Phase 1 trial of FVIII gene transfer for severe hemophilia A using a retroviral construct administered by peripheral intravenous infusion

Abstract

In a phase 1 dose escalation study, 13 subjects with hemophilia A received by peripheral intravenous infusion a retroviral vector carrying a B-domain-deleted human factor VIII (hFVIII) gene. Infusions were well tolerated. Tests for replication competent retrovirus have been negative. Polymerase chain reaction (PCR) analyses demonstrate the persistence of vector gene sequences in peripheral blood mononuclear cells in 3 of 3 subjects tested. Factor VIII was measured in serial samples using both a one-stage clotting assay and a chromogenic assay. While no subject had sustained FVIII increases, 9 subjects had FVIII higher than 1% on at least 2 occasions 5 or more days after infusion of exogenous FVIII, with isolated levels that ranged from 2.3% to 19%. Pharmacokinetic parameters of exogenous FVIII infused into subjects 13 weeks after vector infusion showed an increased half-life (T 1/2 ; P < .02) and area under the curve (AUC, P < .04) compared with prestudy values. Bleeding frequency decreased in 5 subjects compared with historical rates. These results demonstrate that this retroviral vector (hFVIII(V)) is safe and, in some subjects, persists more than a year in peripheral blood mononuclear cells, with measurable factor VIII levels and with increased available FVIII activity (increased T 1/2 and AUC) after infusion of exogenous FVIII concentrate.

Analysis of factor VIII mediated suppression of lentiviral vector titres

“…6,7 The generation of vectors with improved titres appears to be related to the presence of an intron 7,8 which is postulated to counteract transcriptional repression leading to increased mRNA accumulation. 9 Sustained levels of FVIII were not detected in patients administered with a retroviral construct 10 and therefore more recently studies have focused on the use of lentiviral vectors which are capable of transducing a wide variety of terminally differentiated cell types including hepatocytes. 11 Long-term expression of B domain-deleted (BDD) FVIII in murine models has been reported using both human immunodeficiency virus-1 (HIV-1)- [12][13][14] and feline immunodeficiency virus (FIV)-based 15,16 lentiviral vectors; however, plasma levels of FVIII have generally been low.…”

Transient blockade of the inducible costimulator pathway generates long-term tolerance to factor VIII after nonviral gene transfer into hemophilia A mice

“…Gene therapy has been explored as a promising treatment in phase 1 clinical trials. [11][12][13] However, to date, only transient, low-level FVIII protein expression has been achieved because of development of immune responses against FVIII and/or associated gene transfer vectors. In most preclinical experiments using immunocompetent hemophilia A murine and canine models, strong immune responses against FVIII after gene therapy have completely inhibited circulating FVIII activity and thus subverted the effect of gene therapy.…”

Storage and regulated secretion of factor VIII in blood outgrowth endothelial cells

“…2 A number of clinical trials for hemophilia A gene therapy have been performed. 3,4 So far, limited clinical efficacy of gene delivery approaches has been observed. This is primarily caused by limitations in obtaining sufficiently high levels of FVIII in the circulation.…”