Xenotransplantation models allowing the identification and quantification of human Hematopoietic stem cells (HSC) in immunodeficient mice remain the only way to appropriately address human HSC function despite the recent progress in phenotypic characterization. However, these in vivo experiments are technically demanding, time consuming and expensive. Indeed, HSCs engraftment in mouse requires pre-conditioning of animals either by irradiation or cytotoxic drugs to allow homing of injected cells in specific stem cell niches and their subsequent expansion and differentiation in bone marrow. Recently, the development of busulfan pre-conditioning of animals improved the flexibility of experimentation in comparison with irradiation.

In order to further facilitate the organization of these complex experiments we investigated the effect of extending the period between mice pre-conditioning and cell injection on the engraftment efficiency. In the meantime, we also explored the role of busulfan doses, mouse gender and intravenous injection route (caudal or retro orbital) on engraftment efficiency.

We showed that a period of up to 7 days did not modify engraftment efficiency of human HSCs in NSG model. Moreover, retro orbital cell injection to female mice pre-conditioned with 2x25 mg/kg of busulfan seems to be the best adapted schema to detect the human HSC in xenotransplantation experiments.