Immunodeficiency manifests in a reduced resistance to infections and, as a consequence, in an increased susceptibility to disease.
Immunodeficiency can have genetic causes or manifest as a consequence of certain diseases such as HIV
infections, cancer and gut diseases. It may even be induced artificially before bone marrow transplantations. The weakened immune system
makes patients more susceptible to usually harmless pathogens. Persons suffering from immunodeficiencies profit a lot from vaccines and immunotherapies.