Four of the six discontinued FIX prophylaxis and remained free of spontaneous hemorrhage; in the other two, the interval between prophylactic injections was increased

Four of the six discontinued FIX prophylaxis and remained free of spontaneous hemorrhage; in the other two, the interval between prophylactic injections was increased. injections was increased. Of the two participants who received N-Desmethylclozapine the high dose of vector, one experienced a transient, asymptomatic elevation of serum aminotransferase levels, which was associated with the detection of AAV8-capsidspecific T cells in the peripheral blood; the other experienced a N-Desmethylclozapine slight increase in liver-enzyme levels, the cause of which was less obvious. Each of these two participants received a short course of glucocorticoid therapy, which rapidly normalized aminotransferase levels and maintained FIX levels in the range of 3 to 11% of normal values. == CONCLUSIONS == Peripheral-vein infusion of scAAV2/8-LP1-hFIXco resulted in FIX transgene expression at levels sufficient to improve the bleeding phenotype, with few side effects. Although immune-mediated clearance of AAV-transduced hepatocytes remains a concern, this process may be controlled with a short course of glucocorticoids without loss of transgene expression. (Funded by the Medical Research Council as well as others; ClinicalTrials.gov number,NCT00979238.) Hemophilia B is an X-linked bleeding disorder that results from a defect in the gene encoding coagulation factor IX (FIX), a serine protease that is critical for blood clotting. Persons with severe hemophilia B have functional FIX levels that are less than 1% of normal values and have frequent bleeding episodes, which are associated with crippling arthropathy and early death.1,2Current treatment involves frequent intravenous injections of FIX protein concentrate (i.e., two to three times a week). However, this treatment Rabbit Polyclonal to PKC zeta (phospho-Thr410) is usually prophylactic rather than curative, is extremely expensive, and is associated with inhibitor formation. Somatic gene therapy for hemophilia B offers the potential for a cure through continuous endogenous production of FIX after a single administration of vector, especially since a small rise in circulating FIX to at least 1% of normal levels can substantially ameliorate the bleeding phenotype. At present, gene transfer mediated by an adenovirus-associated computer virus (AAV) vector shows the greatest promise for long-term correction of hemophilia B in the preclinical setting.37However, a combined phase 1 and 2 study that involved serotype 2based AAV vectors (AAV2) showed only transient expression of FIX and suggested that stable expression of therapeutic levels of FIX may be limited by a capsid-specific cytotoxic T-cell response against the transduced hepatocytes.8,9 We have tested an approach to treating patients with severe hemophilia B that is distinct from your approaches used in previous clinical trials of AAV-mediated gene transfer in three important respects. First, we developed a codon-optimized FIX (FIXco) expression cassette that is packaged as complementary dimers within a single virion. These self-complementary AAV (scAAV) vectors mediate transgene expression at substantially higher levels than do single-stranded AAV vectors.6,10Second, to circumvent the possibility of humoral immunity to AAV, we pseudotyped these vectors with a capsid of N-Desmethylclozapine serotype 8 (AAV8), which has a lower seroprevalence in humans than does AAV2.11,12Finally, since AAV8 has a strong tropism for the liver, we were able to administer the vector in the peripheral vein a simple, noninvasive approach that is safe for patients with a bleeding diathesis. On the basis of our preclinical security and efficacy data, we conducted a combined phase 1 and 2 clinical trial of scAAV2/8-LP1-hFIXcomediated gene transfer in patients with hemophilia B.6,7,10 == METHODS == == STUDY DESIGN == Patients who met the entry criteria and did not have neutralizing antibodies to AAV8, as determined by an in vivo transduction-inhibition assay (seeTable 1and the Methods section in theSupplementary Appendix, available with the full text of this article at NEJM.org), were enrolled after providing written informed consent. Participants 1 through 5 were recruited in 2010 2010 and Participant 6 was recruited.