Mutant CALR homozygosity results in a transplantable extreme thrombocytosis but does not confer competitive repopulating advantage in serial transplants. (A) Donor chimerism is comparable in the primary noncompetitive BM transplants. BM cells from CALR^del/del or control mice at 7 to 8 months after poly I:C (2 × 10⁶ per recipient) were transplanted into irradiated (1 × 400 cGy) Kit^W41/W41 C57BL/6 recipients (CD45.1). Bar graphs show donor chimerism in peripheral blood, which was analyzed by using flow cytometry with CD45.1 and CD45.2 antibodies and is derived as the percentage of CD45.2⁺ cells in whole nucleated blood. Time course of blood counts is shown, and significantly increased platelet counts were seen in the recipients of CALR^del/del BM. (B) Bone marrow cells from CALR^del/del mice show similar repopulating capacity in peripheral blood of primary competitive transplants. Donor repopulation was assessed by using flow cytometry as detailed in Figure 4E. (C) Bone marrow cells from CALR^del/del mice show similar repopulating capacity in secondary competitive transplants. Donor repopulation was assessed by using flow cytometry of peripheral blood as in Figure 4E; bar graphs show comparable repopulating capacity to multiple lineages in peripheral blood in the secondary competitive transplantation recipients. Data are shown as mean ± SEM. *P < .05; **P < .01; ***P < .001.