John H. McVey

Adenovirus Serotype 5 Hexon Mediates Liver Gene Transfer

Adenoviruses are used extensively as gene transfer agents, both experimentally and clinically. However, targeting of liver cells by adenoviruses compromises their potential efficacy. In cell culture, the adenovirus serotype 5 fiber protein engages the coxsackievirus and adenovirus receptor (CAR) to bind cells. Paradoxically, following intravascular delivery, CAR is not used for liver transduction, implicating alternate pathways. Recently, we demonstrated that coagulation factor (F)X directly binds adenovirus leading to liver infection. Here, we show that FX binds to the Ad5 hexon, not fiber, via an interaction between the FX Gla domain and hypervariable regions of the hexon surface. Binding occurs in multiple human adenovirus serotypes. Liver infection by the FX-Ad5 complex is mediated through a heparin-binding exosite in the FX serine protease domain. This study reveals an unanticipated function for hexon in mediating liver gene transfer in vivo.

Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex.

Mutations in LMAN1 (also called ERGIC-53) result in combined deficiency of factor V and factor VIII (F5F8D), an autosomal recessive bleeding disorder characterized by coordinate reduction of both clotting proteins. LMAN1 is a mannose-binding type 1 transmembrane protein localized to the endoplasmic reticulum–Golgi intermediate compartment (ERGIC; refs. 2,3), suggesting that F5F8D could result from a defect in secretion of factor V and factor VIII (ref. 4). Correctly folded proteins destined for secretion are packaged in the ER into COPII-coated vesicles, which subsequently fuse to form the ERGIC. Secretion of certain abundant proteins suggests a default pathway requiring no export signals (bulk flow; refs. 6,7). An alternative mechanism involves selective packaging of secreted proteins with the help of specific cargo receptors. The latter model would be consistent with mutations in LMAN1 causing a selective block to export of factor V and factor VIII. But ∼30% of individuals with F5F8D have normal levels of LMAN1, suggesting that mutations in another gene may also be associated with F5F8D. Here we show that inactivating mutations in MCFD2 cause F5F8D with a phenotype indistinguishable from that caused by mutations in LMAN1. MCFD2 is localized to the ERGIC through a direct, calcium-dependent interaction with LMAN1. These findings suggest that the MCFD2-LMAN1 complex forms a specific cargo receptor for the ER-to-Golgi transport of selected proteins.

Identification of coagulation factor (F)X binding sites on the adenovirus serotype 5 hexon: effect of mutagenesis on FX interactions and gene transfer

Recent studies have demonstrated the importance of coagulation factor X (FX) in adenovirus (Ad) serotype 5-mediated liver transduction in vivo. FX binds to the adenovirus hexon hypervariable regions (HVRs). Here, we perform a systematic analysis of FX binding to Ad5 HVRs 5 and 7, identifying domains and amino acids critical for this interaction. We constructed a model of the Ad5-FX interaction using crystallographic and cryo-electron microscopic data to identify contact points. Exchanging Ad5 HVR5 or HVR7 from Ad5 to Ad26 (which does not bind FX) diminished FX binding as analyzed by surface plasmon resonance, gene delivery in vitro, and liver transduction in vivo. Exchanging Ad5-HVR5 for Ad26-HVR5 produced deficient virus maturation. Importantly, defined mutagenesis of just 2 amino acids in Ad5-HVR5 circumvented this and was sufficient to block liver gene transfer. In addition, mutation of 4 amino acids in Ad5-HVR7 or a single mutation at position 451 also blocked FX-mediated effects in vitro and in vivo. We therefore define the regions and amino acids on the Ad5 hexon that bind with high affinity to FX thereby better defining adenovirus infectivity pathways. These vectors may be useful for gene therapy applications where evasion of liver transduction is a prerequisite.

