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N S Kenyon

Publications and source records attributed to N S Kenyon.

At least 19 recordsLinked to original sources
PubMed2001

Human islet transplantation: update.

New hope for the treatment of type 1 diabetes has recently emerged from the encouraging results of islet cell transplantation in humans during the last few years. Although still facing considerable problems, the challenge to achieving insulin independence has been overcome in some patients who received an islet graft. However, the success of clinical trials is still limited by the inability to transplant enough viable human islets to compensate for the insulin-deficient state, the number of islets that engraft following transplantation, the rejection process, and the recurrence of autoimmunity. The important advances in immunosuppressive regimens, organ procurement techniques, isolation techniques, and availability of defined collagenase blends have contributed to the continuing promise of making islet cell transplantation the treatment of choice for type 1 diabetes mellitus.

Diabetes Mellitus, Type 1↗
PubMed2001

Prolonged islet graft survival in NOD mice by blockade of the CD40-CD154 pathway of T-cell costimulation.

Allorejection and recurrence of autoimmunity are the major barriers to transplantation of islets of Langerhans for the cure of type 1 diabetes in humans. CD40-CD154 (CD40 ligand) interaction blockade by the use of anti-CD154 monoclonal antibody (mAb) has shown efficacy in preventing allorejection in several models of organ and cell transplantation. Here we report the beneficial effect of the chronic administration of a hamster anti-murine CD154 mAb, MR1, in prolonging islet graft survival in NOD mice. We explored the transplantation of C57BL/6 islets into spontaneously diabetic NOD mice, a combination in which both allogeneic and autoimmune components are implicated in graft loss. Recipients were treated either with an irrelevant control antibody or with MR1. MR1 administration was effective in prolonging allograft survival, but did not provide permanent protection from diabetes recurrence. The autoimmune component of graft loss was studied in spontaneously diabetic NOD mice that received syngeneic islets from young male NOD mice. In this combination, a less dramatic yet substantial delay in diabetes recurrence was observed in the MR1-treated recipients when compared with the control group. Finally, the allogeneic component was explored by transplanting C57BL/6 islets into chemically induced diabetic male NOD mice. In this setting, long-term graft survival (>100 days) was achieved in MR1-treated mice, whereas control recipients rejected their grafts within 25 days. In conclusion, chronic blockade of CD154 results in permanent protection from allorejection and significantly delays recurrence of diabetes in NOD mice.

Animals↗
PubMed2000

Quantitative polymerase chain reaction assessment of chimerism in non-human primates after sex-mismatched islet and bone marrow transplantation.

BACKGROUND: Accurate assessment of chimerism in recipients of islet and bone marrow transplantation (BMT) may allow for a clearer assessment of the role of chimerism in islet engraftment or rejection. A quantitative polymerase chain reaction (PCR) assay was developed for the detection of the sex-determining region of the Y chromosome (SRY) in peripheral blood samples from female non-human primate recipients of allogeneic male islets and vertebral body marrow (VBM) from the same donor. METHODS: The assay incorporates a synthetic internal standard (IS) containing the same primer template sequences as the target to compete for primer annealing and amplification. Each DNA sample was coamplified with a constant amount of IS. The concentration of male DNA in the test samples was calculated from the regression equation of a standard curve that was generated by plotting the logarithm of the ratio of the intensities of SRY to IS PCR products versus the logarithm of known percentages of input male DNA. RESULTS: This method allows for a correction of the variability of efficiency of the PCR technique and also overcomes the drawback of time-consuming competitive PCR. Using this assay, we quantitated the amount of male DNA in samples taken from female baboon recipients of male islets and VBM. There was detectable male donor DNA in the samples taken one day after BMT; pre-BMT samples were negative. This technique works well for samples obtained from rhesus and cynomogus monkeys as well. CONCLUSIONS: It is a practical method for accurately evaluation of chimerism after sex-mismatched allogeneic BMT in non-human primate models.

Animals↗
PubMed1999

Long-term survival and function of intrahepatic islet allografts in rhesus monkeys treated with humanized anti-CD154.

