An AIDS-like condition induced in baboons by HIV-2

Baboon CD8 T cells suppress SIVmac infection in CD4 T cells through contact-dependent production of MIP-1α, MIP-1β, and RANTES

Simian immunodeficiency virus (SIV) infection in rhesus macaques is often characterized by high viremia and CD4 T cell depletion. By contrast, SIV infection in African nonhuman primate natural hosts is typically nonpathogenic despite active viral replication. Baboons are abundant in Africa and have a geographical distribution that overlaps with natural hosts, but they do not harbor SIVs. Previous work has demonstrated baboons are resistant to chronic SIV infection and/or disease in vivo but the underlying mechanisms remain unknown. Using in vitro SIVmac infections, we sought to identify SIV restriction factors in baboons by comparing observations to the pathogenic rhesus macaque model. SIVmac replicated in baboon PBMC but had delayed kinetics compared to rhesus PBMC. However, SIVmac replication in baboon and rhesus isolated CD4 cells were similar to the kinetics seen for rhesus PBMC, demonstrating intracellular restriction factors do not play a strong role in baboon inhibition of SIVmac replication. Here, we show CD8 T cells contribute to the innate SIV-suppressive activity seen in naïve baboon PBMC. As one mechanism of restriction, we identified higher production of MIP-1α, MIP-1β, and RANTES by baboon PBMC. Contact between CD4 and CD8 T cells resulted in maximum production of these chemokines and suppression of viral replication, whereas neutralization of CCR5-binding chemokines in baboon PBMC increased viral loads. Our studies indicate baboon natural restriction of SIVmac replication is largely dependent on CD4-extrinsinc mechanisms mediated, in part, by CD8 T cells.

Human immunodeficiency virus: 25 years of diagnostic and therapeutic strategies and their impact on hepatitis B and C virus

The human immunodeficiency virus (HIV) had spread unrecognized in the human population as sexually transmitted disease and was finally identified by its disease AIDS in 1981. Even after the isolation of the causative agent in 1983, the burden and death rate of AIDS accelerated worldwide especially in young people despite the confection of new drugs capable to inhibit virus replication since 1997. However, at least in industrialised countries, this trend could be reversed by the introduction of combination therapy strategies. The design of new drugs is on going; besides the inhibition of the three enzymes of HIV for replication and maturation (reverse transcriptase, integrase and protease), further drugs inhibits fusion of viral and cellular membranes and virus maturation. On the other hand, viral diagnostics had been considerably improved since the emergence of HIV. There was a need to identify infected people correctly, to follow up the course of immune reconstitution of patients by measuring viral load and CD4 cells, and to analyse drug escape mutations leading to drug resistance. Both the development of drugs and the refined diagnostics have been transferred to the treatment of patients infected with hepatitis B virus (HBV) and hepatitis C virus (HCV). This progress is not completed; there are beneficial aspects in the response of the scientific community to the HIV burden for the management of other viral diseases. These aspects are described in this contribution. Further aspects as handling a stigmatising disease, education of self-responsiveness within sexual relationships, and ways for confection of a protective vaccine are not covered.

Impact of a single amino acid in the variable region 2 of the Old World monkey TRIM5alpha SPRY (B30.2) domain on anti-human immunodeficiency virus type 2 activity

Variable region 1 (V1) of the SPRY domain of TRIM5alpha is a major determinant for species-specific virus restriction in primates. We previously reported that a chimeric TRIM5alpha containing baboon V1 in the background of cynomolgus monkey TRIM5alpha showed potent anti-human immunodeficiency virus type 2 (HIV-2) activity. Since baboons are reportedly sensitive to HIV-2 infection, there was a discrepancy between the ability of baboon TRIM5alpha V1 to restrict HIV-2 and baboon sensitivity to HIV-2. In the study presented here, we examined the roles of V2 and V3 of the baboon TRIM5alpha SPRY domain in its anti-HIV-2 activity. A chimeric TRIM5alpha containing the entire baboon SPRY domain showed weak anti-HIV-2 activity. This attenuation of activity was caused by a single serine-to-proline substitution in baboon TRIM5alpha V2. These findings indicate that the combination of V1 with other variable regions of SPRY is important in anti-HIV-2 activity of primate TRIM5alpha.

Macaque models of human infectious disease

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents—bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease.

Viruses and rickettsiae

In this review I shall try to provide a brief, up-to-date, account of the neuropathology of those viral and rickettsial diseases that are particularly prevalent in tropical regions. These diseases are not, however, exclusive to the tropics. Some, such as AIDS, are common in temperate regions as well, though others are closer to being exclusively tropical, such as some of the arthropod-borne (ARBO) virus encephalides. The latter are dependent for their dissemination on an existence during part of their infectious cycle in insects which are, in turn, climatically and seasonally sensitive. This necessarily limits their geographical distribution. Factors that influence some of the other diseases are less closely dependent on climate and geography and reflect more the social or cultural conditions under which people live. Thus, diseases that depend for their spread on forms of human behavior such as promiscuity or drug abuse (AIDS), or poor hygiene and living conditions (polio, rickettsial diseases) or on contact with domestic and other animals (rabies) may occur in a more widespread distribution, for the tropics are not the only places that afford opportunities for these diseases to flourish. I shall select for discussion aspects of the pathology of these diseases that are currently undergoing investigation but will aim to present these against the backdrop of more established aspects of their pathology. Recent reviews of the pathology of viral encephalitis can be found in Hamilton and Wiley (33) and Esiri and Kennedy (20) and of HIV-1 infection in Price & Sidtis (78) and Scaravilli (85).

Comparison of anti-viral activity of rhesus monkey and cynomolgus monkey TRIM5alphas against human immunodeficiency virus type 2 infection

Human immunodeficiency virus type 2 (HIV-2) strains vary widely in their ability to grow in Old World monkey (OWM) cells. We previously evaluated several HIV-2 isolates for their sensitivity to cynomolgus monkey (CM) TRIM5alpha, an anti-HIV factor in OWM cells, and found that viruses carrying proline at the 120th position of the capsid protein were sensitive to CM TRIM5alpha, whereas those with either alanine or glutamine were resistant. In the study presented here, we tested these HIV-2 isolates for their sensitivity to rhesus monkey (Rh) TRIM5alpha and found that both CM TRIM5alpha-sensitive and -resistant viruses were restricted by Rh TRIM5alpha. The variable region 1 of the SPRY domain of Rh TRIM5alpha appeared to be the determinant of this difference. Furthermore, a mutagenesis study showed that three amino acid residues TFP at the 339th to 341st positions of Rh TRIM5alpha are important for restricting HIV-2 strains resistant to CM TRIM5alpha.

