Identification of committed NK cell progenitors in adult murine bone marrow

Abstract

Natural killer (NK) cells play important roles in innate immunity by lysing tumor and virally infected cells and by producing cytokines including interferon‐γ. While NK cell progenitors have been described in the fetal thymus, NK cell generation from hematopoietic stem cells (HSC) in the bone marrow (BM) occurs throughout life, and in athymic mice and humans. Interleukin (IL)‐15 promotes NK development in vitro and is essential for the generation of normal numbers of NK cells in vivo. By characterizing BM cells expressing IL‐15 receptor components, we found marked heterogeneity within the IL‐2 receptor β chain+ (CD122+) subset, which included cells uniquely committed to the NK lineage. These CD122+ NK cell precursors (NKP) are negative for markers used to identify mature NK cells, including NK1.1, DX5 and members of Ly‐49 family, and fail to demonstrate natural cytotoxicity against susceptible targetcells. In vitro culture of NKP generates mature lytic NK1.1+ cells at high frequencies, while they do not give rise to T, B, myeloid or erythroid cells under appropriate conditions. NKP lack transcripts associated with early B and T cell differentiation (pTα, λ5 and CD3ϵ), but express a group of genes (IL‐15Rα, Id2, GATA‐3 and Ets‐1) and the 2B4 marker, which may define NK cell committment. We propose that NKP represent the earliest adult BM precursor uniquely restricted to the NK cell lineage.

Deletion of PI3K-p85α gene impairs lineage commitment, terminal maturation, cytokine generation and cytotoxicity of NK cells

“…31 In the first stage of NK development, commitment of hematopoietic stem cells (HSCs) into NK precursors (NKPs) occur by the expression of IL-2/IL-15 receptor b chain, CD122. 32 Total percentages of CD3 À CD122 þ , which include both NK and NKT cells were not affected in the BM and spleens of p85a À/À mice (Figure 2b). CD3 À CD122 þ immature NKPs are the earliest known progenitors committed to become NK cells, defined by the absence of mature markers such as NK1.1, NKG2D, NKG2A/C/E, Ly49, CD49b and CD11b.…”

“…NKPs exclusively mature into NK cells and their presence in the adult BM and fetal thymus have been confirmed. 32 This earliest developmental stage of NKPs is defined by the expression of IL-2/IL-15 receptor-b chain, CD122. 32 Both IL-2 and IL-15 cytokines are important in the development and maturation of NK cells.…”

“…32 This earliest developmental stage of NKPs is defined by the expression of IL-2/IL-15 receptor-b chain, CD122. 32 Both IL-2 and IL-15 cytokines are important in the development and maturation of NK cells. 49 Also, expression of CD122 by early progenitors uniquely marks the committed NKPs.…”

“…Here, the 'immature' NKPs start acquiring different Ly49 receptors, whose expression determines the specific repertoire of NK subsets. 32 Analyses of Ly49 expression on p85a À/À NK cells indicated an exclusive reduction in Ly49A, Ly49G2 and Ly49D subsets. Other NK subsets such as Ly49C and Ly49I were unchanged.…”

“…31,32 This terminal maturation is an essential step for the NK cells to achieve full functional competency. NK cells from p85a À/À mice expressed significantly lower levels of CD43 compared to that of WT, whereas the expression of CD11b was unaffected.…”