Reported effects of anti-CD154 treatment on autoimmunity, alloreactivity, and inflammatory events mediated by macrophages and endothelial cells indicated that it might be an ideal agent for the prevention of intrahepatic islet allograft failure. This hypothesis was tested in MHC-mismatched rhesus monkeys. Transplantation of an adequate number of viable islets resulted in engraftment and insulin independence in six of six recipients treated with anti-CD154 (hu5c8) induction plus monthly maintenance therapy (post-operative day >125, >246, >266, >405, >419, >476). Anti-CD154 (hu5c8) displayed no inhibitory effect on islet cell function. For monkeys followed for >100 days, continued improvement in graft function, as determined by first phase insulin release in response to intravenous glucose, was observed after the first 100 days post-transplant. No evidence of toxicity or infectious complications has been observed. All recipients treated with anti-CD154 became specifically nonresponsive to donor cells in mixed lymphocyte reactions. Furthermore, three monkeys are now off therapy (>113, >67, and >54 days off anti-CD154), with continued insulin independence and donor-specific mixed lymphocyte reaction hyporeactivity. In striking contrast to all previously tested strategies, transplantation of an adequate number of functional islets under the cover of anti-CD154 (hu5c8) monotherapy consistently allows for allogeneic islet engraftment and long-term insulin independence in this highly relevant preclinical model.

Animals↗
PubMed1999

Thrombocytopenia after liver transplantation.

BACKGROUND: Thrombocytopenia after orthotopic liver transplantation (OLT) is a well recognized and prevalent early postoperative complication. The etiology, as well as the effect of this phenomenon on transplant outcome, however, are vague. The aims of this study are to identify factors contributing to thrombocytopenia and to ascertain whether there is any correlation with early rejection and ultimate survival. METHODS: This study examines 541 OLTs (541 grafts in 494 patients) that were transplanted at the University of Miami during the 3-year period from June 1994 to September 1997. The patients with severe postoperative thrombocytopenia (nadir platelet count [PLT] < 20,000/mm3), as well as the whole group of patients, were analyzed. The preoperative PLT, intra-operative platelet transfusion requirements, cross-match, recipient and donor cytomegalovirus (CMV) status, infusion of donor bone marrow cells (DBMC), occurrence of early rejection episodes (in the first posttransplant month), and re-transplantation were factors examined for any association with thrombocytopenia. Total bilirubin (TB) and direct bilirubin (dB), hematocrit, white blood cell count (WBC), aspartate aminotransferase and alanine aminotransferase, determined on the day that platelets reached a nadir (nadir day), were also analyzed. RESULTS: In 90.9% of the cases, there was a 56.5%+/-23.5% fall in platelets in the immediate posttransplant period (first 2 weeks), but the mean PLT exceeded preoperative levels during the 3rd and 4th postoperative weeks. The nadir of the drop in the PLT most commonly occurred on posttransplant day 4. For preoperative PLT, platelet transfusions during the operation, re-transplantation, early rejection, cross-match, and recipient CMV status, there was significant statistical correlation with any degree of postoperative thrombocytopenia. Four of these factors, preoperative PLT, intra-operative platelet transfusions, re-transplantation, and early rejection, were found to be independently associated with thrombocytopenia in general. None of them was found to be independently correlated with severe thrombocytopenia. A statistically significant correlation between bilirubin and WBC on the nadir day and the degree of thrombocytopenia was observed. No correlation was found between infusion of DBMC or donor CMV serology and thrombocytopenia. Both the nadir PLT and the percentage of the platelet fall were independent predictive factors (p<0.01 and 0.005, respectively) of patient and graft survival. CONCLUSIONS: Thrombocytopenia in the immediate posttransplant period is correlated with low preoperative PLT, massive platelet transfusions, and re-transplantation. These factors reflect a poor preoperative condition. There is also a correlation with allograft dysfunction, rejection, and poorer patient and graft survival. A rise in the mean PLT after the 2nd postoperative week reflects proper graft function.

Adolescent↗
PubMed1999

Analysis of post-transplant immune status in recipients of liver/bone marrow allografts.

The aims of this study were to assess the effect of donor bone marrow infusion on the reactivity of recipient peripheral blood lymphocytes (PBL) to mitogen and to donor and third-party cells after primary liver allotransplantation and to identify any correlation between altered immunoreactivity and HLA mismatches, occurrence of rejection, and immunosuppression. The immunoreactivity of recipient PBL toward frozen donor splenocytes was evaluated in mixed lymphocyte culture (MLC) (n = 29) and cell-mediated lympholysis (CML) (n = 27) assays in time intervals ranging from 0.7 to 27 months after transplant. Overall, the mean anti-donor MLC stimulation index (SI) fell from 25.6 +/- 5.2 preoperatively to 4.8 +/- 1.7 after transplantation (p < 0.002), with 14 out of 29 (48.3%) patients developing donor-specific MLC hyporeactivity. HLA class II mismatches were significantly associated with recipient post-transplant immune profile (p < 0.05): MLC donor specific hyporesponsiveness was observed in 70%, versus 37% of patients who shared a class II antigen, versus those that did not. Of the control group, 61.1% developed donor-specific nonreactivity versus 27.2% in the donor bone marrow cells (DBMC) group (p = 0.02). Donor-specific CML hyporeactivity was observed after transplantation, independent of DBMC infusion, with mean percentage values of pre- and post-transplant donor-specific lysis of 22.4% +/- 4.1% versus 3.1% +/- 1.6%, p = 0.0004, respectively. Our results suggest that DBMC infusion favors development of nonspecific MLC hyporesponsiveness to donor and third-party alloantigen, with maintenance of reactivity to mitogen and no additional effect on T-cell cytotoxicity.

