“Laboratory animal experiments and animal models performing in HIV/AIDS biomedical research”
Out line 1. Introduction & overview 2. Animal model content 3. Conclusion
1. Introduction - Concept, purposes and overview of animal being used in biomedical research Animal derive from Anima = living organism that can animated Model = object of imitation “Image of man”
Types of animal model - Induced models- Spontaneous models - Negative models- Orphan model
Today “animal models” are used in virtually every field of research in both preclinical and clinical studies The aim of using animal models in biomedical research is to reconcile biologic phenomena between species or to reproduce delineated or prominent characteristic
Animal experiments in scientific purposes - To search for new knowledge - To diagnose diseases - To test new therapeutic technique and new medicines - To detect and analyze drugs, hormones, and other biological compounds - To produce and test vaccines, sera, and other biological compounds - To test for toxicity, carcinogenicity, and teratogenecity of new and old drugs and chemical compounds
Selection of animal models It is virtually impossible to give specific rules for the choice of the best animal model Some general rules -Appropriateness as an analog -Transferability of information -Genetic uniformity of organism -Background knowledge -Cost and availability -Ecological consequences -Generalizability of the results -Size of animal -Numbers needed -Life span -Sex, age of animal -Etc.
2.Animal models in AIDS - Characteristic of AIDS animal models - Classification of the models - Non human primate models - Murine models - Feline models - Large animal model
An Ideal AIDS animal model - The test virus would be HIV itself - The host would be small inexpensive,genetically and immunologically well-characterized animal - The target receptor would be CD4 - The tropism would be comparable with that observed in human - Disease development and mode of virus transmission would resemble the situation observed in human
Classification of HIV/AIDS animal model -Animal immunodeficiency retrovirus
Non human primate model Ape Genus Pan Pan troglodyte (Chimpanzee) Old world monkey Genus Macaca, Papio, Cercocebus, etc
- Chimpanzee can infected with HIV-1 but rarely develop AIDS disease. - No consistent changes in CD4+ cell. - Vaccines study in chimpanzee are potential means of evaluating the efficacy of candidate vaccines designed to prevent human infection.
Study of HIV-2 in monkey Pigtail macaque (Macaca nemestrina) Baboons (Papio cynocephalus)
- This species are susceptible to infection with some isolates of HIV-2. - HIV-2 have been developed that induce AIDS-like disease and depletion of CD4+ cell. - Similarities in disease progression and development of AIDS to human HIV infection.
Study of Simian immunodeficiency virus (SIV) in non human primate model -SIV is lentivirus and close related to HIV-1, HIV-2 -It share up to 50% similarity to HIV-1 in nucleotid level and share about 88% of amino acid homology to HIV-2
- The heterologous host all develop disease that show many parallels to human AIDS, the similarities including -CD4+ lymphoid cell and machrophage tropism -CD4+ cell depletion -Development of opportunistic infection and tumours -Neurological manifestation (Development of disease in macaque monkey is more rapid than human)
-This model is facilitating studies of viral genetics, mechanism of pathogenesis, drug interference, vaccination and immunotherapy Depending on the SIV strain used, on the dose and route of inoculation and on the recipient host species
Non lentivirus primate model Simian retrovirus type D (SRV-D) -The prototype strain is the Mason-Pfizer monkey virus (MPMV) - Originally isolate from Rhesus macaque spontaneuos breast tumour
-SRV-D is non lentivirus but belong to oncovirus subfamily -Genomic organization of SRV-D is more simpler than lentivirus -Can induced simian AIDS (SAIDS) in SIV-negative macaque monkey with short latency period (0.5- 3 years) -SAIDS is characterize by wasting, chronic diarrhoea, bacterial and viral infection, etc. -The cell receptor for SRV-D is not CD4 (and not yet identified) -The viral host range is broader. -The SRV-D model is particularly helpful in studying immunodeficiency induced by a widely occuring oncovirus and model for the investigation of viral genomic determinant and pathogenesis
-Lentivirus (HIV) models Transgenic mice SCID mice -Non lentivirus model Murine leukemia virus (MuLV)
Transgenic mice model -Produce by introducing one or more viral genes into the mouse germ line. -Several transgenic line have been constructed to contain either the full HIV-1 genome or various HIV-1 derived gene -eg. CD4C/HIV mice is constructed to express entire HIV-1 genome in CD4 cell that serve as HIV-1 target -This mice express the transgene at high level in the thymus and moderate level in the spleen and lymph node
-The transgene was not express in cells that were not expected to express CD4. -This mice exhibit other pathologies similar to those demonstrated in HIV-1 infected individuals including wasting, tubulo interstitial nephritis and lung lession but did not appear to die of opportunistic infections. -In contrast transgenic mice constructed without murine CD4 enhancer remain healthy. -Transgenic mice constructed to contain various HIV-1 gene demonstrate that nef is an important determinant in eliciting the pathogenic process
-Transgenic mice can not yet model the process of infection such as viral spread and the emergence of viral variants -This approach may allow close examination of the disease process occurring in tissues and may also useful in exploring therapeutic strategies
SCID-hu model -Rely on transplantation of human tissue in to SCID mice. -Constructed by surgical implantation of human fetal thymus and liver under the kidney capsules of SCID mouse thus support the growth and differentiation of human T and B lymphoid cells. -Support infection with HIV-1 by IP or IV inoculation. -Depletion of human CD4+ cells is observed. -Most of the mice are clinically healthy. -This model lacks of primary immune response. -Unsuitable for the study of immune response to HIV and pathogenesis in secondary lymphoid organ. -Suitable for assessment of antiviral drug and gene therapeutic strategies.
