Experimental infection of rhesus and pig-tailed macaques with macaque rhadinoviruses

The recognition of naturally occurring rhadinoviruses in macaque monkeys has spurred interest in their use as models for human infection with Kaposi sarcoma-associated herpesvirus (human herpesvirus 8). Rhesus macaques (Macaca mulatta) and pig-tailed macaques (Macaca nemestrina) were inoculated intravenously with rhadinovirus isolates derived from these species (rhesus rhadinovirus [RRV] and pig-tailed rhadinovirus [PRV]). Nine rhadinovirus antibody-negative and two rhadinovirus antibody-positive monkeys were used for these experimental inoculations. Antibody-negative animals clearly became infected following virus inoculation since they developed persisting antibody responses to virus and virus was isolated from peripheral blood on repeated occasions following inoculation. Viral sequences were also detected by PCR in lymph node, oral mucosa, skin, and peripheral blood mononuclear cells following inoculation. Experimentally infected animals developed peripheral lymphadenopathy which resolved by 12 weeks following inoculation, and these animals have subsequently remained free of disease. No increased pathogenicity was apparent from cross-species infection, i.e., inoculation of rhesus macaques with PRV or of pig-tailed macaques with RRV, whether the animals were antibody positive or negative at the time of virus inoculation. Coinoculation of additional rhesus monkeys with simian immunodeficiency virus (SIV) isolate SIVmac251 and macaque-derived rhadinovirus resulted in an attenuated antibody response to both agents and shorter mean survival compared to SIVmac251-inoculated controls (155.5 days versus 560.1 days; P < 0.019). Coinfected and immunodeficient macaques died of a variety of opportunistic infections characteristic of simian AIDS. PCR analysis of sorted peripheral blood mononuclear cells indicated a preferential tropism of RRV for CD20(+) B lymphocytes. Our results demonstrate persistent infection of macaque monkeys with RRV and PRV following experimental inoculation, but no specific disease was readily apparent from these infections even in the context of concurrent SIV infection.     

Animal models of AIDS

Animal models of AIDS are essential for understanding the pathogenesis of retrovirus-induced immune deficiency and encephalopathy and for development and testing of new therapies and vaccines. AIDS and related disorders are etiologically linked to members of the lentivirus subfamily of retroviruses; these lymphocytopathic lentiviruses are designated human immuno-deficiency virus type 1 (HIV-1) and human immuno-deficiency virus type 2 (HIV-2). The only animals susceptible to experimental HIV-1 infection are the chimpanzee, gibbon ape, and rabbit but AIDS-like disease has not yet been reported in these species. Macaques can be persistently infected with some strains of HIV-2 but no AIDS-like disease has resulted. It is not yet clear how suitable HIV-infected SCID-hu mice will be as a model for AIDS. Several subfamilies of naturally occurring cytopathic retroviruses cause immune suppression, including fatal immunodeficiency syndromes in chickens, mice, cats, and monkeys. Domestic cats suffer immunosuppression from both an onco-virus, feline leukemia virus, and a member of the lentivirus subfamily, feline immunodeficiency virus (FIV). Asian macaques are susceptible to fatal simian AIDS from a type D retrovirus, indigenous in macaques, and from a lentivirus, simian immunodeficiency virus (SIV), which is indigenous to healthy African monkeys. SIV is the animal lentivirus most closely related to HIV. Of these animal models, the lentivirus infections of cats (FIV) and macaques (SIV) appear to bear the closest similarity in their pathogenesis to HIV infection and AIDS. This review will summarize these various animal model systems for AIDS and illustrate their usefulness for antiviral therapy and vaccinology.     

Plateau levels of viremia correlate with the degree of CD4+-T-cell loss in simian immunodeficiency virus SIVagm-infected pigtailed macaques: variable pathogenicity of natural SIVagm isolates

