Analysis of SIV-specific CTL in the rhesus macaque model of AIDS: the use of simian fibroblasts as an alternative source of target cells for chromium release assays

The simian immunodeficiency virus (SIV) model of AIDS is widely used for the development of human immunodeficiency virus (HIV) vaccine strategies, particularly for the analysis of correlates of protective immunity. As it is not always possible to establish autologous B-lymphoblastoid cell lines (B-LCL) for use as targets in the analysis of cytotoxic T cell (CTL) activity, we have compared B-LCL with primary simian skin cells. Using a well-defined SIV gag-encoded CTL epitope restricted by Mamu A*01 major histocompatibility complex (MHC) class I, we have shown that peripheral blood mononuclear cells (PBMC) from vaccinated and infected macaques can kill MHC class I-matched skin fibroblasts presenting the cognate epitope but that skin fibroblasts are a less sensitive target than B-LCL for the detection of CTL.

Comparison of early plasma RNA loads in different macaque species and the impact of different routes of exposure on SIV/SHIV infection

Various simian immunodeficiency virus (SIV)sm/mac and simian/human immunodeficiency virus (SHIV) strains are used in different macaque species to study AIDS pathogenesis, as well as to evaluate candidate vaccine and anti-retroviral drugs efficacy. In this study we investigated the effect of route of infection, species of macaques and nature of virus stock on early plasma viral RNA load. We monitored the plasma RNA concentrations of 63 rhesus (Macaca mulatta) and cynomolgus macaques (Macaca fascicularis) infected with well-characterised virus stocks administered either by oral, rectal, vaginal or intravenous (i.v.) routes. In SIV(mac)-infected macaques, no significant difference in plasma RNA loads was observed between the rectal, oral and i.v. routes of infection. Cynomolgus macaques developed lower steady state SIV plasma RNA concentrations compared with rhesus macaques and no significant difference was observed between rectal and i.v. routes of infection. In SHIV(89.6p)-infected macaques, no difference between species or between route of infection was observed with this particular chimeric virus.

A conformational C4 peptide polymer vaccine coupled with live recombinant vector priming is immunogenic but does not protect against rectal SIV challenge

The conserved, immunogenic CD4 binding site on the viral envelope is an attractive HIV or SIV vaccine candidate. Polymerization of an 18 amino acid segment derived from the C4 domain of SIV gp120 produced a peptide polymer or "peptomer," having an alpha-helical conformation possibly mimicking a proposed structure of the C4 domain in the unbound native protein. The SIV peptomer and native gp120 were compared as subunit boosts following two adenovirus type 5 host range (Ad5hr)-SIVenv recombinant priming immunizations. Both vaccine regimens successfully elicited SIV-specific CTL responses in five of six immunized macaques. Peptomer-boosted macaques exhibited significantly higher envelope-specific T cell proliferative responses than either the gp120-boosted macaques or controls. Peptomer immunization also elicited peptomer and SIV gp120-specific binding antibodies, but only native gp120 boosting elicited SIV neutralizing antibodies. Upon intrarectal challenge with SIVmac32H, all nine macaques became infected. The solely envelope-based vaccine conferred no protection. However, changing the boosting immunogen to the C4 peptomer did not improve protective efficacy in spite of its elicitation of humoral and cellular immune responses, including robust T-helper activity. In spite of the peptomer's strong immunogenicity and potential for induction of broadly protective immune responses, it was not effective as a subunit vaccine.

