Pluripotent hemopoietic stem cells are c-kit

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Abstract
Pluripotent hemopoietic stem cells (P-HSCs) were thought to be c-kit+, but recent reports indicate that they are c-kitlow. In the present report, we provide evidence using Ly5 congenic mice that P-HSCs are c-kit. Lineage-negative (Lin−)/CD71− cells among bone marrow cells (BMCs) from C57BL/6 Ly5.1 mice were separated into major histocompatibility complex class Ihigh (class Ihigh)/c-kitlow and class Ihigh/c-kit populations. Each population (500 cells) was transplanted into lethally (9.0 Gy) irradiated C57BL/6 Ly5.2 congenic mice along with Ly5.2 (2 × 105) compromised cells. Donor-derived Ly5.1+ cells were detected 6 months after transplantation in primary recipients reconstituted with either class Ihigh/c-kitlow or class Ihigh/c-kit cells. BMCs (1 × 106) from the primary recipients were further transplanted into secondary recipients (Ly5.2 mice) to assess their long term repopulating activity. Six months after bone marrow transplantation, Ly5.1+ cells in all lineages were detected only in secondary recipients that had been given BMCs from the primary recipients reconstituted with class Ihigh/c-kit cells but not in cells that were class Ihigh/c-kitlow. When the BMCs (1 × 106) of these secondary recipients were further transplanted into tertiary recipients, all tertiary recipients that had been given BMCs from the secondary recipients originally reconstituted with Lin−/CD71−/class Ihigh/c-kitlow cells died within 10 days whereas all six tertiary recipients originally reconstituted with Lin−/CD71−/class Ihigh/c-kit cells showed donor (Ly5.1+)-derived cells in their peripheral blood. In the single tertiary recipient that was killed, donor-derived T cells, B cells, macrophages, and granulocytes also were detected in several major hematolymphoid organs. The remaining five mice continue to survive more than 6 months after the tertiary bone marrow transplantation.