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S J Knechtle

Publications and source records attributed to S J Knechtle.

At least 19 recordsLinked to original sources
PubMed2006

The Art and Science of Immunosuppression: the Fifth Annual American Society of Transplant Surgeon's State-of-the-Art Winter Symposium.

The 2005 American Society of Transplant Surgeons (ASTS) Winter Symposium entitled 'The Art and Science of Immunosuppression' explored ways to maximize existing immunosuppressive protocols and to develop new strategies incorporating novel agents and emerging diagnostic technologies to customize immunosuppression and reduce side effects. Several presentations evaluated steroid withdrawal or avoidance protocols reflecting the significant difficulties of bone loss, glucose control and growth retardation in children associated with long-term steroid use. Calcineurin-inhibitor related renal dysfunction of both native and transplanted kidneys was identified as significant, but no consensus was reached concerning effective prevention. Similarly, recurrence of Hepatitis C following liver transplantation was identified as problematic without identifying a preferred immunosuppressive regimen in this setting. Control of T-cell mediated rejection was found to be excellent, but recognition and treatment of non-T cell causes of allograft damage (i.e. B- or NK-cell mediated) was identified as an area of current interest. Immunosuppressive agents under development, such as those blocking co-stimulation or cytokine signals, and JAK-3 inhibitors were discussed. Finally, the available technologies for molecular and genetic diagnostics and the clinical correlation in the post-transplant setting were discussed.

Humans↗
PubMed2006

A new look at blockade of T-cell costimulation: a therapeutic strategy for long-term maintenance immunosuppression.

Activated T cells orchestrate the immune response that results in graft rejection; therefore, a common goal among current immunosuppressive therapies is to block T-cell activation, proliferation and function. Current immunosuppressive regimens that inhibit T cells and immune cells have greatly reduced the incidence of acute rejection following solid-organ transplant. However, the expected improvements in long-term outcomes have not been realized. This may be related to the non-immune side effects of current maintenance immunosuppressants, which target ubiquitously expressed molecules. The focus in transplantation research is shifting in search of maintenance immunosuppressive regimens that might offer improved long-term outcomes by providing efficacy in prevention of acute rejection combined with reduced toxicities. An emerging therapeutic strategy involves an immunoselective maintenance immunosuppressant that inhibits full T-cell activation by blocking the interaction between costimulatory receptor-ligand pairs. This review describes costimulatory pathways and the development of molecules, which inhibit them in the context of transplantation research. Recent clinical data using the selective costimulation blocker, belatacept (LEA29Y), as a part of a CNI-free maintenance immunosuppressive regimen in renal transplantation is highlighted.

Abatacept↗
PubMed2003

Sirolimus monotherapy following Campath-1H induction.

Sirolimus was used as a single agent for maintenance immunosuppression in a pilot trial of 29 primary kidney transplant patients using lymphocyte depletion with Campath-1H as an induction strategy. This allowed sirolimus to be analyzed (dose, blood level, and side effect profile) in the absence of steroid and calcineurin inhibitors. A sirolimus dose of 4 mg/day resulted in blood levels in the 8 to 9 ng/mL range. Of the 29 patients, 8 patients (28%) had rejection. The sirolimus levels were not significantly different in patients with or without rejection. The cardiovascular risk profile in terms of lipid profile and hypertension control was favorable. Increase in cholesterol and triglyceride levels at one month (not statistically significant) necessitated treatment in 60% of patients with decline in levels by 6 and 12 months. Management of hypertension was also favorable with the majority of patients (55%) being on one hypertensive medication. Sirolimus monotherapy was well tolerated on the whole. Wound healing, leukopenia, and anemia were not significant problems. In conclusion, monotherapy has been well tolerated with a favorable side effect profile. However, a rejection rate of 28% was noted.

Follow-Up Studies↗
PubMed2002

Novel immunosuppressive agents in tolerance induction.