A single amino acid of the human immunodeficiency virus type 2 capsid affects its replication in the presence of cynomolgus monkey and human TRIM5alphas

Human immunodeficiency virus type 2 (HIV-2) strains vary widely in their abilities to grow in Old World monkey (OWM) cells such as those of cynomolgus monkeys (CM). We evaluated eight HIV-2 isolates for their sensitivities to CM TRIM5alpha, an anti-HIV factor in OWM cells. We found that different HIV-2 isolates showed differences in their sensitivities to CM TRIM5alpha. Sequence analysis showed that TRIM5alpha-sensitive viruses had proline at the 120th position of the capsid protein (CA), whereas TRIM5alpha-resistant viruses had either alanine or glutamine. Mutagenesis studies indicated that the single amino acid at the 120th position indeed affected the sensitivity of the virus to CM TRIM5alpha.

Going wild: lessons from naturally occurring T-lymphotropic lentiviruses

Over 40 nonhuman primate (NHP) species harbor species-specific simian immunodeficiency viruses (SIVs). Similarly, more than 20 species of nondomestic felids and African hyenids demonstrate seroreactivity against feline immunodeficiency virus (FIV) antigens. While it has been challenging to study the biological implications of nonfatal infections in natural populations, epidemiologic and clinical studies performed thus far have only rarely detected increased morbidity or impaired fecundity/survival of naturally infected SIV- or FIV-seropositive versus -seronegative animals. Cross-species transmissions of these agents are rare in nature but have been used to develop experimental systems to evaluate mechanisms of pathogenicity and to develop animal models of HIV/AIDS. Given that felids and primates are substantially evolutionarily removed yet demonstrate the same pattern of apparently nonpathogenic lentiviral infections, comparison of the biological behaviors of these viruses can yield important implications for host-lentiviral adaptation which are relevant to human HIV/AIDS infection. This review therefore evaluates similarities in epidemiology, lentiviral genotyping, pathogenicity, host immune responses, and cross-species transmission of FIVs and factors associated with the establishment of lentiviral infections in new species. This comparison of consistent patterns in lentivirus biology will expose new directions for scientific inquiry for understanding the basis for virulence versus avirulence.

Paucity of CD4+CCR5+ T cells is a typical feature of natural SIV hosts

In contrast to lentiviral infections of humans and macaques, simian immunodeficiency virus (SIV) infection of natural hosts is nonpathogenic despite high levels of viral replication. However, the mechanisms underlying this absence of disease are unknown. Here we report that natural hosts for SIV infection express remarkably low levels of CCR5 on CD4+ T cells isolated from blood, lymph nodes, and mucosal tissues. Given that this immunologic feature is found in 5 different species of natural SIV hosts (sooty mangabeys, African green monkeys, mandrills, sun-tailed monkeys, and chimpanzees) but is absent in 5 nonnatural/recent hosts (humans, rhesus, pigtail, cynomolgus macaques, and baboons), it may represent a key feature of the coevolution between the virus and its natural hosts that led to a nonpathogenic infection. Beneficial effects of low CCR5 expression on CD4+ T cells may include the reduction of target cells for viral replication and a decreased homing of activated CD4+ T cells to inflamed tissue.

Baboon as a nonhuman primate model for vaccine studies

Nonhuman primates are suitable and valid models to determine the safety, immunogenicity and efficacy of candidate vaccines that are being developed for human application. Among the nonhuman primates, baboons have been found to be ideal for vaccine studies because they are phylogenetically closer to humans, have a similar immune system and response and are available in large numbers. During the last two decades, numerous candidate vaccines have been evaluated in the baboon model.

Non-human primate models for AIDS vaccine research

Since the discovery of simian immunodeficiency viruses (SIV) causing AIDS-like diseases in Asian macaques, non-human primates (NHP) have played an important role in AIDS vaccine research. A multitude of vaccines and immunization approaches have been evaluated, including live attenuated viruses, DNA vaccines, viral and bacterial vectors, subunit proteins, and combinations thereof. Depending on the particular vaccine and model used, varying degrees of protection have been achieved, including prevention of infection, reduction of viral load, and amelioration of disease. In a few instances, potential safety concerns and vaccine-enhanced pathogenicity have also been noted. In the past decade, sophisticated methodologies have been developed to define the mechanisms of protective immunity. However, a clear road map for HIV vaccine development has yet to emerge. This is in part because of the intrinsic nature of the surrogate model and in part because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans. The lack of standardization, the limited models available, and the incomplete understanding of the immunobiology of NHP contribute to the difficulty to extrapolate findings from such models to HIV vaccine development. Until efficacy data become available from studies of parallel vaccine concepts in humans and macaques, the predictive value of any NHP model remains unknown. Towards this end, greater appreciation of the utility and limitations of the NHP model and further developments to better mimic HIV infection in humans will likely help inform future AIDS vaccine efforts.

Direct inoculation of simian immunodeficiency virus from sooty mangabeys in black mangabeys (Lophocebus aterrimus): first evidence of AIDS in a heterologous African species and different pathologic outcomes of experimental infection

