Les Olson

The Ability of Human Schwann Cell Grafts to Promote Regeneration in the Transected Nude Rat Spinal Cord

Advances in the purification and expansion of Schwann cells (SCs) from adult human peripheral nerve, together with biomaterials development, have made the construction of unique grafts with defined properties possible. We have utilized PAN/PVC guidance channels to form solid human SC grafts which can be transplanted either with or without the channel. We studied the ability of grafts placed with and without channels to support regeneration and to influence functional recovery; characteristics of the graft and host/graft interface were also compared. The T9-T10 spinal cord of nude rats was resected and a graft was placed across the gap; methylprednisolone was delivered acutely to decrease secondary injury. Channels minimized the immigration of connective tissue into grafts but contributed to some necrotic tissue loss, especially in the distal spinal cord. Grafts without channels contained more myelinated axons (x = 2129 +/- 785) vs (x = 1442 +/- 514) and were larger in cross-sectional area ( x = 1.53 +/- 0.24 mm2) vs (x = 0.95 +/- 0.86 mm2). The interfaces formed between the host spinal cord and the grafts placed without channels were highly interdigitated and resembled CNS-PNS transition zones; chondroitin sulfate proteoglycans was deposited there. Whereas several neuronal populations including propriospinal, sensory, motoneuronal, and brainstem neurons regenerated into human SC grafts, only propriospinal and sensory neurons were observed to reenter the host spinal cord. Using combinations of anterograde and retrograde tracers, we observed regeneration of propriospinal neurons up to 2.6 mm beyond grafts. We estimate that 1% of the fibers that enter grafts reenter the host spinal cord by 45 days after grafting. Following retrograde tracing from the distal spinal cord, more labeled neurons were unexpectedly found in the region of the dextran amine anterograde tracer injection site where a marked inflammatory reaction had occurred. Animals with bridging grafts obtained modestly higher scores during open field [(x = 8.2 +/- 0.35) vs (x = 6.8 +/- 0.42), P = 0.02] and inclined plane testing (x = 38.6 +/- 0. 542) vs (x = 36.3 +/- 0.53), P = 0.006] than animals with similar grafts in distally capped channels. In summary, this study showed that in the nude rat given methylprednisolone in combination with human SC grafts, some regenerative growth occurred beyond the graft and a modest improvement in function was observed.

Evidence that tacrolimus augments the bioavailability of mycophenolate mofetil through the inhibition of mycophenolic acid glucuronidation.

We previously reported an unexpected augmentation of mycophenolic acid (MPA) levels (trough and AUC0-12) in patients receiving mycophenolate mofetil (MMF) in combination with tacrolimus versus patients receiving the same dose of MMF in combination with cyclosporin A (CsA). This finding was accompanied by a corresponding reduction of the inactive glucuronide metabolite of MPA (MPAG) in patients, suggesting that tacrolimus may effect the conversion of MPA to MPAG by the enzyme UDP-glucuronosyltransferase (UDPGT). To investigate this possibility directly, UDPGT was extracted from human liver and kidney tissue and its activity was characterized using MPA as a substrate in vitro, assessing the conversion of MPA to MPAG using analysis by high-performance liquid chromatography. With crude microsomal preparations, amounts of UDPGT at least 100 times higher in specific activity (i.e., units to milligrams of protein) could be extracted per gram of tissue from kidney as opposed to liver. This result did not appear to be related to the coextraction of a liver-specific UDPGT inhibitor because initial enzyme kinetic values (Vmax and km) were identical for kidney and liver extracts, and further purification of the liver enzyme did not enhance activity (as is seen when inhibitors are removed during purification). With further UDPGT purification (approximately 200-fold) from kidney extracts using a combination of ammonium sulfate precipitation, followed by anion exchange, hydroxyapatite, and size exclusion chromatography, the enzyme was more than 80% pure when assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Initial enzyme kinetic analysis of this purified product showed a km value for MPA of 35.4+/-5.7 microg/mL and a Vmax of 2.87+/-0.31 MPAG produced per hour (n = 7). The addition of clinically relevant concentrations of CsA (200-1,000 ng/mL) or tacrolimus (10-25 ng/mL) resulted in a dose-dependent inhibition of the UDPGT enzyme by both agents with tacrolimus, which was approximately 60-fold more efficient as an inhibitor. The calculated inhibition constants (KI) of tacrolimus and CsA for the purified UDPGT were 27.3+/-5.6 ng/ml and 2,518+/-1473 ng/ml. respectively. Both agents displayed an inhibition profile characteristic of a competitive inhibitor (substrate) that could be demonstrated in a reciprocal experiment with CsA as a substrate, but not with tacrolimus. This finding suggested that the significantly more efficient inhibition of UDPGT by tacrolimus may occur by a more complicated mechanism that is yet to be determined.

