National Antivisection Society
SSC: problems faced in developing vaccines or therapeutics
12 July 2007
SSC: 1) Host-viral/parasite relationship:
(a) For instance some agents such as HCV and malaria intra-hepatic stages cannot be cultured in vitro or, they are is so species specific that they only infect humans or other closely related primates.
ADI Response:
- Human liver tissue has been developed to support the progression of the early, pre blood cell, stage of two human strains of malaria74. This can now be used for studying the biology of liver stage malaria parasite to aid in developing vaccines that target the parasite before it enters the blood cells of its host.
- Hepatitis C virus (HCV) models have been produced that model the clinical progression of the virus, as well as being able to infect naïve cells. This will allow the study of species specific, human host-virus relationship and will contribute to the development of an HCV vaccine75.
- Currently around one third of drug candidates fail in the first human trials. Advanced non-animal techniques allow for larger sample sizes and greater reproducibility76.
- As far back as 1985, an editorial in the medical journal The Lancet stated, “In recent years, many animal tests for the safety of viral vaccines have been replaced by cell-culture tests, which are more sensitive and reliable"77.
- ADI: The use of chimpanzees and other less closely related NHPs are unreliable as models for human specific diseases such as HIV. The chimpanzee is the only non-human animal that can be infected with HIV78, but whereas AIDS destroys human health, chimpanzees infected with HIV manifest, at most, transient swelling of some lymph nodes”79.
- Washington National Primate Research Centre’s pharmaceuticals department had have said, “…a clear road map for HIV vaccine development has yet to emerge….because of the intrinsic nature of the surrogate model and…because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans”. It was also noted “SIV models do not allow direct testing of HIV vaccines. Currently available SHIV models do not adequately represent the spectrum of HIV genotypes and phenotypes.”80.
- Primates, despite their evolutionary closeness to us, are distinct from us in the way they express genes in the brain [’expression’ of a gene is the activity or product that the gene causes to occur in the body]. There are even big differences in gene expression between humans and chimps, although gene expression between chimps and other primates is similar81.
- Researchers in Denmark and the USA have highlighted the need to reconsider the use of primates in research. The team compared genes found in humans to their equivalent genes in chimpanzees. They found that the genes which differ the most between humans and chimpanzees are those related to immune defence and cancer development82.
SSC: (b) An infectious agent may only cause disease due to its specific interaction with the affected host. A good example is HIV-1 which causes disease in almost all humans, but very rarely in chimpanzees.
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