HIV type 1 isolate Z321, the strain used to make a therapeutic HIV type 1 immunogen, is intersubtype recombinant

A near full-length HIV-1 genome from 1966 recovered from formalin-fixed paraffin-embedded tissue

With very little direct biological data of HIV-1 from before the 1980s, far-reaching evolutionary and epidemiological inferences regarding the long prediscovery phase of this pandemic are based on extrapolations by phylodynamic models of HIV-1 genomic sequences gathered mostly over recent decades. Here, using a very sensitive multiplex RT-PCR assay, we screened 1,645 formalin-fixed paraffin-embedded tissue specimens collected for pathology diagnostics in Central Africa between 1958 and 1966. We report the near-complete viral genome in one HIV-1 positive specimen from Kinshasa, Democratic Republic of Congo (DRC), from 1966 ("DRC66")-a nonrecombinant sister lineage to subtype C that constitutes the oldest HIV-1 near full-length genome recovered to date. Root-to-tip plots showed the DRC66 sequence is not an outlier as would be expected if dating estimates from more recent genomes were systematically biased; and inclusion of the DRC66 sequence in tip-dated BEAST analyses did not significantly alter root and internal node age estimates based on post-1978 HIV-1 sequences. There was larger variation in divergence time estimates among datasets that were subsamples of the available HIV-1 genomes from 1978 to 2014, showing the inherent phylogenetic stochasticity across subsets of the real HIV-1 diversity. Our phylogenetic analyses date the origin of the pandemic lineage of HIV-1 to a time period around the turn of the 20th century (1881 to 1918). In conclusion, this unique archival HIV-1 sequence provides direct genomic insight into HIV-1 in 1960s DRC, and, as an ancient-DNA calibrator, it validates our understanding of HIV-1 evolutionary history.

HIV-1 Immunogen: an overview of almost 30 years of clinical testing of a candidate therapeutic vaccine

INTRODUCTION

Although current antiretroviral therapy (ART) has transformed HIV infection into a chronic, manageable disease, ART does not cure HIV infection. Furthermore, the majority of the world's infected individuals live in resource-limited countries in which access to ART is limited. Thus, the development of an effective therapeutic HIV vaccine would be an invaluable treatment alternative.

AREAS COVERED

Developed by the late Dr. Jonas Salk, HIV-1 Immunogen (Remune®) is a candidate therapeutic vaccine that has been studied in thousands of HIV-infected individuals in more than a dozen clinical trials during almost three decades. This Drug Evaluation, which summarizes the results of these trials that have shown the vaccine to be safe and immunogenic, also discusses the contradictory and controversial conclusions drawn from the phases 2, 2/3 and 3 trials that assessed the clinical efficacy of this vaccine.

EXPERT OPINION

Given the lack of unequivocal clinical benefits of HIV-1 Immunogen despite almost 30 years of extensive testing, it does not appear, in our view, that this vaccine is a clinically effective immunotherapy. However, inclusion of this vaccine in the newly proposed 'Kick/Shock and Kill' strategy for HIV eradication, or use as a prophylactic vaccine, could be considered for future trials.

'Patient 0' and the Origin of HIV/AIDS in America

The origin of the HIV/AIDS epidemic in North America remains contentious. A recent study uses phylogenetic and historical approaches to investigate the early history of HIV-1 group M subtype B in North America and shows that 'Patient 0' is not the source of the North American HIV/AIDS epidemic.

Identification of a novel circulating recombinant form (CRF) 36_cpx in Cameroon that combines two CRFs (01_AE and 02_AG) with ancestral lineages of subtypes A and G

An array of CRFs have been identified in Cameroon, the most notable being CRF02_AG. HIV-1 in the East Province of Cameroon is particularly diverse: in a recent study, we found a high proportion of unique recombinant forms (URFs). Herein we describe the analysis of the full-length sequences of two of these URFs, which, after preliminary analysis of gag, pol, and env fragments, appeared to be a novel CRF. This novel strain, CRF36_cpx, contains fragments that can be assigned to the CRF01_AE, CRF02_AG, and subtype A and G radiations. Forty percent of the genome can be classified as CRF02_AG, including regions in gag, pol, env, and the accessory genes. Twenty-seven percent is CRF01_AE, comprising the majority of gag, the beginning of env, and the end of env into the 3' LTR. Twenty percent of the genome can be assigned to subtype A, with segments in pol and env. The remaining 13% of the sequence is classifiable as subtype G, in pol and vpu. The subtype A and G lineages formed by the CRF36_cpx sequences are unique and appear ancestral in nature. CRF36_cpx is both the first to combine more than one CRF and the first to include fragments of CRF02_AG. The ancestral sequences present in CRF36_cpx represent a link to extinct strains, and, potentially, insight into the evolution of HIV-1.

Circulating recombinant form (CRF) 37_cpx: an old strain in Cameroon composed of diverse, genetically distant lineages of subtypes A and G

HIV-1 in Cameroon is genetically diverse, but is predominated by the circulating recombinant form (CRF) 02_AG, which cocirculates among an array of other CRFs, unique recombinant forms (URFs), and all group M subtypes. In particular, our studies of HIV-1 diversity in the East Province found a high proportion of URFs and second generation recombinants (SGRs), suggesting this region of Cameroon may be a breading ground for new CRFs. Herein we present the full-length sequence analysis of one such CRF, composed primarily (66%) of unique, distant lineages of subtypes A and G in alternating regions throughout the genome. This CRF also combines segments in pol and env genes possessing intrasubtype distance (<15%) to the CRF01_AE and CRF02_AG radiations. The genomic composition of this strain comprising gene segments of subtypes A and G as well as CRF01_AE and CRF02_AG defines this strain as a circulating SGR (CSGR), and the 37th CRF to be identified. Furthermore, more than half of CRF19_cpx, a CRF identified in Cuba, clusters with CRF37_cpx, and the clear genetic distance among the viruses in this cluster suggests this strain has been in circulation since the early days of the epidemic. The genetically distant segments comprising CRF37_cpx, which were found to cluster outside the crown groups of previously described viruses, may represent a link to very rare or extinct strains, and, potentially, to understanding the evolutionary history of HIV-1 in this region.

