Evolution of primate oncornaviruses: An endogenous virus from langurs (Presbytis spp.) with related virogene sequences in other Old World monkeys

Gene sequences related to a retrovirus (oncornavirus type D) isolated from a lung cell culture from spectacled langur (Presbytis obscurus) are found in multiple copies (20-40 per haploid genome) in langur cellular DNA; partially homologous virogene sequences are present in the DNA of related Old World monkey species. Primates thus contain gene sequences for at least two distinct classes of genetically transmitted oncornaviruses, the type C class (isolated from baboons) and the type D class described here. The langur virus is partially related to Mason-Pfizer monkey virus, a type D retrovirus isolated from rhesus monkeys. Nucleic acid hybridization studies suggest that Mason-Pfizer monkey virus, now infectious among primates, was derived from an endogenous virus of langurs or from another member of the primate sub-family Colobinae.

Protection of Macaca nemestrina from disease following pathogenic simian immunodeficiency virus (SIV) challenge: utilization of SIV nucleocapsid mutant DNA vaccines with and without an SIV protein boost

Molecular clones were constructed that express nucleocapsid (NC) deletion mutant simian immunodeficiency viruses (SIVs) that are replication defective but capable of completing virtually all of the steps of a single viral infection cycle. These steps include production of particles that are viral RNA deficient yet contain a full complement of processed viral proteins. The mutant particles are ultrastructurally indistinguishable from wild-type virus. Similar to a live attenuated vaccine, this approach should allow immunological presentation of a full range of viral epitopes, without the safety risks of replicating virus. A total of 11 Macaca nemestrina macaques were inoculated with NC mutant SIV expressing DNA, intramuscularly (i.m.) in one study and i.m. and subcutaneously in another study. Six control animals received vector DNA lacking SIV sequences. Only modest and inconsistent humoral responses and no cellular immune responses were observed prior to challenge. Following intravenous challenge with 20 animal infectious doses of the pathogenic SIV(Mne) in a long-term study, all control animals became infected and three of four animals developed progressive SIV disease leading to death. All 11 NC mutant SIV DNA-immunized animals became infected following challenge but typically showed decreased initial peak plasma SIV RNA levels compared to those of control animals (P = 0.0007). In the long-term study, most of the immunized animals had low or undetectable postacute levels of plasma SIV RNA, and no CD4(+) T-cell depletion or clinical evidence of progressive disease, over more than 2 years of observation. Although a subset of immunized and control animals were boosted with SIV(Mne) proteins, no apparent protective benefit was observed. Immunization of macaques with DNA that codes for replication-defective but structurally complete virions appears to protect from or at least delay the onset of AIDS after infection with a pathogenic immunodeficiency virus. With further optimization, this may be a promising approach for vaccine development.

Mucosal challenge of Macaca nemestrina with simian immunodeficiency virus (SIV) following SIV nucleocapsid mutant DNA vaccination

A simian immunodeficiency virus (SIV)(Mne) DNA clone was constructed that produces viruses containing a four amino acid deletion in the second zinc finger of the nucleocapsid (NC) domain of the Gag polyprotein. Viruses produced from this clone, although non-infectious both in vitro and in vivo, complete a majority of the steps in a single retroviral infection cycle. Eight pig-tailed macaques (Macaca nemestrina) were inoculated intramuscularly and subcutaneously three times over the course of 24 weeks with the NC mutant expressing DNA. These macaques, and four controls, were then challenged mucosally (intrarectally) with the homologous virus (SIV Mne CL E11S) and monitored for evidence of infection and clinical disease. Prior to challenge, a measurable humoral immune response was noted in four of eight immunized macaques. After challenge, all 12 macaques became infected, although four immunized animals greatly restricted their viral replication, and one immunized animal that controlled replication remains antibody negative. No disease has been evidence during the 46-week period of monitoring after challenge.

Role of immune responses against the envelope and the core antigens of simian immunodeficiency virus SIVmne in protection against homologous cloned and uncloned virus challenge in Macaques

We previously showed that envelope (gp160)-based vaccines, used in a live recombinant virus priming and subunit protein boosting regimen, protected macaques against intravenous and intrarectal challenges with the homologous simian immunodeficiency virus SIVmne clone E11S. However, the breadth of protection appears to be limited, since the vaccines were only partially effective against intravenous challenge by the uncloned SIVmne. To examine factors that could affect the breadth and the efficacy of this immunization approach, we studied (i) the effect of priming by recombinant vaccinia virus; (ii) the role of surface antigen gp130; and (iii) the role of core antigens (Gag and Pol) in eliciting protective immunity. Results indicate that (i) priming with recombinant vaccinia virus was more effective than subunit antigen in eliciting protective responses; (ii) while both gp130 and gp160 elicited similar levels of SIV-specific antibodies, gp130 was not as effective as gp160 in protection, indicating a possible role for the transmembrane protein in presenting functionally important epitopes; and (iii) although animals immunized with core antigens failed to generate any neutralizing antibody and were infected upon challenge, their virus load was 50- to 100-fold lower than that of the controls, suggesting the importance of cellular immunity or other core-specific immune responses in controlling acute infection. Complete protection against intravenous infection by the pathogenic uncloned SIVmne was achieved by immunization with both the envelope and the core antigens. These results indicate that immune responses to both antigens may contribute to protection and thus argue for the inclusion of multiple antigens in recombinant vaccine designs.

Immunization against SIVmne in macaques using multigenic DNA vaccines

All structural and regulatory genes of SIVmne were cloned into mammalian expression vectors to optimize expression in vitro and immunogenicity in mice. Macaca fascicularis were immunized four times with plasmid DNA (n = 4), or two DNA priming inoculations followed by two boosts of recombinant gp160 plus Gag-Pol particles (n = 4). Following intrarectal challenge with SIVmne, all macaques became infected. Three monkeys immunized with DNA alone maintained low plasma virus loads by 1 year post-challenge; the fourth exhibited high virus loads and significant CD4+ cell decline. Two of the DNA plus boost and three control macaques had high virus loads and associated CD4+ cell decline. Both vaccine protocols elicited antibodies and comparable helper T-cell proliferative responses to gp160. Cytokine mRNA levels in activated peripheral blood mononuclear cells (PBMC) taken at time of challenge suggested a dominant T helper (Th) 1 state in three DNA-immunized and one protein-boosted macaque, which correlated with low virus loads and high CD4+ cell counts post-challenge.

Protection of macaques against intrarectal infection by a combination immunization regimen with recombinant simian immunodeficiency virus SIVmne gp160 vaccines

We previously reported that immunization with recombinant simian immunodeficiency virus SIVmne envelope (gp160) vaccines protected macaques against intravenous challenge by the cloned homologous virus E11S but that this protection was only partially effective against the uncloned virus, SIVmne. In the present study, we examine the protective efficacy of this immunization regimen against infection by a mucosal route. We found that the same gp160-based vaccines were highly effective against intrarectal infection not only with the E11S clone but also with the uncloned SIVmne. Protection against mucosal infection is therefore achievable by parenteral immunization with recombinant envelope vaccines. Protection appears to correlate with high levels of SIV-specific antibodies and, in animals protected against the uncloned virus, the presence of serum-neutralizing activities. To understand the basis for the differential efficacies against the uncloned virus by the intravenous versus the intrarectal routes, we examined viral sequences recovered from the peripheral blood mononuclear cells of animals early after infection by both routes. We previously showed that the majority (85%) of the uncloned SIVmne challenge stock contained V1 sequences homologous to the molecular clone from which the vaccines were made (E11S type), with the remainder (15%) containing multiple conserved changes (the variant types). In contrast to intravenously infected animals, from which either E11S-type or the variant type V1 sequences could be recovered in significant proportions, animals infected intrarectally had predominantly E11S-type sequences. Preferential transmission or amplification of the E11S-type viruses may therefore account in part for the enhanced efficacy of the recombinant gp160 vaccines against the uncloned virus challenge by the intrarectal route compared with the intravenous route.