A unique opportunity for the study of the role of serial passage and cross-species transmission was offered by a series of experiments carried out at the Tulane National Primate Research Center in 1990. To develop an animal model for leprosy, three black mangabeys (BkMs) (Lophocebus aterrimus) were inoculated with lepromatous tissue that had been serially passaged in four sooty mangabeys (SMs) (Cercocebus atys). All three BkMs became infected with simian immunodeficiency virus from SMs (SIVsm) by day 30 postinoculation (p.i.) with lepromatous tissue. One (BkMG140) died 2 years p.i. from causes unrelated to SIV, one (BkMG139) survived for 10 years, whereas the third (BkMG138) was euthanized with AIDS after 5 years. Histopathology revealed a high number of giant cells in tissues from BkMG138, but no SIV-related lesions were found in the remaining two BkMs. Four-color immunofluorescence revealed high levels of SIVsm associated with both giant cells and T lymphocytes in BkMG138 and no detectable SIV in the remaining two. Serum viral load (VL) showed a significant increase (>1 log) during the late stage of the disease in BkMG138, as opposed to a continuous decline in VL in the remaining two BkMs. With the progression to AIDS, neopterin levels increased in BkMG138. This study took on new significance when phylogenetic analysis unexpectedly showed that all four serially inoculated SMs were infected with different SIVsm lineages prior to the beginning of the experiment. Furthermore, the strain infecting the BkMs originated from the last SM in the series. Therefore, the virus infecting BkMs has not been serially passaged. In conclusion, we present the first compelling evidence that direct cross-species transmission of SIV may induce AIDS in heterologous African nonhuman primate (NHP) species. The results showed that cross-species-transmitted SIVsm was well controlled in two of three BkMs for 2 and 10 years, respectively. Finally, this case of AIDS in an African monkey suggests that the dogma of SIV nonpathogenicity in African NHP hosts should be reconsidered.

Human immunodeficiency virus type 2 DNA vaccine provides partial protection from acute baboon infection

We determined if the genetic adjuvants, granulocyte-macrophage colony stimulating factor (GM-CSF) and B7-2, could improve the immunogenicity and efficacy of an HIV-2 DNA vaccine. The vaccine consisted of the HIV-2 tat, nef, gag, and env genes synthesized using optimized codons and formulated with cationic liposomes. Baboons (Papio cynocephalus hamadryas) were immunized by the intramuscular, intradermal, and intranasal routes with these expression constructs and challenged with HIV-2(UC2) by the intravaginal route. In the first month after HIV-2 vaginal challenge, the baboons receiving the HIV-2 DNA vaccine with or without the genetic adjuvants had significant reductions in the viral loads in the peripheral blood mononuclear cells (PBMC) (P = 0.028) while the reductions in their plasma viremia were suggestive of a protective effect (P = 0.1). These data demonstrate that partial protection against HIV-2 vaginal challenge, as measured by reduced viral load, can be achieved using only a DNA vaccine formulation.

Polymorphism of human and primate RANTES, CX3CR1, CCR2 and CXCR4 genes with regard to HIV/SIV infection

Among genes that influence human susceptibility to HIV (human immunodeficiency virus) infection or AIDS (acquired immunodeficiency syndrome) progression, chemokine-receptor and chemokine genes were extensively studied because of their role as HIV co-receptors or co-receptor competitors, respectively. We have studied in non-human primates (chimpanzee, gorilla, gibbon, orang-utan, crab-eating and rhesus macaque, baboon and marmoset) the RANTES, CCR2 and CX3CR1 gene sequences in regions surrounding human mutations that were associated with susceptibility to HIV or AIDS progression: RANTES G-403A and C-28G, CCR2 V64I, CX3CR1 V249I and CX3CR1 T280M. Among these five dimorphisms, only RANTES G-403A is observed in one of the eight primate species studied here (gibbon). This suggests that these mutations appeared recently in humans and probably do not account for variable HIV/SIV disease progression in primates. It is noteworthy that chimpanzees, which are naturally resistant to HIV-1- and HIV-2-induced AIDS, do not have the human mutations associated with delayed disease progression. Inter-species and intra-species polymorphic positions are observed in primates and we discuss the potential impact of these mutations on HIV/SIV disease progression. Particularly, we identified polymorphisms in old-world monkey (OWM) genes, and it could be of great importance to analyse the possible association between these polymorphisms and disease progression in OWM species that are currently used in research for HIV vaccine and therapy.

Vaccine-induced immunity in baboons by using DNA and replication-incompetent adenovirus type 5 vectors expressing a human immunodeficiency virus type 1 gag gene

The cellular immunogenicity of formulated plasmid DNA and replication-defective human adenovirus serotype 5 (Ad5) vaccine vectors expressing a codon-optimized human immunodeficiency virus type 1 gag gene was examined in baboons. The Ad5 vaccine was capable of inducing consistently strong, long-lived CD8(+)-biased T-cell responses and in vitro cytotoxic activities. The DNA vaccine-elicited immune responses were weaker than those elicited by the Ad5 vaccine and highly variable; formulation with chemical adjuvants led to moderate increases in the levels of Gag-specific T cells. Increasing the DNA-primed responses with booster doses of either Ad5 or modified vaccinia virus Ankara vaccines suggests a difference in the relative levels of cytotoxic and helper responses. The implications of these results are discussed.

Novel Kaposi's sarcoma-associated herpesvirus homolog in baboons

Kaposi's sarcoma (KS) and lymphoproliferative diseases induced by KS-associated herpesvirus (KSHV/human herpesvirus 8) cause substantial morbidity and mortality in human immunodeficiency virus-infected individuals. To understand KSHV biology it is useful to investigate closely related rhadinoviruses naturally occurring in nonhuman primates. Here we report evidence for a novel KSHV homolog in captive baboon species (Papio anubis and other). Using degenerate PCR we identified a novel rhadinovirus, PapRV2, that has substantial sequence identity to two essential KSHV genes, the viral polymerase and thymidylate synthase. A subset of animals exhibited detectable PapRV2 viral load in peripheral blood mononuclear cells. Extensive serological analysis of nearly 200 animals in the colony demonstrated that the majority carried cross-reacting antibodies that recognize KSHV or macaque rhadinovirus antigens. Seroreactivity increased with age, similar to the age-specific prevalence of KSHV in the human population. This establishes baboons as a novel resource to investigate rhadinovirus biology, which can be developed into an animal model system for KSHV-associated human diseases, vaccine development, and therapy evaluation.

Kaposi's sarcoma: aetiopathogenesis, histology and clinical features

Kaposi's sarcoma (KS) represents today one of the most common skin cancers in transplanted Mediterranean subjects and, since the epidemic of human immunodeficiency virus/acquired immune deficiency syndrome, in young unmarried single men. The disease has been associated with the recent identified human herpesvirus (HHV)-8 or KS herpesvirus and its incidence in the general population shows a north to south gradient that parallels the HHV-8 increasing prevalence from Nordic countries to sub-Saharan regions. The identification of the aetiopathogenetic mechanisms (viral agents and immunodeficiency) involved in the pathogenesis of KS, are relevant for identifying susceptible subjects (HHV-8 seropositive subjects), monitoring the immune levels in iatrogenic immune suppressed patients, and developing new therapeutic approaches based on antiviral and immune modulators.