Specificity of anti-human leukocyte antigen antibody responses after immunization with Remune, an inactivated HIV-1 vaccine

Antibody responses against human leukocyte antigen (HLA) classes I and II were detected in HIV-1 infected individuals who received a fixed inactivated HIV-1 (Remune) immunotherapy. The response was specific for HLA-B62 and HLA-DR4 concordant with the host cell line, HUT-78, used in vaccine production. These responses were not detected in HLA-B62 and HLA-DR4-positive individuals indicating that immunotherapy did not break tolerance to self-antigens.

CD8+ T-cell-mediated cross-clade protection in the genital tract following intranasal immunization with inactivated human immunodeficiency virus antigen plus CpG oligodeoxynucleotides

Human immunodeficiency virus (HIV) is a mucosally transmitted infection that rapidly targets and depletes CD4+ T cells in mucosal tissues and establishes a major reservoir for viral persistence in gut-associated lymphoid tissues. Therefore, vaccines designed to prevent HIV infections must induce potent and durable mucosal immune responses, especially in the genital tract. Here we investigated whether intranasal (i.n.) immunization with inactivated gp120-depleted HIV-1 antigen (Ag) plus CpG oligodeoxynucleotide (ODN) as an adjuvant induced local immune responses in the genital tract and cross-clade protection against intravaginal (IVAG) challenge. Lymphocytes isolated from the iliac lymph nodes (ILNs) and genital tracts of female mice i.n. immunized with HIV-1 Ag plus CpG showed significant HIV-specific proliferation and produced significantly higher levels of gamma interferon (IFN-gamma) and beta-chemokines than mice immunized with HIV-1 Ag alone or mixed with non-CpG ODN. CD8+ lymphocytes were dramatically increased in the genital tracts of mice immunized with HIV-1 Ag plus CpG, and protection following IVAG challenge with recombinant vaccinia viruses (rVVs) expressing HIV-1 gag was shown to be CD8 dependent. Finally, cross-clade protection was observed between clades A, C, and G but not B following IVAG challenge with rVVs expressing HIV-1 gag from different clades. These studies provide evidence that mucosal (i.n.) immunization induced strong local T-cell-mediated immune responses in the genital tract and cross-clade protection against IVAG challenge.

Delayed progression to AIDS in volunteers treated with long-term HIV-1 Immunogen (REMUNE) therapy in Thailand

OBJECTIVES

To observe the long-term effects of an immune-based therapy HIV-1 Immunogen (REMUNE; Immune Response Corp., Carlsbad, CA, USA) as a first course of treatment designed to sustain the immune system and thus delay the initiation of therapy with antiretroviral drugs and/or delay disease progression.

METHODS

In this open-label, multi-institute extended phase II P2101B study, disease progression, CD4 and CD8 T-cell counts, HIV-1 RNA levels, and genotypic antiretroviral drug resistance were examined in 223 asymptomatic HIV-1-infected Thai volunteers receiving REMUNE every 12 weeks over 132 weeks. A subset of subjects was randomly selected by the physicians to receive antiretroviral drugs for 10 months.

RESULTS

Patients treated with REMUNE demonstrated a low rate of clinical disease progression (0.72 per 100 person-years), higher CD4 and CD8 T-cell counts, higher body weight before and after treatment in the same patient, and stable viral load with no serious adverse events. We found no genotypic evidence of drug resistance in subgroups of patients on REMUNE monotherapy or REMUNE plus antiretrovirals (ARTs).

CONCLUSIONS

This Thai study, like previous US and European studies, confirms that therapeutic immunization of HIV-infected volunteers modifies disease progression, as evidenced by stabilization of CD4 and CD8 T-cell counts, body weight, and viral load. As the majority of asymptomatic patients demonstrated an objective response to immunization, this study suggests that REMUNE may be utilized prior to initiation of antiviral drug therapy when CD4 cell counts are still above the current ART guidelines. Further work should be carried out to examine its potential use in combination with ART in order to reduce the increasingly common occurrence of drug resistance.

The evolution of HIV and its consequences

Since the beginning of the AIDS epidemic in 1981, HIV-1 has demonstrated an amazing ability to mutate. HIV-1 was introduced into the human population in the early to mid twentieth century in central Africa. During ensuing decades, this extraordinary mutational capacity has resulted in the circulation of HIV-1 strains that are quite different from one another, yet still remarkably pathogenic. The potential impact of this viral diversity on treatment, monitoring,and vaccine development is discussed.

HIV type 1 circulating recombinant form CRF09_cpx from west Africa combines subtypes A, F, G, and may share ancestors with CRF02_AG and Z321

Two HIV-1 intersubtype recombinant forms are circulating widely in populations and have become important strains in the pandemic: CRF01_AE in Southeast Asia and CRF02_AG in West and West Central Africa, respectively. Several other circulating recombinant forms (CRF) have also been identified, but with fewer numbers of infections and/or more limited geographic spread. Here we expand knowledge of HIV-1 CRF using clinical samples, principally from West Africa, that were difficult to classify by partial genome sequencing. DNA was extracted from primary patient peripheral blood mononuclear cells (PBMC). The virtually complete HIV-1 genome was amplified by polymerase chain reaction (PCR) and directly sequenced. Additional strains were characterized by partial envelope sequencing. Phylogenetic analysis was used to identify and map intersubtype recombination breakpoints. Four virtually complete genome sequences and two partial envelope sequences represent CRF09_cpx, a newly identified complex recombinant HIV-1 whose principal focus seems to be in West Africa. This recombinant includes segments of subtypes A, F, G, and unclassified genetic material. It shares unique unclassified regions with the early Zaire strain Z321. There are similarities in structure, but considerable genetic distances, between CRF09_cpx and CRF02_AG IbNG. In conclusion, it is possible that this CRF shared common ancestors with both Z321 and CRF02_AG in the course of the pandemic, perhaps arising by recombination between earlier forms of these strains. Although newly identified, at least one infection with CRF09_cpx has already occurred outside of Africa.

Therapeutic immunization with an inactivated HIV-1 Immunogen plus antiretrovirals versus antiretroviral therapy alone in asymptomatic HIV-infected subjects

To determine whether the addition of an inactivated-gp120-depleted HIV-1 Immunogen to antiretrovirals (ARTs) conferred a beneficial effect on delaying time to virologic failure relative to that obtained by ARTs alone, a phase II clinical trial was performed in 243 asymptomatic, ART naïve, HIV-1 seropositive adults. The Cox model showed that HIV-1 Immunogen treatment was associated with a 34% decrease in the risk of virologic failure (P = 0.056). When the analysis incorporated baseline HIV-RNA stratification the risk of virologic failure in the HIV-1 Immunogen Arm was significantly reduced a 37% compared to the IFA placebo Arm (P = 0.034). The data suggest that therapeutic immunization plus ARTs could influence virologic control.

