For example, in the Norsvin Topigs-20 strain, the seroprevalence of antibodies against AAV2 was very high. and AAV2 were less than 1:100, with two exceptions. For total binding IgG, more individuals showed positivity for all the tested serotypes but, in general, the levels were low or zero. Three animals had no antibodies at all against the AAVs tested. Therefore, Gttingen minipigs could be considered an attractive animal model for gene therapy studies. Since some animals were negative for all those AAVs tested, these may be selected and used as donor animals for xenotransplantation. Keywords:adeno-associated viruses (AAVs), seroprevalence, gene therapy, xenotransplantation, Gttingen minipigs == 1. Introduction == Adeno-associated viruses (AAVs) are small (26 nm in diameter) replication-defective, non-enveloped viruses with a linear single-stranded DNA (ssDNA) genome of 4.8 kilobases (kb). They belong to the genusDependoparvovirus, which in turn belongs to the familyParvoviridae[1]. The genome encodes for viral replication, packaging, and capsid assembly proteins, these coding genes are flanked by two inverted terminal repeats (ITRs) [2]. There are at least 13 different AAV subtypes which have different tissue tropisms due to differing interactions with their receptor [3]. In 2012, the first gene therapy product, Glybera, which is based on an AAV gene-delivery approach for the treatment of patients with lipoprotein lipase deficiency, was approved in Europe and, today, AAV vectors are well established in clinical trials for in vivo gene therapy [4]. In 2019, 288 AAV-based clinical trials were registered MPI-0479605 with the US FDA database [5], and this number has increased rapidly until now [4]. Recently, it was shown that AAV-mediated gene replacement therapy was able to effectively rescue elements MPI-0479605 associated with the photoreceptor POLD4 degeneration in Leber congenital amaurosis subtype 4 (LCA4) animal and cell models [6]. The AAV vector has unique features that are beneficial in clinical applications, including broad tropism, low immunogenicity, a relative ease of production, being nonpathogenic, rarely integrating into the host chromosome, and resulting in long-term expression of the transgene. AAVs are commonly used due to their high efficacy of transduction, high safety profile, and ease of production [4]. Naturally occurring AAVs infect both dividing and non-dividing cells in humans and animals and can remain latent in the host in a circular DNA episomal form; although MPI-0479605 integration in the host can occur, it is very infrequent. However, contamination with wild-type AAVs could result in the production of neutralizing antibodies (NAbs), and these can interfere with treatment based on recombinant AAV vectors. The Gttingen minipigs are an attractive animal model in many clinical areas due to their high similarity in anatomy, physiology, and immunology to humans [7,8,9]. Although considered as a large animal model, the Gttingen minipigs are smaller in size compared to other pig breeds, making them more manageable in a laboratory setting. Their cardiovascular, respiratory, digestive, and renal systems, as well as their metabolic functions, are closer to those of humans compared to other animal models. Anatomical similarities are important in studies that involve surgical procedures, medical device testing, or the development of surgical techniques. Gttingen minipigs can be used to model human diseases such as cardiovascular diseases, diabetes, obesity, and metabolic disorders. Because of the similarities of the porcine and human cardiovascular systems, Gttingen minipigs are widely used as a large animal model for cardiovascular diseases [10,11,12]. This allows for the preclinical testing of new therapies and interventions, including gene therapy studies. Additionally, Gttingen minipigs are bred under controlled conditions, offering a high reproducibility when it comes to experimental data and results. As is the MPI-0479605 case for many other animal models used for AAV-based gene-delivery studies, knowing the AAV seroprevalence in Gttingen minipigs is usually highly relevant when considering the selection of animals with lower or no titers of pre-existing antibodies against AAV capsids. For example, in a study by Rapti et al. [13], the prevalence of antibodies against several AAV serotypes was assessed in a variety of small and large animal models (excluding non-human primates (NHPs)). The antibody titers varied widely between species and between serotypes. Rats displayed the lowest level of AAV NAbs, but they were present in all tested species (mice, rats, rabbits, dogs, sheep, and pigs) [13]. When Gttingen minipigs were injected with an AAV1 vector made up of the coding sequence of the sarcoplasmatic reticulum ATPase (SERCA2a), the results showed that this vector genome copies in the heart were less prevalent in the animals with pre-existing neutralizing antibodies 2 days post-injection, demonstrating that even low NAbs against AAV vectors can have a negative transduction effect in vivo [12]. The wide prevalence of cross-reactive antibodies against AAVs in different animal species, including pigs,.