Identification of a new human immunodeficiency virus type 1 distinct from group M and group O

A highly divergent HIV-1 isolate, designated YBF 30, was obtained in 1995 from a 40-year-old Cameroonian woman with AIDS. Depending on the genes studied, phylogenetic analysis showed that YBF30 branched either with SIVcpz-gab or between SIVcpz-gab and HIV-1 group M. The structural genes and tat, vpr, and nef of YBF30 are approximately equidistant from those of HIV-1 group M and SIVcpz-gab. In contrast, vif and rev are closer to HIV-1 group M, and vpu is highly divergent. Using a YBF30 V3 loop peptide enzyme immunoassay, we screened 700 HIV-1-positive sera collected in Cameroon; three reacted strongly with the YBF30 peptides and one was confirmed as being related to YBF30 by genetic analysis of a pol fragment. YBF30 is as distinct from SIVcpz-gab as it is from HIV-1 group M and can thus be considered as the prototype strain of a new human immunodeficiency virus group.

Genetic characterization of accessory genes from human immunodeficiency virus type 1 group O strains

Human immunodeficiency virus type 1 (HIV-1) group O strains have been described as highly divergent, compared with the vast majority of the viruses involved in the worldwide AIDS pandemic, classified in group M. To gain new insights into the diversity and genetic characteristics of group O, we have sequenced the accessory gene region (from vif to vpu) of 14 isolates. Analyses of the deduced amino acid sequences for Vif, Vpr, the first exon of Tat, and Vpu indicate that most of the functional domains of these proteins, as described for group M viruses, are highly conserved and retained among all the group O strains we have characterized. The only difference concerns the Vif phosphorylation sites, which are absent in all of the group O isolates we have sequenced; in contrast, they are well conserved in nearly all of the group M isolates, in which they play critical roles in the regulation of viral replication and infectivity. As already observed for group M isolates, the Vpu protein is also highly diverse among group O strains. Phylogenetic analyses of these sequences indicate that HIV-1 group O can be separated into four different clusters, containing most of the strains we have characterized (except one, which clusters outside of the analyzed viruses). Taking into account the criteria used for clades in group M, we were not able to define group O clades definitively.

Differential diagnosis of HIV type 1 group O and M infection by polymerase chain reaction and PstI restriction analysis of the pol gene fragment

HIV-1 group O serological screening or confirmation strategies so far have not proved 100% sensitive and specific, indicating a lack of antibody reactivity or cross-reactivity with group O antigens. Therefore, genetic analysis currently represents the only method by which confirm presumed HIV-1 group O or group O/M infections. We have optimized the sensitivity (100%) and specificity (100%) of an HIV-1 group O/M-specific PCR of a pol gene fragment. In addition, we report on a highly sensitive (97.2%) and specific (100%) method for differentiation between HIV-1 group O and group M viruses, using PCR and PstI enzyme restriction fragment analysis of a pol fragment. Compared with sequencing, these methods are fast, inexpensive, and simple.

HIV type 1 diversity and the reliability of the heteroduplex mobility assay

We investigated HIV-1 diversity by means of heteroduplex mobility assay (HMA) genotyping. We studied 199 samples from patients originating from 26 countries and living in France. The HMA successfully genotyped 182 (91%) of these samples, as follows: 77 (42%) subtype A, 57 (31%) subtype B, 5 (3%) subtype C, 5 (3%) subtype D, 8 (4%) subtype E, 22 (12%) subtype F, 5 (3%) subtype G, and 3 (2%) subtype H. We were not able to genotype 12 samples by means of the HMA. These latter strains were sequenced, and phylogenetic analyses revealed that they were highly divergent subtype A-, D-, or G-related strains. Eight (of 12) subtype D strains were indeterminate by HMA, owing to the broad intrasubtype diversity, suggesting that new reference subtype D plasmids are required, as previously proposed. Thirty-seven strains belonging to the different subtypes were sequenced, and the results showed perfect concordance with the HMA results. Interlaboratory quality controls confirmed the reliability of the HMA for HIV-1 subtyping, despite the extensive viral variability. However, plasmid selection must be continuously revised to cover viral diversification.

HIV-1 diversity in Romania

OBJECTIVES

To evaluate the prevalence and the dynamics of HIV-1 subtypes in Romanian adults and children, and to investigate the origins of the nosocomial epidemic.

