“…Initial reports suggested no detectable T Only detected in in vitro culture (Spain et al, 1999), homing defect (Fisher et al, 1999) Erythrocyte b Late embryonic anemia of variable severity Myeloid dendritic cells No commitment (Guerriero et al, 2000) Null (Iwama Post-natal An independently targeted Ets2 ES cell line exists, but the generation of knockout mice from these cells has not been reported, and the status of the targeted allele has not been determined ; b Not observed in C57BL/6 back-crossed mice (Fisher and Scott, 1998;Simon, 1998) cells in PU.1 mutant mice homozygous for the ®rst targeted allele (as evidenced by little or no Thy-1, CD4, or CD8 positive cells) (Scott et al, 1994). Subsequent fetal thymic organ culture indicated the presence of a small population of mature T cells, although the predominant population of thymocytes express cell surface markers corresponding to uncommitted T cell progenitors (Spain et al, 1999).…”