Bone Marrow Cells↗
PubMed1999

Long-term survival and function of intrahepatic islet allografts in baboons treated with humanized anti-CD154.

Clinical islet cell transplantation has resulted in insulin independence in a limited number of cases. Rejection, recurrence of autoimmunity, and impairment of normal islet function by conventional immunosuppressive drugs, e.g., steroids, tacrolimus, and cyclosporin A, may all contribute to islet allograft loss. Furthermore, intraportal infusion of allogeneic islets results in the activation of intrahepatic macrophages and endothelial cells, followed by production of proinflammatory mediators that can contribute to islet primary nonfunction. We reasoned that the beneficial effects of anti-CD154 treatment on autoimmunity, alloreactivity, and proinflammatory events mediated by macrophages and endothelial cells made it an ideal agent for the prevention of islet allograft failure. In this study, a nonhuman primate model (Papio hamadryas) was used to assess the effect of humanized anti-CD154 (hu5c8) on allogeneic islet engraftment and function. Nonimmunosuppressed and tacrolimus-treated recipients were insulin independent posttransplant, but rejected their islet allografts in 8 days. Engraftment and insulin independence were achieved in seven of seven baboon recipients of anti-CD154 induction therapy administered on days -1, 3, and 10 relative to the islet transplant. Three of three baboons treated with 20 mg/kg anti-CD154 induction therapy experienced delayed rejection episodes, first detected by elevations in postprandial blood glucose levels, on postoperative day (POD) 31 for one and on POD 58 for the other two. Re-treatment with three doses of anti-CD154 resulted in reversal of rejection in all three animals and in a return to normoglycemia and insulin independence in two of three baboons. It was possible to reverse multiple episodes of rejection with this approach. A loss of functional islet mass, as detected by reduced first-phase insulin release in response to intravenous glucose tolerance testing, was observed after each episode of rejection. One of two baboons treated with 10 mg/kg induction therapy became insulin independent post-transplant but rejected the islet graft on POD 10; the other animal experienced a reversible rejection episode on POD 58 and remained insulin independent and normoglycemic until POD 264. Two additional baboon recipients of allogeneic islets and donor bone marrow (infused on PODs 5 and 11) were treated with induction therapy (PODs -1, 3, 10), followed by initiation of monthly maintenance therapy (for a period of 6 months) on POD 28. Rejection-free graft survival and insulin independence was maintained for 114 and 238 days, with preservation of functional islet mass observed in the absence of rejection. Prevention and reversal of rejection, in the absence of the deleterious effects associated with the use of conventional immunosuppressive drugs, make anti-CD154 a unique agent for further study in islet cell transplantation.

Animals↗
PubMed1998

Continuing observations on the regulatory effects of donor-specific bone marrow cell infusions and chimerism in kidney transplant recipients.