Natural history of intrahepatic canine islet cell autografts.

We have serially followed the function of intrahepatic canine islet autografts in 15 beagle dogs for up to 24 mo. Of these, only 20% sustained normal levels of fasting blood glucose for greater than 15 mo posttransplant. Failure of autograft function was accompanied by a preferential loss of well-granulated beta cells in the engrafted islets. The chronic stimulation of an initially marginal intrahepatic beta-cell mass ultimately resulted in metabolic deterioration and loss of beta cells below the minimal threshold required to maintain normal fasting blood glucose levels. It is possible that transplantation of a larger mass of islets would result in indefinite graft function in dogs. However, it remains to be demonstrated in larger mammals, including humans, whether an islet cell mass that is initially adequate in a heterotropic site such as the liver can remain functionally competent over a prolonged period.

Detection of hepatitis C virus infection among cadaver organ donors: Evidence for low transmission of disease

OBJECTIVE To determine the prevalence of antibodies to hepatitis C virus (anti-HCV) and HCV RNA among cadaver organ donors and to correlate these results with donor liver histologic abnormalities and evidence for transmission of disease through organ transplantation. DESIGN Retrospective testing of stored serum samples from cadaver organ donors for anti-HCV and HCV RNA. SETTING Transplantation service of the University of Miami/Jackson Memorial Medical Center and other cooperative medical centers furnishing follow-up data. SUBJECTS Of 1096 cadaver organ donors harvested between 1 January 1979 and 28 February 1991, 484 had stored serum samples available for analysis. Recipients of organs from recombinant immunoblot assay (RIBA)-positive donors for whom adequate follow-up was available were also included in the analysis. MEASUREMENTS Samples were tested for anti-HCV by enzyme-linked immunosorbent assay (ELISA). Confirmatory testing was done using a second-generation RIBA. Hepatitis C viral RNA was detected in serum using the polymerase chain reaction. Liver biopsies were obtained from the organ donor and interpreted blindly by a pathologist unaware of the clinical data. Liver chemistry profiles and serum sample analysis for HCV RNA were done for transplant recipients. RESULTS From the 484 cadaver organ donors, 89 samples (18%; 95% Cl, 15% to 21%) were reactive by ELISA. Of these, 33 (6.8%; Cl, 4.6% to 9%) were RIBA seropositive. Hepatitis C viral RNA sequences were detected in 50% of the RIBA-positive serum samples tested. Liver tissue was available from 24 of the 33 RIBA-positive donors and showed chronic active hepatitis in 16, chronic persistent hepatitis in 2, and no abnormality in 6. Among the 46 recipients of a kidney from a RIBA-positive donor, 13 (28%; Cl, 15% to 41%) developed post-transplant liver disease, of which only 4 cases were highly suggestive of viral transmission from the donor. Little morbidity and no mortality could be attributed to liver disease in this cohort of recipients. CONCLUSIONS These data suggest that HCV transmission by organ transplantation is low and that the consequences of infection are small. If the medical condition of the potential recipient is so serious that other options no longer exist, the use of an organ from an anti-HCV-seropositive donor should be considered.

Use of older controlled non-heart-beating donors for liver transplantation.

Background. Use of liver grafts from non–heart-beating donors (NHBDs) warrants consideration so to expand the donor pool. Because the results of controlled NHBDs (CNHBDs) were acceptable, we have recently tried to expand the criteria to older CNHBDs. Here, we report our experience using liver grafts from older CNHBDs. Methods. We retrospectively studied our donor records from June 1994 through December 2001. CNHBDs were divided into two groups by age: older donors (O) were more than or equal to 55 years old, and younger donors (Y) were less than 55 years old. We compared donor and recipient demographics and peak laboratory values during the first postoperative week. Results. Twenty-five grafts from CNHBDs were transplanted in our center. Five livers were harvested from O (63±6 years) and 20 were from Y (32±15 years). No differences other than age in donor characteristics were noted between O and Y. Mean age of recipients was 50 years in both groups. Mean cold ischemic time (CIT) was 5.4 hours in O and 7.3 hours in Y (P <.05). Peak glutamic oxaloacetic transaminase (U/L), glutamic pyruvic transaminase (U/L), bilirubin (mg/dL), and prothrombin time (sec) during the first postoperative week were 611, 500, 3.9, and 16 in O and 846, 593, 5.9, and 17 in Y. There were no significant differences between the two groups. The graft survival at 1 year was 80% in O and 70% in Y. Conclusions. In our preliminary experience, recipients of liver grafts from older CNHBDs had an outcome equivalent to that of younger CNHBDs. With the strict evaluation of the donors and brief CIT, liver grafts from older CNHBDs may be used to expand the donor pool.

