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P N Fultz

Publications and source records attributed to P N Fultz.

At least 19 recordsLinked to original sources
PubMed1998

Fine specificity of anti-V3 antibodies induced in chimpanzees by HIV candidate vaccines.

The fine specificity of the anti-V3 antibody responses induced in chimpanzees immunized by various human immunodeficiency type 1 (HIV-1) candidate vaccines and challenged by heterologous strains of HIV-1 was analyzed by enzyme-linked immunosorbent assay (ELISA) and Pepscan epitope mapping. Two chimpanzees immunized with the recombinant canarypox virus ALVAC-HIV (vCP125) expressing gp160MN and boosted with purified gp160MN/LAI alone, then with both immunogens in combination, were not protected against challenge with HIV-1 SF2. Their sera mainly recognized one epitope of the V3 loop, located in the NH2-terminal half. By contrast, immunization of two other chimpanzees with purified gp160MN/LAI and boosting with a synthetic V3MN peptide elicited a strong anti-V3 antibody response with a broader specificity directed against multiple epitopes all along the V3 loop. These chimpanzees were protected against infection by HIV-1 SF2. However, when these two chimpanzees were challenged later with a HIV-1 clade E strain virus, they became infected. We failed to detect any reactivity with the peptide of the ectodomain of gp41 of sera harvested after immunization with the various immunogens or after challenge with HIV-1 SF2 or HIV-1 90CR402. These results demonstrated that anti-V3 antibodies with a restricted fine specificity were induced in chimpanzees immunized with gp160 purified or expressed by recombinant canarypox confirming our previous results obtained in three different species (human, guinea pig and, macaque). In contrast, a boost with the V3 peptide broadened antibody responses, suggesting that the mode of presentation of the V3 loop to the immune system strongly influences the epitope specificity of the resulting antibody response.

AIDS Vaccines↗
PubMed1998

Human and nonhuman primate lymphocytes engrafted into SCID mice reside in unique mesenteric lymphoid structures.

The present study compares the location and phenotype of B lineage lymphocytes in tissues from SCID mice engrafted with PBMC of human, chimpanzee, and pig-tailed macaque origin. In mice repopulated with both human and nonhuman primate lymphocytes, plasma cells were found in the peritoneal cavity in vascularized structures located in the mesentery near the pancreas, intestines, and spleen. The predominant isotype of the plasma cells was IgG; IgM and IgA cells were also present. Kappa and lambda light chains were expressed by 62% and 38% of the Ig-containing cells, respectively. J chain expression occurred in most cells irrespective of the Ig isotype. In the SCID mice engrafted with human lymphocytes, a few IgM-containing cells were found in the spleen; plasma cells were not found in other tissues, including the intestine. The aggregation of plasma cells did not appear to be a result of infection with EBV. T cells were rarely found in the lymphoid aggregates but were recovered from the spleen and peritoneal lavage. Human Ig levels in the serum of engrafted mice reflected the isotype distribution of the cells with IgG > IgM > or = IgA.

Adult↗
PubMed1998

HIV-1/simian immunodeficiency virus infection of human and nonhuman primate lymphocytes results in the migration of CD2+ T cells into the intestine of engrafted SCID mice.

Increased lymphocytic infiltration of intestinal tissues has been observed in patients infected with HIV-1 and in SIV-infected rhesus macaques. To determine whether HIV-1 and SIV infections influence the homing of human and nonhuman primate PBMC to intestinal tissues, we engrafted SCID mice with human or nonhuman primate PBMC and infected them with either cell-free or cell-associated HIV-1 or SIV. In mice that received both PBMC and virus, human or nonhuman primate CD2+ T cells were found in intestinal tissues, primarily in the intraepithelial lymphocyte compartment and lamina propria. Immunomagnetic sorting revealed that these cells were derived from the CD4+ population. Using gag-specific primers, PCR analysis of these tissues detected the presence of HIV-1 proviral DNA. However, in SCID mice that were engrafted with either human or nonhuman primate PBMC and no HIV-1 or SIV, CD2+ T cells were not detected in intestinal tissues. These results indicate that HIV-1 and SIV can modulate the migratory properties of human and nonhuman primate T cells in the SCID mouse model.

