Non-myeloablative regimens for host conditioning have been widely used in clinical hematopoietic stem cell transplantation due to their reduced toxicity on the recipients. But a milder conditioning regimen may require a higher engrafting ability of donor stem cells in competing with endogenous stem cells. Thus, new strategies for enhancing the competitiveness of donor stem cells in non-myeloablative recipients would have important implications for current clinical stem cell trans- plantation. It is known that the absence of p18INK4C (p18) gene can enhance the self-renewal potential of hematopoietic stem cells (HSCs). We applied the approach of competitive bone marrow trans- plantation to evaluate the impact of p18 gene deletion on long-term engraftment of HSCs in sub- lethally irradiated hosts. We found that p18?/? HSCs had a significant advantage over wild-type HSCs during long-term engraftment in the mouse recipients that received a sub-lethal irradiation (5-Gy). The engraftment efficiency of p18?/? HSCs in the sub-lethally irradiated recipients was similar to that in the lethally irradiated (10-Gy) recipients. Our current study demonstrates that enhanced engraftment of donor HSCs in the absence of p18 does not strictly depend on the dose of irradiation used for host conditioning. Therefore, p18 might serve as a potential drug target for increasing the efficacy of stem cell transplant in the patients that are preconditioned with either a myeloablative or non-myeloablative regimen.
