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

Specific pathogen free macaque colonies: a review of principles and recent advances for viral testing and colony management

Specific pathogen free (SPF) macaques provide valuable animal models for biomedical research. In 1989, the National Center for Research Resources [now Office of Research Infrastructure Programs (ORIP)] of the National Institutes of Health initiated experimental research contracts to establish and maintain SPF colonies. The derivation and maintenance of SPF macaque colonies is a complex undertaking requiring knowledge of the biology of the agents for exclusion and normal physiology and behavior of macaques, application of the latest diagnostic technology, facilitiy management, and animal husbandry. This review provides information on the biology of the four viral agents targeted for exclusion in ORIP SPF macaque colonies, describes current state-of-the-art viral diagnostic algorithms, presents data from proficiency testing of diagnostic assays between laboratories at institutions participating in the ORIP SPF program, and outlines management strategies for maintaining the integrity of SPF colonies using results of diagnostic testing as a guide to decision making.

[Epidemiological survey of a captive Chinese rhesus macaque breeding colony in Yunnan for SRV, STLV and BV]

Nonhuman primates are critical resources for biomedical research. Rhesus macaque is a popularly used laboratory nonhuman primate that share many characteristics with humans. However, rhesus macaques are the natural host of two exogenous retroviruses, SRV (simian type D retrovirus) and STLV (simian T lymphotropic virus). SRV and STLV may introduce potentially significant confounding factors into the study of AIDS model. Moreover, B virus (ceropithecine herpesvirus 1) is likely to harm not only rhesus macaque but also humans in experiments involving rhesus macaque. Yunnan province has large-scale breeding colonies of Chinese rhesus macaque. Therefore there is an urgent need for SPF Chinese rhesus macaque colonies. Here we investigated SRV, STLV and BV infections in 411 Chinese rhesus macaque by PCR technique. The results showed that the prevalence of SRV, STLV and BV among Chinese rhesus macaque breeding colony was 19.71% (81/411), 13.38% (55/411) and 23.11% (95/411), respectively. Comparison of viruses infection in different age-groups and male/female of Chinese rhesus macaque was also analyzed. This study will contribute to establishment of SPF Chinese rhesus macaque breeding colony.

Simian retroviruses: infection and disease--implications for immunotoxicology research in primates

Non-human primates have assumed an important role in preclinical safety assessment studies, particularly in the evaluation of biopharmaceutical and immunomodulatory therapies. Naturally occurring simian retrovirus infections may adversely affect the suitability of primates for use in such studies. Various species of non-human primates are the natural hosts for six exogenous retroviruses, representing five genera within the family Retroviridae. Retroviruses establish persistent infections with a broad spectrum of pathogenic potential, ranging from nonpathogenic to highly pathogenic, depending on the variety of the host, virus, and environmental factors. In the context of immunotoxicology, in which the research objective is to specifically evaluate the effect of drugs or biologics on the immune system, the immune modulatory effects of simian retroviruses, which may be subtle or profound, may introduce significant confounding into the studies of immunotoxic effects utilizing non-human primates. Latent or subclinical retrovirus infections are common and research-related procedures may lead to virus reactivation or overt disease. Adverse effects of undetected retrovirus infections on preclinical research include the loss of experimental subjects (and potentially of statistical power) due to increased morbidity and mortality, virus-induced clinical abnormalities, histologic lesions, alteration of physiologic parameters and biologic responses, and interference with in vitro assays and/or cytolytic destruction of primary cell cultures. The aim of this review is to provide an overview of the key biological, clinical, and pathological features of several important simian retroviruses, with emphasis on viruses infecting macaques and other primate species commonly used in preclinical research, and a discussion of the implications of these infections for immunotoxicology and other preclinical research in primates. Adequate pre-study retrovirus screening is essential to exclude retrovirus-infected primates from research protocols.

