiretroviral drugs namely nucleoside RT, non-nucleoside RT, integrase, and entry inhibitors knowing in advance the intrinsic resistance to NNRTIs. Drug target regions were sequenced to determine various polymorphisms and were phylogenetically analyzed. Replication kinetics and fitness assays were performed in U87-CD4(+)CCR5 and CXCR4 cells and peripheral blood mononuclear cells. With all antiretroviral drugs, group O HIV-1 showed higher variability in IC50 values than group M HIV-1. The mean IC50 values for entry and nucleoside reverse transcriptase inhibitor (NRTI) were similar for group O and M HIV-1 isolates. Despite similar susceptibility to maraviroc, the various phenotypic algorithms failed to predict CXCR4 usage based on the V3 Env sequences of group O HIV-1 isolates. Decreased sensitivity of group O HIV-1 to integrase or NNRTIs had no relation to replicative fitness. Group O HIV-1 isolates were 10-fold less sensitive to EVG inhibition than group M HIV-1. These findings suggest that in regions where HIV-1 group O is endemic, first line treatment regimens combining two NRTIs with RAL may provide more sustained virologic responses than the standard regimens involving an NNRTI or protease inhibitors.

Susceptibility of HIV-1 non-B subtypes and recombinant variants to Enfuvirtide

BACKGROUND

Data on susceptibility of HIV-1 non-B subtypes to Enfuvirtide (ENF) is rather limited.

OBJECTIVE

To determine if ENF could be active in vitro against HIV-1 non-B subtypes and how the gp41 genetic variability across variants may influence ENF susceptibility.

METHODS

Using PHENOSCRIPT Env, a recombinant envelope virus assay, ENF susceptibility was investigated in isolates from 19 drug-naive HIV-1-infected individuals harboring non-B subtypes.

RESULTS

Using phylogenetic analyses of the gp41 gene, distinct HIV-1 subtypes were recognized: A (2), C (5), D (1), F (2), G (1), J (1), CRF02_AG (6) and CRF06 (1). Susceptibility to ENF and IC(50) values in vitro could be obtained in only 13 (68.4%) specimens, most likely due to the high genetic variability in HR1 and HR2 regions in the remaining cases. A wide range of IC(50) values with a median of 0.013 microg/ml was observed (range, 0.005-0.180 microg/ml). Natural polymorphisms, but not classical ENF resistance associated mutations within HR1 (residues 36-45) were identified in most non-B viruses.

CONCLUSION

This study provides information about the baseline susceptibility to ENF in antiretroviral-naive subjects infected with different HIV-1 non-B subtypes. Susceptibility to ENF seems to be preserved despite high genetic variability in HR1 and HR2 regions.

Treatment response and drug resistance in patients infected with HIV type 1 group O viruses

Information about the efficacy of antiretroviral drugs in HIV-1 group O strains as well on the virus evolution in terms of resistance development in vivo is very limited. We assessed the clinical, immunological, and virological response to antiretroviral therapy as well as the selection of drug resistance in six HIV-1 group O-infected patients. All but one initiated antiretroviral therapy with two nucleoside reverse transcriptase inhibitors (NRTI) plus one protease inhibitor (PI). At baseline, median plasma HIV-1 group O RNA and CD4 counts were 32,256 (15,770-74,132) copies/ml and 88 cells/microl (13-170), respectively. Four patients reached undetectable plasma viremia 12 weeks after beginning treatment. However, viremia rebounded in one of them due to poor compliance. Another two patients had an initial reduction in plasma HIV-RNA greater than 1 log, but rebounded soon thereafter. At baseline, all patients' viruses revealed changes associated with NNRTI resistance (98G and 181C). Two out of three patients failing therapy developed resistance mutations. One selected changes M41L, E44D, D67N, V75M, M184V, and T215Y at the RT, and G48M, F53L, I54V, V82A, and L90M at the protease. Another selected mutations K70N, V75A, and M184V at the RT, and D30D/N and I84V at the protease while failing on indinavir. Interestingly, both patients showed a shift at codon 181 from C to Y, which might restore NNRTI susceptibility. Sustained viral suppression in HIV-1 group O-infected patients can be successfully achieved using antiretroviral regimens based on two NRTI and a boosted PI. Drug resistance mutations in HIV-1 group O seem to be selected at similar positions to those in HIV-1 group M viruses.

Are fusion inhibitors active against all HIV variants?

Genetic sequence alignment of the transmembrane region from HIV-1 group O and HIV-2 isolates was performed to examine their potential susceptibility to fusion inhibitors enfuvirtide (T-20) and T-1249. A high genetic diversity within the HRI and HR2 domains was found, which should compromise any antiviral effect of T-20 on HIV-2 and HIV-1 group O viruses. However, conserved sequences in the gp41 regions from HIV-1 group O involved in T-1249 susceptibility might result in a much broader antiviral effect of T-1249 on HIV-1 variants. In contrast, genetic diversity in those regions make unlikely any activity of these compounds on HIV-2.