CCR7/CCR9 DKO mice have a severe ETP defect. (A) BM from WT and CCR7/CCR9 DKO mice were analyzed by flow cytometry to determine frequencies of the indicated progenitors. Shown is the mean ± SEM for 9 WT and 10 CCR7/CCR9 DKO mice. (B) Thymic cellularities from WT and CCR7/CCR9 DKO mice were calculated. Shown is the mean ± SEM. *P < .05 compared with the WT control. (C) WT and CCR7/CCR9 DKO thymi were analyzed by flow cytometry for thymic progenitors. Representative FACS profiles are shown. (D) Absolute numbers of thymic progenitor populations were calculated. Shown is the mean ± SEM. *P < .05 and **P < .01 compared with the corresponding WT controls.