Animals↗
PubMed1998

Severe combined immunodeficient mice engrafted with macaque peripheral blood leukocytes support replication of SIVsmm.

Peripheral blood leukocytes (PBLs) from normal pigtail macaques were engrafted into severe combined immunodeficient C.B-17 scid/scid (SCID) mice to develop a small animal model in which to study and identify genetic determinants responsible for the acutely lethal disease syndrome induced by SIVsmmPBj14 (SIV-PBj14) in pigtail macaques. In vivo infection of macaques with SIV-PBj14 results in acute disease in all animals and death of most animals, depending on the route of infection, due to immune activation and production of inflammatory cytokines. A small animal model in which a similar acute disease syndrome was induced would facilitate screening of virus variants to identify regions of the SIV-PBj14 genome responsible for the unique phenotype. Although intraperitoneal inoculation of SCID mice with SIV-PBj14-infected PBLs or uninfected PBLs followed by cell-free SIV-PBj14 produced chimeric mac-PBL-SCID mice that supported SIV replication, obvious clinical signs of disease were not observed. SIV-infected macaque PBLs were recovered from spleen, bone marrow, peripheral blood, and the peritoneal cavity; cell-free SIV was recovered from peritoneal lavage fluid and serum or plasma. PBLs that were mitogen stimulated and SIV-PBj14 infected in vitro migrated rapidly and were recovered from the spleen and bone marrow as early as 1 day after inoculation of mice. The mac-PBL-SCID model may be useful for screening potential drug or immunomodulatory therapies before testing in macaques.

Animals↗
PubMed1998

HIV-1 Vpr increases viral expression by manipulation of the cell cycle: a mechanism for selection of Vpr in vivo.

The human immunodeficiency virus type 1 (HIV-1) encodes a protein, called Vpr, that prevents proliferation of infected cells by arresting them in G2 of the cell cycle. This Vpr-mediated cell-cycle arrest is also conserved among highly divergent simian immunodeficiency viruses, suggesting an important role in the virus life cycle. However, it has been unclear how this could be a selective advantage for the virus. Here we provide evidence that expression of the viral genome is optimal in the G2 phase of the cell cycle, and that Vpr increases virus production by delaying cells at the point of the cell cycle where the long terminal repeat (LTR) is most active. Although Vpr is selected against when virus is adapted to tissue culture, we show that selection for Vpr function in vivo occurs in both humans and chimpanzees infected with HIV-1. These results suggest a novel mechanism for maximizing virus production in the face of rapid killing of infected target cells.

Animals↗
PubMed1998

Extensive diversification of human immunodeficiency virus type 1 subtype B strains during dual infection of a chimpanzee that progressed to AIDS.

A chimpanzee (C-499) infected for more than 9 years with two subtype B isolates of human immunodeficiency virus type 1 (HIV-1), one (HIV-1(SF2)) that replicates poorly and one (HIV-1(LAV-1b)) that replicates efficiently in chimpanzees, died of AIDS 11 years after initial infection (F. J. Novembre et al., J. Virol. 71:4086-4091, 1997). Nucleotide sequence and phylogenetic analyses of the C2 to V5 region of env (C2-V5env) in proviral DNA from peripheral blood lymphocytes obtained 22 months before death revealed two distinct virus populations. One of these populations appeared to be a recombinant in env, having the V3 loop from HIV-1(SF2) and the V4-V5 region from HIV-1(LAV-1b); the other population had evolved from HIV-1(LAV-1b). In addition to C2-V5env, the entire p17gag and nef genes were sequenced; however, based on nucleotide sequences and phylogeny, whether the progenitor of the p17gag and nef genes was SF2 or LAV-1b could not be determined. Compared to the two original viruses, the divergence of all clones of C2-V5env ranged from 9.37 to 20.2%, that of p17gag ranged from 3.11 to 9.29%, and that of nef ranged from 4.02 to 7.9%. In contrast, compared to the maximum variation of 20.2% in C2-V5env for C-499, the maximum diversities in C2-V5env in proviruses from two chimpanzees infected with HIV-1(LAV-1b) for 9 and 10 years were 9.65 and 2.48%, respectively. These results demonstrate that (i) two distinct HIV-1 populations can coexist and undergo extensive diversification in chimpanzees with progressive HIV-1-induced disease and (ii) recombination between two subtype B strains occurred even though the second strain was inoculated 15 months after the first one. Furthermore, evaluation of env genes from three chimpanzees infected with the same strain suggests that the magnitude of HIV-1 diversification could be related to higher viral burdens, manifestations of disease, and/or dual infection.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Loss of CD4+ T cells in human immunodeficiency virus type 1-infected chimpanzees is associated with increased lymphocyte apoptosis.

