Impact of amino acid substitutions in the V2 and C2 regions of human immunodeficiency virus type 1 CRF01_AE envelope glycoprotein gp120 on viral neutralization susceptibility to broadly neutralizing antibodies specific for the CD4 binding site.

BACKGROUND: The CD4 binding site (CD4bs) of envelope glycoprotein (Env) gp120 is a functionally conserved, important target of anti-human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies. Two neutralizing human monoclonal antibodies, IgG1 b12 (b12) and VRC01, are broadly reactive neutralizing antibodies which recognize conformational epitopes that overlap the CD4bs of Env gp120; however, many CRF01_AE viruses are resistant to neutralization mediated by these antibodies. We examined the mechanism underlying the b12 resistance of the viruses using CRF01_AE Env (AE-Env)-recombinant viruses in this study. RESULTS: Our results showed that an amino acid substitution at position 185 in the V2 region of gp120 played a crucial role in regulating the b12 susceptibility of AE-Env-recombinant viruses by cooperating with 2 previously reported potential N-linked glycosylation (PNLG) sites at positions 186 (N186) and 197 (N197) in the V2 and C2 regions of Env gp120. The amino acid residue at position 185 and 2 PNLG sites were responsible for the b12 resistance of 21 of 23 (>91%) AE-Env clones tested. Namely, the introduction of aspartic acid at position 185 (D185) conferred b12 susceptibility of 12 resistant AE-Env clones in the absence of N186 and/or N197, while the introduction of glycine at position 185 (G185) reduced the b12 susceptibility of 9 susceptible AE-Env clones in the absence of N186 and/or N197. In addition, these amino acid mutations altered the VRC01 susceptibility of many AE-Env clones. CONCLUSIONS: We propose that the V2 and C2 regions of AE-Env gp120 contain the major determinants of viral resistance to CD4bs antibodies. CRF01_AE is a major circulating recombinant form of HIV-1 prevalent in Southeast Asia. Our data may provide important information to understand the molecular mechanism regulating the neutralization susceptibility of CRF01_AE viruses to CD4bs antibodies.

Two N-linked glycosylation sites in the V2 and C2 regions of human immunodeficiency virus type 1 CRF01_AE envelope glycoprotein gp120 regulate viral neutralization susceptibility to the human monoclonal antibody specific for the CD4 binding domain.

A recombinant human monoclonal antibody, IgG1 b12 (b12), recognizes a conformational epitope on human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) gp120 that overlaps the CD4 binding domain. Although b12 is able to broadly neutralize HIV-1 subtype B, C, and D viruses, many HIV-1 CRF01_AE viruses are resistant to b12-mediated neutralization. In this report, we examined the molecular mechanisms underlying the low neutralization susceptibility of CRF01_AE viruses to b12, using recently established CRF01_AE Env recombinant viruses. Our results showed that two potential N-linked glycosylation (PNLG) sites in the V2 and C2 regions of Env gp120 played an important role in regulating the susceptibility of CRF01_AE Env to b12. The locations of these PNLG sites correspond to amino acid positions 186 and 197 in HXB2 Env gp120; thus, they are designated N186 and N197 in this study. Removal of N186 significantly conferred the b12 susceptibility of 2 resistant CRF01_AE Env clones, 65CC4 and 107CC2, while the introduction of N186 reduced the b12 susceptibility of a susceptible CRF01_AE Env clone, 65CC1. In addition, removal of both N186 and N197 conferred the b12 susceptibility of 3 resistant CRF01_AE Env clones, 45PB1, 62PL1, and 101PL1, whereas the removal of either N186 or N197 was not sufficient to confer the b12 susceptibility of these CRF01_AE Env clones. Finally, removal of N197 conferred the b12 susceptibility of 2 resistant CRF01_AE Env clones lacking N186, 55PL1 and 102CC2. Taken together, we propose that two PNLG sites, N186 and N197, in Env gp120 are important determinants of the b12 resistance of CRF01_AE viruses.

CRF01_AE-specific neutralizing activity observed in plasma derived from HIV-1-infected Thai patients residing in northern Thailand: comparison of neutralizing breadth and potency between plasma derived from rapid and slow progressors.

