Session 4
Genetics



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Session 4 Genetics

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources This page in the original is blank.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Nonhuman Primates in Genetic Research on Common Diseases John L. VandeBerg, PhD,*,† and Sarah Williams-Blangero, PhD† The leading causes of death in the United States are heart disease and cancer, with diabetes ranking sixth (Minino and Smith 2001). In addition to the health burden of these multifactorial diseases, progressive chronic conditions such as osteoporosis are associated with significant costs for health care and quality of life (Siris and others 2001; Tosteson and others 2001). From a global perspective, parasitic diseases such as schistosomiasis and Chagas’ disease (American trypanosomiasis) present tremendous health burdens in developing countries (Chan 1997; Murray and Lopez 1997). Genetic approaches to these leading causes of morbidity and mortality seek to characterize the genetic components that influence susceptibility to disease processes. Statistical and molecular genetic techniques are used to quantify genetic influences on disease-associated traits and, ultimately, to identify the specific loci determining patterns of variation. Knowledge of the genes responsible for susceptibility can be used to target treatments or recommend lifestyle changes (e.g., dietary restrictions) to the individuals most likely to develop disease. This information can *   Southwest National Primate Research Center †   Department of Genetics, Southwest Foundation for Biomedical Research, San Antonio, Texas

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources also facilitate drug discovery through identification of biological mechanisms to serve as novel targets in pharmacological development (Dykes 1996; Gelbert and Gregg 1997). The dramatic progress in genetics that has occurred in the last decade has revolutionized the study of genetic susceptibility to complex diseases. The development of the human gene map, sequencing of the human genome, technological improvements that allow rapid large-scale genotyping of population samples, and advances in statistical genetic methods have created unprecedented opportunity for genetic research on common complex diseases. For disease processes that occur at a frequency of 10% or greater, an analytical design utilizing extended pedigrees drawn at random from the population (i.e., not selected with respect to disease characteristics) is optimal (Almasy and Blangero 2000). The statistical power of this approach is a function of the size and complexity of the pedigree (Blangero and others 2000; Dyer and others 2001). Extended pedigrees that are not selected on the basis of disease phenotype are useful for analysis of any normal or disease-related trait that is common in the population. Thus, once genotype data are generated for a study of a given common disease, the pedigree becomes an invaluable resource for studies of other traits. Nonhuman primate colonies frequently have complex pedigree structures, making them well suited to genetic analyses of common diseases. Nonhuman primates serve as excellent models for human disease studies because of their phylogenetic proximity to humans, the large degree of conservation of gene maps between human and nonhuman primates, the genetic and physiological similarities between humans and nonhuman primates, and the natural occurrence of many of the complex diseases that represent the greatest health burdens to the human population (VandeBerg and Williams-Blangero 1996, 1997). Many complex diseases, including heart disease, diabetes, hypertension, osteoporosis, schistosomiasis, and Chagas’ disease, occur naturally in at-risk nonhuman primates. However, genetic studies in nonhuman primates should be directed toward those diseases for which nonhuman primates offer scientific advantages, rather than simply toward those for which nonhuman primates are suitable animal models. For example, the baboon is an excellent animal model for studies of pathology and immunology in schistosomiasis (Nyindo and Farah 1999). However, it is not an ideal model for studying the genetic determinants of susceptibility to infection with Schistosoma mansoni. First, complex extended human pedigrees are available in areas that experience high rates of disease prevalence (Bethony and others 2001; Marquet and others 1996), whereas it would be impractical logistically and financially to subject the

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources number of pedigreed nonhuman primates needed for a genetic epidemiological study to a challenge with S. mansoni. In contrast, the baboon is an excellent model for genetic studies of susceptibility to another parasitic infection, American trypanosomiasis or T. cruzi infection. Chagas’ disease is the leading cause of heart disease in Latin America, and it can result in a short-term acute illness or a long-term chronic condition characterized by progressive cardiomyopathy or megaesophagus and megacolon. While large extended human pedigrees with high rates of infection are available for genetic study (Williams-Blangero and others 1997), parallel genetic studies in baboons can shed light on the genetic determinants of pathology and progression of other correlates of infection that are impractical to quantify over time in a longitudinal human study (Williams and others 2000). For example, regular tissue biopsies and radiographic assessments are possible with nonhuman primates to a degree not feasible for human populations living in the remote rural areas where the disease is prevalent. Nonhuman primates are ideal models for genetic studies of complex disease processes that have significant environmental components. For example, the level of dietary control possible with pedigreed nonhuman primates allows explicit assessment of the interactions between genetic effects and dietary effects in determining physiological correlates of heart disease. Genetic epidemiological studies of atherosclerosis and its correlates in the baboon model provided the first documentation of a genotype by diet interaction effect for serum cholesterol variation in a primate (MacCluer and others 1988). This was the first explicit evidence for a genetic basis to response to dietary