Background Mesenchymal stem cells (MSC), multipotential non-hematopoietic progenitors, can be isolated from various tissues and can modulate allogeneic immune cell responses. These properties make MSC as a promising potential treatment of autoimmune diseases.1 Our previous studies have found that bone marrow-derived (BM)-MSC from systemic lupus erythematosus (SLE) patients are defective structurally and functionally,2 treatment with modified and optimised MSC may bring a better effect on patients with autoimmune diseases. Most efforts have relied on adeno- and lentiviral vectors for delivering genes to MSC. Effective as these vectors may be, concerns regarding their immunogenicity and, in the case of lentivirus, the risk of insertional mutagenesis, have led to the pursuit of safer alternatives. Among these, adeno-associated virus (AAV) holds several advantages as a vector for human gene therapy. There are many serotypes of AAV available, and certain serotypes have been found to transduce specific cell types more efficiently than others.
Objectives To determine the efficiency of different serotypes of AAV vectors for their ability to mediate transduction of different sources of MSC and assess whether AAV transduction affects MSC multipotentiality.
Methods Serotypes 1, 2, 5, 6, 8, 9, PHP and DJ of AAV vectors were constructed in Viral Core, Boston Children’s Hospital. The enhanced green fluorescent protein (eGFP) gene under transcriptional control of a CAG promoter was cloned into the AAV vector backbone. MSC derived from umbilical cord (UC), BM and amniotic fluid (AF) were isolated and approximately 1 × 105 MSC were used for transductions with AAV vectors. eGFP expression was evaluated 3 days after transduction by fluorescence microscopy and flow cytometry. The capacity of MSC to differentiate in vitro was assessed.
AAV serotype DJ vector was the most efficient in transducing MSC. AAV was added directly to the medium at 5 multiplicities of infection (MOI), 41% UC–MSC was transduced by AAV2/DJ, while the transfection is 0.47%, 0.3%, 10.5%, 0.3%, 1.84%, 0.06%, 0.16% by AAV2/1, AAV2/2, AAV2/5, AAC2/6, AAV2/8, AAV2/9, AAV2/PHP (Fig 1A). Transduction efficiencies ranged from 73.5% for MOI 10% to 91.3% for MOI 320 in UC–MSC (Fig 1B).
MSC derived from different tissues share a comparable level of transduction with the same AAV vector serotype. In our result, AAV2/DJ was the most efficient in transducing UC–MSC and AF–MSC.
AAV2/DJ transduced MSC retained the same multipotential activity to differentiate into osteogenic and adipogenic lineage as comparable to un–transduced cells.
Conclusions AAV2/DJ vector can be used as a highly efficient tool to modify MSC ex vivo for therapeutic transplantation for autoimmune diseases.
References  Liang J, Wang D, Dominique F, Sun L. Mesenchymal stem cells for treating autoimmune diseases: The Chinese experience from lab to clinics. Curr Res Transl Med.2016;64(2):115–20.
 Sun L, Akiyama K, Zhang H, et al. Mesenchymal stem cell transplantation reverses multiorgan dysfunction in systemic lupus erythematosus mice and humans. Stem Cells2009;27(6):1421–32.
Disclosure of Interest None declared
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