Daclizumab induction, tacrolimus, mycophenolate mofetil and steroids as an immunosuppression regimen for primary kidney transplant recipients.

Background. Recent reports have demonstrated the efficacy of interleukin-2-receptor blockers in lowering the incidence of early acute rejection in cyclosporine-treated kidney recipients when compared to patients not induced with an antibody product. The addition of daclizumab to a tacrolimus-mycophenolate mofetil-based immunosuppressive protocol was tested to evaluate whether there might be an additional reduction of the risk of rejection after renal transplantation. Methods. Since March 1998, we studied the effect of daclizumab in a nonrandomized, prospective study of 233 sequential recipients of first renal transplant. They were retrospective compared with a control group of 225 renal transplant recipients receiving a 10-day course of OKT3 induction, and tacrolimus, mycophenolate mofetil, and methylprednisolone maintenance. The study group received the same immunosuppressive regimen with the addition of daclizumab at 1 mg/kg for five doses over 10 weeks in the place of OKT3 therapy. There was at least 1HLA DR antigen compatibility match present between all donors and recipients. Patients were followed for 1 year after renal transplantation for the incidence of biopsy-proven acute rejection, patient and graft survival, and adverse events. Results. At 12 months, patient and graft survival for the daclizumab was 98 and 96 vs. 96 and 94% for the OKT3 group, respectively, and were not statistically different. Acute rejection rates (<6 months) were lower in the daclizumab group as compared with the OKT3 group, i.e., 5 (2.1%) vs. 16 (7.1%) (P =0.011) respectively. The incidence of infection requiring hospitalization appeared to be lower with daclizumab (7.3 vs. 16%, P <0.0036) with a similar trend with cyclomegalovirus infection, i.e., 1.6 vs. 4%, respectively (P =0.14). Conclusions. The combination of daclizumab, tacrolimus, mycophenolate mofetil, and steroids is safe and effective for kidney transplant recipients in lowering the incidence of early acute rejection and without any increase in morbidity when compared to our previous protocol, which may have an eventual impact in long-term graft survival.

Microangiopathy in kidney and simultaneous pancreas/kidney recipients treated with tacrolimus: Evidence of endothelin and cytokine involvement

BACKGROUND In the past 3 years, three transplant recipients [one kidney, two simultaneous pancreas/kidney (SPK)] developed a thrombotic thrombocytopenic purpura-like clinical syndrome. This was characterized by an abrupt fall in the hematocrit and platelet count with evidence of hemolysis (fragmented red blood cells and schistocytes) and transplant kidney dysfunction during the first 2 weeks after transplantation. This was also associated with pancreatic dysfunction in the two SPK recipients. In all three patients, elevated tacrolimus levels (>24 ng/ml) occurred. METHODS Serum cytokine and endothelin levels were determined retrospectively from stored (-70 degrees C) sera. RESULTS In each case tacrolimus was discontinued, and treatment with plasmapheresis, fresh frozen plasma, steroids, and OKT3 was begun. The clinical courses varied from mild (one patient), to moderate (one patient), to severe (one patient), complicated with seizures and coma. Each patient responded clinically and ultimately was converted to cyclosporine A, and/or mycophenolate mofetil. These clinical events were associated with a rise in serum levels of endothelin and several cytokines. Levels of endothelin were elevated at 209+/-137 pg/ml, particularly in the severe episode where peak levels reached 480 pg/ml (normal 0-20 pg/ml). Peak levels of IL-8 (104+/-36 pg/ml), interleukin- (IL) 10 (238+/-105 pg/ml), and/or IL-12 (306+/-119 pg(ml) mean+/-SE, occurred during or before the clinical event. Serum levels of tumor necrosis factor-a and interferon-gamma were elevated in 2 patients while levels of IL-2, IL-4, and IL-6 were not elevated during the acute phase. CONCLUSIONS These data are consistent with a mechanism of microangiopathy involving endothelial cell injury (associated with tacrolimus treatment), and accompanied by cytokines (IL-10, IL-12, tumor necrosis factor-a, interferon-gamma) that affect expression of adhesion molecules, chemokines (IL-8) that direct the influx of white blood cells and endothelins that may exacerbate underlying hypertension and increase shear force-related red blood cell destruction.

The human bone marrow as an immunoregulatory organ.

