“…Moreover, low levels of the membrane enzyme ecto-5'-nucleotidase (5'NT) are consistently found in CBL and are similar to the values found in leukaemic cells from chronic Iymphocytic leukaemia [7,10], Some thymic factors, among them thymosin fraction 5 (TMS-F5), can induce several differentiation changes in immature T cells of murine or human origin [17], Several of the TMS-F5 component peptides have been purified to homogeneity and sequeneed. Among them, thymosin alpha, (TMS-a,) seemed to induce the differentiation of early T precursors at high concentrations and of more mature T-cell subsets at low concentrations [16,17], Different stages of T-cell differentiation can be characterized by specific patterns of the purine degradative enzymes adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), and 5'NT, with a fall of ADA and a rise in PNP and 5'NT during maturation [2,8,14], Since TMS-F5 and TMS-a, induced changes in purine enzyme pattern and in surface phenotypic markers of normal human thymocytes and leukaemie cells [5,6,9], the effects of TMS-F5 and TMS-Oj on the purine enzymes and phenotypic markers of cord blood lymphocytes, whose T cells are more mature than thymocytes, have been studied.…”