Observational study of recombinant factor VIII-Fc, rFVIIIFc, in hemophilia A.

INTRODUCTION: rFVIIIFc (Eloctate) is an extended-half-life recombinant factor VIII-Fc fusion protein that may promote factor VIII (FVIII) tolerance through Fc immunoregulatory properties. Yet, little is known regarding its immunogenicity in patients with hemophilia A (HA) or in HA with inhibitors (HA-I), including tolerized, immune tolerance induction (ITI)-refractory, or ITI-naïve. METHODS: We reviewed medical records of 60 patients, including 2 previously-untreated patients (PUPs) and 58 previously-treated patients (PTPs), cared for between 01/01/06 and 06/01/17, on whom anti-FVIII antibody data were available before and after initiating rFVIIIFc. Continuous data were analyzed by student's t-test, and discrete data by chi square or Fisher's exact test. RESULTS: After initiating rFVIIIFc, one of two HA PUPs developed a low-responding (LR) inhibitor after 10 exposures, which resolved (anti-VIII<0.6 B.U.) within 8 additional exposures, while none of 41 HA PTPS developed an inhibitor. Among 19 HA-I PTPs with detectable inhibitors prior to rFVIIIFc, 5 developed an anamnestic response to rFVIIIFc, including 1 of 8 (12.5%) low-responding (LR), and 4 of 9 (44.9%) high-responding (HR), of whom 3 were ITI-naïve and 1 ITI-refractory. Inhibitors resolved in 4 HR within 2 months of continuing rFVIIIFc (median) but persisted in 1 LR at low titer. The remaining 11 HA-I PTPs, including 4 HR and seven LR, had no detectable inhibitor at the time of or after initiating rFVIIIFc. DISCUSSION: rFVIIIFc was immunogenic in HA PUPs and in HA-I PTPs persistently ITI-naïve or ITI-refractory, with inhibitor resolution in the majority. rFVIIIFc immunogenicity appears to be similar to other FVIII products.

Emicizumab prophylaxis in patients with haemophilia A with and without inhibitors.

INTRODUCTION: Emicizumab is a bispecific monoclonal antibody that mimics factor VIII (FVIII) by binding to factors IXa and X to promote hemostasis in haemophilia A (HA) and HA with inhibitors (HA-I). As emicizumab differs biochemically from FVIII, there is interest in its real-world haemostatic efficacy. AIM: To describe real-world patient experience with emicizumab by retrospective chart review. METHODS: We reviewed medical records of patients cared for at the Hemophilia Center of Western PA, who initiated emicizumab following its licensure, and on whom bleeding events and factor use were available. Comparisons between groups were done by Student's t test for continuous data and by chi-square or Fisher's exact test for discrete data. RESULTS: A total of 42 patients whose charts were reviewed included 18 (42.9%) with HA and 24 (52.1%) with HA-I. Groups were similar in age, 17 (40.5%) <18 years, race, and haemophilia severity, and initiated weekly subcutaneous emicizumab 1.5 mg/kg, following 4-week induction. Fourteen (33.3%) experienced at least one breakthrough bleed, of which 11 (44.0%) were joint bleeds, with an annualized bleed rate (ABR), 0.9 ± 0.3, not different between groups, P = .251. Surgical procedures were performed in 10 (23.8%), of whom 4 (40.0%) had postoperative bleeding and one developed postoperative thrombosis in association with FEIBA despite emicizumab discontinuation 1 month preoperatively. Local skin reactions occurred in three and headache in one. Overall, 85.0% of those who rated their health indicated it was improved. DISCUSSION: Despite breakthrough bleeds and postoperative thrombosis associated with emicizumab, most HA and HA-I experienced improved health.

Xenopus TACC2 is a microtubule plus end-tracking protein that can promote microtubule polymerization during embryonic development.