Induction of transplantation tolerance remains a much sought-after but elusive goal with a potential promise of rendering patients free of long-term immunosuppressive drugs while maintaining good organ transplant function indefinitely. All currently studied strategies toward transplantation tolerance include using immunosuppressive agents for a limited time period to achieve tolerance. There are a growing number of agents that lend themselves to tolerance induction and these agents are considered herein. Such agents generally fall into the categories of lymphocyte depletion, costimulation blockade, and adjunctive agents such as rapamycin. Preliminary data using donor stem cells suggests that embryonic stem cells may have substantial advantages over conventional donor bone marrow for tolerance induction. These preliminary results are briefly reviewed as well. Tolerance has been achieved in a small number of organ transplant patients and such successes suggest that progress in the clinical arena is happening and is an obtainable result.

Animals↗
PubMed2001

Graft survival in a rhesus renal transplant model after immunotoxin-mediated T-cell depletion is enhanced by mycophenolate and steroids.

BACKGROUND: Anti-CD3 immunotoxin (IT), a T-cell-depleting agent, prolongs survival of renal allografts in a rhesus monkey model without the need for long-term immunosuppression. In this study we sought to further prolong allograft survival by giving short-term conventional immunosuppression simultaneous with IT administration. METHODS: MHC class II mismatched, juvenile rhesus monkeys were paired as donor and recipient for renal transplantation. Recipients received two to three daily doses of IT starting on the day of transplantation. Additional immunosuppression was given for no more than 60 days. Graft function was monitored by serum creatinine and renal biopsies. Flow cytometry was used to monitor T-cell recovery. RESULTS: Graft survival time (GST) in animals receiving IT was prolonged compared with controls with 50% of IT-treated monkeys surviving >100 days. Animals treated with IT plus mycophenolate mofetil (MMF) and steroids had significantly enhanced GST (mean GST, 305 days) compared with those treated with IT alone (mean GST, 94 days). In contrast, addition of cyclosporine or 40-O-[2-Hydroxyethyl]rapamycin did not significantly increase graft survival time. A comparison among animals from all treatment groups with short (<100 days) and long (>100 days) GST demonstrated that those with the shorter GST had a higher blood T-cell count 2 weeks after transplantation. Full recovery of CD4+ T cells required longer than 6 months. CONCLUSIONS: A combination with MMF and steroids given for 4 days after renal allograft transplantation significantly increases GST in IT-treated monkeys. We hypothesize that MMF and steroids suppress the initial T-cell activation mediated by IT.

Animals↗
PubMed2001

Successful conversion from conventional immunosuppression to anti-CD154 monoclonal antibody costimulatory molecule blockade in rhesus renal allograft recipients.

BACKGROUND: Several conventional forms of immunosuppression have been shown to antagonize the efficacy of anti-CD154 monoclonal antibody- (mAb) based costimulatory molecule blockade immunotherapy. Our objective was to determine if allograft recipients treated with a conventional immunosuppressive regimen could be sequentially converted to anti-CD154 mAb monotherapy without compromising graft survival. METHODS: Outbred juvenile rhesus monkeys underwent renal allotransplantation from MHC-disparate donors. After a 60-day course of triple therapy immunosuppression with steroids, cyclosporine, and mycophenolate mofetil, monkeys were treated with: (1) cessation of all immunosuppression (control); (2) seven monthly doses of 20 mg/kg hu5C8 (maintenance), or; (3) 20 mg/kg hu5C8 on posttransplant days 60, 61, 64, 71, 79, and 88 followed by five monthly doses (induction+maintenance). Graft rejection was defined by elevation in serum creatinine>1.5 mg/dl combined with histologic evidence of rejection. RESULTS: Graft survival for the three groups were as follows: group 1 (control): 70, 75, >279 days; group 2 (maintenance): 83, 349, >293 days, and; group 3 (induction+maintenance): 355, >377, >314 days. Acute rejection developing in two of four monkeys after treatment with conventional immunosuppression was successfully reversed with intensive hu5C8 monotherapy. CONCLUSIONS: Renal allograft recipients can be successfully converted to CD154 blockade monotherapy after 60 days of conventional immunosuppression. An induction phase of anti-CD154 mAb appears to be necessary for optimal conversion. Therefore, although concurrent administration of conventional immunosuppressive agents including steroids and calcineurin inhibitors has been shown to inhibit the efficacy of CD154 blockade, sequential conversion from these agents to CD154 blockade appears to be effective.

