Trough Level of Mycophenolic Acid Did Not Affect De Novo DSA Development in Kidney Transplantation.

INTRODUCTION: Mycophenolate mofetil has improved long-term outcomes of kidney transplantation. However, the impact of mycophenolic acid (MPA) trough level on the development of de novo donor-specific anti-HLA antibody (DSA) is unclear. We examined the relation between MPA trough level and de novo DSA development. METHOD: We retrospectively studied 617 kidney recipients whose MPA trough level and de novo DSA data were available. All patients underwent primary kidney transplant from living donors from 2008 to 2014, and were chronically treated with a calcineurin inhibitor, mycophenolate mofetil, and +/- steroids. They were equally divided into 4 groups according to the mean trough level of MPA (mMPA) at 1 year post-transplantation: Group 1, mMPA < 2.14 ng/mL (n = 152); Group 2, mMPA 2.14-2.83 ng/mL (n = 157); Group 3, mMPA 2.83-3.57 ng/mL (n = 153); and Group 4, mMPA ≥ 3.57 ng/mL (n = 155). The groups were compared by incidence rate of de novo DSA, graft survival rate, and renal function. RESULTS: The incidence rates of de novo DSA were 33.3% in Group 1, 23.7% in Group 2, 22.9% in Group 3, and 30.3% in Group 4 (P = .158). Although there was no significant difference in graft survival rates, a significant difference of renal functions was noted: the higher the renal function, the lower the MPA trough level. CONCLUSION: The mMPA trough level at 1 year post-transplantation was not statistically associated with the incidence rate of de novo DSA after kidney transplantation.

Stepwise minimization of the immunosuppressive therapy in pediatric liver transplantation. A conceptual approach towards operational tolerance.

The evolution of immunosuppression in pediatric liver transplantation has been characterized by a steady reduction of the immunosuppressive load, including removal of anti-lymphocyte antibodies, with the aim to reduce the incidence of EBV-related post-transplant lymphoproliferative disorders. Acute rejection rates were studied retrospectively over two decades of pediatric liver transplantation, according to the successive immunoprophylactic regimens. 318 primary pediatric liver transplant recipients, included between 1984 and 2004 in successive prospective trials, were analyzed, with respect to the impact of the immunosuppressive protocol on acute rejection occurrence. A progressive decrease of rejection incidences was observed, which corresponded to reduced immunosuppressive load and to transplant eras. Such trend might be related to changing approaches towards acute rejection histology and therapy by transplant clinicians, but also to the stepwise minimization of immunosuppressive protocols, putatively enhancing graft acceptance. We hypothesize that the recent population of liver transplant recipients with low immunosuppression might be more suitable for progressive immunosuppression withdrawal trial, with the aim to reach ultimately operational tolerance.

Involvement of altered B7 expression in dioxin immunotoxicity: B7 transfection restores the CTL but not the autoantibody response to the P815 mastocytoma.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a highly toxic environmental contaminant, suppresses both CTL and cytotoxic alloantibody production in C57BL/6 mice challenged with allogeneic P815 tumor cells. Recent evidence suggests that TCDD interferes with the initial activation of CD4+ Th cells, possibly through an indirect mechanism. In this study, we examined the effect of TCDD on the expression of the important costimulatory molecules, B7-1 and B7-2, in P815 allograft immunity. Expression of B7-2, but not B7-1, was up-regulated on splenic B220+ and Mac-1+ cells in P815-challenged mice. Exposure to TCDD significantly decreased the expression of B7-2 on B220+ and Mac-1+ cells in P815-challenged mice. Providing exogenous B7-mediated costimulation, in the form of B7-transfected P815 tumor cells, induced CTL activity in TCDD-treated mice by a mechanism that was independent of CD4+ T cells. In contrast, B7-transfected P815 cells did not restore the cytotoxic alloantibody response in TCDD-treated mice. These results are consistent with a model in which MHC class II-, B7-transfected P815 tumor cells can directly activate CD8+ CTL precursors but cannot directly stimulate CD4+ T helper cells required for B cell activation. These results also demonstrate that CTL precursors in TCDD-treated mice are functional and able to differentiate into effector CTL provided they receive adequate costimulation via B7 and suggest that defective costimulation, through reduced B7-2 expression, may play a role in TCDD-induced immunotoxicity. In support of this hypothesis, we show that blocking B7-2/CD28 interactions, and to a lesser degree B7-1/CD28 interactions, suppressed the alloimmune responses to P815 tumor cells, which further indicates that B7-2 represents the dominant B7 molecule involved in the generation of an immune response to allogeneic P815 tumor cells.

