Biomedical subjects
D K Cooper
Publications and source records attributed to D K Cooper.
Pig hematopoietic cell chimerism in baboons conditioned with a nonmyeloablative regimen and CD154 blockade.
BACKGROUND: In an attempt to induce mixed hematopoietic chimerism and transplantation tolerance in the pig-to-primate model, we have infused high-dose porcine peripheral blood progenitor cells (PBPC) into baboons pretreated with a nonmyeloablative regimen and anti-CD154 monoclonal antibody (mAb). METHODS: Group 1 baboons (n=2) received a nonmyeloablative regimen including whole body irradiation, pharmacological immunosuppression, porcine hematopoietic growth factors, and immunoadsorption of anti-Galalpha1,3Gal (Gal) antibody before infusion of high doses of PBPC (2.7-4.6x10(10) cells/kg). In group 2 (n=5), cyclosporine was replaced by anti-CD154 mAb. Group 3 (n=3) received the group 1 regimen plus anti-CD154 mAb. RESULTS: In group 1, pig chimerism was detected in the blood by flow cytometry (FACS) for 5 days (with a maximum of 14%), and continuously up to 13 days by polymerase chain reaction (PCR). In group 2, pig chimerism was detectable for 5 days by FACS (maximum 33%) and continuously up to 28 days by PCR. In group 3, initial pig chimerism was detectable for 5 days by FACS (maximum 73%). Two of three baboons showed reappearance of pig cells on days 11 and 16, respectively. In one, in which no anti-Gal IgG could be detected for 30 days, pig cells were documented in the blood by FACS on days 16-22 (maximum 6% on day 19) and pig colony-forming cells were present in the blood on days 19-33, which we interpreted as evidence of engraftment. Microchimerism was continuous by PCR up to 33 days. CONCLUSIONS: These results suggest that there is no absolute barrier to pig hematopoietic cell engraftment in primates, and that this may be facilitated if the return of anti-Gal IgG can be prevented.
Transplantation of islets of Langerhans: new developments.
The clinical results recently reported by the Edmonton group in recipients of allogeneic islet grafts, all of whom achieved at least temporary insulin independence, has rekindled interest in transplantation of islets of Langerhans as a means to cure diabetes. Long-term islet graft survival has been achieved in a non-human primate pre-clinical model with a protocol of T-cell signaling blockade using a new monoclonal antibody. Islet xenotransplantation (namely the use of animal islets, with the aim of transplanting them into humans), or stem cell technology (the controlled differentiation of stem cells to obtain specialised cells for the treatment of diabetes) are other procedures currently being evaluated in animal models. The recent clinical success suggests that, in the near future, diabetes might be treated by islet transplantation early in the clinical course of the disease before the development of complications, and without the risks associated with conventional immunosuppression.
Pig kidney transplantation in baboons: anti-Gal(alpha)1-3Gal IgM alone is associated with acute humoral xenograft rejection and disseminated intravascular coagulation.
BACKGROUND: Kidneys harvested from miniature swine or pigs transgenic for human decay-accelerating factor (hDAF) were transplanted into baboons receiving an anti-CD154 monoclonal antibody (mAb) and either a whole body irradiation (WBI)- or cyclophosphamide (CPP)-based immunosuppressive regimen. METHODS: Group 1 baboons (n=3) underwent induction therapy with WBI and thymic irradiation, pretransplantation antithymocyte globulin, and immunoadsorption of anti-Gal(alpha)1-3Gal (Gal) antibody (Ab). After transplantation of a miniature swine kidney, maintenance therapy comprised cobra venom factor, mycophenolate mofetil, and an anti-CD154 mAb (for 14-28 days). In group 2 (n=2), WBI was replaced by CPP in the induction protocol. Group 3 (n=3) animals received the group 2 regimen, but underwent transplantation with hDAF pig kidneys. RESULTS: Group 1 and 2 animals developed features of disseminated intravascular coagulation (DIC), with reductions of fibrinogen and platelets and increases of prothrombin time, partial thromboplastin time, and fibrin split products. Graft survival was for 6-13 days. Histology showed mild acute humoral xenograft rejection (AHXR) of the kidneys, but severe rejection of the ureters. Group 3 animals developed features of DIC in two of three cases during the fourth week, with AHXR in the third case. Graft survival was for 28 (n=1) or 29 (n=2) days. Histology of day 15 biopsy specimens showed minimal focal mononuclear cellular infiltrates, with predominantly CD3+ cells. By days 28 and 29, kidneys showed mild-to-moderate features of AHXR. In all groups, the humoral response was manifest by reappearance of anti-Gal IgM below baseline level, with no or low return of anti-Gal IgG. All excised kidneys showed IgM deposition, but no complement and no or minimal IgG deposition. No baboon showed a rebound of anti-Gal Ab immediately after excision of the graft, and anti-Gal Ab increased over pretransplantation levels only when anti-CD154 mAb was discontinued. CONCLUSIONS: DIC was observed with WBI- or CPP-based therapy, and after miniature swine or hDAF kidney transplantation. AHXR+/-DIC was observed in all recipients even in the absence of complement and no or low levels of anti-Gal IgG, but was significantly delayed in the hDAF recipients. These results confirm our earlier observation that CD154 blockade prevents T cell-dependent sensitization in baboons to pig antigens, but that baseline natural anti-Gal Ab production is not inhibited. We suggest that IgM deposition, even in the absence of IgG and complement, leads to endothelial cell activation with the development of DIC, even when there are only minimal histologic changes of AHXR.