Microtubule dynamics is regulated by plus end-tracking proteins (+TIPs), which localize to the plus ends of microtubules (MTs). We previously showed that TACC1 and TACC3, members of the transforming acidic coiled-coil protein family, can act as +TIPs to regulate MT dynamics in Xenopus laevis Here we characterize TACC2 as a +TIP that localizes to MT plus ends in front of EB1 and overlapping with TACC1 and TACC3 in multiple embryonic cell types. We also show that TACC2 can promote MT polymerization in mesenchymal cells but not neuronal growth cones, thus displaying cell-type specificity. Structure-function analysis demonstrates that the C-terminal region of TACC2 is both necessary and sufficient to localize to MT plus ends and promote increased rates of MT polymerization, whereas the N-terminal region cannot bind to MT plus ends but can act in a dominant-negative capacity to reduce polymerization rates. Finally, we analyze mRNA expression patterns in Xenopus embryos for each TACC protein and observe neural enrichment of TACC3 expression compared with TACC1 and TACC2, which are also expressed in mesodermal tissues, including somites. Overall these data provide a novel assessment of all three TACC proteins as a family of +TIPs by highlighting the unique attributes of each, as well as their collective characteristics.

Using Xenopus laevis retinal and spinal neurons to study mechanisms of axon guidance in vivo and in vitro.

The intricate and precise establishment of neuronal connections in the developing nervous system relies on accurate navigation of growing axons. Since Ramón y Cajal's discovery of the growth cone, the phenomenon of axon guidance has been revealed as a coordinated operation of guidance molecules, receptors, secondary messengers, and responses driven by the dynamic cytoskeleton within the growth cone. With the advent of new and accelerating techniques, Xenopus laevis emerged as a robust model to investigate neuronal circuit formation during development. We present here the advantages of the Xenopus nervous system to our growing understanding of axon guidance.

Xenopus TACC1 is a microtubule plus-end tracking protein that can regulate microtubule dynamics during embryonic development.

Microtubule plus-end dynamics are regulated by a family of proteins called plus-end tracking proteins (+TIPs). We recently demonstrated that the transforming acidic coiled-coil (TACC) domain family member, TACC3, can function as a +TIP to regulate microtubule dynamics in Xenopus laevis embryonic cells. Although it has been previously reported that TACC3 is the only TACC family member that exists in Xenopus, our examination of its genome determined that Xenopus, like all other vertebrates, contains three TACC family members. Here, we investigate the localization and function of Xenopus TACC1, the founding member of the TACC family. We demonstrate that it can act as a +TIP to regulate microtubule dynamics, and that the conserved C-terminal TACC domain is required for its localization to plus-ends. We also show that, in Xenopus embryonic mesenchymal cells, TACC1 and TACC3 are each required for maintaining normal microtubule growth speed but exhibit some functional redundancy in the regulation of microtubule growth lifetime. Given the conservation of TACC1 in Xenopus and other vertebrates, we propose that Xenopus laevis is a useful system to investigate unexplored cell biological functions of TACC1 and other TACC family members in the regulation of microtubule dynamics.

TACC3 is a microtubule plus end-tracking protein that promotes axon elongation and also regulates microtubule plus end dynamics in multiple embryonic cell types.

Microtubule plus end dynamics are regulated by a conserved family of proteins called plus end-tracking proteins (+TIPs). It is unclear how various +TIPs interact with each other and with plus ends to control microtubule behavior. The centrosome-associated protein TACC3, a member of the transforming acidic coiled-coil (TACC) domain family, has been implicated in regulating several aspects of microtubule dynamics. However, TACC3 has not been shown to function as a +TIP in vertebrates. Here we show that TACC3 promotes axon outgrowth and regulates microtubule dynamics by increasing microtubule plus end velocities in vivo. We also demonstrate that TACC3 acts as a +TIP in multiple embryonic cell types and that this requires the conserved C-terminal TACC domain. Using high-resolution live-imaging data on tagged +TIPs, we show that TACC3 localizes to the extreme microtubule plus end, where it lies distal to the microtubule polymerization marker EB1 and directly overlaps with the microtubule polymerase XMAP215. TACC3 also plays a role in regulating XMAP215 stability and localizing XMAP215 to microtubule plus ends. Taken together, our results implicate TACC3 as a +TIP that functions with XMAP215 to regulate microtubule plus end dynamics.