Limited potential of AAV-mediated gene therapy in transducing human mesenchymal stem cells for bone repair applications
Authors: Venus Vakhshori
Heidy Morales
Osamu Sugiyama
Sofia Bougioukli
Daniel Oakes
Morgan Chateau
Jay R Lieberman
Paula Cannon
Donald Longjohn
Journal: Gene Therapy (2021)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Adeno-associated viral vectors; AAV; gene therapy; bone repair; BMP-2
Affiliations: Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA. ., Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA., Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.

Abstract:  Adeno-associated viral vectors (AAV) are unique in their ability to transduce a variety of both dividing and nondividing cells, with significantly lower risk of random genomic integration and with no known pathogenicity in humans, but their role in ex vivo regional gene therapy for bone repair has not been definitively established. The goal of this study was to test the ability of AAV vectors carrying the cDNA for BMP-2 to transduce human mesenchymal stem cells (MSCs), produce BMP-2, and induce osteogenesis in vitro as compared with lentiviral gene therapy with a two-step transcriptional amplification system lentiviral vector (LV-TSTA). To this end, we created two AAV vectors (serotypes 2 and 6) expressing the target transgene; eGFP or BMP-2. Transduction of human MSCs isolated from bone marrow (BMSCs) or adipose tissue (ASCs) with AAV2-eGFP and AAV6-eGFP led to low transduction efficiency (BMSCs: 3.57% and 8.82%, respectively, ASCs: 6.17 and 20.2%, respectively) and mean fluorescence intensity as seen with FACS analysis 7 days following transduction, even at MOIs as high as 106. In contrast, strong eGFP expression was detectable in all of the cell types post transduction with LV-TSTA-eGFP. Transduction with BMP-2 producing vectors led to minimal BMP-2 production in AAV-transduced cells 2 and 7 days following transduction. In addition, transduction of ASCs and BMSCs with AAV2-BMP-2 and AAV6-BMP-2 did not enhance their osteogenic potential as seen with an alizarin red assay. In contrast, the LV-TSTA-BMP-2-transduced cells were characterized by an abundant BMP-2 production and induction of the osteogenic phenotype in vitro (p &lt; 0.001 vs. AAV2 and 6). Our results demonstrate that the AAV2 and AAV6 vectors cannot induce a significant transgene expression in human BMSCs and ASCs, even at MOIs as high as 106. The LV-TSTA vector is significantly superior in transducing human MSCs; thus this vector would be preferable when developing an ex vivo regional gene therapy strategy for clinical use in orthopedic surgery applications. 

Retracted: No

PubPeer comments:
 Fig 2B: Appears to be the same panel as Fig 4F from Mazumdar et al. 2012 (doi: [10.1128 jvi.06577-11] ) ![file] ![file] , 
 I agree that the bands apparently look similar between these two publications 6-7 years back. Now, it is very difficult to track results from the original experiment. However, the results presented from multiple experiments including qPCR and flow cytometry suggested increased CD55 expression, and the concerns raised do not compromise the theme of our publications. Moreover, subsequent follow-up work and publications further emphasized CD55 upregulation by HCV (For example, Fig. 1A - The Journal of Immunology, 1127-1136, 2016). , 
 #1  Appears to be the same panel as Fig 4F from Mazumdar et al. 2012 The same apart from the horizontal flip of one slice and the ambiguity whether it shows CD55 or P-C EBP-beta. ,