LEARNING OBJECTIVE

This article should enable the reader: (i) to learn about the clinical and molecular aspects of KS in order to have a multidisciplinary approach to a tumour that shows unique features; (ii) to consider the role of viral agents and immunity; and (iii) to recognize properties of an opportunistic neoplasm. The identification of the HHV-8 role in KS pathogenesis should establish a relevant tool in the clinical management of KS patients.

Expression patterns of phenotypic markers on lymphocytes from human immunodeficiency virus type 2-infected baboons

The development of AIDS in HIV-1-infected humans is associated with profound changes in the expression patterns of lymphocyte phenotypic markers associated with increased immune activation and with decreased recall immune responses. In assessing these immunologic changes in an animal model, we characterized the expression patterns of immune activation markers on lymphocyte subsets during the acute, chronic, and end stages of HIV-2 infection in baboons. Using flow cytometry, we identified 21 human-specific monoclonal antibodies that were cross-reactive with baboon lymphocytes; however, expression of only 2 of these markers was altered significantly after HIV-2 infection. We found an increase in baboon class II antigen (as measured by anti-HLA-DR) in the CD4(+) T cell subset within 8 weeks of infection (p = 0.045). Moreover, after 1 year of infection, CD11b was downregulated on CD8(+) T lymphocytes (p = 0.027). This downregulation of CD11b was consistently observed in all of the groups of baboons that were chronically infected with three different HIV-2 isolates. In addition, we found substantial downregulation of the interleukin 2 receptor (CD25) and upregulation of class II antigen on CD8(+) lymphocytes in a baboon with an AIDS-like disease. These and other phenotypic markers of immune activation may facilitate characterization of the immunopathogenesis of AIDS in nonhuman primate animal models.

Increased virus replication and virulence after serial passage of human immunodeficiency virus type 2 in baboons

Similar to human immunodeficiency virus type 1 (HIV-1) infection of humans, the natural history of HIV-2 infection in baboons (Papio cynocephalus) is a slow and chronic disease that generally takes several years before an AIDS-like condition develops. To shorten the amount of time to the development of disease, we performed five serial passages of HIV-2(UC2) in baboons by using blood and bone marrow samples during the acute phase of infection when viral loads were at high levels. After these serial passages, virus levels in plasma, peripheral blood mononuclear cells (PBMC) and lymphatic tissues in the acutely infected baboons were increased. Within 1 year of the HIV-2 infection, all of the inoculated baboons showed specific signs of AIDS-related disease progression within the lymphatic tissues, such as vascular proliferation and lymphoid depletion. The HIV-2(UC2) recovered after four serial passages showed increased kinetics of viral replication in baboon PBMC and cytopathicity. This study suggests that the HIV-2 isolate recovered after several serial passages in baboons will be useful in future studies of AIDS pathogenesis and vaccine development by using this animal model.

Immune responses in baboons vaccinated with HIV-2 genetic expression libraries

Immunization using genetic expression libraries may be an improvement over conventional DNA immunization using a single gene because more epitopes are simultaneously presented to the immune system. In this study, we evaluated the effectiveness of an HIV-2 vaccine made from a genomic expression library in baboons. We found that HIV-2 expression library immunization induced HIV-2-specific memory responses but low levels of CD8+ cell anti-viral responses and neutralizing antibodies. After intravenous virus challenge using a homologous pathogenic variant, HIV-2UC2/9429, viral loads were similar in the HIV-2-immunized and control baboons. We conclude that although immunization using HIV-2 expression libraries induces immune responses, this approach does not provide protection in baboons against intravenous challenge with HIV-2.

OspE-related, OspF-related, and Elp lipoproteins are immunogenic in baboons experimentally infected with Borrelia burgdorferi and in human lyme disease patients

Presently, the rhesus macaque is the only nonhuman primate animal model utilized for the study of Lyme disease. While this animal model closely mimics human disease, rhesus macaques can harbor the herpes B virus, which is often lethal to humans; macaques also do not express the full complement of immunoglobulin G (IgG) subclasses found in humans. Conversely, baboons contain the full complement of IgG subclasses and do not harbor the herpes B virus. For these reasons, baboons have been increasingly utilized as the basis for models of infectious diseases and studies assessing the safety and immunogenicity of new vaccines. Here we analyzed the capability of baboons to become infected with Borrelia burgdorferi, the agent of Lyme disease. Combined culture and PCR analyses of tick- and syringe-infected animals indicated that baboons are a sufficient host for B. burgdorferi. Analysis of the antibody responses in infected baboons over a 48-week period revealed that antibodies are generated early during infection against many borrelial antigens, including the various OspE, OspF, and Elp paralogs that are encoded on the ubiquitous 32-kb circular plasmids (cp32s). By using the baboon sera generated by experimental infection it was determined that a combination of two cp32-encoded lipoproteins, OspE and ElpB1, resulted in highly specific and sensitive detection of B. burgdorferi infection. An expanded analysis, which included 39 different human Lyme disease patients, revealed that a combination of the OspE and ElpB1 lipoproteins could be the basis for a new serodiagnostic assay for Lyme disease. Importantly, this novel serodiagnostic test would be useful independent of prior OspA vaccination status.

Conserved CXCR4 usage and enhanced replicative capacity of HIV-2/287, an isolate highly pathogenic in Macaca nemestrina

OBJECTIVE

To investigate viral properties that contribute to the pathogenic potential of HIV-2 in macaques.

DESIGN

We compared HIV-2/287, a virus highly pathogenic in Macaca nemestrina, with its non-pathogenic progenitor HIV-2 EHO, for coreceptor usage and ability to infect human and macaque peripheral blood mononuclear cells (PBMC).

METHODS

Coreceptor usage was determined in GHOST cells expressing known coreceptors, and in PBMC with coreceptor-specific inhibitors. Infectivity in PBMC was determined by virus titration and p27 antigen production. Early and late products of reverse transcription were measured by PCR with primers specific for the long terminal repeat (LTR), or the gag region, respectively.

