TP-5 is a pentapeptide containing active site of the thymic hormone, thymopoietin. It has been shown to exert effects on multiple components of human and animal immune system both in vivo and in vitro. Initial studies demonstrated it to be necessary for T lymphocyte maturation. Its effects on other parts of the immune system are primarily immunostimulatory, and the drug can be used to correct immunodeficiencies resulting from several causes. TP-5 has been shown to improve survival rates in multiple animal studies where the animal has been rendered immunodeficient prior to septic challenge. It has also been successful in preventing and treating infections in a number of human studies. Evaluation of the exact mechanism by which the drug improves survival has demonstrated that it is of complex nature, involving interactions between various types of white blood cells.