CD40-CD154 pathway blockade requires host macrophages to induce humoral unresponsiveness to pig hematopoietic cells in baboons.
The effect of CD154 blockade and macrophage depletion or inhibition on baboon humoral and cellular immune responses to pig antigens was studied in a pig-to-baboon peripheral blood mobilized progenitor cell (PBPC) transplantation model aimed at inducing tolerance. We infused pig PBPCs in baboons pretreated with a nonmyeloablative regimen along with murine anti-human CD154 monoclonal antibody (mAb) and macrophage-depleting or -inhibiting agents. Group 1 baboons (n=2) underwent a nonmyeloablative regimen and immunoadsorption of anti-Gal(alpha)1,3Gal (Gal) antibody (Ab) before intravenous infusion of high doses (1.3-4.6 x 10(10)cells/kg) of PBPCs. In group 2 (n=5), cyclosporine was replaced by 8 doses of anti-CD154 mAb over 14 days. Group 3 (n=3) received the group 2 regimen plus medronate liposomes (n=2) or commercially available human intravenous immunoglobulin G depleted of anti-Gal Ab (n=1) to deplete/inhibit recipient macrophages. Group 1 developed sensitization to Gal and also developed new Ab to non-Gal porcine antigens within 10 to 20 days. In group 2, no sensitization to Gal or non-Gal determinants was seen, but Gal-reactive antibodies did return to their preleukocyte transplantation levels. CD154 blockade, therefore, induced humoral unresponsiveness to pig cells. In group 3, sensitization to Gal was seen in all three baboons at 20 days, and Abs against new porcine determinants developed in one baboon. The depletion or inhibition of host macrophages, therefore, prevented the induction of humoral unresponsiveness by CD154 blockade. These results suggest that CD154 blockade induces humoral unresponsiveness by a mechanism that involves the indirect pathway of antigen presentation. In vitro investigation of baboon anti-pig mixed lymphocyte reaction confirmed that only the indirect pathway is efficiently blocked by anti-CD154 mAb. The mechanism in which blockade of the CD40-CD154 pathway induces its effect remains to be determined, but it could involve the generation of regulatory cells capable of suppressing the direct pathway.
Clearance of mobilized porcine peripheral blood progenitor cells is delayed by depletion of the phagocytic reticuloendothelial system in baboons.
