Aseda Tena

Results of Gal-Knockout porcine thymokidney xenografts

Clinical transplantation for the treatment of end‐stage organ disease is limited by a shortage of donor organs. Successful xenotransplantation could immediately overcome this limitation. The development of homozygous α1,3‐galactosyltransferase knockout (GalT‐KO) pigs removed hyperacute rejection as the major immunologic hurdle to xenotransplantation. Nevertheless, GalT‐KO organs stimulate robust immunologic responses that are not prevented by immunosuppressive drugs. Murine studies show that recipient thymopoiesis in thymic xenografts induces xenotolerance. We transplanted life‐supporting composite thymokidneys (composite thymus and kidneys) prepared in GalT‐KO miniature swine to baboons in an attempt to induce tolerance in a preclinical xenotransplant model. Here, we report the results of seven xenogenic thymokidney transplants using a steroid‐free immunosuppressive regimen that eliminated whole‐body irradiation in all but one recipient. The regimen resulted in average recipient survival of over 50 days. This was associated with donor‐specific unresponsiveness in vitro and early baboon thymopoiesis in the porcine thymus tissue of these grafts, suggesting the development of T‐cell tolerance. The kidney grafts had no signs of cellular infiltration or deposition of IgG, and no grafts were lost due to rejection. These results show that xenogeneic thymus transplantation can support early primate thymopoiesis, which in turn may induce T‐cell tolerance to solid organ xenografts.

In vivo imaging of autologous islet grafts in the liver and under the kidney capsule in non-human primates

Objective. As islet transplantation begins to show promise as a clinical method, there is a critical need for reliable, noninvasive techniques to monitor islet graft survival. Previous work in our laboratory has shown that human islets labeled with a superparamagnetic iron oxide contrast agent and transplanted into mice could be detected by magnetic resonance imaging (MRI). The potential translation of these findings to the clinical situation requires validation of our methodology in a non-human primate model, which we have now carried out in baboons (Papio hamadryas) and reported here. Research Design and Methods. For islet labeling, we adapted the Food and Drug Administration-approved superparamagnetic iron oxide contrast agent, Feridex, which is used clinically for liver imaging. After partial pancreatectomy, Feridex-labeled islets were prepared and autotransplanted underneath the renal capsule and into the liver. Longitudinal in vivo MRI at days 1, 3, 8, 16, 23, and 30 after transplantation was performed to track the islet grafts. Results. The renal subcapsular islet graft was easily detectable on T2*-weighted MR images as a pocket of signal loss disrupting the contour of the kidney at the transplantation site. Islets transplanted in the liver appeared as distinct signal voids dispersed throughout the liver parenchyma. A semiautomated computational analysis of our MRI data established the feasibility of monitoring both the renal and intrahepatic grafts during the studied posttransplantation period. Conclusion. This study establishes a method for the noninvasive, longitudinal detection of pancreatic islets transplanted into non-human primates using a low-field clinical MRI system.

Transgenic Expression of Human CD47 Markedly Increases Engraftment in a Murine Model of Pig-to-Human Hematopoietic Cell Transplantation

Mixed chimerism approaches for induction of tolerance of solid organ transplants have been applied successfully in animal models and in the clinic. However, in xenogeneic models (pig‐to‐primate), host macrophages participate in the rapid clearance of porcine hematopoietic progenitor cells, hindering the ability to achieve mixed chimerism. CD47 is a cell‐surface molecule that interacts in a species‐specific manner with SIRPα receptors on macrophages to inhibit phagocytosis and expression of human CD47 (hCD47) on porcine cells has been shown to inhibit phagocytosis by primate macrophages. We report here the generation of hCD47 transgenic GalT‐KO miniature swine that express hCD47 in all blood cell lineages. The effect of hCD47 expression on xenogeneic hematopoietic engraftment was tested in an in vivo mouse model of human hematopoietic cell engraftment. High‐level porcine chimerism was observed in the bone marrow of hCD47 progenitor cell recipients and smaller but readily measurable chimerism levels were observed in the peripheral blood of these recipients. In contrast, transplantation of WT progenitor cells resulted in little or no bone marrow engraftment and no detectable peripheral chimerism. These results demonstrate a substantial protective effect of hCD47 expression on engraftment and persistence of porcine cells in this model, presumably by modulation of macrophage phagocytosis.

