SYNTHETIC THYMIC FRACTION .5. EFFECTS OF HIGH-DOSE ADMINISTRATION ON CIRCULATING LYMPHOCYTES IN PATIENTS

The synthetic pentapeptide (Arg-Lys-Asp-Val-Tyr; TP-5) corresponding t o the active site of the hormone thymopoietin, was given at the dose o f 300 mg/m(2)/day (I day), higher than the usually administered, to a group of 27 immunodepressed patients in order to determine the tolerab ility and the immunomodulatory activity. The examination of a series o f hematological parameters including counts of differential clustering of lymphocytes by cytofluorimetric analysis was performed 24 hr and 4 8 hr after treatment and repeated at different intervals up to 14 days after treatment TP-5 caused a significant increase of circulating lym phocytes and particularly of CD3+CD4+ and CD3+CD8+ subtypes, peaking a t 48 hr and maintaining the increased values up to the last examinatio n on day 14 from treatment. A faster increase (zenith at 24 hr) was ob served for CD4+ cells, in comparison with CD8+ cells (zenith at 48 hr) . The number of patients that increased total lymphocytes or lymphocyt e subset after treatment ranged between 52.6 (CD4+ cells) and 69.2% (N K cells), whereas about 7.7% (NK cells) to 36.9% (CD4+ cells) remained unchanged and a smaller amount of 10.5% (CD4+ and CD8+ cells) or 23.1 % (NK cells) showed a decrease greater than 10% of their respective ba sal value. No significant relationship between responders and non-resp onders can be found on the basis of previous treatments, cancer type, sex or age.