DESIGN

A total of 1000 serum and plasma samples, from adults (n = 579) and children (n = 421) who were diagnosed as being HIV-1-infected during 1990-1997 in 39 of the 41 Romanian districts, were serotyped. Viral DNA was isolated from blood samples of 84 patients and the viruses were genotyped.

METHODS

Serotyping was performed with a peptide subtype-specific enzyme immunoassay (SSEIA), based on in vitro competition for antibody binding between the representative V3 peptides of the different clades (A-F). Proviral HIV-1 DNA was genotyped by heteroduplex mobility assay or by sequence analysis of the C2-V3 env region.

RESULTS

SSEIA showed that 93% of the samples from horizontally infected children were serotype F, 1% were serotype B, and the remaining 6% were uninterpretable. In vertically infected children, 74% of strains were serotype F, 10% were serotype A, 3% were serotype B, and 3% were serotype E. Serotype F was also the dominant subtype in adults (68%), but serotypes A, B, C, D and E were also detected. SSEIA gave indeterminate results in 7% of cases. A strong correlation (90%) between serotyping and genotyping for subtype F was found. Analysis of the relative incidence of the different serotypes over a 7-year period (1990-1997) showed a stable distribution.

CONCLUSIONS

Subtype F largely dominates the epidemiology of HIV-1 infection in both children and adults in Romania, although other major subtypes are present. The predominance of subtype F in Romania may be a future potential source of HIV-1 variability in Europe.

Human immunodeficiency virus type 1 subtype F reverse transcriptase sequence and drug susceptibility

We sequenced and phylogenetically analyzed the reverse transcriptase (RT) regions of the pol genes of 14 human immunodeficiency virus type 1 (HIV-1) isolates from Romanian patients, which were classified as subtype F on the basis of env gene structure. The RT sequences showed that the strains clustered phylogenetically and were equidistant from other HIV-1 subtypes as shown by the neighbor-joining and maximum-likelihood methods, allowing us to define HIV-1 subtype F according to the pol classification. The subtype F RT sequences differed from reported group M RT sequences by 10.94% (for nucleotides) and 7.6% (for amino acids). Phenotypic analysis of subtype F susceptibility to three classes of antiretroviral compounds showed an increase in the 50% inhibitory concentration of the tetrahydroimidazo[4,5,1-jk] [1,4]-benzodiazepin-2-(1H)-one and -thione (TIBO) derivate R82913 for one strain which was naturally resistant to this compound. This first report of subtype F pol sequences confirms the perfect correlation between the phylogenetic positions determined by env and pol analyses and suggests that virus variability might influence the efficacy of antiretroviral treatments. This finding warrants a global evaluation of the phenotypic and genotypic susceptibility of HIV-1 subtypes to antiretroviral drugs.

Highly sensitive method for amplification of human immunodeficiency virus type 2 DNA

We evaluated a new human immunodeficiency virus type 2 (HIV-2) DNA amplification strategy based on peripheral blood mononuclear cell long PCR (XL PCR) followed by nested PCR amplification. The primers used were located in the highly conserved long terminal repeat and in the pol regions of the genome. Five primer pairs corresponding to different regions of the HIV-2 env gene were used in the nested step. Samples from 42 patients were tested, which yielded positive amplification with at least two primer pairs in 40 (95%) samples. A primer pair (EB2/EB5) located on the V3 region succeeded in amplifying proviral DNA in 40 samples.

HIV-1 detection in cervicovaginal secretions during pregnancy

OBJECTIVE

To assess the reproducibility of and factors associated with HIV detection in cervicovaginal secretions (CVS).

DESIGN

Longitudinal study of 43 HIV-1-infected pregnant women in Paris.

METHODS

HIV DNA was detected in peripheral blood mononuclear cells (PBMC) by Amplicor and gag nested polymerase chain reaction (PCR) assays. The HIV genotype was determined by heteroduplex mobility assay. Amplicor and gag nested PCR assays were performed on serial CVS samples for HIV DNA detection, and the HIV Monitor test was used for HIV RNA detection in plasma and CVS.

RESULTS

A total of 144 CVS samples were collected from the women included in the study. HIV-1 DNA was detected in 36 (25%) of the 144 samples, from 16 (37.2%) of the 43 women. Results of HIV-1 DNA detection were concordant in the first two samples in 27 (84.4%) of the 32 women with at least two CVS samples. The last CVS sample collected in each woman was HIV-1 DNA-positive in 13 (30.2%) of the 43 women. Three factors were found to be independently associated with HIV-1 DNA detection in CVS: HIV-1 subtype B, absence of zidovudine therapy, and microbial cervicovaginal infection. HIV RNA was detected in CVS from 10 (23.3%) out of 43 women and correlated with DNA detection in the same sample and HIV RNA detection in plasma.