saturated fats and cholesterol. A Program Project from the National Heart, Lung, and Blood Institute (P01 HL28972) has supported research on the genetics of cardiovascular disease risk factors in the pedigreed baboon colony at the Southwest Foundation for Biomedical Research for the last 20 years. The initial documentation of a genotype by diet interaction effect on cholesterol variation by MacCluer and colleagues (1988) has subsequently been refined, and numerous aspects of lipoprotein variation in response to diet have been investigated (e.g., Mahaney and others 1999a; Rainwater and others 1998, 1999). With the completion of a baboon framework gene map (Rogers and others 2000) and the genotyping of all animals in the pedigreed colony for approximately 325 markers spaced evenly across the genome, linkage analyses are being pursued to localize and ultimately to identify the individual genes involved (Cox and others 2002). The discovery of genetic effects and dietary interaction effects on cardiovascular disease risk factors was made possible by the ability to experimentally manipulate the diet in the

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources baboon model, a technique not possible in large-scale studies of human populations. Osteoporosis is a major health problem in the United States. One of the primary risk factors for development of osteoporosis is low bone mineral density. Genetic studies of this disease in human populations are hampered by the need to assess bone mineral density in the large numbers of related individuals required for genetic epidemiological analysis and the immeasurable variability in lifetime diet and exercise patterns. The same baboon population studied for the cardiovascular disease studies was assessed for bone mineral density, taking advantage of the pedigree and genotypic data generated for the population. Measures of bone mass and bone mineral density traits exhibit moderate to high heritability in baboons, with between 40 and 67% of the variation attributable to genetic factors (Kammerer and others 1995). A preliminary genome screen for genes influencing bone mineral density traits and other correlates of osteoporosis has localized genes with significant genetic effects on chromosomes 6, 11, and 12 (Mahaney and others 1997, 1999b). These results suggest that the baboon model will be informative for fully characterizing the genetic components of susceptibility to osteoporosis. As is the case with heart disease, knowledge of the genes involved in determining susceptibility may eventually allow targeting of diet and exercise programs to those likely to develop disease and may ultimately lead to new pharmacological interventions. The examples above illustrate the great utility of nonhuman primate models for characterizing the genetic components of complex diseases that are major health burdens throughout the developed and developing world. Linkage analyses localizing genes with significant effects on trait variability have been conducted for a broad range of disease traits in the single pedigreed baboon population, indicating the tremendous value of a pedigreed and genotyped colony for biomedical research. Already, genes influencing risk factors for cardiovascular disease, Chagas’ disease, osteoporosis, hypertension (Kammerer and others 2001), and hormone levels (Martin and others 2001a,b) have already been localized in this population. Ongoing studies are assessing the genetic components of temperament traits (e.g., Kaplan and others 2001a,b) and correlates of psychiatric disease (Jeffrey Rogers, unpublished data) in the baboon model. Future research will focus on the detailed characterization and ultimate identification of quantitative trait loci. Clearly nonhuman primate colonies have tremendous potential for use in the identification of genes that influence common diseases. However, the utility of nonhuman primate colonies for genetic research relies on several key sets of data. First and foremost, detailed pedigree records must be available. If single male breeding groups are used, pedigree data

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources alone may be sufficient for reconstruction of pedigrees to be used in genetic epidemiological analysis. If multimale breeding groups are used, genetic marker data will be critical for resolving paternity and maternity errors. The identification of specific genes with significant effects on disease traits requires linkage analysis of genetic marker data in conjunction with disease trait data and information about the distribution of genes across chromosomes. Although a gene map exists for baboons, none is available for any other nonhuman primate species. The development of gene maps for nonhuman primate species commonly used in biomedical research will be another critical step in developing genetic research with nonhuman primates. Just as the human genome sequence has been extremely informative for investigators trying to move from gene localization to gene identification in human studies, genome sequence data will be extremely valuable for genetic research with nonhuman primates. The priority for sequencing should be placed on the species most commonly used in biomedical research and, particularly in genetic epidemiological research, the baboon and the rhesus macaque. There is tremendous potential for future genetic research on nonhuman primates. However, progress in genetic research with nonhuman primates will require a significant investment in the development of pedigreed colonies of nonhuman primates, genotyping and gene mapping efforts in species to be used for genetic research, and the development of sequence information for genetically well-characterized species. Genetic management and improvements in genetic resources will be critical if the benefits of the genome revolution are to be fully realized in research with nonhuman primates. ACKNOWLEDGMENTS Research reviewed in this article was supported by NIH grants P51 RR13986, P01 HL28972, and R01 RR08122. REFERENCES Almasy, L. and J. Blangero. 2000. Challenges for genetic analysis in the 21st century: Localizing and characterizing genes for common complex diseases and their quantitative risk factors. GeneScreen 1:113-116. Bethony, J., Gazzinelli, A., Lopes, A., Pereira, W., Alves-Oliveira, L., Williams-Blangero, S., Blangero, J., LoVerde, P., Correa-Oliveira, R. 2001. Genetic epidemiology of fecal egg excretion during Schistosoma mansoni infection in an endemic area in Minas Gerais, Brazil. Mem Inst Oswaldo Cruz 96(Suppl):49-55.