A viable mouse model of factor X deficiency provides evidence for maternal transfer of factor X

BACKGROUND

Activated factor X (FXa) is a vitamin K-dependent serine protease that plays a pivotal role in blood coagulation by converting prothrombin to thrombin. There are no reports of humans with complete deficiency of FX, and knockout of murine F10 is embryonic or perinatal lethal.

OBJECTIVE

We sought to generate a viable mouse model of FX deficiency.

METHODS

We used a socket-targeting construct to generate F10-knockout mice by eliminating F10 exon 8 (knockout allele termed F10(tm1Ccmt), abbreviated as '-'; wild-type '+'), and a plug-targeting construct to generate mice expressing a FX variant with normal antigen levels but low levels of FX activity [4-9% normal in humans carrying the defect, Pro343-->Ser, termed FX Friuli (mutant allele termed F10(tm2Ccmt), abbreviated as F)].

RESULTS

F10 knockout mice exhibited embryonic or perinatal lethality. In contrast, homozygous Friuli mice [F10 (F/F)] had FX activity levels of approximately 5.5% (sufficient to rescue both embryonic and perinatal lethality), but developed age-dependent iron deposition and cardiac fibrosis. Interestingly, F10 (-/F) mice with FX activity levels of 1-3% also showed complete rescue of lethality. Further study of this model provides evidence supporting a role of maternal FX transfer in the embryonic survival.

CONCLUSIONS

We demonstrate that, while complete absence of FX is incompatible with murine survival, minimal FX activity as low as 1-3% is sufficient to rescue the lethal phenotype. This viable low-FX mouse model will facilitate the development of FX-directed therapies as well as investigation of the FX role in embryonic development.

A viable mouse model of factor X deficiency provides evidence for maternal transfer of factor X

BACKGROUND

Activated factor X (FXa) is a vitamin K-dependent serine protease that plays a pivotal role in blood coagulation by converting prothrombin to thrombin. There are no reports of humans with complete deficiency of FX, and knockout of murine F10 is embryonic or perinatal lethal.

OBJECTIVE

We sought to generate a viable mouse model of FX deficiency.

METHODS

We used a socket-targeting construct to generate F10-knockout mice by eliminating F10 exon 8 (knockout allele termed F10(tm1Ccmt), abbreviated as '-'; wild-type '+'), and a plug-targeting construct to generate mice expressing a FX variant with normal antigen levels but low levels of FX activity [4-9% normal in humans carrying the defect, Pro343-->Ser, termed FX Friuli (mutant allele termed F10(tm2Ccmt), abbreviated as F)].

RESULTS

F10 knockout mice exhibited embryonic or perinatal lethality. In contrast, homozygous Friuli mice [F10 (F/F)] had FX activity levels of approximately 5.5% (sufficient to rescue both embryonic and perinatal lethality), but developed age-dependent iron deposition and cardiac fibrosis. Interestingly, F10 (-/F) mice with FX activity levels of 1-3% also showed complete rescue of lethality. Further study of this model provides evidence supporting a role of maternal FX transfer in the embryonic survival.

CONCLUSIONS

We demonstrate that, while complete absence of FX is incompatible with murine survival, minimal FX activity as low as 1-3% is sufficient to rescue the lethal phenotype. This viable low-FX mouse model will facilitate the development of FX-directed therapies as well as investigation of the FX role in embryonic development.

The enhancing effects of the light chain on heavy chain secretion in split delivery of factor VIII gene

Coagulation factor VIII (FVIII) is secreted as a heterodimer consisting of a heavy chain (HC) and a light chain (LC), which can be expressed independently and reassociate with recovery of biological activity. Because of the size limitation of adeno-associated virus (AAV) vectors, a strategy for delivering the HC and LC separately has been developed. However, the FVIII HC is secreted 10-100-fold less efficiently than the LC. In this study, we demonstrated that the F309S mutation and enhanced B-domain glycosylations alone are not sufficient to improve FVIII HC secretion, which suggested a role of the FVIII LC in regulating HC secretion. To characterize this role of the FVIII LC, we compared FVIII HC secretion with and without the LC via post-translational protein trans-splicing. As demonstrated in vitro, ligation of the LC to the HC significantly increased HC secretion. Such HC secretion increases were also confirmed in vivo by hydrodynamic injection of FVIII intein plasmids into hemophilia A mice. Moreover, similar enhancement of HC secretion can also be observed when the LC is supplied in trans, which is probably due to the spontaneous association of the HC and the LC in the secretion pathway. In sum, enhancing the secretion of the FVIII HC polypeptide may require the proper association of the FVIII LC polypeptide in cis or in trans. These results may be helpful in designing new strategies to improve FVIII gene delivery.

Modulation of tolerance to the transgene product in a nonhuman primate model of AAV-mediated gene transfer to liver

Adeno-associated virus (AAV)-mediated gene transfer of factor IX (F.IX) to the liver results in long-term expression of transgene in experimental animals, but only short-term expression in humans. Loss of F.IX expression is likely due to a cytotoxic immune response to the AAV capsid, which results in clearance of transduced hepatocytes. We used a nonhuman primate model to assess the safety of AAV gene transfer coupled with an anti-T-cell regimen designed to block this immune response. Administration of a 3-drug regimen consisting of mycophenolate mofetil (MMF), sirolimus, and the anti-IL-2 receptor antibody daclizumab consistently resulted in formation of inhibitory antibodies to human F.IX following hepatic artery administration of an AAV-hF.IX vector, whereas a 2-drug regimen consisting only of MMF and sirolimus did not. Administration of daclizumab was accompanied by a dramatic drop in the population of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs). We conclude that choice of immunosuppression (IS) regimen can modulate immune responses to the transgene product upon hepatic gene transfer in subjects not fully tolerant; and that induction of transgene tolerance may depend on a population of antigen-specific Tregs.

A prospective study on the prevalence and risk factors for neonatal thrombocytopenia and platelet alloimmunization among 9332 unselected Brazilian newborns

BACKGROUND

Neonatal thrombocytopenia (NT) occurs in 0.5 to 0.9% of unselected Caucasian newborns. However, the prevalence of this complication in other populations is unknown. In this study the prevalence/causes of NT was determined in Brazilian newborns, a population characterized by admixture among Indigenous, Africans, and Caucasians.