Protection from pathogenic SIV challenge using multigenic DNA vaccines

To assess DNA immunization as a strategy for protecting against HIV infection in humans, we utilized SIVmne infection of Macaca fascicularis as a vaccine challenge model with moderate pathogenic potential. We compared the efficacy of DNA immunization alone and in combination with subunit protein boosts. All of the structural and regulatory genes of SIVmne clone 8 were cloned into mammalian expression vectors under the control of the CMV IE-1 promoter. Eight M. fascicularis were immunized twice with 3 mg of plasmid DNA divided between two sites; intramuscular and intradermal. Four primed macaques received a further two DNA immunizations at weeks 16-36, while the second group of four were boosted with 250 microg recombinant gp160 plus 250 microg recombinant Gag-Pol particles formulated in MF-59 adjuvant. Half of the controls received four immunizations of vector DNA; half received two vector DNA and two adjuvant immunizations. As expected, humoral immune responses were stronger in the macaques receiving subunit boosts, but responses were sustained in both groups. Significant neutralizing antibody titers to SIVmne were detected in one of the subunit-boosted animals and in none of the DNA-only animals prior to challenge. T-cell proliferative responses to gp160 and to Gag were detected in all immunized animals after three immunizations, and these responses increased after four immunizations. Cytokine profiles in PHA-stimulated PBMC taken on the day of challenge showed trends toward Thl responses in 2/4 macaques in the DNA vaccinated group and in 1/4 of the DNA plus subunit vaccinated macaques; Th2 responses in 3/4 DNA plus subunit-immunized macaques; and Th0 responses in 4/4 controls. In bulk CTL culture, SIV specific lysis was low or undetectable, even after four immunizations. However, stable SIV Gag-Pol- and env-specific T-cell clones (CD3+ CD8+) were isolated after only two DNA immunizations, and Gag-Pol- and Nef-specific CTL lines were isolated on the day of challenge. All animals were challenged at week 38 with SIVmne uncloned stock by the intrarectal route. Based on antibody anamnestic responses (western, ELISA, and neutralizing antibodies) and virus detection methods (co-culture of PBMC and LNMC, nested set PCR- of DNA from PBMC and LNMC, and plasma QC-PCR), there were major differences between the groups in the challenge outcome. Surprisingly, sustained low virus loads were observed only in the DNA group, suggesting that four immunizations with DNA only elicited more effective immune responses than two DNA primes combined with two protein boosts. Multigenic DNA vaccines such as these, bearing all structural and regulatory genes, show significant promise and may be a safe alternative to live-attenuated vaccines.

Nucleocapsid protein zinc-finger mutants of simian immunodeficiency virus strain mne produce virions that are replication defective in vitro and in vivo

All retroviruses (except the spumaretroviruses) contain a nucleocapsid (NC) protein that encodes one or two copies of the Zn2+-finger sequence -Cys-X2-Cys-X4-His-X4-Cys-. This region has been shown to be essential for recognition and packaging of the genomic RNA during virion particle assembly. Additionally, this region has been shown to be involved in early infection events in a wide spectrum of retroviruses, including mammalian type C [e.g., murine leukemia virus (MuLV)], human immunodeficiency virus type 1 (HIV-1), Rous sarcoma virus, and other retroviruses. Mutations in the two Zn2+-fingers of the NC protein of simian immunodeficiency virus strain Mne [SIV(Mne)] have been generated. The resulting virions contained the normal complement of processed viral proteins with densities indistinguishable from wild-type SIV(Mne). All of the mutants had electron micrograph morphologies similar to those of immature particles observed in wild-type preparations. RNA packaging was less affected by mutations in the NC protein of SIV(Mne) than has been observed for similar mutants in the MuLV and HIV-1 systems. Nevertheless, in vitro replication of SIV(Mne) NC mutants was impaired to levels comparable to those observed for MuLV and HIV-1 NC mutants; replication defective NC mutants are typically 10(5)- to 10(6)-fold less infectious than similar levels of wild-type virus. One mutant, DeltaCys33-Cys36, was also found to be noninfectious in vivo when mutant virus was administered intravenously to a pig-tailed macaque. NC mutations can therefore be used to generate replication defective virions for candidate vaccines in the SIV macaque model for primate lentiviral diseases.

Limited breadth of the protective immunity elicited by simian immunodeficiency virus SIVmne gp160 vaccines in a combination immunization regimen

We previously reported that immunization with recombinant simian immunodeficiency virus SIVmne envelope (gp160) vaccines protected macaques against an intravenous challenge by the cloned homologous virus, E11S. In this study, we confirmed this observation and found that the vaccines were effective not only against virus grown on human T-cell lines but also against virus grown on macaque peripheral blood mononuclear cells (PBMC). The breadth of protection, however, was limited. In three experiments, 3 of 10 animals challenged with the parental uncloned SIVmne were completely protected. Of the remaining animals, three were transiently virus positive and four were persistently positive after challenge, as were 10 nonimmunized control animals. Protection was not correlated with levels of serum-neutralizing antibodies against the homologous SIVmne or a related virus, SIVmac251. To gain further insight into the protective mechanism, we analyzed nucleotide sequences in the envelope region of the uncloned challenge virus and compared them with those present in the PBMC of infected animals. The majority (85%) of the uncloned challenge virus was homologous to the molecular clone from which the vaccines were made (E11S type). The remaining 15% contained conserved changes in the V1 region (variant types). Control animals infected with this uncloned virus had different proportions of the two genotypes, whereas three of four immunized but persistently infected animals had >99% of the variant types early after infection. These results indicate that the protective immunity elicited by recombinant gp160 vaccines is restricted primarily to the homologous virus and suggest the possibility that immune responses directed to the V1 region of the envelope protein play a role in protection.