RESULTS

Both viruses preferentially infect HOS-CD4 cells expressing CXCR4. Inhibition by CXCR4-specific peptide TW70 and monoclonal antibody 12G5 indicated that both viruses use predominantly CXCR4 to infect macaque and human PBMC. HIV-2/287 showed greater infectivity than HIV-2 EHO in macaque cells, but the situation was reversed in human cells. Kinetic analysis of reverse transcription products revealed no restriction in reverse transcription following HIV-2 EHO infection of macaque PBMC. However, comparison of the level of newly initiated HIV-2 EHO DNA in macaque and human PBMC indicated that there is an early restriction, prior to the initiation of reverse transcription.

CONCLUSIONS

Results indicate that the adaptation of HIV-2 EHO in M. nemestrina to a highly pathogenic virus HIV-2/287 is not correlated with a shift in or an expansion of coreceptor usage, but with the acquisition of an ability to overcome restrictions for growth in macaque PBMC.

Infection in xenotransplantation

Advances in transplantation immunology have enhanced the possibility of xenotransplantation as a therapeutic option for end-stage organ failure. The potential spread of animal-derived pathogens to the recipient and to the general population, termed "xenosis," is a potential complication of interspecies transplantation. Recognition of such novel infections may be complicated by infections due to altered microbiologic behavior and clinical symptomatology of these organisms, particularly in the immunocompromised xenograft recipient. Particular concern exists over the activation of latent viruses, including retroviruses, from xenograft tissues. Based on experience with human allogeneic transplantation, those pathogens considered most likely to cause human disease can be excluded prospectively from herds of animals developed for organ donation. Research is needed into the activation and behavior of retroviruses and other potential pathogens in xenotransplantation. Xenotransplantation may also provide unique opportunities not only for the care of patients with organ failure, but in the therapy of individuals with chronic infections to which the xenograft may be resistant. Clinical protocols must be developed so as to enhance the safety of the recipient and of the community-at-large.

Mutations of the 3' untranslated region of the SDF1 gene in apes and monkeys: potential impact on sensitivity to AIDS induced by lentiviruses

The comparison of the stromal cell-derived factor-1 (SDF1) gene 3' untranslated region (3'UTR) of four great ape and four monkey species with their human counterparts shows that the human SDF1-3'A mutation is present in primate species that are the most susceptible to lentivirus-induced AIDS and is absent in species that are particularly resistant to lentivirus-induced AIDS. The results enlighten the possible relationship between SDF1-3'UTR polymorphism and sensitivity to AIDS.

Epidemiology and pathogenesis of Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma (KS) occurs in Europe and the Mediterranean countries (classic KS) and Africa (endemic KS), immunosuppressed patients (iatrogenic or post-transplant KS) and those with acquired immune deficiency syndrome (AIDS), especially among those who acquired human immunodeficiency virus sexually (AIDS-KS). KS-associated herpesvirus (KSHV or HHV-8) is unusual among herpesviruses in having a restricted geographical distribution. Like KS, which it induces in immunosuppressed or elderly people, the virus is prevalent in Africa, in Mediterranean countries, among Jews and Arabs and certain Amerindians. Distinct KSHV genotypes occur in different parts of the world, but have not been identified as having a differential pathogenesis. KSHV is aetiologically linked to three distinct neoplasms: (i) KS, (ii) primary effusion lymphoma, and (iii) plasmablastic multicentric Castleman's disease. The histogenesis, clonality and pathology of the tumours are described, together with the epidemiology and possible modes of transmission of the virus.

The restricted cellular host range of human herpesvirus 8

DESIGN

A selection of primary and transformed cell types were evaluated for their susceptibility to infection with human herpesvirus 8 (HHV-8)/Kaposi's sarcoma-associated herpesvirus.

METHODS

Sources of HHV-8 included Kaposi's sarcoma lesion punch biopsies that were either cocultured directly with target cells or that were first cocultured with human lymphocytes to derive HHV-8-containing fluids that were inoculated onto target cells. HHV-8 was also obtained from primary effusion lymphoma-derived cell lines. Techniques to detect infection included the PCR, immunofluorescence assays and in situ hybridization.

RESULTS

Susceptible cells included human umbilical cord blood mononuclear cells (UCMC), adult CD19 B cells, macrophages and certain endothelial cells of human and animal origin, including some that are transformed with human papilloma virus type 16 E6 and E7 genes. The infection of lymphocytes did not yield established lymphoblastoid cell lines (LCL) and virus infection persisted for only 4-7 days. However, long-term HHV-8 infection of UCMC could be achieved by coinfection with Epstein-Barr virus. HHV-8 could also infect UCMC LCL recently derived by Epstein-Barr virus transformation, but long-established LCL could not be infected with HHV-8.

CONCLUSIONS

These data provide further biological evidence in cell culture for the limited cellular host range of HHV-8 to CD19 B cells, macrophages, and certain endothelial cells.

Primate models of AIDS

The primate models of AIDS provide insights into pathogenesis, transmission, and immune responses to infection and are useful in testing vaccines and drugs. The HIV-1/chimpanzee, SIV(mac)/macaque, and SHIV/macaque models are the most widely used. The advantages and drawbacks of these and other models are discussed.

HIV-1-trans-activating (Tat) protein: both a target and a tool in therapeutic approaches

Tat proteins (trans-activating proteins) are present in all known lentiviruses and are early RNA binding proteins that regulate transcription. Tat from the human immunodeficiency virus type-1 is a protein comprising 86 amino acids and encoded by 2 exons. The first 72 amino acids are encoded by exon 1 and exhibit full trans-activating activity. The second exon encodes a 14-amino-acid C-terminal sequence that is not required for trans-activation but does contain an RGD motif, which is important in binding to alphavbeta3 and alpha5beta1 integrins. Tat has an unusual property for a transcription factor; it can be released and enter cells freely, yet still retain its activity, enabling it to up-regulate a number of genes. Tat also has an angiogenic effect; it is a potent growth factor for Kaposi sarcoma-derived spindle cells, and, separately, it has been shown to bind to a specific receptor, Flk-1/KDR, on vascular smooth muscle cells, as well as to integrin-like receptors present on rat skeletal muscle cells and the lymphocyte cell line H9. It appears that the basic domain of tat is important, not only for translocation but also for nuclear localisation and trans-activation of cellular genes. As such, targeting of tat protein or, more simply, the basic domain provides great scope for therapeutic intervention in HIV-1 infection. There is also opportunity for tat to be used as a molecular tool; the protein can be manipulated to deliver non-permeable compounds into cells, an approach that already has been employed using ovalbumin, beta-galactosidase, horseradish peroxidase, and caspase-3.