HIV type 1 antigen-responsive CD4+ T-lymphocytes in exposed yet HIV Type 1 seronegative Ugandans

CD4(+) T cell help is important for the functionality of CD8(+) cytotoxic T-lymphocytes (CTLs) in limiting viral replication and may contribute to mediation of apparent resistance to HIV-1 infection in exposed seronegative (ESN) individuals. Using five HIV-1 antigens in an intracellular cytokine assay, the presence of specific antigen-responsive interferon- gamma-positive (IFN-gamma(+)) CD69(+) CD4(+) T-lymphocytes was evaluated in ESNs, their seropositive partners, and unexposed seronegative controls. Ten ESNs (five females, five uncircumcised males) were identified from 10 HIV-1 serodiscordant couples with a history of frequent unprotected sexual intercourse. All ESNs and controls were negative on two EIAs and for HIV-1 proviral DNA. The frequency of ESNs with antigen-responsive IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes ranged from three to five of eight for the different HIV-1 antigens. Six of eight ESNs tested had a positive response to at least one of the five antigens. Responses were on average 3.5 times higher among seropositives compared to ESNs and absent in the five unexposed controls. A negative correlation was noted between responses in ESNs and the plasma viral load of their seropositive spouse. Clade-specific and cross-clade reactivity were noted in both ESNs and seropositive partners tested. The findings confirm that ESNs are in a state of HIV-1-specific immune activation and suggest that HIV-1-specific IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes in addition to HIV-1-specific CD8(+) CTLs already described by others are potential immunological correlates of protection from persistent HIV-1 infection.

HIV-specific immunity during structured antiviral drug treatment interruption

The immunologic correlates associated with control of viremia in HIV disease are poorly understood. We hypothesized that structured antiviral drug treatment interruptions could be utilized to better understand the relationship between HIV-specific immunity and viral replication. We thus examined the effects of two 8 weeks antiviral structured treatment interruptions (STIs) in a cohort of HIV-1 chronically infected individuals on highly active antiretroviral treatment (HAART) with (n = 13) and without (n = 12) therapeutic HIV immunizations. In this study, we observed that p24 gag antigen (np24) stimulated MIP-1beta levels and T helper immune responses prior to antiviral drug discontinuation were associated with control of viremia. Stronger and earlier production of gag peptide stimulated gamma interferon was observed in the immunized group during the structured antiviral drug interruptions. These results support the concept that HIV-specific immune responses are associated with control of viremia. Further study of immune-based therapies that enhance HIV-specific immunity is warranted.

Analysis of partial pol and env sequences indicates a high prevalence of HIV type 1 recombinant strains circulating in Gabon

Forty-one HIV-1 strains from Gabonese patients were studied according to the following strategy: nested polymerase chain reaction were performed to obtain an approximately 1,100-bp fragment containing the protease gene and the 5' half of the reverse transcriptase gene. Additional amplifications were carried out to obtain an approximately 700-bp fragment encompassing the C2V3 env gene. Fragments of 600 to 1,200 bp in the gag gene overlapping the pol sequences were used for the study of recombination patterns. Phylogenetic analyses of the different fragments were used to investigate HIV-1 diversity in Gabon. Thirty-one strains were sequenced in the env and pol genes and phylogenetic analyses classified them as subtype A (n = 2), D (n = 4), G (n = 1), H (n = 1), CRF02 (n = 8), and CRF MAL-like (n = 6); in addition, there were 6 unique recombinant forms and 1 unclassified strain, and in 2 cases pol/env sequences classified strains as subtype D whereas gag phylogeny classified them as subtype A. In 10 cases only 1 fragment was available: 4 env (2 subtype D, 1 subtype H, and 1 subtype U) and 6 pol (1 subtype A, 1 subtype C, 2 subtype G, and 2 subtype U). Minor mutations associated with viral resistance to antiretroviral drugs were observed in more than 80% of analyzed strains. Our study confirms the extensive HIV-1 diversity found in Central Africa, with more than 70% of strains from Gabon exhibiting discordant clustering in pol and env genomic regions and less than 60% concordance between sequencing and heteroduplex mobility assay genotyping. These findings highlight the fact that Central Africa represents the epicenter for the origin of HIV-1. The strategy of sequencing pol in association with env has proved to be useful for analysis of the recombinant strains. The main advantage of this approach is that it also allows for evaluation of genotypic susceptibility to antiretroviral drugs without the need for supplementary analyses.

Maternal and newborn immunization with a human immunodeficiency virus-1 immunogen in a rodent model

We examined immunization with an inactivated, gp120-depleted human immunodeficiency virus (HIV) antigen in incomplete Freund's adjuvant (IFA), also containing a sequence of immunostimulatory (ISS) DNA, during the last trimester of pregnancy and neonatally in a rat model. Pregnant rats were immunized in the third trimester and their litters were immunized during the newborn period. In addition, litters of rats from non-immunized mothers were immunized during the neonatal period. As another control, pregnant rats were immunized and their litters analysed. Supernants from peripheral blood mononuclear cells (PBMCs) were assayed from newborns at 4 weeks of age for HIV-specific interferon-gamma (IFN-gamma), HIV-specific regulated on activation, normal, T-cell expressed, and secreted (RANTES), and serum for p24 antigen-specific immunoglobulin G (IgG) production. In the animals whose pregnant mothers were immunized and were also immunized during the neonatal period, we observed HIV-specific IFN-gamma production and HIV-specific RANTES production, but weak p24 IgG antibody production. Animals immunized only during the neonatal period developed the highest levels of HIV-specific IFN-gamma production, but somewhat lower levels of HIV-specific RANTES and p24 IgG antibody production. The group of animals whose mothers had received immunizations during the last trimester of pregnancy, but were not immunized during the neonatal period, developed the strongest p24 IgG antibody levels, but little or undetectable HIV-specific IFN-gamma or RANTES production. Neonatal immunization resulted primarily in cell-mediated immune responses, while animals born to mothers who were immunized during the last trimester had primarily an antibody-mediated immune response. Immunization of pregnant animals followed by neonatal immunization resulted in a mixed cell-mediated/antibody type profile in the neonatal animal. Future studies should provide insights into neonatal immunity and potential vaccine approaches to prevent neonatal infection and perinatal transmission.

