Since cell-mediated immunity is mediated by T-lymphocytes (T-cells) and their effectors response and interactions with other immune cells, any defect in T cells production results in impaired protection to viral and other intracellular parasitic pathogens.
The reason for deficiency may be inherited or due to abnormality in thymus functions. Even though B cell levels are normal, T cell deficiency cause impaired immune response.
Even though rare, several inherited T-cell disorders such as Ataxia telangiectasia, Chronic mucocutaneous candidiasis, DiGeorge syndrome, Severe combined immunodeficiency (SCID), Wiskott-Aldrich syndrome (WAS), Adenosine deaminase deficiency and Purine nucleoside phosphorylase deficiency have been identified.
In severe inherited T-cell defects, such as severe combined immunodeficiency, bone marrow or stem cell transplantation or gene therapy may help in protecting the patient.
If the defect is owing to functional defects of thymus, possible treatment is neither transplantation of thymic epithelial cells, or thymic hormone replacement to boost T cell production.