Thrombin generation and bleeding in haemophilia inhibitor patients during immune tolerance induction.

BACKGROUND: Inhibitor formation complicates haemophilia treatment and requires immune tolerance induction to rid inhibitors over 5 BU. In the prospective, randomized International Immune Tolerance Study, immune tolerance induction was equally effective with high-dose (HD) (200 IU kg-1 day-1 ) and low-dose (LD) (50 IU kg-1 3× per week) factor VIII, but haemorrhages were twofold higher in the LD arm. This finding was unexpected as inhibitors neutralize FVIII activity. We hypothesized that the thrombin generation assay (TGA), a global measure of clot formation, might predict bleeding better than FVIII levels. METHODS: We evaluated TGA using relipidated tissue factor (TF) on 83 thawed, recalcified corn trypsin inhibitor/citrate plasma samples from 31 subjects (17 HD, 14 LD) who participated on the ITI study, and who had sufficient sample available and appropriate informed consent. RESULTS: There were no significant differences in peak thrombin, estimated thrombin potential, maximum rate or lag time between HD and LD arms; between pre-, during and post-ITI time points, or after FVIII spiking. In 19 subjects (12 HD, 7 LD) with anti-FVIII<1.0 BU, the prevalence of non-neutralizing antibody (NNA) and neutralizing antibody (NA) was 89.5% (17/19), and the latter strongly correlated with anti-VIII titer, r = 0.73 [95% CI: 0.55, 0.88]. CONCLUSION: In haemophilia inhibitor patients, thrombin generation is present, but does not predict bleeding risk. Following tolerance induction, NNA remains detectable in the majority.

Dopaminergic neurons protected from degeneration by GDNF gene therapy.

Glial cell line-derived neurotrophic factor (GDNF) supports growth and survival of dopaminergic (DA) neurons. A replication-defective adenoviral (Ad) vector encoding human GDNF injected near the rat substantia nigra was found to protect DA neurons from the progressive degeneration induced by the neurotoxin 6-hydroxydopamine (6-OHDA) injected into the striatum. Ad GDNF gene therapy reduced loss of DA neurons approximately threefold 6 weeks after 6-OHDA lesion, as compared with no treatment or injection of Ad lacZ or Ad mGDNF (encoding a biologically inactive deletion mutant GDNF). These results suggest that Ad vector-mediated GDNF gene therapy may slow the DA neuronal cell loss in humans with Parkinson's disease.

Mechanisms regulating the development of oligodendrocytes and central nervous system myelin.

Oligodendrocytes and the myelin they produce are a remarkable vertebrate specialization that enables rapid and efficient nerve conduction within the central nervous system. The generation of myelin during development involves a finely-tuned pathway of oligodendrocyte precursor specification, proliferation and migration followed by differentiation and the subsequent myelination of appropriate axons. In this review we summarize the molecular mechanisms known to regulate each of these processes, including the extracellular ligands that promote or inhibit development of the oligodendrocyte lineage, the intracellular pathways they signal through and the key transcription factors that mediate their effects. Many of these regulatory mechanisms have recurring roles in regulating several transitions during oligodendrocyte development, highlighting their importance. It is also highly likely that many of these developmental mechanisms will also be involved in myelin repair in human neurological disease.

Lack of viral escape and defective in vivo activation of human immunodeficiency virus type 1-specific cytotoxic T lymphocytes in rapidly progressive infection.

Human immunodeficiency virus type 1 (HIV-1)-specific immune responses over the course of rapidly progressive infection are not well defined. Detailed longitudinal analyses of neutralizing antibodies, lymphocyte proliferation, in vivo-activated and memory cytotoxic T-lymphocyte (CTL) responses, and viral sequence variation were performed on a patient who presented with acute HIV-1 infection, developed an AIDS-defining illness 13 months later, and died 45 months after presentation. Neutralizing-antibody responses remained weak throughout, and no HIV-1-specific lymphocyte proliferative responses were seen even early in the disease course. Strong in vivo-activated CTL directed against Env and Pol epitopes were present at the time of the initial drop in viremia but were quickly lost. Memory CTL against Env and Pol epitopes were detected throughout the course of infection; however, these CTL were not activated in vivo. Despite an initially narrow CTL response, new epitopes were not targeted as the disease progressed. Viral sequencing showed the emergence of variants within the two targeted CTL epitopes; however, viral variants within the immunodominant Env epitope were well recognized by CTL, and there was no evidence of viral escape from immune system detection within this epitope. These data demonstrate a narrowly directed, static CTL response in a patient with rapidly progressive disease. We also show that disease progression can occur in the presence of persistent memory CTL recognition of autologous epitopes and in the absence of detectable escape from CTL responses, consistent with an in vivo defect in activation of CTL.

Persistence of human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte clones in a subject with rapid disease progression.

We longitudinally measured T-cell receptor transcript frequencies of human immunodeficiency virus type 1 (HIV-1) specific cytotoxic T lymphocytes (CTL) in an individual with rapidly progressive disease and high levels of viremia. CTL clones elicited during acute HIV-1 infection were present at the time of death, despite absent functional CTL responses, arguing against clonal deletion as a mechanism for the decline of CTL responses observed during HIV-1 infection.

Enhanced gene transfer to rabbit jugular veins by an adenovirus containing a cyclic RGD motif in the HI loop of the fiber knob.

Gene therapy using recombinant adenoviral vectors represents a promising therapeutic tool to prevent vein graft stenosis, the main complication of coronary artery bypass grafting. However, the low transduction efficiency of vascular smooth muscle cells and endothelial cells (EC) is a potential limitation, presumably due to the low levels of functional adenovirus receptor (coxsackie:adenovirus receptor; CAR). Designing vectors specifically targeted to alpha(v) integrins is a strategy that might overcome the poor expression of CAR in vascular smooth muscle cells and EC. RGD, a receptor-binding motif that can interact with alpha(v) integrins, was inserted into the HI loop and at the C-terminus of the adenoviral fiber protein in two separate adenovirus vectors encoding a beta-galactosidase reporter gene. Av1nBgCRGD (C-terminus) and Av1nBgHIRGD (HI loop) were evaluated in EC in culture and in jugular vein organ culture. Transduction of primary rat and rabbit EC with Av1nBgHIRGD was significantly more efficient when compared to Av1nBgCRGD or Av1nBg. Transduction of mouse, rat and rabbit jugular veins in organ culture using Av1nBg showed that adenovirus-mediated gene expression was greatest in rabbit jugular veins compared to rat and mouse veins. Av1nBgHIRGD augmented gene expression approximately four-fold in rabbit jugular veins when compared to Av1nBg. Histochemical analysis showed that numerous EC but few smooth muscle cells were transduced at all vector concentrations. A substantial number of adventitial fibroblasts were transduced only at the highest vector concentrations of Av1nBgHIRGD. These findings demonstrate that integrin-targeted vectors allow for enhanced gene delivery to veins and strengthen the viability of adenoviral-mediated gene transfer of therapeutic transgenes to human veins prior to vein grafting.