STUDY DESIGN

A prospective study was carried out in a 3-year period, to determine the prevalence and causes of thrombocytopenia in cord blood samples. Genotyping for HPA 1-5 systems was performed in pairs of mother/neonates with and without thrombocytopenia. All mothers with genotypic mismatches from each group were tested for HPA-specific antibody using the MAIPA technique to identify alloimmunization.

RESULTS

Platelet counts <100 x 10(9)/L were detected in 1.5% of 9,332 unselected newborns. In 0.15%, platelet count was <50 x 10(9)/L. Clinically significant bleeding was rare. Underlying diseases were present in 48% of the thrombocytopenic cases. HPA 1-5 system genotype mismatches occurred in 50% of gestations, but did not predict the risk for thrombocytopenia. Notably, mismatched genotypes for HPA-5 were slightly increased in the thrombocytopenic group. The presence of anti-HPA-5b antibodies was observed in 0.05% of unselected pregnancies, but increased to 12% among mothers of neonates with thrombocytopenia and mismatched genotype (N = 51).

CONCLUSIONS

Neonatal thrombocytopenia is common among Brazilian newborns at rates comparable with those described among Caucasians. These data suggest that screening for genotypic HPA mismatch, followed by an HPA-specific immunoassay system, particularly for the HPA-5 system, among mothers of newborns with thrombocytopenia in our population would allow the identification of pregnancies at risk of alloimmune thrombocytopenia.

Three novel mutations in the activin receptor-like kinase 1 (ALK-1) gene in hereditary hemorrhagic telangiectasia type 2 in Brazilian patients

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Rendu-Weber disease is a systemic fibrovascular dysplasia with an autosomal dominant inheritance pattern. Mutations in two genes, endoglin and ALK-1, are known to cause HHT, both of which mediate signaling by transforming growth factor beta ligands in vascular endothelial cells. Ten patients were analyzed. Diagnosis of HHT was carried out by means of family history, recurrent bleeding, and the presence of multiple telangiectases lesions. Conformation-sensitive gel electrophoresis analyses with consistent abnormal migration patterns were cloned and sequenced using the MegaBace 1000 DNA automated analyzer. Three novel mutations were identified in the coding sequence of the ALK-1 gene in five patients and their families, which demonstrated clinical manifestations of HHT type 2. These mutations included a G insertion and a T deletion of single base pairs in exons 3 and 7, as well as missense mutations in exons 7 and 8 of the ALK-1 gene. These data indicate that loss-of-function mutations in a single allele of the ALK1 locus are sufficient to contribute to defects in maintaining endothelial integrity. We suggest the high rate of mutation detection and the small size of the ALK-1 gene make genomic sequencing a viable diagnostic test for HHT2.

Evidence of multiyear factor IX expression by AAV-mediated gene transfer to skeletal muscle in an individual with severe hemophilia B

In a phase I study, administration of an AAV2-FIX vector into the skeletal muscle of eight hemophilia B subjects proved safe and achieved local gene transfer and FIX expression for at least 10 months after vector injection, the last time point assessed by muscle biopsy. In hemophilia B dogs we have demonstrated FIX in both muscle biopsies and circulation >4 years following AAV2-FIX injection. Because circulating FIX levels remained less than 1% of normal in human subjects from the study, the duration of AAV2-mediated transgene expression in humans is unknown. We sought to determine if FIX gene transfer and expression persisted locally at injection sites. Muscle biopsies were obtained from one subject 3.7 years following treatment and revealed transgene FIX DNA and protein by quantitative PCR, DNA fluorescence in situ hybridization, and immunohistochemistry for FIX. These results demonstrate, for the first time, multiyear FIX expression by AAV2 vector in humans and suggest that improved muscle delivery provides effective treatment for protein deficiencies or muscle-specific diseases.

Inadvertent Germline Transmission of AAV2 Vector: Findings in a Rabbit Model Correlate with Those in a Human Clinical Trial

The risk of germline transmission of vector sequences in humans is a major safety concern, because the enrollment of subjects of reproductive age in early-phase clinical trials of gene transfer continues to increase. In a study of adult men with hemophilia B, adeno-associated virus serotype 2 (AAV2) delivered to the liver via the hepatic artery resulted in unexpected transient vector dissemination to the semen. Here we report that intravenous AAV2 injection in rabbits proved a useful model to assess biologic parameters of vector dissemination to the semen. Detectable vector sequences in semen disappeared in a dose-dependent and time-dependent fashion. AAV infectious particles were present only as long as day 4 after injection and were undetectable thereafter. The kinetics of vector clearance was faster in the semen fractions enriched for motile sperm than in the total semen. In addition, increased frequency of semen sampling accelerated the clearance of vector sequences from semen. Long-term follow-up, spanning hundreds of spermatogenesis cycles, showed that there was no recurrence of detectable vector sequences in semen, thus reducing the probability of inadvertent transduction of early spermatogonia not committed to differentiation at the time of vector injection. We conclude that AAV2 presents minimal germline transmission risk for humans.

Successful transduction of liver in hemophilia by AAV-Factor IX and limitations imposed by the host immune response

We have previously shown that a single portal vein infusion of a recombinant adeno-associated viral vector (rAAV) expressing canine Factor IX (F.IX) resulted in long-term expression of therapeutic levels of F.IX in dogs with severe hemophilia B. We carried out a phase 1/2 dose-escalation clinical study to extend this approach to humans with severe hemophilia B. rAAV-2 vector expressing human F.IX was infused through the hepatic artery into seven subjects. The data show that: (i) vector infusion at doses up to 2 x 10(12) vg/kg was not associated with acute or long-lasting toxicity; (ii) therapeutic levels of F.IX were achieved at the highest dose tested; (iii) duration of expression at therapeutic levels was limited to a period of approximately 8 weeks; (iv) a gradual decline in F.IX was accompanied by a transient asymptomatic elevation of liver transaminases that resolved without treatment. Further studies suggested that destruction of transduced hepatocytes by cell-mediated immunity targeting antigens of the AAV capsid caused both the decline in F.IX and the transient transaminitis. We conclude that rAAV-2 vectors can transduce human hepatocytes in vivo to result in therapeutically relevant levels of F.IX, but that future studies in humans may require immunomodulation to achieve long-term expression.

