Kidney transplantation has been one of the major medical advances of the past 30 years. However, tissue availability remains a major obstacle. This can potentially be overcome by the use of undifferentiated or partially developed kidney precursor cells derived from early embryos and fetal tissue. Here, transplantation in mice reveals the earliest gestational time point at which kidney precursor cells, of both human and pig origin, differentiate into functional nephrons and not into other, non-renal professional cell types. Moreover, successful organogenesis is achieved when using the early kidney precursors, but not later-gestation kidneys. The formed, miniature kidneys are functional as evidenced by the dilute urine they produce. In addition, decreased immunogenicity of the transplants of early human and pig kidney precursors compared with adult kidney transplants is demonstrated in vivo. Our data pinpoint a window of human and pig kidney organogenesis that may be optimal for transplantation in humans.

The relationship between intermembrane spacing, adhesion efficiency, and lateral organization of adhesion receptors has not been established for any adhesion system. We have utilized the CD2 ligand CD48 with two (wild type CD48 (CD48-WT)), four (CD48-CD2), or five (CD48-CD22) Ig-like domains. CD48-WT was 10-fold more efficient in mediating adhesion than CD48-CD2 or CD48-CD22. Electron tomography of contact areas with planar bilayers demonstrated average intermembrane spacing of 12.8 nm with CD48-WT, 14.7 nm with CD48-CD2, and 15.6 nm with CD48-CD22. Both CD48-CD2 and CD48-CD22 chimeras segregated completely from CD48-WT in mixed contact areas. In contrast, CD48-CD2 and CD48-CD22 co-localized when mixed contacts were formed. Confocal imaging of immunological synapses formed between primary T lymphocytes and Chinese hamster ovary cells presenting major histocompatibility complex-peptide complexes, and different forms of CD48 demonstrated that CD48-CD2 and CD48-CD22 induce an eccentric CD2/T cell antigen receptor cluster. We propose that this reorganization of the immunological synapse sequesters the T cell antigen receptor in a location where it cannot interact with its ligand and dramatically reduces T cell sensitivity.

OBJECTIVEDefining an optimal costimulatory blockade–based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice.RESEARCH DESIGN AND METHODSConsidering that anti-CD40L was found to be thrombotic in humans, we sought to test alternative costimulatory blockade agents already in clinical use, including CTLA4-Ig, anti-LFA1, and anti-CD48. These agents were tested in conjunction with T-cell debulking by anti-CD4 and anti-CD8 antibodies or with conventional immunosuppressive drugs. Engraftment and functional development of E42 pig pancreatic tissue was monitored by immunohistology and by measuring pig insulin blood levels.RESULTSFetal pig pancreatic tissue harvested at E42, or even as early as at E28, was fiercely rejected in C57BL/6 mice and in Lewis rats. A novel immune suppression comprising anti-LFA1, anti-CD48, and FTY720 afforded optimal growth and functional development. Cessation of treatment with anti-LFA1 and anti-CD48 at 3 months posttransplant did not lead to graft rejection, and graft maintenance could be achieved for >8 months with twice-weekly low-dose FTY720 treatment. These grafts exhibited normal morphology and were functional, as revealed by the high pig insulin blood levels in the transplanted mice and by the ability of the recipients to resist alloxan induced diabetes.CONCLUSIONSThis novel protocol, comprising agents that simulate those approved for clinical use, offer an attractive approach for embryonic xenogeneic transplantation. Further studies in nonhuman primates are warranted.

Immature dendritic cells (imDCs) can have a tolerizing effect under normal conditions or after transplantation. However, because of the significant heterogeneity of this cell population, it is extremely difficult to study the mechanisms that mediate the tolerance induced or to harness the application of imDCs for clinical use. In the present study, we describe the generation of a highly defined population of imDCs from hematopoietic progenitors and the direct visualization of the fate of TCR-transgenic alloreactive CD4 ؉ and CD8 ؉ T cells after encountering cognate or noncognate imDCs. Whereas CD4 ؉ T cells were deleted via an MHC-independent mechanism through the NO system, CD8 ؉ T-cell deletion was found to occur through a unique MHCdependent, perforin-based killing mechanism involving activation of TLR7 and signaling through Triggering Receptor-1 Expressed on Myeloid cells (TREM-1). This novel subpopulation of perforinexpressing imDCs was also detected in various lymphoid tissues in normal animals and its frequency was markedly enhanced after GM-CSF administration. IntroductionCentral and peripheral tolerance mechanisms are critical for the establishment of a robust immune response that can distinguish between self-and nonself-antigens. Although the majority of self-specific T cells are deleted by negative selection in the thymus, some self-reactive T cells are spared and can reach peripheral organs. 1,2 A wealth of evidence indicates that dendritic cells (DCs) have tolerogenic capacity in their immature state (imDCs). [3][4][5][6][7][8] In the context of allogeneic organ transplantation, infusion of imDCs expressing the relevant MHC-peptide complex can prolong allograft survival in vivo. 7,[9][10][11][12] At the same time, imDCs can become immunogenic on maturation/activation in the presence of a danger signal such as lipopolysaccharide (LPS). However, this simplistic paradigm was recently challenged by the demonstration that fully mature DCs can also induce tolerance under the appropriate conditions, [13][14][15][16][17] suggesting a more complex decision-making process in which the net effect of Ag dose, DC lineage, DC maturation and activation state, and the cytokine milieu at the site of inflammation determine whether immunogenic or tolerogenic DC activity will prevail. 18 The tolerogenic potential of immature or mature DCs can be further extended to the resolution of inflammatory responses to pathogens. 19 Lymphoid organs, including spleen, bone marrow (BM), lymph nodes, and thymus, contain multiple DC subpopulations largely defined by their distinct anatomical location and phenotypes. 20,21 For example, the mouse spleen harbors plasmacytoid DCs (pDCs) and the CD8 ϩ and CD8 Ϫ subsets of classic DCs (cDCs). 20 Apart from the major steady-state dichotomy of differentiation into pDCs versus cDCs, an additional distinct monocyte-derived DC subset with phenotypic characteristics of cDCs is recruited to sites of inflammation. 22 The phenotypic heterogeneity of DCs and growing data on their distinct origins p...