Supportive evidence that apoptosis contributes to loss of CD4+ lymphocytes in human immunodeficiency virus type 1 (HIV-1)-infected humans comes from an apparent lack of abnormal apoptosis in apathogenic lentivirus infections of nonhuman primates, including HIV-1 infection of chimpanzees. Two female chimpanzees were inoculated, one cervically and the other intravenously, with HIV-1 derived from the LAI/LAV-1b strain, which was isolated from a chimpanzee infected with the virus for 8 years. Within 6 weeks of infection, both recipient chimpanzees developed a progressive loss of CD4+ T cells which correlated with persistently high viral burdens and increased levels of CD4+ T-cell apoptosis both in vitro and in vivo. Lymph nodes from both animals also revealed evidence of immune hyperactivation. Intermediate levels of T-cell apoptosis in both peripheral blood and lymph nodes were seen in a third chimpanzee that had been infected with the LAI/LAV-1b strain for 9 years; this animal has maintained depressed CD4/CD8 T-cell ratios for the last 3 years. Similar analyses of cells from 4 uninfected animals and 10 other HIV-1-infected chimpanzees without loss of CD4+ cells revealed no difference in levels of apoptosis in these two control groups. These results demonstrate a correlation between immune hyperactivation, T-cell apoptosis, and chronic loss of CD4+ T cells in HIV-1-infected chimpanzees, providing additional evidence that apoptosis is an important factor in T-cell loss in AIDS. Furthermore, the results show that some HIV-1 strains are pathogenic for chimpanzees and that this species is not inherently resistant to HIV-1-induced disease.

Animals↗
PubMed1997

IgA immunity in HIV type 1-infected chimpanzees. I. Systemic immunity.

HIV infection in humans causes various aberrancies in both the cellular and humoral immune systems, including functional abnormalities of B lymphocytes. In many instances, dysfunction occurs in the regulation of serum IgA, resulting in elevated concentrations of this immunoglobulin isotype. To determine whether HIV-1-infected chimpanzees develop IgA abnormalities similar to those observed in humans, we quantified total IgA, IgG, and IgM levels in sera collected longitudinally from six HIV-infected chimpanzees and one uninfected control animal. In comparison to immunoglobulin levels in the uninfected animal, two of the six infected chimpanzees exhibited increases in serum immunoglobulins following infection with HIV. Two other infected animals showed a marked decrease in the three isotypes within 10 months of exposure to HIV, followed by a return to baseline levels. The remaining two HIV-infected chimpanzees displayed serum immunoglobulin levels that paralleled the baseline levels and did not show great deviation over a period of 20 to 45 months postinfection. ELISA analyses of the IgA subclasses revealed possible abnormalities of the IgA2 subclass within the two animals that did not display irregular IgA, IgG, or IgM responses to HIV-1. Specific IgG, IgA, IgA1, and IgA2 antibodies to HIV antigens were detected by an enzyme immunoassay (EIA) kit and by Western blot analysis with IgA, IgA1, and IgA2 antibodies directed against the env, gag, and pol gene products. Because IgG can mask the detection of HIV-specific IgA antibodies in infected humans, Western blots and EIAs were also performed on IgG-depleted chimpanzee sera. The results demonstrated that in some instances, IgA reactivity against HIV antigens can be enhanced on removal of IgG. This study indicates that HIV-1 is capable of inducing abnormalities in serum IgA expression in chimpanzees. These results might further understanding of how HIV affects humoral responses in infected humans.

Animals↗
PubMed1997

IgA immunity in HIV type 1-infected chimpanzees. II. Mucosal immunity.