Combining miR-10b–Targeted Nanotherapy with Low-Dose Doxorubicin Elicits Durable Regressions of Metastatic Breast Cancer

The therapeutic promise of microRNA (miRNA) in cancer has yet to be realized. In this study, we identified and therapeutically exploited a new role for miR-10b at the metastatic site, which links its overexpression to tumor cell viability and proliferation. In the protocol developed, we combined a miR-10b-inhibitory nanodrug with low-dose anthracycline to achieve complete durable regressions of metastatic disease in a murine model of metastatic breast cancer. Mechanistic investigations suggested a potent antiproliferative, proapoptotic effect of the nanodrug in the metastatic cells, potentiated by a cell-cycle arrest produced by administration of the low-dose anthracycline. miR-10b was overexpressed specifically in cells with high metastatic potential, suggesting a role for this miRNA as a metastasis-specific therapeutic target. Taken together, our results implied the existence of pathways that regulate the viability and proliferation of tumor cells only after they have acquired the ability to grow at distant metastatic sites. As illustrated by miR-10b targeting, such metastasis-dependent apoptotic pathways would offer attractive targets for further therapeutic exploration.

Prolonged Survival of Pig Skin on Baboons After Administration of Pig Cells Expressing Human CD47.

BackgroundSuccessful xenotransplantation will likely depend, in part, on the induction of immunological tolerance, because the high levels of immunosuppression otherwise required would likely have unacceptable side effects. Rapid clearance of administered porcine hematopoietic stem cells by primate macrophages has hampered previous attempts to induce tolerance through mixed hematopoietic chimerism across a pig-to-primate barrier. Phagocytosis is normally inhibited by binding of cell surface protein CD47 to macrophage signal regulatory protein &agr; receptors. However, pig CD47 has previously been shown to be ineffective in transducing signals through primate signal regulatory protein &agr;. MethodsMobilized peripheral blood hematopoietic cells from transgenic swine expressing high or low levels of human CD47 were infused into conditioned baboons at 3 time points over a 9-week period. Xenogeneic peripheral blood chimerism was assessed after each infusion. Split thickness skin grafts from the hematopoietic cell donor swine were placed on recipients 5 weeks after the last cell infusion and 7 weeks after the discontinuation of all immunosuppression to test immune response. ResultsThe level and duration of transient chimerism were substantially greater in baboons receiving hematopoietic cells from a pig expressing high levels of human CD47. Skin graft survival on high CD47 recipients was prolonged as well, in 1 case showing no signs of rejection at least 53 days after placement. ConclusionsProlongation of transient porcine chimerism via transgenic expression of human CD47 in a primate model is associated with an immune modulating effect, leading to markedly prolonged survival of donor swine skin xenografts that may be applicable to clinical solid organ xenotransplantation.

High Incidence of Xenogenic Bone Marrow Engraftment in Pig-to-Baboon Intra-Bone Bone Marrow Transplantation

Previous attempts of α‐1,3‐galactocyltransferase knockout (GalTKO) pig bone marrow (BM) transplantation (Tx) into baboons have demonstrated a loss of macro‐chimerism within 24 h in most cases. In order to achieve improved engraftment with persistence of peripheral chimerism, we have developed a new strategy of intra‐bone BM (IBBM) Tx. Six baboons received GalTKO BM cells, with one‐half of the cells transplanted into the bilateral tibiae directly and the remaining cells injected intravenously (IBBM/BM‐Tx) with a conditioning immunosuppressive regimen. In order to assess immune responses induced by the combined IBBM/BM‐Tx, three recipients received donor SLA‐matched GalTKO kidneys in the peri‐operative period of IBBM/BM‐Tx (Group 1), and the others received kidneys 2 months after IBBM/BM‐Tx (Group 2). Peripheral macro‐chimerism was continuously detectable for up to 13 days (mean 7.7 days; range 3–13) post‐IBBM/BM‐Tx and in three animals, macro‐chimerism reappeared at days 10, 14 and 21. Pig CFUs, indicating porcine progenitor cell engraftment, were detected in the host BM in four of six recipients on days 14, 15, 19 and 28. In addition, anti‐pig unresponsiveness was observed by in vitro assays. GalTKO/pCMV‐kidneys survived for extended periods (47 and 60 days). This strategy may provide a potent adjunct for inducing xenogeneic tolerance through BM‐Tx.

Reversal of age-related thymic involution by an LHRH agonist in miniature swine.

UNLABELLED BACKGROUND AND AIMS OF STUDY: We have previously demonstrated a requirement for the presence of a juvenile thymus for the induction of transplantation tolerance to renal allografts by a short-course of calcineurin inhibition in miniature swine. We have also shown that aged, involuted thymi can be rejuvenated when transplanted as vascularized thymic lobes into juvenile swine recipients. The present studies were aimed at elucidating the extrinsic factors facilitating this restoration of function in the aged thymus. In particular, we tested the impact of sex steroid blockade by Luteinizing Hormone-Releasing Hormone (LHRH). MATERIALS AND METHODS 30 naive animals (25 males and 5 females) were used for measurement of serum testosterone levels. 3 mature male pigs (aged at 22, 22 and 29 months old) were used to test the effects of Lupron (LHRH analog) injection at 45 mg (per 70-80 kg body weight) as a 3-month depot on testosterone levels and thymic rejuvenation. Thymic rejuvenation was assessed by histology, flow cytometric analysis, morphometric analysis and TREC assays. RESULTS Hormonal alterations were induced by Lupron and resulted in macroscopic and histologic regeneration of the thymus of aged animals within 2 months, as evidenced by restoration of juvenile thymus architecture and increased cellularity. Two animals that were evaluated for TREC both showed increased levels in the periphery following Lupron treatment. CONCLUSION Treatment of aged animals with Lupron leads to thymic rejuventaion in adult miniature swine. This result could expand the applicability of thymus-dependent tolerance-inducing regimens to adult recipients.