Factor V Leiden improves in vivo hemostasis in murine hemophilia models

The role of factor V Leiden (FVL) as a modifier of the severe hemophilia phenotype is still unclear. We used mice with hemophilia A or B crossed with FVL to elucidate in vivo parameters of hemostasis. Real-time thrombus formation in the microcirculation was monitored by deposition of labeled platelets upon laser-induced endothelial injury using widefield microscopy in living animals. No thrombi formed in hemophilic A or B mice following vascular injuries. However, hemophilic mice, either heterozygous or homozygous for FVL, formed clots at all injured sites. Injection of purified activated FV into hemophilic A or B mice could mimic the in vivo effect of FVL. In contrast to these responses to a laser injury in a microvascular bed, FVL did not provide sustained hemostasis following damage of large vessels in a ferric chloride carotid artery injury model, despite of the improvement of clotting times and high circulating thrombin levels. Together these data provide evidence that FVL has the ability to improve the hemophilia A or B phenotype, but this effect is principally evident at the microcirculation level following a particular vascular injury. Our observations may partly explain the heterogeneous clinical evidence of the beneficial role of FVL in hemophilia.

The inhibitory effects of anticoagulation on in vivo gene transfer by adeno-associated viral or adenoviral vectors

Identifying factors that influence gene transfer efficacy is critical for a successful gene-based clinical study. Here we demonstrate that in vivo AAV-2-mediated gene transfer is efficiently inhibited by unfractionated heparin, but not by a heparin preparation containing mainly low-molecular-weight forms (LMWH). Surprisingly, inhibitors of thrombin or factor Xa (F.Xa) significantly reduced AAV-2 transduction in a dose-dependent manner. These effects were independent of the vector promoter, transgene, or strain of mice. Expression by alternate AAV serotypes 5 and 8 was not affected by anticoagulant drugs, which suggests an AAV-2-specific effect. Moreover, AAV-2-mediated gene expression was diminished in mice with deficiency in thrombin generation (factor IX deficiency) and enhanced in mice with procoagulant phenotype due to factor V Leiden. In addition, inhibitors of F.Xa diminished adenovirus-mediated gene expression. These results demonstrated that coagulation activity itself is critical to ensure optimal viral vector transduction. Since intravascular delivery of vectors often requires the use of anticoagulants, the use of LMWH appears to be safe. These observations are of relevance for approaches using AAV-2 or adenoviral vectors, especially in early phase studies designed to identify the minimum therapeutic doses.

Factor IX variants improve gene therapy efficacy for hemophilia B

Intramuscular injection of adeno-associated viral (AAV) vector to skeletal muscle of humans with hemophilia B is safe, but higher doses are required to achieve therapeutic factor IX (F.IX) levels. The efficacy of this approach is hampered by the retention of F.IX in muscle extracellular spaces and by the limiting capacity of muscle to synthesize fully active F.IX at high expression rates. To overcome these limitations, we constructed AAV vectors encoding F.IX variants for muscle- or liver-directed expression in hemophilia B mice. Circulating F.IX levels following intramuscular injection of AAV-F.IX-K5A/V10K, a variant with low-affinity to extracellular matrix, were 2-5 fold higher compared with wild-type (WT) F.IX, while the protein-specific activities remained similar. Expression of F.IX-R338A generated a protein with 2- or 6-fold higher specific activity than F.IX-WT following vector delivery to skeletal muscle or liver, respectively. F.IX-WT and variant forms provide effective hemostasis in vivo upon challenge by tail-clipping assay. Importantly, intramuscular injection of AAV-F.IX variants did not trigger antibody formation to F.IX in mice tolerant to F.IX-WT. These studies demonstrate that F.IX variants provide a promising strategy to improve the efficacy for a variety of gene-based therapies for hemophilia B.

Platelet glycoprotein Ibalpha polymorphisms modulate the risk for myocardial infarction

Platelet glycoprotein Iba (GPIba) gene polymorphisms have been reported to affect the risk of developing coronary heart disease. Here, within the GPIba gene, we determine the association between the variable number of tandem repeats (VNTR), the -5C/T Kozak sequence dimorphism, and the human platelet antigen (HPA)-2 polymorphisms with occurrence of myocardial infarction (MI). Patients (n=180) presenting survivors of MI were compared to 180 controls matched by age, gender, and race. Carriers of VNTR-CD genotype had a 2-fold higher risk for MI compared to controls. The prevalence of VNTR-BC was lower among patients than among controls (P=.007). These data are in agreement with recent reports of increased plug formation by human platelets containing VNTRCD but no other VNTR genotypes. Among patients, the number of vessels severely occluded was greater among carriers of the D-allele (P=.019) or VNTR-CD (P=.026) and lower among carriers of the C-allele (P=.003) or VNTR-CC (P=.0009) compared to non-carriers of these alleles. No influence was seen with the Kozak or HPA-2 polymorphisms. Determination of VNTR of the GPIba gene may prove useful for identifying high-risk individuals for MI.

Characterization of mild coagulation factor VII deficiency: activity and clearance of the Arg315Trp and Arg315Lys variants in the Cys310-Cys329 loop (c170s)

BACKGROUND AND OBJECTIVES

Arginine 315 in factor VII (FVII) belongs to a solvent-exposed loop involved in direct interaction with the co-factor (tissue factor, TF), in transmission of TF-induced effects and potentially in FVIIa inactivation. Natural FVII variants at position 315 provide peculiar models for structure-function studies.

DESIGN AND METHODS

We characterized a mild coagulation FVII deficiency associated with reduced FVII activity (26%) and antigen (67%). Mutations were searched by FVII gene sequencing. FVII variants were created by mutagenesis of FVII cDNA and characterized through expression in HEK293 cells followed by functional studies. FVII antigen in media was estimated by immunoassay while FVII activity was assessed by prothrombin-time based and FXa generation assays. FVII variants were injected into mice to investigate their recovery and half-life. One-way ANOVA was used to test statistical significance.

RESULTS

The patient was double heterozygous for a novel R315W mutation and for the R304Q substitution (FVII Padua) previously demonstrated to impair TF binding. The recombinant 315W-FVII was normally expressed in medium but showed a markedly reduced coagulant function (52%) and activity towards factor X (FX) in plasma (34%). Moreover, the 315W-FVII showed significantly decreased recovery of the protein (20%) and a slightly shorter half-life (8.6 min) as compared to wt-FVII (50% and 10.7 min). We also studied the conservative R315K change that was responsible for low recovery (20%) and a decreased half-life (7 min) of a FVII variant with virtually normal FVII antigen and activity levels.

