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Preclinical Research

In preclinical research, scientists test their ideas for new biomedical prevention strategies in laboratory experiments or in animals. Clinical research (see below) refers to studies in humans. Preclinical research encompasses everything that happens before a candidate is considered for human testing. Preclinical research answers a range of questions. First, scientists will see if their idea for a new strategy shows any promise. They might take an experimental microbicide and combine it with HIV in a laboratory experiment to see if the microbicide stops HIV activity. (Experiments that happen in lab dishes or test tubes but not in animals are called in vitro experiments. Experiments in animals and people are called in vivo experiments.)

If there's evidence that the experimental strategy works in in vitro experiments, it may be moved to in vivo experiments in animals, so as to gather additional information. This can include information on an experimental candidate's safety, dosing strategy, and toxicity, as well as more information on whether the candidate might have an HIV risk-reduction benefit. Mice, rabbits, guinea pigs and monkeys (non-human primates) are some of the animals used to evaluate potential candidates in preclinical in vivo experiments.

The exact questions asked during preclinical research depend on the specific strategy being tested. Vaccine studies can look for immune responses in the animals' blood. Microbicide studies can look for any irritation in the rectal or vaginal linings of the animals. Studies in non-human primates are conducted to get a preliminary idea of whether the candidate might reduce the risk of HIV infection. In these experiments, animals in the experimental arm of the study receive the candidate (e.g., a candidate vaccine or microbicide or ARV drug).

These animals are then exposed to or "challenged" with strains of SIV or SHIV (two families of HIV-like viruses that can cause disease in monkeys). If animals that receive the experimental strategy have different responses to the challenge than animals that did not receive the experimental strategy (the control arm of the study), then this is preliminary evidence of some risk-reduction benefit. However, these animal studies can't predict with certainty whether a product will provide protection in people—non-human primates and humans differ in their immune systems and responses to HIV or HIV-like viruses. This is one reason why research in humans is so important and the research process is so uncertain.