Leukemic Priming of Resting NK Cells Is Killer Ig-like Receptor Independent but Requires CD15-Mediated CD2 Ligation and Natural Cytotoxicity Receptors

Abstract

Resting human NK cells require a two-stage activation process that we have previously described as “priming” and “triggering.” NK-sensitive tumor cells provide both priming and triggering signals. NK-resistant tumors evade lysis, mostly by failure to prime; however, we recently reported a tumor cell line (CTV-1) that primes resting NK cells but fails to trigger lysis. In this article, we report two additional leukemia cell lines that prime NK cells but are resistant to lysis. Tumor-mediated NK priming is via CD2 binding to a ligand within CD15 on the tumor cell. NK-resistant RAJI cells became susceptible to NK lysis following transfection and expression of CD15. Blockade of CD15 on K562 cells or on CD15+ RAJI cells significantly inhibited lysis, as did blockade of CD2 on resting NK cells. NK priming via CD2 induced CD16 shedding, releasing CD3ζ to the CD2, leading to its phosphorylation and the subsequent phosphorylation of linker for activation of T cells and STAT-5 and synthesis of IFN-γ. Blockade of C-type lectin receptors significantly suppressed the tumor-mediated priming of NK cells, whereas blockade of Ig-superfamily–like receptors had no effect at the NK-priming stage. Tumor priming of resting NK cells was irrespective of HLA expression, and blockade of HLA–killer Ig-like receptor interactions did not influence the incidence or degree of priming. However, CD15–CD2 interactions were critical for NK priming and were required, even in the absence of HLA-mediated NK inhibition. Tumor-mediated priming led to a sustained primed state, and the activated NK cells retained the ability to lyse NK-resistant tumors, even after cryopreservation.

Tumor-priming converts NK cells to memory-like NK cells

“…Adaptive immune features of human NK cells have so far been described in HCMV-infection [9][10][11]25,26,31,[37][38][39][40][41][42] or upon proinflammatory cytokine stimulation. 13,14,24,31 To our knowledge, an enhancement of NK cell functionality via tumor-priming has only been described in the context of priming with the CTV-1 cell line, where target cell lysis is critically dependent on CD69 triggering 23 and STAT5 signaling, 43 and for feeder (i.e., RPMI8866, Epstein-Barr lymphoblastoid cell line or K562) expanded NK cells. As enhanced cytotoxicity for tumor-activated NK cells (T-ANKs) and feeder-expanded NK cells is limited to the immediate post-priming period, is critically dependent on extensive activation and is non-selective, we feel that both do not bear features of adaptive NK cells and are therefore not comparable to TIML-NK cells.…”

NK cell CD16 surface expression and function is regulated by a disintegrin and metalloprotease-17 (ADAM17)

“…42 Further studies are required to determine the exact role of soluble CD16 cleaved from NK cells. Sabry et al 43 described shedding of CD16 after stimulation of NK cells with a leukemic cell line, CTV-1. They hypothesized that shedding of CD16 might enable CD3z, which dimerizes with CD16, to associate with CD2.…”

Leukemia-induced phenotypic and functional defects in natural killer cells predict failure to achieve remission in acute myeloid leukemia

“…Our data support previous reports of synergy among NK receptors and the requirement for a 2-stage process of activation and triggering for target cell lysis. [43][44][45] Another possible cause for this discrepancy may be due to differences in phenotyping techniques. Because CD56 is often aberrantly expressed on AML blasts, we first gated out blasts expressing CD13, 33 or 34 to separate these from NK-AML cells in our study.…”