Generation of Th1 immune responses to inactivated, gp120-depleted HIV-1 in mice with a dominant Th2 biased immune profile via immunostimulatory [correction of imunostimulatory] oligonucleotides--relevance to AIDS vaccines in developing countries

Vaccination against HIV-1 of hosts with a dominant Th2 immune profile may fail to induce essential protective Th1 immune responses. By using Schistosoma-infected mice, with a pre-existent Th2 immune background, we demonstrate that oligodeoxynucleotides (ODN) containing unmethylated cytosine-phosphate-guanosine (CpG) immunostimulatory sequences co-administered with inactivated, gp120-depleted HIV-1 viral particles (HIV-1 immunogen) lead to potent Th1 anti-HIV-1 immune responses overcoming the Th2 bias. In contrast, Schistosoma-infected mice immunized with HIV-1 immunogen in incomplete Freund's adjuvant only, induced Th2 anti-HIV-1 immune responses. These findings strongly support the advisability of using CpG ODN as a Th1 inducing adjuvant when immunizing human populations with a strong pre-existent Th2 immune profile.

Predictors of HIV-specific lymphocyte proliferative immune responses induced by therapeutic vaccination

We treated a cohort of 38 HIV-infected individuals with a therapeutic vaccine (REMUNE, HIV-1 Immunogen) in an open label study. We then determined whether baseline parameters, such as CD4 cell count, viral load and IgG levels, were predictive of the magnitude of the HIV-specific lymphocyte proliferative responses (LPRs). We demonstrate herein that there is a significant enhancement from baseline for both HIV and p24 antigen-stimulated LPRs after immunization. Using a responder definition of a stimulation index of >5 on at least two post-immunization time-points, 29/38 (76%) responded to HIV-1 antigen while 27/38 (71%) responded to native p24 antigen. Viral load and total IgG were negatively correlated, while CD4 cell counts were positively associated with the magnitude of the HIV antigen LPR. In a multivariable analysis, baseline CD4 was the best predictor of HIV antigen LPR post-immunization.

Long-term follow-up of HIV-1-infected Thai patients immunized with Remune monotherapy

PURPOSE

The purpose of this 2-year follow-up study was to investigate the long-term effect of Remune as monotherapy for HIV-1 infection.

BACKGROUND

Participants previously enrolled in the phase II double-blind, randomized, adjuvant-controlled study of the HIV-1 Immunogen (Remune) were followed for 2 years. Open-label immunization with Remune monotherapy was given to each participant every 12 weeks. Remune, a gp 120-depleted HIV-1 that was inactivated in beta-propiolactone and irradiation, was emulsified with mineral oil (incomplete Freund's adjuvant).

METHOD

In Study 2101B, the effect of four doses of Remune given every 12 weeks over 40 weeks was compared to placebo in 297 asymptomatic type E HIV-infected patients [Churdboonchart et al., 2000]. A group of 17 volunteers were separated into a subset study and another 57 were excluded from analysis due to discontinuation or addition of other treatments. This 2-year follow-up study continued with open-label dosing of HIV-1 Immunogen every 12 weeks for the remaining 223 patients. Changes in CD4+ cells, CD8+ cells, and body weight were monitored at each patient visit.

RESULTS

Overall, immunizations were safe; common adverse events were tolerable injection site reactions. CD4+ T-cell counts remained stable over the 132-week observation period for this cohort with a slight increase of 36.01 cells/microL. CD8+ T-cell counts showed an increase from baseline during the follow-up period (415.21 cells/microL). Furthermore, we also observed an increase in body weight from baseline (1.08 kg) at week 132. In addition, baseline CD4 count appeared to predict CD4 count at week 132 (slope = 0.31, p <.0001).

CONCLUSION

These results suggest that long-term treatment of HIV-1 infection with Remune monotherapy is safe and results in a stabilization of CD4+ counts. Furthermore, it is likely that HIV-1 therapeutic immunization may show its greatest clinical benefit in participants with higher CD4+ cell counts. Such an approach may have important ramifications in developing countries where access to antiviral drugs is limited and also in early chronic HIV-1 infection when CD4+ cells are still over 300 cells/microL in order to limit the cost and toxicity.

Using human immunodeficiency virus type 1 sequences to infer historical features of the acquired immune deficiency syndrome epidemic and human immunodeficiency virus evolution

In earlier work, human immunodeficiency virus type 1 (HIV-1) sequences were analysed to estimate the timing of the ancestral sequence of the main group of HIV-1, the virus that is responsible for the acquired immune deficiency syndrome pandemic, yielding a best estimate of 1931 (95% confidence interval of 1915-1941). That work will be briefly reviewed, outlining how phylogenetic tools were extended to incorporate improved evolutionary models, how the molecular clock model was adapted to incorporate variable periods of latency, and how the approach was validated by correctly estimating the timing of two historically documented dates. The advantages, limitations, and assumptions of the approach will be summarized, with particular consideration of the implications of branch length uncertainty and recombination. We have recently undertaken new phylogenetic analysis of an extremely diverse set of human immunodeficiency virus envelope sequences from the Democratic Republic of the Congo (the DRC, formerly Zaire). This analysis both corroborates and extends the conclusions of our original study. Coalescent methods were used to infer the demographic history of the HIV-1 epidemic in the DRC, and the results suggest an increase in the exponential growth rate of the infected population through time.

Expression of perforin on HIV-1-specific CD8+ lymphocytes after immunization with a gp120-depleted, whole-killed HIV-1 immunogen

We examined HIV-1 antigen specific intracellular expression of perforin on CD4+ and CD8+ lymphocytes in subjects with chronic HIV-1 infection on antiviral drug therapy after immunization with a gp120-depleted, whole killed HIV-1 immunogen (inactivated, gp120-depleted HIV-1 in IFA, REMUNE). Based upon previous results, we hypothesized that the restoration of adequate T helper immune responses by vaccination against HIV-1 could result in the augmentation of CD8+ lymphocyte immune responses measured as perforin expression. In the current study we observed an increase in the frequency of perforin in CD8+ lymphocytes in HIV infected individuals immunized with a gp120-depleted HIV-1 immunogen while on antiviral drug therapy. Furthermore, the frequency of HIV-specific CD8+ perforin expressing cells correlated with the T helper immune response as measured by the lymphocyte proliferative response (LPR). The induction of such responses with immunization may have direct antiviral consequences and is being studied in ongoing clinical trials.