Convergent evolution of SIV env after independent inoculation of rhesus macaques with infectious proviral DNA

The env gene of three simian immunodeficiency virus (SIV) variants developed convergent mutations during disease progression in six rhesus macaques. The monkeys had been inoculated with supercoiled plasmids encoding infectious proviruses of SIVmac239 (a pathogenic, wild-type strain), SIVdelta3 (the live attenuated vaccine strain derived from SIVmac239), or SIVdelta3+ (a pathogenic progeny virus that had evolved from SIVdelta3). All six monkeys developed immunodeficiency and progressed to fatal disease. Although many divergent mutations arose in env among the different hosts, three regions consistently mutated in all monkeys studied; these similar mutations developed independently even though the animals had received only a single infectious molecular clone rather than standard viral inocula that contain viral quasispecies. Together, these data indicate that the env genes of SIVmac239, SIVdelta3, and SIVdelta3+, in the context of different proviral backbones, evolve similarly in different hosts during disease progression.

Live attenuated, nef-deleted SIV is pathogenic in most adult macaques after prolonged observation

OBJECTIVE

A live attenuated SIV vaccine strain, termed SIVmac239Delta3 and containing large deletions in, and the negative regulatory element, was previously shown to cause AIDS mostly in monkeys vaccinated as infants. In the present study, we demonstrate that SIVmac239Delta3 is pathogenic in most vaccinated adult monkeys, given enough time.

METHODS

Eleven rhesus macaques vaccinated as adults with SIVmac239Delta3 were followed for extended periods (up to 6.8 years).

RESULTS

We found signs of immune dysregulation in all 11 adult vaccinees. All animals developed persistently inverted CD4 : CD8 T-cell ratios, seven (64%) had persistent recurrent viremia, and six (55%) had decreased CD4 T-cell counts (< 500 x 10 cells/l). Further signs included low CD4CD29 lymphocyte subsets, loss of anti-Gag antibodies, anemia, thrombocytopenia, wasting, and opportunistic infections. Two adult vaccinees (18%) subsequently developed AIDS. Development of chronic, recurrent viremia with plasma viral RNA loads > or = 10 copies/ml and cytoviremia was a poor prognostic sign.

CONCLUSION

Our data demonstrate that with time, a live attenuated, multiply deleted SIV vaccine can cause immune dysregulation in most vaccine recipients, even in initially immune competent, healthy adults. Immune dysfunction can progress to full AIDS. However, pathogenic effects became evident only several years after vaccination. Thus, mass vaccination of humans with similarly constructed live attenuated HIV vaccines, recently suggested for countries with high HIV-1 transmission rates, seems contraindicated.

Simian retrovirus infections: potential confounding variables in primate toxicology studies

Various species of nonhuman primates are natural hosts for 6 exogenous retroviruses, including gibbon-ape leukemia virus (GaLV), simian sarcoma virus, simian T-lymphotropic virus (STLV), simian immunodeficiency virus (SIV), simian type D retrovirus (SRV), and simian foamy virus (SFV). These viruses establish persistent infections with a broad spectrum of pathogenic potential, ranging from highly pathogenic to nonpathogenic, depending on various host, virus, and environmental factors. Latent or subclinical infections are common, and various procedures associated with experimental protocols may lead to virus reactivation and disease. Adverse effects on toxicologic research by undetected retroviral infections can occur in several ways, including loss of experimental subjects (and statistical power) due to increased morbidity and mortality. In addition, results may be confounded by virus-induced clinical abnormalities, histologic lesions, alteration of physiologic parameters and responses, and interference with in vitro assays and/or destruction of primary cell cultures. Key clinical and epidemiological features of several important retroviruses are reviewed, with emphasis on viruses infecting species of macaques most commonly used as research subjects in primate toxicology studies. Examples of actual and potential confounding of toxicologic studies by retroviruses are discussed, including altered cytokine profiles in healthy STLV carriers, and clinical and pathological abnormalities induced by SRV infection. Adequate prestudy viral screening is critical to exclude retrovirus-infected primates from toxicologic research protocols and prevent potential confounding of research results.