Chemical inactivation of retroviral infectivity by targeting nucleocapsid protein zinc fingers: a candidate SIV vaccine

Although most viral vaccines used in humans have been composed of live attenuated viruses or whole killed viral particles, the latter approach has received little attention in research on experimental primate immunodeficiency virus vaccines. Inactivation procedures involving heat or formalin appear to adversely affect the viral envelope proteins. Recently we have inactivated human immunodeficiency virus type 1 (HIV-1) with the compound 2,2'-dithiodipyridine (Aldrithiol-2, Aldrich, Milwaukee, WI), which inactivates infectivity of retroviruses by covalently modifying the nucleocapsid zinc finger motifs. HIV-1 inactivated with Aldrithiol-2 retained the conformational and functional integrity of the viral and virion-associated cellular proteins on the viral membrane. We have extended our studies of zinc finger targeted inactivation to simian immunodeficiency virus (SIV) and evaluated the feasibility of applying the procedures to large scale (>30 l) production and purification of the primate immunodeficiency viruses. There was no detectable residual infectivity of SIV after treatment with 1 mM Aldrithiol-2 (>5 logs inactivation). Treatment with Aldrithiol-2 resulted in extensive reaction with the nucleocapsid protein of treated virus, as shown by immunoblot and high-performance liquid chromatography (HPLC) analysis. As expected, the virion gp120SU appeared to be completely unreactive with Aldrithiol-2. Sucrose gradient purification and concentration procedures resulted in little loss of viral infectivity or virion-associated gp120SU. When tested in a gp120-CD4 dependent cell binding assay, the inactivated virus bound to cells comparably to the untreated virus. Analysis of gp120-CD4 mediated postbinding fusion events showed that the inactivated virus could induce CD4-dependent fusion with efficiencies similar to the untreated virus. Inactivation and processing of primate immunodeficiency viruses by methods described here results in highly concentrated virus preparations that retain their envelope proteins in a native configuration. These inactivated virus preparations should be useful in whole killed-particle vaccine experiments as well as laboratory reagents to prepare antisera, including monoclonal antibodies, and to study noninfective virion-cell interactions.

Macaques infected with cloned simian immunodeficiency virus show recurring nef gene alterations

We compared nef gene sequences isolated by polymerase chain reaction from peripheral blood lymphocyte DNA of macaques that had been inoculated with either biologically (E11S) or molecularly (clone 8) cloned SIV/Mne. Two samples from each animal obtained either early (weeks 2-8) or late (weeks 21-137) after infection were analyzed. Three substitutions in the predicted Nef amino acid sequence were seen in all animals at the late time point, and two other substitutions were seen in all except one. Two of the common exchanges are located approximately 40 residues apart in the Nef core sequence but are juxtaposed on the tertiary structure as judged by computer modeling using the structure of the HIV Nef core protein as a guide. Most recurrent in vivo changes replaced a residue found in the cloned Nef sequence with one present in a consensus derived by aligning the Nef sequences of the SIV/Sm clade. Recombinant virus containing a macaque-adapted (MA nef) nef on the clone 8 backbone was 3-fold more infectious on SMAGI cells than the original virus. A lymphocyte line infected with SIV-clone 8-MAnef contained a large proportion of cells carrying provirus with defective nef genes. These findings suggest that the nef gene of the cloned SIV/Mne had undergone attenuating mutations during propagation in tissue culture that were "corrected" in vivo.

Effectiveness of postinoculation (R)-9-(2-phosphonylmethoxypropyl) adenine treatment for prevention of persistent simian immunodeficiency virus SIVmne infection depends critically on timing of initiation and duration of treatment

(R)-9-(2-Phosphonylmethoxypropyl)adenine (PMPA), an acyclic nucleoside phosphonate analog, is one of a new class of potent antiretroviral agents. Previously, we showed that PMPA treatment for 28 days prevented establishment of persistent simian immunodeficiency virus (SIV) infection in macaques even when therapy was initiated 24 h after intravenous virus inoculation. In the present study, we tested regimens involving different intervals between intravenous inoculation with SIV and initiation of PMPA treatment, as well as different durations of treatment, for the ability to prevent establishment of persistent infection. Twenty-four cynomolgus macaques (Macaca fascicularis) were studied for 46 weeks after inoculation with SIV. All mock-treated control macaques showed evidence of productive infection within 2 weeks postinoculation (p.i.). All macaques that were treated with PMPA for 28 days beginning 24 h p.i. showed no evidence of viral replication following discontinuation of PMPA treatment. However, extending the time to initiation of treatment from 24 to 48 or 72 h p.i. or decreasing the duration of treatment reduced effectiveness in preventing establishment of persistent infection. Only half of the macaques treated for 10 days, and none of those treated for 3 days, were completely protected when treatment was initiated at 24 h. Despite the reduced efficacy of delayed and shortened treatment, all PMPA-treated macaques that were not protected showed delays in the onset of cell-associated and plasma viremia and antibody responses compared with mock controls. These results clearly show that both the time between virus exposure and initiation of PMPA treatment as well as the duration of treatment are crucial factors for prevention of acute SIV infection in the macaque model.

Sequence diversity of SIV(Mne) Nef in vivo and in vitro

We have compared nef gene sequences isolated by PCR from peripheral blood lymphocyte DNA of macaques which had been inoculated with either biologically or molecularly cloned SIV(Mne). Two samples from each animal obtained either early after infection (week 2-8) or after significant CD4+ depletion (week 21-137) were analyzed. Three substitutions in the predicted Nef amino acid sequence were seen in all animals at the late time point, and two more in all but one. Two of the common exchanges are located about 40 residues apart in the Nef core sequence, but are in proximity on the tertiary structure as judged by computer modelling using the structure of the HIV Nef core protein as a guide. Most recurring in vivo changes replaced a residue found in the cloned Nef sequence with one present in a consensus derived by aligning the Nef sequences of the SIVsm/HIV-2 groups. Animals inoculated with virus already containing the "late version" nef gene developed a more aggressive disease. The macaque adapted (MA)nef conferred a threefold higher infectivity to the cloned virus, but had no effects on CD4 downregulation. Propagation of virus with MAnef in tissue culture resulted in the rapid emergence of variants with newly attenuated nef. These findings suggest that the selective pressure on nef in vivo and in vitro are different.

Focal segmental glomerulosclerosis in primates infected with a simian immunodeficiency virus

Focal and segmental glomerulosclerosis (FSG) with endothelial tubuloreticular inclusions (TRIs) is the typical lesion of human HIV-associated glomerulopathy. Autopsy studies showed the presence of FSG in 3 of 15 macaques dying 15-120 weeks after experimental infection with a simian immunodeficiency virus (SIVMne). Ultrastructural studies generally revealed numerous endothelial TRIs (also present in normals), mesangial expansion, and evidence of mesangial cell injury. One additional animal had a small-vessel polyarteritis with a proliferative and focally crescentic glomerulonephritis; seven animals had mild, multifocal interstitial nephritis. All animals had documented viremia after infection; 14 of 15 developed antibodies to SIV postinoculation. Additional postmortem findings included severe enterocolitis, encephalitis, and opportunistic infections. In contrast, autopsy studies of macaques infected with a type D simian retrovirus (SAIDS-D/Washington, SRV-2) for similar periods of time (n = 40) showed no evidence of FSG. One SRV-infected animal had a mild proliferative glomerulonephritis. These studies indicate SIV-infected primates may provide a relevant model for study of human HIV-associated nephropathy. They also indicate the variable pathology that can be seen in primate infections of distinct retrovirus types, each of which produces a simian immunodeficiency state that resembles human AIDS.