INTERPRETATION AND CONCLUSIONS

These findings suggest a dual role of R315 for FVII function and clearance, and indicate that substitutions at this position have appreciable effects on human FVII biology, compatible with residual FVII function and thus with mild FVII deficiency.

Novel hemophilia B mouse models exhibiting a range of mutations in the Factor IX gene

Animal models have been critical to the development of novel therapeutics in hemophilia. A deficiency of current murine models of hemophilia B is that they are all due to gene deletions, a type of mutation that is relatively rare in the human hemophilia population. We generated mice with a range of mutations in the Factor IX (F.IX) gene; these more faithfully reflect the types of mutations that cause disease in the human population. Transgenic mice expressing either wild-type human F.IX (hF.IX), or F.IX variants with premature translation termination codons, or missense mutations, under the control of the murine transthyretin promoter, were generated and crossed with mice carrying a large deletion of the murine F.IX gene. Gene copy number, F.IX transcript levels in the liver, intrahepatocyte protein expression, and circulating levels of F.IX protein in the mice were determined and compared with data generated by transient transfection assays using the same F.IX variants. Mice were injected with a viral vector expressing hF.IX and displayed a range of immune responses to the transgene product, depending on the underlying mutation. These new mouse models faithfully mimic the mutations causing human disease, and will prove useful for testing novel therapies for hemophilia. (Blood. 2004;104:2767-2774)

Regional intravascular delivery of AAV-2-F.IX to skeletal muscle achieves long-term correction of hemophilia B in a large animal model

In earlier work, we showed that adeno-associated virus-mediated delivery of a Factor IX gene to skeletal muscle by direct intramuscular injection resulted in therapeutic levels of circulating Factor IX in mice. However, achievement of target doses in humans proved impractical because of the large number of injections required. We used a novel intravascular delivery technique to achieve successful transduction of extensive areas of skeletal muscle in a large animal with hemophilia. We provide here the first report of long-term (> 3 years, with observation ongoing), robust Factor IX expression (circulating levels of 4%-14%) by muscle-directed gene transfer in a large animal, resulting in essentially complete correction of the bleeding disorder in hemophilic dogs. The results of this translational study establish an experimental basis for clinical studies of this delivery method in humans with hemophilia B. These findings also have immediate relevance for gene transfer in patients with muscular dystrophy.

Genetic variability of platelet glycoprotein Ibalpha gene

Platelet membrane glycoprotein (GP) Ibalpha is a critical component of platelet adhesion complex to subendothelium structures following tissue injury or pathological surfaces, such as atherosclerotic plaques. Polymorphisms of the GPIbalpha gene have been associated with a high risk for occlusive vascular disease, and its distribution varies considerably among distinct populations. These polymorphisms comprise the human platelet antigen (HPA)-2 system, the -5C/T dimorphism of the Kozak sequence, and the variable number of tandem 39-bp repeats (VNTR). Here we report the prevalence of the GPIbalpha gene polymorphisms among Brazilians, a highly ethnically diverse population. We analyzed 492 subjects of European, African, or Indigenous origin. It was possible to determine ten distinct haplotypes. The most common ( reverse similar 40%) haplotype was the Kozak-TT/HPA-2aa/VNTR-CC for both Caucasian and African descent. However, among Indigenous, Kozak-TT/HPA-2aa/VNTR-CC and Kozak-TC/HPA-2aa/VNTR-CC were equally present. Although a strong linkage disequilibrium between VNTR and HPA-2 polymorphism had also been observed, here we determined incomplete linkage disequilibrium in 10% of subjects from all ethnic groups. VNTR-E, a rare variant lacking the 39-bp repeat, was identified in two unrelated subjects, and functional platelet studies revealed no abnormalities. The VNTR-A allele, the largest variant containing four copies of the repeats, was not identified in this population. However, homozygosity for the VNTR-A allele (Kozak-TT/HPA-2aa/VNTR-AA) was determined in two distinct species of nonhuman primates. These results suggest a greater complex evolutionary mechanism in the macroglycoprotein region of the GPIbalpha gene and may be useful in the design of gene-disease association studies for vascular disease.

Follow-up of sickle cell disease patients with priapism treated by hydroxyurea

Hydroxyurea is one of the most successfully used therapies for sickle cell disease. Results of many clinical trials point to hydroxyurea administration for patients with frequent painful crises and acute chest syndrome. Priapism is one of the complications that could be prevented by hydroxyurea, but there are few reports demonstrating the results. Since November 1993, hydroxyurea has been used in our clinic for preventing priapism in patients with stuttering or major attacks who are still capable of achieving intercourse on demand. Five patients were enrolled in the study, and 4 cases benefited by this treatment. After the initial treatment for the acute attack, all five patients developed stuttering priapism. Hydroxyurea was then introduced at the initial dose of 10 mg/kg, and as the hydroxyurea dosage increased, the number or length of priapism episodes decreased. One to two months after the maximal dose (20-35 mg/kg) was introduced, the episodes disappeared. In two patients, we were forced to administer over 30 mg hydroxyurea/kg to abort the episodes, and, in another patient, 25 mg/kg was necessary. All patients present normal sexual activity. Hydroxyurea was discontinued in two patients, but stuttering priapism reappeared. Hydroxyurea was then re-introduced, and priapism disappeared. One patient, using 20 mg hydroxyurea/kg, had a 6-year remission of priapism after hydroxyurea administration; however, he experienced stuttering priapism, 1 month before a major attack, that progressed to impotence. During that month, he did not seek medical attention. In conclusion, the data here presented suggests that hydroxyurea may prevent priapism attacks in sickle cell disease, probably at higher doses than usually prescribed for painful crisis prevention.

Novel therapeutic approach for hemophilia using gene delivery of an engineered secreted activated Factor VII

Hemophilia is a bleeding disorder caused by mutations in the genes encoding coagulation Factor VIII (FVIII) or FIX. Current treatment is through intravenous infusion of the missing protein. The major complication of treatment is the development of neutralizing Ab's to the clotting factor. Infusion of recombinant activated human Factor VII (rhFVIIa), driving procoagulant reactions independently of human FVIII (hFVIII) or hFIX, has been successful in such patients and could in theory provide hemostasis in all hemophilia patients. However, its high cost and short half-life have limited its use. Here, we report a novel treatment strategy with a recombinant adeno-associated virus vector delivering a modified FVII transgene that can be intracellularly processed and secreted as activated FVII (FVIIa). We show long-term expression, as well as phenotypic correction of hemophilia B mice following gene transfer of the murine FVIIa homolog, with no evidence of thrombotic complications at these doses. These data hold promise for a potential treatment for hemophilia and other bleeding disorders.