Association of primate T-cell lymphotropic virus infection of pig-tailed macaques with high mortality

Natural infection of humans with human T-cell lymphotropic virus type I (HTLV-I) and of old world nonhuman primates with the simian counterpart, STLV-I, is associated with development of neoplastic disease in a small percentage of individuals after long latent periods. HTLV-I is also the etiologic agent of a more rapidly progressive neurologic disease, HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Macaques have been used experimentally in studies to evaluate HTLV-I candidate vaccines for efficacy, but no evidence of disease was observed. Here we report experimental infection of pig-tailed macaques with STLV-I(sm) and HTLV-I(ACH), both of which were associated with a disease syndrome characterized by rapid onset, hypothermia, lethargy, and death within hours to days. Other pathologic sequelae included diarrhea, rash, bladder dysfunction, weight loss, and, in one animal, arthropathy. Both retroviruses were detected in the central nervous systems of some animals, either by culture or by direct antigen capture for p19 Gag in cerebrospinal fluid. Although virus was recovered throughout infection from peripheral blood mononuclear cells (PBMC), all infected macaques maintained low antiviral antibody titers and stable proviral burdens, which generally ranged between 10 and 100 copies per 10(6) PBMC. However, of 13 macaques infected with HTLV-I(ACH) or STLV-I(sm), seven animals (54%) died between 35 weeks and 412 years after infection. This unexpected high mortality within a relatively short time suggests that infection of pig-tailed macaques might be a useful model for studying immune responses to and pathologic events resulting from HTLV-I infection.

Quantitation of simian cytokine and beta-chemokine mRNAs, using real-time reverse transcriptase-polymerase chain reaction: variations in expression during chronic primate lentivirus infection

Cytokines and beta-chemokines are important mediators of the immune system and are expressed in many infectious diseases. To study cytokine and beta-chemokine profiles during pathogenesis of lentiviral infection and progression to AIDS in rhesus macaques, we established new quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assays based on TaqMan chemistry. Using synthetic RNA standards, we quantified mRNAs of IL-2, IL-4, IL-6, IL-10, IL-12 p40, interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), RANTES, macrophage inflammatory protein 1 alpha (MIP-1 alpha), and MIP-1 beta in unstimulated peripheral blood mononuclear cells (PBMCs) and lymph nodes from macaques chronically infected with SIV or SHIV. Viremic monkeys with decreased CD4(+) T cell counts (<500 cells/microl) had significantly higher IL-10 mRNA expression than uninfected controls, which parallels the findings in HIV-1-infected humans. In addition, MIP-1 alpha, MIP-1 beta, and RANTES mRNA expression increased in viremic monkeys with decreased CD4(+) T cell counts; gene expression was inversely correlated with CD4(+) T cell counts, but not viral load. The newly established quantitative real-time RT-PCR assays will allow the determination of cytokine and beta-chemokine patterns in rhesus macaques in studies of microbial pathogenesis or vaccine development.

Postnatal passive immunization of neonatal macaques with a triple combination of human monoclonal antibodies against oral simian-human immunodeficiency virus challenge

