Suppression of the immune system is a condition in which the ability of the immune system to fight infections and diseases is weakened or suppressed. This condition can occur naturally, such as in babies whose immune systems are not yet fully developed, or it can be caused by drugs that suppress the immune system, such as chemotherapy drugs used to treat cancer.

Suppression of the immune system can also occur as a result of an autoimmune disease in which the body mistakenly attacks its own healthy cells and tissues. People who have undergone an organ transplant may also need immunosuppressive drugs to prevent their body from rejecting the new organ.

While immunosuppression can be helpful in certain medical situations, it may leave people vulnerable to infections and other diseases that they would not otherwise be susceptible to. :

https://www.cancer.gov/publications/dictionaries/cancer-terms/def/immunosuppression