Recombinant subunit vaccines as an approach to study correlates of protection against primate lentivirus infection

Using pathogenic simian immunodeficiency virus (SIV) infection of macaques as a model, we explored the limits of the protective immunity elicited by recombinant subunit vaccines and examined factors that affect their efficacy. Envelope gp 160 vaccines, when used in a live recombinant virus-priming and subunit-protein-boosting regimen, protected macaques against a low-dose, intravenous infection by a cloned homologous virus SIVmne E11S. The same regimen was also effective against intrarectal challenge by the same virus and against intravenous challenge by E11S grown on primary macaque peripheral blood mononuclear cells (PBMC). However, only limited protection was observed against uncloned SIVmne. Priming with live recombinant virus was more effective than immunization with subunit gp 160 alone, indicating a potential advantage of native antigen presentation and the possible role of cell-mediated immunity in protection. Whole gp 160 was more effective than the surface antigen (gp 130), even though both antigens elicited similar levels of neutralizing antibodies. Animals immunized with the core (gag-pol) antigens failed to generate any neutralizing antibody and were all infected following challenge. However, their proviral load was 10-100-fold lower than that of the control animals, indicating that immune mechanisms such as cytotoxic T lymphocytes (CTL) may play a role. Finally, animals immunized with both the core and the envelope antigens generated significant protective immunity, even with relatively low neutralizing antibodies. Taken together, these results indicate that multiple mechanisms may contribute to protection. It may therefore be advantageous to incorporate multiple antigens in the design of recombinant subunit vaccines against acquired immunodeficiency syndrome (AIDS).

Autoimmunity in chronic active Helicobacter hepatitis of mice. Serum antibodies and expression of heat shock protein 70 in liver

Male A/JCr mice with naturally occurring Helicobacter hepaticus infection develop a progressive chronic active hepatitis and liver tumors, despite the presence of serum antibodies to Helicobacter proteins. A rabbit antiserum prepared against the bacterial proteins immunoreacted with hepatocytes present in liver sections from infected mice with progressive lesions. We found that sera from these mice contained IgG antibodies that reacted in immunoblots with recombinant heat shock protein 70 (DmaK from Escherichia coli) but not with heat shock protein 60 (GroEL) or heat shock protein 10 (GroES). A rabbit antibody to heat shock protein 70 reacted with H. hepaticus in tissue sections and to a H. hepaticus protein (70 kd) in Western blots. Immunohistochemistry and in situ hybridization for heat shock protein 70 revealed that individual hepatocytes and other cells expressed the protein in livers with hepatitis but not usually in normal livers. Liver tumors and preneoplastic lesions in infected mice did not usually express heat shock protein 70 except focally in a few tumors. In situ hybridization for H. hepaticus 16S rRNA showed that the bacteria was found throughout the liver associated with hepatitis but not within tumors. CD3+ T lymphocytes were found in close association with hepatic lesions. These data suggest a role for autoimmunity in progressive hepatitis and carcinogenesis in livers infected with H. hepaticus.

Prevention of SIV infection in macaques by (R)-9-(2-phosphonylmethoxypropyl)adenine

The efficacy of pre- and postexposure treatment with the antiviral compound (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) was tested against simian immunodeficiency virus (SIV) in macaques as a model for human immunodeficiency virus (HIV). PMPA was administered subcutaneously once daily beginning either 48 hours before, 4 hours after, or 24 hours after virus inoculation. Treatment continued for 4 weeks and the virologic, immunologic, and clinical status of the macaques was monitored for up to 56 weeks. PMPA prevented SIV infection in all macaques without toxicity, whereas all control macaques became infected. These results suggest a potential role for PMPA prophylaxis against early HIV infection in cases of known exposure.

Macaques immunized with HLA-DR are protected from challenge with simian immunodeficiency virus

Macaques immunized with uninfected human cells have been shown to be protected from challenge with simian immunodeficiency virus (SIV) propagated in human cells. To identify the potential antigens involved in this protection, macaques were immunized with uninfected human cells, sucrose density gradient-purified culture fluid from uninfected human cells (mock virus), beta-2 microglobulin (beta 2M), immunoaffinity-purified HLA class I and class II proteins from these human cells, and adjuvant. Although all macaques immunized with beta 2M and HLA class I developed high antibody titers to beta 2M, these animals were not protected from a subsequent challenge with infectious SIV grown in human cells. In contrast, the macaques immunized with class II protein (HLA-DR) and mock virus developed antibodies to class II protein and were protected from the intravenous infectious virus challenge. The class II protein- and mock virus-immunized animals which were protected from challenge were given boosters of the appropriate antigen and challenged with the same SIV propagated in macaque cells. All animals became infected, indicating that the protection seen with human class II protein did not extend to protection from infection with SIV containing macaque class II proteins. Since the virus released from SIV-infected macaque cells would contain macaque class II proteins, our results suggest that the initial SIV infected was completely prevented. In addition, the lack of protection from challenge with SIV propagated in macaque cells provided strong evidence that the protection was due to an immune response to the cellular proteins and not to epitopes cross-reactive between class II proteins and the viral proteins, since the identical virus proteins were present in both challenge stocks. These results are the first demonstration that immunization with a purified cellular protein can protect from virus infection.

Progression to AIDS in macaques is associated with changes in the replication, tropism, and cytopathic properties of the simian immunodeficiency virus variant population

Human immunodeficiency virus type 1 (HIV-1) typically evolves from a macrophage-tropic, noncytopathic virus at early asymptomatic stages of infection to a T-cell-tropic, cytopathic, and syncytia-inducing virus population as humans progress to AIDS. This suggests that changes in virus phenotype may influence disease. Because simian immunodeficiency virus (SIV) infection in macaques is a common model system for HIV-1 pathogenesis, we determined whether SIV infection in macaques that develop simian AIDS is associated with a similar shift in viral tropism, replication, and cytopathic properties. The virus that infected the monkeys (SIVMneCL8) and predominated at early times in infection is a macrophage-tropic virus that replicates with relatively low efficiency in human T cell lines. The variant populations that arise in macaques as they progress to AIDS are more infectious for human T cell lines, exhibiting enhanced replication in CEM x 174 cells and an expanded host range that includes Molt-4 Clone 8 cells. Infections starting with equal doses of the viruses demonstrated that the late variants are cytopathic and syncytia-inducing compared to SIVMneCL8, but the variants replicate less efficiently in primary macaque macrophages. V3 sequences were generally conserved between the early and the late variants, suggesting that changes in SIVMne tropism, replication, and cytopathicity were apparently not due to alterations in V3. This study demonstrates important similarities in the phenotypic viral changes that accompany development of AIDS in SIV and HIV-1 infections and suggest that SIV may provide a model system for determining whether the rapidly replicating, T-cell-tropic cytopathic variants present late in infection and disease are indeed important in determining progression to AIDS.

Characterization of infectious type D retrovirus from baboons

Infectious virus resembling type D simian retrovirus (SRV) was isolated from Ethiopian baboons (Papio cynocephalus) (SRV-Pc) housed at the University of Washington Regional Primate Research Center. When baboon peripheral blood mononuclear cells (PBMC) or tissues were cocultured with the H-9 human T-cell line or the Raji human B-cell line, large multinucleated syncytia positive for SRV-2 antigens were observed microscopically. Immunoblot analysis of purified SRV-Pc from cell culture supernatants demonstrated that the viral core and envelope proteins reacted with rabbit anti-SRV-2 serum. Fresh PBMC and cocultured cells were positive by polymerase chain reaction using two different sets of SRV-2 primers. Preliminary sequence analysis of two separate isolates from portions of the SRV-Pc p27 and gp20 regions revealed homology with SRV-1, SRV-2, and Mason-Pfizer monkey virus. The homologies in the p27 segment were 91-94% and the homologies in the gp20 segment were 72-75%.