Simian immunodeficiency virus from African green monkeys (SIVagm) results in asymptomatic infection in its natural host species. The virus is not inherently apathogenic, since infection of pigtailed (PT) macaques (Macaca nemestrina) with one isolate of SIVagm results in an immunodeficiency syndrome characterized by progressive CD4+-T-cell depletion and opportunistic infections. This virus was passaged once in a PT macaque and, thus, may not be entirely reflective of the virulence of the parental strain. The goal of the present study was to assess the pathogenicity of the PT-passaged isolate (SIVagm9063) and two primary SIVagm isolates in PT macaques, including the parental strain of the PT-passaged variant. Infection of macaques with any of the three isolates resulted in high levels of primary plasma viremia by 1 week after inoculation. Viremia was quickly controlled following infection with SIVagm155; these animals have maintained CD4+-T-cell subsets and remain healthy. The plateau levels among SIVagm90- and SIVagm9063-inoculated macaques varied widely from 100 to 1 million copies/ml of plasma. Three of four animals from each of these groups progressed to AIDS. Setpoint viremia and the degree of CD4+-T-cell loss at 6 months postinfection were not significantly different between macaques inoculated with SIVagm90 and SIVagm9063. However these parameters were significantly different in SIVagm155-inoculated macaques (P values of <0.01). Considering all the macaques, the degree of CD4+-T-cell loss by 6 months postinfection correlated with the plateau levels of viremia. Thus, similar to SIVsm/mac infection of macaques and human AIDS, viral load is an excellent prognostic indicator of disease course. The inherent pathogenicity of natural SIVagm isolates varies, but such natural isolates are capable of inducing AIDS in macaques without prior macaque passage.     

Specific pathogen-free macaques: definition, history, and current production

Specific pathogen-free (SPF) macaque colonies are now requested frequently as a resource for research. Such colonies were originally conceived as a means to cull diseased animals from research-dedicated colonies, with the goal of eliminating debilitating or fatal infectious agents from the colony to improve the reproductive capacity of captive research animals. The initial pathogen of concern was Mycobacterium tuberculosis (M.tb.), recognized for many years as a pathogen of nonhuman primates as well as a human health target. More recently attention has focused on four viral pathogens as the basis for an SPF colony: simian type D retrovirus (SRV), simian immunodeficiency virus (SIV), simian T cell lymphotropic/leukemia virus (STLV), and Cercopithecine herpesvirus 1 (CHV-1). New technologies, breeding, and maintenance schemes have emerged to develop and provide SPF primates for research. In this review we focus on the nonhuman primates (NHPs) most common to North American NHP research facilities, Asian macaques, and the most common current research application of these animals, modeling of human AIDS.     

A molecularly cloned, pathogenic, neutralization-resistant simian immunodeficiency virus, SIVsmE543-3.

An infectious molecular clone of simian immunodeficiency virus SIVsm was derived from a biological isolate obtained late in disease from an immunodeficient rhesus macaque (E543) with SIV-induced encephalitis. The molecularly cloned virus, SIVsmE543-3, replicated well in macaque peripheral blood mononuclear cells and monocyte-derived macrophages and resisted neutralization by heterologous sera which broadly neutralized genetically diverse SIV variants in vitro. SIVsmE543-3 was infectious and induced AIDS when inoculated intravenously into pig-tailed macaques (Macaca nemestrina). Two of four infected macaques developed no measurable SIV-specific antibody and succumbed to a wasting syndrome and SIV-induced meningoencephalitis by 14 and 33 weeks postinfection. The other two macaques developed antibodies reactive in Western blot and virus neutralization assays. One macaque was sacrificed at 1 year postinoculation, and the survivor has evidence of immunodeficiency, characterized by persistently low CD4 lymphocyte subsets in the peripheral blood. Plasma samples from these latter animals neutralized SIVsmE543-3 but with much lower efficiency than neutralization of other related SIV strains, confirming the difficulty by which this molecularly cloned virus is neutralized in vitro. SIVsmE543-3 will provide a valuable reagent for studying SIV-induced encephalitis, mapping determinants of neutralization, and determining the in vivo significance of resistance to neutralization in vitro.     

Infection of macaque monkeys with simian immunodeficiency virus from African green monkeys: virulence and activation of latent infection

The virulence of three isolates of simian immunodeficiency virus from African green monkeys (SIVagm) was studied in rhesus and pigtailed macaques. None of 15 rhesus monkeys and one of four pigtailed monkeys died from infection during the time they were studied (up to 33 months). SIVagm was only isolated from rhesus monkeys for up to 2 months after inoculation. However, when these animals were secondarily infected with Simian acquired immunodeficiency syndrome retrovirus type 1 (SRV-1), SIVagm was activated and isolated. Dual infection caused increased mortality.     