Animals↗
PubMed2001

Immunotoxin FN18-CRM9 induces stronger T cell signaling than unconjugated monoclonal antibody FN18.

BACKGROUND: The T-cell receptor (TCR)/CD3 complex is the target of therapeutic strategies aimed at prolonging allograft survival. The immunotoxin FN18-CRM9, composed of the anti-CD3 monoclonal antibody FN18 and the mutated diphtheria toxin CRM9, is useful for prolonging allograft survival in preclinical models of transplantation. To explore the influence of conjugation of the mutated diphtheria toxin on functional activation of the TCR/CD3 complex, we compared the effects of FN18-CRM9 and unconjugated FN18 on protein tyrosine phosphorylation and ligand/receptor internalization in purified monkey peripheral blood T cells. METHODS: Purified normal rhesus monkey T cells were incubated with unconjugated FN18 or conjugated FN18-CRM9 and examined for differences in antibody binding, tyrosine phosphorylation, and CD3 internalization. RESULTS: Binding cross-inhibition studies demonstrated that both compounds were able to inhibit fluorescein isothiocyanate-FN18 binding to CD3 with similar efficacy and potency. However, FN18-CRM9 was more potent than FN18 in triggering the phosphorylation of several proteins on tyrosine residues and in inducing CD3 internalization. The tyrosine kinase inhibitor genistein blocked FN18-CRM9-induced protein tyrosine phosphorylation and CD3 internalization, suggesting that tyrosine phosphorylation is involved in the internalization of the immunotoxin. Interestingly, in FN18-CRM9- but not FN18-treated cells, there was a gradual decrease in cellular CD3 protein levels within 24 and 48 hr; such a decrease was not observed with the control protein Csk. CONCLUSIONS: Our findings suggest that the conjugation of the mutated diphtheria toxin CRM9 to FN18 modulates the monoclonal antibody-mediated cross-linking of the TCR/CD3 complex, leading to a stronger protein tyrosine phosphorylation and CD3 internalization. This may in turn contribute to the greater efficacy of the immunotoxin in prolonging allograft survival.

Amino Acid Motifs↗
PubMed2001

Treatment with immunotoxin.