Chronic active hepatitis in mice caused by Helicobacter hepaticus

Helicobacter infections cause chronic gastroenteritis in humans and several animal species. We recently discovered a new Helicobacter (H. hepaticus) that is the etiological agent of a unique chronic active hepatitis in mice. Natural infection appeared to be acquired early in life in enzootically infected colonies. Liver lesions arose as focal necrosis and focal nonsuppurative inflammation by 1 to 4 months of age in susceptible mouse strains. By 6 to 8 months, extensive liver involvement included hepatocytomegaly, bile ductular (oval cell) hyperplasia, and cholangitis. There was an age-related increase in proliferating cell nuclear antigen hepatocyte nuclear labeling index. The bacteria were usually found within bile canaliculi as determined by ultrastructural evaluation of liver lesions, the Steiner modification of the Warthin-Starry stain and immunohistochemistry with a rabbit antibody to Helicobacter pylori. Naturally infected mice showed an age-related increase in serum IgG antibodies to Helicobacter hepaticus proteins. The disease was experimentally reproduced by intraperitoneal injection of liver suspensions from affected livers or bacteria cultivated in vitro. The earliest lesions of the experimental disease appeared 4 weeks after injection. The course of spontaneous and experimental infection was slow and insidious and resulted in high titers of antibodies to bacterial proteins. This chronic bacterial infection represents a new model of chronic liver disease.

T-cell proliferation to subinfectious SIV correlates with lack of infection after challenge of macaques

OBJECTIVES

To analyze correlates of protection in macaques exposed to SIV.

METHODS

Peripheral blood mononuclear cells (PBMC) from macaques inoculated intrarectally with various dilutions of SIV were examined for their in vitro proliferative response to SIV envelope peptides and generation of SIV-specific antibodies. Some macaques previously exposed intravenously to subinfectious doses of SIV were subsequently challenged 16 months later with an infectious intrarectal dose of SIV.

RESULTS

The viral-specific immune responses of macaques exposed to infectious doses of SIV were characterized by generation of antibodies and weak or undetectable T-cell-mediated responses. In contrast, macaques inoculated with doses of SIV below the threshold required for seroconversion and recovery of virus exhibited T-cell proliferation in response to SIV envelope synthetic peptides. The macaques that had previously been exposed to SIV resisted the subsequent virus challenge, whereas the naive macaques (never exposed to SIV) all became infected.

CONCLUSIONS

The inability to productively infect macaques previously exposed to subinfectious doses of SIV suggests that a T-cell-mediated response may confer long-term protection against infection, and that AIDS vaccines should be designed to optimize the cellular arm of the immune response.

Intrarectal inoculation of macaques by the simian immunodeficiency virus, SIVmne E11S: CD4+ depletion and AIDS

Macaca nemestrina and Macaca fascicularis were inoculated with various doses of a single-cell clone of SIVmne-infected HuT 78 cells (E11S) by both the intravenous and intrarectal routes. Animals inoculated intravenously at each dose seroconverted and virus was isolated from peripheral blood mononuclear cells, but only the high-dose intrarectally exposed macaques became viremic and seroconverted. However, some seronegative, virus isolation negative intrarectally inoculated macaques showed evidence of infection and disease.

Infectivity of titered doses of simian immunodeficiency virus clone E11S inoculated intravenously into rhesus macaques (Macaca mulatta)

The macaque infectious dose (MID) of a single-cell clone of simian immunodeficiency virus isolated from a pig-tailed macaque (SIV/Mne clone E11S) was determined in rhesus macaques (Macaca mulatta). Twenty-one macaques were inoculated with 10-fold dilutions of the virus stock (three or four animals per dose). The virologic and clinical status of these animals was monitored for 26 weeks. The 25% MID (MID25) occurred at a 10(5)-fold dilution of the viral stock.

Preexposure prophylaxis with 9-(2-phosphonylmethoxyethyl)adenine against simian immunodeficiency virus infection in macaques

A reverse transcriptase inhibitor, 9-(2-phosphonylmethoxyethyl)adenine (PMEA), was evaluated for efficacy against acute simian immunodeficiency virus (SIV) infection in juvenile macaques (Macaca fascicularis). Macaques were pretreated subcutaneously with PMEA for 48 h before SIV inoculation. Drug treatment continued for an additional 28 days. Efficacy of PMEA was determined by detection of SIV in blood, SIV DNA in peripheral blood mononuclear cells, and SIV antibodies. Protection from acute SIV infection occurred in 83% of macaques treated with 20 mg/kg/day versus 50% of macaques treated with 10 mg/kg/day. Several PMEA-treated macaques developed mild dermatitis that disappeared when the 4-week therapy ended. The results of these experiments indicate that preexposure prophylaxis with PMEA can prevent acute SIV infection in macaques. Since PMEA demonstrates profound inhibition of retrovirus infection, it may have utility as a chemoprophylactic agent for humans exposed to SIV or human immunodeficiency virus.

Infectivity and pathogenesis of titered dosages of simian immunodeficiency virus experimentally inoculated into longtailed macaques (Macaca fascicularis)

The 50% macaque infectious dose (MID50) and pathogenesis of uncloned simian immunodeficiency virus (isolated from a pigtailed macaque, SIVmne) was determined in longtailed macaques (Macaca fascicularis). Five pairs of macaques were inoculated with 10-fold dilutions of the virus stock, and one macaque was mock-infected. The virologic and clinical status of these macaques was monitored for up to 80 weeks. The MID50 of SIVmne was determined to be 10(2) cell culture infectious dose of the original virus stock. In order to test the infectivity and pathogenesis of an established viral dose, six additional macaques were inoculated with 10x MID50 (10(3) cell culture infectious dose) of the SIVmne. The virologic and clinical status of these macaques was monitored for 40 weeks. All of the macaques inoculated with 10x MID50 or greater became infected as evidenced by seroconversion and consistent virus isolation from peripheral blood mononuclear cells. Macaques infected with SIVmne had an initial sharp decrease in CD2, CD20, CD4, CD8, and CD4CD29 lymphocyte subsets, whereas the CD4:CD8 ratio increased. Viremic macaques developed persistent slight to moderate peripheral lymphadenopathy approximately 3 to 4 weeks after inoculation. Four macaques subsequently died of AIDS-like disease at 29, 33, 42, and 80 weeks after inoculation. Data obtained from the viral titration study and the acute infection model will aid in the development of animal trials to evaluate antiretroviral therapies and preventive vaccines against human immunodeficiency virus infection.

Effect of dosing frequency on ZDV prophylaxis in macaques infected with simian immunodeficiency virus

The effect of dosing frequency on zidovudine (ZDV) prophylaxis against simian immunodeficiency virus (SIV) infection was examined in long-tailed macaque monkeys (Macaca fascicularis). The results indicate that dosing frequency is extremely important for drug efficacy. The monkeys were divided into three groups based on dosing frequencies of 6-, 8-, or 12-h intervals. All were given a total daily dose of 100 mg/kg of ZDV. The drug was administered subcutaneously starting 24 h before SIV inoculation, and treatment continued for an additional 28 days. With the total daily dose held constant, ZDV was most therapeutic when administered at 12-h intervals, less effective at 8-h intervals, and least effective at 6-h intervals. These results indicate that early ZDV treatment based on infrequent but high dosages may increase the antiretroviral effect of the drug. These findings could serve as a model for ZDV chemoprophylaxis in humans. In cases involving accidental exposure to SIV or human immunodeficiency virus (HIV-1 or HIV-2), immediate, high-dosage therapies may be most therapeutic.

