Some genetic defects can lead to excessive immune responses, which can cause fatal harm to patients. In a recent study, a German research team used the CRISPR-Cas9 gene editing tool to correct these defects and normalize the immune response. The relevant research paper was published in the journal Science Immunology on the 2nd. Familial hemophagocytic lymphohistiocytosis (FHL) is a rare immune system disease that typically occurs in infants and young children under 18 months of age, with a high mortality rate. It is caused by gene mutations that prevent cytotoxic T cells from functioning properly. Cytotoxic T cells specifically secrete various cytokines to participate in immune responses and have a killing effect on certain viruses, tumor cells, etc. If children with FHL are infected with EB virus, cytotoxic T cells cannot eliminate the infected cells, which can lead to uncontrolled immune response. And this can trigger cytokine storms and excessive inflammatory reactions, affecting the entire human body. In the latest study, researchers from the Max Delbrueck Molecular Medical Center in Germany used the CRISPR-Cas9 gene editing tool to successfully repair defective cytotoxic T cells in mice and two critically ill infants. The repaired T cell function was normal, and the mice also recovered from FHL. The researchers first altered the perforin gene in mice (a genetic defect commonly found in FHL patients), causing complete loss or severe damage to its function, resulting in symptoms similar to EB virus infection in the mice. Due to the inability of defective cytotoxic T cells to eliminate the EB virus, the affected B cells began to proliferate wildly, leading to an excessive immune response. Subsequently, the research team collected T memory stem cells from mouse blood, which are long-lived T cells that have matured into active cytotoxic T cells. They used the CRISPR-Cas9 gene editing tool to repair their defective perforin gene and injected the corrected cells back into the mouse body. The results showed that the immune response in the animal's body weakened and symptoms disappeared. The same strategy also applies to two sick infants. (Lai Xin She)