Human Lymphoid and Myeloid Cell Development in NOD/LtSz-scid IL2rγ^null Mice Engrafted with Mobilized Human Hematopoietic Stem Cells.

We have developed, characterized, and validated a new genetic stock of IL-2r common γ (gamma) chain deficient NOD/LtSz-scid (NOD-scid IL2rγ^null) mice that support high levels of human hematopoietic stem cell (HSC) engraftment and multilineage differentiation. Histology, flow cytometry, and functional assays document a severe depletion of lymphocytes and NK cells in NOD-scid IL2rγ^null mice. These mice survive beyond 16 months of age and untreated as well as sub-lethally irradiated NOD-scid IL2rγ^null mice are resistant to the development of lymphomas and are “non-leaky” throughout life. Intravenous injection of sub-lethally irradiated NOD-scid IL2rγ^null mice with 7 x 10⁵ human mobilized CD34⁺ stem cells leads to high levels of multilineage engraftment. At 10 weeks after engraftment, percentages of human hematopoietic CD45⁺ cells are six-fold higher in the bone marrow of NOD-scid IL2rγ^null mice as compared to NOD-scid controls. Human CD45⁺ cells include immature and mature B cells, NK cells, myeloid cells, plasmacytoid dendritic cells and HSCs. Spleens from engrafted NOD-scid IL2rγ^null mice contain high percentages of immature and mature B cells but low percentages of T cells. Treatment with human Fc-IL7 fusion protein leads to a high percentage of human CD4⁺CD8⁺ immature thymocytes and high percentages of CD4⁺CD8⁻ and CD4⁻CD8⁺ mature human T cells in the spleen and blood. Validation of de novo human T cell development was carried out by quantifying T cell receptor excision circles in thymocytes and by analyses of TCRβ repertoire diversity. Human T cell function was evidenced by proliferative responses to PHA and streptococcal superantigen. NOD-scid IL2rγ^null mice engrafted with human HSC generate differentiated functional human T and B cells and provide an in vivo model of multilineage human hematopoietic cell engraftment.