CONCLUSIONS

DNA and RNA PCR can be used to detect HIV in cells and supernatants of CVS. These techniques may be useful in cohort studies to investigate HIV transmission and to evaluate the efficacy of antiretroviral drugs to reduce HIV excretion.

Susceptibility of human immunodeficiency virus type 1 group O isolates to antiretroviral agents: in vitro phenotypic and genotypic analyses

We investigated the phenotypic and genotypic susceptibility of 11 human immunodeficiency virus type 1 (HIV-1) group O strains to nucleoside and nonnucleoside reverse transcriptase (RT) inhibitors and protease inhibitors in vitro. Phenotypic susceptibility was determined by using a standardized in vitro assay of RT inhibition, taking into account the replication kinetics of each strain. HIV-1 group M and HIV-2 isolates were used as references. DNA from cocultured peripheral blood mononuclear cells was amplified by using pol-specific group O primers and cloned for sequencing. Group O isolates were highly sensitive to nucleoside inhibitors, but six isolates were naturally highly resistant to all of the nonnucleoside RT inhibitors tested. Phylogenetic analysis of the pol gene showed that these isolates formed a separate cluster within group O, and genotypic analysis revealed a tyrosine-to-cysteine substitution at residue 181. Differences in susceptibility to saquinavir and ritonavir (RTV) were not significant between group O and group M isolates, although the 50% inhibitory concentration of RTV for group O isolates was higher than that for the HIV-1 subtype B strains. The study of HIV-1 group O susceptibility to antiretroviral drugs revealed that the viruses tested had specific phenotypic characteristics contrasting with the group M phenotypic expression.

Synthetic peptide ELISAs for detection of and discrimination between group M and group O HIV type 1 infection

We developed and evaluated two peptide-based immunoassays to confirm and discriminate between group M and group O HIV-1 infection. These assays are based on in vitro competition for antibody binding between M and O peptides. The first EIA is based on competition between group M and group O gp41 immunodominant domains and the second on competition between group O and group M V3 regions of gp120. Two panels of sera were used: the first consisted of 109 sera collected from 27 group O- and 92 group M-infected patients in whom the HIV isolates had been genotyped by sequencing or heteroduplex mobility assay. In this panel, the combination of the two assays correctly discriminated 106 samples (100% group O and 96.7% group M samples). The second panel, used for the field evaluation of the two assays, consisted of 157 samples from HIV-1-infected Cameroonian patients, 33 strains having been genotyped. The combination of the two techniques in a serogrouping algorithm discriminated 147 of these samples, 74 being HIV-1 group O and 73 group M. These results always correlated with genotyping results. The 10 sera that were not successfully classified by these assays were from early seroconverters. Altogether, the two assays clearly differentiated 263 of 276 (94.9%) samples in the two panels. On the basis of the genotyping results, the positive predictive value for group discrimination in the two panels was 100% for both GSEIA assays. Our peptide-blocking group-specific EIAs for differentiation and confirmation of HIV-1 group M and group O infection are complementary tools for epidemiological studies and surveillance of HIV-1 group O strain trafficking.

Diversity of the immunodominant epitope of gp41 of HIV-1 subtype O and its validity for antibody detection

The immunodominant regions of the gp41 from 13 HIV-1 subtype O strains from Cameroon, 11 from France and one from Germany were sequenced. The amino acid sequences were compared to those of the 3 published HIV-1 subtype O isolates, ANT70, MVP-5180 and VAU. All HIV-1 subtype O isolates had a very conserved amino acid sequence in this region and showed a subtype O specific structure. Within the cysteine loop there was a positive charge of two basic amino acids, arginine and lysine. Only two strains (CM.6778 and CM.8161) showed an acidic amino acid in this loop. None of the isolates showed the same amino acid sequence in this immunodominant region. A 25 residue peptide from the immunodominant domain of gp41 of the MVP-5180 strain was synthesized, cycled to form the cysteine-loop and coated to microtiter plates. Antibody binding was detected by indirect ELISA using an enzyme labeled anti-human IgG. Out of 111 anti-HIV-1 positive specimens, collected mainly from Cameroonian HIV infected patients, only 10 were not reactive in this assay. The 42 anti-HIV-1 subtype O positive specimens gave all a reaction above cut off. Despite the diversity found in the amino acid sequences within the 25 isolates a peptide-based indirect ELISA representing the immunodominant epitope of the strain MVP-5180 successfully detected all the anti-HIV-O sera so far tested, pointing to the importance of adding such a peptide for correct identification of HIV-1 subtype O infected patients, while some assays without HIV-O specific antigens partially fail to detect all anti-HIV-O specimens.