Replication of simian immunodeficiency virus (SIV) in ex vivo lymph nodes as a means to assess susceptibility of macaques in vivo

Six macaques, apparently uninfected, following low-dose exposure to the pathogenic SIV(mac251) and SIV(SME660) by the mucosal route, were used in a pilot study to investigate whether infectability of ex vivo lymph nodes could predict resistance and/or susceptibility to SIV infection in vivo. Of six macaques exposed to the less-pathogenic virus SIV(MNE), four resisted viral infection. Analysis of the susceptibility of the PBMC of these four animals before SIV(MNE) challenge indicated that all of them were resistant to infection by the SIV(BK28) isolate and, in three of them, this resistance was dependent on CD8+ T cells. Blocks of lymph nodes of these four macaques were resistant to SIV(MNE) infection ex vivo following SIV(MNE) viral challenge exposure. However, the same blocks from the same animals were permissive to the more virulent SIV(251(32H)). Accordingly, three of these macaques were readily infected following challenge exposure with SIV(251(32H)). Lymphoproliferative responses in blood or lymph nodes, local C-C chemokine production in the lymph-node explants, and cytotoxic T-cell activity measured throughout the study did not correlate with ex vivo resistance or susceptibility to in vivo infection. In conclusion, PBMC and lymph-node resistance or susceptibility to infection ex vivo appeared to correlate with in vivo infectivity and, thus, these approaches should be further tested for their predictive value for in vivo infection.

The role of gammadelta T cells in generating antiviral factors and beta-chemokines in protection against mucosal simian immunodeficiency virus infection

In view of the role of gammadelta(+) T cells in mucosal protection against infection, the proportion of gamma delta T cells was examined in cells eluted from lymphoid and mucosal tissues of macaques immunized with simian immunodeficiency virus (SIV) gp120 and p27 in alum and challenged with live SIV by the rectal mucosal route. This revealed a significant increase in gammadelta T cells eluted from the rectal mucosa (p < 0.01) and the related iliac lymph nodes (p < 0.0001) in protected as compared with infected macaques. Preferential homing of PKH-26-labeled gammadelta(+) T cells from the primed iliac lymph nodes to the rectal and cervico-vaginal mucosa was demonstrated after targeted iliac lymph node as compared with i. m. immunization. Investigations of the mechanism of protection revealed that gammadelta(+) T cells can generate antiviral factors, RANTES, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta which can prevent SIV infection by binding to the CCR5 coreceptors. Up-regulation of gammadelta(+) T cells was demonstrated by immunization of macaques with heat shock protein (HSP)70 linked to peptides and with granulocyte-macrophage colony-stimulating factor (GM-CSF). This was confirmed by in vitro studies showing that GM-CSF can up-regulate gammadelta(+) T cells from macaques immunized with HSP-linked peptides but not those from naive animals. We suggest that a novel strategy of immunization with HSP70 linked to antigen may generate both cognate immunity to the antigen and innate immunity by virtue of up-regulation of gammadelta(+) T cells. These cells generate antiviral factors and the three beta-chemokines that prevent binding and transmission of SIV or M-tropic HIV by the CCR5 coreceptor.

Up-regulation of beta-chemokines and down-modulation of CCR5 co-receptors inhibit simian immunodeficiency virus transmission in non-human primates

A non-cognate mechanism of protection against human immunodeficiency virus-1 (HIV-1) infection involves up-regulation of beta-chemokines, which bind and may down-modulate the CCR5 co-receptors, thereby preventing transmission of M-tropic HIV-1. The objective of this investigation was to evaluate this mechanism in vivo in non-human primates. Rhesus macaques were immunized by a modified targeted lymph nodes (TLN) route with recombinant simian immunodeficiency virus (SIV) glycoprotein 120 (gp120) and p27 in alum, and adsorbed recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) with either interleukin (IL)-2 or IL-4. Immunization induced significant increases in the concentrations of CD8 cell-derived suppressor factor (CD8-SF), regulated on activation normal T cells expressed and secreted (RANTES), macrophage inflammatory protein (MIP)-1alpha and MIP-1beta, and down-modulation of the proportion of cells expressing CCR5 (r = 0.737, P<0.05). The macaques were then challenged with SIVmac 220 by the rectal mucosal route. The plasma SIVmac RNA showed a significant inverse correlation with the CD8-SF or the concentration of the three beta-chemokines (r = 0.831 and 0.824, P<0.01), but a positive correlation between the proportion of CCR5+ cells and SIVmac RNA (r = 0.613, P = 0.05). These results demonstrate for the first time in vivo that immunization up-regulates beta-chemokines, which may down-modulate CCR5 co-receptors, and both functions are significantly correlated with the viral load. Hence, the non-cognate beta-chemokine-CCR5 mechanism should be considered as complementary to specific immunity in vaccination against HIV.

