Haploidentical bone marrow transplantation in primary immune deficiency: stem cell selection and manipulation

Since the early 1980s T-cell depletion has allowed haploidentical bone marrow transplantation to be performed in patients with primary immunodeficiency for whom a matched sibling donor was not available, without causing severe graft versus host disease (GVHD). This review article presents the available data in the literature on survival, GVHD, and immune reconstitution in different categories of patients, with special emphasis on the impact of different T-cell depletion methods.

Growth enhancement by embryonic fibroblasts upon cotransplantation of noncommitted pig embryonic tissues with fully committed organs

BACKGROUND

We recently defined the optimal gestational time windows for the transplantation of several embryonic tissues. We showed that the liver and kidney obtained from E28 pig embryos can grow and differentiate normally after transplantation, whereas 1 week earlier in gestation, these tissues develop into teratoma-like structures or fibrotic mass. In this study, we investigated whether cotransplantation of E28 with E21 tissue could control its tumorogenic potential, or alternatively whether the stem cells derived from the earlier tissue contribute to the growth of the more committed one.

METHODS

Pig embryonic precursors from E21 and E28 gestational age were transplanted alone or together, into nonobese diabetic/severe combined immunodeficiency mice, and their growth and differentiation was evaluated by immunohistology. In situ analysis, based on sex disparity between the E21 and E28 tissues, was used to identify the tissue source. In some experiments, mouse embryonic fibroblasts (MEF) were cotransplanted with E28 liver, and their effect was evaluated.

RESULTS

E28 tissues could not abrogate the propensity of the cells within the undifferentiated tissue to form teratoma-like structures. However, E21 kidney or liver tissue markedly enhanced the growth and function of E28 kidney, liver, and heart grafts. Moreover, similar growth enhancement was observed on coimplantation of E28 liver tissue with MEF or on infusion of MEF culture medium, indicating that this enhancement is likely mediated through soluble factors secreted by the fibroblasts.

CONCLUSION

Our results suggest a novel approach for the enhancement of growth and differentiation of transplanted embryonic tissues by the use of soluble factors secreted by embryonic fibroblasts.

Embryonic porcine skin precursors can successfully develop into integrated skin without teratoma formation posttransplantation in nude mouse model

How to improve the wound healing quality of severe burn patients is still a challenge due to lack of skin appendages and rete ridges, no matter how much progress has been made in the fields of either stem cell or tissue engineering. We thus systematically studied the growth potential and differentiation capacity of porcine embryonic skin precursors. Implantation of embryonic skin precursors (PESPs) of different gestational ages in nude mice can generate the integrity skin, including epidermis, dermis and skin appendages, such as sweat gland, hair follicle, sebaceous gland, etc.. PESPs of embryonic day 42 possess the maximal growth potential, while, the safe window time of PESPs transplantation for prevention of teratoma risk is E56 or later. In conclusion, PESPs can form the 3 dimensional structures of skin with all necessary skin appendages. Our data strongly indicate that porcine embryonic skin precursors harvested from E56 of minipig may provide new hope for high-quality healing of extensive burns and traumas.

Impulse conduction and gap junctional remodelling by endothelin-1 in cultured neonatal rat ventricular myocytes

Endothelin-1 (ET-1) is an important contributor to ventricular hypertrophy and failure, which are associated with arrhythmogenesis and sudden death. To elucidate the mechanism(s) underlying the arrhythmogenic effects of ET-1 we tested the hypothesis that long-term (24 hrs) exposure to ET-1 impairs impulse conduction in cultures of neonatal rat ventricular myocytes (NRVM). NRVM were seeded on micro-electrode-arrays (MEAs, Multi Channel Systems, Reutlingen, Germany) and exposed to 50 nM ET-1 for 24 hrs. Hypertrophy was assessed by morphological and molecular methods. Consecutive recordings of paced activation times from the same cultures were conducted at baseline and after 3, 6 and 24 hrs, and activation maps for each time period constructed. Gap junctional Cx43 expression was assessed using Western blot and confocal microscopy of immunofluorescence staining using anti-Cx43 antibodies. ET-1 caused hypertrophy as indicated by a 70% increase in mRNA for atrial natriuretic peptide (P < 0.05), and increased cell areas (P < 0.05) compared to control. ET-1 also caused a time-dependent decrease in conduction velocity that was evident after 3 hrs of exposure to ET-1, and was augmented at 24 hrs, compared to controls (P < 0.01). ET-1 increased total Cx43 protein by approximately 40% (P < 0.05) without affecting non- phosphorylated Cx43 (NP-Cx43) protein expression. Quantitative confocal microscopy showed a approximately 30% decrease in the Cx43 immunofluorescence per field in the ET-1 group (P < 0.05) and a reduced field stain intensity (P < 0.05), compared to controls. ET-1-induced hypertrophy was accompanied by reduction in conduction velocity and gap junctional remodelling. The reduction in conduction velocity may play a role in ET-1 induced susceptibility to arrhythmogenesis.