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Blangero, J., Williams, J.T., Almasy, L. 2000. Quantitative trait locus mapping using human pedigrees. Hum Biol 72:35-62. Chan, M-S. 1997. The global burden of intestinal nematode infections—Fifty years on. Parasitol Today 13:438-443. Cox, L.A., Birnbaum, S., VandeBerg, J.L. 2002. Identification of candidate genes regulating HDL cholesterol using a chromosomal region expression array. Genome Res (In Press). Dyer, T.D., Blangero, J., Williams, J.T., Goring, H.H.H., Mahaney, M.C. 2001. The effect of pedigree complexity on quantitative trait linkage analysis. Genet Epidemiol 21:S236-S243. Dykes, C.W. 1996. Genes, disease, and medicine. Br J Clin Pharmacol 42:683-695. Gelbert, L.M. and R.E. Gregg. 1997. Will genetics really revolutionize the drug discovery process? Curr Opin Biotechnol 8:69-74. Kammerer, C.M., Cox, L.A., Mahaney, M.C., Rogers, J., Shade, R.E. 2001. Sodium-lithium countertransport activity is linked to chromosome 5 in baboons . Hypertension 37:398-402. Kammerer, C.M., Sparks, M.L., Rogers, J. 1995. Effects of age, sex, and heredity on measures of bone mass in baboons (Papio hamadryas). J Med Primatol 24:236-242. Kaplan, J.R., Brent, L., Comuzzie, A.G., Martin, L., Manuck, S.B., Worlein, J., Rogers, J. 2001a. Heritability of responses to novel objects among pedigreed baboons. Am J Phys Anthropol Suppl 32:87-88. Kaplan, J., Brent, L., Martin, L., Comuzzie, A., Worlein, J., Manuck, S., Rogers, J. 2001b. Temperament derived from heritable, behavioral response to novelty in pedigreed baboons (Papio hamadryas). Am J Primatol 54:83-84. MacCluer, J.W., Kammerer, C.M., Blangero, J., Dyke, B., Mott, G.E., VandeBerg, J.L., McGill, H.C. 1988. Pedigree analysis of HDL cholesterol concentration in baboons on two diets. Am J Hum Genet 43:401-413. Mahaney, M.C., Blangero, J., Rainwater, D.L., Mott, G.E., Comuzzie, A.G., MacCluer, J.W., VandeBerg, J.L. 1999a. Pleiotropy and genotype by diet interaction in a baboon model for atherosclerosis. A multivariate quantitative genetic analysis of HDL subfractions in two dietary environments. Arterioscler Thromb Vasc Biol 19:1134-1141. Mahaney, M.C., Czerwinski, S.A., Rogers, J. 1999b. Possible quantitative trait loci for serum levels of human cartilage glycoprotein-39 (YKL40) and osteocalcin (OC) in pedigreed baboons map to human chromosomes 6 and 12. J Bone Min Res 14(Suppl 1):S142. Mahaney, M.C., Morin, P., Rodríguez, L.A., Newman, D.E., Rogers, J. 1997. A quantitative trait locus on chromosome 11 may influence bone mineral density at several sites: Linkage analysis in pedigreed baboons. J Bone Min Res 12(Suppl 1):S118. Marquet, S., Abel, L., Hillaire, D., Dessein, H., Kalil, J., Feingold, J., Weissenbach, J., Dessain, A.J. 1996. Genetic localization of a locus controlling intensity of infection by Schistosoma mansoni on chromsome 5q31-q33. Nat Genet 14:181-184. Martin, L.J., Blangero, J., Rogers, J., Mahaney, M.C., Hixson, J.E., Carey, K.D., Comuzzie, A.G. 2001a. A quantitative trait locus influencing activin-to-estrogen ratio in pedigreed baboons maps to a region homologous to human chromosome 19. Hum Biol 73:787-800. Martin, L.J., Blangero, J., Rogers, J., Mahaney, M.C., Hixson, J.E., Carey, K.D., Morin, P.A., Comuzzie, A.G. 2001b. A quantitative trait locus influencing estrogen levels maps to a region homologous to human chromosome 20. Physiol Genomics 5:75-80. Minino, A.M. and B.L. Smith. 2001. Deaths: Preliminary data for 2000. National Vital Statistics Reports 49(12):1-40. Murray, C.J.L. and A.D. Lopez. 1997. Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study. Lancet 349:1436-1442.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Nyindo, M. and I.O. Farah. 1999. The baboon as a nonhuman primate model of human schistosome infection. Parasitol. Today 15:478-482. Rainwater, D.L., Kammerer, C.M., Hixson, J.E., Carey, K.D., Rice, K.S., Dyke, B., VandeBerg, J.F., Slifer, S.H., Atwood, L.D., McGill, H.C., VandeBerg, J.L. 1998. Two major loci control variation in β-lipoprotein cholesterol and response to dietary fat and cholesterol in baboons. Arterioscler Thromb Vasc Biol 18:1061-1068. Rainwater, D.L., Kammerer, C.M., VandeBerg, J.L. 1999. Evidence that multiple genes influence baseline concentrations and diet response of Lp(a) in baboons. Arterioscler Thromb Vasc Biol 19:2696-2700. Rogers, J., Mahaney, M.C., Witte, S.M., Nair, S., Newman, D., Wedel, S., Rodriguez, L.A., Rice, K.S., Slifer, S.H., Perelygin, A., Slifer, M., Palladino-Negro, P., Newman, T., Chambers, K., Joslyn, G., Parry, P., Morin, P.A. 2000. A genetic linkage map of the baboon (Papio hamadryas) genome based on human microsatellite polymorphisms. Genomics 67:237-247. Siris, E.S., Miller, P.D., Barrett-Connor, E., Faulkner, K.G., Wehren, L.E., Abbott, T.A., Berger, M.L., Santora, A.C., Sherwood, L.M. 2001. Identification and fracture outcomes of undiagnosed low bone mineral density in postmenopausal women: Results from the National Osteoporosis Risk Assessment. JAMA 286:2815-2822. Tosteson, A.N., Gabriel, S.E., Grove, M.R., Moncur, M.M., Kneeland, T.S., Melton, L.J. 2001. Impact of hip and vertebral fractures on quality-adjusted life years. Osteoporosis Int 12:1042-1049. VandeBerg, J.L., Williams-Blangero, S. 1996. Strategies for using nonhuman primates in genetic research on multifactorial diseases. Lab Anim Sci 46:146-151. VandeBerg, J.L., Williams-Blangero, S. 1997. Advantages and limitations of nonhuman primates as animal models in genetic research on complex disease. J Med Primatol 26:113-119. Williams, J.T., Williams-Blangero, S., Mahaney, M.C., Rogers, J., Blangero, J., VandeBerg, J.L. 2000. Seropositivity to Trypanosoma cruzi in baboons is linked to a QTL on the analog of chromosome 2q. Am J Trop Med Hyg 62(3, Suppl): 195. Williams-Blangero, S., VandeBerg, J.L., Blangero, J., Teixeira, A.R.L. 1997. Genetic epidemiology of seropositivity for T. cruzi infection in rural Goias, Brazil. Am J Trop Med Hyg 57:538-543.