Safety and efficacy of factor IX gene transfer to skeletal muscle in murine and canine hemophilia B models by adeno-associated viral vector serotype 1

Adeno-associated viral (AAV) vectors (serotype 2) efficiently transduce skeletal muscle, and have been used as gene delivery vehicles for hemophilia B and for muscular dystrophies in experimental animals and humans. Recent reports suggest that AAV vectors based on serotypes 1, 5, and 7 transduce murine skeletal muscle much more efficiently than AAV-2, with reported increases in expression ranging from 2-fold to 1000-fold. We sought to determine whether this increased efficacy could be observed in species other than mice. In immunodeficient mice we saw 10- to 20-fold higher levels of human factor IX (hF.IX) expression at a range of doses, and in hemophilic dogs we observed approximately 50-fold higher levels of expression. The increase in transgene expression was due partly to higher gene copy number and a larger number of cells transduced at each injection site. In all immunocompetent animals injected with AAV-1, inhibitory antibodies to F.IX developed, but in immunocompetent mice treated with high doses of vector, inhibitory antibodies eventually disappeared. These studies emphasize that the increased efficacy of AAV-1 vectors carries a risk of inhibitor formation, and that further studies will be required to define doses and treatment regimens that result in tolerance rather than immunity to F.IX.

Induction of immune tolerance to coagulation factor IX antigen by in vivo hepatic gene transfer

Gene replacement therapy is an attractive approach for treatment of genetic disease, but may be complicated by the risk of a neutralizing immune response to the therapeutic gene product. There are examples of humoral and cellular immune responses against the transgene product as well as absence of such responses, depending on vector design and the underlying mutation in the dysfunctional gene. It has been unclear, however, whether transgene expression can induce tolerance to the therapeutic antigen. Here, we demonstrate induction of immune tolerance to a secreted human coagulation factor IX (hF.IX) antigen by adeno-associated viral gene transfer to the liver. Tolerized mice showed absence of anti-hF.IX and substantially reduced in vitro T cell responses after immunization with hF.IX in adjuvant. Tolerance induction was antigen specific, affected a broad range of Th cell subsets, and was favored by higher levels of transgene expression as determined by promoter strength, vector dose, and mouse strain. Hepatocyte-derived hF.IX expression induced regulatory CD4(+) T cells that can suppress anti-hF.IX formation after adoptive transfer. With a strain-dependent rate of success, tolerance to murine F.IX was induced in mice with a large F.IX gene deletion, supporting the relevance of these data for treatment of hemophilia B and other genetic diseases.

AAV-mediated factor IX gene transfer to skeletal muscle in patients with severe hemophilia B

Hemophilia B is an X-linked coagulopathy caused by absence of functional coagulation factor IX (F.IX). Previously, we established an experimental basis for gene transfer as a method of treating the disease in mice and hemophilic dogs through intramuscular injection of a recombinant adeno-associated viral (rAAV) vector expressing F.IX. In this study we investigated the safety of this approach in patients with hemophilia B. In an open-label dose-escalation study, adult men with severe hemophilia B (F.IX < 1%) due to a missense mutation were injected at multiple intramuscular sites with an rAAV vector. At doses ranging from 2 x 10(11) vector genomes (vg)/kg to 1.8 x 10(12) vg/kg, there was no evidence of local or systemic toxicity up to 40 months after injection. Muscle biopsies of injection sites performed 2 to 10 months after vector administration confirmed gene transfer as evidenced by Southern blot and transgene expression as evidenced by immunohistochemical staining. Pre-existing high-titer antibodies to AAV did not prevent gene transfer or expression. Despite strong evidence for gene transfer and expression, circulating levels of F.IX were in all cases less than 2% and most were less than 1%. Although more extensive transduction of muscle fibers will be required to develop a therapy that reliably raises circulating levels to more than 1% in all subjects, these results of the first parenteral administration of rAAV demonstrate that administration of AAV vector by the intramuscular route is safe at the doses tested and effects gene transfer and expression in humans in a manner similar to that seen in animals.

Prevalence of factor VII deficiency and molecular characterization of the F7 gene in Brazilian patients

The prevalence of factor VII (FVII) deficiency in 267 Brazilian patients was estimated to be 4.1%, including one patient with significant bleeding, five with minor bleeding and five patients asymptomatic. Only one novel mutation 8926G <-- T (I140S) was seen in one patient. The other mutations were 10828G <-- A (R304Q) in three patients, 10846G <-- T (C310F) in one patient, and 10909G <-- A (G331D) in one patient. Except for one homozygous patient (C310F) with a severe deficiency, only one allele was affected in all other instances. An inverse association between F7 polymorphisms and FVII activity were found in these patients, as those with higher levels of FVII activity presented the genotype described in the literature as related to reduced FVII activity. As the R304Q mutation was the most frequent in these patients, and may be associated with an asymptomatic form of the disease, particularly in Blacks, we examined this mutation and FVII activity in 49 Blacks and 49 Caucasian blood donors with no clinical bleeding. None of the individuals showed the R304Q mutation, and FVII activity was normal in all of them, thus indicating that FVII deficiency is not common in normal individuals of these two ethnic groups in Brazil. This is the first study in South America to examine the prevalence and molecular basis of FVII deficiency, including the description of a novel mutation.

Improved hepatic gene transfer by using an adeno-associated virus serotype 5 vector

Adeno-associated viral (AAV) vectors have been shown to direct stable gene transfer and expression in hepatocytes, which makes them attractive tools for treatment of inherited disorders such as hemophilia B. While substantial levels of coagulation factor IX (F.IX) have been achieved using AAV serotype 2 vectors, use of a serotype 5 vector further improves transduction efficiency and levels of F.IX transgene expression by 3- to 10-fold. In addition, the AAV-5 vector transduces a higher proportion of hepatocytes ( approximately 15%). The subpopulations of hepatocytes transduced with either vector widely overlap, with the AAV-5 vector transducing additional hepatocytes and showing a wider area of transgene expression throughout the liver parenchyma.

