Figure 1. Conditional knockout strategies for STAT5 deletion in the hematopoietic system. (A) We have previously studied HSC with interferon-induced deletion of STAT5 using the Mx1-Cre system. This approach gives conditional deletion of STAT5 in adult mice. The limitation of the approach is the need to wait for the interferon response to subside before subsequent analysis. (B) Since 2006 various other groups have conditionally knocked out STAT5 floxed alleles of STAT5A and STAT5B that were generated by Lothar Hennighausen (NIDDK). These knockouts include expression of Cre recombinase in early hematopoietic stem cells (and vascular progenitors), as well as T cells, B cells, NK cells, and dendritic cell lineages.