Only CLP^F have multilymphoid potential in vivo. (A-D) FACS analysis of spleens 3 weeks after intravenous transplantation of 10³ CLP^F or CLP^F− into Ly5 congenic, sublethally (400 rad) irradiated hosts and control mice that received sham transplants. (A) Host cells are Ly5.1⁺ whereas donor-derived cells are Ly5.2⁺. (B,C) FACS plots showing T cell (TCRαβ⁺), B cell (CD19⁺), or NK cell (Nk1.1⁺) cell reconstitution of the spleen after pregating on either Ly5.1⁺ host cells (left panels) or Ly5.2⁺ donor-derived cells (middle and right panels). Both Flk2⁻ and Flk2⁺ CLPs gave rise to B cells but donor-derived T cells and NK cells were only detectable in CLP^F reconstituted mice. (D) FACS plots showing absence of myeloid cells (Mac-1⁺Gr-1⁺) from donor-derived Flk2⁻ fraction cells or CLP^F. (E) Thymi from irradiated (400 rads) host Ly5.2⁺ animals 3 weeks after intravenous (i.v.) transplantation of 10³ CLP^F or Flk2⁻ fraction cells in comparison to animals that received sham transplants (PBS) were analyzed for donor derived Ly5.1⁺ progeny. 3 weeks after transplantation CLP^F derived thymocytes were responsible for roughly two-thirds of the thymus cellularity in mice that received transplants whereas the Flk2⁻ fraction yielded no thymic cells. (F) Thymic reconstitution after intrathymic injection of 10³ Ly5.1⁺ CLP^F or Flk2⁻ fraction cells into irradiated (400 rads) Ly5.2⁺ recipient mice. Numbers on plots are percentages of gated cells.