Derivation and characterization of a highly pathogenic isolate of human immunodeficiency virus type 2 that causes rapid CD4+ cell depletion in Macaca nemestrina

With few exceptions, humans are the only species known to develop acquired immunodeficiency syndrome (AIDS) after human immunodeficiency virus (HIV) infection. We report here that an isolate of HIV type 2, EHO, readily established persistent infection in 100% of Macaca nemestrina in three consecutive transmission studies. Of the eight infected animals, five showed persistently high virus load and six developed AIDS-like diseases or CD4+ cell depletion within 4 years of infection. The pathology and clinical signs closely parallel those of HIV-1 infection of humans, including lymphadenopathy, anemia, CD4+ cell depletion, and opportunistic infections. A cell-free virus stock was established from the lymph nodes of an animal that developed AIDS-like diseases. This virus, HIV-2/287, was highly pathogenic in M. nemestrina, causing CD4+ cell depletion within 2-8 weeks postinfection. While both HIV-2 EHO and HIV-2/287 use predominantly CXCR4, the latter shows greatly enhanced replicative capacity in macaque peripheral blood mononuclear cells (PBMCs). The establishment of a human immunodeficiency virus that causes rapid and reproducible CD4 cell depletion in macaques could facilitate the study of HIV pathogenesis and the development of effective vaccines and therapy against AIDS.     

A combination DNA and attenuated simian immunodeficiency virus vaccine strategy provides enhanced protection from simian/human immunodeficiency virus-induced disease

Among the most effective vaccine candidates tested in the simian immunodeficiency virus (SIV)/macaque system, live attenuated viruses have been shown to provide the best protection from challenge. To investigate if preimmunization would increase the level of protection afforded by live attenuated SIVmac239Deltanef (Deltanef), macaques were given two priming immunizations of DNA encoding SIV Gag and Pol proteins, with control macaques receiving vector DNA immunizations. In macaques receiving the SIV DNA inoculation, SIV-specific cellular but not humoral responses were readily detectable 2 weeks after the second DNA inoculation. Following boosting with live attenuated virus, control of Deltanef replication was superior in SIV-DNA-primed macaques versus vector-DNA-primed macaques and was correlated with higher levels of CD8+/gamma-interferon-positive and/or interleukin-2-positive cells. Challenge with an intravenous inoculation of simian/human immunodeficiency virus (SHIV) strain SHIV89.6p resulted in infection of all animals. However, macaques receiving SIV DNA as the priming immunizations had statistically lower viral loads than control animals and did not develop signs of disease, whereas three of seven macaques receiving vector DNA showed severe CD4+ T-cell decline, with development of AIDS in one of these animals. No correlation of immune responses to protection from disease could be derived from our analyses. These results demonstrate that addition of a DNA prime to a live attenuated virus provided better protection from disease following challenge than live attenuated virus alone.     

Chimeric simian/human immunodeficiency virus that causes progressive loss of CD4+ T cells and AIDS in pig-tailed macaques.

By animal-to-animal passage of simian/human immunodeficiency virus (SHIV) in pig-tailed macaques, we have developed a macaque model of human immunodeficiency virus type 1 (HIV-1) disease in humans. Passaging was begun with a chimeric virus containing the env gene of HIV-1 HXBc2 and the gag and pol genes of simian immunodeficiency virus SIVmac239. SHIV was passaged serially in cohorts of two macaques each, using bone marrow-to-bone marrow transfers at 5, 5, and 16 weeks for passages 2, 3, and 4, respectively. The fifth passage was done by using cell-free virus isolated from cerebrospinal fluid of a passage 4 macaque. The virus became more virulent with each passage. Virus replication was restricted in all three animals in passages 1 and 2 but not in five of the six animals in passages 3, 4, and 5. In these animals, intense virus replication in the lymphoid tissues resulted in almost total elimination of CD4+ T cells within weeks of inoculation, and three of these animals developed AIDS in less than 1 year. The more uniform virus-host interaction initiated by the cell-free virus in the passage 5 animals contrasted with a more variable pattern of disease initiated by infectious bone marrow cells during earlier passages. The virulent cell-free SHIV can now be used to screen the efficacy of vaccines directed against the envelope of HIV-1.     

Rhesus macaques inoculated with molecularly cloned simian immunodeficiency virus

We have isolated a biologically active molecular clone of simian immunodeficiency virus (SIV), SIVmac 1A11, originally obtained from a rhesus macaque at the New England Regional Primate Research Center. Virus derived from cells transfected with this clone is cytopathic for rhesus peripheral blood mononuclear cells, replicates in cultures of rhesus macrophages, and infects rhesus macaques when inoculated intravenously. Six macaques inoculated with SIVmac 1A11 all became infected and produced antibodies to viral envelope glycoproteins that neutralized virus. Antibodies to viral core proteins were detected in only one animal. No clinical signs of disease were observed throughout 7 months postinoculation.     