Prolonged survival of hamster-to-rat pulmonary xenografts by tacrolimus (FK506) and cyclophosphamide.

BACKGROUND: Severe shortage of donor organs in clinical lung transplantation prompted us to investigate the potential use of pulmonary xenografts. The purpose of this study was to determine whether an immunosuppressive regimen of tacrolimus (FK506) and cyclophosphamide would prolong the survival of hamster-to-rat pulmonary xenografts. METHOD: Left lung transplantation was done with male Golden Syrian hamsters used as donors and inbred male Lewis rats as recipients. Control animals (n = 10) received no immunosuppressive drugs whereas experimental animals (n = 6) were treated with tacrolimus and cyclophosphamide. Tacrolimus was administered intramuscularly at a dosage of 2 mg/kg per day on postoperative days 0 to 4, followed by 1 mg/kg per day on days 5 to 29 and 0.5 mg/kg per day on days 30 to 99. Cyclophosphamide (8 mg/kg per day) was administered orally from the day before transplantation to day 8. After transplantation the animals were monitored by chest radiography. Recipient animals were killed at timed intervals (days 60 and 100) and when the chest radiograph showed complete opacification of the transplanted lung. At necropsy, pulmonary xenografts were examined histologically for evidence of rejection, which was graded on a scale of 0 (no rejection) to 4 (severe rejection). Antihamster lymphocytotoxic antibody titer was also measured in recipient animals after transplantation. RESULTS: Pulmonary xenografts in the control animals had a median [correction of medium] survival time of 3 days, whereas the median survival in treated animals was more than 74 days. All pulmonary xenografts in control animals had severe rejection on day 3 after transplantation, whereas those in the treated animals had no rejection on days 60 and 100. The lymphocytotoxic antibody titers in control animals increased from 1:16 before operation to 1:4096 on day 3 (p < 0.01). In the treated animals, the lymphocytotoxic antibody titer on day 21 was 1: 8, which was not different from the preoperative value (1:16). CONCLUSION: These results indicate that a combination of tacrolimus and a short course of cyclophosphamide prolongs the survival of pulmonary xenografts in a hamster-to-rat model.

Autogenic thymocytotoxic IgG antibody in normal guinea pigs.

Normal guinea pig serum (GPS) was confirmed to be cytotoxic for guinea pig thymocytes at 4 degrees C. Approximately 50% of the cells were sensitive for the cytotoxic action of GPS (4 h incubation). Binding of IgG and, to a smaller extent, IgM to the thymocyte surface was shown after incubation with GPS. Absorption of GPS with protein A agarose (which removes immunoglobulins), heat inactivation (56 degrees C, which removes complement activity) or treatment with 2-mercaptoethanol (2-me) (which affected binding of IgG and IgM to thymocytes) abolished the cytotoxic activity. After gel filtration chromatography with Sephadex G-150, the cytotoxic activity was found in fractions with molecular weights comparable to that of IgG. This is different from reports of others on natural thymocytotoxic antibodies (NTA) where IgM was found to be the dominant thymocytotoxic antibody. The toxic activity in GPS was readily absorbed by autogenic bone marrow, spleen, lymph node and thymus cells. In contrast to normal thymocytes, mitogen stimulated thymus cells were totally resistant to the cytotoxic activity. In summary, it is suggested that the thymocytotoxic activity in GPS at 4 degrees C is mediated by IgG and complement and is directed against immature thymocytes. The antigenic determinant is also present on cells in other lymphoid organs.