BACKGROUND: Continued follow-up of a series of donor bone marrow cell (DBMC)-infused first cadaver renal transplant recipients is described (n=58), now at a 36-month actuarial time point postoperatively. Serial polymerase chain reaction-flow cytometry (PCR-Flow) and cellular immune assays of iliac crest bone marrow aspirates and peripheral blood have begun to be compared with concomitantly transplanted recipients of living-related donor (LRD) kidneys and donor marrow infusions given the same immunosuppressive regimen (n=16). There have also been comparisons (36 months) with 188 controls transplanted concomitantly, i.e., recipients of first cadaver kidney transplants, who did not receive bone marrow. METHODS: Each group was given equivalent immunosuppressive regimens of OKT3 anti-T cell induction and maintenance tacrolimus, mycophenolate mofetil, and methylprednisolone. Actuarial patient and graft survival have been 96% and 93%, respectively, in the controls and 91% and 91%, respectively, in the DBMC-infused recipients. Trough levels of tacrolimus were significantly lower in the DBMC-infused group. RESULTS: In PCR-Flow measurements, in peripheral blood up to 6 months postoperatively, there were higher levels of chimerism, i.e., in the total number of donor cells, as well as the donor CD3+ and CD34+ subsets in the LRD recipients administered DBMC infusions, compared with cadaver DBMC recipients, supporting the notion of a positive effect of histocompatibility on chimerism levels. In PCR-Flow measurements of recipient iliac crest bone marrow aspirates as in previous studies on peripheral blood, early acute rejection episodes (<1 month) were found to be associated with a later (6-14 months) decrease in donor cell lineage chimerism. However, a trend toward recovery of chimeric levels occurred by 21-28 months in a second iliac crest marrow aspirate 1 year after the first aspirate in the DBMC-infused recipients who experienced such early rejection episodes. This was in contrast to the controls in whom there were sustained low levels of iliac crest bone marrow chimerism at both the earlier and later intervals (i.e., no chimeric recovery), with 17/183 surviving controls progressing into chronic rejection. This has not yet been seen in the DBMC-infused group (0/54). In in vitro observations on cellular immune reactivity at 1 year postoperatively, decreased peripheral blood lymphocyte proliferative reactions were seen in response to phytohemagglutinin and Staph-A mitogens, as well as to cytomegalovirus and Epstein-Barr viral protein antigens in the DBMC-infused group versus the controls. Chronic immunosuppression did not seem to effect a vigorous in vitro inhibitory (regulatory) activity of bone marrow taken from these transplant recipients 2 years postoperatively in mixed lymphocyte culture and cell-mediated lympholysis reactions, using allogeneic responding cells from "normal" laboratory volunteers. Autologous peripheral blood lymphoproliferative responses to phytohemagglutinin and Staph-A mitogens, as well as to cytomegalovirus and Epstein-Barr virus protein antigens, were also regulated by either organ donor (non-immunosuppressed) bone marrow cells or by transplant recipient (immunosuppressed) bone marrow cells. What appeared to be disparate between the DBMC-infused and control groups (both immunosuppressed) was the trend for the (autologous) bone marrow suppressive effect on antiviral lymphoproliferative responses, to be stronger in the DBMC-infused group, who also had significantly (>one order of magnitude) higher levels of chimerism (P=0.01). CONCLUSIONS: It is concluded that the establishment of a chimeric state in DBMC-infused recipients, albeit of relatively low magnitude (approximately 1% at 2 years in recipient iliac crest bone marrow), has had a definite regulatory effect on immune responses. These results, therefore, add weight to the "causal" horn of the dilemma as to whether donor cell chimerism is a cause or an effect of

Bone Marrow Cells↗
PubMed1998

Islet transplantation: present and future perspectives.

Islet cell transplantation can potentially normalize blood glucose levels and stop the progression of clinical complications, and if the transplant is done early in the course of the disease complications may be prevented. Remarkable progress has been made in recent years and islet cell transplantation has resulted in normalization of metabolic control in several patients with Type 1 diabetes in the absence of hypoglycemia. Only a few patients, however, have achieved insulin independence. Issues relating to islet cell engraftment within the liver, prevention of rejection and recurrent autoimmunity, and identification of alternative immunosuppressive drugs that do not adversely affect islet cell function remain to be solved. Thus far, the need for chronic, generalized immunosuppression to prevent rejection of the islets has limited the indication to those patients who have already received another transplant or to those who simultaneously receive islets and another organ (generally a kidney). Identification of immunointervention protocols that allow for engraftment in the absence of deleterious effects on the islets and prevent rejection and recurrent autoimmunity would make this procedure suitable for all patients, including children who have not yet developed long-term complications of the disease.

Clinical Trials as Topic↗
PubMed1997

Donor peripheral blood stem cell infusions in recipients of living-related liver allografts.

BACKGROUND: In this pilot study, donor peripheral blood stem cell (DPBSC) infusions were performed in three recipients of living-related liver transplants (LRLT). METHODS: DPBSCs were obtained by leukapheresis after mobilization with granulocyte-colony-stimulating factor (Filgrastim). Donor leukapheresis was performed on the 5th postoperative day, and half of the DPBSCs were infused into the recipient on the day of collection. The second half of the pheresed product was cryopreserved for delayed administration. RESULTS: Results from preliminary studies of chimerism in LRLT recipients, at 20 weeks posttransplant, suggested that the levels of donor cells detected in LRLT recipients treated with DPBSC infusions may be higher than those observed for recipients of cadaver donor liver allografts and vertebral body marrow infusions. CONCLUSIONS: The results of this pilot study indicate that administration of mobilized DPBSC to recipients of LRLT is a feasible procedure for both donor and recipient.

Adult↗