(A) Four patients in 1 trial and (B) 10 patients in a later trial received 1

(A) Four patients in 1 trial and (B) 10 patients in a later trial received 1.8 1011 vector genomes, all bilateral intraputaminal infusion. exclusion of seropositive subjects is required in many clinical studies evaluating such therapy [4]. Conversely, administration of recombinant AAV vector may itself elicit an immune response, depending on such factors as an anatomic site of administration (Fig. ?11) [7-36] and vector dosage [7, 28, 36]. Open in a separate window Fig. (1) Features of different sites for gene therapy administration [7,36]. AAV, adeno-associated virus; AAV2, adeno-associated virus serotype 2; AAV9, adeno-associated virus serotype 9; CNS, central nervous system; CSF, cerebrospinal fluid. Colematt Getty Images. (CSF and corresponded with neurotoxic effects in some cases [16, 33]. Furthermore, CSF administration may not protect against the effects of preexisting peripheral neutralizing antibodies, as evidenced by a nearly complete lack of CNS gene transduction following intrathecal administration of AAV vectorCmediated gene therapy in seropositive nonhuman primates [32]. Nevertheless, given the capacity for widespread CNS transduction this route, CSF-administered gene therapy may be particularly advantageous in conditions that affect both the brain and spinal cord [35, 43]. At present, early-phase human trials of such therapy are ongoing for several CNS disorders, including for mucopolysaccharidosis types I [8] and II [9, 10], neuronal ceroid lipofuscinosis [11, 12], GM2 gangliosidosis [13, 14], and giant axonal neuropathy [15]. Other sites such as the subretinal space have been investigated for inherited retinal disorders, with little to no detectable immune response to the therapy [3, 5, 28]. Compartmentalized sites within the CNS and the eye, such as GSK2190915 the brain parenchyma and retina, benefit from adaptations protecting them from destructive inflammatory responses [22, 28]. Direct delivery of viral vectors into these sites eliminates or reduces the impact of preexisting humoral immunity, in contrast to systemic delivery [25, 28, 44]. Other factors that may GSK2190915 contribute to a lower risk of immunogenicity of vector-based gene therapy administered GSK2190915 these sites include avoidance of widespread vector biodistribution and the need for relatively low vector doses (gene (AAV2-hAADC) [45, 52]. Since most of the AADC activity is found in the striatum [56], local delivery of the gene is expected to alleviate symptoms. Indeed, intraputaminal administration of AAV2-hAADC improved motor function in a clinical trial of 4 children with AADC deficiency. In this trial, anti- AAV2 antibody titers were measured at baseline and after treatment with AAV2-hAADC [52]. All patients had a negative antibody titer at baseline, as measured by an enzyme-linked immunosorbent assay (ELISA) method developed GSK2190915 for rapid screening of neutralizing antibodies using whole vector particles as antigens. In the ELISA, a neutralizing GSK2190915 antibody titer of 1 1:32 in cell transduction assay corresponded to an optical density (OD) of 0.5 [57]. Antibody titers increased slightly in 2 patients after gene transfer (Fig. ?2A2A). There was no correlation between antibody titer and clinical outcomes; all 4 patients showed improvements in motor function [52]. A later clinical trial included 10 patients with AADC deficiency. Anti-AAV2 antibody titers were measured at baseline and every 3 months after gene therapy. All patients had a negative antibody titer (0.1 OD) at baseline, as measured by ELISA. Antibody titers increased in all patients after ICAM3 gene therapy and declined over time. Antibody titer did not impact motor function improvement (Fig. ?2B2B) [45]. Results from a study conducted by a separate group of investigators showed improved motor function despite elevated antibody titers (1:56C1:28,000) in 6 patients with AADC deficiency at 6 months after treatment with AAV2-hAADC [58]. Although the detailed process of antibody formation against AAV2 capsid remains unknown, leakage of vector particles into the CSF or interstitial fluid during infusion was the most likely mechanism eliciting an immune reaction. Importantly, the antibodies raised against AAV2.