Vaginal wash fluids from chimpanzees cervically infected with HIV-1 and saliva from intravenously and cervically infected chimpanzees were analyzed for total IgA, IgA1, IgA2, IgG, and albumin concentrations and for reactivity against HIV-1. No overt abnormalities were detected in salivary immunoglobulin or albumin concentrations in either group of animals. Anti-HIV IgA and IgA subclass antibodies were demonstrated in saliva from five of six intravenously infected chimpanzees and in two of four cervically infected animals, with titers ranging from 1:5 to 1:20. HIV-specific IgG antibodies could be detected in saliva from half of the systemically infected group, the highest titer being 1:2560, whereas the highest anti-HIV IgG titer in the mucosally infected group was 1:20. Western blot analyses of the first saliva samples obtained after initial virus exposure revealed IgG, IgA, and IgA subclass antibodies directed at the env, gag, or pol gene products in both groups of chimpanzees. Examination of IgG, IgA, IgA1, and IgA2 concentrations in vaginal washes from cervically infected animals showed that IgG levels were highest, but IgA and IgA subclass reactivities against HIV-1 were more prominent than that of IgG. These results demonstrate that systemic infection of chimpanzees with HIV-1 elicits mucosal responses specific for HIV, and vaginal infection of chimpanzees induces a common mucosal immune response reminiscent of that in humans.

Albumins↗
PubMed1997

Isolation of sooty mangabey simian T-cell leukemia virus type I [STLV-I(sm)] and characterization of a mangabey T-cell line coinfected with STLV-I(sm) and simian immunodeficiency virus SIVsmmPBj14.

It has been postulated that dual infections of humans with human immunodeficiency virus (HIV) and human T-cell leukemia/lymphotropic virus (HTLV) may potentiate disease progression. Counterparts of both of these pathogenic human retroviruses have been identified in various simian species indigenous to Asia and Africa, including sooty mangabey monkeys (Cercocebus atys). Using peripheral blood mononuclear cells (PBMC) from a mangabey naturally infected with both SIV and STLV-I, T-cell lines were established and maintained continuously for more than 3 years; these cell lines harbored only a newly identified mangabey STLV-I(sm) or both STLV-I(sm) and the acutely lethal variant SIVsmmPBj14. The dually infected cell line (FEd-P14) was established by de novo infection of mangabey PBMC with SIVsmmPBj14. This cell line was characterized by multiple assays which showed that structural proteins encoded by both viruses were produced in large quantities, but that the predominant viral glycoprotein on the cell surface was the STLV-I(sm) Env. Unusual interactions of the two retroviral glycoproteins were suggested by the formation of syncytia between Raji and the FEd-P14 cells, but not between Raji and simian cells infected with only one retrovirus or human cells infected with HTLV-I. The STLV-I(sm) strain obtained from the sooty mangabey was transmitted to normal macaque and mangabey PBMC and was shown to be unique by sequencing of the entire env gene. STLV-I(sm) from this African species was more closely related to "cosmopolitan" HTLV-I strains than to the prototypic STLV-I from an Asian pig-tailed macaque. In vitro and in vivo studies of STLV-I(sm) and SIVsmm, both isolated from a naturally infected mangabey monkey, may provide insight into disease induction and manifestations associated with coinfection by their human counterparts.

Animals↗
PubMed1997

Detection of simian T cell leukemia virus type I infection in seronegative macaques.

Simian species of Asian and African origin are naturally infected with the simian T cell leukemia virus type I (STLV-I). Like the closely related human T cell leukemia virus type I (HTLV-I), STLV-I is primarily cell associated, and typical infections exhibit low viral burdens. Four macaques experimentally inoculated with a new STLV-I strain isolated from a sooty mangabey monkey were examined over extended periods of time for signs of infection by (1) commercial enzyme immunoassay and immunoblot assay for cross-reactive serum antibodies to HTLV-I, (2) commercial HTLV-I p24gag antigen-capture assay on supernatants from cocultures of macaque peripheral blood mononuclear cells (PBMCs) with human PBMCs, and (3) nested PCR amplification of proviral sequences in macaque PBMC DNA. The nested PCR assay was 100% specific and detected a single STLV-I copy in 150,000 PBMCs. In addition, our data show that experimental infection of macaques with STLV-I can be serologically silent for more than 43 months.

Animals↗
PubMed1997

Challenge of chimpanzees immunized with a recombinant canarypox-HIV-1 virus.

