Disease In Rhesus Monkeys Research Articles

Natural history of Ebola virus disease in rhesus monkeys shows viral variant emergence dynamics and tissue-specific host responses

Ebola virus (EBOV) causes Ebola virus disease (EVD), marked by severe hemorrhagic fever; however, the mechanisms underlying the disease remain unclear. To assess the molecular basis of EVD across time, we performed RNA sequencing on 17 tissues from a natural history study of 21 rhesus monkeys, developing new methods to characterize host-pathogen dynamics. We identified alterations in host gene expression with previously unknown tissue-specific changes, including downregulation of genes related to tissue connectivity. EBOV was widely disseminated throughout the body; using a new, broadly applicable deconvolution method, we found that viral load correlated with increased monocyte presence. Patterns of viral variation between tissues differentiated primary infections from compartmentalized infections, and several variants impacted viral fitness in a EBOV/Kikwit minigenome system, suggesting that functionally significant variants can emerge during early infection. This comprehensive portrait of host-pathogen dynamics in EVD illuminates new features of pathogenesis and establishes resources to study other emerging pathogens.

A Primate Model for Viral Hemorrhagic Fever.

Lymphocytic choriomeningitis virus strain WE (LCMV-WE), a Risk Group 3 virus, causes a disease in rhesus monkeys that closely resembles human infection with Lassa fever virus, a Risk Group 4 agent. Three stages of disease progression have been defined and profiled in this model: pre-viremic, viremic, and terminal. The earliest or pre-viremic stage reveals changes in the blood profile predictive of the later stages of disease. In order to identify whether specific changes are pathognomonic, it was necessary to perform a parallel infection with an attenuated virus (LCMV-Armstrong). Here we review the use of nonhuman primates to model viral hemorrhagic fever and offer a step-by-step guide to using a rhesus macaque model for Lassa fever.

Efficacy of Galidesivir against Ebola Virus Disease in Rhesus Monkeys

BackgroundThe recent re-emergence of Ebola virus in the Democratic Republic of the Congo serves as a stark reminder of the 2013–2016 Ebola virus (EBOV), which resulted in >11,000 deaths. To date, there are no approved therapeutics or vaccines for EBOV disease (EVD). Galidesivir (BCX4430) is an adenosine nucleoside analogue designed to inhibit viral RNA polymerase activity indirectly through non-obligate RNA chain termination. Galidesivir exhibits in vitro antiviral activity against a broad spectrum of negative- and positive-sense RNA viruses. In vivo, galidesivir has shown antiviral activity against various viruses and provides 100% protection against Marburg virus disease in cynomolgus macaques, when administered either 1 or 2 days post infection. Initial exploratory studies in a rhesus macaque model of EVD showed that 25 mg/kg galidesivir administered twice daily (BID) IM beginning immediately following viral challenge protected 100% (6 of 6) of animals.MethodsPharmacokinetic modeling based on galidesivir levels in healthy and EBOV-infected animals predicted that a loading-dose regimen could decrease time to steady-state, potentially advantageous when extending the time of treatment initiation. To test the efficacy of a loading dose regimen, 100 mg/kg was administered BID either 2 or 3 days after challenge, followed by maintenance doses of 25 mg/kg BID for a total duration of 11 days.ResultsSix of 6 (100%) rhesus monkeys survived after receiving loading doses on day 2, and 4 of 6 (67%) animals survived after receiving loading doses beginning day 3. In the dosing regimen that conferred 100% protection, the animals exhibited either no behavioral depression or only mild and transient behavioral depression. In all treated groups, there was a significant reduction of plasma viral RNA concentrations during the acute phase of disease.ConclusionGalidesivir protects rhesus monkeys against an otherwise lethal EBOV challenge. Administered by IM injection, Phase 1 human clinical studies of single and multiple ascending doses have shown galidesivir to be generally safe and well tolerated up to 10 mg/kg daily for seven days. Additional clinical studies are planned to evaluate the safety and tolerability of galidesivir administered by IV infusion. Supported by NIAID (NIH), HHSN272201300017C.Disclosures S. MacLennan, BioCryst: Employee, Salary. A. Mathis, BioCryst Pharmaceuticals: Employee, Salary. E. Giuliano, BioCryst: Employee, Salary. R. Taylor, BioCryst Pharmaceuticals: Employee, Salary. W. Sheridan, BioCryst Pharmaceuticals: Employee, Salary.