The effect of route of immunization on mucosal immunity and protection

In macaques, the route of immunization has a profound effect on the immune response. Augmenting rectal or vaginal immunization with oral or nasal immunization enhanced the secretory IgA, serum IgG, and T cell responses. However, targeted iliac lymph node (TILN) immunization with recombinant simian immunodeficiency virus (SIV) gp120 and p27 elicited the most consistent mucosal antibody responses in the rectum, vagina, urine, seminal fluid, and blood. Both mucosal and TILN immunization induced specific CD4+ T cell proliferative responses in the iliac lymph nodes, which drain these mucosal surfaces, and in the splenic and circulating T cells. Rectal mucosal challenge with cell-free SIV induced total protection in 4 of 7 macaques that were immunized by the TILN route, and, compared with unimmunized macaques or those immunized by the mucosal route (P<.001), it induced a >90% decrease in virus load in 3 of them. Protection from mucosal rectal infection with SIV was significantly associated with an increase in the CD8 suppressor factor (which was generated by the iliac lymph node), RANTES, and MIP-1beta (P<.01).

Live attenuated simian immunodeficiency virus (SIV)mac in macaques can induce protection against mucosal infection with SIVsm

OBJECTIVE

To investigate whether vaccination of macaques with attenuated simian immunodeficiency virus (SIV)macC8 could induce long-term protective immunity against rectal exposure to SIVsm and intravenous exposure to the more divergent HIV-2.

DESIGN AND METHODS

Eight months after vaccination with live attenuated SIVmacC8, four cynomolgus monkeys were challenged with SIVsm intrarectally and another four vaccinated monkeys were challenged with HIV-2 intravenously. Sixteen months after SIVmacC8 vaccination, another two monkeys were challenged with SIVsm across the rectal mucosa. Two vaccinees shown to be protected against SIVsm were rechallenged 8 months after the first challenge. Ten naive animals were used as controls. Serum antigenaemia, virus isolation, antibody responses, cell-mediated immunity and CD4+ and CD8+ T-cell subpopulations were monitored. PCR-based assays were used to distinguish between virus populations.

RESULTS

At the time of challenge, eight out of 10 vaccinees were PCR-positive for SIVmacC8 DNA but no virus could be isolated from peripheral blood mononuclear cells. After SIVsm challenge, three out of six vaccinees were repeatedly SIVsm PCR-negative. In one of the three infected monkeys, the challenge virus was initially suppressed but the monkey ultimately developed AIDS after increased replication of the pathogenic virus. Rechallenged monkeys remained protected. All HIV-2-challenged vaccinees became superinfected. All controls became infected with either SIVsm or HIV-2. At the time of challenge the vaccinees had neutralizing antibodies to SIVmac but no demonstrable cross-neutralizing antibodies to SIVsm or HIV-2. Titres of antigen-binding or neutralizing antibodies did not correlate with protection. Cytotoxic T-cell responses to SIV Gag/Pol and virus-specific T-cell proliferative responses were low.

CONCLUSION

The live attenuated SIVmacC8 vaccine was able to induce long-term protection against heterologous intrarectal SIVsm challenge in a proportion of macaques but not against the more divergent HIV-2, which was given intravenously.

Recombinant vaccine-induced protection against the highly pathogenic simian immunodeficiency virus SIV(mac251): dependence on route of challenge exposure