Hu-PBL-SCID models -Constructed by transplantation of human peripheral blood lymphocytes (PBL) or cord blood lymphocytes into the peritoneal cavity of SCID mice. -Can infected with HIV-1. -Cause depletion of human T cell. -Most of the mice are clinically healthy. -Limitation is inability to consistently elicit primary immune responses. -This model is useful for assessing viral pathogenic properties, passive immune therapies, testing of anti-HIV drugs and vaccines strategies.
Non lentivirus murine model Murine acquire immunodeficiency syndrome (MAIDS) -Induce by murine leukemia virus (MuLV). -Mice infected with MuLV exhibit common clinical features as human AIDS. -Involving T,B lymphocyte dysfunction -Enhance susceptibility to infection, etc. -Murine AIDS is rapidly induce (8-12 weeks) and mice die in 6 months. -This model suitable for study of retrovirus-induced. immunodeficiency disease, testing candidate antiviral agent and study genetic resistant to retroviral immunodeficiency.
Feline retrovirus Lentivirus model - Feline immunodeficiency virus (FIV) Non lentivirus model - Feline leukemia virus (FeLV-FAIDS)
FIV -Cause by lentivirus (but not close related to HIV) -FIV and HIV share basic structural features and. commonalities of their life cycle. -FIV infects CNS and results in predictable pathophysiology similar to HIV-1. -Suitable for study mechanisms by which lentiviruses influence CNS function -Useful model for human AIDS mechanisms of pathogenesis (eg. neuropathogenesis) and investigation of drug treatment, vaccination.
FeLV -Cause AIDS-like disease in cats. -Onset of clinical immunodeficiency prefigure by replication of variant virus in bone marrow,other tissues. -FeLV induce FAIDS is characterize by persistence FeLV infection, lymphoid depletion, opportunistic infection, diarrhoea, weight loss, etc. -This model use to evaluate antiviral agent which act on steps in the replication cycle which are conserve among retroviruses (eg, protease, reverse trancriptase ) and can be use to assess experimental single agent or combine anti viral therapies for retrovirus infection and disease.
Large animal model Equine infectious anemia virus (EIAV) Visna-maedi virus (VMV) Caprine arthritis-encephalitis virus (CAEV)
-Cause by lentivirus (not closely related to HIV). -Not much practically use in research as the smaller animal. -Use for study about pathogenesis of retrovirus infection -The viruses are not T-lymphotropic and do not cause immunodeficiency.
Clinical manifestation of lentivirus infection in natural hosts
3.Conclusion - Advantages and disadvantages between different species. - Benefits and problems of using animal model - Extrapolation - Future prospects
Chimpanzee -98.5% genetic resemble to human. -Can infected with HIV-1. -Good model for study cross reactive immune response. -It rarely develop disease. -It cant be use in sufficient numbers to provide statistically significant results. -Large size. -Expensive. -Not easy to handle.
Monkeys -About 93% genetic similarity to human. -Can provide enough numbers for study. -Can be infected by many type of SIV,HIV2 -Results from different SIV strain can not be reliably extrapolate to one another. -Not easy to handle. -Large size. -expensive -Hight risks of zoonosis.
Mice -Small size,easy to handle inexpensive. -High reproductive,short generation time and life span. -Know about genetic makeup. -Large number available in many strain. -Can create desired system by genetic engineering. -SCID mice does not have a standard human immune system. -Incomplete and low number of repopulating human lymphoid cells -SCID mice does not develop AIDS like disease
Cats -Not large size. -Not difficult to handle. -Not much expensive. -Can be infected with FIV,FeLV and develop immunodeficiency like syndrome. -Cause nearly identical disease to HIV infection. -Cat is far related genetic to human. -FIV,FeLV are not closely related to HIV.
Benefits and problems of using animal model Benefits -Animal studies of toxicity, efficacy and pharmacokinetics provide valuable scientific information toward identifying potentially useful antiviral agents -Helps approximate how drugs/vaccines might perform in human. -Helps to understand some certain mechanism of disease and therapeutic agent observed in animal model. -Study in animal is able to induced certain condition that can not be done in human.
Problems -Preclinical studies generally are inadequate to predic whether an anti viral agent will be both effective and safe when administered to human.(it is not until the agent enters clinical trail in humans that is potential can be ascertained). -There are large differences in the host cell enzymes affinities for a specific antiviral compound among species. -Difficulties between interspecies evaluation.
Extrapolation Because there’re different between species and every animal behave not same to human, to minimize misinterprete of the results,the extrapolation should meet some general requirement. -Taking a plurispecies approach. -Metabolic patterns and speed must match between species. -Confounding variables of metabolism must be controll. -Experimental design and the life situation of the target species must correspond.
Future prospects Most model have their great potential in pathogenesis,immune- response analysis, vaccines and therapies study. Accordingly the challenge for the future is to utilize the increasing knowledge of molecular mechanism of HIV and HIV replication to elucidate all aspects of the virus host relationships fully and thereby to understand mechanism of pathogenesis in AIDS further. Question like antibody enhancement of virus infection, induction of auto immunity, presence of viral super antigens responsible for T cell depletion and development of immune cell dysfunction and tumours can should all be investigated in animal model in the near future and there’re tendency to developments in the field of small animal models for HIV disease.