Comparison and characterization of immunoglobulin G subclasses among primate species

Little information is available on the immunoglobulin G (IgG) subclasses expressed in the sera of nonhuman primate species. To address this issue, we compared the IgG subclasses found in humans (IgG1, IgG2, IgG3, and IgG4) to those of nonhuman primates, such as baboons and macaques. Cross-reactive antihuman IgG subtype-specific reagents were identified and used to analyze purified IgG from sera by solid-phase enzyme-linked immunosorbent assay. Protein A-purified human IgG obtained from sera was composed of IgG1, IgG2, IgG3, and IgG4, whereas baboon and macaque IgG was composed of IgG1, IgG2, and IgG4. Protein G-purified human IgG was composed of IgG1, IgG2, IgG3, and IgG4, whereas baboon and macaque IgG was composed of IgG1, IgG2, and IgG4. To test the possibility that baboon and macaque IgG3 is actually present, but is outcompeted for binding to proteins A and G by the other more abundant IgG subclasses, we repurified the IgG from sera that did not bind either protein A or protein G. We found a baboon IgG3 population in the sera that did not bind protein A, but bound protein G. No IgG3 subtype was detectable in macaque sera. These data suggest that baboon sera, like human sera, contain four IgG subtypes, whereas macaque sera exhibit only three of the human subclass analogs. In addition, the IgG subtype-specific reagents were shown to be useful in determining the IgG subclass distribution following vaccination of baboons with hepatitis B surface antigen.

Progress and challenges in therapies for AIDS in nonhuman primate models

Efforts to develop animal models for human immunodeficiency virus type-1 (HIV-1) vaccine testing have focused on lentivirus infection of nonhuman primates. A long-term goal of this primate research is to utilize the models to understand the mechanisms of pathogenesis leading to AIDS. Because the time to disease is compressed relative to HIV infection in humans, therapeutic strategies and compounds can be tested in nonhuman primate models in a shorter time frame and under more controlled conditions than are possible in many clinical studies. Recent interventive studies in primates using antiviral drugs or passive immune globulin (IgG) have demonstrated that multiple log reductions in plasma virus can be achieved and sustained, with accompanying health benefits. Information gained about timing and dosage may be of utility in designing clinical studies. The development of reliable and predictable animal models for effective therapies and vaccines against AIDS remains a critical priority for primate research.

Proviral load and immune function in blood and lymph node during HIV-1 and HIV-2 infection

Proviral load as well as lymphocyte phenotype and function were compared in peripheral blood and lymph node compartments of 17 HIV-1, 12 HIV-2 and three dually infected patients with lymphadenopathy. The mean percentage (95% confidence interval (CI)) of CD4+ cells was higher in lymph node mononuclear cells (LNMC) than in peripheral blood mononuclear cells (PBMC) in both infections, being 26.7% (21. 1%, 32.3%) and 15.3% (10.4%, 20.2%), respectively, for HIV-1-infected patients (P = 0.0001) and 32.3% (22.7%, 41.9%) and 22. 1% (13.6%, 30.6%), respectively, for HIV-2-infected patients (P = 0. 02). In both types of infection, proviral load adjusted for number of CD4+ cells was higher in LNMC than in PBMC: the geometric mean (95% CI) was 8937 (4991; 16 003) and 4384 (2260; 8503), respectively, for HIV-1 patients (P = 0.02) and 1624 (382; 6898) and 551 (147; 2058) DNA copies, respectively, for HIV-2 patients (P = 0.05). Proviral load in both compartments was closely correlated (HIV-1, r = 0.60, P = 0.01; and HIV-2, r = 0.83, P = 0.0003). In both infections, proliferation and interferon-gamma (IFN-gamma) production in response to purified protein derivative (PPD) was lower in LNMC than in PBMC, both of which, in turn, were lower than in healthy controls. These results indicate that in HIV-2 as in HIV-1 infection, infected cells have a tropism for the lymph nodes resulting in higher viral load in this compartment and lower lymphocyte responses to the recall antigen PPD which may increase susceptibility to tuberculosis.

Distinct pathogenic sequela in rhesus macaques infected with CCR5 or CXCR4 utilizing SHIVs

Infection of macaques with chimeric simian-human immunodeficiency virus (SHIV) provides an excellent in vivo model for examining the influence of envelope on HIV-1 pathogenesis. Infection with a pathogenic CCR5 (R5)-specific enveloped virus, SHIVSF162P, was compared with infection with the CXCR4 (X4)-specific SHIVSF33A.2. Despite comparable levels of viral replication, animals infected with the R5 and X4 SHIV had distinct pathogenic outcomes. SHIVSF162P caused a dramatic loss of CD4+ intestinal T cells followed by a gradual depletion in peripheral CD4+ T cells, whereas infection with SHIVSF33A.2 caused a profound loss in peripheral T cells that was not paralleled in the intestine. These results suggest a critical role of co-receptor utilization in viral pathogenesis and provide a reliable in vivo model for preclinical examination of HIV-1 vaccines and therapeutic agents in the context of the HIV-1 envelope protein.

Infection and xenotransplantation. Developing strategies to minimize risk

Infection in transplantation results from interaction between the level of immune suppression and the epidemiologic exposures of the recipient. "Xenosis," infection in xenotransplantation, may be increased beyond that of allotransplantation because: (1) the xenograft may serve as a permissive focus of infection for donor-derived organisms; (2) these organisms may be unknown or xenotropic; (3) microbiologic assays may be unavailable; (4) clinical syndromes due to such novel pathogens may not be recognized; (5) the necessary level of immune suppression may be greater than for allotransplantation; (6) donor-derived organisms may acquire new (e.g., genetic) characteristics in the human host; (7) the presence of immune suppression and the high, intrinsic rate of infection may mask the presence of xenosis; and (8) MHC-incompatibility may reduce the efficacy of the immune response within the xenograft. Because immunocompromised individuals are sentinels for infection by many types of novel infectious agents, and because there is some unknown level of risk that such pathogens will spread to the general population, microbiologic studies must be initiated in tandem with preclinical and clinical studies of xenotransplantation.