It was 45 years ago that in a virtual revolution in thinking in immunology there developed the acceptance and the subsequent expansion of two new dogmas: (1) that to eliminate toxins and pathogens as the major mode of defense, individual immune cells were, in their ontogeny of differentiation, internally programmed to react singly and then clonally against the virtually limitless individual stimuli of the outside world (1–3); (2) that before this programming was manifested the immune system would fail to recognize any antigenic stimulus as foreign, thereby not differentiating non-self from self-recognition. This allowed for non-self-antigens, if introduced in this early stage, to be immunologically tolerated on subsequent testing. In the chronology of the evolution of these two dogmas, there were the earlier descriptions of specific immunological paralysis and unresponsiveness to certain defined polysaccharides and haptens demonstrated in adult mice and guinea pigs respectively by Felton (4) and Chase (5). It remained for Medawar and his colleagues (6) in allotransplantation experiments to clearly define “acquired specific immunological tolerance” as an ontogenic concept involving the lack of maturation or differentiation were tolerance to be evoked. As early as 1953, Billingham, Brent, and Medawar demonstrated that allogeneic donor bone marrow-derived cells could confer such a specifically acquired tolerant state to the immune system of the murine recipient before self versus non-self recognition occurred in immune ontogeny, the test being subsequent acceptance of skin allografts from the same donors. The developmental processes of positive versus negative selection only a decade later began to be demonstrated to predominantly involve the thymus gland in maturational events of cells of the recipient immune system in studies first performed in neonatal rodents (7). By experimental manipulation of the immune system predominantly involving immunoablation by whole body x-irradiation, these findings of specific immunological tolerance as a result of the infusion of bone marrow-derived cells could be extended to adult animals as the system regenerated from stem cells in the bone marrow of either that of the donor (8), the recipient (9), or both (10). Nonetheless, except in the setting of clinical bone marrow transplantation using major (lethal) immunoablation followed by the salvage and replacement of the recipient immunohematopoietic system with donor cell lineages and only in the context of little or no donor-recipient MHC disparity, with few exceptions (11–15), to date, specific immunological tolerance in organ transplantation in humans has not been possible.

Hypercoagulable state associated with kidney–pancreas transplantation. Thromboelastogram-directed anti-coagulation and implications for future therapy

Abstract:  Background:  The clinical consequences of type 1 diabetes mellitus (IDDM) include diabetic triopathy: retinopathy, nephropathy, and neuropathy, as well as microangiopathy, accelerated atherosclerotic disease, and hypercoagulability. The etiology of the hypercoagulability is multifactorial, involving various clotting factors or pathways (for example platelets, fibrinogen, individual components of the clotting system and/or fibrinolysis in different studies). The development of end‐stage renal disease (ESRD), with the uremia‐related platelet effect has the potential to protect from the existing hypercoagulable state. This has important implications for surgery, particularly simultaneous pancreas–kidney (SPK) transplantation, where the pancreas has historically been prone to thrombosis. This has led us to perform intra‐operative thromboelastograms (TEGs) to evaluate the patients current coagulation status.

Density dependent regulation of human Schwann cell proliferation.

Cessation of division is prerequisite for Schwann cell differentiation but regulation of this critical function is poorly understood. Heregulin/forskolin‐induced growth of human Schwann cells (HSCs) in vitro was found to be strongly regulated by cell density and thus could model some aspects of negative growth‐regulation in vivo. To better understand this phenomenon, the production of an autocrine growth‐inhibitor and the role of contact‐inhibition were investigated. The possible involvement of two membrane proteins, contactinhibin (CI) and peripheral myelin protein 22 (PMP22) in regulating growth was studied. Thymidine‐labeling of HSCs on collagen‐coated dishes was inhibited at cell densities less than one tenth of the density at maximal growth‐inhibition. Medium from high density cultures did not inhibit the thymidine‐labeling of HSCs at low density, a result that argues against the production of a soluble inhibitor. The expression of CI and PMP22 in nerve and HSCs, and the effect of a function‐blocking antibody to CI on HSC growth, were determined. CI was detected in fresh nerve by western blotting, and could easily be detected by immunocytochemistry in cultured HSCs by five days and for several weeks thereafter. Twenty‐four hour treatment with anti‐CI antibody did not increase the thymidine‐labeling of HSCs at any density but a significant increase in HSC number was observed in cultures treated with anti‐CI for 20 days. This increase was not related to decreased cell death. PMP22, unlike other myelin proteins, was not down‐regulated after nerve dissociation and by seven days nearly all HSCs were PMP22 positive. These results provide evidence for a contact‐mediated mechanism of growth‐regulation in HSCs and suggest that CI is involved in this mechanism. GLIA 30:165–177, 2000.