Natural killer cell differentiation

Ian Moore Bennett, Thomas Jefferson University


While a critical role for Natural Killer (NK) cells in innate and adaptive immune responses has been established, relatively little is known about the differentiation of these cells from hematopoietic progenitors. Human NK cell differentiation from immature lineage negative (Lin$\sp-)$ umbilical cord blood cells was examined in vitro. Cells expressing differentiation antigens of mature NK cells (CD56, CD16, CD2, CD8, NKR-P1A) were generated from Lin$\sp-$ cells cultured with interleukin (IL)-2 and a murine bone marrow stromal cell line expressing the human membrane-bound form of stem cell factor. Two subsets of NK cells were identified in these cultures, one of which expressed both NKR-P1A and CD56 and, in variable proportions, all other NK cell differentiation antigens. The second subset expressed only NKR-P1A and, unlike the former, was not cytotoxic against the prototypic NK-sensitive K562 cell line. Neither subset expressed interferon (IFN)-gamma mRNA nor could it be induced by stimulation with phorbol di-ester and Ca$\sp{2+}$ ionophore, but both expressed tumor necrosis factor (TNF) alpha mRNA and the cytotoxic granule-associated proteins TIA-1, perforin, and serine esterase-1. After 10-d culture with IL-2, IL-12, and irradiated B lymphoblastoid cells, approximately 45% of the purified NKR-P1A$\sp+$/CD56$\sp-$ cells became CD56 positive, and the same cultures contained cells capable of cytotoxicity and IFN-gamma production. These results indicate that within the CD3$\sp-$ cell population expressing only NKR-P1A exist cells at an intermediate, functionally immature stage of NK cell differentiation, and that effector functions develop in these cells, concomitantly with CD56 expression, in the presence of IL-12. These cells likely represent the counterpart of a CD3$\sp-$/NKR-P1A$\sp+$/CD56$\sp-$/CD16$\sp-$ cell subset that, as shown here, is detectable both in adult and neonatal circulating lymphocytes. We have also investigated the ability of IL-12 and IL-15 to support NK cell differentiation from NK cell progenitors. These cytokines, like IL-2, are potent stimulators of mature NK cells, but only IL-15 shares with IL-2, in combination with mSCF, the capacity to induce differentiation of the progenitor cells present in the Lin$\sp-$ cord blood population. Exogenous rIL-12 is not only incapable of supporting differentiation of NK cells from Lin$\sp-$ cells but also inhibits the IL-2-induced differentiation of these cells, at least in part independently from induced production of IFN-$\gamma$ and TNF-$\alpha.$ Extending previous studies defining the generation of NK cells from their progenitors, our results provide new information on phenotypic characteristics of NK cells at previously unidentified stages of differentiation, the sequential acquisition of specific effector functions, and the role of distinct cytokines in this process.

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Recommended Citation

Bennett, Ian Moore, "Natural killer cell differentiation" (1998). ProQuest ETD Collection - Thomas Jefferson University. AAI9829078.