INTRODUCTION: Attempts to achieve immunological tolerance to porcine tissues in nonhuman primates through establishment of mixed hematopoietic chimerism are hindered by the rapid clearance of mobilized porcine leukocytes, containing progenitor cells (pPBPCs), from the circulation. Eighteen hours after infusing 1-2 x 10(10) pPBPC/kg into baboons that had been depleted of circulating anti-alphaGal and complement, these cells are almost undetectable by flow cytometry. The aim of the present study was to identify mechanisms that contribute to rapid clearance of pPBPCs in the baboon. This was achieved by depleting, or blocking the Fc-receptors of, cells of the phagocytic reticuloendothelial system (RES) using medronate liposomes (MLs) or intravenous immunoglobulin (IVIg), respectively. METHODS: Baboons (preliminary studies, n=4) were used in a dose-finding and toxicity study to assess the effect of MLs on macrophage depletion in vivo. In another study, baboons (n=9) received a nonmyeloablative conditioning regimen (NMCR) aimed at inducing immunological tolerance, including splenectomy, whole body irradiation (300 cGy) or cyclophosphamide (80 mg/kg), thymic irradiation (700 cGy), T-cell depletion, complement depletion with cobra venom factor, mycophenolate mofetil, anti-CD154 monoclonal antibody, and multiple extracorporeal immunoadsorptions of anti-alphaGal antibodies. The baboons were divided into three groups: Group 1 (n=5) NMCR+pPBPC transplantation; Group 2 (n=2) NMCR+ML+pPBPC transplantation; and Group 3 (n=2) NMCR+IVIg+pPBPC transplantation. Detection of pig cells in the blood was assessed by fluorescence-activated cell sorter and polymerase chain reaction (PCR). RESULTS PRELIMINARY STUDIES: ML effectively depleted macrophages from the circulation in a dose-dependent manner. Group 1: On average, 14% pig cells were detected 2 hr postinfusion of 1 x 10(10) pPBPC/kg. After 18 hr, there were generally less than 1.5% pig cells detectable. Group 2: Substantially higher levels of pig cell chimerism (55-78%) were detected 2 hr postinfusion, even when a smaller number (0.5-1 x 10(10)/kg) of pPBPCs had been infused, and these levels were better sustained 18 hr later (10-52%). Group 3: In one baboon, 4.4% pig cells were detected 2 hr after infusion of 1 x 10(10) pPBPC/kg. After 18 hr, however, 7.4% pig cells were detected. A second baboon died 2 hr after infusion of 4 x 10(10) pPBPC/kg, with a total white blood cell count of 90,000, of which 70% were pig cells. No differences in microchimerism could be detected between the groups as determined by PCR. CONCLUSIONS: This is the first study to report an efficient decrease of phagocytic function by depletion of macrophages with MLs in a large-animal model. Depletion of macrophages with MLs led to initial higher chimerism and prolonged the survival of circulating pig cells in baboons. Blockade of macrophage function with IVIg had a more modest effect. Cells of the RES, therefore, play a major role in clearing pPBPCs from the circulation in baboons. Depletion or blockade of the RES may contribute to achieving mixed hematopoietic chimerism and induction of tolerance to a discordant xenograft.
Modulation of platelet aggregation in baboons: implications for mixed chimerism in xenotransplantation. I. The roles of individual components of a transplantation conditioning regimen and of pig peripheral blood progenitor cells.
BACKGROUND: The induction of tolerance to pig antigens in primates may facilitate the development of successful clinical xenotransplantation protocols. The infusion of mobilized porcine peripheral blood leukocytes (PBPCs, comprised of approximately 2% peripheral blood progenitor cells) into splenectomized preconditioned baboons, intended to induce mixed hematopoietic cell chimerism, however, results in a severe thrombotic microangiopathy (TM) that includes pronounced thrombocytopenia. Because the mechanisms responsible for this phenomenon are unclear, we have explored the effects of individual components of the conditioning regimen, of therapeutic adjuncts, and of PBPCs on platelet aggregation. METHODS: Groups of splenectomized baboons (n = at least 2 in each group) were treated with single components of the conditioning regimen--whole body irradiation (WBI), antithymocyte globulin (ATG), extracorporeal immunoadsorption (EI), mycophenolate mofetil (MMF), anti-CD40L monoclonal antibody (mAb), cobra venom factor (CVF), pig hematopoietic growth factors (interleukin-3 (pIL3) and stem cell factor (pSCF))--or with potential adjuncts, prostacyclin (PGI2), heparin, methylprednisolone, and eptifibatide (a GPIIb/IIIa antagonist). Blood samples were collected and platelet-rich plasma (PRP) was prepared. Using light transmission aggregometry, the extent of aggregation induced by platelet agonists (thrombin, adenosine diphosphate (ADP), collagen, ristocetin, and arachidonic acid) was determined in vitro. PRP was also prepared from untreated baboons, PBPCs were added, and platelet aggregation was measured in the absence of exogenous platelet agonists. RESULTS: WBI, ATG, MMF, anti-CD40L mAb, CVF, pIL3, pSCF, and PGI2 had no effect on purified baboon platelet aggregation profiles in vitro. Eptifibatide markedly inhibited platelet aggregation induced by all standard agonists. EI or heparin inhibited thrombin-induced platelet aggregation, and methylprednisolone inhibited ADP-induced aggregation to some extent. In vitro addition of PBPCs to PRP stimulated platelet aggregation in the absence of any agonists. Prior treatment of baboons with eptifibatide, however, inhibited this effect by 70% to 80%. CONCLUSIONS: Aggregation of baboon platelets and TM is directly induced by PBPCs, but not by individual components of the conditioning regimen. GPIIb/IIIa antagonists, such as eptifibatide, interfere directly with xenogeneic PBPC-platelet interactions and may further ameliorate TM in the pig-to-primate model.