To develop prophylaxis against mother-to-child human immunodeficiency virus (HIV) transmission, we established a simian-human immunodeficiency virus (SHIV) infection model in neonatal macaques that mimics intrapartum mucosal virus exposure (T. W. Baba et al., AIDS Res. Hum. Retroviruses 10:351-357, 1994). Using this model, neonates were protected from mucosal SHIV-vpu(+) challenge by pre- and postnatal treatment with a combination of three human neutralizing monoclonal antibodies (MAbs), F105, 2G12, and 2F5 (Baba et al., Nat. Med. 6:200-206, 2000). In the present study, we used this MAb combination only postnatally, thereby significantly reducing the quantity of antibodies necessary and rendering their potential use in humans more practical. We protected two neonates with this regimen against oral SHIV-vpu(+) challenge, while four untreated control animals became persistently infected. Thus, synergistic MAbs protect when used as immunoprophylaxis without the prenatal dose. We then determined in vitro the optimal MAb combination against the more pathogenic SHIV89.6P, a chimeric virus encoding env of the primary HIV89.6. Remarkably, the most potent combination included IgG1b12, which alone does not neutralize SHIV89.6P. We administered the combination of MAbs IgG1b12, 2F5, and 2G12 postnatally to four neonates. One of the four infants remained uninfected after oral challenge with SHIV89.6P, and two infants had no or a delayed CD4(+) T-cell decline. In contrast, all control animals had dramatic drops in their CD4(+) T cells by 2 weeks postexposure. We conclude that our triple MAb combination partially protected against mucosal challenge with the highly pathogenic SHIV89.6P. Thus, combination immunoprophylaxis with passively administered synergistic human MAbs may play a role in the clinical prevention of mother-to-infant transmission of HIV type 1.

The discovery of two new divergent STLVs has implications for the evolution and epidemiology of HTLVs

We have isolated and characterised two divergent simian T-lymphotropic viruses (STLV), not belonging to the established human and simian T-lymphotropic virus lineages HTLV-1/STLV-1 and HTLV-2. STLV-L, from an Eritrean sacred baboon (Papio hamadryas), has been typed as a third type of simian T-lymphotropic virus, distinct from HTLV-1/STLV-1 and HTLV-2. The other virus, isolated from Congolese bonobos (Pan paniscus), is a distinct member of the HTLV-2 clade and has been designated STLV-2. The isolation of these two simian viruses shows that the spectrum of HTLVs/STLVs is larger than previously expected. Our data indicate that the two lineages STLV-L and HTLV-2/STLV-2 are of African origin, while the HTLV-1/STLV-1 lineage has been shown to be of Asian origin. These data, together with our phylogenetic analyses, suggest an African origin of the HTLV/STLV ancestor, which provides new clues about virus dissemination. Furthermore, the atypical serological profiles exhibited by STLV-L or STLV-2 infected animals in western blot, raise questions about the efficiency of current screening methods to type highly divergent HTLVs/STLVs. Considering the growing interest in xenotransplantations, more epidemiological and biological knowledge of simian and human T-lymphotropic viruses is necessary to estimate the risk of interspecies transmissions.

Persistent infection of rhesus macaques by the rev-independent Nef(-) simian immunodeficiency virus SIVmac239: replication kinetics and genomic stability

We generated previously a Nef(-), replication-competent clone of SIVmac239 in which the Rev protein and the Rev-responsive element were replaced by the constitutive transport element (CTE) of simian retrovirus type 1 (A. S. von Gegerfelt and B. K. Felber, Virology 232:291-299, 1997). In the present report, we show that this virus was able to infect and replicate in rhesus macaques. The Rev-independent Nef(-) simian immunodeficiency virus induced a persistent humoral immune response in all monkeys, although viral loads were very low. Upon propagation in the monkeys, the genotype remained stable and the virus retained its in vitro growth characteristics. The infected monkeys showed normal hematological values and no signs of disease at more than 18 months post-virus exposure. Therefore, replacement of the essential Rev regulation by the CTE generated a virus variant that retained its replicative capacity both in vitro and in vivo, albeit at low levels.

Viremia and AIDS in rhesus macaques after intramuscular inoculation of plasmid DNA encoding full-length SIVmac239

We have succeeded in stably maintaining the entire genome of SIVmac239 as a plasmid clone. Supercoiled proviral plasmid DNA was inoculated intramuscularly into two adult rhesus macaques and into a neonate. All three animals became viremic and seroconverted. Viral kinetics were followed prospectively by quantitative competitive reverse transcriptase polymerase chain reaction (QC-RT-PCR), measurement of proviral DNA load in peripheral blood mononuclear cells (PBMCs) by PCR, and virus isolation by cocultivation. The infant developed high virus loads and succumbed to AIDS and SIV-associated nephropathy at 10 weeks postinoculation. Both adults are still living but have progressed to AIDS; one adult has also developed severe thrombocytopenia. We conclude that infection through intramuscular inoculation of cloned plasmid DNA encoding the entire proviral genome is reproducible and will provide a useful tool for studying viral pathogenesis.

