Analysis of parameters that affect human hematopoietic cell outputs in mutant c-kit-immunodeficient mice.

Xenograft models are transforming our understanding of the output capabilities of primitive human hematopoietic cells in vivo. However, many variables that affect posttransplantation reconstitution dynamics remain poorly understood. Here, we show that an equivalent level of human chimerism can be regenerated from human CD34(+) cord blood cells transplanted intravenously either with or without additional radiation-inactivated cells into 2- to 6-month-old NOD-Rag1(-/-)-IL2Rγc(-/-) (NRG) mice given a more radioprotective conditioning regimen than is possible in conventionally used, repair-deficient NOD-Prkdc(scid/scid)-IL2Rγc(-/-) (NSG) hosts. Comparison of sublethally irradiated and non-irradiated NRG mice and W(41)/W(41) derivatives showed superior chimerism in the W(41)-deficient recipients, with some differential effects on different lineage outputs. Consistently superior outputs were observed in female recipients regardless of their genotype, age, or pretransplantation conditioning, with greater differences apparent later after transplantation. These results define key parameters for optimizing the sensitivity and minimizing the intraexperimental variability of human hematopoietic xenografts generated in increasingly supportive immunodeficient host mice. Exp Hematol 2017 Apr; 48:41-49

A Dominant-Negative Isoform of IKAROS Expands Primitive Normal Human Hematopoietic Cells

Disrupted IKAROS activity is a recurrent feature of some human leukemias, but effects on normal human hematopoietic cells are largely unknown. Here, we used lentivirally mediated expression of a dominant-negative isoform of IKAROS (IK6) to block normal IKAROS activity in primitive human cord blood cells and their progeny. This produced a marked (10-fold) increase in serially transplantable multipotent IK6+ cells as well as increased outputs of normally differentiating B cells and granulocytes in transplanted immunodeficient mice, without producing leukemia. Accompanying T/natural killer (NK) cell outputs were unaltered, and erythroid and platelet production was reduced. Mechanistically, IK6 specifically increased human granulopoietic progenitor sensitivity to two growth factors and activated CREB and its targets (c-FOS and Cyclin B1). In more primitive human cells, IK6 prematurely initiated a B cell transcriptional program without affecting the hematopoietic stem cell-associated gene expression profile. Some of these effects were species specific, thus identifying novel roles of IKAROS in regulating normal human hematopoietic cells