Expression of an early myelopoietic antigen (CD33) on a subset of human umbilical cord blood-derived natural killer cells.

A new subset of natural killer (NK) cells was identified in human umbilical cord blood. This subset of CD56+/CD3- NK cells co-expressed the CD33 antigen, which is present on early hematopoietic progenitors confined to the myeloid lineage. The percentage of the CD56+/CD33+ cells among the CD56+/CD3- NK cells was 7.9 +/- 6.6% (n = 27) with a range of 1.4-25.5% and a considerable individual variability. Additionally, the majority of freshly isolated CD56+/CD33+ cells co-expressed the CD2 and CD7 antigen, a minor proportion co-expressed the CD8 antigen but essentially all of the cells stained negative for CD16 and CD57. Morphological analysis of the CD56+/CD33+ cells showed the features of large agranular lymphocytes. From some of the samples, the CD56+/CD33+ NK cells were cultivated and expanded in vitro by incubation of the cells with interleukin 2 (IL-2) for up to 50 days. Morphological analysis of the cultured CD56+/CD33+ cells showed the features of large granular lymphocytes (LGL). The IL-2-expanded CD56+/CD33+ NK cells showed only a low cytolytic activity against K562 target cells, whereas most of the NK activity of the expanded cells was contributed by the CD56+/CD33- NK cells.