A pilot study on inducing Graves' disease in rhesus monkeys

Objective To induce Graves' disease in rhesus monkeys,which would exhibit greater similarity to Graves' patients than previous rodent models.Methods Adult female rhesus macaques were injected intramuscularly with 6× 1010 particles adenovirus expressing the A-subunit of TSHR (A-sub-Ad) or EGFP-Ad five times by three weeks intervals,and sera were prepared from blood samples collected at several time points during the immunization regimen.The animals were euthanized 4 weeks after the final injection to obtain blood,spleen cells,thyroid glands and other organs.Results After final immunization,the monkeys injected with A-sub-Ad showed characteristic of Graves' disease.Compared to controls,all the test monkeys had significant higher TRAb levels,half of them had increased TT4 and FT4,and 75％ developed goiter.Conclusion The non-human primate model of Graves' disease was successfully established,which would provide an ideal tool for further understanding of the pathogenesis of Graves' disease in human. Key words: Thyrotropin receptor; A-subunit; Graves' disease; Animal model; Rhesus monkeys

Extending healthy life span--from yeast to humans.

When the food intake of organisms such as yeast and rodents is reduced (dietary restriction), they live longer than organisms fed a normal diet. A similar effect is seen when the activity of nutrient-sensing pathways is reduced by mutations or chemical inhibitors. In rodents, both dietary restriction and decreased nutrient-sensing pathway activity can lower the incidence of age-related loss of function and disease, including tumors and neurodegeneration. Dietary restriction also increases life span and protects against diabetes, cancer, and cardiovascular disease in rhesus monkeys, and in humans it causes changes that protect against these age-related pathologies. Tumors and diabetes are also uncommon in humans with mutations in the growth hormone receptor, and natural genetic variants in nutrient-sensing pathways are associated with increased human life span. Dietary restriction and reduced activity of nutrient-sensing pathways may thus slow aging by similar mechanisms, which have been conserved during evolution. We discuss these findings and their potential application to prevention of age-related disease and promotion of healthy aging in humans, and the challenge of possible negative side effects.

Comprehensive analysis of Rhesus lymphocryptovirus microRNA expression.

Rhesus lymphocryptovirus (rLCV) and Epstein-Barr virus (EBV) are closely related gammaherpesviruses that infect and cause disease in rhesus monkeys and humans, respectively. Thus, rLCV is an important model system for EBV pathogenesis. Both rLCV and EBV express microRNAs (miRNAs), several conserved in sequence and genomic location. We have applied deep sequencing technology to obtain an inventory of rLCV miRNA expression in latently rLCV-infected monkey B cells. Our data confirm the presence of all previously identified mature rLCV miRNAs and have resulted in the discovery of 21 new mature miRNAs arising from previously identified precursor miRNAs (pre-miRNAs), as well as two novel pre-miRNAs (rL1-34 and rL1-35) that together generate four new mature miRNAs. Thus, the total number of rLCV-encoded pre-miRNAs is 35 and the total number of rLCV mature miRNAs is 68, the most of any virus examined. The exact 5' and 3' ends of all mature rLCV miRNAs were pinpointed, many showing marked sequence and length heterogeneity that could modulate function. We further demonstrate that rLCV mature miRNAs associate with Argonaute proteins in rLCV-infected B cells.

Development of Alcoholic Fatty Liver and Fibrosis in Rhesus Monkeys Fed a Low n‐3 Fatty Acid Diet

The amount and type of dietary fat seem to be important factors that modulate the development of alcohol-induced liver steatosis and fibrosis. Various alcohol-feeding studies in animals have been used to model some of the symptoms that occur in liver disease in humans. Rhesus monkeys (Macaca mulatta) were maintained on a diet that had a very low concentration of alpha-linolenic acid and were given free access to an artificially sweetened 7% ethanol solution. Control and ethanol-consuming animals were maintained on a diet in which the linoleate content was adequate (1.4% of energy); however, alpha-linoleate represented only 0.08% of energy. Liver specimens were obtained, and the fatty acid composition of the liver phospholipids, cholesterol esters, and triglycerides of the two groups were compared at 5 years and histopathology of tissue samples were compared at 3 and 5 years. The mean consumption of ethanol for this group over a 5-year period was 2.4 g.kg.day. As a consequence of the ethanol-dietary treatment, there were significantly lower concentrations of several polyunsaturated fatty acids in the liver phospholipids of the alcohol-treated group, including arachidonic acid and most of the n-3 fatty acids and particularly docosahexaenoic acid, when compared with dietary controls. Liver specimens from animals in the ethanol group at 5 years showed a marked degree of steatosis, both focal and diffuse cellular necrosis, and an increase in the development of fibrosis compared with specimens obtained at 3 years and with those from dietary controls, in which there was no evidence of fibrotic lesions. These findings suggest that the advancement of ethanol-induced liver disease in rhesus monkeys may be modulated by the amount and type of dietary essential fatty acids and that a marginal intake of n-3 fatty acids may be a permissive factor in the development of liver disease in primates.