Serological and virological characterization of HIV-1 group O infection in Cameroon

OBJECTIVES

To study the presence of HIV-1 group O infection among HIV-infected people in Cameroon and to further characterize the HIV-1 group O infections.

DESIGN AND METHODS

During a 2-year survey (1994-1995), all samples tested positive in screening methods in the National Reference and Public Health Laboratory, Centre Pasteur, Yaoundé, Cameroon were identified as HIV-1 group M, HIV-1 group O or HIV-2 by using a serological algorithm. HIV-1 group M and HIV-1 group O were distinguished on the basis of competitive enzyme-linked immunosorbent assay (ELISA) reactivity against gp41 group M recombinant protein. HIV-1 group O infections were confirmed by using group O-specific V3 synthetic peptides. HIV-1 group O strains were isolated by lymphocyte cocultures, proviral DNA was amplified with specific primers, and sequencing was performed on the C2V3 and gag regions.

RESULTS

Of the 8,331 screened samples, 3,193 were HIV-reactive, 2,376 (74%) of which were considered to belong to group M. The 817 (26%) that had reacted poorly or not at all against group M gp41 were further characterized: 10 were confirmed as HIV-2 and 82 as HIV-1 group O, the others being indeterminate (n = 285) or negative (n = 440). The frequency of group O relative to group M ranged from 1% in Far North province to 6.3% in the capital. There was no difference in sex, age or frequency of clinical manifestations between group M and group O infections. Group O infection was confirmed in a subset of cases by polymerase chain reaction (n = 14), with perfect concordance. Sequencing and phylogenetic analyses confirmed the high variability inside group O.

CONCLUSIONS

Group O and group M epidemiological patterns are known to be similar so the reason for the lower prevalence of group O remains to be found. The wide distribution of group O infection in all Cameroonian provinces underlines the importance of further characterizing the epidemic spread and diffusion of this group.

Lack of screening test sensitivity during HIV-1 non-subtype B seroconversions

OBJECTIVE

To evaluate the serological consequences of HIV-1 group M diversity we studied the ability of screening tests to detect anti-HIV antibodies in early seroconverters infected by different HIV subtypes.

SETTING

Virology Department, Bichat-Claude Bernard Hospital, Paris, France.

DESIGN AND METHODS

Symptomatic patients with serial samples and with infective strains characterized by heteroduplex mobility assay. In each case, two sera were selected. The first (pre-seroconversion sample) was the last p24 antigen-positive/Western blot-non-reactive sample. The second (seroconversion sample) was the first Western blot-reactive sample. One second-generation enzyme immunoassay (EIA; Abbott) based on anti-human immunoglobulin (Ig) G-conjugate and three third generation EIA (Abbott; Enzygnost; Genscreen) based on the double antigen sandwich principle, detecting IgM and IgG, were used.

RESULTS

Ten patients had subtype B strains and nine had non-B strains (seven were A, one E and one G). The Abbott third-generation test was more sensitive than the second generation test for pre-seroconversion subtype B samples (nine versus four out of 10; P < 0.05), but not for non-B subtypes; only two of the nine non-B sera tested were positive by both EIA. Positivity rates and optical densities differed (P < 0.05) between B and non-B subtypes in all third-generation EIA. There was no significant difference between the subtype B and non-B groups with regard to the interval between the pre-seroconversion sample and the seroconversion sample (subtype B, 6.7 +/- 2.6 days; non-B, 5.2 +/- 1.7 days). No significant difference in positivity rates and optical densities were found between B and non-B subtypes in these seroconversion samples.

CONCLUSION

The shorter time since HIV infection required for sera to become reactive in third-generation EIA screening tests is due to better sensitivity for subtype B strains only. These results stress the importance of strict donor selection, the need to test screening kits against large panels of all subtypes, and the place of p24 antigen testing in closing the window of seroconversion.