Vaccine protection from infection and/or disease induced by highly pathogenic simian immunodeficiency virus (SIV) strain SIV(mac251) in the rhesus macaque model is a challenging task. Thus far, the only approach that has been reported to protect a fraction of macaques from infection following intravenous challenge with SIV(mac251) was the use of a live attenuated SIV vaccine. In the present study, the gag, pol, and env genes of SIV(K6W) were expressed in the NYVAC vector, a genetically engineered derivative of the vaccinia virus Copenhagen strain that displays a highly attenuated phenotype in humans. In addition, the genes for the alpha and beta chains of interleukin-12 (IL-12), as well as the IL-2 gene, were expressed in separate NYVAC vectors and inoculated intramuscularly, in conjunction with or separate from the NYVAC-SIV vaccine, in 40 macaques. The overall cytotoxic T-lymphocyte (CTL) response was greater, at the expense of proliferative and humoral responses, in animals immunized with NYVAC-SIV and NYVAC-IL-12 than in animals immunized with the NYVAC-SIV vaccine alone. At the end of the immunization regimen, half of the animals were challenged with SIV(mac251) by the intravenous route and the other half were exposed to SIV(mac251) intrarectally. Significantly, five of the eleven vaccinees exposed mucosally to SIV(mac251) showed a transient peak of viremia 1 week after viral challenge and subsequently appeared to clear viral infection. In contrast, all 12 animals inoculated intravenously became infected, but 5 to 6 months after viral challenge, 4 animals were able to control viral expression and appeared to progress to disease more slowly than control animals. Protection did not appear to be associated with any of the measured immunological parameters. Further modulation of immune responses by coadministration of NYVAC-cytokine recombinants did not appear to influence the outcome of viral challenge. The fact that the NYVAC-SIV recombinant vaccine appears to be effective per se in the animal model that best mirrors human AIDS supports the idea that the development of a highly attenuated poxvirus-based vaccine candidate can be a valuable approach to significantly decrease the spread of human immunodeficiency virus (HIV) infection by the mucosal route.

Protective mucosal immunity elicited by targeted lymph node immunization with a subunit SIV envelope and core vaccine in macaques

Prevention of sexually transmitted HIV infection was first investigated in non-human primates by mucosal immunization via the rectal, vaginal or male urethral route. This was compared with subcutaneous targeted iliac lymph node (TILN) and systemic intramuscular immunization in non-human primates. TILN immunization elicited the most consistent mucosal sIgA and IgG antibody response in the rectum, vagina, urine and seminal fluid, as well as in blood. Both mucosal and TILN immunization induced a specific CD4+ T cell proliferative response in the iliac lymph nodes which drain these mucosal surfaces, and in the splenic and circulating T cells. In the next experiment macaques were immunized by the TILN route with SIV gp120 and p27 in alum. Rectal mucosal challenge with SIVmac 32H J5 molecular clone (or cell-free virus) induced total protection in four out of seven macaques, compared with infection in 13 of 14 unimmunized macaques or immunized by other routes (p = 0.025). The remaining three macaques immunized by the TILN route showed either decrease in viral load (> 90%) or transient viraemia, indicating that all seven TILN immunized macaques showed total or partial protection of rectal transmission by SIV (p = 0.001). Protection was associated with significant increase in the iliac lymph nodes IgA antibody secreting cells to p27 (p < 0.02), CD8-suppressor factor inhibiting replication of SIV in CD4+ T cells (p < 0.01) and the chemokines RANTES and MIP-1 beta (p < 0.01). We suggest that administration of gp120 and p27 by the TILN route may elicit protective B and T cell immunity which can significantly prevent rectal transmission of SIV or HIV.

Evidence for the persistence of monoclonal expansions of CD8+ T cells following primary simian immunodeficiency virus infection

A longitudinal study of the CD8+ TCR variable (Vbeta) chain repertoire was performed in rhesus macaques experimentally infected with simian immunodeficiency virus (SIV) using both TCR Vbeta chain-specific monoclonal antibodies and TCR beta chain CDR3 length analysis. Expansions of subpopulations of CD8+ T cells were detected during the acute phase of SIV infection. In all monkeys studied, monoclonal expansions persisted for at least 18 months and increasingly dominated the repertoire of CD8+ T cells expressing the relevant Vbeta chain. This study shows that persistent CD8+ T cell expansions develop in response to a virus infection. This is important not only for our understanding of the T cell response to viruses but also for understanding the factors that determine the normal CD8+ TCR repertoire.