Retroperitoneal fibromatosis and acquired immunodeficiency syndrome in macaques: clinical and immunologic studies

A simian acquired immunodeficiency syndrome (SAIDS) associated with retroperitoneal fibromatosis (RF) has been observed in several species of macaque at the Washington Regional Primate Research Center. Clinical signs were recurrent diarrhea, weight loss, mesenteric lymphadenopathy, and opportunistic infections. Most affected macaques in the later stages of illness showed marked immunodeficiency. Response of peripheral blood mononuclear cells to mitogens was impaired significantly. There was sharply depressed primary and secondary antibody response to the T-cell dependent antigen, bacteriophage phi X174. Affected monkeys did not switch from IgM to IgG antibody following a secondary immunization, as did normal macaques. Twenty-four (67%) of 36 affected animals with progressive RF or deteriorated stages of illness had hypoproteinemia and hypoalbuminemia. Quantitative serum immunoglobulins of 23 cases showed that eight (35%) had hypogammaglobulinemia, six (26%) had hypergammaglobulinemia, and the remainder (39%) were within the normal range. Opportunistic infections were predominantly bacterial pathogens. Type D retrovirus appeared to be closely associated with RF-affected macaques (12/12 or 100%). The case fatality rate (including animals sacrificed after prolonged illness) was 98%. The leading cause of death was due directly to RF lesions in 43%, to enterocolitis in 36%, septicemia in 12%, amyloidosis in 5%, and malignant lymphoma (2%). Clinical, immunologic and pathologic changes reveal an acquired immunodeficiency syndrome that has many similarities to human AIDS. SAIDS and RF may be a useful model for studying human AIDS.     

Derivation and characterization of a highly pathogenic isolate of human immunodeficiency virus type 2 that causes rapid CD4+ cell depletion in Macaca nemestrina

With few exceptions, humans are the only species known to develop acquired immunodeficiency syndrome (AIDS) after human immunodeficiency virus (HIV) infection. We report here that an isolate of HIV type 2, EHO, readily established persistent infection in 100% of Macaca nemestrina in three consecutive transmission studies. Of the eight infected animals, five showed persistently high virus load and six developed AIDS-like diseases or CD4⁺ cell depletion within 4 years of infection. The pathology and clinical signs closely parallel those of HIV-1 infection of humans, including lymphadenopathy, anemia, CD4⁺ cell depletion, and opportunistic infections. A cell-free virus stock was established from the lymph nodes of an animal that developed AIDS-like diseases. This virus, HIV-2/287, was highly pathogenic in M. nemestrina, causing CD4⁺ cell depletion within 2–8 weeks post-infection. While both HIV-2 EHO and HIV-2/287 use predominantly CXCR4, the latter shows greatly enhanced replicative capacity in macaque peripheral blood mononuclear cells (PBMCs). The establishment of a human immunodeficiency virus that causes rapid and reproducible CD4⁺ cell depletion in macaques could facilitate the study of HIV pathogenesis and the development of effective vaccines and therapy against AIDS.     

Viremia control following antiretroviral treatment and therapeutic immunization during primary SIV251 infection of macaques

Prolonged antiretroviral therapy (ART) is not likely to eradicate human immunodeficiency virus type I (HIV-I) infection. Here we explore the effect of therapeutic immunization in the context of ART during primary infection using the simian immunodeficiency virus (SIV251) macaque model. Vaccination of rhesus macaques with the highly attenuated poxvirus-based NYVAC-SIV vaccine expressing structural genes elicited vigorous virus-specific CD4 + and CD8+ T cell responses in macaques that responded effectively to ART. Following discontinuation of a six-month ART regimen, viral rebound occurred in most animals, but was transient in six of eight vaccinated animals. Viral rebound was also transient in four of seven mock-vaccinated control animals. These data establish the importance of antiretroviral treatment during primary infection and demonstrate that virus-specific immune responses in the infected host can be expanded by therapeutic immunization.     

Isolation of a type D retrovirus from B-cell lymphomas of a patient with AIDS.