Genetic variation in a human immunodeficiency virus type 2 live-virus Macaca nemestrina vaccine model

Four pigtailed macaques were inoculated with an infectious, apathogenic human immunodeficiency virus type 2 (HIV-2) molecular clone (HIV-2KR) and subsequently challenged with a highly pathogenic strain, HIV-2287, together with two naive control animals. After challenge, two animals inoculated with a high dose of the immunizing strain were protected from CD4 decline and immunodeficiency. To examine the role of genetic heterogeneity in protection, fragments of the env gene were amplified from peripheral blood mononuclear cell DNA and plasma RNA of challenged animals by PCR, examined by using a heteroduplex tracking assay (HTA), and sequenced. By HTA, variation was detected principally within the V1 and V2 regions of envelope. Extent of variation in viral DNA clones as assessed by HTA correlated with inoculum size, as did the degree of variation in sequences of clones derived from viral DNA. Conversely, a rapid reduction in the number of plasma viral RNA variants was noted by HTA at 8 weeks postinfection in protected animals; this reduction was not present in naive or unprotected macaques. Sequences derived from plasma viral RNA were found to be more closely related than corresponding viral DNA sequences, and protection correlated with a significant reduction in variation in plasma RNA sequences in animals given the identical inocula of HIV-2287. Nonsynonymous mutations were significantly less prevalent in the protected animals. An additional potential glycosylation site was predicted to be present in the V2 region in all but one clone, and amino acid signatures related to protection were identified in viral DNA and RNA clones within both the V1 and V2 regions. Examination of the role of viral variation in this HIV-2 live-virus vaccine model may provide valuable insights into immunopathogenesis.

Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma (KS) is a vascular tumor predominantly found in the immunosuppressed. Epidemiologic studies suggest that an infective agent is the etiologic culprit. Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus-8 (HHV-8), is a gamma human herpesvirus present in all epidemiologic forms of KS and also in a rare type of a B cell lymphoma, primary effusion lymphoma (PEL). In addition, this virus is present in most biopsies from human immunodeficiency virus (HIV)-associated multicentric Castleman's disease (MCD). MCD is a lymphoproliferative disorder with, like KS, a prominent microvasculature. The genome of KSHV contains the expected open reading frames (ORFs) encoding for enzymes and viral structural proteins found in other herpesviruses, but it also contains an unprecedented number of ORFs pirated during viral evolution from cellular genes. These include proteins that may alter cellular growth (e.g., Bcl-2 and cyclin homologs), induce angiogenesis (e.g., chemokine, chemokine receptor, and cytokine homologs), and regulate antiviral immunity (e.g., CD21 and interferon regulatory factor homologs). No ORF with sequence similarity to the Epstein-Barr nuclear antigens (EBNAs) and latent membrane proteins (LMPs) of Epstein-Barr virus (EBV) is present, but proteins analogous to these in structure and in latent expression are found [e.g., ORF 73 encoding for KSHV latent nuclear antigen (LNA-1) and K12 encoding for a possible latent membrane protein]. Current serologic assays confirm the strong association of infection with KSHV and risk of KS development. The mechanism of how this new virus may trigger the precipitation of KS is still unclear.

Phylogenetic analysis of SIV and STLV type I in mandrills (Mandrillus sphinx): indications that intracolony transmissions are predominantly the result of male-to-male aggressive contacts

Natural SIVmnd and STLVmnd infections of mandrills in a colony at the Centre International de Recherches Médicales de Franceville (CIRMF) in Gabon were investigated by genetic analysis to determine the extent of intracolony transmission. SIVmnd pol sequence analysis indicates that the six strains present in the colony belong to the SIVmnd lentivirus subgroup previously defined according to the only available prototype sequence (SIVmndGB1), which originated from the same colony. The intraanimal nucleotide diversity (1.1-3.1%) was similar in range to that reported in individuals infected by other HIV/SIVs. The interanimal diversity (0.5-4.3%) was not significantly different from that observed in each individual mandrill, indicating an epidemiological link among the SIVmnd isolates of distinct animals within the colony. Phylogenetic analysis of these isolates, together with seroepidemiological and behavior surveillance within the colony, indicates a predominant male-to-male transmission of SIVmnd that probably occurred during bouts of interanimal aggression. Moreover, our results suggest one case of vertical transmission of SIVmnd from a naturally infected founder female to one of her six offspring. The first genetic analysis of STLV isolates from mandrills is also reported here. Partial tax/rex sequences were used to evaluate the diversity between seven STLVmnd isolates and their phylogenetic relationships with other known strains of human and nonhuman primate T cell leukemia virus, types I and II (PTLV-I/II). They all belong to the PTLV-I subtype, but two genetically distinct STLVmnd groups were evidenced within the mandrill colony. The phylogenetic analyses of the STLVmnd isolates, together with seroepidemiological and behavior surveillance of the mandrills, indicate that intracolony transmissions of STLVmnd are also predominantly the result of male-to-male aggressive contacts.

Transient virus infection and pathogenesis of a new HIV type 2 isolate, UC12, in baboons

We have previously shown that baboons (Papio cynocephalus) can be persistently infected with HIV-2 and some baboons progress to an AIDS-like disease with a CD4+ T cell decline, cachexia, alopecia, and Kaposi's sarcoma-like fibromatosis. In this study, we found that a new virus isolate, HIV-2UC12, replicated to high levels in baboon peripheral blood mononuclear cells (PBMCs) in vitro. Three baboons were subsequently inoculated and had plasma viral RNA loads that peaked between 15,000 and 7000 copies/ml at 2 weeks postinfection. Virus was isolated from the PBMCs for up to 6 months. Although PBMCs were subsequently virus culture negative, virus could be recovered from the spleen, lymph nodes, and tonsils, indicating that HIV-2 was sequestered within these lymphoid tissues. HIV-2-associated pathology included follicular lysis, vascular proliferation, and lymphoid depletion. This study indicated that HIV-2UC12 infection in baboons can cause HIV-associated pathological abnormalities within the lymphatic tissues and that the high level of HIV-2UC12 replication in vitro was not predictive of replication in vivo.