Pig embryonic pancreatic tissue as a source for transplantation in diabetes: transient treatment with anti-LFA1, anti-CD48, and FTY720 enables long-term graft maintenance in mice with only mild ongoing immunosuppression

OBJECTIVE

Defining an optimal costimulatory blockade-based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice.

RESEARCH DESIGN AND METHODS

Considering 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.

RESULTS

Fetal 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.

CONCLUSIONS

This 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.

Mechanical load induced by glass microspheres releases angiogenic factors from neonatal rat ventricular myocytes cultures and causes arrhythmias

In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 μm, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm², they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-β (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P<0.05) and endothelial cell tube formation by 120% (P<0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias.

Nanoscale increases in CD2-CD48-mediated intermembrane spacing decrease adhesion and reorganize the immunological synapse

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.

Reconstruction of cell lineage trees in mice

The cell lineage tree of a multicellular organism represents its history of cell divisions from the very first cell, the zygote. A new method for high-resolution reconstruction of parts of such cell lineage trees was recently developed based on phylogenetic analysis of somatic mutations accumulated during normal development of an organism. In this study we apply this method in mice to reconstruct the lineage trees of distinct cell types. We address for the first time basic questions in developmental biology of higher organisms, namely what is the correlation between the lineage relation among cells and their (1) function, (2) physical proximity and (3) anatomical proximity. We analyzed B-cells, kidney-, mesenchymal- and hematopoietic-stem cells, as well as satellite cells, which are adult skeletal muscle stem cells isolated from their niche on the muscle fibers (myofibers) from various skeletal muscles. Our results demonstrate that all analyzed cell types are intermingled in the lineage tree, indicating that none of these cell types are single exclusive clones. We also show a significant correlation between the physical proximity of satellite cells within muscles and their lineage. Furthermore, we show that satellite cells obtained from a single myofiber are significantly clustered in the lineage tree, reflecting their common developmental origin. Lineage analysis based on somatic mutations enables performing high resolution reconstruction of lineage trees in mice and humans, which can provide fundamental insights to many aspects of their development and tissue maintenance.

Embryonic porcine liver as a source for transplantation: advantage of intact liver implants over isolated hepatoblasts in overcoming homeostatic inhibition by the quiescent host liver

Cell therapy as an alternative to orthotopic liver transplantation represents a major challenge, since negligible proliferation of isolated hepatocytes occurs after transplantation because of the stringent homeostatic control displayed by the host liver. Thus, different modalities of liver injury as part of the pretransplant conditioning are a prerequisite for this approach. The major objective of the present study was to test whether xenotransplantation of pig fetal liver fragments, in which potential cell-cell and cell-stroma interactions are spared, might afford more robust growth and proliferation compared with isolated pig fetal hepatoblasts. After transplantation into SCID mice, fetal liver tissue fragments exhibited marked growth and proliferation, in the setting of a quiescent host liver, compared with isolated fetal hepatoblasts harvested at the same gestational age (embryonic day 28). The proliferative advantage of fetal pig liver fragments was clearly demonstrated by immunohistochemical and morphometric assays and was observed not only after implantation into the liver but also into extrahepatic sites, such as the spleen and the subrenal capsule. The presence of all types of nonparenchymal liver cells that is crucial for normal liver development and regeneration was demonstrated in the implants. Preservation of the three-dimensional structure in pig fetal liver fragments enables autonomous proliferation of transplanted hepatic cells in the setting of a quiescent host liver, without any requirement for liver injury in the pretransplant conditioning. The marked proliferation and functional maturation exhibited by the pig fetal liver fragments suggests that it could afford a preferable source for transplantation.