HIV type 1 diversity in northern Paris, France

During a 6-month period, we studied the diversity of HIV-1 subtypes in 392 adult patients seen in Bichat-Claude Bernard Hospital, northern Paris, France. All the samples were serotyped and a subset was genotyped by means of HMA. Serotyping was performed with a new peptide subtype-specific EIA (SSEIA), based on in vitro competition for antibody binding between the representative V3 peptides of the different clades (A to E). HMA with plasmids from clades A to H gave unambiguous results on 105 of the 116 samples tested. The agreement between SSEIA and HMA was 36/41 for subtype B, 2/2 for subtype D, and 4/5 for subtype E. We found a discrepancy in the results between clade A and C: the patients with sera reacting to peptide C were confirmed by HMA as being infected by clade A strains. Three patients reactive with peptide A were infected by a subtype F. These results indicate that peptide cross-reactivity, even in the SSEIA format, hinders serotyping. In 11 samples, all from African patients, the subtype remained indeterminate because PCR or HMA failed. Caucasian patients (n = 223) were mainly infected by subtype B. HMA and/or SSEIA revealed non-subtype B infection in 14 Caucasians, who were infected by the sexual route overseas or in France. Patients originating from other countries (mainly in Africa) exhibited a broad strain diversity, with most of the different subtypes so far described being represented. This study confirms the frequency of subtype B strains in Caucasians living in France, but emphasizes the emergence of the different HIV-1 subtypes in Paris, together with the extent of strain trafficking. Discordances between serotype and genotype assays confirm that both tests require additional development.

Detection of circulating human immunodeficiency virus type 2 in plasma by reverse transcription polymerase chain reaction

Genomic RNA was detected using a reverse transcription (RT) nested polymerase chain reaction (PCR) method on plasma from 24 HIV2-infected patients. Results were interpreted based on immune and clinical status and results of plasma and cellular viraemia assays. Amplification of RNA extracted from plasma was positive in 13 of the 24 cases studied (54%). There was a negative correlation between the detection of RNA in plasma and the patients' CD4+ cell counts: all 5 patients with counts below 200 x 10(6)/l were RT-PCR RNA-positive, compared to only 4 of the 12 patients with counts above 500 x 10(6)/l. Cellular viraemia was positive in 12 of the 24 patients, and the results correlated with the CD4+ cell count. HIV2 was isolated from the plasma of 3 of the 24 patients, all of whom had CD4+ cell counts below 200 x 10(6)/l. The small viral load in HIV2-infected patients before the onset of immunodeficiency appeared to be a major limiting factor in the detection of the virus with current tests. The low percentage of RNA-positive plasma samples contrasts with the high rate of positivity in HIV1-infected patients. Differences in viral load and replication between HIV1 and HIV2 correlate with differences in the epidemiology and pathogenicity of the two viruses.

Variability of human immunodeficiency virus type 1 group O strains isolated from Cameroonian patients living in France

Human immunodeficiency virus type 1 (HIV-1) nucleotide sequences encoding p24Gag and the Env C2V3 region were obtained from seven patients who were selected on the basis of having paradoxical seronegativity on a subset of HIV enzyme-linked immunosorbent assay detection kits and having atypical Western blot (immunoblot) reactivity. Sequence analyses showed that all of these strains were more closely related to the recently described Cameroonian HIV isolates of group O (HIV-1 outlier) than to group M (HIV-1 major). All seven patients had Cameroonian origins but were living in France at the time the blood samples were taken. Characterization of a large number of group M strains has to date revealed eight distinct genetic subtypes (A to H). Genetic distances between sequences from available group O isolates were generally comparable to those observed in M intersubtype sequence comparisons, showing that the group O viruses are genetically very diverse. Analysis of sequences from these seven new viral strains, combined with the three previously characterized group O strains, revealed few discernable phylogenetic clustering patterns among the 10 patients' viral sequences. The level of diversity among group O sequences suggests that they may have a comparable (or greater) age than the M group sequences, although for unknown reasons, the latter group dispersed first and is the dominant lineage in the pandemic.

[Virulence of human immunodeficiency virus]

Virulence is relative capacity of a virus, compared to other closely related viruses, to produce disease in a host. Viral strains considered as virulent have been described in HIV-1 infected patients. They are characterized in vitro by enhanced cellular host range, rapid kinetic of replication and increased capacity of syncytium induction. Some genetic modification of the V3 loop in the envelope gene have been associated with the emergence of these strains. But at AIDS diagnosis, and even at the terminal stage of AIDS, only about half of the patients harbour syncytium inducing variants. There are much evidence for continuous viral replication throughout all stages of HIV-1 infection. There is no viral latency state in the natural HIV infection. This increasing viral burden might have a pivotal role in the pathogenesis of HIV disease. HIV-2 is less pathogenic than HIV-1. The nature of the viral determinants responsible for this reduced virulence remains unknown. In the simian immunodeficiency virus model, virulent and avirulent strains have been described and the nef gene seems to have a critical role in pathogenicity.