BACKGROUND: Development of a protective vaccine against human immunodeficiency virus type 1 (HIV-1) is an important subject in the field of medical sciences; however, it has not yet been achieved. Potent and broadly neutralizing antibodies are found in the plasma of some HIV-1-infected patients, whereas such antibody responses have failed to be induced by currently used vaccine antigens. In order to develop effective vaccine antigens, it is important to reveal the molecular mechanism of how strong humoral immune responses are induced in infected patients. As part of such studies, we examined the correlation between the anti-HIV-1 neutralizing antibody response and disease progression. METHODOLOGY/PRINCIPAL FINDINGS: We evaluated the anti-HIV-1 neutralizing activity of plasma derived from 33 rapid and 34 slow progressors residing in northern Thailand. The level of neutralizing activity varied considerably among plasmas, and no statistically significant differences in the potency and breadth of neutralizing activities were observed overall between plasma derived from rapid and slow progressors; however, plasma of 4 slow progressors showed neutralizing activity against all target viruses, whereas none of the plasma of rapid progressors showed such neutralizing activity. In addition, 21% and 9% of plasmas derived from slow and rapid progressors inhibited the replication of more than 80% of CRF01_AE Env-recombinant viruses tested, respectively. Neutralization of subtype B and C Env-recombinant viruses by the selected plasma was also examined; however, these plasma samples inhibited the replication of only a few viruses tested. CONCLUSIONS/SIGNIFICANCE: Although no statistically significant differences were observed in the potency and breadth of anti-HIV-1 neutralizing activities between plasma derived from rapid and slow progressors, several plasma samples derived from slow progressors neutralized CRF01_AE Env-recombinant viruses more frequently than those from rapid progressors. In addition, plasma derived from HIV-1-infected Thai patients showed CRF01_AE-specific neutralizing activity.

Appearance of Drug Resistance-Associated Mutations in Human Immunodeficiency Virus Type 1 CRF01_AE Integrase Derived from Drug-Naive Thai Patients.

CRF01_AE is a major subtype of human immunodeficiency virus type 1 (HIV-1) circulating in Southeast Asia, including Thailand. We performed genotypic studies on HIV-1 CRF01_AE integrase derived from plasma samples from drug-naive Thai patients. Direct sequencing of amplified CRF01_AE integrase genes revealed that although no primary mutations associated with drug resistance to integrase inhibitors were detected, at least one secondary mutation was found in 96% of samples. Our results indicate that the impact of these mutations on the baseline drug susceptibility of CRF01_AE viruses to integrase inhibitors may need to be addressed prior to the introduction of these drugs in Southeast Asian countries, including Thailand.

The role of lysine residue at amino acid position 165 of human immunodeficiency virus type 1 CRF01_AE Gag in reducing viral drug susceptibility to protease inhibitors.

Recombinant human immunodeficiency virus type 1 (HIV-1) containing a CRF01_AE Gag, AE-Gag62, was significantly less susceptible to protease inhibitors (PIs) than the subtype B reference strain, NL4-3; therefore, the mechanism of how AE-Gag62 reduced viral drug susceptibility to PIs was studied in this report. The results showed that the lysine residue at amino acid position 165 (K165) of AE-Gag62 played a role in reducing the drug susceptibility of the recombinant virus to PIs. In addition, K165 potentially appears more frequently in CRF01_AE viruses than in the viruses of other major HIV-1 subtypes. Although K165 had no effect on the extent of recombinant protease-mediated in vitro Gag cleavage, it enhanced the incorporation of the Gag-Pol precursor protein, p160, into virions. Taken together, these results suggest that K165 of CRF01_AE Gag affects the regulation of virion assembly or maturation, and reduces viral drug susceptibility to PIs.

Design and evaluation of antiretroviral peptides corresponding to the C-terminal heptad repeat region (C-HR) of human immunodeficiency virus type 1 envelope glycoprotein gp41.

Two alpha-helical heptad repeats, N-HR and C-HR, located in the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp41, play an important role in membrane fusion by forming a 6-helix bundle. C34, a peptide mimicking C-HR, inhibits the formation of the 6-helix bundle; thus, it has potential as a novel antiretroviral compound. In order to improve the inhibitory effect of C34 on HIV-1 replication, we designed new C34-derived peptides based on computational analysis of the stable conformation of the 6-helix bundle. Newly designed peptides showed a stronger inhibitory effect on the replication of recombinant viruses containing CRF01_AE, subtype B or subtype C Env than C34 or a fusion inhibitor, T-20. In addition, these peptides inhibited the replication of a T-20-resistant virus. We propose that these peptides could be applied to develop novel antiretroviral compounds to inhibit the replication of various subtypes of HIV-1 as well as of T-20-resistant variants.

Detection of drug resistance-associated and background mutations in human immunodeficiency virus type 1 CRF01_AE protease and reverse transcriptase derived from drug treatment-naive patients residing in central Thailand.

CRF01_AE is a major subtype of human immunodeficiency virus type 1 (HIV-1) circulating in Southeast Asia, including Thailand. We performed genotypic studies on HIV-1 CRF01_AE protease (PR) and reverse transcriptase (RT) derived from plasma samples from drug treatment-naive patients residing in central Thailand. Direct sequencing of amplified CRF01_AE PR and RT genes revealed that drug resistance-associated as well as background mutations were frequently detected in CRF01_AE PR. In contrast, although several background mutations were detected, no drug resistance-associated mutations were observed in CRF01_AE RT. Antiretroviral drugs, including PR inhibitors, have been increasingly used in Thailand. To achieve effective antiretroviral therapy, we propose that it is important to reveal the prevalence of drug resistance-associated mutations among drug treatment-naive patients by further surveillance studies.

