Humanized Mice

Take a PDX humanized mouse, for example. This is a mouse engrafted with a human tumor, known as patient-derived xenograft (PDX), that is sometimes used as an avatar to guide customized patient care and more typically used to conduct pre-clinical trials for new cancer drugs. Scientists can take a tumor from a patient, cut it into pieces, and put these pieces into multiple mice. Each fragment then grows and can then be divided into pieces and put into additional mice. Through this process, dozens of humanized mice are created, each with tumors nearly identical to each other and to the original human patient’s tumor. Scientists can treat different groups of PDX mice with alternative drugs, drug combinations, and drug sequences allowing them to determine which approach works best to eliminate a very specific tumor type.

Another powerful approach is to re-create parts of the humanized immune system with a mouse. In this instance, a mouse with little or no mouse immune system is injected with specific human stem cells typically derived either from fetal tissue or cord blood. These cells create human T cells, B cells, and other immune cells in the mouse enabling scientists to explore how human immune systems attack a wide range of diseases including, for instance, polio, SARS-CoV-2 virus, cancer, and others. These mice can also be used to test how well both chemical and biologically based pharmaceuticals can treat infectious diseases, different types of cancer, and irregularities of the immune system like diabetes and lupus.

Through DNA editing technologies scientists are able to break a strand of DNA at a very precise location and either eliminate a short stretch of genetic code or add code from another organism. When the DNA in a mouse embryo is broken in this way and a human genetic sequence is inserted into its genome, scientists can study how a human gene or a specific genetic variation functions or impacts human health. Humanized mice can also be treated with alternative therapies to see if a disease-causing genomic abnormality can be stopped or mitigated.

Humanized mice can be created in a wide variety of ways and, in so doing, scientists gain the ability to learn more about how we, as humans, develop, grow, and fend off disease. Humanized mice also enable the testing of therapies to help us manage or cure diseases when our own systems fail us.