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Genetic Considerations in the Management of Captive Nonhuman Primates Sarah Williams-Blangero, PhD,* and John L. VandeBerg, PhD*,† INTRODUCTION Genetic management is an important component of the management of nonhuman primate colonies regardless of whether the animals will be used for genetic or nongenetic research (VandeBerg 1995; Williams-Blangero 1993). Genetic management techniques can be used to maintain the long-term viability of nonhuman primate colonies for continued production of healthy breeders. In addition, genetic management approaches can be used to generate well-characterized research subjects for genetic studies and to allow selection of optimal groups of unrelated animals for use in nongenetic experimental protocols. Genetic considerations are important at multiple levels for the management of captive nonhuman primate populations. Genetic variability between subspecies, between geographic groups, and within populations has important implications for both management and research (Williams-Blangero and others 2002). The genetic characteristics of the breeding population significantly influence the productivity and stability of a captive nonhuman primate colony. *   Department of Genetics, Southwest Foundation for Biomedical Research †   Southwest National Primate Research Center, San Antonio, Texas

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources GENETIC VARIATIONS BETWEEN SUBSPECIES Subspecies of nonhuman primates are not always easy to distinguish on the basis of physical characteristics. However, significant genetic differences between subspecies may affect the reproduction rates in mixed-subspecies populations and the experimental utility of hybrid animals (Kohn and others 2001; Moore and others 1990; VandeBerg and others 1990b; Williams-Blangero and others 1990). Genetic variation between subspecies as assessed by genetic markers is expected to be reflected in differences for biomedically relevant traits between subspecies. For example, significant genetic differences exist among the baboon (Papio hamadryas s.l.) subspecies maintained at the Southwest Foundation for Biomedical Research (Williams-Blangero and others 1990). The genetic distances between the subspecies are mirrored by differences in phenotypic variability for lipoprotein traits (Williams-Blangero and Rainwater 1991; Williams-Blangero and others 1990). The baboon population at the Southwest Foundation is being used in ongoing genome scans for genes influencing risk factors associated with cardiovascular disease and osteoporosis (VandeBerg and Williams-Blangero 2002). The animals are predominantly olive baboons (P.h. anubis), but a significant amount of admixture with yellow baboons (P.h. cynocephalus) has occurred in the past. Subspecies admixture, as measured by percentage of genes derived from the P.h. cynocephalus subspecies, has been identified as an important covariate in genetic analyses of both lipoprotein levels and bone mineral density (Mahaney and others 1995, 1999a). Ideally, nonhuman primate colonies should be composed of a single subspecies. However, if admixture has occurred in the past, breeding histories can be used to estimate individual admixture in terms of percentage of genes derived from the less predominant species. This measure can then be used as a covariate in genetic analyses of data from hybrid animals, and as a means for identifying hybrid individuals to be eliminated from the breeding population. GENETIC VARIATIONS BETWEEN POPULATIONS WITH DIFFERENT GEOGRAPHIC ORIGINS Significant genetic differences that have biomedical relevance may exist between populations of the same species derived from geographically distinct regions. Therefore, it is important to consider between-population genetic differences even when subspecies are not formally recognized. The differences between rhesus macaques (Macaca mulatta) derived from India and those of Chinese origin clearly demonstrate the relevance

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources SIV RNA in plasma of SIV-infected animals during the first few weeks after IVAG inoculation. Most importantly, our results demonstrate that both Chinese-origin and Indian-origin rhesus macaques are well suited for AIDS-related studies that require mucosal SIV infection. ACKNOWLEDGMENTS This work was supported by Public Health Service grant RR00169 from the National Center for Research Resources; grants AI39109 (M.L.M), AI39435 (C.J.M), and AI35545 (C.J.M) from the National Institute of Allergy and Infectious Diseases; and Elizabeth Glaser Scientist award 8-97 (M.L.M) from the Elizabeth Glaser Pediatric AIDS Foundation. REFERENCES Daniel M.D., N.L. Letvin, P.K. Sehgal, G. Hunsmann, D.K. Schmidt, N.W. King, and R.C. Desrosiers. 1987. Long-term persistent infection of macaque monkeys with the simian immunodeficiency virus. J Gen Virol 68:3183-3189. Joag S. V., E.B. Stephens, R.J. Adams, L. Foresman, and O. Narayan. 1994. Pathogenesis of SIVmac infection in Chinese and Indian rhesus macaques: Effects of splenectomy on virus burden. Virology 200:436-446. Kimata J.T., L. Kuller, D.B. Anderson, P. Dailey, and J. Overbaugh. 1999. Emerging cytopathic and antigenic simian immunodeficiency virus variants influence AIDS progression. Nat Med 5:535-541. Lewis M., S. Bellah, K. McKinnon, J. Yalley-Ogunro, P. Zack, W. Elkins, R. Desrosiers, and G. Eddy. 1994. Titration and characterization of two rhesus-derived SIVmac challenge stocks. AIDS Res Hum Retrovirus 10:213-292. Lu Y., C.D. Pauza, X. Lü, D.C. Montefiori, and C.J. Miller. 1998. Rhesus macaques that become systemically infected with pathogenic SHIV 89.6-PD after intravenous, rectal, or vaginal inoculation and fail to make an antiviral antibody response rapidly develop AIDS. J AIDS Hum Retrovir 19:6-18. Marthas M.L., D. Lu, M.C. Penedo, A.G. Hendrickx, and C.J. Miller. 2001. Titration of an SIVmac251 stock by vaginal inoculation of Indian and Chinese origin rhesus macaques: transmission efficiency, viral loads, and antibody responses. AIDS Res Hum Retrovirus 17:1455-1466. Miller C., N. Alexander, A. Gettie, A. Hendrickx, and P. Marx. 1992. The effect of contraceptives containing nonoxynol-9 on the genital transmission of simain immunodeficiency virus in rhesus macaques. Fertil Steril 57:1126-1128. Miller C., N. Alexander, S. Sutjipto, S. Joye, A. Hendrickx, M. Jennings, and P. Marx. 1990. Effect of virus dose and nonoxynol-9 on the genital transmission of SIV in rhesus macaques. J Med Primatol 19:401-409. Morin P.A., S. Kanthaswamy, and D.G. Smith. 