Why do we need to test drugs on mice when we can test on human cells and tissues?

Scientists have learned many things about human biology and disease from studying tissues, such as blood or tumors, in a petri dish. But to study how a disease really works, scientists need a living model system that can stand in for people. For example, isolating HIV, the virus responsible for causing AIDS, in a test tube, won’t provide information about how HIV attacks the body.

If you wanted to know why your car wasn’t running right, just looking at the shock absorber wouldn’t provide all the information you needed. The same is true for understanding human physiology: The whole is greater, and much more complex, than the sum of its parts.

Instead, scientists study diseases including AIDS, cancer, heart disease, Alzheimer’s disease and many other deadly diseases using laboratory mice. Humans and mice may not look alike, but almost all the genes in mice share functions with genes in humans. So, humans and mice get the same diseases for the same reasons.

Every disease has a distinctive set of gene variations, and scientists can study the disease by working with mice with the same genetic profile. That way they can track how the disease starts and progresses, and test possible treatments to make sure they work before they are tested in patients.