Improvement of natural killer activity and of T cells after thymopoietin pentapeptide therapy in a patient with severe combined immunodeficiency.

The case of an 18-month-old child, affected by malnutrition, severe interstitial pneumonia and immunological abnormalities is reported. Since the age of 10 months, the infant suffered from severe recurrent infections and failure to thrive. Immunological studies revealed a striking decrease of T lymphocytes and of natural killer (NK) function. Serum immunoglobulins, salivary IgA, natural isohaemagglutinins, Fc-IgG receptor-bearing cells and suppressor T lymphocytes were absent, together with an impaired de novo DNA synthesis after PHA, Con A, PWM and Cowan I strain from Staphylococcus aureus stimulation. In vitro incubation of the patient's lymphocytes with TP-5, a thymopoietin-derived synthetic pentapeptide, resulted in improvement of sheep rosettes, Fc-IgG receptor-positive lymphocytes and NK activity. The child was therefore treated with TP-5 for 8 months and his clinical condition improved as well as the number of T cells, Fc-IgG-positive lymphocytes and NK function. However, humoral immunity remained persistently depressed. We suggest that this child could be classified as affected by 'late-onset severe combined immunodeficiency'. In vitro assays with thymic hormones or synthetic drugs that mimic the action of thymic hormones should be performed and this therapy could be applied in the treatment of some of these heterogeneous syndromes, especially when an immunological reconstitution with bone marrow or fetal graft cannot be attempted.