1997. Simple sequence repeat (SSR) polymorphisms for colony management and population genetics in rhesus macaques (Macaca mulatta). Am J Primatol 42:199-213.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources Session 4: Panel Discussion Participants: John L. VandeBerg—Session Chair, Southwest Foundation for Biomedical Research, USA Sarah Williams-Blangero—Southwest Foundation for Biomedical Research, USA Thomas Friedrich—Wisconsin National Primate Research Center, USA Marta L. Marthas—California National Primate Research Center, USA QUESTIONS AND ANSWERS PARTICIPANT A: Dr. Friedrich, you referred to the similarity in the Mamu system to that in the human in terms of regulation of escape. Could you please give us a little more detail. DR. FRIEDRICH (Thomas Friedrich, Wisconsin National Primate Research Center): I will give you as much detail as I can. I think Dr. Marthas might like to comment as she alluded to some of the similarities between the human MHC system and the rhesus in her talk. Basically, at a very simplistic level, there is a high degree of similarity. We do see selection for escape variant viruses by certain specific CTL in the human system. The escape is much more difficult to define in humans because they are infected with a heterogeneous population of viruses. By the time you get a human subject to study, it is usually too late to be able to define the actual genotype of the infecting strain of virus. It is much

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources more difficult to compare the viral sequences that you isolate from humans with earlier strains and to define this kind of thing. As opposed to the macaque system, we can knowingly infect them with clonal viruses. That said, as Dr. Marthas discussed, there are certain alleles in the human that are associated with either a susceptibility to a rapid progression in AIDS or a resistance. HLA B-27 and B-57, for example, are associated with slow progression. There are reports of human long-term nonprogressors, as they call them, which look clinically like the three SIV controllers that I described. They have low virus loads in the chronic phase of infection. They often have antigen-specific CD4 responses, which you would not normally detect. They have CTL responses that you might expect would have selected for escape variance, which they do not seem to have done, and so on. At that level, there is definitely a high degree of similarity between our models of what goes on in HIV-infected humans. DR. KRAISELBURD (Edmundo Kraiselburd, Department of Microbiology Medical Sciences, Puerto Rico): Congratulations to individuals on the Genetics Panel for an excellent presentation. My question for Dr. Marthas is, do you have any data in terms of the disease preparation in the Chinese (rhesus)? In other words, we know there is a relationship between the nadir; is there progression? I have seen some data for the rhesus macaque, which is a slow progressor. Second, of the rhesus that we have in Puerto Rico, 20% are Mamu-A*01 positive. I understand that some of your monkeys came from Puerto Rico. I would like you to comment on the fact that we did not see any relationship of the few monkeys that we tested in terms of disease preparation and Mamu-A*01 marker. DR. MARTHAS (Martha L. Marthas, California National Primate Research Center): For this study, we did not measure long-term progression, which we originally began to titrate, so we purposely ended the study by 6 weeks. However, from other studies, the animals that have the controlled viremia, like the ones Dr. Friedrich described, are expected to continue long term. They have a more prolonged or delayed AIDS. If the animals, for whatever reason, had a high set point or did not control, they would have a more rapid progression to disease. Dr. Mark’s group, which studies Indian versus Chinese, is similar although there are a couple of differences. First, they did an intravenous inoculation, which can make a difference in how the virus affects the animals. Second, they had a small sample size of Indians. If I had picked any two of my animals, I might have obtained a result similar to theirs. Their Chinese results looked very similar to ours initially. I would predict that if they were followed, some of those animals would have been very controlled.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources The second question was A1 and why different groups see differences in the way Mamu-A*01 progresses. My hypothesis is that Mamu-A*01 may be a marker for something else. It happens to be convenient. I would predict that based on the human, there are linkages to equilibrium; however, there are associations that are nonrandom between Class 1 and other alleles on that same chromosome. So it might be that Mamu-A*01, from different geographic locations originally (we do not know where all of our Wisconsins or Indians came from) might be associated with something else that is controlling. Our Mamu-A*01 is tracking from Mamu-A*01, but it is not associated with whatever the other important alleles are tracking. DR. FRIEDRICH: I agree with Dr. Marthas. I told you about our second experiment: we inoculated another set of three Mamu-A*01/ Mamu-B*17 double-positive animals. Because our laboratory does a lot of work on CTL responses, we were fervently hoping to find recapitulation of the scenario that took place with our first set of Mamu-A*01/Mamu-B*17 animals. Unfortunately, the animals did not control. As Dr. Marthas was saying, although certain MHC Class 1 molecules basically may be markers for the ability of these animals to control, and we may be able to understand the ways in which these molecules may contribute to the overall control that we see, we simply do not know enough yet about macaque genetics to identify with certainty the other factors that might be influencing this ability. The experiment we performed recently shows that it is not only two MHC Class 1 alleles which is not surprising but is still disappointing. DR. ROBERTS (Jeffrey Roberts, University of California at Davis): I have two questions pertaining to issues of population management. First, Dr. VandeBerg, in terms of the desire to maintain large populations of animals for pedigree, does the population at Southwest contribute to the availability of aged animals down the line, both in terms of genetic studies and availability of cost-effective production of aged animals? Second, Dr. VandeBerg or Dr. Williams-Blangero, in large multimale groups particularly at Southwest, are you concerned about having these large populations and about very cost-effective housing? If you have determined that there are males that have not contributed to the gene pool effectively for social reasons or whatever, do you advocate strategies to harvest those males at certain points either for indoor-timed mating or for other means of assisted reproductive technology to maximize their contribution? DR. VANDEBERG (John VandeBerg, Southwest Foundation for Biomedical Research): With regard to aged animals, indeed, by maintaining these pedigreed animals throughout their lives, clearly we do end up with animals that have reached the end of their useful reproductive careers. We channel them into a specific group that we call the pedigree