Phenotypic studies on recombinant human immunodeficiency virus type 1 (HIV-1) containing CRF01_AE env gene derived from HIV-1-infected patient, residing in central Thailand.

Human immunodeficiency virus type 1 (HIV-1) env genes were cloned from blood samples of HIV-1-infected Thai patients, and 35 infectious CRF01_AE envelope glycoprotein (Env)-recombinant viruses were established. In this report, we examined the neutralization susceptibility of these viruses to human monoclonal antibodies, 2G12, IgG1 b12, 2F5 and 4E10, pooled patient plasma, coreceptor antagonists and fusion inhibitor, T-20. The neutralization susceptibility of CRF01_AE Env-recombinant viruses to 2F5, 4E10, patient plasma, coreceptor antagonists and T-20 varied, while most viruses showed low susceptibility to 2G12 and IgG1 b12. Several dual-tropic viruses showed lower susceptibility to 2F5 and 4E10 than CXCR4- or CCR5-tropic viruses. Neutralization susceptibility of the CRF01_AE Env-recombinant virus to pooled patient plasma was negatively correlated with the length of the V1/V2 region or the number of potential N-linked glycosylation sites in conserved regions of gp120. No correlation was found between the coreceptor usage and neutralization susceptibility of the virus to T-20, whereas several dual-tropic viruses showed higher susceptibility to coreceptor antagonists than CXCR4- or CCR5-tropic viruses. We propose that these CRF01_AE Env-recombinant viruses are useful to further study the molecular mechanism of the susceptibility of CRF01_AE Env to neutralizing antibodies and viral entry inhibitors.

Genotypic characterization of CRF01_AE env genes derived from human immunodeficiency virus type 1-infected patients residing in central Thailand.

CRF01_AE is a major subtype of human immunodeficiency virus type 1 (HIV-1) circulating in Southeast Asia, including Thailand. HIV-1 env genes were amplified by polymerase chain reaction from blood samples of HIV-1-infected patients residing in Thailand in 2006, and cloned into the pNL4-3-derived reporter viral construct. Generated envelope protein (Env)-recombinant virus was examined for its infectivity, and then 35 infectious CRF01_AE Env-recombinant viruses were selected. Sequencing analysis revealed that the interclone variation of the deduced amino acid sequences was higher in CRF01_AE env genes isolated in 2006 than in those isolated in the early 1990s, suggesting that env gene variation has been increasing gradually among CRF01_AE viruses prevalent in Thailand. We also examined the characteristics of the deduced amino acid sequences of 35 CRF01_AE env genes. Our results may provide useful information to help in better understanding the genotype of env genes of CRF01_AE viruses currently circulating in Thailand.

Impact of amino acid variations in Gag and protease of HIV type 1 CRF01_AE strains on drug susceptibility of virus to protease inhibitors.

BACKGROUND: Protease (PR) inhibitors (PIs) were designed against subtype B virus of human immunodeficiency virus type 1 (HIV-1), but believed to retain its activity against most of the other subtypes. CRF01_AE PR (AE-PR) contains background mutations that are presumed to alter the drug susceptibility of PR. In addition, amino acid variations found in HIV-1 Gag potentially affect the drug susceptibility or catalytic efficiency of PR. METHODS: We studied the impact of naturally occurring amino acid substitutions found in AE-PR and CRF01_AE Gag (AE-Gag) on the drug susceptibility of PR to 9 currently available PIs, using the pNL4-3-derived luciferase reporter virus containing AE-Gag and/or AE-PR genes derived from drug treatment-naïve, HIV-1-infected Thai patients. RESULTS: Sequencing analysis revealed that several mutations were detected in deduced amino acid sequences of AE-PR and AE-Gag genes, as compared to these genes of pNL4-3. Drug susceptibility tests revealed that AE-PR showed a variety of susceptibilities to 9 PIs compared with pNL4-3 PR. In addition, AE-Gag significantly reduced the drug susceptibility of AE-PR and pNL4-3 PR. CONCLUSION: Our results suggest that amino acid variations in AE-PR and AE-Gag play roles in determining the drug susceptibility of CRF01_AE viruses to PIs.

Identification of the suppressive factors for human immunodeficiency virus type-1 replication using the siRNA mini-library directed against host cellular genes.

We performed the screening to find the novel host factors affecting human immunodeficiency virus type-1 (HIV-1) replication using the siRNA mini-library consisted with 257 siRNAs directed against cellular genes. J111 cells, a human acute monocytic leukemia cell line, were transfected with individual siRNA, followed by either infected or transfected with the HIV-1 molecular clone with luciferase reporter gene in 96-well plate format. The results showed that six siRNAs significantly enhanced the HIV-1 replication in J111 cells, indicating that the target cellular genes of those siRNAs may negatively regulate HIV-1 replication in normal cell culture condition. We also discuss the possible mechanisms by which those cellular proteins regulate viral replication.