Influence of vector dose on factor IX-specific T and B cell responses in muscle-directed gene therapy

Intramuscular injection of an adeno-associated virus (AAV) vector has resulted in vector dose-dependent, stable expression of canine factor IX (cF.IX) in hemophilia B dogs with an F.IX missense mutation (Herzog et al., Nat. Med. 1999;5:56-63). The use of a species-specific transgene allowed us to study risks and characteristics of antibody formation against the therapeutic transgene product. We analyzed seven dogs that had been injected at a single time point at multiple intramuscular sites with varying vector doses (dose per kilogram, dose per animal, dose per site). Comparison of individual animals suggests an increased likelihood of inhibitory anti-cF.IX (inhibitor) development with increased vector doses, with dose per site showing the strongest correlation with the risk of inhibitor formation. In six of seven animals, such immune responses were either absent or transient, and therefore did not prevent sustained systemic expression of cF.IX. Transient inhibitory/neutralizing anti-cF.IX responses occurred at vector doses of 2 x 10(12)/site, whereas a 6-fold higher dose resulted in a longer lasting, higher titer inhibitor. Anti-cF.IX was efficiently blocked in an eighth animal that was injected with a high vector dose per site, but in addition received transient immune suppression. Inhibitor formation was characterized by synthesis of two IgG subclasses and in vitro proliferation of lymphocytes to cF.IX antigen, indicating a helper T cell-dependent mechanism. Anti-cF.IX formation is likely influenced by the extent of local antigen presentation and may be avoided by limited vector doses or by transient immune modulation.

Sustained phenotypic correction of hemophilia B dogs with a factor IX null mutation by liver-directed gene therapy

Hemophilia B is an X-linked coagulopathy caused by absence of functional coagulation factor IX (FIX). Using adeno-associated virus (AAV)-mediated, liver-directed gene therapy, we achieved long-term (> 17 months) substantial correction of canine hemophilia B in 3 of 4 animals, including 2 dogs with an FIX null mutation. This was accomplished with a comparatively low dose of 1 x 10(12) vector genomes/kg. Canine FIX (cFIX) levels rose to 5% to 12% of normal, high enough to result in nearly complete phenotypic correction of the disease. Activated clotting times and whole blood clotting times were normalized, activated partial thromboplastin times were substantially reduced, and anti-cFIX was not detected. The fourth animal, also a null mutation dog, showed transient expression (4 weeks), but subsequently developed neutralizing anti-cFIX (inhibitor). Previous work in the canine null mutation model has invariably resulted in inhibitor formation following treatment by either gene or protein replacement therapies. This study demonstrates that hepatic AAV gene transfer can result in sustained therapeutic expression in a large animal model characterized by increased risk of a neutralizing anti-FIX response.

Antithrombin deficiency in Brazilian patients with venous thrombosis: molecular characterization of a single splice site mutation, an insertion and a de novo point mutation

The prevalence of antithrombin (AT) deficiency in 342 unselected Brazilian patients with venous thrombosis was 1.16%, which increased to 3% when only patients under the age of 50 or with a familial history of thrombosis were considered. In two patients, a clinical (contraceptive use) or genetic risk factor (factor V Leiden and C677T in the methylene tetrahydrofolate reductase gene [MTHFR]) was identified and corroborated the hypothesis that an interaction of factors accounted for the appearance of thrombosis. However, no risk factor other than AT deficiency was identified in one patient with an important clinical and family history of spontaneous thrombosis. Three mutations were identified in these patients: a G-->A transition in intron 5 at position +1 (5'-->3'), three base insertions corresponding to arginine at position 5383 in exon 3A, and a G-->A transition at 13328, corresponding to an Ala404Thr de novo mutation. The polymorphisms in the genes coding for coagulation factors XII and XIII and fibrinogen normally associated with an increased risk for venous thrombosis were not related to thrombosis in these patients. This is the first study in South America to assess the prevalence of AT deficiency and to report the molecular characterization of the mutations involved.

Lack of germline transmission of vector sequences following systemic administration of recombinant AAV-2 vector in males

A potential consequence of systemic administration of viral vectors is the inadvertent introduction of foreign DNA into recipient germ cells. To evaluate the safety of in vivo recombinant adeno-associated virus (rAAV) mediated gene transfer approaches for hemophilia B, we explored the risk of germline transmission of vector sequences following intramuscular (IM) injection of rAAV in four species of male animals (mouse, rat, rabbit and dog). In vector biodistribution studies in mice and rats, there is a dose-dependent increase in the likelihood that vector sequences can be detected in gonadal DNA using a sensitive PCR technique. However, in dogs DNA extracted from semen is negative for vector sequences. To address this discrepancy, studies were done in rabbits, and both semen and testicular DNAs were analyzed for the presence of vector sequences. These studies showed that no AAV vector sequences were detected in DNA extracted from rabbit semen samples collected at time points ranging from 7 to 90 days following IM injection of 1 x 10(13) vector genomes rAAV (vg) per kg. In contrast, DNA extracted from gonadal tissue was positive for vector sequences, but the positive signals diminished in number and strength with time. By FISH analysis, AAV signals were localized to the testis basement membrane and the interstitial space; no intracellular signal was observed. We observed similar findings following hepatic artery administration of rAAV in rats and dogs, suggesting that our findings are independent of the route of administration of vector. Attempts to transduce isolated murine spermatogonia directly with AAV-lacZ were unsuccessful. In clinical studies human subjects injected IM with an AAV vector at doses up to 2 x 10(12) vg/kg have shown no evidence of vector sequences in semen. Together, these studies suggest that rAAV introduced into skeletal muscle or the hepatic artery does not transduce male germ cells efficiently. We conclude that the risk of inadvertent germline transmission of vector sequences following IM or hepatic artery injection of AAV-2 vectors is extremely low.

Risk and prevention of anti-factor IX formation in AAV-mediated gene transfer in the context of a large deletion of F9

The safety of several gene therapy approaches for treatment of the severe, X-linked bleeding disorder hemophilia is currently being evaluated in early phase clinical trials. One strategy seeks to correct deficiency of functional coagulation factor IX (hemophilia B) by intramuscular (IM) administration of an adeno-associated viral (AAV) vector. A potentially serious complication of any treatment for hemophilia is formation of inhibitory antibodies against the coagulation factor protein, a risk that increases in the setting of null mutations in the factor IX gene (F9). Here, we describe hemophilia B mice with a large F9 deletion that form inhibitors within 1 to 2 months after IM administration of an AAV vector expressing mouse F9 or after repeated intravenous infusion of mouse F9 concentrate. In both cases, inhibitors are primarily IgG1 immunoglobulins representing a Th2-driven humoral immune response. We further demonstrate that anti-mouse F9 antibody formation in the gene-based approach can be reduced by transient immune modulation at the time of vector administration. Moreover, this maneuver resulted in complete absence of anti-mouse F9 and sustained expression of functional mouse F9 in some hemophilia B mice, particularly in those animals treated with the immunosuppressive drug cyclophosphamide. These data have direct relevance for design of clinical trials and strategies aimed at avoiding immune responses against a secreted transgene product.

