Belatacept-Resistant Rejection Is Associated With CD28+ Memory CD8 T Cells.

Recently, newer therapies have been designed to more specifically target rejection in an effort to improve efficacy and limit unwanted toxicity. Belatacept, a CD28-CD80/86 specific reagent, is associated with superior patient survival and graft function compared with traditional therapy, but its adoption as a mainstay immunosuppressive therapy has been tempered by increased rejection rates. It is essential that the underlying mechanisms associated with this rejection be elucidated before belatacept is more widely used. To that end, we designed a study in a nonhuman primate kidney transplant model where animals were treated with either a belatacept- or a tacrolimus-based immunosuppressive regimen. Interestingly, we found that elevated pretransplant frequencies of CD28+ CD8+ TEMRA cells are associated with rejection on belatacept but not tacrolimus treatment. Further analysis showed that the CD28+ CD8+ TEMRA cells rapidly lose CD28 expression after transplant in those animals that go on to reject with the allograft infiltrate being predominantly CD28- . These data suggest that CD28+ memory T cells may be resistant to belatacept, capable of further differentiation including loss of CD28 expression while maintaining effector function. The unique signaling requirements of CD28+ memory T cells provide opportunities for the development of targeted therapies, which may synergize with belatacept to prevent costimulation-independent rejection.

Anti-Leukocyte Function-Associated Antigen 1 Therapy in a Nonhuman Primate Renal Transplant Model of Costimulation Blockade-Resistant Rejection.

Costimulation blockade with the fusion protein belatacept provides a desirable side effect profile and improvement in renal function compared with calcineurin inhibition in renal transplantation. This comes at the cost of increased rates of early acute rejection. Blockade of the integrin molecule leukocyte function-associated antigen 1 (LFA-1) has been shown to be an effective adjuvant to costimulation blockade in a rigorous nonhuman primate (NHP) model of islet transplantation; therefore, we sought to test this combination in an NHP renal transplant model. Rhesus macaques received belatacept maintenance therapy with or without the addition of LFA-1 blockade, which was achieved using a murine-derived LFA-1-specific antibody TS1/22. Additional experiments were performed using chimeric rhesus IgG1 (TS1/22R1) or IgG4 (TS1/22R4) variants, each engineered to limit antibody clearance. Despite evidence of proper binding to the target molecule and impaired cellular egress from the intravascular space indicative of a therapeutic effect similar to prior islet studies, LFA-1 blockade failed to significantly prolong graft survival. Furthermore, evidence of impaired protective immunity against cytomegalovirus was observed. These data highlight the difficulties in translating treatment regimens between organ models and suggest that the primarily vascularized renal model is more robust with regard to belatacept-resistant rejection than the islet model.

Dual islet transplantation modeling of the instant blood-mediated inflammatory reaction.

Islet xenotransplantation is a potential treatment for diabetes without the limitations of tissue availability. Although successful experimentally, early islet loss remains substantial and attributed to an instant blood-mediated inflammatory reaction (IBMIR). This syndrome of islet destruction has been incompletely defined and characterization in pig-to-primate models has been hampered by logistical and statistical limitations of large animal studies. To further investigate IBMIR, we developed a novel in vivo dual islet transplant model to precisely characterize IBMIR as proof-of-concept that this model can serve to properly control experiments comparing modified xenoislet preparations. WT and α1,3-galactosyltransferase knockout (GTKO) neonatal porcine islets were studied in nonimmunosuppressed rhesus macaques. Inert polyethylene microspheres served as a control for the effects of portal embolization. Digital analysis of immunohistochemistry targeting IBMIR mediators was performed at 1 and 24 h after intraportal islet infusion. Early findings observed in transplanted islets include complement and antibody deposition, and infiltration by neutrophils, macrophages and platelets. Insulin, complement, antibody, neutrophils, macrophages and platelets were similar between GTKO and WT islets, with increasing macrophage infiltration at 24 h in both phenotypes. This model provides an objective and internally controlled study of distinct islet preparations and documents the temporal histology of IBMIR.

Enhanced de novo alloantibody and antibody-mediated injury in rhesus macaques.