A complex human immunodeficiency virus type 1 A/G/J recombinant virus isolated from a seronegative patient with AIDS from Benin, West Africa

A human immunodeficiency virus type 1 (HIV-1(B76)) originating from Benin (West Africa) was isolated and characterized. The patient had severe clinical AIDS and presented an unusual serological profile. Only one out of five different detection assays was able to demonstrate the presence of antibodies to HIV, whereas confirmatory assays remained indeterminate. In contrast, both plasma viral load and p24 antigen level were unusually high. HIV-1 infection was proved by viral RNA and proviral DNA amplification. HIV-1(B76) partially purified lysate reacted strongly with all anti-HIV-1-positive sera from the region but B76 plasma did not react with subtype A control viral antigen. This patient is likely to have had severe acquired immune dysfunction explaining her lack of immunological reactivity. Phylogenetic analysis of the genome identified a complex HIV-1 A/G/J recombinant. The gag and pol genes, and the majority of nef,are characteristic of subtype A; the gag/pol junction, the 3' end of pol, vpu and env genes were characteristic of subtype G; vif, vpr and the 5' end of nef were subtype J. In addition, part of the HIV-1(B76) genome had considerable sequence similarity with the previously described CRF06 cpx (BFP90) isolate. HIV-1(B76) did not exhibit any remarkable replication properties or cell tropism in vitro.

The effects of an HIV-1 immunogen (Remune) on viral load, CD4 cell counts and HIV-specific immunity in a double-blind, randomized, adjuvant-controlled subset study in HIV infected subjects regardless of concomitant antiviral drugs

OBJECTIVE

We examined the activity of an HIV-1 immunogen (Remune) on viral load, CD4 cells and HIV-1 specific immunity.

METHODS

Plasma and peripheral blood mononuclear cells were obtained in a predefined random subset of subjects (n = 252) from a multicentre, double-blind, adjuvant-controlled phase III clinical endpoint study.

RESULTS

The subjects treated with the HIV-1 immunogen had a significantly greater decline in viral load at multiple time points (P < 0.05), a trend towards increased CD4+ T cell counts and significantly enhanced HIV-1 specific immune responses as measured by HIV-1 lymphocyte proliferation (P < 0.001) compared to the adjuvant control group. Furthermore, in the HIV-1 immunogen treated group, enhanced HIV-1 specific lymphocyte proliferative immune responses were associated with decreased HIV-1 plasma RNA.

CONCLUSION

These results suggest that, in a predefined, random subset of subjects, a beneficial effect of the HIV-1 immunogen was observed on viral load, CD4+ T cells, and HIV-specific immunity. These differences were observed in a background of multiple drug therapies. Ongoing trials are evaluating the effect of the combination of this HIV-1 specific, immune-based therapy with potent antiviral drug therapy on virological outcomes.

Identification of a complex env subtype E HIV type 1 virus from the democratic republic of congo, recombinant with A, G, H, J, K, and unknown subtypes

Up to now, all known env subtype E viruses (CRF01-AE) have had the same mosaic structure with subtype A, and no other env subtype E HIV-1 viruses with non-A subtypes in their genomes have been described. In this report we describe the full-length genome sequence of an env subtype E isolate with a recombinant genome different from the prototype CRF01-AE strains. The 97CD-KTB49 strain, obtained from a tuberculosis patient in Kinshasa, has a complex mosaic genome involving subtypes A, E, G, H, J, K, and several unknown fragments. The U sequences formed well-separated clusters together with previously described unknown fragments from CRF04-cpx (subtype I), and from Z321, the oldest intersubtype recombinant isolated in 1976 in the Democratic Republic of Congo. The complex recombinant virus from our study is not an isolated strain; partial sequencing of a second strain, 97CD-KFE45, confirmed the breakpoints observed in the 97CD-KTB49 strain in the regions sequenced. The complexity of these recombinant strains suggests a longstanding presence of subtype E in Central Africa.

HIV-Specific CD4(+) and CD8(+) immune responses are generated with a gp120-depleted, whole-killed HIV-1 immunogen with CpG immunostimulatory sequences of DNA

We examined the adjuvant effects of a synthetic CpG oligodeoxynucleotide immunostimulatory sequence (ISS) using a whole-killed, gp120-depleted HIV antigen (HIV-1 antigen) in a Lewis rat model. We hypothesized that HIV-1-specific CD4(+) T helper (Th) immune responses could be enhanced when an ISS was combined with an HIV-1 antigen in incomplete Freund's adjuvant (IFA). We also reasoned that if such Th responses were sufficient, such a combination might also induce HIV-specific CD8(+) T cell immune responses. Here we demonstrate that the HIV-1 antigen in IFA combined with ISS stimulates both CD4(+) and CD8(+) HIV-specific immune responses as measured by interferon-gamma (IFN-gamma) in the ELISPOT assay. A strong correlation between these CD4(+) and CD8(+) responses was demonstrated. Furthermore, we found that the HIV-1 antigen in IFA with ISS as an adjuvant stimulated strong antibody responses to core antigen (p24). These studies suggest that the combination of the whole-killed, gp120-depleted HIV-1 antigen in IFA with ISS may be an ideal candidate to test in nonhuman primates and in human studies as a preventive HIV-1 vaccine.

Cell-mediated immune responses to autologous virus in HIV-1-seropositive individuals after treatment with an HIV-1 immunogen

OBJECTIVE

We hypothesized that cell mediated immune responses to an HIV-1 immunogen (whole-killed, gp120-depleted HIV-1 in IFA, REMUNE) would include those to autologous virus.

METHODS

Five chronically HIV-1 infected individuals were examined for HIV-specific immune responses to their own virus (autologous viral antigen) after treatment with an HIV-1 immunogen.

RESULTS

Subjects had low proliferative responses to HIV and p24 antigens prior to immunization and mounted strong lymphocyte proliferative responses to the immunizing HIV-1 virus, native p24, and autologous viral antigen post immunization. Similarly, subjects produced low amounts of interferon-gamma in response to HIV and p24 antigens prior to immunization and increased their interferon-gamma production in response to HIV-1, native p24, and to autologous antigen post-immunization. Furthermore, beta-chemokine responses measured as migratory inhibitory protein-1beta production were low at baseline in response to HIV-1 and native p24 antigens and were enhanced post immunization to HIV-1, native p24, and autologous antigen.

