Infecting Pigtail Macaques with HIV
Comparative evaluation of simian, simian-human and human immunodeficiency virus infections in the pigtail macaque model
C. Jane Batten, Robert De Rose, Kim Wilson, Michael B. Agy, Socheata Chea, Ivan Stratov, David C. Montefiori and Stephen J. Kent
Indian rhesus macaques were the non human primate of choice in research of human immunodeficiency virus (HIV), but because of high demand and intense competition for use, their supply has depleted. Pigtail macaques (PTM) have been used as an alternative because they are readily available from breeding colonies. These monkeys react to simian immunodeficiency virus in a similar manner to humans infected with HIV.
In this study, researchers compared the level of infection and the immune response by PTMs inoculated with a range of lentiviruses.
Although the authors stated that this has never been done before, all of these viruses have been tested on a wide range of macaques. TheSIVmac251 is already known as the ‘gold standard’ in that it results in not only an infected monkey, but a sick monkey, and whose disease pathway is similar to that of humans.
Lentiviruses - These are retroviruses which include HIV. They are usually slow to develop and have a long incubation period.
Immune response - This is a defence function of the body that protects against invading pathogens and disease using B- lymphocytes
Fifty four macaques were used and they were kept in a physical containment level three. This is a laboratory that is fully enclosed, has washable surfaces, minimal furniture and laboratory workers must wear protective clothing. There is no mention of whether the monkeys were housed singly or in groups and I assumed that any natural material such as tree branches for climbing was not included in their housing arrangements.
The authors stated that all experiments were performed according to the National Institutes of Health guidelines of animal welfare. NIH is an American standard even though the study was conducted in Melbourne. The Australian standard emphasises the importance of an enriched environment. Clearly these monkeys did not have enrichment and were in the study for at least twenty one weeks. The research was approved by the University of Melbourne Ethics Committee.
A selection of viruses in the SIV, SHIV and HIV-1 groups were administered in three ways to the macaques; intravenously, intravaginally and intrarectally. This choice was to mimic the transmission of disease in humans. Although they state that the monkeys were anaesthetised prior to procedures, they also say that some of the infusions took place over two days, so it is not clear what part of the procedure they were anaesthetised for. The viruses were obtained from tissue banks and from new born monkeys who had also been infected.
Parameters which were studied include:
- Virology or in this case, the level of live reproducing viruses.
- Immunity response, which was measured by analysing T-cell levels in the blood.
The research mentions the tests used, but does not detail the number of blood tests and tissue samples that these monkeys endured, nor does it mention if the monkeys have been trained to accept having procedures performed on them. As chronically high stress levels can affect immunity it is important to know these details, particularly as these animals may have been used in previous research. Again these details are missing from the report.
All monkeys became infected with a virus but outcomes were markedly different within the group.
Infection by HIV-1 (the only virus relevant to humans) resulted in infection but no illness.
SIV showed high levels of viral replication and a gradual decline in the numbers of specific T cells indicating failure of the immune system.
The intrarectal doses of SHIV resulted in an aggressive infection within three weeks and development of AIDS symptoms. However, SHIV infection does not mimic natural HIV-1 in humans. It targets a different T cell and until now, even the most promising SHIV is variable in its results of illness. This outcome is the same across many monkey species.
A total of twenty seven monkeys were euthanized during the study as a result of AIDS related illness such as respiratory illness, weight loss, diarrhoea and lethargy. The viruses causing theses symptoms were those which most closely replicated the disease in humans.
There is no mention of the outcome of the remaining animals that were now infected with lentiviruses. In the interests of cost efficiency they might be used again, but as Australia does not have retirement facilities for these animals the only other option is to kill them.
Researchers concluded that PTMs responded to the viruses similarly to Indian rhesus macaques and therefore would be a good substitute. However, they already knew that monkeys infected with HIV-1 do not respond in the same way to humans and they knew that the infection in monkeys with SIVs and SHIVs show significant variability in results and do not reliably mimic HIV in humans. Therefore, the research is repetitive.
There is a lack of transparency in this report about the treatment of the 54 macaques. This is achieved by insufficient details regarding the housing, number and nature of tests conducted on them and the outcome after the study. The complex and technical language also ensures that very few people in the public would be able to scrutinise the report let alone make a judgement on its merits.
The purpose of this research was to provide a baseline for yet another species of NHP in the quest for a vaccine. The authors said that the variability in results using the most promising virus, SIV, could ‘probably’ be explained by differences in the genes involved in immunity. If there are variations within the same species of monkey then these variations would be greater between different species.
There is no evidence of the Reduce, Refine and Replace recommendation made by the NHMRC as the purpose of the study was to find another species of monkey not to explore a non animal method. The three ‘R’s would have been more effectively achieved by using living human sufferers of HIV infection and tissue samples from the Australian HIV Observational Database.
What the experts say
Dr Andre Menache, BSc (zoology), BSc(Hons), BVSc, MRCVS
Mosby’s Dictionary of Medicine, Nursing and Health Professions, P. Harris, S.Nagy, N. Vardaxis. 2006, Elsevier, Sydney.
The Welfare of Non-human Primates used in Research, Report of the Scientific Committee of Animal Health and Animal Welfare. 2002, European Commission.