Passively transferred antibodies directed against conserved regions of SIV envelope protect macaques from SIV infection

Inactivated plasma collected from either SIV-infected or peptide-vaccinated macaques was transferred into 17 naive rhesus monkeys. Two additional macaques received normal plasma and served as controls. Following transfer all 19 monkeys were inoculated with SIV. While the controls became infected and were virus-isolation-positive, 3 of 6 recipients of SIV peptide vaccine plasma and 9 of 11 recipients of SIV-infected monkey plasma were protected. None of the 12 protected animals became virus-isolation-positive or seroconverted within 100 days of follow-up. One, however was SIV-PCR-positive. All 12 protected animals were rechallenged 100 days after the initial inoculation; 8 became infected and yielded virus as expected, but 4 remained uninfected. One of the latter was the SIV-PCR-positive monkey mentioned above, suggesting that cryptic SIV infection may be of significance in immunological protection. The results demonstrate that envelope anti-peptide antibodies have similar protective potential in vivo as antibodies directed to the whole virus. In vitro neutralization competition assays performed with sera from vaccinated macaques in the presence of the free peptides suggest that of the four conserved envelope peptides of the vaccine, the two originating from gp41 rather than the two from gp120 are responsible for inducing the neutralizing anti-syncytial activity.

Detection of serum antibodies in Ethiopian baboons that cross-react with SIV, HTLV-I, and type D retroviral antigens

Baboons (Papio cynocephalus) imported from Ethiopia were screened for antibodies to various primate retroviruses by immunoblotting. Antibodies that cross-reacted with SIV/Mne or with type D viral antigens were detected in approximately one-third of these animals. In addition, 20% of these baboons had antibodies that cross-reacted with HTLV-I viral antigens. These data suggest that wild-caught baboons are infected with retroviruses only partially related to known primate viral isolates.

Protection of vaccinia-primed macaques against SIVmne infection by combination immunization with recombinant vaccinia virus and SIVmne gp160

Two Macaca fascicularis with preexisting immunity to vaccinia virus were immunized twice with recombinant vaccinia virus expressing SIVmne gp160. Their SIV-specific antibody responses were lower than that of vaccinia-naive animals immunized similarly. Upon repeated boosting with gp160, the SIV-specific antibody titers in vaccinia-primed animals reached similar levels as vaccinia-naive animals and with comparable neutralizing titers. Both animals were protected against repeated intravenous challenge with low-dose SIVmne E11S. These results are significant because SIVmne E11S infection in M. fascicularis is pathogenic and leads to AIDS-like diseases.

Long-term protection of macaques against high-dose type D retrovirus challenge after immunization with recombinant vaccinia virus expressing envelope glycoproteins

Recombinant vaccinia virus expressing the envelope proteins of type D retrovirus-Washington (SRV-2/W) was used to immunize macaques against SRV-2 infection. Four immunized macaques which had resisted a prior low-dose challenge were rechallenged with a high dose (10(6) infectious particles) of SRV-2 two years after being immunized. All four non-immunized control macaques became infected, but the four vaccinated animals resisted this intravenous challenge, as determined by the inability to detect SRV-2 in peripheral blood mononuclear cells and by the lack of seroconversion to new viral antigens.

Intra-amniotic inoculation of pigtailed macaque (Macaca nemestrina) fetuses with SIV and HIV-1

Six pregnant pigtailed macaques (Macaca nemestrina) were inoculated intra-amniotically (i.a.) with SIVMne. All became viremic and seroconverted; three viable offspring were SIV-positive and at autopsy showed disseminated viral infection; one of three abortuses had SIV-infected thymic macrophages. Three of five pregnant macaques inoculated i.v. and/or i.a. with HIV-1LAI became virus-positive, and four seroconverted, suggesting fetal-maternal transmission. One abortus had HIV-1-antigen in lymph nodes and brain; one infant, culture-positive at birth, died at age 11 days of disseminated HIV-1 infection.

Prevention of transmission of simian immunodeficiency virus from vaccinated macaques that developed transient virus infection following challenge

Macaque immunization with a mixture of four SIV peptides from conserved hydrophilic envelope regions has been shown to prevent virus persistence following challenge with SIVmne/E11s. Data shown here demonstrate that lymph node cells from all vaccinated monkeys and peripheral blood lymphocytes from one of the vaccinees were positive in a SIV-pol 'nested' polymerase chain reaction (PCR) amplification analysis. However, by 37 months after infection, all immunized monkeys were healthy while two of three controls had died and the remaining animal was virus culture-positive and had declining CD4+ lymphocytes. Viable lymph node cells and peripheral lymphoid cells in blood were transferred from the three immunized macaques to individual susceptible macaques. As a control for the transfer, one of the vaccine experiment controls that was actively producing virus in its peripheral blood was used. None of the recipients of cells from the vaccinated macaques seroconverted and all were virus coculture- and PCR-negative 25 weeks post-transfer (p.t.). The recipient of cells from the control infected macaque became positive in these tests by 2-3 weeks p.t. These results suggest that, while peptide-vaccinated macaques permitted some level of SIV replication following challenge, the vaccine prevented disease progression and virus transmission.

Cellular proteins bound to immunodeficiency viruses: implications for pathogenesis and vaccines

Cellular proteins associated with immunodeficiency viruses were identified by determination of the amino acid sequence of the proteins and peptides present in sucrose density gradient-purified human immunodeficiency virus (HIV)-1, HIV-2, and simian immunodeficiency virus (SIV). beta 2 microglobulin (beta 2m) and the alpha and beta chains of human lymphocyte antigen (HLA) DR were present in virus preparations at one-fifth the concentration of Gag on a molar basis. Antisera to HLA DR, beta 2 m, as well as HLA class I precipitated intact viral particles, suggesting that these cellular proteins were physically associated with the surface of the virus. Antisera to class I, beta 2m, and HLA DR also inhibited infection of cultured cells by both HIV-1 and SIV. The specific, selective association of these cellular proteins in a physiologically relevant manner has major implications for our understanding of the infection process and the pathogenesis of immunodeficiency viruses and should be considered in the design of vaccines.

Transmission of SIVMne from female to male Macaca nemestrina

Three SIVMne-infected female pigtailed macaques (Macaca nemestrina) were mated with two SIV-negative males. The females exhibited signs of SAIDS and SIVMne was readily isolated from peripheral blood mononuclear cells (PBMC). Both males became infected with SIVMne, developed SAIDS, and died. This is the first documented case of the transmission of SIVMne between adult macaques housed together. Although transmission through scratching or biting cannot be ruled out, heterosexual transmission appears the most likely mode of SIVMne transmission in this study.

Evaluation of protective efficacy of recombinant subunit vaccines against simian immunodeficiency virus infection of macaques

Simian immunodeficiency virus (SIV) was used as a model to study the protective efficacy of an immunization regimen currently being evaluated as candidate vaccines against HIV in human subjects. Four Macaca fascicularis were first immunized with recombinant vaccinia virus expressing the envelope glycoprotein gp160 of SIVmne and then boosted with subunit gp160. Both cell-mediated and humoral immune responses against SIV, including neutralizing antibodies, were elicited. The macaques were shown to be protected from a homologous virus infection as determined by serology, lymphocyte cocultivation, polymerase chain reactions and in vivo transmission analyses. Four unimmunized control animals were readily infected. However, viremia in infected control animals could decrease substantially following the initial phase of infection so that persistent infection might not be readily detectable.