To evaluate the potential protective efficacy of a live recombinant human immunodeficiency virus type 1 (HIV-1) canarypox vaccine candidate, two chimpanzees were immunized five times with ALVAC-HIV-1 vCP250, a recombinant canarypox virus that expresses the HIV-1[IIIB(LAI)] gp120/TM, gag, and protease gene products. One month after the last booster inoculation, the animals were challenged by intravenous injection of cell-associated virus in the form of peripheral blood mononuclear cells from an HIV-1[IIIB(LAI)]-infected chimpanzee. One chimpanzee with a neutralizing antibody titer to HIV-1[IIIB(LAI)] of 128 at the time of challenge was protected, whereas both the second animal, with a neutralizing antibody titer of 32, and a naive control animal became infected. At 5 months after challenge, the protected chimpanzee and a third animal, previously immunized with various HIV-1[MN] antigens, were given a booster inoculation. The two animals were challenged intravenously 5 weeks later with twenty 50% tissue culture infectious doses of cell-free HIV-1[DH12], a heterologous subtype B isolate. Neither chimpanzee had neutralizing antibodies to HIV-1[DH12], and neither one was protected from infection with this isolate. The immune responses elicited by vaccination against HIV-1[IIIB(LAI)] or HIV-1[MN] did not, therefore, protect the animals from challenge with the heterologous cell-free HIV-1[DH12].

AIDS Vaccines↗
PubMed1997

Characterization and titration of an HIV type 1 subtype E chimpanzee challenge stock.

A subtype E human immunodeficiency virus type 1 (HIV-1) isolate from the Central African Republic (E/90CR402) was adapted to growth on chimpanzee peripheral blood mononuclear cells (PBMCs) by cocultivation of irradiated, infected human PBMCs with chimpanzee PBMCs. The resulting virus was passaged in chimpanzee PBMCs to generate a stock of chimpanzee-adapted virus. Although its V3 region sequence was identical to that of the parental isolate, the chimpanzee-adapted virus had a syncytium-inducing phenotype as opposed to the non-syncytium-inducing phenotype of the parental virus. After demonstrating in one animal each that the passaged virus could infect chimpanzees following intravenous (i.v.) or cervical inoculation, the i.v. infectious titer of the stock was determined. Exposure of three chimpanzees to different doses of the virus indicated that the titer was between 2 and 5 TCID50. Thus, the HIV-1 E/90CR402 chimpanzee challenge stock established persistent infections in chimpanzees by both the i.v. and genital routes and should be valuable for future HIV-1 vaccine studies to evaluate cross-protection between HIV-1 subtypes.

Animals↗
PubMed1997

Loss of the SIVsmmPBj14 phenotype and nef genotype during long-term survival of macaques infected by mucosal routes.

The ability of the simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj14) to activate and induce proliferation of quiescent peripheral blood lymphocytes from macaques is an in vitro correlate of its acutely lethal in vivo phenotype. SIV-PBj14 differs from other SIV strains by encoding tyrosine at amino acid 17 (Y17) in Nef, which generates an activation motif important for signal transduction. Although intravenous inoculation of pig-tailed macaques with SIV-PBj14 uniformly leads to death within 2 weeks, inoculation by mucosal routes results in persistent infections that progress to AIDS. In the present study, we determined whether viruses in long-term survivors retained not only the Nef Y17 residue but also the biologic properties associated with rapid disease-and death. Viruses reisolated at early and late times after mucosal infection of macaques with SIV-PBj14 were tested in vivo for acute lethality and in vitro for the ability to replicate in and induce activation and proliferation of quiescent macaque lymphocytes. In addition, the coding sequence for the first 55 amino acids in Nef was amplified from proviral DNA or plasma virion RNA by PCR or RT-PCR, respectively, and nucleotide sequences were obtained. The results showed that the majority of the quasispecies that persisted as disease progressed not only lost biological properties unique to SIV-PBj14, but also lost through mutation either Y17 or Y28 in Nef, which together were part of the activation motif. In the case of Y17, these mutations were stepwise to histidine then arginine, the amino acid encoded in this position in other SIV strains. We conclude, therefore, that replicative properties of the acutely lethal virus provide no selective advantage during long-term infections with SIV-PBj14 and that disruption of the activation motif in Nef is associated with loss of the acutely lethal phenotype.