T-cell depletion prior to or beginning at the time of transplantation has been shown to be a valuable adjunct to the induction of immunological unresponsiveness. Both total lymphoid irradiation and anti-lymphocyte globulin have been used for this purpose in experimental models of transplantation as well as in human organ transplant recipients. However, these methods of T-cell depletion are limited in their ability to deplete T cells selectively due to non-specific targeting and limited efficacy. A new anti-CD3 immunotoxin has been developed with a far more potent ability to deplete T cells selectively as measured by flow cytometry analysis of peripheral blood T lymphocytes as well as lymph node lymphocytes. This immunotoxin is well tolerated by rhesus monkeys when administered in vivo. When administered as a single immunosuppressive agent pretransplant, it substantially promotes allograft survival, inducing tolerance in at least one-third of recipients as measured by subsequent acceptance of donor skin grafts and rejection of third-party skin grafts. When administered on the day of transplant in combination with steroid pretreatment and a brief course of deoxyspergualin or mycophenolate mofetil (4 to 14 days), long-term unresponsiveness is also produced and in a more reliable manner than using immunotoxin alone. A new immunotoxin directed at the human CD3epsilon has been developed with excellent potency in T-cell killing and lacking the Fc portion of the CD3 antibody. This construct may be useful for T-cell depletion in humans and has a potential application in tolerance induction in human organ transplantation. Lessons learned from anti-CD3 immunotoxin in the non-human primate model to date include (i) profound (2-3 log) depletion of T-cells can be accomplished safely without inducing lymphoma or infection, (ii) such depletion is a useful adjunct for tolerance induction to allogeneic organ transplants, and (iii) tolerance to both allogeneic renal transplants and xenogeneic islet transplants has been accomplished using such strategies to date in non-human primates and in pigs. Immunotoxin may be useful for the induction of chimerism using strategies that include donor bone marrow infusion. Successful strategies for tolerance induction have also been developed using immunotoxin without the adjunct of donor bone marrow or stem cell infusion. Clinical application of immunotoxin will use a newly engineered construct with the potential for causing cytokine release, less susceptibility to neutralization by anti-diphtheria antibody and not dependent on chemical conjugation of an antibody and toxin. The usefulness of immunotoxin is directly related to its tremendous potency for depleting T cells. Based on results in nonhuman primates, it is anticipated that it will become a useful agent in tolerance induction in humans.

Animals↗
PubMed2001

Tolerance and near-tolerance strategies in monkeys and their application to human renal transplantation.

Studies in non-human primates to evaluate tolerance strategies in organ transplantation have led to innovation in human transplantation. The two strategies we have studied in detail in non-human primates are T-cell depletion by anti-CD3 immunotoxin and co-stimulation blockade. Each of these strategies has been extended into early human trials in renal transplantation. The results of these human and non-human primate studies are summarized. Continued progress in better and safer immunosuppressive methods remains closely linked to research using non-human primates. However, there has not been a one-to-one correspondence between efficacy in the primate and efficacy in humans. Rather, principles can be derived from non-human primate studies that can be extended into human trials with the knowledge that regimens will likely differ in humans compared to non-human primates.

Animals↗
PubMed2001

Living-unrelated renal transplantation at the University of Wisconsin.

Since 1984, we have performed 243 living-unrelated renal transplants at the University of Wisconsin. Rejection occurred in 47% of the patients. Graft loss occurred in 59 patients and 39 patients died. Graft survival in LURD transplants at 10 years is 54% and 43% at 15 years. Patient survival is 68% at 10 years and 54% at 15 years. These long-term results demonstrate that LURD is equivalent to haploidentical renal transplantation and superior to cadaveric transplantation. Husband-to-wife donation demonstrated improved graft survival when compared with wife-to-husband and nonspousal donation. Living-unrelated renal transplantation has been utilized successfully at the University of Wisconsin and may help to alleviate the donor shortage.

Academic Medical Centers↗
PubMed2000

Increased glomerular deposits of von Willebrand factor in chronic, but not acute, rejection of primate renal allografts.

BACKGROUND: In our previously described primate renal allograft model, T cell ablation leads to long-term graft survival. The role of endothelial cell alteration in chronic rejection was examined in our model. METHODS: Renal transplants were performed in rhesus monkeys using a T cell- depleting immunotoxin, FN18-CRM9. Sections from 10 rejected kidneys (5 acute and 7 chronic rejection) were examined after immunohistochemical staining for expression of endothelium-related proteins [von Willebrand factor (vWF), CD62P, and CD31], fibrinogen, and a macrophage marker (CD68). Glomerular staining for each antigen was graded on a semiquantitative scale. RESULTS: Intense staining for vWF was consistently observed in glomerular endothelium, subendothelium, and mesangium in all kidneys removed due to chronic rejection. vWF staining was weak in kidneys showing acute rejection. The difference in glomerular staining was statistically significant. Staining for vWF in extraglomerular vessels was nearly identical in kidneys showing acute and chronic rejection. Expression of CD62P was increased in extraglomerular vessels in allografts with chronic rejection, but the glomeruli showed little or no staining. There was no significant difference in the glomerular staining for CD62P or CD31 in organs showing acute and chronic rejection. Fibrinogen staining of glomerular mesangium was seen in kidneys with chronic rejection. Macrophages (CD68+) infiltrating glomeruli were more numerous in kidneys showing chronic rejection. CONCLUSION: Increased glomerular deposition of vWF in renal allografts showing chronic rejection, without increased staining for CD62P or CD31, suggests increased constitutive secretion of vWF from endothelial cells as a component of the mechanism of chronic rejection in our model.