Protection of macaques against SIV infection by subunit vaccines of SIV envelope glycoprotein gp160

Simian immunodeficiency virus (SIV) is a primate lentivirus related to human immunodeficiency viruses and is an etiologic agent for acquired immunodeficiency syndrome (AIDS)-like diseases in macaques. To date, only inactivated whole virus vaccines have been shown to protect macaques against SIV infection. Protective immunity was elicited by recombinant subunit vaccines. Four Macaca fascicularis were immunized with recombinant vaccinia virus expressing SIVmne gp160 and were boosted with gp160 produced in baculovirus-infected cells. All four animals were protected against an intravenous challenge of the homologous virus at one to nine animal-infectious doses. These results indicate that immunization with viral envelope antigens alone is sufficient to elicit protective immunity against a primate immunodeficiency virus. The combination immunization regimen, similar to one now being evaluated in humans as candidate human immunodeficiency virus (HIV)-1 vaccines, appears to be an effective way to elicit such immune responses.

Variation in simian immunodeficiency virus env is confined to V1 and V4 during progression to simian AIDS

We have monitored changes in the simian immunodeficiency virus (SIV) envelope (env) gene in two macaques which developed AIDS after inoculation with a molecular clone of SIV. As the animals progressed to AIDS, selection occurred for viruses with variation in two discrete regions (V1 and V4) but not for viruses with changes in the region of SIV env that corresponds to the immunodominant, V3 loop of human immunodeficiency virus. Within the highly variable domains, the vast majority of nucleotide changes encoded an amino acid change (98%), suggesting that these envelope variants had evolved as a result of phenotypic selection. Analysis of the biological properties of these variants, which have been selected for in the host, may be useful in defining the mechanisms underlying viral persistence and progression to simian AIDS.

Protection of macaques with a simian immunodeficiency virus envelope peptide vaccine based on conserved human immunodeficiency virus type 1 sequences

This report describes the vaccination of rhesus macaques with peptides selected from regions of the simian immunodeficiency virus (SIV) envelope that are hydrophilic, immunoreactive, and highly homologous with corresponding conserved envelope sequences of the human immunodeficiency virus (HIV). The peptides, produced as beta-galactosidase fusion proteins, induced virus-neutralizing and peptide-specific antibodies. After challenge with virulent virus, controls became virus positive and developed gradually rising antibody titers to SIV over 63 weeks. Immunized macaques developed a postchallenge anamnestic response to SIVenv antigens within 3-6 weeks followed by a gradual, fluctuating decline in SIV antibody titers and partial or total suppression of detectable SIV. Virus suppression correlated with prechallenge neutralizing antibody titers. Although the average CD4+ cell count in the blood of immunized macaques remained constant, the control macaques exhibited a progressive decrease developing about week 55 after challenge. The conserved nature of the HIV and SIV peptides and the similar humoral immunoreactivity in the respective hosts suggest that homologous HIV peptides may be important components of a successful immunization strategy.

Viral and cellular gene expression in CD4+ human lymphoid cell lines infected by the simian immunodeficiency virus, SIV/Mne

Our laboratory has undertaken an analysis of cellular and viral gene expression in CD4+ human lymphoid cell lines infected by the human and simian immunodeficiency viruses, HIV-1 and SIV/Mne, respectively. The purpose of the current study was to: (i) examine the effects of SIV/Mne infection on host macromolecular synthesis and compare the results to those in the HIV-1 system; and (ii) investigate the mechanisms responsible for the restriction of SIV/Mne infection in CD4 positive lymphoid cells which are readily infected by HIV-1. First we determined that SIV does not impose selective blocks on host macromolecular synthesis, unlike HIV-1, which induces both the selective inhibition of cellular protein synthesis and the degradation of cellular mRNAs (Agy, M., Wambach, M., Foy, K., and Katze, M. G., 1990, Virology 177, 251-258). No such selective reduction in cellular mRNA stability or protein synthesis was observed in cells infected by SIV/Mne. Additional differences between SIV and HIV-1 were observed using a panel of CD4+ human cell lines. While HIV-1-infected all cell lines. SIV/Mne efficiently infected only the MT-4, C8166, and 174 x CEM cell lines. Repeated efforts to infect CEM or Jurkat cells were unsuccessful as determined by PCR analysis of viral DNA. HUT 78 cells supported a limited infection detectable only by PCR analysis. These data suggest the block in viral replication in the nonsusceptible cell lines is at an early step. Interestingly, all the SIV susceptible cells were virally transformed, C8166 and MT-4 by HTLV-1, and 174 x CEM by Epstein-Barr virus. Furthermore FACS analysis revealed that all susceptible cells expressed two B cell associated markers, B7/BB1 and CD40. These observations taken together highlight differences between the HIV and SIV viruses, and suggest that for efficient replication, SIV/Mne may require an additional cell surface molecule, cofactors provided by transforming viruses, or a complex interplay between the two.

Maternal-fetal transmission of SIV in macaques: disseminated adenovirus infection in an offspring with congenital SIV infection

To develop a nonhuman primate model for maternal-fetal transmission of HIV infection, we have inoculated pregnant Macaca nemestrina with uncloned SIVMne. Three animals inoculated during the third trimester delivered healthy infants. One of the three infants, a male born 31 days after the mother was inoculated with SIV, became virus-positive but failed to produce SIV-specific antibody and died with overt simian immunodeficiency and disseminated adenovirus (SV20) infection at age six and one-half months. SIV and adenovirus antigen could be demonstrated by immunohistochemical methods in multiple organ systems.

In vitro screening for antiretroviral agents against simian immunodeficiency virus (SIV)

Simian immunodeficiency virus (SIV), which causes an acquired immunodeficiency syndrome in macaques, is a lentivirus that is morphologically, antigenically, genetically, and biologically similar to the human immunodeficiency virus (HIV). Because of these similarities, the SIV model represents a unique opportunity for in vitro and in vivo testing of antiretroviral agents. Since antiretroviral agents may exhibit different properties in different cells in vitro, more than one cell line may be necessary to evaluate the efficacy and modes of action of an antiretroviral agent. Initially we tested ten cell lines for their permissiveness to five SIV isolates. One B-cell line (AA-2) and one T-cell line (HuT 78) were selected to test antiretroviral agents since both were extremely permissive for SIVmac251, an isolate with a high rate of infectivity. Using this optimized in vitro testing protocol, we screened ten antiretroviral agents for their ability to inhibit SIV replication. Six of the compounds completely inhibited SIV viral antigen expression. Based on the selectivity index, 3'-azido-3'-dideoxythymidine, 3'-azido-2',3'-dideoxyuridine, and 3'-fluoro-3'-deoxythymidine appear to be the most efficacious antiretroviral agents against SIVmac251. Several different assays for determining viral antigen inhibition were conducted and the results of these assays were comparable. Our results demonstrate that the SIV in vitro model is a valuable screening tool for determining the efficacy and toxicity of new antiretroviral agents.

