Apc^min MDS/MPD is predominantly cell extrinsic. (A) Transplantation of 10⁶ bone marrow cells from Apc^min MDS/MPD into sublethally irradiated CD45.1 recipients. White cell count (WCC × 10³/μL), hematocrit (HCT%), and donor cell chimerism (%)16 weeks after transplantation. WCC: 9.9 × 10³/μL Apc^min versus 11.5 × 10³/μL WT, P = .12; HCT: 42.5% Apc^min versus 42.9% WT, P = .81; 51.4% Apc^min versus 53.4% WT, P = .75. (B) Bone marrow transplantation of 1 × 10⁶ CD45.1 congenic bone marrow cells into sublethally irradiated Apc^min or WT recipients. Sublethal irradiation was used because of previous reports describing intolerance of lethal irradiation in Apc^min mice.⁵  WCC × 10³/μL, HCT%, spleen weight (g) WCC: 8.64 × 10³/μL Apc^min versus 7.53 × 10³/μL WT, P = .59; HCT: 17.3% Apc^min versus 31.8% WT, P = .01; spleen: 0.41 g Apc^min versus 0.11 g WT, P < .01. (C) Peripheral blood parameters, including red cell count (RCC × 10⁶/μL), hematocrit (HCT%), mean corpuscular volume (MCV fl), mean corpuscular hemoglobin (pg), red cell distribution width (RDW%), and platelet count (×10³/μL).