Modulation of platelet aggregation in baboons: implications for mixed chimerism in xenotransplantation. II. The effects of cyclophosphamide on pig peripheral blood progenitor cell-induced aggregation.
BACKGROUND: The induction of tolerance to pig antigens in primates may facilitate the development of successful clinical xenotransplantation protocols. The infusion of mobilized porcine peripheral blood leukocytes (PBPCs, comprised of approximately 2% peripheral blood progenitor cells) into splenectomized preconditioned (whole body irradiation (WBI)-based) baboons, intended to induce mixed hematopoietic cell chimerism, however, results in a severe thrombotic microangiopathy (TM) that includes pronounced thrombocytopenia. Previous studies have indicated that the infused PBPCs initiate platelet aggregation, but that the various individual components of the conditioning regimen are not associated with the development of aggregation. We have now investigated the effects of cyclophosphamide (CPP) as an alternative to WBI on platelet aggregation. METHODS: Splenectomized baboons (n=3) were treated with CPP. Blood samples were collected and platelet-rich plasma (PRP) was prepared. Using light transmission aggregometry, the extent of aggregation induced by platelet agonists (thrombin, adenosine diphosphate (ADP), collagen, ristocetin, and arachidonic acid) was determined in vitro. PRP was also prepared from untreated baboons and from baboons receiving CPP, PBPCs were added, and platelet aggregation was measured in the absence of exogenous platelet agonists. RESULTS: CPP markedly inhibited platelet aggregation induced by all standard agonists. In vitro addition of PBPCs to PRP stimulated platelet aggregation in the absence of any agonists. Prior treatment of baboons with CPP, however, inhibited this effect by 55% to 65%. TM was not evident in baboons receiving a conditioning regimen that included CPP instead of WBI. CONCLUSIONS: Aggregation of baboon platelets and TM is directly induced by PBPCs. CPP has direct anti-aggregatory properties and may provide an alternative strategy to WBI in this pig-to-primate model intended to induce mixed hematopoietic cell chimerism.
Mechanisms of thrombotic microangiopathy following xenogeneic hematopoietic progenitor cell transplantation.
INTRODUCTION: Attempts to induce tolerance though mixed hematopoietic chimerism in the discordant pig-to-baboon xenotransplantation model are sometimes complicated by a potentially fatal thrombotic microangiopathy in the recipient baboons. This state develops immediately after the infusion of porcine mobilized peripheral blood leukocytes, containing progenitor cells (PBPC). In our study, we examined the interaction of infused porcine PBPC with recipient platelets in vivo in baboons and investigated the underlying mechanisms using an in vitro model. METHODS: Two naïve baboons and six baboons preconditioned with irradiation and immunosuppression that received porcine PBPC were evaluated in vivo. The interaction of porcine and baboon PBPC with baboon platelets was investigated by an in vitro platelet aggregation assay. Fresh and cryopreserved PBPC were evaluated as well as PBPC obtained from growth-factor mobilized and unmobilized pigs. Furthermore, cellular subsets of PBPC were assessed for potential to induce platelet aggregation. Immunohistochemical staining was performed on platelet-leukocyte aggregates and potential inhibition of aggregation with anti-P-selectin and anti-CD154 mAbs, or eptifibatide (a GPIIb/IIIa receptor antagonist), was tested. RESULTS: All baboons that received porcine PBPC rapidly developed marked thrombocytopenia (<20,000/microl), elevated serum lactate dehydrogenase (>1,500U/liter), schistocytosis, and platelet aggregates on blood smear. Three baboons died (two untreated and one preconditioned), and substantive platelet aggregates containing porcine leukocytes were observed in the microvasculature of lungs and kidneys. In vitro, porcine, but not baboon, PBPC induced aggregation of baboon platelets in a dose-dependent manner. Immunohistological examination of these aggregates confirmed the incorporation of porcine leukocytes. Cryopreserved PBPC caused less aggregation than fresh PBPC, and growth-factor-mobilized PBPC induced less aggregation than unmobilized PBPC. Aggregation was fully abrogated by the addition of eptifibatide, and modulated by anti-P-selectin and anti-CD154 monoclonal antibodies that recognize adhesion receptors on activated platelets. Purified fractions (granulocytes, CD2+, and CD- cells) of porcine PBPC did not initiate aggregation, whereas addition of exogenous porcine PBPC membranes (erythrocytes, dead cells, and/or platelets) to the purified fractions exacerbated the aggregation response. CONCLUSIONS: These data indicate that porcine PBPC mediate aggregation of baboon platelets. This process likely contributes to the thrombotic microangiopathy observed after PBPC transplantation in the pig-to-baboon model. Eptifibatide can fully abrogate platelet aggregation induced by porcine PBPC in vitro. Purification of the progenitor cells from porcine PBPC and/or treatment of baboons with eptifibatide may be beneficial.