Acute Disease↗
PubMed2000

Long-term results of liver transplantation in older patients 60 years of age and older.

BACKGROUND: Advances in perioperative care and immunosuppression have enabled clinicians to broaden the indications for organ transplantation. Advanced age is no longer considered a contraindication to transplantation at most centers. Although short-term studies of elderly liver transplant recipients have demonstrated that the incidence of complications and overall patient survival are similar to those of younger adults, transplant center-specific, long-term data are not available. METHODS: From August of 1984 to September of 1997, 91 patients 60 years of age or older received primary liver transplants at the University of Wisconsin, Madison. This group of patients was compared with a group of younger adults (n=387) ranging in age from 18 to 59 years who received primary liver transplants during the same period. The most common indications for transplantation in both groups were Laennec's cirrhosis, hepatitis C, primary biliary cirrhosis, primary sclerosing cholangitis, and cryptogenic cirrhosis. There was no difference in the preoperative severity of illness between the groups. Results. The length of hospitalization was the same for both groups, and there were no significant differences in the incidence of rejection, infection (surgical or opportunistic), repeat operation, readmission, or repeat transplantation between the groups. The only significant difference identified between the groups was long-term survival. Five-year patient survival was 52% in the older group and 75% in the younger group (P<0.05). Ten-year patient survival was 35% in the older group and 60% in the younger group (P<0.05). The most common cause of late mortality in elderly liver recipients was malignancy (35.0%), whereas most of the young adult deaths were the result of infectious complications (24.2%). CONCLUSION: Although older recipients at this center did as well as younger recipients in the early years after liver transplantation, long-term survival results were not as encouraging.

Aged↗
PubMed2000

Potentiation of CD3-induced expression of the linker for activation of T cells (LAT) by the calcineurin inhibitors cyclosporin A and FK506.

The activation of blood cells, including T cells, triggers intracellular signals that control the expression of critical molecules, including cytokines and cytokine receptors. We show that T-cell receptor (TCR) ligation increases the cellular level of the protein linker for activation of T cells (LAT), a molecule critical for T-cell development and function. T-cell activation increased LAT messenger RNA, as determined by reverse transcription-polymerase chain reaction and by Northern blotting. The TCR-induced increase in LAT expression involved the activation of the serine/threonine kinases PKC and MEK, because inhibitors of these kinases blocked the increase in LAT. Accordingly, the PKC activator phorbol myristate acetate up-regulated LAT expression. Strikingly, the calcineurin inhibitors cyclosporin A (CsA) and FK506 strongly potentiated TCR-induced LAT expression, suggesting that the activation of calcineurin following TCR ligation negatively regulates LAT expression. Accordingly, Ca(++ )ionophores, which can activate calcineurin by increasing intracellular Ca(++), blocked the TCR-induced increase in cellular LAT. CsA and FK506 blocked the Ca(++ )ionophores' inhibitory effect on LAT expression. Notably, CsA and FK506 preferentially up-regulated TCR-induced LAT expression; under the same conditions, these compounds did not increase the expression of 14 other molecules that previously had been implicated in T-cell activation. These data show that TCR-induced LAT expression involves the activation of the PKC-Erk pathway and is negatively regulated by the activation of calcineurin. Furthermore, the potentiation of TCR-induced LAT expression by CsA and FK506 suggests that the action of these agents involves up-regulating the cellular level of critical signaling molecules. These findings may have important therapeutic implications. (Blood. 2000;95:2733-2741)

Adaptor Proteins, Signal Transducing↗
PubMed2000

Regulation of T cell receptor- and CD28-induced tyrosine phosphorylation of the focal adhesion tyrosine kinases Pyk2 and Fak by protein kinase C. A role for protein tyrosine phosphatases.