The effects of low dietary levels of polyunsaturates on alcohol-induced liver disease in rhesus monkeys.

Rhesus monkeys that were maintained on a diet containing low, yet adequate, amounts of vitamins C and E and in which linoleate and linolenate represented 1.4% and 0.08% of the total caloric intake, respectively, developed liver fibrosis after consuming alcohol (mean, 2.6 g kg(-1) d[-1]) over a period of 3 years. In the liver, several polyunsaturated fatty acids including 18:2n6, 20:4n6, and 22:6n3 decreased compared with dietary controls, and similar findings were also observed in plasma lipoproteins and erythrocytes. The amount of alcohol consumed correlated positively with plasma lipid peroxidation products, 4-hydroxynonenal (4-HNE) and 8-isoprostane F2alpha, and negatively with 20:4n6 and 22:6n3 levels. These findings imply that alcoholics who also have a marginal intake of essential fatty acids and antioxidants in their diets may be at an increased risk of developing liver disease.

The effects of low dietary levels of polyunsaturates on alcohol-induced liver disease in rhesus monkeys

Rhesus monkeys that were maintained on a diet containing low, yet adequate, amounts of vitamins C and E and in which linoleate and linolenate represented 1.4% and 0.08% of the total caloric intake, respectively, developed liver fibrosis after consuming alcohol (mean, 2.6 g kg-1 d-1) over a period of 3 years. In the liver, several polyunsaturated fatty acids including 18:2n6, 20:4n6, and 22:6n3 decreased compared with dietary controls, and similar findings were also observed in plasma lipoproteins and erythrocytes. The amount of alcohol consumed correlated positively with plasma lipid peroxidation products, 4-hydroxynonenal (4-HNE) and 8-isoprostane F2α, and negatively with 20:4n6 and 22:6n3 levels. These findings imply that alcoholics who also have a marginal intake of essential fatty acids and antioxidants in their diets may be at an increased risk of developing liver disease. (Hepatology 1997 Dec;26(6):1386-92)

The effect of ketoprofen creams on periodontal disease in rhesus monkeys.

Ketoprofen creams were evaluated for the treatment of periodontal disease in a placebo-controlled, double-blind study in the rhesus monkeys, Macaca mulatta. Two formulations containing ketoprofen (1%), with or without vitamin E, were evaluated against appropriate controls (8 monkeys per group). Two weeks prior to treatment, the animals received prophylaxis on only the left side of the mouth (spontaneous model). Selected teeth on the right side of the mouth were ligated (ligature model). The creams were administered to the gingiva once daily at a standard dose of 1.8 ml per monkey for 6 months. Clinical assessments were made 2 wk before initiation, at baseline and 1, 2, 3 and 6 months post-treatment. The clinical parameters included plaque formation, gingival redness, edema, bleeding on probing and Ramfjord Attachment Level measurements (RAL). Radiographs were taken at 2 wk before initiation, baseline and at 3 and 6 months post-treatment. Digital, subtraction radiography was used to measure vertical linear bone loss along the interproximal root surfaces of the left and right mandibular first molars. Gingival crevicular fluid (GCF) was collected for biochemical assays on PGE2, TxB2, LTB4, IL-1 beta and TNF alpha. There were no significant differences among groups with respect to gingival indices. Radiographic data demonstrated significant positive effects on bone activity in both groups treated with ketoprofen formulations with improvement over time in the ligature model (0.01 < or = p < or = 0.04). The placebo group exhibited bone loss of 1.96 +/- 0.48 and 1.40 +/- 0.56 mm per site at 3 and 6 months, respectively. The group treated with ketoprofen cream showed an apparent bone gain of 0.28 +/- 0.41 and 0.78 +/- 0.47 mm per site at 3 and 6 months, respectively. The group treated with ketoprofen cream containing vitamin E showed a mean bone loss of 0.41-0.48 mm per site at 3 months with improvement to an apparent bone gain of 0.31 +/- 0.44 mm per site at 6 months. The biochemical data demonstrated early and significant suppression of GCF-LTB4 by both ketoprofen formulations at 1 month, which preceded the significant suppression of GCF-PGE2 at 2 and 3 months in the ligature model (p < 0.003) and at 2 to 6 months in the spontaneous model (p < 0.02). We conclude that ketoprofen at 1% level in suitable topical vehicles can effectively inhibit GCF-LTB4 and GCF-PGE2 and positively alter alveolar bone activity in the ligature-induced model of periodontitis in the monkey.