Codon optimization of human factor VIII cDNAs leads to high-level expression

Gene therapy for hemophilia A would be facilitated by development of smaller expression cassettes encoding factor VIII (FVIII), which demonstrate improved biosynthesis and/or enhanced biologic properties. B domain deleted (BDD) FVIII retains full procoagulant function and is expressed at higher levels than wild-type FVIII. However, a partial BDD FVIII, leaving an N-terminal 226 amino acid stretch (N6), increases in vitro secretion of FVIII tenfold compared with BDD-FVIII. In this study, we tested various BDD constructs in the context of either wild-type or codon-optimized cDNA sequences expressed under control of the strong, ubiquitous Spleen Focus Forming Virus promoter within a self-inactivating HIV-based lentiviral vector. Transduced 293T cells in vitro demonstrated detectable FVIII activity. Hemophilic mice treated with lentiviral vectors showed expression of FVIII activity and phenotypic correction sustained over 250 days. Importantly, codon-optimized constructs achieved an unprecedented 29- to 44-fold increase in expression, yielding more than 200% normal human FVIII levels. Addition of B domain sequences to BDD-FVIII did not significantly increase in vivo expression. These significant findings demonstrate that shorter FVIII constructs that can be more easily accommodated in viral vectors can result in increased therapeutic efficacy and may deliver effective gene therapy for hemophilia A.

Therapeutic levels of FVIII following a single peripheral vein administration of rAAV vector encoding a novel human factor VIII variant

Recombinant adeno-associated virus (rAAV) vectors encoding human factor VIII (hFVIII) were systematically evaluated for hemophilia A (HA) gene therapy. A 5.7-kb rAAV-expression cassette (rAAV-HLP-codop-hFVIII-N6) containing a codon-optimized hFVIII cDNA in which a 226 amino acid (aa) B-domain spacer replaced the entire B domain and a hybrid liver-specific promoter (HLP) mediated 10-fold higher hFVIII levels in mice compared with non-codon-optimized variants. A further twofold improvement in potency was achieved by replacing the 226-aa N6 spacer with a novel 17-aa peptide (V3) in which 6 glycosylation triplets from the B domain were juxtaposed. The resulting 5.2-kb rAAV-HLP-codop-hFVIII-V3 cassette was more efficiently packaged within AAV virions and mediated supraphysiologic hFVIII expression (732 ± 162% of normal) in HA knock-out mice following administration of 2 × 10(12) vector genomes/kg, a vector dose shown to be safe in subjects with hemophilia B. Stable hFVIII expression at 15 ± 4% of normal was observed at this dose in a nonhuman primate. hFVIII expression above 100% was observed in 3 macaques that received a higher dose of either this vector or the N6 variant. These animals developed neutralizing anti-FVIII antibodies that were abrogated with transient immunosuppression. Therefore, rAAV-HLP-codop-hFVIII-V3 substantially improves the prospects of effective HA gene therapy.

An in-frame insertion in the prion protein gene in familial Creutzfeldt-Jakob disease.

In a pedigree with Creutzfeldt-Jakob disease we identified a 144-bp insertion in the open reading frame of the prion protein (PrP) gene. The insertion is in-frame and codes for 6 extra uninterrupted octapeptide repeats in addition to the 5 that are normally present in the N-terminal region of the protein. The possibility that this mutation may prove relevant to elucidating the mechanism of horizontal transmission of the spongiform encephalopathies is discussed.

Factor VII deficiency and the FVII mutation database.

Factor VII (FVII) is a zymogen for a vitamin K‐dependent serine protease essential for the initiation of blood coagulation. It is synthesized primarily in the liver and circulates in plasma at a concentration of approximately 0.5 μg/ml (10 nmol/L). The FVII gene (F7) is located on chromosome 13 (13q34), consists of 9 exons, and spans approximately 12kb. It encodes a mature protein of 406 amino acids, which has an N‐terminal domain (Gla) post‐translationally modified by γ‐carboxylation of glutamic acid residues, two domains with homology to epidermal growth factor (EGF1 and 2), and a C‐terminal serine protease domain. The single chain zymogen is activated by proteolytic cleavage at Arg152‐Ile153. There are 238 individuals described in the world literature with mutations in their F7 genes (FVII mutation database; europium.csc.mrc.ac.uk). Complete absence of FVII activity in plasma is usually incompatible with life, and individuals die shortly after birth due to severe hemorrhage. The majority of individuals with mutations in their F7 gene(s), however, are either asymptomatic or the clinical phenotype is unknown. In general, a severe bleeding phenotype is only observed in individuals homozygous for a mutation in their F7 genes with FVII activities (FVII:C) below 2% of normal, however, a considerable proportion of individuals with a mild‐moderate bleeding phenotype have similar FVII:C by in vitro assay. The failure of in vitro tests to differentiate between these groups may be due to lack of sensitivity in the assays to the very low amounts of FVII:C, which are sufficient to initiate coagulation in vivo. A number of polymorphisms have been identified in the F7 gene and some have been shown to influence plasma FVII antigen levels. Hum Mutat 17:3–17, 2001.