An atypical syncytial variant of a high-grade Burkitt's-type B-cell lymphoma from a patient with AIDS who was seropositive for human immunodeficiency virus type 1 was studied. A productive type D retrovirus infection was identified in early-passage cell lines derived from two lymphomas from this patient. Nucleotide and amino acid sequence analysis as well as immunologic reactivity indicated that the isolated virus was highly related to Mason-Pfizer monkey virus (MPMV). MPMV is an immunosuppressive type D retrovirus that causes an AIDS-like syndrome in rhesus macaques. Amplification of DNA from the patient's diagnostic bone marrow biopsy specimen by polymerase chain reaction generated the appropriate MPMV-specific fragments and indicated that the patient was infected with the MPMV-like retrovirus. In addition, the patient's serum contained antibodies which recognized type D viral env proteins (gp70 and gp20) and gag proteins (p27 and p14). Although there have been reports of human cell lines infected with type D retroviruses and of type D-reactive human sera, this is the first evidence of a type D retrovirus infection in a human confirmed by virus isolation, serum reactivity, and viral DNA identification in tumor tissue.     

Inoculation of baboons and macaques with simian immunodeficiency virus/Mne, a primate lentivirus closely related to human immunodeficiency virus type 2

A primate lymphotropic lentivirus was isolated on the human T-cell line HuT 78 after cocultivation of a lymph node from a pig-tailed macaque (Macaca nemestrina) that had died with malignant lymphoma. This isolate, originally designated M. nemestrina immunodeficiency virus (MnIV) and now classified as simian immunodeficiency virus (SIV/Mne), was inoculated intravenously into three juvenile rhesus monkeys (Macaca mulatta), three juvenile pig-tailed macaques (M. nemestrina), and two juvenile baboons (Papio cynocephalus). All six macaques became viremic by 3 weeks after inoculation, whereas neither of the baboons developed viremia. One pig-tailed macaque died at 15 weeks with suppurative peritonitis secondary to ulcerative, necrotizing colitis. Immunologic abnormalities included a marked decrease in CD4+ peripheral blood lymphocytes. Although five macaques mounted an antibody response to SIV/Mne, the animal that died at 15 weeks remained antibody negative. Three other macaques (two rhesus and one pig-tailed) died 66 to 87 weeks after inoculation after exhibiting progressive weight loss, anemia, and diarrhea. Histopathologic findings at necropsy included various manifestations of immune deficiency, nephropathy, subacute encephalitis, pancreatitis, adenocarcinoma, and lymphoid atrophy. SIV/Mne could be readily isolated from the spleens and lymph nodes of all necropsied macaques, and from the cerebrospinal fluid, brains, bone marrow, livers, and pancreas of some of the animals. SIV antigens were localized by avidin-biotin immunohistochemistry to pancreatic islet cells and to bone marrow endothelial cells. The data suggest that African baboons may be resistant to infection by SIV/Mne, whereas Asian macaques are susceptible to infection with this pathogenic primate lentivirus.     

Characterization of infectious molecular clones of simian immunodeficiency virus (SIVmac) and human immunodeficiency virus type 2: persistent infection of rhesus monkeys with molecularly cloned SIVmac.

Infection of macaque monkeys with simian immunodeficiency virus (SIV) is probably the best animal model currently available for studying acquired immunodeficiency syndrome. In this report, we describe three infectious molecular clones of SIVmac and one of human immunodeficiency virus type 2 (HIV-2) and their use in the study of cell and species specificity, animal infection, and the relationship of gene sequence to function. Replication of the cloned viruses in different cell lines varied dramatically. Some human CD4+ cell lines (HUT 78 and MT-4) supported the replication of SIVmac and HIV-2, while others (CEM and Jurkat-T) supported the replication of HIV-2 but not SIVmac. Growth of cloned virus in macaque lymphocytes in vitro was predictive of macaque infection in vivo. Macaque lymphocytes supported the replication of SIVmac239 and SIVmac251 but not SIVmac142 or HIV-2ROD. Using virus recovery and antibody response as criteria for infection, macaques that received cloned SIVmac251 and SIVmac239 became infected, while macaques receiving cloned SIVmac142 and HIV-2ROD did not become infected. Nucleotide sequences from the envelope region of all four cloned viruses demonstrated that there is considerable flexibility in the location of the translational termination (stop) signal. These infectious molecular clones will be very useful for future studies directed at the molecular basis for persistence, pathogenicity, tropism, and cell and species specificity.     

Elimination of type D retrovirus infection from group-housed rhesus monkeys using serial testing and removal.