Anti-major histocompatibility complex antibody responses to simian B cells do not protect macaques against SIVmac infection

Macaques have been protected against infection with human cell-grown SIVmac by immunization with antigens encoded by the human major histocompatibility complex (MHC). Here, we investigated the efficacy of alloimmunization with simian B cells expressing high levels of MHC class I and class II molecules to confer protection against systemic challenge with simian-grown SIVmac. Eight rhesus macaques were vaccinated with glutaraldehyde-fixed and beta-propiolactone-inactivated herpesvirus papio-transformed B cells. Four of the macaques received 5 doses, the others 10. Animals were challenged with rhesus macaque spleen-derived cell-free SIVmac. Allogeneic B cells elicited antibody responses to rhesus MHC class I and II but failed to protect animals against infection. Anti-MHC class I antibodies were restricted in specificity and failed to recognize MHC class I from some B lymphoblastoid cell lines (B-LCLs) including a B-LCL from the animal in whose cells the challenge virus was grown. Vaccinated animals responded to self-MHC class I antigens but not to self-MHC class II antigens from peripheral blood mononuclear cells (PBMCs). Animals that underwent the shorter immunization regimen had transiently enhanced PBMC-associated virus loads after challenge, whereas the average virus-infected cell load was reduced in animals that underwent the more extensive immunization. These results suggest that antibody responses to allogeneic MHC molecules do not protect against infection with immunodeficiency lentiviruses.

Mechanisms of protection induced by attenuated simian immunodeficiency virus. IV. Protection against challenge with virus grown in autologous simian cells

Attenuated simian immunodeficiency virus (SIV) induces potent protection against infection with wild-type virus, but the mechanism of this immunity remains obscure. Allogeneic antibodies, which arise within animals as a result of SIV infection, might protect against challenge with exogenous SIV grown in allogeneic cells. To test this hypothesis, eight macaques were infected with attenuated SIV and subsequently challenged with wild-type SIV grown in autologous cells or heterologous cells. The results clearly demonstrated that animals infected with attenuated SIV are protected against wild-type SIV grown in autologous or heterologous cells. Thus, the hypothesis that live attenuated SIV protects by the induction of allogeneic antibodies is not tenable.

Protective mucosal immunity elicited by targeted iliac lymph node immunization with a subunit SIV envelope and core vaccine in macaques

Prevention of sexually transmitted HIV infection was investigated in macaques by immunization with a recombinant SIV (simian immunodeficiency virus) envelope gp 120 and core p27 vaccine. In two independent series of experiments, we used the novel targeted iliac lymph node (TILN) route of immunization, aiming close to the iliac lymph nodes draining the genitorectal mucosa. Rectal challenge with the SIVmac 32H J5 molecular clone in two series induced total protection in four out of seven macaques immunized by TILN, compared with infection in 13 of 14 unimmunized macaques or immunized by other routes (P = 0.025). The remaining three macaques showed either a decrease in viral load ( > 90%) or transient viremia, indicating that all seven TILN-immunized macaques showed total or partial protection (P = 0.001). Protection was associated with significant increase in the iliac lymph nodes of IgA antibody-secreting cells to p27 (P < 0.02), CD8-suppressor factor (P < 0.01), and the chemokines RANTES and MIP-1 beta (P < 0.01).

Early suppression of SIV replication by CD8+ nef-specific cytotoxic T cells in vaccinated macaques

In order to develop a successful subunit vaccine against infection with the human immunodeficiency virus (HIV), protective immune effector functions must be identified. Until now, there has been only indirect evidence that HIV-specific cytotoxic T lymphocytes (CTLs) fulfill this role. Using the macaque simian immunodeficiency virus (SIV) model, the protective potential of nef-specific CTLs, stimulated by vaccination, was examined in animals challenged with a high intravenous dose of the pathogenic simian immunodeficiency virus, SIVmac251(32H)(pJ5). An inverse correlation was found between the vaccine-induced nef-specific CTL precursor frequency and virus load measured after challenge. In addition, the early decline in viraemia, observed in both vaccinated and unvaccinated control animals was associated with the development of virus-specific CTL activity and not with the presence of virus-specific neutralizing antibodies. The results imply that vaccines that stimulate strong CTL responses could protect against HIV infection.