Tolerance induction in presensitized bone marrow recipients by veto CTLs: effective deletion of host anti-donor memory effector cells

Veto cells have been defined as cells capable of inducing apoptosis of effector CD8 cells recognizing their disparate MHC Ags. Tolerance induced by donor-type veto cells is desirable, because it is restricted to depletion of anti-donor clones without depletion of other immune specificities. It has been shown that anti-third party CTLs exhibit marked veto activity with reduced capacity to induce graft-vs-host disease, when tested on naive effector cells. However, presensitized T cells could play an important role in graft rejection, and therefore, their sensitivity to veto cells could be critical to the implementation of the latter cells in bone marrow transplantation. To address this question, we compared naive and presensitized TCR transgenic effector CD8 T cells, bearing a TCR against H-2(d). Both cell types exhibited similar predisposition to killing by veto CTLs in vitro, and this killing was dependent in both cell types on Fas-FasL signaling as shown by using Fas-deficient CD8 T cells from (lprx2c) F(1) mice. When tested in a stringent mouse model, in which bone marrow rejection is mediated by adoptively transferred host type T cells into lethally irradiated recipients, veto CTLs were equally effective in overcoming rejection of naive or presensitized host T cells.

From 'megadose' haploidentical hematopoietic stem cell transplants in acute leukemia to tolerance induction in organ transplantation

The first successful demonstration that effective T cell depletion can enable immune reconstitution without causing graft vs. host disease (GVHD) in SCID patients was achieved in 1980 using lectin-separated haploidentical hematopoietic stem cells. Recipients exhibited immune tolerance towards donor antigens with a follow-up of more than 2 decades. In leukemia patients undergoing supralethal radio- and chemotherapy, T cell-depleted transplants are vigorously rejected by residual host T cells; this barrier was first overcome in 1993 by the use of megadose stem cell transplants. This clinical observation can be explained, in part, by the demonstration that cells within the CD34 compartment, as well as their immediate early myeloid progeny, are endowed with veto activity. Engraftment of mismatched hematopoietic stem cells following reduced intensity conditioning, still represents a major challenge. Progress made recently in murine studies by different approaches including the use of new co-stimulatory blockade agents, as well as by tolerance inducing cells such as anti-3rd party veto CTLs, NK T cells, and T regulatory cells, suggests several promising modalities for clinical translation.

Large-scale generation of human allodepleted anti-3rd party lymphocytes

Although adoptive transfer of donor lymphocytes protects from infections and relapse after allogeneic hematopoietic stem cell transplantation in both mice and in men, it is associated with a high risk of graft versus host disease (GvHD) which rises with HLA mismatching and the number of T lymphocytes that are infused. Elimination/reduction of alloreactive donor T lymphocytes is an appealing approach and several strategies have been proposed. Here we describe generation of anti-3rd party T lymphocytes under conditions of IL-2 deprivation and their effects in a pre-clinical murine model. Our results clearly indicated that anti-3rd party T lymphocytes generated on a large scale by means of IL-2 deprivation maintain a broad T cell repertoire, do not proliferate in a mixed lymphocyte reaction and do not cause GvHD in NOD-SCID mice. These anti-3rd party lymphocytes contain a large adaptive T regulatory cell subset which might contribute to in vitro and in vivo immune modulation.

