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ObjectivesThe objective of this study was to evaluate the performance of pediatric pharmacogenetic-based dose prediction models by using an independent cohort of pediatric patients from a multicenter trial.MethodsClinical and genetic data (CYP2C9 [cytochrome P450 2C9] and VKORC1 [vitamin K epoxide reductase]) were collected from pediatric patients aged 3 months to 17 years who were receiving warfarin as part of standard care at 3 separate clinical sites. The accuracy of 8 previously published pediatric pharmacogenetic-based dose models was evaluated in the validation cohort by comparing predicted maintenance doses to actual stable warfarin doses. The predictive ability was assessed by using the proportion of variance (R(2)), mean prediction error (MPE), and the percentage of predictions that fell within 20% of the actual maintenance dose.ResultsThirty-two children reached a stable international normalized ratio and were included in the validation cohort. The pharmacogenetic-based warfarin dose models showed a proportion of variance ranging from 35% to 78% and an MPE ranging from -2.67 to 0.85 mg/day in the validation cohort. Overall, the model developed by Hamberg et al showed the best performance in the validation cohort (R(2) = 78%; MPE = 0.15 mg/day) with 38% of the predictions falling within 20% of observed doses.ConclusionsPharmacogenetic-based algorithms provide better predictions than a fixed-dose approach, although an optimal dose algorithm has not yet been developed.

Thrombocytopenia and thrombosis following treatment with the integrin [alpha]IIb[beta]3 antagonist eptifibatide are rare complications caused by patient antibodies specific for ligand-occupied [alpha]IIb[beta]3. Whether such antibodies induce platelet clearance by simple opsonization, by inducing mild platelet activation, or both is poorly understood. To gain insight into the mechanism by which eptifibatide-dependent antibodies initiate platelet clearance, we incubated normal human platelets with patient serum containing an [alpha]IIb[beta]3-specific, eptifibatide-dependent antibody. We observed that in the presence of eptifibatide, patient IgG induced platelet secretion and aggregation as well as tyrosine phosphorylation of the integrin [beta]3 cytoplasmic domain, the platelet Fc[gamma]RIIa Fc receptor, the protein-tyrosine kinase Syk, and phospholipase C[gamma]2. Each activation event was inhibited by preincubation of the platelets with Fab fragments of the Fc[gamma]RIIa-specific mAb IV.3 or with the Src family kinase inhibitor PP2. Patient serum plus eptifibatide did not, however, activate platelets from a patient with a variant form of Glanzmann thrombasthenia that expressed normal levels of Fc[gamma]RIIa and the [alpha]IIb[beta]3 complex but lacked most of the [beta]3 cytoplasmic domain. Taken together, these data suggest a novel mechanism whereby eptifibatide-dependent antibodies engage the integrin [beta]3 subunit such that Fc[gamma]RIIa and its down-stream signaling components become activated, resulting in thrombocytopenia and a predisposition to thrombosis., Introduction The integrin [alpha]IIb[beta]3 (also known as glycoprotein IIb-IIIa [GPIIb-IIIa]) is a member of the integrin family of cell adhesion receptors and is essential for normal hemostasis (1). Following platelet [...]

A 12-year-old girl presented with weakness, diplopia, and lethargy after a prodrome of gastroenteritis. Laboratory studies were compatible with a diagnosis of hemolytic uremic syndrome. She developed seizures that were controlled by diphenylbydantoin and valium. In spite of peritoneal dialysis and fresh frozen plasma infusions, she progressed to a left hemiplegia associated with a brain scan finding of decreased blood flow in the right middle cerebral artery perfusion area. A 5 liter whole blood exchange transfusion did not improve the neurological status or low platelet count. Daily plasma exchanges with fresh frozen plasma replacement resulted in normal platelet count within 48 hours and was followed by progressive improvement in neurological status. Platelet agglutinating factor decreased to control levels. A repeat brain scan was normal. [ABSTRACT FROM AUTHOR]

Abstract: Hepatitis C virus (HCV) has a high rate of replication and lacks RNA-proofreading capabilities, thereby leading to variant or mutant viruses circulating within the host as a quasispecies. Previous work in our laboratory identified viral variants that emerged in a class-II immunodominant epitope NS3358-375 of the non-structural-3 (NS3) protein region of HCV, the sequence of which is based on genotype 1A, the most prevalent genotype in the United States. Further work suggested that positive immune selection pressure was driving viral variation. Paradoxically, viral variants account for only a small percentage of the circulating virus in human beings and in chimpanzees, suggesting that passive evasion is not the only means of escape by HCV. This observation suggests a unique pathogenesis for HCV as it persists in the host. In the current study, we hypothesize that viral variants are acting as altered peptide ligands (APLs). To test this hypothesis, we used cloned T cells specific for NS3358-375 peptide, which demonstrated attenuated T-cell and interferon-γ (IFN-γ) responses to individual variant peptides, when compared with the NS3358-375 stimulated T-cell clones. Furthermore, such variants could act as APLs, based on their ability to antagonize the IFN-γ proliferative responses of clones specific for NS3358-375. In addition, major histocompatibility complex (MHC) class II tetramer staining demonstrated that variant peptide–MHC complexes were able to specifically bind to NS3358-375 T-cell clones and that both the variant and NS3358-375 tetramers were able to bind to the same CD4+ T cells. Taken together, the results suggest that viral variants may act as APL to effectively blunt the T-cell response to an important HCV epitope. [Copyright &y& Elsevier]

Thrombocytopenia and thrombosis following treatment with the integrin αIIbβ3 antagonist eptifibatide are rare complications caused by patient antibodies specific for ligand-occupied αIIbβ3. Whether such antibodies induce platelet clearance by simple opsonization, by inducing mild platelet activation, or both is poorly understood. To gain insight into the mechanism by which eptifibatide-dependent antibodies initiate platelet clearance, we incubated normal human platelets with patient serum containing an αIIbβ3-specific, eptifibatide-dependent antibody. We observed that in the presence of eptifibatide, patient IgG induced platelet secretion and aggregation as well as tyrosine phosphorylation of the integrin β3 cytoplasmic domain, the platelet FcγRIIa Fc receptor, the protein-tyrosine kinase Syk, and phospholipase Cγ2. Each activation event was inhibited by preincubation of the platelets with Fab fragments of the FcγRIIa-specific mAb IV.3 or with the Src family kinase inhibitor PP2. Patient serum plus eptifibatide did not, however, activate platelets from a patient with a variant form of Glanzmann thrombasthenia that expressed normal levels of FcγRIIa and the αIIbβ3 complex but lacked most of the β3 cytoplasmic domain. Taken together, these data suggest a novel mechanism whereby eptifibatide-dependent antibodies engage the integrin β3 subunit such that FcγRIIa and its downstream signaling components become activated, resulting in thrombocytopenia and a predisposition to thrombosis. [ABSTRACT FROM AUTHOR]