CORD-BLOOD T-LYMPHOCYTES LACK CONSTITUTIVE PERFORIN EXPRESSION IN CONTRAST TO ADULT PERIPHERAL-BLOOD T-LYMPHOCYTES

Perforin is the cytolytic pore-forming protein, which alone can be res ponsible for the lethal hit in one of the killing mechanisms used by n atural killer (NK) cells or cytotoxic T lymphocytes. In this study, pe rforin expression was investigated in cord blood (CB) lymphocytes to d etermine their killing potential in vivo. The majority of CB CD3(-) NK cells had the protein. Compared with adult perforin-positive NK cells , a significantly lower percentage of cells expressing CD56 and CD57, the related neural cell adhesion molecules, was found (P = .0001). Per forin was also present in a unique immature CB NK-cell subset, charact erized by cytoplasmic CD3 antigen (Ag) expression. In CB, very few CD8 perforin-positive T lymphocytes could be detected, but they were in s ignificant numbers in adult peripheral blood (P = .02). A substantial proportion of these cells (70% +/- 23%) lacked the CD28 T-cell coactiv ation Ag, and they were able to exert NK-like, major histocompatibilit y complex nonrestricted cytolytic activity. CD4(+) and gamma delta-T c ells expressing perforin were absent from CB, but low numbers of such cells were detected in adult peripheral blood (P = .0001). Therefore, the spontaneous cytolytic activity of CB lymphocytes appeared to be de pendent on well-represented perforin-positive NK cells, which were sho wn to efficiently lyse NK-sensitive target cells. (C) 1995 by The Amer ican Society of Hematology.