Protection by attenuated simian immunodeficiency virus in macaques against challenge with virus-infected cells

A vaccine against AIDS will probably have to protect against challenge both by viable virus-infected cells and by cell-free virus. Eight cynomolgus macaques infected with attenuated simian immunodeficiency virus (SIV) were challenged (four each) with cell-free and cell-associated SIV. All were protected, whereas eight controls were all infected after challenge. These findings show that live-attenuated vaccine can confer protection against SIV in macaques. Extrapolation to human beings will require extensive evaluation of the safety of attenuated retroviruses. Alternatively, the mechanism of this potent protection must be understood and reproduced by less hazardous means.

An experimental chemically inactivated HIV-1 vaccine induces antibodies that neutralize homologous and heterologous viruses

We have developed a unique multiple step procedure to inactivate human immunodeficiency virus chemically with a very high safety margin while retaining antigenically active structural virion proteins, including gp120, in the final immunogen. The whole virus preparation (1-10 micrograms per dose) was highly immunogenic in a variety of small mammals and induced antibodies that recognized homologous and heterologous strains of HIV-1. Sera from immunized animals bound to peptides representing the entire sequence of the external glycoprotein gp120. Neutralizing antibodies active against the homologous immunizing strain and against heterologous HIV-1 strains were also elicited. Sera with virus neutralizing activity did not bind to MHC class I proteins derived from the human cell line used to grow the virus.

Antibodies to human and non-human primate cellular and culture medium components in macaques vaccinated with the simian immunodeficiency virus

Inactivated simian immunodeficiency virus (SIV) grown in a human T-cell line induces protection from infection by the virus in macaques. However, observations that immunization with uninfected human T cells or with SIV-1 prepared in human T cells can also induce protection, has raised the possibility that protective antigens could be of human cellular origin. Sera from animals immunized with fixed infected and uninfected human T cells, as well as from animals immunized with partially purified cell-free SIV have been examined for their ability to bind to human and macaque peripheral blood mononuclear cells (PBMC) and to-components present in fetal calf serum (FCS) in which the cells were grown. Analysis by flow cytometry suggests that antibodies to human cell surface antigens can be elicited with both inactivated SIV grown in human T cells and by uninfected T cells. There was a significant association between the presence of anti-cell antibodies and protection from infection. However, anti-cell surface antibodies were not detected with macaque mononuclear cells by flow cytometry or by immunoprecipitation, unless these cells were first treated with FCS or activated by a mitogen. Immunoprecipitation of resting human PBMC with sera from immunized animals suggests the presence of antibodies to class I heavy and light chains [beta 2-microglobulin (beta 2 m)] and to bovine beta 2m, which may originate in FCS used to grow the cell line. Antibodies to CD4 were also found in sera from animals immunized with SIV grown in human T cells. We suggest that human cellular components augmented by FCS elicit anti-class I heavy chain, beta 2m, CD4 and FCS antibodies which may be responsible for protection against SIV infection in macaques.

Major histocompatibility complex class I-associated vaccine protection from simian immunodeficiency virus-infected peripheral blood cells

To evaluate the effectiveness of vaccine protection from infected cells from another individual of the same species, vaccinated rhesus macaques (Macaca mulatta) were challenged with peripheral blood mononuclear cells from another animal diagnosed with acquired immune deficiency syndrome (AIDS). Half of the simian immunodeficiency virus (SIV)-vaccinated animals challenged were protected, whereas unprotected vaccinates progressed as rapidly to AIDS. Protection was unrelated to either total antibody titers to human cells, used in the production of the vaccine, to HLA antibodies or to virus neutralizing activity. However, analysis of the serotype of each animal revealed that all animals protected against cell-associated virus challenge were those which were SIV vaccinated and which shared a particular major histocompatibility complex (MHC) class I allele (Mamu-A26) with the donor of the infected cells. Cytotoxic T lymphocytes (CTL) specific for SIV envelope protein were detected in three of four protected animals vs. one of four unprotected animals, suggesting a possible role of MHC class I-restricted CTL in protection from infected blood cells. These findings have possible implications for the design of vaccines for intracellular pathogens such as human immunodeficiency virus (HIV).