Anti-CD154 monoclonal antibody and thromboembolism.
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Christiaan Neethling Barnard.
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Christiaan Barnard and his contributions to heart transplantation.
Christiaan (Chris) Barnard was born in South Africa in 1922 and qualified in medicine at the University of Cape Town in 1946. Following surgical training in Cape Town and Minneapolis, Barnard established a successful open heart surgery program at Groote Schuur Hospital. In 1967, he led the team that performed the world's first human-to-human heart transplant. Although his first patient survived only 18 days, 4 of his first 10 patients survived for more than 1 year, 2 living for 13 and 23 years, respectively. With his junior colleague, Jaques Losman, Barnard then developed the operation of heterotopic heart transplantation. In 1981, his group was the first to successfully transport donor hearts using a hypothermic perfusion storage device. Several studies on the hemodynamic and metabolic sequelae of brain death were carried out in his department. Barnard retired from the University of Cape Town in 1983 at the age of 61. Now in his 79th year, he continues to pursue his interest in writing for the public. In the words of one of his former colleagues, he is a "surgical visionary and simply the most unforgettable character of the second generation of cardiac surgeons."
Cardiac hyperacute rejection: a new look or a skewed look at an old problem?
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Assessment of methotrexate as a potential immunosuppressive agent in baboons.
Methotrexate is an anti-proliferative agent that affects both T-cell and B-cell immunity, and therefore might be expected to suppress antibody (Ab) production. Although it has been used in xenotransplantation studies to suppress anti-pig Ab production, it has always been used in combination with other immunosuppressants. The purpose of this study was to measure its effect as a single immunosuppressant on anti-Gal Ab production in baboons (n=4). Pharmacokinetic studies showed that methotrexate was not detected in the blood when administered per os. Prolonged daily IV or IM administration (i) reduced T-cell and B-cell numbers by 50% to 70% and modestly reduced responsiveness on mixed lymphocyte reaction (but only at toxic doses) and (ii) did not result in lowered anti-Gal Ab levels, only marginally reducing the rate of return of Ab after extracorporeal immunoadsorption. Our observations would suggest that methotrexate will not contribute significantly to immunosuppressive regimens in the baboon at non-toxic doses.
Effects of specific anti-B and/or anti-plasma cell immunotherapy on antibody production in baboons: depletion of CD20- and CD22-positive B cells does not result in significantly decreased production of anti-alphaGal antibody.
Anti-Galalpha1-3Gal antibodies (antialphaGal Ab) are a major barrier to clinical xenotransplantation as they are believed to initiate both hyperacute and acute humoral rejection. Extracorporeal immunoadsorption (EIA) with alphaGal oligosaccharide columns temporarily depletes antialphaGal Ab, but their return is ultimately associated with graft destruction. We therefore assessed the ability of two immunotoxins (IT) and two monoclonal antibodies (mAb) to deplete B and/or plasma cells both in vitro and in vivo in baboons, and to observe the rate of return of antialphaGal Ab following EIA. The effects of the mouse anti-human IT anti-CD22-ricin A (proportional to CD22-IT, directed against a B cell determinant) and anti-CD38-ricin A (proportional to CD38-IT, B and plasma cell determinant) and the mouse anti-human anti-CD38 mAb (proportional to CD38 mAb) and mouse/human chimeric anti-human anti-CD20 mAb (proportional to CD20 mAb, Rituximab, B cell determinant) on B and plasma cell depletion and antialphaGal Ab production were assessed both in vitro and in vivo in baboons (n = 9) that had previously undergone splenectomy. For comparison, two baboons received nonmyeloablative whole body irradiation (WBI) (300 cGy), and one received myeloablative WBI (900 cGy). Depletion of B cells was monitored by flow cytometry of blood, bone marrow (BM) and lymph nodes (LN), staining with anti-CD20 and/or anti-CD22 mAbs, and by histology of LN. EIA was carried out after the therapy and antialphaGal Ab levels were measured daily. In vitro proportional to CD22-IT inhibited protein synthesis in the human Daudi B cell line more effectively than proportional to CD38-IT. Upon differentiation of B cells into plasma