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources geriatric baboon colony. We actually have more than 200 baboons in that colony now that are older than 17 or 18 years. Some are nearly 30 years old! We are developing some new research programs to study the aging process in those animals. They all are pedigreed and genotyped, and they will have been breeders to get to that age. They will have many progeny—grand progeny and perhaps great grand progeny—in the population. They are an extraordinarily valuable resource. It costs nothing to get them into the geriatric colony in the sense that they were productively used for research and breeding throughout their useful lives. As for equalizing numbers of progeny from breeders, one of the most effective ways to deal with that situation is to harvest selectively. It may not be necessary to equalize the number of progeny of various males or females, but what you harvest for terminal experiments are an unequal number of progeny from particular parents so that you are very careful when you save back your breeders that you have equalized the genetic contributions from your females and from as many males as you can use in the particular breeding scheme. We effectively follow that process with our colony. DR. WILLIAMS-BLANGERO (Sarah Williams-Blangero, Southwest Foundation for Biomedical Research): For the pedigreed section of the colony, we use all single male breeding. DR. LYONS (Dr. Leslie A. Lyons, University of California at Davis): Dr. Friedrich, I think Dr. Marthas’ point about linkage to equilibrium is extremely valid. Do you know how your monkeys were related in either of your studies? DR. FRIEDRICH: The monkeys we used for that study were not related to each other. Beyond that, I really cannot tell you. We can find that information in our colony records because they are kept in an animal and sire-dam triplicate, as described in previous talks. There is no easy way for us to go beyond that and determine what other genetic factors might be playing a role in these animals, short of sequencing their entire MHC side and finding out what happened. DR. LYONS: Along those lines, would you suggest that while we are waiting for other sources of exports or identifying other populations of animals, we could genotype those animals and establish pedigrees so that we could bring in known different varieties of these animals to help our colonies. In other words, should we help those other countries get their animals genetically characterized? DR. VANDEBERG: Such a plan would need to be carefully constructed with clear goals and a clear understanding of the actual potential for sending those particular animals to this country or to another country for research purposes. DR. HEARN (John Hearn, Australian National University): First, Drs.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources VandeBerg and Williams-Blangero, the issue of pedigreed and genotyped colonies is clearly a major added value that, spread more broadly, can not only give us high quality research and design but can perhaps also reduce the number of animals required in particular questions. Do you think we are at a stage where you could recommend a set of minimal criteria for genetic characterization and management of colonies in general as a separate issue to the kind of in-depth analysis that you would need for each specific disease, that has both cost and practicality connotations? DR. WILLIAMS-BLANGERO: At a minimum, to begin constructing the pedigree only from the colony records gives you enough information to begin quantitative genetic analysis. With this information, which you can obtain from basic colony records for many nonhuman primate colonies, you can begin to ask the simple question: how much variation in this trait is attributable to genetics? As you ask these questions in conjunction with the existing phenotypic data on normal variation and traits in which you might be interested and on disease traits that are recorded in the clinical records, you can get an idea about productive directions for a true genome scan or more detailed genetic research. I think at whatever level you can feasibly do this, you enhance the value of the colony tremendously by adding any pedigree information. If you have genetic markers that are generated as part of other studies, and can contribute that information back into the colony to use for paternity testing and other purposes, it is of great value for enhancing the colony for genetic research. DR. VANDEBERG: Let me add to that, however, that there are circumstances in which it is appropriate and cost-effective to produce animals in large breeding groups, such as our corrals or 6-acre breeding corral, which has about 600 baboons in it. I think the answer to your question must be tailored to the breeding situation, so there are situations where it is appropriate to have small breeding groups, large breeding groups, and so forth. Certainly, for genetic research, if it is economically feasible and practical to have single male breeding groups, that arrangement is by far the most valuable for genetic research, especially in the absence of markers to sort out paternity. I think it would be difficult to give an overall set of minimum recommendations that would fit all breeding situations. I think they will have to be tailored to specific breeding situations and particular breeding objectives. DR. HEARN: Thank you. My next question concerns emerging diseases—the next AIDS or, in particular, the transmission of viruses or zoonoses between nonhuman primate populations and humans. In captive colonies, or specifically in the wild where around the world there are particular areas where humans and nonhuman primates come into close