Type D retrovirus was successfully eliminated from an infected population of group-housed rhesus monkeys by serial testing of all animals for virus and antibody and subsequent removal of positives. This population of 53 rhesus had been housed together for 1 year prior to the initiation of the test and removal program, with six deaths from type D retrovirus-induced immunodeficiency disease occurring during this period. No new infections were detected after four rounds of testing. Of the 47 animals present at the start of the testing program, 17 (35%) remained after the elimination of type D virus from this group. These animals and their offspring have remained healthy and antibody negative for more than 2 years. These results demonstrate that elimination of type D retroviruses from rhesus macaque colonies is feasible, and that the objective of establishing and maintaining retrovirus-free colonies is realistic and achievable.     

Intravaginal inoculation of rhesus macaques with cell-free simian immunodeficiency virus results in persistent or transient viremia.

The simian immunodeficiency virus (SIV)-rhesus macaque model of heterosexual human immunodeficiency virus transmission consists of atraumatic application of cell-free SIVmac onto the intact vaginal mucosa of mature female rhesus macaques. This procedure results in systemic infection, and eventually infected animals develop the clinical signs and pathologic changes of simian AIDS. To achieve 100% transmission with the virus stocks used to date, multiple intravaginal inoculations are required. The current titration study utilized two stocks of SIVmac and demonstrated that a single intravaginal dose of cell-free SIV can reliably produce infection in rhesus macaques. This study also demonstrated that some animals intravaginally inoculated with cell-free SIVmac develop transient viremia characterized by a limited ability to isolate virus from peripheral blood mononuclear cells and lymph node mononuclear cells and no seroconversion to SIV antigen. SIV could be isolated from the peripheral lymph nodes of transiently viremic animals only during periods of viremia and not at times when SIV was not detected in circulating mononuclear cells. Thus, peripheral lymphoid tissues were not reservoirs of infection in the transiently viremic animals. Taken together, these results suggest either that the SIV infection was cleared in the transiently viremic animals or that SIV infection is limited to a compartment of the genital mucosal immune system that cannot be assessed by monitoring SIV infection in peripheral blood mononuclear cells and peripheral lymphoid tissue.     

Neutralizing Polyclonal IgG Present during Acute Infection Prevents Rapid Disease Onset in Simian-Human Immunodeficiency Virus SHIVSF162P3-Infected Infant Rhesus Macaques

Simian-human immunodeficiency virus (SHIV) models for human immunodeficiency virus (HIV) infection have been widely used in passive studies with HIV neutralizing antibodies (NAbs) to test for protection against infection. However, because SHIV-infected adult macaques often rapidly control plasma viremia and any resulting pathogenesis is minor, the model has been unsuitable for studying the impact of antibodies on pathogenesis in infected animals. We found that SHIV_SF162P3 infection in 1-month-old rhesus macaques not only results in high persistent plasma viremia but also leads to very rapid disease progression within 12 to 16 weeks. In this model, passive transfer of high doses of neutralizing IgG (SHIVIG) prevents infection. Here, we show that at lower doses, SHIVIG reduces both plasma and peripheral blood mononuclear cell (PBMC)-associated viremia and mitigates pathogenesis in infected animals. Moreover, production of endogenous NAbs correlated with lower set-point viremia and 100% survival of infected animals. New SHIV models are needed to investigate whether passively transferred antibodies or antibodies elicited by vaccination that fall short of providing sterilizing immunity impact disease progression or influence immune responses. The 1-month-old rhesus macaque SHIV model of infection provides a new tool to investigate the effects of antibodies on viral replication and clearance, mechanisms of B cell maintenance, and the induction of adaptive immunity in disease progression.     

The pigtail macaque MHC class I allele Mane-A*10 presents an immundominant SIV Gag epitope: identification, tetramer development and implications of immune escape and reversion

The pigtail macaque (Macaca nemestrina) is a common model for the study of AIDS. The pigtail major histocompatibility complex class I allele Mane-A*10 restricts an immunodominant simian immunodeficiency virus (SIV) Gag epitope (KP9) which rapidly mutates to escape T cell recognition following acute simian/human immunodeficiency virus infection. Two technologies for the detection of Mane-A*10 in outbred pigtail macaques were developed: reference strand-mediated conformational analysis and sequence-specific primer polymerase chain reaction. A Mane-A*10/KP9 tetramer was then developed to quantify CD8(+) T lymphocytes primed by multigenic DNA vaccination, which have previously been difficult to detect using standard interferon-gamma-based T cell assays. We also demonstrate mutational escape at KP9 following acute SIV infection. Mane-A*10(+) animals have lower set point SIV levels than Mane-A*10(-) animals, suggesting a significant fitness cost of escape. These studies pave the way for a more robust understanding of HIV vaccines in pigtail macaques.