NOD Hematopoietic Stem Cells Exhibit Autonomous Behavior and a Competitive Advantage in Allogeneic Recipients That Maps to the Idd9 Locus.

Multiple hematopoietic defects have been defined in NOD mice and in humans with type I diabetes, including defects in myeloid cells and antigen presenting cells that correlate with diabetes progression. Since the replacement of HSC in NOD mice can eliminate the progression of autoimmunity and control on-going autoimmune responses, we characterized the function of HSC from NOD mice. We found that purified HSC from NOD mice have an autonomous behavior when transplanted in allogeneic recipient strains as reflected by significantly enhanced engraftment in allogeneic recipients. NOD HSC were able to compete for engraftment with syngeneic HSC even when the NOD and syngeneic HSC were given at a 1:1 ratio. NOD BMC produced a higher number of splenic colonies compared to B10.BR BMC in the allogeneic day 12 CFU-S assay. We also demonstrated that NOD HSC had a high resistance to irradiation, as reflected by the cell survival 20 hours after irradiation and in the in vitro CFC assay. These data suggest that NOD HSC escape alloreactivity and compete with normal HSC. The enhanced engraftment ability in allogeneic recipients of NOD HSC was not due to an increase in frequency of primitive HSC, enumerated by day 35 cobblestone area forming cells (CAFC). This finding was further confirmed by the fact that there was no difference in the long-term repopulating cell phenotype (CD49e⁺/CD49d^dim) between HSC obtained from NOD, B10.BR or C57BL/10 mice. Notably, NOD bone marrow cells exhibit significantly enhanced chemotaxis to SDF-1 in vitro and significantly increased HSC adhesion to primary stroma. This was associated with an increase in the expression of VCAM-1, ICAM-1 and ICAM-2 on NOD HSC. Using NOD mice congenic at selected Idd loci with C57BL/10, we determined that the enhanced engraftment potential of NOD HSC mapped to the Idd9 (insulin-dependent diabetes) locus and, as such, the TNF receptor family as well as ski/sno genes may be involved in the mechanism underlying the autonomy of NOD HSC. In conclusion, NOD HSC exhibit increased autonomy in vivo and in vitro compared to non-diabetic strains, and engraft better in allogeneic recipients, possibly due to enhanced migration and adherence to the microenvironment. This finding may be of interest for a better understanding of disease pathogenesis and in developing cell-based strategies to cure diabetes.