CONCLUSIONS

In this study HIV-specific immune responses to autologous virus were observed after treatment with an HIV-specific immunogen.

Unprecedented degree of human immunodeficiency virus type 1 (HIV-1) group M genetic diversity in the Democratic Republic of Congo suggests that the HIV-1 pandemic originated in Central Africa

The purpose of this study was to document the genetic diversity of human immunodeficiency virus type 1 (HIV-1) in the Democratic Republic of Congo (DRC; formerly Zaire). A total of 247 HIV-1-positive samples, collected during an epidemiologic survey conducted in 1997 in three regions (Kinshasa [the capital], Bwamanda [in the north], and Mbuyi-Maya [in the south]), were genetically characterized in the env V3-V5 region. All known subtypes were found to cocirculate, and for 6% of the samples the subtype could not be identified. Subtype A is predominant, with prevalences decreasing from north to south (69% in the north, 53% in the capital city, and 46% in the south). Subtype C, D, G, and H prevalences range from 7 to 9%, whereas subtype F, J, K, and CRF01-AE strains represent 2 to 4% of the samples; only one subtype B strain was identified. The highest prevalence (25%) of subtype C was in the south, and CRF01-AE was seen mainly in the north. The high intersubtype variability among the V3-V5 sequences is the most probable reason for the low (45%) efficiency of subtype A-specific PCR and HMA (heteroduplex mobility assay). Eighteen (29%) of 62 samples had discordant subtype designations between env and gag. Sequence analysis of the entire envelope from 13 samples confirmed the high degree of diversity and complexity of HIV-1 strains in the DRC; 9 had a complex recombinant structure in gp160, involving fragments of known and unknown subtypes. Interestingly, the unknown fragments from the different strains did not cluster together. Overall, the high number of HIV-1 subtypes cocirculating, the high intrasubtype diversity, and the high numbers of possible recombinant viruses as well as different unclassified strains are all in agreement with an old and mature epidemic in the DRC, suggesting that this region is the epicenter of HIV-1 group M.

A double-blind, adjuvant-controlled trial of human immunodeficiency virus type 1 (HIV-1) immunogen (Remune) monotherapy in asymptomatic, HIV-1-infected thai subjects with CD4-cell counts of >300

We examined the effect of a human immunodeficiency virus (HIV)-specific immune-based therapy in Thailand, where access to antiviral drug therapy is limited. A 40-week trial was conducted with 297 asymptomatic, HIV-infected Thai subjects with CD4-cell counts greater than 300 microl/mm(3). Subjects were randomized to receive either HIV type 1 (HIV-1) immunogen (Remune; inactivated HIV-1 from which gp120 is depleted in incomplete Freund's adjuvant or adjuvant control at 0, 12, 24, and 36 weeks at five different clinical sites in Thailand. Neither group received antiviral drug therapy. The a priori primary endpoint for the trial was changes in CD4-cell counts with secondary parameters of percent changes in CD8-cell counts (percent CD4, CD8, and CD4/CD8) and body weight. Subsets of subjects were also examined for changes in plasma HIV-1 RNA levels, Western blot immunoreactivity, and HIV-1 delayed-type hypersensitivity (DTH) skin test reactivity. There was a significant difference in changes in CD4-cell counts that favored the HIV-1 immunogen-treated group compared to those for the adjuvant-treated control group (P<0.05). On average, for HIV-1 immunogen-treated subjects CD4-cell counts increased by 84 cells by week 40, whereas the increase for the control group was 38 cells by week 40. This increase in CD4-cell count was associated with increased HIV-specific immunogenicity, as shown by Western blotting and enhanced HIV-1 DTH skin reactivity. No significant differences in adverse events were observed between the groups. The results of this trial suggest that HIV-1 immunogen is safe and significantly increases CD4-cell counts and HIV-specific immunity compared to those achieved with the adjuvant control in asymptomatic HIV-1-infected subjects not taking antiviral drugs.

T-helper-cell proliferative responses to whole-killed human immunodeficiency virus type 1 (HIV-1) and p24 antigens of different clades in HIV-1-infected subjects vaccinated with HIV-1 immunogen (Remune)

The discovery of multiple subtypes of human immunodeficiency virus type 1 (HIV-1) worldwide has created new challenges for the development of both therapeutic and preventive AIDS vaccines. We examined T-helper proliferative responses to HIV-1 clade A, B, C, G, and E whole-killed virus and to HIV-1 clade G and B core (p24) antigens in HIV-1-infected subjects taking potent antiviral drugs who received HIV immunogen (Remune) therapeutic vaccination. Subjects who were immunized mounted strong proliferative responses to both whole virus and core antigens of the different clades. These results suggest that a whole-killed immunogen may have broad applications as a therapeutic as well as a preventive vaccine in the current multiclade HIV-1 pandemic.

Molecular characterization of a recombinant HIV type 1 isolate (A/G/E/?): unidentified regions may be derived from parental subtype E sequences

Recombination is one of several factors contributing to the genetic diversity of HIV-1, which is divided into group M (itself comprising 11 subtypes, A-K) and two other groups named O and N. In the present study, the full-length genome of an HIV-1 isolate obtained from a Greek subject (GR17) infected in the Democratic Republic of the Congo (formerly Zaire) was analyzed to reveal a novel mosaic sequence composed of subtypes A, G, and E and regions of indeterminate classification. In particular, most of pol and tat/vpu, as well as the region encoding intracellular domain of gp41, did not cluster with any of the previously characterized HIV-1 subtypes. The clustering of the LTR of GR17 with subtype E was suggestive of a subtype E origin of the unclassified regions. However, the identification of distinct characteristics in the LTR, such as two functional NF-kappaB sites and a distinct TAR element, compared with those of circulating (A/E) recombinants, suggests that the partial subtype E sequences found in GR17 and the mosaic viruses (A/E) have not derived from each other. These results provide evidence that parental subtype E may have existed in the geographic area of Central Africa.

Enhancement of HIV type 1 antigen-specific CD4+ T cell memory in subjects with chronic HIV type 1 infection receiving an HIV type 1 immunogen

We examined HIV-1 specific memory helper T immune responses in chronically HIV-infected subjects who received an immune-based therapy (HIV-1 immunogen, Remune). Subjects in this study exhibited significant increases (p < 0.05) in the frequency of helper T memory cells expressing interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in response to HIV-1 antigens in vitro. The frequencies of HIV-specific memory T cells increased after successive immunizations and exhibited a correlation with the standard tritiated thymidine incorporation lymphocyte proliferation assay (r = 0.72, p < 0.0008). These results support the notion that HIV-specific memory immune responses can be stimulated in subjects with chronic HIV infection. Further investigations are warranted to determine whether the induction of such responses is associated with virologic control.