Sequences and phylogenetic analysis of the nef gene from Thai subjects harboring subtype E HIV-1.

It has been demonstrated that nef-defective SIV can cause attenuated disease in rhesus monkeys and that animals immunized with a similar construct can be protected when challenged with wild-type, pathogenic SIV. This finding has sparked interest in the nef gene of HIV-1. It remains unclear, however, whether nef serves an analogous role in human HIV-1 infection; Deacon et al. have reported an association of deletions in the nef gene with an attenuated disease course in humans, although other work does not support a strict correlation between the structure or function of nef and rates of disease progression. The nef gene product has been shown to influence the infectivity and pathogenicity of HIV-1. nef may also have a role in the immune response to HIV-1. The current database of nef sequences is derived almost exclusively from subtype B viruses. The authors therefore sought to develop a database of nef sequences from subjects infected with HIV-1 subtype E. Whole-blood samples were collected from 103 male commercial sex workers in Chiang Mai, Thailand. 17 tested positive for infection with HIV-1, 16 of whom were infected with subtype E by gp120 characterization. Intersubject variation in subtype E nef genes at the nucleotide level ranged from 2.1-7.8%. Thai subtype E nef sequences are more tightly clustered than subtype B nef sequences, analogous to what is seen in env. The authors note that their subtype E nef sequences do not share the genotypic polymorphism in the area of residues 10-30 noted with subtype B nef. These data confirm the need to develop a set of subtype E-specific reagents.

Zidovudine treatment prolongs survival and decreases virus load in the central nervous system of rhesus macaques infected perinatally with simian immunodeficiency virus.

To assess the potential therapeutic effects of zidovudine, rhesus macaques were inoculated with simian immunodeficiency virus (SIV) strain SMM/B670 at birth and infused either continuously or intermittently with zidovudine for 6-7 months. Zidovudine did not prevent infection but did significantly increase survival time, which was associated with lower serum p26 viral core antigen levels, a lower virus burden in the cerebrospinal fluid (CSF), and lower CSF quinolinic acid levels than in untreated monkeys. Two of 5 infected, untreated monkeys developed motor impairment within 6 months following infection, whereas motor impairments did not occur in infected, zidovudine-treated monkeys until after the drug was discontinued. Zidovudine treatment was well tolerated by rhesus infants with minimal, transient side effects. These results demonstrate that zidovudine treatment significantly decreases virus load within the central nervous system (CNS) and delays the onset of CNS dysfunction and immune disease in rhesus monkeys perinatally infected with SIV.

Morphological changes in lymph nodes and expression of VCAM1 and cytokines at the late stages of SIV-induced disease in rhesus monkeys

Four patterns of structural alterations were found in lymph nodes (LNs) from rhesus monkeys 17 to 34 months after infection with simian immunodeficiency virus (SIV-mac251). SIV p27gag antigen and viral particles were localized either between the processes of follicular dendritic cells (FDCs) or in the cytoplasm of macrophages. In hyperplastic follicles, enlarged germinal centres contained numerous Ki67+ proliferating centroblasts which were rather rare in light zones occupied by the CD23+ FDC network. Involuted follicles contained a small number of Ki67+ centroblasts and the CD23 labelling was limited to a very small apical zone. A correlation was found between the morphological characteristics of the follicles (hyperplasia-involution) and the level of expression of the vascular cell adhesion molecule 1 (VCAM1) on FDCs. A gradient in VCAM1 intensity with no expression in the subcapsular-intermediary sinuses, low membrane labelling in the mantle and strong expression in the FDC network was observed. IL1 alpha+ and IL6+ (interleukin) cells (lymphocytes and macrophages) were detected in the mantle, the interfollicular area and the medulla of LNs. Expression of the tumour necrosis factor alpha and ultrastructural markers of interferon alpha production were found in a few FDC and macrophages. Our findings indicate a close relationship between the morphofunctional properties of FDC and the LN structure in SIV infection.

