A 10 patient case report on the impact of plasmapheresis upon neutralizing factors against adeno-associated virus (AAV) types 1, 2, 6, and 8.

Adeno-associated viruses (AAV) are small, nonenveloped single-stranded DNA viruses which require helper viruses to facilitate efficient replication. These recombinant viruses are some of the most promising candidates for therapeutic gene transfer to treat many genetic and acquired diseases. Nevertheless, the presence of humoral responses to the wild-type AAV common among humans is one of the limitations of in vivo transduction efficacy in humans using cognate recombinant vector. In this study, based on the serum samples that we were able to collect from various clinical situations, we studied the impact of one to five plasmapheresis (PP), at 1-5 day intervals on neutralizing factor (NAF) titers specific for AAV types 1, 2, 6, and 8 in seropositive patients with diverse pathologies and immunosuppressor treatments. We show that frequent sessions of PP result in drastic reduction of NAF specific for AAV1, 2, 6, and 8 to undetectable levels or titers <1:5, mainly when initial titers, i.e., before the first PP were ≤1:20. Altogether, these results show that the use of PP and its possible association with pharmacological immunosuppressive treatments may help to design optimal management of seropositive patients for AAV gene therapy treatments.

Prevalence of serum IgG and neutralizing factors against adeno-associated virus (AAV) types 1, 2, 5, 6, 8, and 9 in the healthy population: implications for gene therapy using AAV vectors.

Adeno-associated viruses (AAVs) are small, nonenveloped single-stranded DNA viruses that require helper viruses to facilitate efficient replication. Despite the presence of humoral responses to the wild-type AAV in humans, AAV remains one of the most promising candidates for therapeutic gene transfer to treat many genetic and acquired diseases. Characterization of the IgG subclass responses to AAV and study of the prevalence of both IgG and neutralizing factors to AAV types 1, 2, 5, 6, 8, and 9 in the human population are of importance for the development of new strategies to overcome these immune responses. Natural exposure to AAV types 1, 2, 5, 6, 8, and 9 can result in the production of antibodies from all four IgG subclasses, with a predominant IgG1 response and low IgG2, IgG3, and IgG4 responses. Prevalences of anti-AAV1 and -AAV2 total IgG determined by enzyme-linked immunosorbent assay were higher (67 and 72%) than those of anti-AAV5 (40%), anti-AAV6 (46%), anti-AAV8 (38%), and anti-AAV9 (47%). Furthermore, data showed that cross-reactions are important. The two highest neutralizing factor seroprevalences were observed for AAV2 (59%) and AAV1 (50.5%) and the lowest were observed for AAV8 (19%) and AAV5 (3.2%). Vectors based on AAV5, AAV8, and AAV9 may have an advantage for gene therapy in humans. Furthermore, among individuals seropositive for AAV5, AAV8, and AAV9, about 70-100% present low titers. Better characterization of the preexisting humoral responses to the AAV capsid and cross-reactivity will allow development of new strategies to circumvent AAV acquired immune responses.