Stem Cells: Immunology and Immunomodulation

Multipotent progenitor cells have the ability to differentiate in vitro into tissue-specific cells under the proper cellular signaling conditions. Because of this intrinsic property, pluripotent derived stem cells from embryonic tissues, induced from genetic reprogramming of somatic cells or from mesenchymal cells, have become the focus of many regenerative medicine studies directed toward application to clinical settings. Generation of retinal pigment epithelium derived from patient-specific, induced pluripotent stem cells may create the ability to recapitulate the disease state and screen new therapeutics, improving upon the limited treatment strategies currently available for afflicted patients. However, the method of delivery, cell culture differentiation, and immunological rejection are some of the limitations that continue to influence ongoing attempts for clinical applications. Understanding stem cell properties and the immune responses these cells elicit in vitro and in vivo will be of importance for designing successful protocols to overcome these immunological limitations. This chapter examines the immunological and immunomodulatory properties of multipotent stem cells in an attempt to provide insights for successful cellular transplantation.

Quantification of baboon thymopoiesis in porcine thymokidney xenografts by the signal-joining T-cell receptor excision circle assay.

Background. Transplantation of vascularized donor thymic tissue along with a kidney transplant has markedly improved graft survival across the discordant pig-to-baboon xenogeneic barrier. To quantify the production of baboon T cells by the porcine thymic tissue, we recently developed an assay to measure the excised DNA products of baboon T-cell receptor (TCR) gene rearrangement (signal-joining TCR excision circles, sjTREC). Methods. Initial polymerase chain reaction (PCR) analysis documented that TCR &dgr;REC-&psgr;J&agr; rearrangement occurs in baboons. Primers, specific to baboon sjTREC sequence were designed and used to quantify sjTREC molecules in peripheral blood mononuclear cells and thymic tissue using a quantitative PCR assay. Results. sjTREC levels were higher in phenotypically naïve (CD3+CD45RA++) T cells (650 copies/100,000 cells) than in phenotypically memory (CD3+CD45RAlow) T cells, with sjTREC below the limit of detection (40 copies/100,000 cells). Surgical removal of the native thymus in two baboons led to a significant decrease of sjTREC in peripheral blood (from 1104 and 920 copies to 184 and 190 copies/100,000 cells, respectively), confirming the role of the thymus in maintaining the peripheral T-cell pool. In two thymectomized baboons that received porcine thymokidney xenografts, sjTREC levels remained low in the peripheral blood (<40 copies/100,000 cells), but increased to 52 and 192 copies/100,000 cells in thymic biopsies, implying that baboon thymopoiesis had begun to occur in the porcine thymic xenografts. Conclusions. Baboon sjTREC can be quantified by quantitative PCR using primers specific to baboon sequence. Initial results suggest that baboon thymopoiesis occurs in vascularized porcine thymus xenografts.

Monitoring of Allogeneic Islet Grafts in Nonhuman Primates Using MRI.

Background Information regarding the longevity of transplanted pancreatic islet grafts could provide valuable information for treatment options. In our previous studies, we showed that isolated autologous pancreatic islets could be labeled with iron oxide nanoparticles and monitored after transplantation using MRI. Here, we report on in vivo monitoring of a secondary damage that occurs at the later stages because of allogeneic immune rejection. Methods In the proof-of-principle studies, iron oxide-labeled autologous pancreatic islets were transplanted under the renal capsules of nonhuman primates. To demonstrate acute graft loss, the animals were injected with streptozotocin. Graft monitoring was performed by in vivo MRI. Next, iron oxide-labeled allogeneic islets were transplanted into the liver and monitored by MRI after withdrawal of immunosuppression. Results In autologous model, we observed a pronounced drop in graft volume after streptozotocin challenge as assessed by MRI. In allogeneic model of islet transplantation, there was an initial islet loss after the procedure followed by relative stabilization of the graft volume. After immunosuppression was discontinued, there was a noticeable drop in graft volume that gradually continued during the course of the study. Importantly, the loss of graft volume observed on MR preceded the raise in blood glucose. Conclusions This study demonstrated that in vivo MRI was able to reveal graft volume loss before any changes in blood glucose that can be measured by standard methods. We believe that these results could provide means for clinicians to follow islet fate noninvasively and longitudinally using clinically relevant scanners.