An early increase in somatostatin mRNA expression in the frontal cortex of rhesus monkeys infected with simian immunodeficiency virus.

Motor and cognitive impairment is common in human immunodeficiency virus disease in humans and simian immunodeficiency virus (SIV) disease in rhesus monkeys. We have examined peptide neurotransmitter expression in the frontal cortex of SIV-infected rhesus monkeys to identify alterations in cortical neurons that might explain this impairment. A 2-fold higher number of preprosomatostatin (SRIF) mRNA-positive interneurons was observed in layer IV of frontal cortex in two separate cohorts of SIV-infected animals compared to uninfected controls. Increased SRIF mRNA expression in layer IV was independent of clinical signs of immunodeficiency disease and was associated with both motor and cognitive impairment. Altered SRIF mRNA expression in deeper cortical layers was associated specifically with motor impairment. Increased SRIF mRNA expression occurred without detectable changes in cortical cell density. These data suggest two mechanisms for cortical dysfunction associated with lentivirus infection. Increased SRIF mRNA expression in layer IV may be due to altered patterns of activity in cortical afferents that project to layer IV, while increased SRIF mRNA expression in deeper cortical layers could reflect susceptibility to locally generated mediators in response to primate lentivirus infection of the brain. Altered function of somatostatinergic interneurons may contribute to primate lentivirus-induced encephalopathy.

Different patterns of neuropathological disease in rhesus monkeys infected by simian immunodeficiency virus, and their relation to the humoral immune response

The brains of 21 rhesus monkeys inoculated with SIVMAC251 were examined after intervals ranging from 3 to 27 months and compared with five uninoculated controls. Eighteen animals became infected and individually exhibited several distinct patterns of disease. Nine (50%) had largely intramural leptomeningeal venous infiltrates (LMVI) without multinucleate giant cells (MGC) or foamy macrophages. Three (17%) had only MGC lesions, involving the cerebral parenchyma. One had both patterns and five (33%) neither. The controls had sparse and tiny LMVI only, similar to three inoculated animals that did not become infected. Immunohistochemistry showed the predominance of T and B lymphocytes in LMVI and choroid plexus mononuclear lesions but a predominance of macrophages over lymphocytes in the MGC lesions. Specific disease patterns differed in their association with the humoral immune response. Animals with LMVI were all hypergammaglobulinaemic when killed compared to pre-inoculation levels, and the size of the change in serum immunoglobulin concentration was positively correlated with a quantitative index of LMVI density. Furthermore, their post-mortem lymph node histology was hyperplastic. In contrast, animals found at autopsy to have MGC brain lesions were hypogammaglobulinaemic compared to preinoculation. The results are consistent with two phases in SIV-associated disease: one characterized by LMVI and hypergammaglobulinaemia and another featuring MGC and hypogammaglobulinaemia.

Efficacy of SIV/DeltaB670 glycoprotein-enriched and glycoprotein-depleted subunit vaccines in protecting against infection and disease in rhesus monkeys

Immunization with an inactivated whole-virus vaccine is highly effective in preventing lentivirus infection. The viral protein(s) essential to the induction of protective responses, however, have not been identified. To define the role of virion components in the induction of protective immunity, we evaluated the efficacy of glycoprotein-enriched and glycoprotein-depleted simian immunodeficiency virus (SIV) subunit vaccines prepared by lentil-lectin affinity chromatography of gradient-purified virions using the immunization and challenge regimen previously found successful with an inactivated whole-virus vaccine. Infection was determined by successful recovery of virus, the induction of SIV-specific antibody responses, and infection of naive recipients by inoculation with lymph-node-derived lymphocytes from the vaccinates. Immunization with the glycoprotein-enriched preparation prevented infection in two out of four monkeys, whereas the glycoprotein-depleted vaccine failed to prevent infection in all four vaccinates tested. However, the glycoprotein-depleted vaccine appeared to moderate the progression of SIV-induced disease compared with non-immunized infected control monkeys inoculated with the same challenge dose. These data suggest that subunit vaccines containing sufficient quantities of viral glycoproteins can protect against SIV infection, whereas subunit vaccines composed predominantly of viral core proteins cannot. The development of effective vaccines against HIV infection should include studies on the optimum presentation of the viral envelope glycoproteins to produce long-term broadly protective immune responses.

