P0963 - Enhancement of Transamniotic Stem Cell Therapy for Spina Bifida by Genetic Engineering of Donor Mesenchymal Stem Cells with an Fgf2 Transgene

Background/Purpose: Transamniotic stem cell therapy (TRASCET) with mesenchymal stem cells (MSCs) induces partial or complete prenatal coverage of experimental spina bifida in a subset of fetuses. Variation in fibroblast growth factor-2 (Fgf2) expression at the defect has been associated with increased coverage. We examined whether engineered overexpression of Fgf2 in donor MSCs could enhance the coverage rate.

Methods: Pregnant Sprague-Dawley dams (n=24) exposed to retinoic acid for induction of fetal spina bifida were divided in three groups. An untreated group had no further manipulations. Two groups received volume-matched intra-amniotic injections into all fetuses (n=157) of a suspension of labeled amniotic fluid-derived MSCs (afMSCs), either without further manipulation (afMSC; n=85) or transduced with an Fgf2 transgene (Fgf2-afMSC; n=72) on gestational day 17 (term=21-22 days). Infused afMSCs consisted of syngeneic Lewis rat cells phenotyped by flow cytometry. Fgf2 mRNA expression and protein levels were measured by RT-qPCR and ELISA, respectively, in both cell populations prior to administration in vivo. Defect coverage was categorized at term by the presence of a characteristic rudimentary neoskin confirmed histologically by HE and pan-cytokeratin immunohistochemistry. Statistical comparisons were by logistic regression.

Results: Fgf2 mRNA expression and protein levels were 10.1-fold and 3.1-fold higher, respectively, in Fgf2-afMSCs than in native afMSCs. Among 84 survivors with isolated spina bifida, 71 had definitive histology. Defect coverage (partial or complete) rates in both the afMSC (38.5%) and Fgf2-afMSC (73.3%) groups were statistically significantly higher than in the untreated group (10%; p<0.001 for both). There was a significantly higher rate of coverage in the Fgf2-afMSC group compared with the afMSC group (p=0.025).

Conclusions: Fgf2 overexpression in donor mesenchymal stem cells increases defect coverage rates in a rodent model of transamniotic stem cell therapy for spina bifida. Genetic engineering of donor cells is a promising strategy for the enhancement of this emerging therapy.