Thymosin activity in patients with cellular immunodeficiency.

An extract of calf thymus, thymosin, induces an increase in percentage of T-cell rosettes when incubated in vitro with sheep erythrocytes and lymphocytes from patients with primary immunodeficiency diseases or viral illness. Precursor lymphocytes are required for this increase to occur. The percentage of T-cell rosettes, when they are normal, is not increased further upon incubation with thymosin. A patient with thymic hypoplasia and immunoglobulin synthesis was selected to receive thymosin in vivo when her T-cell rosettes had increased from 15 to 48 per cent after in vitro incubation with thymosin. During therapy, she clinically improved, the percentage of T-cell rosettes gradually increased to normal, and positive delayed hypersensitivity skin tests developed. Thymosin may be useful clinically for partial reconstitution of cellular immunity. An increased percentage of T-cell rosettes after incubation with thymosin in vitro may predict which patients will respond to thymosin therapy in vivo.