Spread of distinct human immunodeficiency virus type 1 AG recombinant lineages in Africa

To identify new subtype G human immunodeficiency virus type 1 (HIV-1) strains and AG recombinant forms, we collected 28 serum samples from immigrants to the Netherlands from 12 countries throughout Africa. Based on the gag sequences 22 isolates were identified as subtype A or G. Phylogenetic analysis of discontinuous regions of the gag (726 nt), pol (1176 nt) and env (276 nt) genes revealed 13 AG recombinants with the mosaic structure A(gag)/G(pol)/A(env), three with A(gag)/G(pol)/G(env) and one other with A(gag) /G(pol)/G(env), in addition to 'pure' subtypes A(gag)/A(pol)/A(env) (n=1) and G(gag)/G(pol)/G(env) (n=4). To analyse the crossover points in more detail, a new RT-PCR was developed resulting in a large contiguous sequence of 2600 nt from the gag region to half the pol region. All the 13 A(gag)/G(pol)/A(env) recombinants appeared to belong to the circulating recombinant form (CRF) AG (IbNG). The three A(gag)/G(pol) /G(env) recombinants differed from the CRF AG (IbNG) subtype, suggesting the identification of a new CRF subtype. The recovery of AG recombinants from African countries a thousand miles apart indicates the active spread of new recombinants.

Presence of multiple HIV subtypes and a high frequency of subtype chimeric viruses in heterosexually infected women

The HIV-1 subtype distribution was determined in 41 HIV-positive women (-8% of all HIV-infected women in Denmark) belonging to different risk groups. HIV p17 gag and env gene subtypes were determined by DNA sequence analysis. Five different HIV subtypes were detected across all patients. Most HIV-1-positive women of Danish origin carried subtype B viruses, and a minority had virus belonging to subtypes A or C. All injecting drug users (IDUs) were infected with HIV subtype B viruses, whereas all non-B subtypes were present in cases linked to heterosexual transmission. In contrast, all women of African origin carried non-B HIV subtypes (subtypes A, C, D, or G) regardless of transmission mode. Of these women, 21% infected with non-B HIV subtypes appeared to be infected by subtype chimeric viruses and 7% were jointly infected with viruses belonging to two different subtypes (A and C). Data demonstrate a preferential representation of non-B HIV subtypes in women infected through heterosexual contact, as well as a high degree of recombination between viruses derived from endemic areas in which several HIV subtypes predominate. Combined with the increased incidence of heterosexual transmission of HIV, the results imply that an increased subtype diversity can be anticipated in newly infected individuals.

Cell-associated HIV-1 messenger RNA and DNA in T-helper cell and monocytes in asymptomatic HIV-1-infected subjects on HAART plus an inactivated HIV-1 immunogen

OBJECTIVE

We examined the effect of an HIV-1-specific immune-based therapy on cell-associated HIV-1 DNA and RNA.

DESIGN

Five HIV-1-infected subjects receiving HIV-1 immunogen plus HAART were compared with three HIV-1-infected subjects who received incomplete Freund's adjuvant (IFA) plus HAART.

METHODS

Cell-associated HIV-1 RNA or DNA in lymphocytes and monocytes was determined using a dual immunophenotyping/in situ hybridization assay with or without in situ PCR amplification.

RESULTS

Cell-associated HIV-1 RNA in CD4 cells correlated with plasma RNA overall. CD4, HIV-1 gag-pol messenger (m)RNA+ cells decreased in the immunogen plus HAART group compared with the IFA plus HAART group. Decreases in HIV-1 DNA+ CD4 cells were observed in the immunogen plus HAART compared with the IFA plus HAART group. Decreases in HIV-1 gag-pol mRNA+ monocytes were observed in the immunogen plus HAART group compared with the IFA plus HAART group. Consistent with the findings in CD4 cells, decreases in HIV-1 DNA+ monocytes were observed in the immunogen plus HAART group compared with the IFA plus HAART group.

CONCLUSIONS

These preliminary observations support the rationale for examining the combination of immune-based therapies and antiretroviral drugs for effective HIV-1 control.

Distinct expression patterns and transforming properties of multiple isoforms of Ost, an exchange factor for RhoA and Cdc42

A search for transforming genes expressed in brain led to the identification of a novel isoform of Ost, an exchange factor for RhoA and Cdc42. In addition to the Dbl-homology (DH) and pleckstrin-homology (PH) domains identified in the original Ost, this isoform contained a SH3 domain and a novel HIV-Tat related (TR) domain. The presence or absence of these domains in Ost defined multiple isoforms of the protein. RT - PCR and in situ hybridization analysis revealed that these isoforms were generated by tissue-specific and developmentally restricted alternative splicing events. Whereas deletion of the N-terminus activated the transforming properties of Ost, the presence of the SH3 domain reduced the transforming activity of the protein. This inhibition was relieved by the presence of a TR domain, which contained a potential SH3 ligand sequence. The transforming activity of all Ost isoforms was inhibited by dominant negative forms of the Rho family proteins. Expression of Ost isoforms potently induced the formation of actin stress fibers and filopodia as well as JNK activity and AP1- and SRF-regulated transcriptional pathways. Ost transfectants also displayed elevated levels of cyclins A and D1, suggesting that the de-regulation of these cyclins is linked to Ost-mediated transformation.

