Unlicensed U-NK cells promote allogeneic BMC engraftment through increased GM-CSF production that requires MHCI interaction and consequent SHP-1 phosphorylation. Twenty-four hours after coculture of irradiated allo- or synBMC cells with activated sorted B6 licensed and unlicensed NK cells, adherent NK cells were collected and RT-PCR–assessed. (A) Fold change of cytokine expression is shown for licensed and unlicensed NK cells that were exposure to irradiated allo- or synBMCs. Data are represented as fold change mRNA expression of L-NK data. (B) Fold change ratio between GM-CSF and IFNg is shown. To study engraftment, BMCs were collected after 24 hours of culture with NK cells, and CFU-c per BM was determined. (C) Blockade of GM-CSF with anti–GM-CSF prevents the unlicensed NK cell–dependent engraftment. (D) Inhibition of SHP-1 with SSG prevents alloBMC engraftment Ly49G2⁺ NK cell–dependent to a similar extent than GM-CSF blockade measured by CFU-c/BM. (E) Fold change of GM-CSF:IFNg ratio is shown for unlicensed NK cells exposed to allogeneic BMCs after GM-CSF blockade and SHP-1 inhibition. Data are representative of at least 2 experiments with n = 3 (mean ± SEM). One-way analysis of variance was used to assess significance (*P < .05, **P < .01, ***P < .001; n.d., not detected, n.s., not significant).