Benjamin Dekel

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.

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection

Humanized BALBu2009/u2009c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen‐loaded dendritic cells together with autologous PBMC from HBV‐naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide‐specific CTL responses against the immunodominant epitope HBc18u2009–u200927 were induced by HBc particle or DNA vaccination of chimera engrafted with HBV‐naive PBMC. Finally, strong HBc‐specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self‐limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in ourmodel and clinical studies.

Antigen-specific B and T cells in human/mouse radiation chimera following immunization in vivo.

Adoptive transfer of human peripheral blood mononuclear cells (PBMC) into mice with severe combined immunodeficiency (SCID) or into lethally irradiated BALB/c mice radioprotected with SCID bone marrow, leads to marked engraftment of human T and B cells. In such chimeras, human serum antibody responses can be stimulated readily by vaccination with recall antigens, but the detection of antigen‐specific functional T or B cells has been extremely difficult. In the present study, we were able to detect by Elispot analysis high frequencies of immunoglobulin G (IgG)‐secreting B cells and mitogen‐responsive interferon‐γ (IFN‐γ) or interleukin‐4 (IL‐4)‐secreting Tu2003cells in peritoneum and spleen of human/BALB/c chimeric mice during the first 3 weeks after PBMC transfer. Moreover, specific memory responses were elicited by vaccination with tetanus toxoid (TT) or hepatitis B virus (HBV) surface (HBs) antigen of chimeric mice transplanted with PBMC derived from TT‐ or HBV‐immune donors. Substantially higher TT‐specific B‐cell frequencies were found during the first 3 weeks after vaccination in mice challenged with the specific antigen compared to the levels found in control animals. High numbers of TT‐specific IFN‐γ‐secreting Tu2003cells persisted in the peritoneum of vaccinated, but not of unvaccinated, animals during the entire observation period, but only low numbers of specific IL‐4‐secreting Tu2003cells were found in vaccinated mice. Similar results were achieved following vaccination with HBs antigen of chimeric mice, transplanted with PBMC of HBV immunized donors. Thus, TT or HBsAg‐specific antibody responses in our model correlate closely with the existence of specific IFN‐γ‐secreting T helper 1/0 cells. Furthermore, these results show that adoptive transfer of human PBMC into lethally irradiated mice provides an efficient approach to generate specific B‐cell fusion partners for the production of human monoclonal antibodies and specific T‐cell lines for adoptive cell therapy of malignant or infectious diseases.

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.

Human/BALB radiation chimera engrafted with splenocytes from patients with idiopathic thrombocytopenic purpura produce human platelet antibodies

We have previously shown that lethally irradiated normal strains of mice, radioprotected with severe combined immunodeficient (SCID) bone marrow, can be engrafted with human peripheral blood mononuclear cells (PBMC). The human/mouse radiation chimera can mount marked humoral and cellular responses to recall antigens, as well as primary responses. In the present study, we adoptively transferred splenocytes from patients with chronic immune thrombocytopenic purpura (ITP) into lethally irradiated BALB/c mice, radioprotected with SCID bone marrow. High titres of total human immunoglobulin appeared as early as 2 weeks post‐transplant and declined after 6 weeks, while human anti‐human platelet antibodies were detected 2–8 weeks after the transfer of splenocytes. The immunoglobulin G (IgG) fraction contained antibodies against glycoprotein (GP) IIb/IIIa (CD41) or GPIb/IX (CD42). The human platelet antibodies showed a low level of cross‐reactivity with mouse platelets, and thrombocytopenia in the animals was not observed. Splenocytes from individual ITP patients differed in their capacity to produce either human platelet antibodies or total human immunoglobulin. Furthermore, antibodies produced in the murine system were not always identical to the original antibodies present in the serum of the patients. The study of the serological aspects of autoantibodies against human platelets in an animal model might be useful for the investigation of potential therapeutics in ITP.

Human/mouse radiation chimera generated from PBMC of B chronic lymphocytic leukemia patients with autoimmune hemolytic anemia produce anti-human red cell antibodies

Previous studies performed in our laboratory have shown that B-CLL cells are involved in the production of anti-red cell auto-antibodies, providing a possible mechanism for the auto-immune hemolytic anemia occurring during the course of B-CLL. In order to confirm this hypothesis, we attempted to transfer human B-CLL with AIHA to immunodeficient mice. Peripheral blood mononuclear cells (PBMC) from 11 B-CLL patients suffering from AIHA were transplanted into the peritoneal cavity of lethally irradiated Balb/c mice reconstituted with SCID bone marrow. Chimeric mice generated from PBMC of these patients (in stage III–IV of the disease) exhibited an engraftment profile with dominance of tumor cells and minuscule levels of T cells. Eighty-five percent of the chimeric mice generated from 10 out of the 11 B-CLL patients with Coombs’-positive AIHA, produced human Ig with anti-human red cell specificity as detected by indirect anti-globulin test. In addition, anti-red cell auto-antibodies were produced in 36% of chimeric mice generated from PBMC of Coombs’-negative B-CLL. In contrast, control experiments in which splenic cells from idiopathic AIHA or PBMC from normal donors were transplanted, failed to produce anti-RBC. This in vivo model further supports the relationship between the B cell expansion and the autoimmune hemolytic process.

Modulation of the immune response by fetal kidney allografts

Abstractu2002Fetal kidneys modulate the allogeneic immune response by a synergistic effect: first, fetal kidney tissue tropism is abrogated by the initial relative lack of adhesion molecules. Second, the reduced expression of major histocompatibility complex (MHC) determinants is less effective in inducing the alloantigen-primed T cell response, which in turn induces the downregulation of Th1 cytokines, β chemokines, and Fas ligand, but spares protective Th2 cytokines, and leads to minimal induction of MHC and adhesion molecules on immature renal parenchymal elements. Thus, at the onset and during this altered rejection process, cellular recruitment to the fetal renal site is less prominent than to the adult renal tissue, and effector cells in the fetal graft are less activated.