Natural Killer Cell
Natural killer cells are part of the innate immune system that is always on patrol. They detect healthy cells via the MHC I protein. Lack of expression of MHC I on cells with intracellular infections such as viruses stimulate natural killer cells to kill the infected cell with the proteins perforin 1 (PRF1), granzymes (GZM), and fas ligand (FasL).
Killer T-cells, or CD8+ T-cells, are part of the adaptive immune system. They are activated by dendritic cells and attack infected cells that present foreign antigen via their MHC I proteins. They also use perforin 1 (PRF1), granzymes (GZM), and fas ligand (FasL) to kill infected cells.
Chimeric antigen receptor (CAR) T cells are genetically engineered T-cells to express a receptor that incorporates and Fab fragment of an antibody against a tumor antigen. These cells are then able to specifically target and kill cancer cells that express the antigen.
Classical Natural Killer Deficiency
Classical natural killer deficiency (cNKD) is characterized by a loss of natural killer cells. Due to the absence of these cells that normally kill virally infected cells, individuals with this disease are often infected with viral infections, of which hepatitis is the most common.
Acute rejection of a transplanted organ can be mediated by cytotoxic T-cells. They recognized the transplanted organ as foreign largely due to different HLA proteins on the organ. They then attack and kill the cells of the transplant leading to organ rejection and failure.
Graft vs. Host
Graft vs. Host (GvH) is the opposite of organ rejection. In this disease, immune cells such as T-cells from the donor that comes along with a transplanted organ, recognize the host cells as foreign, and start attacking the host. As every cell in the host body appears foreign to the donor cells, this leads to large scale multisystem organ failure.
cNKD -> Killer Lymphocyte
The only treatment for cNKD is to treat any infections that arise from it, such as hepatitis infections which can be treated with the antivirals ledipasvir and sofosbuvir. These medications block the NS5A and NS5B hepatitis proteins and block it from replicating.
Acute Rejection -> Killer Lymphocyte
To prevent the further loss of the transplanted organ, recombinant anti-thymocyte globulin (rATG) can be used to deplete the body of T-cells that are attacking the organ. rATG is an antibody against T-cells.
Graft vs. Host -> CAR-T Cell
As graft vs. host (GvH) are donor T-cells attacking the body, a strong immunosuppressive is necessary to stop them. The glucocorticoid methylprednisolone can be used, which decreases the expression of pro-inflammatory genes and inhibits immune cell activity.