Haemophilia A diagnosis by analysis of a hypervariable dinucleotide repeat within the factor VIII gene

The diagnosis of haemophilia A and the identification of carriers has greatly improved with knowledge of the structure of the gene for factor VIII. This has permitted the defect to be tracked in families by the study of restriction fragment length polymorphisms (RFLPs), irrespective of the nature of the molecular defect. However, this approach is time-consuming and the information yielded falls away as more polymorphisms are added. Within the factor VIII gene lies another source of polymorphism, a dinucleotide repeat sequence of varying length known as (CA)n. Conventional mapping localised this (CA)n repeat to intron 13. The polymerase chain reaction, used to examine (CA)n variability in genomic DNA from 25 males and 67 females, revealed eight allelic bands between n = 16 and n = 24. 91% of females were heterozygous for this repeat, and family studies showed X-linked mendelian inheritance with allelic frequencies ranging from 1% to 45%. The intron 13 (CA)n repeat is tightly linked with established RFLPs and tracks with haemophilia A in family studies. The analysis requires DNA from other family members, and relatives of sporadic cases of haemophilia A are only amenable to exclusion. Nonetheless, this intron 13 (CA)n repeat provides the most highly informative marker so far available for factor VIII gene tracking studies in haemophilia A kindreds and a result can be available within a day.

450 million years of hemostasis

Summary.  In mammalian blood coagulation, five proteases (factor VII [FVII]; factor IX [FIX]; factor X [FX]; protein C [PC] and prothrombin [PT]) act with five cofactors (tissue factor [TF]; factor V [FV]; factor VIII [FVIII]; thrombomodulin and protein S) to control the generation of fibrin. Biochemical evidence, molecular cloning data and comparative sequence analysis support the existence of all components of this network in all jawed vertebrates, and strongly suggest that it evolved before the divergence of teleosts over 430 million years ago. Phylogenetic analysis of the amino acid sequences of the Gla–EGF1–EGF2–SP domain serine proteases (FVII, FIX, FX, PC) and the A domain‐containing cofactors (FV and FVIII) strongly supports the evolution of the blood coagulation network through two rounds of gene duplication, and supports the hypothesis that vertebrate evolution benefited from two global genome duplications. The jawless vertebrates (hagfish and lamprey) that diverged over 450 million years ago have a blood coagulation network involving TF, PT and fibrinogen. Preliminary evidence indicates that they may have a smaller complement of Gla–EGF1–EGF2–SP domain proteins, suggesting the existence of a ‘primitive’ coagulation system in jawless vertebrates.

Expression of the human calcitonin/CGRP gene in lung and thyroid carcinoma.

Nucleotide sequence analysis of a partially processed polyadenylated precursor RNA transcript shows that the human calcitonin gene in common with the rat calcitonin gene, encodes calcitonin and the calcitonin gene related peptide (CGRP). Using hybridisation probes specific to calcitonin mRNA, intron, coding and non‐coding regions of the CGRP mRNA, we demonstrate by Southern blotting the existence of a second human CGRP gene, and by RNA blotting and S1 mapping, the differential expression of calcitonin and CGRP in medullary thyroid carcinoma and human lung tumour cell‐lines. These studies implicate the requirement for separate post‐transcriptional events in the differential expression of calcitonin and CGRP from a single gene, the preferential use of splice acceptor sites for the synthesis of CGRP mRNA, and post‐transcriptional cleavage modulated by a trans‐acting gene product for the synthesis of calcitonin mRNA. Studies using antisera raised against CGRP and calcitonin, demonstrate elevated circulating levels of plasma CGRP in medullary thyroid carcinoma which do not parallel calcitonin levels, and the presence of CGRP in secretions from lung tumour cell‐lines. These studies indicate that CGRP is a tumour marker of diagnostic and possibly prognostic value in the management of lung and thyroid tumours.