RAG2 knockout (KO) mice represent a specialized type of genetically modified laboratory mouse. Scientists engineer these mice to lack a functional recombination activating gene 2 (RAG2). This genetic alteration results in a profound deficiency in their immune system, making them unable to produce mature T and B lymphocytes. Due to this unique characteristic, RAG2 KO mice serve as important tools in scientific investigation, particularly for understanding human diseases and testing new therapies.
The Role of RAG2 and Immune Development
The RAG2 gene plays a specific role in adaptive immune system development. It works with RAG1 to form a protein complex responsible for V(D)J recombination. This process precisely cuts and rejoins DNA segments to create diverse antigen receptors on T and B lymphocytes. This ability allows the immune system to recognize and respond to countless pathogens.
In RAG2 KO mice, the absence of a functional RAG2 gene prevents V(D)J recombination. This blockage halts T and B cell maturation at early progenitor stages. Consequently, these mice do not develop mature T or B lymphocytes, resulting in a severe immunodeficiency that closely resembles Severe Combined Immunodeficiency (SCID) in humans. Their lymphoid organs, such as the thymus and spleen, often appear hypoplastic due to the lack of these developing immune cells.
Applications in Biomedical Research
RAG2 KO mice are widely used in biomedical research because their compromised immune system allows for the engraftment of foreign tissues and cells without rejection. This enables the creation of “humanized” mouse models, where human cells, tissues, or even entire immune systems can be introduced and studied. For instance, human hematopoietic stem cells can be engrafted into these mice, leading to the development of human immune cells that allow researchers to investigate human-specific immune responses and diseases. These models are useful for evaluating novel therapeutic strategies, such as cell-based treatments or gene therapies, by observing their effects on human cells in a living system.
They are also instrumental in cancer research, serving as platforms to grow and study human tumors. Human cancer cells can be implanted into RAG2 KO mice, forming xenografts that mimic human tumor growth and behavior. This allows scientists to test new anti-cancer drugs and therapies without interference from a mouse immune response, providing valuable insights into potential treatments for human cancers. Their immunodeficient status also makes them suitable for infectious disease research. Researchers can infect these mice with human-specific pathogens, such as viruses or bacteria, and study disease progression and potential treatments without a robust mouse immune reaction. This provides a controlled environment to understand pathogen virulence and test vaccines or antiviral medications.
Caring for RAG2 KO Mice in Research
Due to their severe immunodeficiency, RAG2 KO mice require highly controlled and sterile environments to ensure their survival and the validity of research outcomes. They must be housed under specific pathogen-free conditions to prevent infections. This often involves specialized containment units, such as isolators or individually ventilated cages, which maintain a sterile air supply and prevent exposure to environmental pathogens.
All materials introduced into their environment, including food, water, and bedding, must be sterilized before use. Researchers and animal care staff must follow strict aseptic techniques when handling these mice, typically involving sterile gloves, gowns, and masks, to minimize pathogen transmission. These rigorous husbandry practices are paramount, as even common environmental microbes can be lethal to RAG2 KO mice, compromising research integrity and animal welfare.