OHSU Researchers Produce First Genetically Modified Monkey: Background Information


Background information on genetic modification of primates

Currently scientists have an arsenal of mouse models available to study the genetic basis of numerous diseases and disorders, some of which are being discovered by deciphering the human genome. Many of these mouse models have been produced through the introduction of new genetic material, or DNA, to the animal and express such diseases as cystic fibrosis, muscular dystrophy and cancer. Although these mouse models have been invaluable in furthering the understanding of the genetic basis of diseases, many of these models do not accurately mimic the symptoms seen in patients.

The intent of this research is to develop and optimize techniques currently used to produce mouse disease models in an animal more closely related to humans, the monkey. Once optimized techniques are available to produce genetically modified monkeys, relevant disease models can be produced, which will lead to improved therapies and ultimately cures.

In order to produce a genetically modified monkey, Anthony Chan, Ph.D., and colleagues introduced the GFP gene (green fluorescent protein) to monkey eggs, which expressed a green protein. The GFP gene was used due to the ease in detection, it is commonly used throughout research labs, and it's been proven safe in animal models. After the GFP gene entered the egg, fertilization was accomplished by injecting a single sperm into the egg, known as intracytoplasmic sperm injection (ICSI).

The GFP gene was transmitted to the monkey egg using a neutralized retroviral vector. Most commonly, viruses are associated with illnesses. However, scientists and physicians utilize neutralized vectors to both produce transgenic animals for disease models and use similar viruses to treat diseases in humans. Viruses have the unique ability to introduce DNA into cells, thus scientists take advantage of this ability to introduce genetic information to produce relevant animal models or clinical treatments to patients. These viruses have been modified with no ability to replicate or cause disease.

Chan began with 224 monkey eggs, and while using two versions of the viral vector (each varied in their control switch, also known as a promoter), he chose 40 embryos to transfer to surrogate monkey females, at two embryos per monkey surrogate. From these transfers, five pregnancies were established, consisting of one blighted pregnancy (no fetal development), one set of twins and three single pregnancies.

At approximately halfway through the pregnancy, the twins were unfortunately lost to miscarriage, but each of the three single pregnancies led to healthy offspring, one carrying the GFP reporter gene, who is named ANDi. The name ANDi was chosen due to the method in which the reporter gene (GFP) incorporates into the monkey's DNA. The reporter gene is first copied in a reverse orientation and then is inserted into the monkey's DNA (inserted DNA backward = ANDi). The miscarriages also were carrying the GFP gene.

This work demonstrates that through the use of a modified virus, scientists now can produce genetically modified monkeys to use as improved models of human disease. With the availability of improved animal models, treatments and cures will more quickly move from laboratories to patients.