The haploidentical option for high-risk haematological malignancies

Much progress has been made in the clinical, biological and technical aspects of the T-cell-depleted full-haplotype mismatched transplants for acute leukaemia. Our experience demonstrates that infusing a megadose of extensively T-cell-depleted haematopoietic peripheral blood stem cells after an immuno-myeloablative conditioning regimen in acute leukaemia patients ensures sustained engraftment with minimal GvHD without the need of any post-transplant immunosuppressive treatment. Since our first successful pilot study, our efforts have concentrated on developing new conditioning regimens, optimising the graft processing and improving the post-transplant immunological recovery. The results we have so far achieved in more than 200 high-risk acute leukaemia patients show that haploidentical transplantation is now a clinical reality. Because virtually all patients have a mismatched family member, who is immediately available, mismatched transplantation should be offered as a viable option to high-risk acute leukaemia patients who do not have, or cannot find, a matched donor.

Hematopoietic stem cell transplantation across major genetic barriers

The first successful demonstration that effective T cell depletion can enable immune reconstitution without causing graft versus host disease (GVHD) was achieved in 1980 using lectin-separated hematopoietic stem cells. In leukemia patients undergoing supralethal radio- and chemotherapy, T cell-depleted transplants are vigorously rejected by residual host T cells; this barrier was first overcome in 1993 by the use of megadose stem cell transplants. This clinical observation can be explained, in part, by the demonstration that cells within the CD34 compartments, as well as their immediate early myeloid progeny, are endowed with veto activity. Engraftment of mismatched hematopoietic stem cells following reduced intensity conditioning, still represents a major challenge. Progress has been made recently by using anti-3rd party veto CTLs and T regulatory cells.

Correction of hemophilia as a proof of concept for treatment of monogenic diseases by fetal spleen transplantation

Previous clinical attempts to correct genetic deficiencies such as hemophilia or Gaucher disease by transplantation of allogeneic spleen were associated with aggressive graft versus host disease, mediated by mature T cells derived from the donor spleen. We show that a fetal pig spleen harvested at the embryonic day 42 stage, before the appearance of T cells, exhibited optimal growth potential upon transplantation into SCID mice, and the growing tissue expressed factor VIII. Transplantation of embryonic day 42 spleen tissue into hemophilic SCID mice led to complete alleviation of hemophilia within 2-3 months after transplant, as demonstrated by tail bleeding and by assays for factor VIII blood levels. These results provide a proof of principle to the concept that transplantation of a fetal spleen, obtained from a developmental stage before the appearance of T cells, could provide a novel treatment modality for genetic deficiencies of an enzyme or a factor that can be replaced by the growing spleen tissue.

Hematopoietic stem cell transplantation across major genetic barriers: tolerance induction by megadose CD34 cells and other veto cells

Studies in mice and humans demonstrate that transplantation of hematopoietic progenitors in numbers larger than commonly used overcomes major genetic barriers. In vitro studies suggest that veto cells, within the population of hematopoietic progenitors, facilitate this favorable outcome. Tolerance induction can be further enhanced by other veto cells. Perhaps the most potent veto cell is the CD8(+) CTL. However, this cell is also associated with marked GVHD, which can be separated from the veto activity by generating anti-third party CTLs under IL-2 deprivation.

Isolation and characterization of nontubular sca-1+lin- multipotent stem/progenitor cells from adult mouse kidney

Tissue engineering and cell therapy approaches aim to take advantage of the repopulating ability and plasticity of multipotent stem cells to regenerate lost or diseased tissue. Recently, stage-specific embryonic kidney progenitor tissue was used to regenerate nephrons. Through fluorescence-activated cell sorting, microarray analysis, in vitro differentiation assays, mixed lymphocyte reaction, and a model of ischemic kidney injury, this study sought to identify and characterize multipotent organ stem/progenitor cells in the adult kidney. Herein is reported the existence of nontubular cells that express stem cell antigen-1 (Sca-1). This population of small cells includes a CD45-negative fraction that lacks hematopoietic stem cell and lineage markers and resides in the renal interstitial space. In addition, these cells are enriched for beta1-integrin, are cytokeratin negative, and show minimal expression of surface markers that typically are found on bone marrow-derived mesenchymal stem cells. Global gene profiling reveals enrichment for many genes downstream of developmental signaling molecules and self-renewal pathways, such as TGF-beta/bone morphogenic protein, Wnt, or fibroblast growth factor, as well as for those that are involved in specification of mesodermal lineages (myocyte enhancer factor 2A, YY1-associated factor 2, and filamin-beta). In vitro, they are plastic adherent and slowly proliferating and result in inhibition of alloreactive CD8(+) T cells, indicative of an immune-privileged behavior. Furthermore, clonal-derived lines can be differentiated into myogenic, osteogenic, adipogenic, and neural lineages. Finally, when injected directly into the renal parenchyma, shortly after ischemic/reperfusion injury, renal Sca-1(+)Lin(-) cells, derived from ROSA26 reporter mice, adopt a tubular phenotype and potentially could contribute to kidney repair. These data define a unique phenotype for adult kidney-derived cells, which have potential as stem cells and may contribute to the regeneration of injured kidneys.

