Abstract: Mixed chimerism induces donor-specific transplantation tolerance to organ allografts. Strategies to establish mixed chimerism using partial conditioning having significantly reduced the morbidity associated with conditioning. The donor hematopoietic cell lineage(s) responsible for the induction and subsequent maintenance of tolerance in partially conditioned recipients are not defined at present. As one approaches the threshold for nonmyeloablative conditioning, donor factors that influence the induction of tolerance have become apparent. In this invention, recipient B10 (H2b) mice were pretreated in vivo with anti-??-TCR and anti-CD8 mAbs 3 days before TBI (day 0) and transplanted with 15×106 allogeneic (B10.BR;H2k) marrow cells. Engraftment occurred in 20%, 75% and 94% of animals conditioned with 100, 200 or 300 cGy TBI once month post BMT, respectively.

Abstract: CD8+/TCR? bone marrow cells facilitate engraftment of hemapoietic stem cells (HSQ in allogeneic recipients without causing graft versus host disease. The present invention identifies the main subpopulation (55-65%) of CD8+/TCR? facilitating cells (FQ as plasmacytoid precursor dendritic cells (p-preDC). The present invention notably demonstrates that FC and p-preDC share many phenotypic, morphological, functional features, including IFN-? production, activation and survival after stimulation, and expansion and maturation after FIO-Ligand (FL) treatment. FL mobilized FC, the majority of which express a pre-DC phenotype, facilitate HSC engraftment. Although p-preDC significantly enhance HSC engraftment, they do so with less efficiency than FC. The present invention for the first time defines a direct functional role for p-preDC in HSC engraftment and will have a significant impact on strategies to design effective facilitating cell-based therapies for transplantation.

Abstract: The invention provides for methods of screening for compounds that increase the expression of P-selectin, SDF-1, and/or CXCR4 on facilitatory cells (FCs). The invention also provides for methods of screening for compounds that increase the level of p-predendritic cells (p-pre DC) without substantially decreasing the level of natural killer (NK) cells in a population of FCs. The invention further provides for methods of characterizing the facilitating capability of FCs by evaluating such cells for the amount of P-selectin, SDF-1, and/or CXCR4.

Abstract: This invention provides a method of achieving a higher rate of allogeneic hematopoietic stem cell engraftment by either (i) matching the major histocompatibility complex class I K locus between donors and recipients or (ii) identifying how class I K on HSC interact with FC (CD8/33Kd receptor complex) works thus allowing one to bypass the need for FC. The MHC loci which are essential for curable engraftment of purified allogeneic HSC are identified by the methods of this invention. This invention further demonstrates that the MHC class I K molecule is essential for maintaining the self-renewal capability of purified HSC. Moreover, interaction between the HSC and FC via the MHC class I K molecule provides a regulatory function to promote engraftment and survival of allogeneic HSC.

Abstract: This invention demonstrates that FC function via TNF-? to affect function of HSC. FC from TNF-? deficient mice are impaired in facilitating HSC engraftment in both the syngeneic and allogeneic models. Co-incubation of FC with HSC results in significant increase in TNF-? at the mRNA and protein level, and increase in transcript for Bcl-3 in HSC. Furthermore, neutralization of TNF-? results in the loss of FC ability to increase HSC clonogenicity and survival, as well as to upregulate Bcl-2 transcript in HSC, demonstrating a critical role for TNF-? in FC function. These results offer a mechanism of action for HSC regulation by accessory cells in the bone marrow and confirm the advantage of their co-transplantation with HSC to improve graft efficiency.

Abstract: The present invention provides for cellular compositions which facilitate engraftment of hematopoietic stem cells from a syngeneic, allogeneic or xenogeneic donor. The cellular compositions of the invention facilitate engraftment while minimizing the risk of graft versus host disease in the graft recipient. According to a preferred embodiment of the invention, a cell composition is provided, which cell composition comprises hematopoietic stem cells, such as CD34+ cells and/or facilitating cells, in combination with ?? TCR+ T cells. The invention also relates to methods of using the cellular compositions of the invention to induce donor specific tolerance in a recipient, thus allowing the transplantation of donor organs, cells and tissues. Also disclosed are methods of treating leukemia and cancer as well as infectious diseases caused by viruses.