Molecular and biological characterization of simian immunodeficiency virus macaque strain 32H proviral clones containing nef size variants

The proviral genome of the 32H reisolate of simian immunodeficiency of macaques (SIVmac32H) has been cloned and sequenced. Including both long terminal repeats, it is 10277 base pairs in length and contains open reading frames for all known SIV genes (gag, pol, vif, vpx, vpr, tat, rev, env and nef). This is the first report of an infectious SIVmac molecular clone which contains no premature termination codons. Three molecular clones of SIVmac32H have been constructed differing in sequence only within their last 1.2 kb. Two of the molecular clones, SIVmac32H(pJ5) and SIVmac32H (pC8), differ in the nef coding region by an in-frame deletion of four amino acids in pC8 and two conservative amino acid changes; other nucleotide changes in the 3' LTR were not associated with known functionally critical motifs. The third clone, SIVmac32H(pB1), contains the last 1.2 kb of the SIVmac251 clone pBK28. The biological properties of virus produced after electroporation of these clones into C8166 cells has been assessed by infection of rhesus and cynomolgus macaques, time to seroconversion and by induction of cytopathic effects upon co-cultivation of infected rhesus peripheral blood lymphocytes with C8166 cells. The viruses obtained from these clones have identical growth kinetics in vitro but differ in their ability to persist in macaques. Macaques infected with pJ5 derived virus remain viraemic longer than macaques infected with pC8-derived virus. PCR analysis of circulating provirus indicates that the nef gene evolved over time in pJ5 virus-infected macaques, whereas late in infection in pC8 virus-infected macaques the nef gene remained invariant in sequence. These results support the observation that a nef deletion mutant of SIVmac239 lost its pathogenic potential and resulted in low-level viraemia when rhesus macaques were infected. Virus challenge pools for vaccine studies have been prepared for pJ5 using both human and monkey cell substrates and these stocks have been titrated both in vitro and in vivo. Virus has also been prepared from pC8 and titrated in vitro. This virus pool is being assessed as an attenuated live-virus vaccine in macaques. Since only virus originating from the SIVmac239 molecular clone is known to cause AIDS-like symptoms in rhesus macaques consistently, the SIVmac32H molecular clones should tell us more about which viral sequence features are important for the pathogenesis of AIDS.

Whole inactivated SIV vaccine grown on human cells fails to protect against homologous SIV grown on simian cells

Several groups have reported protection against experimental SIV infection in macaques immunized with a whole inactivated virus vaccine. The aim of the current study was to investigate whether five macaques vaccinated with whole inactivated SIV and previously shown to be protected against challenge with two divergent strains of SIV grown on human cells could resist challenge with a subsequent homologous SIV grown on macaque cells. We show here that this same vaccine did not protect when the challenge virus was grown on primary cells of monkey origin.

A formalin inactivated whole SIVmac vaccine in Ribi adjuvant protects against homologous and heterologous SIV challenge

Eight monkeys were immunized at 0, 4, 9, and 18 weeks with a total of 2 mg of formalin inactivated SIVmac vaccine with Ribi adjuvant. Two weeks after the last booster four immunized monkeys and two controls were challenged with 10 MID50 of live homologous virus SIVmac, and the remaining four vaccinated animals along with two controls were challenged with the heterologous SIVsm strain. All eight vaccinated monkeys resisted the virus challenge, whereas all controls became infected. Three months after the first challenge the monkeys were rechallenged with the same virus strain, without further boosting. Two of four vaccinated monkeys were still resistant to the homologous SIV strain, and three of four monkeys were resistant to the heterologous SIVsm strain. This study demonstrates vaccine induced cross-protection between SIV strains.