The T cell receptor (TCR)-CD3 complex and the costimulatory molecule CD28 are critical for T cell function. Both receptors utilize protein tyrosine kinases (PTKs) for the phosphorylation of various signaling molecules, a process that is critical for the function of both receptors. The PTKs of the focal adhesion family, Pyk2 and Fak, have been implicated in the signaling of TCR and CD28. We show here evidence for the regulation of TCR- and CD28-induced tyrosine phosphorylation of the focal adhesion PTKs by protein kinase C (PKC). Thus, treating Jurkat T cells with the PKC activator phorbol 12-myristate 13-acetate (PMA) rapidly and strongly reversed receptor-induced tyrosine phosphorylation of the focal adhesion PTKs. In contrast, PMA did not affect TCR-induced tyrosine phosphorylation of CD3zeta or the PTKs Fyn and Zap-70. However, PMA induced a strong and rapid dephosphorylation of the linker molecule for activation of T cells. PMA failed to induce the dephosphorylation of proteins in PKC-depleted cells or in cells pretreated with the PKC inhibitor Ro-31-8220, confirming the role of PKC in mediating the PMA effect on receptor-induced protein tyrosine phosphorylation. The involvement of protein tyrosine phosphatases (PTPases) in mediating the dephosphorylation of the focal adhesion PTKs was confirmed by the failure of PMA to dephosphorylate Pyk2 in cells pretreated with the PTPase inhibitor orthovanadate. These results implicate PKC in the regulation of receptor-induced tyrosine phosphorylation of the focal adhesion PTKs in T cells. The data also suggest a role for PTPases in the PKC action.

Antigens, CD↗
PubMed2000

Knowledge about transplantation tolerance gained in primates.

Research in transplantation tolerance relies on application of successful strategies in a nonhuman-primate organ transplant model for preclinical testing. Three principal approaches are being evaluated: hematopoietic chimerism, lymphocyte depletion and costimulation blockade. Interactive work in these three areas has yielded much new information on mechanisms of tolerance and opened the door to pilot clinical trials. Clinical application of xenotransplantation is likely to depend on such strategies.

Animals↗
PubMed2000

Liver transplantation from controlled non-heart-beating donors.

BACKGROUND: The use of organs from non-heart-beating donors (NHBDs) has been proposed as one way to increase the donor pool. However, few centers have transplanted livers from NHBDs. We report here the results of 19 liver transplants from controlled NHBDs. METHODS: From January 1993 through August 1999, 364 liver transplantations were performed from heart-beating donors (HBDs) and 19 liver transplantations were performed from NHBDs. Donor and recipient characteristics, posttransplant complications, and patient and allograft survival were compared. RESULTS: No differences in hepatic artery, portal vein, or biliary complications were noted between the groups. However, the rate of primary nonfunction was higher in recipients of livers from NHBDs (10.5% vs. 1.3%; P = .04). No difference in patient survival was seen between recipients of NHBDs or HBDs (72.6% vs. 84.8%; P =.36); however, allograft survival was lower in recipients who received livers from NHBDs (53.8% vs. 80.9%; P =.007). CONCLUSIONS: Liver transplantation from controlled NHBDs results in similar patient survival and post-transplant complications. However, primary nonfunction was higher and allograft survival was less in recipients of livers from NHBDs. The results of liver transplantation from controlled NHBDs are encouraging and should continue to be cautiously pursued as one way to help alleviate the current shortage of donor livers.

Adult↗