Muscle-directed gene transfer and transient immune suppression result in sustained partial correction of canine hemophilia B caused by a null mutation

The X-linked bleeding disorder hemophilia B is caused by absence of functional blood coagulation factor IX (F9) and can be treated by adeno-associated viral (AAV) mediated gene transfer to skeletal muscle. The safety of this approach is currently being evaluated in a phase I clinical trial. Efficacy of this and several other gene therapy strategies has been addressed in hemophilia B dogs, an important preclinical model of the disease. While previously published data demonstrated sustained expression of canine F9 in dogs with a missense mutation in the gene F9, we show here that AAV-mediated canine F9 gene transfer to skeletal muscle of hemophilia B dogs carrying a null mutation of F9 (causing an early stop codon and an unstable mRNA) results in induction of inhibitory anti-canine F9 at comparable vector doses (1 x 10(12) vector genomes/kg). Thus, the risk of inhibitor formation following AAV-mediated F9 gene therapy may be influenced by the nature of the underlying mutation in F9. Transient immune suppression with cyclophosphamide at the time of vector administration blocked formation of anti-canine F9 antibodies in the one animal treated with this approach. Treatment with this combination of gene transfer and transient immune modulation has resulted in sustained expression (>8 months) of canine F9 at levels sufficient for partial correction of coagulation parameters.

Detection of somatic mutations of the PIG-A gene in Brazilian patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal syndrome characterized by intravascular hemolysis mediated by complement, thrombotic events and alterations in hematopoiesis. Basically, the molecular events which underlie the complexity of the syndrome consist of the absence of the glycosylphosphatidylinositol (GPI) anchor as a consequence of somatic mutations in the PIG-A gene, located on the X chromosome. The GPI group is responsible for the attachment of many proteins to the cytoplasmic membrane. Two of them, CD55 and CD59, have a major role in the inhibition of the action of complement on the cellular membrane of blood cells. The absence of GPI biosynthesis can lead to PNH. Since mutations in the PIG-A gene are always present in patients with PNH, the aim of this study was to characterize the mutations in the PIG-A gene in Brazilian patients. The analysis of the PIG-A gene was performed using DNA samples derived from bone marrow and peripheral blood. Conformation-sensitive gel electrophoresis was used for screening the mutation and sequencing methods were used to identify the mutations. Molecular analysis permitted the identification of three point mutations in three patients: one G-->A transition in the 5' portion of the second intron, one T-->A substitution in the second base of codon 430 (Leu430-->stop), and one deletion DeltaA in the third base of codon 63. This study represents the first description of mutations in the PIG-A gene in a Brazilian population.

Increased risk for acute myeloid leukaemia in individuals with glutathione S-transferase mu 1 (GSTM1) and theta 1 (GSTT1) gene defects

OBJECTIVES

Glutathione S-transferases (GST) modulate the effects of exposure to various cytotoxic and genotoxic agents, including those associated with increased risks of the myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML) and aplastic anemia (AA). Both the GST mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null variant allele in which the entire gene is absent. In this study, we tested whether null genotypes for the GSTM1 and GSTT1 genes altered the risks for MDS, AML and AA.

METHODS

Genomic DNA from 49 MDS, 38 AML and 37 AA patients and 276 controls was analysed using the polymerase chain reaction (PCR).

RESULTS

The frequencies of GSTM1 (73.6%) and GSTT1 (34.2%) null genotypes were significantly higher in AML patients than in the controls (36.9 and 18.1%, respectively). A higher frequency of the combined null genotype for both genes was also observed in patients with AML (26.3% compared with 5.0% in the controls). In contrast, no differences in the frequencies of the null genotypes were found among MDS patients, AA patients and the controls.

CONCLUSION

Our observation of a 4.7-fold (95% CI: 2.1-11.0) and 2.3-fold (95% CI: 1.0-5.2) increased risk associated with the GSTM1 and GSTT1 null genotypes, respectively, and a 6.6-fold (95% CI: 2.4-7.9) increased risk associated with the combined null genotype presents preliminary evidence that the inherited absence of this carcinogen detoxification pathway may be an important determinant of AML.

Intravenous administration of an E1/E3-deleted adenoviral vector induces tolerance to factor IX in C57BL/6 mice

Inbred immunocompetent C57BL/6 mice have been a favored strain to study transgene expression of human blood coagulation factor IX (hF.IX) from viral vectors because systemic expression of the secreted protein is not limited by antibody responses following intravenous (i.v.) injection of vector. For example, i.v. injection of an adenoviral (Ad) vector results in sustained expression of hF.IX in normal or hemophilic C57BL/6 mice, while anti-hF.IX antibodies rapidly emerge in other strains (Gene Therapy 4: 473; Blood 91: 784). To investigate these observations further, we injected naive C57BL/6 mice and C57BL/6 mice with pre-existing anti-hF.IX with Ad-hF.IX vector via peripheral vein. All mice expressed hF.IX antigen without detectable anti-hF.IX, even when challenged with hF.IX in different immunogenic settings at later time points. Moreover, in mice with pre-existing immunity, anti-hF.IX titers diminished to undetectable levels after i.v. administration of Ad-hF.IX. Lymphocytes from mice that had received Ad-hF.IX i.v. failed to proliferate when stimulated with hF.IX in vitro after the animals had been repeatedly challenged with hF.IX protein formulated in complete Freund's adjuvant. Thus, absence of anti-hF.IX in C57BL/6 mice after i.v. injection of Ad vector is not due to ignorance to the foreign transgene product. Similar experiments in other strains showed that immune tolerance to hF.IX does not correlate with the strain haplotype or expression of IL-10 cytokine. Given the well-documented immunogenicity of the first-generation adenoviral vector, data from C57BL/6 mice may therefore grossly underestimate immunological consequences in certain gene therapy protocols.