An isolate of human immunodeficiency virus type 1 originally classified as subtype I represents a complex mosaic comprising three different group M subtypes (A, G, and I)

Full-length reference clones and sequences are currently available for eight human immunodeficiency virus type 1 (HIV-1) group M subtypes (A through H), but none have been reported for subtypes I and J, which have only been identified in a few individuals. Phylogenetic information for subtype I, in particular, is limited since only about 400 bp of env gene sequences have been determined for just two epidemiologically linked viruses infecting a couple who were heterosexual intravenous drug users from Cyprus. To characterize subtype I in greater detail, we employed long-range PCR to clone a full-length provirus (94CY032.3) from an isolate obtained from one of the individuals originally reported to be infected with this subtype. Phylogenetic analysis of C2-V3 env gene sequences confirmed that 94CY032.3 was closely related to sequences previously classified as subtype I. However, analysis of the remainder of its genome revealed various regions in which 94CY032.3 was significantly clustered with either subtype A or subtype G. Only sequences located in vpr and nef, as well as the middle portions of pol and env, formed independent lineages roughly equidistant from all other known subtypes. Since these latter regions most likely have a common origin, we classify them all as subtype I. These results thus indicate that the originally reported prototypic subtype I isolate 94CY032 represents a triple recombinant (A/G/I) with at least 11 points of recombination crossover. We also screened HIV-1 recombinants with regions of uncertain subtype assignment for the presence of subtype I sequences. This analysis revealed that two of the earliest mosaics from Africa, Z321B (A/G/?) and MAL (A/D/?), contain short segments of sequence which clustered closely with the subtype I domains of 94CY032.3. Since Z321 was isolated in 1976, subtype I as well as subtypes A and G must have existed in Central Africa prior to that date. The discovery of subtype I in HIV-1 hybrids from widely distant geographic locations also suggests a more widespread distribution of this virus subtype, or at least segments of it, than previously recognized.

Effect of HIV-specific immune-based therapy in subjects infected with HIV-1 subtype E in Thailand

OBJECTIVE

To examine the effect of treatment with an inactivated, gp120-depleted, HIV-1 immunogen (Remune) in 30 Thai subjects infected with HIV-1 subtype E.

DESIGN

Sixty-week open-label study.

METHODS

Thirty HIV-positive volunteers with CD4 cell counts > or = 300 x 10(6)/l were given intramuscular injections of Remune into the triceps muscle on day 1 and then at weeks 4, 8, 12, 24, 36, 48 and 60.

RESULTS

Treatment with Remune was well-tolerated and augmented HIV-1-specific immune responses. Furthermore, subjects had a significant increase in CD4 cell count (P < 0.0001), CD4 cell percentage (P < 0.0001), CD8 cell percentage (P < 0.0001), and body weight (P < 0.0001) compared with pretreatment levels. Fourteen subjects with detectable viral load at day 1 showed a decrease at week 60 (P=0.04). Retrospective Western blot analysis showed 23 subjects with increased intensity of antibody bands and 15 patients showed development of new reactivities to HIV proteins, especially towards p17 and p15.

CONCLUSION

These results indicate that HIV-specific immune-based therapeutic approaches such as Remune should be further examined in countries with different clades of HIV-1 and where access to antiviral drug therapies is limited.

Full genome sequences of human immunodeficiency virus type 1 subtypes G and A/G intersubtype recombinants

Multiple genetic subtypes and intersubtype recombinant strains have been identified among isolates of HIV-1. The greatest diversity of strains has been recovered from Central Africa, where mixtures of subtypes and recombinant forms have been recovered. However, many of the HIV-1 subtypes and recombinants have been characterized by partial rather than full-length genome sequencing. Here we report the first two virtually full-length genome sequences from HIV-1 subtype G, isolated in Sweden and Finland but originating in Congo and Kenya, and from two Djibouti isolates sharing the A/G recombinant structure of Nigerian isolate, IbNG. By comparison with reference sequences of other subtypes, it appears that the subtype G strains are largely nonrecombinant, while the Djibouti strains show alternating segments from subtypes A and G. In the cytoplasmic domain of the gp41 protein of the Djibouti viruses the E, G, and IbNG strains form a single cluster, separate from subtype A, clouding the subtype origin of these particular segments. Within the resolution of current technology, the structure of the Djibouti strains is identical to that of IbNG, establishing for the first time the geographic spread of this recombinant in Africa. The geographic spread of the IbNG-like strains suggests that, like the subtype E recombinants, these should be given a specific name to facilitate future identification and tracking; the name "IbNG subtype" is proposed.

Cross-clade immune responses after immunization with a whole-killed gp120-depleted human immunodeficiency virus type-1 immunogen in incomplete Freund's adjuvant (HIV-1 immunogen, REMUNE) in human immunodeficiency virus type-1 seropositive subjects

Lymphocyte proliferation responses to gp120-depleted HZ321 virus (clade A) antigen were compared to BAL human immunodeficiency virus (HIV) virus antigen (clade B) responses, clade E HIV virus antigen responses, and purified native p24 antigen responses in 15 human immunodeficiency virus type-1 (HIV-1) seropositive subjects immunized with a whole-killed inactivated gp120-depleted HIV-1 antigen in Incomplete Freund's adjuvant (HIV-1 immunogen, REMUNE). A significant increase in lymphocyte proliferation to HZ321 antigen was observed after immunization with the HIV-1 immunogen (p = 0.02). A strong association was demonstrated between the HIV-1 immunizing antigen, HZ321, and native p24 antigen responses (r = 0.80, p < 0.0001). Furthermore, a strong association in terms of proliferative responses was demonstrated between HZ321 virus (clade A) responses and BAL virus (clade B) (r = 0.95, p < 0.0001) and clade E virus antigen (r = 0.92, p < 0.0001). Proliferative responses to HIV antigens also correlated with baseline CD4 counts. Taken together, these results support the specificity of immune responses induced by REMUNE (HIV-1 immunogen). The development of cross-reactive immune responses between clades and to the more conserved epitopes of the virus have implications in the development of therapeutic and prophylactic HIV vaccines.

Human immunodeficiency virus type 1 intersubtype (B/E) recombination in a superinfected chimpanzee

Genetic characterization of a large number of human immunodeficiency virus type 1 (HIV-1) isolates indicates that at least 10% of all strains have mosaic genomes generated by recombination between viruses of the same or different subtypes or clades. What is not known, however, is the time between infection with the first and second HIV-1 strains as well as the time between infection with the second strain and the recombinational event. After 32 months of infection with HIV-1(LAI(IIIB)), a chimpanzee was inoculated intravenously and became infected with a subtype E strain, HIV-1(90CR402). With PCR amplification, DNA heteroduplex analysis, and DNA sequencing, both parental strains and two distinct recombinant proviruses were found in genomic DNA from lymph node tissue obtained 24 weeks after exposure to HIV-1(90CR402). These results show (i) that antiviral immune responses established by long-term infection with an HIV-1 subtype B strain did not prevent infection by a subtype E strain and (ii) that both strains actively replicated and produced sufficient quantities of virus to coinfect the same cell(s), resulting in recombinant viruses.