Multiple imprinted and stemness genes provide a link between normal and tumor progenitor cells of the developing human kidney

Wilms' tumor (WT), the embryonic kidney malignancy, is suggested to evolve from a progenitor cell population of uninduced metanephric blastema, which typically gives rise to nephrons. However, apart from blastema, WT specimens frequently contain cells that have differentiated into renal tubular or stromal phenotypes, complicating their analysis. We aimed to define tumor-progenitor genes that function in normal kidney development using WT xenografts (WISH-WT), in which the blastema accumulates with serial passages at the expense of differentiated cells. Herein, we did transcriptional profiling using oligonucleotide microarrays of WISH-WT, WT source, human fetal and adult kidneys, and primary and metastatic renal cell carcinoma. Among the most significantly up-regulated genes in WISH-WT, we identified a surprising number of paternally expressed genes (PEG1/MEST, PEG3, PEG5/NNAT, PEG10, IGF2, and DLK1), as well as Meis homeobox genes [myeloid ecotropic viral integration site 1 homologue 1 (MEIS1) and MEIS2], which suppress cell differentiation and maintain self-renewal. A comparison between independent WISH-WT and WT samples by real-time PCR showed most of these genes to be highly overexpressed in the xenografts. Concomitantly, they were significantly induced in human fetal kidneys, strictly developmentally regulated throughout mouse nephrogenesis and overexpressed in the normal rat metanephric blastema. Furthermore, in vitro differentiation of the uninduced blastema leads to rapid down-regulation of PEG3, DLK1, and MEIS1. Interestingly, ischemic/reperfusion injury to adult mouse kidneys reinduced the expression of PEG3, PEG10, DLK1, and MEIS1, hence simulating embryogenesis. Thus, multiple imprinted and stemness genes that function to expand the renal progenitor cell population may lead to evolution and maintenance of WT.

Overcoming T cell-mediated rejection of bone marrow allografts by T-regulatory cells: synergism with veto cells and rapamycin

Recently, we have shown that anti-third-party cytotoxic T lymphocytes (CTLs) depleted of alloreactivity against the host are endowed with marked veto activity and can facilitate bone marrow (BM) allografting without graft-versus-host disease. We also demonstrated synergism between rapamycin (RAPA) and the veto cells. CD4(+)CD25(+) T-regulatory (Treg) cells are suppressor cells that can enhance alloengraftment. We investigated whether donor Tregs would be synergistic with veto CTLs and RAPA in augmenting alloengraftment or, conversely, would suppress veto CTL effects. Lethally irradiated C3H mice were transplanted at day 2 after irradiation with Balb-nude BM. Graft rejection was induced by purified host-type T cells infused 1 day prior to BMT. The addition of Tregs led to moderate enhancement of engraftment. RAPA at different doses was synergistic with Tregs. The addition of veto CTLs to Tregs enabled reducing the effective RAPA dose fourfold. Combining all three agents was necessary to overcome rejection at low-dose RAPA. Chimerism analysis at 5 to 9 months revealed a significant presence of host-type cells coexisting with the predominant donor T cells, suggesting that tolerance had been attained. The synergistic effects between Tregs, veto CTLs, and RAPA offer an attractive approach for facilitating alloengraftment.