Experimental chagas' disease in rhesus monkeys. I. Clinical parasitological, hematological and anatomo-pathological studies in the acute and indeterminate phase of the disease

Rhesus monkeys (Macaca mulatta) were infected subcutaneously with 1.0 x 10(4) to 1.5 x 10(4) metacyclic trypomastigotes of Trypanosoma cruzi (Colombian strain). Parasitological and immunological parameters were evaluated in these animals for periods of 1 month to over 3 years. A chagoma was observed between the 3rd and the 13th day after infection (a.i.) and patent parasitaemia between the 13th and 59th day a.i.. Thereafter, parasites were demonstrated only by haemoculture and/or xenodiagnosis. Circulating specific IgM and IgG antibodies were observed as early as in the 2nd week a.i. IgG levels persisted until the end of the experiment, but IgM antibodies were detectable nine months a.i. Haematological alterations comprised leucocytosis and lymphocytosis. Electrocardiographic alterations were minor and transient, similar to those observed in non-lethal human acute Chagas' myocarditis. Myocarditis and myositis, characterized by multiple foci of lympho-histiocyte inflammatory infiltrate, were present in monkeys sacrificed on the 41st, 70th and 76th day but not in the animal sacrificed 3 years and 3 months a. i.. The results suggest that Chagas' disease in rhesus monkeys reproduces the acute and indeterminate phases of human Chagas' disease.

Trypanosoma cruzi: experimental Chagas' disease in Rhesus monkeys. II. Ultraestructural and cytochemical studies of peroxidase and acid phosphatase activities

Ultrastructural and cytochemical studies of peroxidase and acid phosphatase were performed in skin, lymph node and heart muscle tissue of rhesus monkeys with experimental Chagas' disease. At the site of inoculation there was a proliferative reaction with the presence of immature macrophages revealed by peroxidase technique. At the lymph node a diffuse inflammatory exudate with mononuclear cells, fibroblasts and immature activated macrophages reproduces the human pattern of acute Chagas' disease inflammatory lesions. The heart muscle cells present different degrees of degenerative alterations and a striking increase in the number of lysosomal profiles that exhibit acid hydrolase reaction product. A strong inflammatory reaction was present due to lymphocytic infiltrate or due to eosinophil granulocytes associated to ruptured cells. The present study provides some experimental evidences that the monkey model could be used as a reliable model to characterize histopathological alterations of the human disease.

Ocular manifestation of simian immunodeficiency syndrome (SAIDS)

The management of opportunistic infections is a significant problem in acquired immunodeficiency syndrome (AIDS) and the development of more effective chemotherapeutic agents is needed. We present the ocular manifestations of an AIDS-like disease in rhesus monkeys experimentally infected with simian immunodeficiency virus (SIV) at the Delta Regional Primate Research Center. These findings consisted of rubeosis in the anterior segment and retinitis, optic neuritis, choroiditis and panophthalmitis in the posterior segment of the eye. Investigation of the retinas by electron microscopy revealed SIV in both eyes of one animal and a herpes virus in two animals. Serology confirmed cytomegalovirus (CMV) as the likely agent. This primate model will prove useful for both further investigations of the possible interaction between immunosuppressive lentiviruses and CMV in ocular disease and antiviral drug testing.

The gag-specific cytotoxic T lymphocytes in rhesus monkeys infected with the simian immunodeficiency virus of macaques.

The simian immunodeficiency virus of macaques (SIVmac) is a lentivirus which induces an AIDS-like disease in rhesus monkeys. We have explored the virus-specific cellular immune response in SIVmac-infected rhesus monkeys. Con A-activated, IL-2 expanded PBL of some SIVmac-infected rhesus monkeys lyse autologous B lymphoblastoid cell lines infected with a recombinant vaccinia virus that carries the SIVmac gag gene. This lysis is mediated by CD8+ lymphocytes and is MHC class I restricted. Moreover, these effector lymphocytes do not express the NK cell-associated molecules NKH1 or CD16. These cells are, therefore, CTL. In a limited prospective study of SIVmac-infected rhesus monkeys, the presence of the SIVmac gag-specific CTL activity in PBL correlated with both a reduced efficiency in isolating SIVmac from PBL of these monkeys and their extended survival. This method for assessing SIVmac gag-specific cellular immunity in rhesus monkeys will be important not only in investigating the immunopathogenesis of SIVmac-induced disease, but also in evaluating the capacity of candidate AIDS vaccines to elicit a cell-mediated immune response in this animal model.