Paraoxonase Polymorphisms and the Risk of Arterial Ischemic Stroke among Young Adults

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Despite extensive investigation, the etiology of arterial ischemic stroke (AIS) in the young remains unknown in one-third of patients. Serum paraoxonase (PON) is an HDL-associated esterase that hydrolyzes products of lipid peroxidation and prevents the oxidation of LDL, thus exerting anti-oxidant and anti-atherogenic effects. PON levels have been shown to be significantly reduced in patients with coronary artery disease. Two common polymorphisms in the PON gene, the 55 Leu (L allele)→ Met (M allele) and the 192 Gln (A allele)→ Arg (B allele) substitutions, influence PON activity in a gene-dose dependent manner. As the association of these polymorphisms with cardiovascular disease and stroke is controversial, we investigated their role in a young population with AIS. We carried out a cross-sectional study including 138 patients (84 women, 54 men; mean age: 32.9 years) with a first AIS before the age of 45 years and 102 age-matched controls. The diagnosis of AIS was based on clinical and neuroimaging findings. Fragments of the coding region of the PON gene encompassing the 192 and 55 polymorphisms were analyzed by PCR amplification and posterior restriction endonuclease digestion. Among patients, 17.4% were found to be homozygous and 46.4% heterozygous for the B allele at position 192, compared to 8.8% and 38.3% respectively among controls. This yielded a significantly higher allele frequency of the 192 B allele among patients than controls: 0.406 vs. 0.279, P=0.0056, OR=1.76 (CI=1.17–2.65). Regarding the PON 55 L allele, there was no significant difference between patients and controls (P=0.59). The presence of hyperlipidemia, diabetes mellitus and smoking, factors known to influence PON levels, were analyzed in the patient and control groups and did not significantly alter the difference in allele frequencies. These findings suggest that the PON 192 B allele is associated with an increased risk of AIS among young adults. However, studies including a larger number of patients and analyzing the effect of PON on atherosclerosis are necessary to better understand the role of these observations in the development of AIS in the young.

Posttranslational modifications of recombinant myotube-synthesized human factor IX

Recent data demonstrate that the introduction into skeletal muscle of an adeno-associated viral (AAV) vector expressing blood coagulation factor IX (F.IX) can result in long-term expression of the transgene product and amelioration of the bleeding diathesis in animals with hemophilia B. These data suggest that biologically active F.IX can be synthesized in skeletal muscle. Factor IX undergoes extensive posttranslational modifications in the liver, the normal site of synthesis. In addition to affecting specific activity, these posttranslational modifications can also affect recovery, half-life in the circulation, and the immunogenicity of the protein. Before initiating a human trial of an AAV-mediated, muscle-directed approach for treating hemophilia B, a detailed biochemical analysis of F.IX synthesized in skeletal muscle was carried out. As a model system, human myotubes transduced with an AAV vector expressing F.IX was used. F.IX was purified from conditioned medium using a novel strategy designed to purify material representative of all species of rF.IX in the medium. Purified F.IX was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequence analysis, chemical gamma-carboxyglutamyl analysis, carbohydrate analysis, assays for tyrosine sulfation, and serine phosphorylation, and for specific activity. Results show that myotube-synthesized F.IX has specific activity similar to that of liver-synthesized F.IX. Posttranslational modifications critical for specific activity, including removal of the signal sequence and propeptide, and gamma-carboxylation of the N-terminal glutamic acid residues, are also similar, but carbohydrate analysis and assessment of tyrosine sulfation and serine phosphorylation disclose differences. In vivo experiments in mice showed that these differences affect recovery but not half-life of muscle-synthesized F.IX.

The impact of the search for thrombophilia risk factors among antiphospholipid syndrome patients with thrombosis

Thrombosis is a major clinical feature of the antiphospholipid syndrome. Interactions between genetic and acquired factors could contribute to thrombosis development. In this study, we evaluated 40 patients with antiphospholipid syndrome and thrombosis, 31 primary and nine secondary to systemic lupus erythemathosus, to estimate the carrier rates of factor V Leiden, 20210A --> G prothrombin variant and 677C --> T in the MTHFR gene. Protein C, protein S and antithrombin were measured in 30 patients, with a median of 100.66 +/- 23.86, 93.57 +/- 36.44 and 98.8 +/- 5.67%, respectively. None of the patients were deficient on these natural anticoagulants. No significant variation was found between the patient group and the controls, regarding the prevalence of homozygotes for the mutated 677T allele (2.5 versus 5.4%), or heterozygotes for factor V Leiden (0 versus 0.7%). Despite the fact that these mutations are relatively common in Brazilian thrombophilic patients, its low prevalence in this cohort of patients suggest that these genetic alterations are not risk factors for thrombosis in antiphospholipid syndrome. The prevalence of the mutated allele 20210A of the prothrombin gene was higher in patients when compared with controls (5 versus 0.7%; P = 0.01), suggesting that prothrombin variant could increase the risk of thrombosis in patients with antiphospholipid syndrome.

Possible association between cytomegalovirus infection and gastrointestinal bleeding in hemophiliac patients

Cytomegalovirus (CMV) infection is of major concern in immunocompromised and immunosuppressed patients. Prior to the introduction of HIV-1 antibody screening and efficient virucidal processes to inactivate viruses, individuals with a factor VIII or factor IX deficiency had a high risk of contracting HIV-1 infection through the infusion of contaminated blood products. In addition, blood products were also frequently associated with alterations in immune function. This study investigated the frequency of active CMV infection and its clinical relevance in Brazilian hemophiliacs. One hundred hemophiliacs were screened for the presence of CMV-DNA in their blood using nested PCR. Twenty-five out of 100 patients (25%) were positive for CMV-DNA and 24 of these 100 patients (24%) were HIV-1 positive; 6 of these 24 (25%) were positive for CMV-DNA. A similar frequency was observed among HIV-1-negative patients. In 60 hemophiliacs, the clinical relevance of the CMV infection was assessed. Twenty-one patients were positive for CMV-DNA. Of these, 10 had gastrointestinal bleeding compared to only 9 of 39 patients who were CMV-DNA negative (p = 0.05; chi(2) test). These data indicate a high prevalence of active CMV infection in Brazilian hemophiliac patients, irrespective of whether the patients were or were not infected by HIV-1. There was a possible association between the presence of CMV and the occurrence of gastrointestinal bleeding.