Characterization of a molecular clone of HIV type 2 infectious for Macaca nemestrina

A lambda phage clone containing a full-length HIV-2 provirus, designated HIV-2KR, was obtained from the genomic DNA of Molt4 clone 8 (Molt4/8) lymphoblastic cells infected with the HIV-2PEI2 strain. HIV-2KR is genetically distinct from known HIV-2 isolates, possessing both a unique deletion in the LTR promoter region, and a long rev reading frame. It is replication competent in vitro after transfection into Molt4/8 cells, replicates in a variety of established human T lymphoblastic (Molt-3, Molt4/8, SupT1, H9, C8166) and myelomonocytic (U937) cell lines, and displays prominent cytopathic effects on infection of Molt4/8 cells, reflecting usage of both CCR5 and CXCR4 coreceptors. In addition, HIV-2KR was found to be infectious for human and Macaca nemestrina peripheral blood lymphocytes, and primary human monocyte-macrophage cultures. Intravenous inoculation of cell-free virus into M. nemestrina resulted in infection characterized by transient, low-level viremia and modest temporary decline in CD4 lymphocyte numbers, making HIV-2KR the first HIV-2 molecular clone reported to be infectious for this primate species.

Linear and cyclic peptides mimicking the disulfide loops in HIV-2 envelope glycoprotein induced antibodies with different specificity

The aim of this study was to compare the immunogenicity and antigenicity of cyclic and linear peptides that mimic the disulfide loops in HIV-2ROD gp125. Based on the hypothetical assignment of intrachain disulfide bonds in HIV-2 envelope glycoprotein, peptides expected to mimic all 11 disulfide-bonded domains were synthesized, oxidized or cysteine-alkylated; they were then purified and characterized. Rabbits were immunized with either linear cysteine-alkylated peptides (L1-L11) or cyclic oxidized peptides (C1-C11). All peptides except 7L elicited antibodies with titers between 10(3) and 5 x 10(6). Anti-peptide C (2, 3, 4, 7, 8, 9, 11) and anti-peptide L (2, 3, 8, 9, 11) antibodies recognized the native HIV-2 gp 125. Moreover, we found that cyclization of the peptides significantly increased the level of anti-peptide antibodies reacting with the intact antigen protein. Deglycosylation increased the level of protein reactivity of anti-peptide antibodies and rendered the epitopes in peptides 5, 6, 10 accessible, which were masked in the native protein. Peptide 1 induced antibodies reacting only with the denatured reduced gp125 HIV-2. In addition, while anti-peptide L antibodies reacted better with L peptide (called "linear" structural specificity), anti-peptide C antibodies reacted similarly with L and C peptides (called "broad" structural specificity). Interestingly, the "broad" structural specificity of antibodies correlated with reactivity against native gp125. Although none of these anti-peptide antisera displayed neutralizing activity against HIV-2ROD, these results support the hypothesis that the structural restriction of peptides have a major influence upon the generation of more specific antibodies for recognizing the intact protein.

Aetiology of Kaposi's sarcoma: current understanding and implications for therapy

Kaposi's sarcoma is an angiogenic neoplasm composed of endothelial and spindle cells. The enormous increase in Kaposi's sarcoma with HIV infection, and recent discovery that a new human herpesvirus (Kaposi's sarcoma-associated herpesvirus, also called human herpesvirus 8) is present in this tumor, has activated intense interest in the aetiology, epidemiology and pathogenesis of this disease. Today, Kaposi's sarcoma is one of the most frequent neoplasms in men under 50 years old in the USA, and in some African countries it is the most common tumour overall.

CD8+ cells from HIV-2-infected baboons control HIV replication

OBJECTIVE

To analyze the CD8+ cell antiviral immune response in HIV-2-infected baboons.

DESIGN

Baboons were infected with clinical isolates of HIV-2, CD8+ cells were isolated from phytohemagglutinin (PHA)-stimulated baboon peripheral blood mononuclear cells (PBMC). These cells were cultured with PHA-stimulated CD4+ cells acutely infected with HIV-2 at several CD8+:CD4+ cell ratios. Control of HIV-2 replication was determined by comparing peak levels of HIV-2 replication in fluids from CD8+:CD4+ cell cocultures with those in fluids from infected CD4+ cells cultured alone.

RESULTS

CD8+ cells from HIV-2-infected baboons inhibited HIV-2 replication in acutely infected autologous CD4+ cells to a significantly greater extent than did CD8+ cells from uninfected baboons (P = 0.0001). At the beginning of the acute phase of HIV-2 infection, CD8+ cells showed either a transient reduction or loss in the antiviral activity. In some cases the CD8+ cell response enhanced HIV-2 replication. Subsequently, the strength of the CD8+ cell antiviral activity increased concomitant with a decrease in the HIV-2 load in the PBMC. Suppression of HIV replication could be demonstrated with filtered fluid from CD8+ cells. Other studies indicated that infected CD4+ cells are lost during coculture of CD8+ cells with infected CD4+ cells.

CONCLUSIONS

CD8+ cells of HIV-2-infected baboons develop substantial anti-HIV-2 activity following HIV-2 infection, which may account in part for the low frequency of pathogenesis in HIV-2-infected baboons. Studies to elucidate the mechanism of this CD8+ cell antiviral activity suggest that it is mediated in part by a soluble antiviral factor, but primarily in association with the loss of infected CD4+ cells.

High degree of sensitivity of the simian immunodeficiency virus (SIVmac) envelope glycoprotein subunit association to amino acid changes in the glycoprotein 41 ectodomain

The infection of macaques by simian immunodeficiency virus (SIVmac) represents an attractive model to study the pathogenic determinants of primate and human immunodeficiency viruses. The utility of this model would be enhanced if genetic changes in human immunodeficiency virus (HIV-1) associated with interesting in vitro properties would, when introduced into SIVmac, result in similar phenotypes. In this study, we introduced amino acid changes into the SIVmac239 envelope glycoproteins that, in the context of the HIV-1 envelope glycoproteins, disproportionately attenuated in vitro cytopathic effects compared with the viral replication rate. Amino acid changes in the SIVmac239 gp41 ectodomain altered the noncovalent association of the gp120 and gp41 glycoproteins significantly more than did analogous changes in the HIV-1 envelope glycoproteins. Decreases in the affinity of the gp120-gp41 interaction were observed and were associated with a dramatic attenuation of virus replication not seen in the HIV-1 studies. The increased sensitivity of the SIVmac gp120-gp41 interaction to amino acid changes presents an obstacle to the direct extension of results obtained with the HIV-1 envelope glycoproteins to the SIVmacaque model.