Severe combined immunodeficiency (SCID) has many phenotypes, including those which result in the formation of T cells but render them incapable of an optimal level of proliferation following stimulation by an antigen. Phytohaemagglutinin (PHA) is a mitogen commonly used to assess T-cell proliferation, although anti-CD2/CD3/CD28-coated beads may provide a more physiological trigger. Some patient…