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources contact, and increasingly in areas where there is great ecological pressure, the situation is being set up for potential transmission. Are we ready, or should we be starting to investigate that issue? DR. MARTHAS: I think it is important to set the boundaries and to let people know about this exposure. Participants at a recent meeting in Keystone, Colorado, were talking about HIV pathogenesis and starting to look at two different things: wild chimpanzees in preserves and SIV isolates. They are finding SIV isolates in chimpanzees using noninvasive methods like fecal and urine sampling. They are able to detect and indeed find these additional SIV isolates in populations that would not have been able to be tested before. By documenting and analysis, they are able to show that there are multiple crossover points from chimpanzees—multiple lineages of what is now an SIV that could potentially then go from chimpanzee to humans. How did the SIV get into the chimpanzees? To make a long story short again, the answer is probably from other monkeys because chimps are known to hunt and eat other monkey species. That probability was, in fact, documented by a person looking and finding a variety of other species new SIV isolates in a variety of species that had not previously been found before. The more we look, the more we are finding it. There is more potential for human exposure and other nonhuman primates to retroviruses in this case, so we conjecture that it is exposure to any pathogen— parasites or other blood borne transmission. With respect to your conservation question and human intervention, the most recent evidence is that the way the person sampled the 20 or more species of primates in Cameroon and central Africa was by going to bush meat markets. They sampled meat from monkeys that had been killed for human consumption. While consumption might not be the worst case scenario, certainly the preparing and hunting of those animals exposed the people and then exposed a broader population by eating the animals. I think it is very important, but we do not have an answer for how to deal with it. DR. FRIEDRICH: Dr. Marthas lead into the current hypothesis for the transmission of HIV into humans. First, HIV began as zoonoses probably through the consumption of chimpanzees in bush meat that was infected with the precursor of HIV. We have this information from the work of Beatrice Hahn and Betty Korber. I do not know what primate centers and investigators of disease in nonhuman primates can do to be prepared for this kind of eventuality. We can only make public these findings so that people understand that by placing themselves and nonhuman primates at risk in these high-pressure ecological environments, it is more likely that we are going to find this sort of transmission occurring in the future. As Dr. Marthas said, the more you look, the more SIV

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources isolates you find, which is more potential for another zoonoses to occur in humans. In addition, there is every reason to believe there are other viruses we have yet to discover that could do the same thing. DR. VANDEBERG: I would like to add that I think the primate centers and the primate community in general are actually very poorly prepared to deal with these issues in part because we do not have the facilities that are required. Our biosafety level 3 facilities are woefully inadequate in this country, and I am sure around the world, to deal with those kinds of issues. We do not have any biosafety level 4 laboratories capable of housing living animals. At our primate center, we are turning down studies that require biosafety level 3 facilities including studies on tuberculosis, anthrax, and West Nile virus. We are not meeting the current needs for lack of facilities, and we are certainly not in a position to meet the emerging needs that we do not even know of today. The base grant budgets for the primate centers have been essentially flat over the 5-year doubling of the NIH budget. We have struggled to maintain what we have, not only in terms of facilities but also in terms of personnel. We are not in a position to recruit the personnel that are needed to establish the critical masses of scientists required for those kinds of investigations. In regard to the potential of transmission of disease from chimpanzees, as we scale down the number of chimpanzees that are available for biomedical research, it is entirely possible that at some future point there will be another disease emerge, like AIDS or HIV. With the incredibly long generation time of chimpanzees, it would be very difficult to scale up that population if they were needed for research for a disease of that nature. DR. ROBERTS: I would like to say that as we look at bringing additional primate sources into the United States, if we cannot genetically characterize them, one of the most crucial things is to establish the provenience of those animals. Where are they originating? When you look at the range of facilities in China, if you can specify the geographic origin of those populations, it helps incredibly in terms of both looking at the genetics of those populations and also developing genetic tools to compare those populations. DR. VANDEBERG: I would like to reinforce that point. The large variation that Dr. Marthas described in the Chinese rhesus may well be a consequence of geographic origin, a wide variety of geographic origin of animals. We talk about Chinese and Indian rhesus as if each population were homogeneous. Certainly they are not. Chinese rhesus from one part of China might behave very differently in these kinds of experiments than Chinese rhesus from another part of China. Thank you for mentioning that difference.