Acute Disease↗
PubMed1997

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.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Poliovirus replicons that express the gag or the envelope surface protein of simian immunodeficiency virus SIV(smm) PBj14.

Poliovirus genomes encoding the complete gag or env surface gene of the simian immunodeficiency virus SIV(smm) PBj14 (SIV-PBj14) were constructed. The in vitro-transcribed RNA from these genomes, referred to as replicons, have the capacity for self-replication when transfected into tissue culture cells. Serial passage of the replicons containing the SIV-PBj14 gag or SIV-PBj14 env (SU) genes with a recombinant vaccinia virus, VV-P1, which provides P1 in trans, resulted in the encapsidation of these replicons. Infection of cells with the encapsidated replicons that encode gag, referred to as vIC-SIV-PBj14 Gag, resulted in the production of a 55-kDa protein that was released from the infected cells. Using a sucrose density-gradient analysis, the protein was found to sediment at a density consistent with that of a virus-like particle. Infection of cells with a replicon that encodes the env SU gene, referred to as vIC-SIV-PBj14 SU, resulted in the production of two SIV-PBj14 envelope-related intracellular proteins. One of these proteins had a molecular mass consistent with that of the unglycosylated SIV-PBj14 SU protein (63 kDa); the second protein had a higher molecular mass (>160 kDa). Characterization of this larger protein revealed that it was glycosylated and possibly represented a dimer of the SU protein. A pulse-chase analysis of cells infected with vIC-SIV-PBj14 SU demonstrated that a 110- to 130-kDa protein was released, which is consistent with the molecular mass of the SIV-PBj14 SU protein. The results of these studies demonstrate that poliovirus replicons can be used to express foreign proteins, including glycoproteins, which retain many of the physical features of the native protein.

Amino Acid Sequence↗
PubMed1996

The heterosexual human immunodeficiency virus type 1 epidemic in Thailand is caused by an intersubtype (A/E) recombinant of African origin.

Since 1989, human immunodeficiency virus type 1 (HIV-1) has spread explosively through the heterosexual population in Thailand. This epidemic is caused primarily by viruses classified as "subtype E", which, on the basis of limited sequence comparisons, appear to represent hybrids of subtypes A (gag) and E (env). However, the true evolutionary origins of "subtype E" viruses are still obscure since no complete genomes have been analyzed, and only one full-length subtype A sequence has been available for phylogenetic comparison. In this study, we determined full-length proviral sequences for "subtype E" viruses from Thailand (93TH253) and the Central African Republic (90CR402) and for a subtype A virus from Uganda (92UG037). We also sequenced the long terminal repeat (LTR) regions from 16 virus strains representing clades A, C, E, F, and G. Detailed phylogenetic analyses of these sequences indicated that "subtype E" viruses do indeed represent A/E recombinants with multiple points of crossover along their genomes. The extracellular portion of env, parts of vif and vpr, as well as most of the LTR are of subtype E origin, whereas the remainder of the genome is of subtype A origin. The possibility that the discordant phylogenetic positions of "subtype E" viruses in gag- and env-derived trees are the result of unusual rates or patterns of evolution was also considered but was ruled out on the basis of two lines of evidence: (i) phylogenetic trees constructed for synonymous and nonsynonymous substitutions yielded the same discordant branching orders for "subtype E" gag and env gene sequences, thus excluding selection-driven evolution, and (ii) multiple crossovers in the viral genome are most consistent with the copy choice model of recombination and have been observed in other documented examples of HIV-1 intersubtype recombination. Thai and CAR "subtype E" viruses exhibited the same pattern of A/E mosaicism, indicating that the recombination event occurred in Africa prior to the spread of virus to Asia. Finally, all "subtype E" viruses were found to contain a distinctive two-nucleotide bulge in their transactivation response (TAR) elements. This feature was present only in viruses which also contained a subtype A 5' pol region (i.e., subtype A viruses or A/D and A/E recombinants), raising the possibility of a functional linkage between the TAR region and the polymerase. The implications of epidemic spread of a recombinant HIV-1 strain to viral natural history and vaccine development are discussed.

Africa↗