cells, however, less inhibition of protein synthesis after proportional to CD22-IT treatment was observed. Depleting CD20-positive cells in vitro from a baboon spleen cell population already depleted of granulocytes, monocytes, and T cells led to a relative enrichment of CD20-negative cells, that is plasma cells, and consequently resulted in a significant increase in antialphaGal Ab production by the remaining cells, whereas depleting CD38-positive cells resulted in a significant decrease in antialphaGal Ab production. In vivo, WBI (300 or 900 cGy) resulted in 100% B cell depletion in blood and BM, > 80% depletion in LN, with substantial recovery of B cells after 21 days and only transient reduction in antialphaGal Ab after EIA. Proportional to CD22-IT depleted B cells by > 97% in blood and BM, and by 60% in LN, but a rebound of B cells was observed after 14 and 62 days in LN and blood, respectively. At 7 days, serum antialphaGal IgG and IgM Ab levels were reduced by a maximum of 40-45% followed by a rebound to levels up to 12-fold that of baseline antialphaGal Ab by day 83 in one baboon. The results obtained with proportional to CD38-IT were inconclusive. This may have been, in part, due to inadequate conjugation of the toxin. Cell coating was 100% with proportional to CD38 mAb, but no changes in antialphaGal Ab production were observed. Proportional to CD20 mAb resulted in 100% depletion of B cells in blood and BM, and 80% in LN, with recovery of B cells starting at day 42. Adding 150cGy WBI at this time led to 100% depletion of B cells in the BM and LN. Although B cell depletion in blood and BM persisted for > 3 months, the reduction of serum antialphaGal IgG or IgM Ab levels was not sustained beyond 2 days. Proportional to CD20 mAb + WBI totally and efficiently depleted CD20- and CD22-positive B cells in blood, BM, and LN for > 3 months in vivo, but there was no sustained clinically significant reduction in serum antialphaGal Ab. The majority of antibody secretors are CD38-positive cells, but targeting these cells in vitro or in vivo with proportional to CD38-IT was not very effective. These observations suggest that CD20-and CD22-positive B cells are not the major source of antialphaGal Ab production. Future efforts will be directed towards suppression of plasma cell function.
Porcine hematopoietic cell xenotransplantation in nonhuman primates is complicated by thrombotic microangiopathy.
Thrombotic microangiopathy (TM) is a serious complication of bone marrow transplantation (BMT) that resembles thrombotic thrombocytopenic purpura (TTP). In attempting to achieve hematopoietic cell chimerism in the pig-to-baboon model, we have observed TM following infusion of high doses (>10(10) cells/kg) of porcine peripheral blood mobilized progenitor cells (PBPC) into baboons. We performed investigations to analyze the pathobiology of this TM and to test therapeutic interventions to ameliorate it. PBPC were obtained by leukapheresis of cytokine-stimulated swine. The initial observations were made in two baboons that underwent a non-myeloablative regimen (NMR) prior to PBPC transplantation (TX) (group 1). We then studied three experimental groups. Group 2 (n = 2) received NMR without PBPC TX. Group 3 (n = 2) received PBPC TX alone. Group 4 (n = 6) received NMR + PBPC TX combined with prostacyclin, low-dose heparin, methylprednisolone, and cyclosporine was replaced by anti-CD40L mAb in five cases. Baboons in groups 1 and 3 developed severe thrombocytopenia (<10,000/mm3), intravascular hemolysis with schistocytosis (>10/high powered field (hpf)), increase in plasma lactate dehydrogenase (LDH) (2500-9000 U/l), transient neurologic changes, renal insufficiency, and purpura. Autopsy on two baboons confirmed extensive platelet thrombi in the microcirculation, and, similar to clinical BMT-associated TM/TTP, no unusually large vWF multimers or changes in vWF protease activity were observed in the plasma of baboons with TM. In group 2, self-limited thrombocytopenia occurred for 10-15 days following NMR. Group 4 baboons developed thrombocytopenia (<20,000/mm3) rarely requiring platelet transfusion, minimal schistocytosis (<3/hpf), minor increase in LDH (<1000 U/l), with no clinical sequelae. We conclude that high-dose porcine PBPC infusion into baboons induces a microangiopathic state with vWF biochemical parameters resembling clinical BMT-associated TM/TTP and that administration of antithrombotic and anti-inflammatory agents can ameliorate this complication.
"Literature update 1999, part 3".
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