Comparative study of single and nested PCR for the detection of proviral HIV2 DNA

We have tested seven pairs of primers for the detection of HIV2 DNA by single PCR in positive cultures from 21 infected patients. Four of these primer pairs were then used in a comparative study of single and nested PCR for the detection of HIV2 in fresh lymphocytes from 33 patients infected by the virus. HIV2 DNA was detected in 17 of the 33 patients (51.5%) by single PCR and 29/33 (88%) by nested PCR. All the patients negative in both nested and single PCR were asymptomatic and had CD4+ lymphocyte counts of at least 500 x 10(6)/l. This lack of PCR sensitivity for the detection of proviral HIV2 DNA in fresh lymphocytes cannot be totally attributed to genetic variability and may be related to a low viral load in asymptomatic HIV2-infected patients.

HIV-1/HIV-2 seronegativity in HIV-1 subtype O infected patients

Nine patients with atypical HIV-1 western blot profiles were diagnosed as having HIV-1 subtype O infection. All the patients were living in France; eight originated from Cameroon and one from France. Lymphocyte DNA amplification by the polymerase chain reaction was only positive when HIV-1 subtype O specific primers were used. Preliminary sequence analysis of amplified products and serological reactivity against a specific subtype O synthetic env peptide confirmed HIV-1 subtype O infection. HIV-1/HIV-2 enzyme-linked immunosorbent assays, especially those based on env peptides or on the sandwich format, can be negative in HIV-1 subtype O infection.

[Reactivity differences between serums of patients infected with HIV-2 and HIV-1 antigens according to the patients' geographic origin]

We tested 98 sera from HIV-2-infected patients for cross-reactivity with HIV-1 antigens in a competitive EIA test and western blotting. The sera were obtained during epidemiological surveys in Cape Verde Islands (n = 47) and Mali (n = 51). There were significantly more cross reactions with sera from Mali. Similar results were obtained with sera from African patients resident in France. Samples from HIV-2-infected patients from Burkina Faso, Ghana, Ivory Coast and Mali were more often reactive with HIV-1 antigens than were those from HIV-2-infected patients from the western Atlantic coast (Cape Verde, Guinea Bissau and Senegal). These data underline the importance of using specific tests for HIV-2 sero-positivity, and the need to include a panel of HIV-2-positive sera of different geographic origins in quality control kits.

Cellular and plasma viral load in patients infected with HIV-2

OBJECTIVE

To determine circulating viral load in HIV-2-infected individuals.

METHODS

Viral load was determined in 40 HIV-2-infected adults using standardized quantitative cell and qualitative plasma viraemia assays. We also tested for proviral HIV-2 DNA using single and nested polymerase chain reaction (PCR) in fresh lymphocytes from 27 subjects. The results were compared, on the basis of the CD4+ lymphocyte count, with our published data for HIV-1 infection.

RESULTS

HIV-2 was isolated from peripheral blood mononuclear cells (PBMC) from 19 individuals and plasma from four patients. The rate of cell and plasma viraemia positivity correlated with the CD4+ cell count and HIV-2 virus load increased as the CD4+ cell count fell. The cellular HIV-2 load in the patients with a CD4+ count < 200 x 10(6)/l was similar to reported values for HIV-1, but the HIV-2 isolation rate from the plasma of these individuals was significantly lower than for HIV-1. When the CD4+ count was between 200 and 500 x 10(6)/l, the rate of HIV-2 isolation from plasma and the cellular virus load were both significantly lower than for HIV-1. When the CD4+ count was > 500 x 10(6)/l, HIV-1 and HIV-2 were undetectable in plasma and HIV-1 was isolated from PBMC in significantly more cases than HIV-2. By single PCR, amplification were positive in 14 out of 27 subjects and there was a correlation between positivity and CD4+ cell count. By nested PCR, only four of the 27 subjects, all with a high CD4+ count, remained negative.

CONCLUSIONS

Differences in viral load between individuals infected with HIV-2 and those infected with HIV-1 could partly account for reported differences in the pathogenicity of the two viruses.