DOCK2 is critical for CD8(+) TCR(-) graft facilitating cells to enhance engraftment of hematopoietic stem and progenitor cells.

CD8(+) TCR(-) graft facilitating cells (FCs) enhance engraftment of hematopoietic stem cells (HSCs) in allogeneic and syngeneic recipients. The mechanisms by which FCs promote HSC engraftment and tolerance induction have not been fully elucidated. Here, we provide data to support a critical role for dedicator of cytokinesis 2 (DOCK2) in multiple aspects of FCs function. DOCK2(-/-) FCs exhibit compromised facilitative function in vivo as evidenced by the loss of engraftment-enhancing capability for c-Kit(+) Sca-1(+) lineage(-) (KSL) cells, and compromised ability to promote KSL cell homing and lodgment in hematopoietic niche. Deletion of DOCK2 abrogates the ability of FCs to induce differentiation of naïve CD4(+) CD25(-) T cells into FoxP3(+) regulatory T cells and interleukin-10-producing type 1 regulatory T cells in vitro. Moreover, DOCK2(-/-) FCs are unable to promote survival of KSL cells when cocultured with KSL cells. DOCK2(-/-) FCs also exhibit compromised migration to stroma-derived factor-1 in vitro and impaired homing to the bone marrow in vivo. In conclusion, our results demonstrate that DOCK2 is critical for FCs to maintain its immunomodulatory function and exert its trophic effects on KSL cells. These findings may have direct clinical relevance to promote HSC engraftment for treatment of autoimmunity, hemoglobinopathies, and to induce transplantation tolerance.

Immune reconstitution/immunocompetence in recipients of kidney plus hematopoietic stem/facilitating cell transplants.

Nineteen subjects have more than 18 months' follow-up in a phase IIb tolerance protocol in HLA-mismatched recipients of living donor kidney plus facilitating cell enriched hematopoietic stem cell allografts (FCRx). Reduced intensity conditioning preceded a kidney allograft, followed the next day by FCRx. Twelve have achieved stable donor chimerism and have been successfully taken off immunosuppression (IS). We prospectively evaluated immune reconstitution and immunocompetence. Return of CD4 and CD8 T central and effector memory cell populations was rapid. T-cell receptor (TCR) Excision Circle analysis showed a significant proportion of chimeric cells produced were being produced de novo. The TCR repertoires posttransplant in chimeric subjects were nearly as diverse as pretransplant donors and recipients, and were comparable to subjects with transient chimerism who underwent autologous reconstitution. Subjects with persistent chimerism developed few serious infections when off IS. The majority of infectious complications occurred while subjects were still on conventional IS. BK viruria and viremia resolved after cessation of IS and no tissue-invasive cytomegalovirus infections occurred. Notably, although 2 of 4 transiently or nonchimeric subjects experienced recurrence of their underlying autoimmune disorders, none of the chimeric subjects have, suggesting that self-tolerance is induced in addition to tolerance to alloantigen. No persistently chimeric subject has developed donor-specific antibody, and renal function has remained within normal limits. Patients were successfully vaccinated per The American Society for Blood and Marrow Transplantation guidelines without loss of chimerism or rejection. Memory for hepatitis vaccination persisted after transplantation. Chimeric subjects generated immune responses to pneumococcal vaccine. These data suggest that immune reconstitution and immunocompetence are maintained in persistently chimeric subjects.

Plasmacytoid precursor dendritic cells from NOD mice exhibit impaired function: are they a component of diabetes pathogenesis?

OBJECTIVE: Plasmacytoid precursor dendritic cell facilitating cells (p-preDC FCs) play a critical role in facilitation of syngeneic and allogeneic hematopoietic stem cell (HSC) engraftment. Here, we evaluated the phenotype and function of CD8(+)/TCR(-) FCs from NOD mice. RESEARCH DESIGN AND METHODS: The phenotype of CD8(+)/TCR(-) FCs was analyzed by flow cytometry using sorted FCs from NOD, NOR, or B6 mice. The function of NOD FCs was evaluated by colony-forming cell (CFC) assay in vitro and syngeneic or allogeneic HSC transplantation in vivo. RESULTS: We report for the first time that NOD FCs are functionally impaired. They fail to facilitate engraftment of syngeneic and allogeneic HSCs in vivo and do not enhance HSC clonogenicity in vitro. NOD FCs contain subpopulations similar to those previously described in B6 FCs, including p-preDC, CD19(+), NK1.1(+)DX5(+), and myeloid cells. However, the CD19(+) and NK1.1(+)DX5(+) subpopulations are significantly decreased in number in NOD FCs compared with disease-resistant controls. Removal of the CD19(+) or NK1.1(+)DX5(+) subpopulations from FCs did not significantly affect facilitation. Notably, Flt3 ligand (FL) treatment of NOD donors expanded FC total in peripheral blood and restored facilitating function in vivo. CONCLUSIONS: These data demonstrate that NOD FCs exhibit significantly impaired function that is reversible, since FL restored production of functional FCs in NOD mice and suggest that FL plays an important role in the regulation and development of FC function. FCs may therefore be linked to diabetes pathogenesis and prevention.