Combined immunodeficiency due to CD70 deficiency is a rare, inherited disorder that affects the immune system. It is caused by mutations in the CD70 gene, which is responsible for producing a protein called CD70. People with this disorder have a weakened immune system, which makes them more susceptible to infections. Symptoms may include recurrent infections, failure to thrive, and an increased risk of developing certain types of cancer. Treatment typically involves a combination of medications, immunoglobulin therapy, and bone marrow transplantation.