Date Published: March 21, 2019
Publisher: Public Library of Science
Author(s): Pengfei Li, Eva Boenzli, Regina Hofmann-Lehmann, A. Katrin Helfer-Hungerbuehler, John A. Chiorini.
Adeno-associated virus (AAV) vectors represent promising candidates for gene therapy; however, pre-existing neutralizing antibodies (NAb) may reduce AAV vector delivery efficiency. In this study, the presence of AAV NAb was investigated in cats, which serve as a larger and outbred animal model for the prediction of gene therapy outcomes in humans but also in cats.Serum/plasma samples from 230 client-owned Swiss cats and 20 specified pathogen-free cats were investigated for NAb to AAV1, AAV2, AAV5, AAV6, AAV7, AAV8 and AAV9 using in vitro transduction inhibition and a beta-galactosidase assay. NAb to all tested AAV serotypes were found. Of the client-owned cats, 53% had NAb to one or more of the AAV serotypes. NAb (≥1:10) were found at frequencies of 5% (AAV6) to 28% (AAV7). The highest titers were found against AAV7 (≥1:160). The NAb prevalence to AAV2, AAV7 and AAV9 differed geographically. Regarding titers ≥1:10 against single AAV serotypes, age, breed and sex of the cats were not associated with the NAb prevalence. Cats with titers ≥1:20 against AAV2 and titers ≥1:40 against AAV7 were significantly younger than cats with low/no titers, and purebred cats were significantly more likely than non-purebred cats to have NAb to AAV2 (≥1:40). Additionally, regarding NAb to all AAV combined, female cats were significantly more likely than male cats to have NAb titers ≥1:40. Preliminary data using AAV-DJ indicated that less pre-existing NAb to the hybrid AAV-DJ can be expected compared to the wild-type AAV serotypes. AAV NAb will need to be taken into account for future in vivo gene therapy studies in cats.
Treatment of many genetic and acquired diseases remains a challenge. At present, curative treatments are often nonexistent, inefficient or toxic [1, 2]. Thus, new classes of therapeutics are being developed; these development efforts include the investigation and application of gene therapy. Adeno-associated virus (AAV)-based vectors represent promising candidates for therapeutic gene transfer due to the assumed lack of involvement in human diseases and their display of relatively low immunogenicity . AAV has been used as a vector for over 20 years  in more than 100 clinical trials. Several of these trials show great promise, such as gene therapy for hemophilia B [5, 6], Leber’s congenital amaurosis [7, 8] and Parkinson’s disease . Few AAV-vector-mediated gene therapies have already been approved in Europe including Alipogene Tiparvovec, a treatment of lipoprotein lipase deficiency as well as Luxturna a one-time gene therapy for the treatment of an inherited retinal dystrophy [10, 11].
The present study focused on investigating NAb against seven different AAV serotypes in the domestic cat population of Switzerland. This is the first study to use an in vitro transduction inhibition assay to test for biologically active NAb to AAVs in cats, as well as the first investigation of AAV seroprevalence in a large number of cats (n = 250). There has been only one previous study on the subject in cats; that study was smaller and examined total antibodies to AAVs in cats using an ELISA technique .
Compared with the prevalence of NAb against AAV in humans, the prevalence of NAb in cats was reduced, ranging from 5%–28%. A low prevalence of NAb against AAV in cats supports its applicability for gene therapy. However, due to the potential hindrance of NAb during gene therapy and the currently rather high effort necessary for gene therapy, prescreening of the individual animals for the presence of NAb to the AAV serotype in question may be advisable.