Simian immunodeficiency virus is restricted to a subset of blood CD4+ lymphocytes that includes memory cells

HIV and the related simian immunodeficiency virus (SIV), which causes AIDS in macaques, infect only a small percentage of CD4+ lymphocytes at any point during the disease. We have identified three distinct cellular phenotypes within the CD4+ subpopulation in macaques, based on cell surface expression of CD44 and CD45R, which putatively represent successive stages of postthymic proliferation and functional maturation. Two of these subsets, CD44hi CD45R+, which contained virtually all circulating cells in cycle, and CD44hi CD45R-, which was noncycling and has been linked to immunologic memory, were selectively depleted in SIV-infected animals at an asymptomatic stage of disease. To test whether SIV infection was restricted to cells with this phenotype in vivo, we used the polymerase chain reaction to sensitively detect SIV DNA in purified subpopulations of CD4+ lymphocytes. We found that SIV exclusively infected blood lymphocytes expressing high levels of CD44. Within this subset infection occurred not only in the fraction containing actively proliferating cells (CD45R+), but also in resting, putative memory cells (CD45R-). These data directly demonstrate that cellular maturation stages of normal postthymic T lymphocyte differentiation are important factors in permitting lentivirus infection in vivo, and that noncycling, memory T cells may be a reservoir for SIV.

Simian immunodeficiency virus is restricted to a subset of blood CD4+ lymphocytes that includes memory cells

HIV and the related simian immunodeficiency virus (SIV), which causes AIDS in macaques, infect only a small percentage of CD4+ lymphocytes at any point during the disease. We have identified three distinct cellular phenotypes within the CD4+ subpopulation in macaques, based on cell surface expression of CD44 and CD45R, which putatively represent successive stages of postthymic proliferation and functional maturation. Two of these subsets, CD44hi CD45R+, which contained virtually all circulating cells in cycle, and CD44hi CD45R-, which was noncycling and has been linked to immunologic memory, were selectively depleted in SIV-infected animals at an asymptomatic stage of disease. To test whether SIV infection was restricted to cells with this phenotype in vivo, we used the polymerase chain reaction to sensitively detect SIV DNA in purified subpopulations of CD4+ lymphocytes. We found that SIV exclusively infected blood lymphocytes expressing high levels of CD44. Within this subset infection occurred not only in the fraction containing actively proliferating cells (CD45R+), but also in resting, putative memory cells (CD45R-). These data directly demonstrate that cellular maturation stages of normal postthymic T lymphocyte differentiation are important factors in permitting lentivirus infection in vivo, and that noncycling, memory T cells may be a reservoir for SIV.

Evidence that HIV-1 gag precursor shares antigenic sites with the major capsid protein of human cytomegalovirus

A rabbit antiserum prepared against disrupted sucrose-banded HIV-1 virus (strain FRE-3) reacted with antigens present in nuclear inclusions, pathognomonic for human cytomegalovirus (HCMV). This cross-reactivity was observed in autopsy specimens from individuals infected with CMV, in the presence or absence of co-infection with HIV-1. A Towbin immunoassay showed that the serum reacted specifically with the HCMV major capsid protein (MCP, 153 kDa), both in the nuclear fraction of infected cells and in virions. Direct evidence that these proteins share antigenic determinants was provided by the two-way cross-reactivity of affinity-selected antibodies (i.e., anti-MCP with HIV-1 gag precursor Pr55; anti-Pr55 with MCP). All four strains of HCMV tested showed this reactivity, but the counterpart proteins of simian CMV and herpes simplex virus type 1 did not, indicating that the determinant is not common to all herpes group viruses.

CD4 and CD8 T cells from SIV-infected macaques have defective signaling responses after perturbation of either CD3 or CD2 receptors

Single-cell clones, designated E11S, C11R, and A1S, were obtained from the HuT-78 T cell line persistently infected with an isolate of Simian immunodeficiency virus (SIV), SIV/Mne. The infected clones, unlike uncloned uninfected HuT-78 cells, no longer expressed the CD4 marker and, after their CD3 receptors were cross-linked, had dramatically reduced intracellular free calcium ([Ca2+]i) responses. In one clone, E11S, the unresponsiveness was not limited to the inositol phospholipid pathway of signaling since a reduction in CD3-mediated activation of protein tyrosine kinase-dependent phosphorylation also was evident in this SIV-infected clone. These results led us to test whether T lymphocytes from animals infected with SIV had defective [Ca2+]i responses prior to detectable changes in CD4 levels or lymphadenopathy. The [Ca2+]i responses to both CD3 mAb and CD2 mAb were 10-50% less in T cells from Walter Reed stage 2 animals than in healthy controls. This anergy was more pronounced in chronically infected animals progressing to Walter Reed stage 3/4. The responses of these animals could not be augmented even when combinations of CD3 and CD4 mAb were used. Both CD4+CD44lo T cells, which are not infected with SIV, and the CD4+CD44hi T cell subset, previously shown to be the reservoir of SIV infection in blood, had pronounced defective responses to CD3 mAb. Similarly, both CD4+ and CD8+ T cells were consistently unresponsive in chronically infected animals, again implying that an indirect mechanism, rather than SIV infection per se, may be responsible for this immune dysfunction.

Antigen capture assay for detection of simian type D retroviruses in cell cultures and plasma samples

A rapid, sensitive and specific antigen capture (AC) assay has been established for the detection of p27 core protein of SAIDS type-D retrovirus (SRV). SRV p27 antigen in test samples was identified on rabbit anti-p27 IgG-coated microtiter plates by the addition of biotinylated rabbit anti-p27 IgG. This assay was specific for the p27 core protein of SRV-1 and SRV-2 and provided semi-quantitative results in less than 7 hours. Results of the AC assay were highly correlated with those of reverse transcriptase (RT), immunofluorescence and immunoblotting assays. However, the AC assay was faster and more sensitive than the other three assays. The AC assay also provided a rapid diagnostic tool for the detection of SRV in plasma, serum and peripheral blood lymphocyte cocultures. In addition to mass screening of SRV infection in macaque colonies, the AC assay also will be valuable for monitoring the efficacy of antiretroviral agents against SRV in vitro and in vivo.

Protection of macaques against simian AIDS by immunization with a recombinant vaccinia virus expressing the envelope glycoproteins of simian type D retrovirus

Simian AIDS (SAIDS) is an endemic disease of macaques that shares many characteristics with AIDS in humans. SAIDS is etiologically linked to infection by a type D retrovirus, SAIDS retrovirus (SRV). Immunization with an inactivated whole-virus vaccine was shown to protect macaques against infection by SRV serotype 1. To identify the antigen(s) responsible for eliciting protective immunity, we have constructed a recombinant vaccinia virus (v-senv5) that expresses the envelope glycoproteins of SRV serotype 2 (SRV-2/W). Pig-tailed macaques (Macaca nemestrina) immunized with v-senv5 showed lymphoproliferative responses to purified SRV-2/W. They also generated antibodies that neutralized SRV-2/W infectivity in vitro and mediated antibody-dependent cellular cytotoxicity against SRV-2-infected cells. Four v-senv5-immunized animals, together with four control animals, were challenged intravenously with 5 x 10(3) tissue culture infectious doses of SRV-2/W. As early as 2 weeks after challenge, three of four control animals became viremic, and two of these three animals also seroconverted. The animal that was viremic but remained antibody negative died of symptoms of SRV infection 6 1/2 weeks after challenge. In contrast, all four v-senv5-immunized animals remained healthy, virus-free, and seropositive against only the immunizing envelope antigens. These results indicate that immunization with a recombinant vaccinia virus expressing the envelope antigens of SRV-2/W protects primates from infection by a retrovirus that causes immunodeficiency diseases.