Population sequence analysis of a simian immunodeficiency virus (32H reisolate of SIVmac251): a virus stock used for international vaccine studies

The virus structural genes gag and env (both gp120 and gp41 regions) of the 32H isolate of SIVmac251 were amplified using the polymerase chain reaction (PCR). The proviral template used in the PCR was DNA isolated from cells used to prepare several experimental SIV vaccines, which have been tested in simians, and a standard challenge stock of virus, which has been used in international collaborative studies. The PCR products were cloned and the nucleotide sequences of several clones were determined for each gene. From a comparison of the sequences obtained the predominant amino acid sequences of gag and env were predicted and the degree of sequence heterogeneity was determined. Conserved and more variable regions of each protein were identified. The gp120 region of env was more heterogeneous than gag or the transmembrane protein of env (gp41). Within gp120, sequence variability was concentrated to specific regions equivalent to the V1, V2, and, to a lesser extent, the C1 regions identified for human immunodeficiency virus type 1 (HIV-1). In contrast the region equivalent to the hypervariable "V3-loop" of HIV-1 was highly conserved. The implications of the data is discussed in relation to the ability of this virus stock to prepare effective vaccines against SIV.

Preliminary report: protection of cynomolgus macaques against simian immunodeficiency virus by fixed infected-cell vaccine

Cynomolgus macaques were vaccinated with inactivated simian immunodeficiency virus-infected cells and 'Quil-A' as adjuvant at 0, 4, 8, and 36 weeks or at 0, 4, 8, and 16 weeks. 2 weeks later these animals, together with a similar unvaccinated group, were challenged with 10 MID50 (50% monkey infectious doses) of a pool of SIVmac251 previously titrated in vivo. Virus was repeatedly isolated from unvaccinated animals on at least five separate occasions and proviral DNA was detected in circulating lymphocytes by polymerase chain reaction amplification. By contrast, virus and proviral DNA were not found in any of the vaccinated animals. However, the same vaccination regimen used after live virus challenge did not eliminate virus from previously infected macaques.

Induction of immunoglobulin G Fc receptors by recombinant vaccinia viruses expressing glycoproteins E and I of herpes simplex virus type 1

Glycoprotein E (gE) of herpes simplex virus type 1 (HSV-1) will bind immunoglobulin G (IgG) (Fc) affinity columns (R. B. Bauke and P. G. Spear, J. Virol. 32:779-789, 1979), but recent evidence suggests that the HSV-1 Fc receptor is composed of a complex of gE and glycoprotein I (gI) and that both gI and gE are required for Fc receptor activity (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987; D. C. Johnson, M. C. Frame, M. W. Ligas, A. M. Cross, and N. D. Stow, J. Virol. 62:1347-1354, 1988). We have expressed gE and gI, either alone or in combination, on the surface of HeLa cells by using recombinant vaccinia viruses and have measured Fc receptor activity by Fc-rosetting or IgG-binding assays. Expression of gE alone resulted in the induction of Fc receptor activity, while expression of gI alone gave no detectable Fc binding. Coexpression of gE and gI resulted in higher levels of IgG binding than did expression of gE alone, despite the fact that under conditions of coexpression, the levels of surface gE were reduced. We propose that gE and gI together form a receptor of higher affinity than gE alone and that HSV-1 therefore has the potential to induce two Fc receptors of different affinities.

The use of the polymerase chain reaction for the detection of Simian immunodeficiency virus in experimentally infected macaques

A rapid, non-radioactive assay for the detection of proviral Simian immunodeficiency virus (SIV) in tissue-culture cells is described. The assay is based on the co-amplification of the SIV env and gag genes by the polymerase chain reaction (PCR). When the gag PCR product is blotted onto a nylon membrane and hybridised to a radioactive oligonucleotide probe, the assay can also be used to detect the SIV gag gene in DNA isolated directly from experimentally infected cynomolgus macaque lymphocytes. This provides a valuable assay for the presence of proviral SIV during animal trials of AIDS vaccines and chemotherapeutics.