Chronic allograft rejection is a major impediment to long-term transplant success. Humoral immune responses to alloantigens are a growing clinical problem in transplantation, with mounting evidence associating alloantibodies with the development of chronic rejection. Nearly a third of transplant recipients develop de novo antibodies, for which no established therapies are effective at preventing or eliminating, highlighting the need for a nonhuman primate model of antibody-mediated rejection. In this report, we demonstrate that depletion using anti-CD3 immunotoxin (IT) combined with maintenance immunosuppression that included tacrolimus with or without alefacept reliably prolonged renal allograft survival in rhesus monkeys. In these animals, a preferential skewing toward CD4 repopulation and proliferation was observed, particularly with the addition of alefacept. Furthermore, alefacept-treated animals demonstrated increased alloantibody production (100%) and morphologic features of antibody-mediated injury. In vitro, alefacept was found to enhance CD4 effector memory T cell proliferation. In conclusion, alefacept administration after depletion and with tacrolimus promotes a CD4+memory T cell and alloantibody response, with morphologic changes reflecting antibody-mediated allograft injury. Early and consistent de novo alloantibody production with associated histological changes makes this nonhuman primate model an attractive candidate for evaluating targeted therapeutics.

The paradigm of Huntington disease.

I recall it as vividly as though it had occurred but yesterday. It made a most enduring impression upon my boyish mind which was my very first impulse to choosing chorea as my virgin contribution to medical lore. Driving with my father through a wooded road leading from East Hampton to Amagansett we suddenly came upon two women, mother and daughter, both tall and thin, almost cadaverous, both bowing, twisting, grimacing. I stared in wonderment, almost in fear. What could it mean? My father paused to speak with them and we passed on. Then my Gamaliel-like instruction began; my medical education had its inception. From this point on, my interest in the disease has never wholly ceased. [George Huntington, at 59, recalling how at the age of 8 years he first saw Huntington disease while traveling with his physician father on his professional rounds in 1858].

Open-label trial of oral nalmefene therapy for the pruritus of cholestasis.

The aims of this study were to determine whether long-term oral administration of the opiate antagonist nalmefene is associated with any beneficial effects in patients with pruritus secondary to cholestatic liver disease and to assess the safety of long-term administration of this drug to these patients. Fourteen patients with unrelieved chronic pruritus of cholestasis were studied. Scratching activity, independent of limb movements, was recorded continuously for 24-hour periods before and during treatment with an initial ameliorating dose of nalmefene. Simultaneously, during these periods, visual analogue scores (VASs) of pruritus were recorded every 4 hours while patients were awake. The dose of nalmefene, which initially was 2 mg orally twice daily, was increased during the study, usually until a satisfactory clinical response was achieved. Five patients experienced a transient opioid withdrawal-like reaction that did not preclude continuing with nalmefene therapy. Serum biochemical indices of cholestasis did not change appreciably during treatment. Thirteen patients reported amelioration of the perception of pruritus on nalmefene. In 5 patients, exacerbations of pruritus occurred approximately 4 weeks after an initial ameliorating dose had been reached; these exacerbations were managed by increasing the dose. Baseline mean values for VAS and scratching activity were higher than corresponding means during nalmefene therapy in 13 (P = .002) and 12 (P = .013) patients, respectively. Possible tolerance to nalmefene occurred in 3 patients. Three patients experienced marked exacerbation of pruritus after nalmefene therapy was suddenly discontinued. Blood levels of nalmefene were consistent with normal pharmacokinetics of the drug. These results suggest that nalmefene may have a favorable risk-to-benefit ratio when it is administered orally long-term to patients with the pruritus of cholestasis.

Carbamazepine but not valproate induces bupropion metabolism.

Bupropion (BUP) may be less likely than other antidepressants to cause switches into mania and rapid cycling, suggesting utility in bipolar disorder. The combination of BUP with the mood-stabilizing anticonvulsants carbamazepine (CBZ) or valproate (VPA) is a strategy that might further lessen the risk of mania. CBZ induces, and to a lesser extent VPA inhibits the hepatic metabolism of various medications, but their effects on BUP have not been previously studied. Inpatients with mood disorders had pharmacokinetic profiles of BUP and metabolites assessed after single, oral, 150-mg doses of BUP while receiving placebo (N = 17) or during chronic blind CBZ (N = 12) or VPA (N = 5) monotherapy. CBZ but not VPA therapy decreased BUP peak concentrations (Cmax) by 87% (p < 0.0001) and 24-h area under the curve (AUC) by 90% (p < 0.0001), threohydrobupropion Cmax by 81% (p <0.0009) and AUC by 86% (p < 0.002), and erythropydrobupropion Cmax by 86% (p < 0.05) and AUC by 96% (p < 0.05). CBZ increased hydroxybupropion (H-BUP) Cmax by 71% (p < 0.007) and AUC by 50% (p < 0.09) and H-BUP AUC by 94% (p < 0.02). Thus, CBZ markedly decreased BUP and increased H-BUP concentrations, whereas VPA did not affect BUP but increased H-BUP concentrations. Further studies are required to determine how these differential effects of CBZ and VPA on BUP pharmacokinetics influence the tolerability and efficacy of combination therapies with these agents.