Embryonic pig pancreatic tissue transplantation for the treatment of diabetes

BACKGROUND

Transplantation of embryonic pig pancreatic tissue as a source of insulin has been suggested for the cure of diabetes. However, previous limited clinical trials failed in their attempts to treat diabetic patients by transplantation of advanced gestational age porcine embryonic pancreas. In the present study we examined growth potential, functionality, and immunogenicity of pig embryonic pancreatic tissue harvested at different gestational ages.

METHODS AND FINDINGS

Implantation of embryonic pig pancreatic tissues of different gestational ages in SCID mice reveals that embryonic day 42 (E42) pig pancreas can enable a massive growth of pig islets for prolonged periods and restore normoglycemia in diabetic mice. Furthermore, both direct and indirect T cell rejection responses to the xenogeneic tissue demonstrated that E42 tissue, in comparison to E56 or later embryonic tissues, exhibits markedly reduced immunogenicity. Finally, fully immunocompetent diabetic mice grafted with the E42 pig pancreatic tissue and treated with an immunosuppression protocol comprising CTLA4-Ig and anti-CD40 ligand (anti-CD40L) attained normal blood glucose levels, eliminating the need for insulin.

CONCLUSIONS

These results emphasize the importance of selecting embryonic tissue of the correct gestational age for optimal growth and function and for reduced immunogenicity, and provide a proof of principle for the therapeutic potential of E42 embryonic pig pancreatic tissue transplantation in diabetes.

Transplantation of Human Hematopoietic Stem Cells into Ischemic and Growing Kidneys Suggests a Role in Vasculogenesis but Not Tubulogenesis

Transplantation of murine bone marrow-derived stem cells has been reported recently to promote regeneration of the injured kidney. We investigated the potential of human adult CD34(+) progenitor cells to undergo renal differentiation once xenotransplanted into ischemic and developing kidneys. Immunostaining with human-specific antibodies for tubular cells (broad-spectrum cytokeratin), endothelial cells (CD31, PECAM), stromal cells (vimentin), and hematopoietic cells (pan-leukocyte CD45) demonstrated that although kidney ischemia enhanced engraftment of human cells, they were mostly hematopoietic cells (CD45(+)) residing in the interstitial spaces. Few other engrafted cells demonstrated an endothelial phenotype (human CD31(+)in morphologically appearing peritubular capillaries), but no evidence of tubular or stromal cells of human origin was found. Upregulation of SDF1 and HIF1 transcript levels in the ischemic kidneys might explain the diffuse engraftment of CD45(+)cells following injury. Similarly, when embryonic kidneys rudiments were co-transplanted with human CD34(+)cells in mice, we found both human CD45(+)and CD31(+)cells in the periphery of the developing renal grafts, whereas parenchymal elements failed to stain. In addition, human CD34(+)cells had no effect on kidney growth and differentiation. This first demonstration of human CD34(+)stem cell transplantation into injured and developing kidneys indicates that these cells do not readily acquire a tubular phenotype and are restricted mainly to hematopoietic and, to a lesser extent, to endothelial lineages. Efforts should be made to identify additional stem cell sources applicable for kidney growth and regeneration.

Tolerance induction by third-party "off-the-shelf" CD4+CD25+ Treg cells

OBJECTIVE

Recent reports have shown that donor or host CD4(+)CD25(+) Treg cells can be used to control GVHD or graft rejection following allogeneic BMT in mice. In the present study we investigated the potential of third-party Treg cells compared to donor-type cells to facilitate BM allografting.

METHODS

Graft rejection is assessed in a mouse model of T cell-mediated BM allograft rejection. Lethally irradiated C3H mice are transplanted at day 2 after irradiation with T cell-depleted Balb/Nude BM. Graft rejection is induced by purified host-type T cells infused one day prior to BMT. Cells tested for their facilitating activity are added to the T cell-depleted BM allograft.

RESULTS

Naïve or ex vivo-expanded third-party Treg cells can effectively enhance engraftment of T cell-depleted BM allografts, exhibiting reactivity in vitro and in vivo similar to that found for donor-type Treg cells.

CONCLUSION

The use of third-party Treg cells in contrast to donor-type cells could allow advanced preparation of a large bank of Treg cells (off-the-shelf), with all the appropriate quality controls required for cell therapy.