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources DR. ERWIN (Dr. Joseph M. Erwin, BIOQUAL and the Foundation for Comparative and Conservation Biology): I want to underscore the value of this morning’s presentations, particularly with regard to phenotypic characterization. The goals of genomics and the promise of proteomics cannot be appropriately realized unless there is a phenomic or phenotypic characterization component that parallels them. We have heard that, fortunately, some of that characterization is going on. The support of partially characterized and pedigreed colonies is absolutely critical. Furthermore, I think there is the potential for some of the circumstances such as Mauritius, where there is a genetically homogeneous population that came from a relatively small number of founders and the St. Kitts African green population. Some of those island populations are essentially the best that we have in regard to inbred populations. We do not know what the potential is for genetic studies from those sources. I think it helps to recognize that there is potential for working out some of the genetic risk factors and verifying them within the pedigreed colonies, then going to some of these relatively genetically well-defined biogeographic populations and selecting the animals that are appropriate for whatever the target research is. I think it could add some efficiencies, and one could even extend that selection to some of the other introduced populations such as the Macaca nigra population on Ba chang, the Macaca fascicularis population on Cabaña, the Macaca fascicularis population on Angour in Balow, and a number of other populations of this kind that could become tremendously valuable. We must not neglect the other captive populations that exist but are currently not well supported. I think most of you are aware of a population of 300 chimpanzees that is now available and in need of support. I am trying to help develop such a support effort. So if you are concerned about this as much as I am, please contact me. PARTICIPANT B: A message to take home is that making a switch to a whole different species would be of enormous consequence to a laboratory—even after establishing all of the norms and different information that we have on them, including the simple subtleties we see between the Chinese- and Indian-derived rhesus that sometimes are of great importance to a study. If you look at the other differences between the Chinese-and Indian-derived rhesus, you have differences in aggressiveness, serotonin, and alcohol consumption in blood chemistries. Those differences could be very relevant. Adding to what Dr. Erwin said, if you have a question on aggression, perhaps you would want to look at the more aggressive species as a good model. It really depends on what your model is in many cases if you are just beginning, but if you were already established, it would be quite difficult to make a switch.

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources DR. VANDEBERG: I agree it is very difficult to make a switch. I think it is not practical for an individual investigator to make that kind of a switch, particularly in the short term. However, if resources were committed to establish baseline data on some alternative species to rhesus over a period of time and those baseline data were developed and made available, it would be much easier for investigators beginning projects to choose a species other than rhesus. It may be possible for investigators at some point to switch, and it may be necessary if there are no rhesus available to them. However, the individual investigator is not in a position to make that switch by him- or herself. We must have support for developing the baseline data for many physiological characters for some of these other species that are readily available. DR. PALMOUR (Dr. Roberta Palmour, McGill University): I would like to respond to Dr. Erwin about the monkeys on St. Kitts. First, we do have a pedigreed colony. We have been doing genetic studies within that pedigreed colony, which is quite large now. Second, we have done some work looking at the genetic variability on the island. Although it is certainly the case that the genetic variability is restricted by comparison with African vervets, there is a significant amount of genetic variability even from these 1000 founders. It is not that we have an inbred colony, but we do have a genetically restricted colony. I think one of the important points for the whole field is that by looking at different sources of variability, we will have models of different aspects of human traits. I think this point will be very important. I know Dr. VandeBerg and Dr. Williams-Blangero agree because they too have been doing this kind of work. PARTICIPANT C: Is there a Macaca fascicularis equivalent to Mamu AO*1, and do you have any plans of expanding into cynos as an SIV model? DR. FRIEDRICH: It depends on the equivalent. If you want to talk about an MHC allele that may or may not be associated with protection or relative control of SIV, it is quite possible. I am not familiar with any M. fascicularis data so I cannot tell you for certain. If you want to talk about an allele that would encode a molecule that would bind the same types of peptides or act in the same type of way, I would guess probably not. DR. MARTHAS: I do not think there has been a systematic study, for instance, in M. fascicularis or other species. It could be done. I know from looking generally at a sequence database that there are similar sequences in MHC alleles where they have been studied for baboons, cynos, and rhesus. However, I do not think anyone has systematically gone through and tested them for whether you can obtain functional data or recognition by reagents. It is important to develop reagents that are either species specific or could work across multiple species. DR. ERWIN: I also have asked several people that question because it

OCR for page 105
International Perspectives: The Future of Nonhuman Primate Resources seems to me a very high priority that for African greens from St. Kitts and Mauritian cynos, this kind of work should be done. I appreciate that MHC is difficult to work with, but it seems to be a very high priority in the context of the discussions we are having at this meeting with regard to limited supply of rhesus. DR. VANDEBERG: I would like to thank everyone in the audience for that wonderful discussion. It was extremely productive and exactly what we had hoped this session would become. Please join me in thanking the presenters.