Live attenuated, multiply deleted simian immunodeficiency virus causes AIDS in infant and adult macaques

A substantial risk in using live attenuated, multiply deleted viruses as vaccines against AIDS is their potential to induce AIDS. A mutant of the simian immunodeficiency virus (SIV) with large deletions in nef and vpr and in the negative regulatory element induced AIDS in six of eight infant macaques vaccinated orally or intravenously. Early signs of immune dysfunction were seen in the remaining two offspring. Prolonged follow-up of sixteen vaccinated adult macaques also showed resurgence of chronic viremia in four animals: two of these developed early signs of disease and one died of AIDS. We conclude that this multiply deleted SIV is pathogenic and that human AIDS vaccines built on similar prototypes may cause AIDS.

Isolation and characterization of a neuropathogenic simian immunodeficiency virus derived from a sooty mangabey

Transfusion of blood from a simian immunodeficiency virus (SIV)- and simian T-cell lymphotropic virus-infected sooty mangabey (designated FGb) to rhesus and pig-tailed macaques resulted in the development of neurologic disease in addition to AIDS. To investigate the role of SIV in neurologic disease, virus was isolated from a lymph node of a pig-tailed macaque (designated PGm) and the cerebrospinal fluid of a rhesus macaque (designated ROn2) and passaged to additional macaques. SIV-related neuropathogenic effects were observed in 100% of the pig-tailed macaques inoculated with either virus. Lesions in these animals included extensive formation of SIV RNA-positive giant cells in the brain parenchyma and meninges. Based upon morphology, the majority of infected cells in both lymphoid and brain tissue appeared to be of macrophage lineage. The virus isolates replicated very well in pig-tailed and rhesus macaque peripheral blood mononuclear cells (PBMC) with rapid kinetics. Differential replicative abilities were observed in both PBMC and macrophage populations, with viruses growing to higher titers in pig-tailed macaque cells than in rhesus macaque cells. An infectious molecular clone of virus derived from the isolate from macaque PGm (PGm5.3) was generated and was shown to have in vitro replication characteristics similar to those of the uncloned virus stock. While molecular analyses of this virus revealed its similarity to SIV isolates from sooty mangabeys, significant amino acid differences in Env and Nef were observed. This virus should provide an excellent system for investigating the mechanism of lentivirus-induced neurologic disease.

Spontaneous anaplastic large cell lymphoma in a chimpanzee: a clinicopathological and immunohistochemical study

An anaplastic large cell lymphoma with disseminated abdominal metastases was diagnosed in a 35-year-old male chimpanzee. Clinically, the animal displayed lethargy, weight loss, ascites, and abdominal distention. Imaging studies showed several large abdominal masses. At necropsy, variably sized masses of neoplastic mesenteric lymph nodes that encompassed several intestinal loops were present throughout the abdomen. The largest mass measured 9 x 5 cm and had cauliflower-like protrusions into the jejunal lumen. The entire abdominal cavity was covered by a sheet of neoplastic tissue. Histopathologically, the tumor consisted of solid sheets of proliferating lymphoid cells forming a cohesive growth that filled the lymph node sinuses. The tumor had invaded the intestinal wall. Anaplastic large cell lymphoma was diagnosed from immunohistochemistry findings on the basis of positive reaction to the CD3 and CD30 markers and negative reaction to the CD20 marker. Serologic analysis revealed positive titers for Epstein-Barr, cytomegalo-, and varicella-zoster viruses. Both serologic and virologic studies showed no evidence of detectable retroviral infection. This type of tumor has not been reported before in the chimpanzee.