Enhanced engraftment of human cells in RAG2/γc double-knockout mice after treatment with CL2MDP liposomes

Objective The ability of human cells to repopulate the bone marrow of nonobese diabetic immunodeficient mice (NOD/SCID) is commonly used as a standard assay to quantify the primitive human hematopoietic stem cell population. We studied the applicability of the immunodeficient RAG2−/−γc−/− double-knockout mouse for this purpose. Methods RAG2−/−γc−/− mice and NOD/SCID mice were injected intravenously (i.v.) with umbilical cord blood–derived CD34+ cells and engraftment was quantified by determining the human CD45+ cell chimerism in bone marrow at several time points. RAG2−/−γc−/− were pretreated with total-body irradiation and depleted of macrophages in liver, spleen, and bone marrow by i.v. injection of clodronate diphosphonate containing liposomes. Results We demonstrated that the frequency of chimerism and the level of engraftment in macrophage-depleted RAG2−/−γc−/− largely resemble that in NOD/SCID mice. Also similar is the multilineage differentiation pattern in the two mouse strains at 7 weeks after transplantation, with a prominent outgrowth in RAG2−/−γc−/− of CD19+ cells (88% ± 10%). Cells of other lineages were clearly less frequent: 9% ± 2% myeloid cells and 0.1% ± 0.1% erythroid cells. As for immature progenitors, 6% ± 1% of the human cells express the CD34 antigen and 0.4% ± 0.1% have the CD34+,CD33,38,71− phenotype. The presence of human committed progenitors (i.e., CFU-GM/BFU-E) was evident. The persistence of human cells at 4 months after transplantation shows that the RAG2−/−γc−/− support long-term maintenance of human hematopoiesis. Conclusion Our findings indicate that macrophage-depleted RAG2−/−γc−/− are a suitable model for studying human hematopoiesis including multipotential stem cells, and long-term repopulation.