312. Gene Correction of LGMD2A Patient-Specific iPS Cells for Targeted Autologous Cell Therapy

Limb girdle muscular dystrophy type 2A (LGMD2A), an incurable autosomal recessive disorder and the most common form of LGMD, is characterized by symmetric and progressive weakness of limb-girdle muscles leading to loss of ambulation. LGMD2A is caused by mutations in the Calpain 3 (CAPN3) gene which encodes a muscle-specific intracellular calcium-sensitive cysteine protease, hypothesized to act as a gate keeper for proper assembly and maintenance of the sarcomere. A cell therapy based on induced pluripotent stem (iPS) cells has the potential for treating muscular dystrophy. We have demonstrated that transplantation of skeletal muscle progenitors obtained from disease-free human iPS cells can restore muscle contractility in a mouse model for Duchenne Muscular Dystrophy. The goal of this study is to apply gene editing tools to correct the CAPN3 mutation in LGMD2A iPS cells, and to determine the feasibility of an iPS-cell based autologous cell therapy for LGMD2A. Here we investigated two approaches to genetically correct a LGMD2A patient-specific iPS cell line with homozygous deletion of exon 17 to 24 in the CAPN3 gene. The first approach consisted of knocking in the coding region of CAPN3 cDNA with SV40 polyadenylation signal sequence downstream in exon 1 of the endogenous CAPN3 gene by CRISPR-CAS9 induced double stranded break (DSB) mediated homology directed DNA repair from exogenous donor template, allowing for universal correction of all types of CAPN3 mutations. PCR, sequencing and Southern blot analysis on iPS colonies post- genome editing confirmed the integration of the cDNA in exon 1 of the CAPN3 gene. The second approach involved inserting the missing exons 17-24 with SV40 polyadenylation signal sequence downstream contiguous with the exon 16 of the endogenous CAPN3 gene. PCR and sequencing analysis on iPS colonies post-genome editing confirmed proper integration in this approach as well. LGMD2A iPS cell clones, genetically corrected using these two gene editing methods will be differentiated into skeletal muscle progenitors using conditional expression of Pax7, as previously described by our group, and evaluated in vitro and in vivo for restoration of full length CAPN3. For the latter, we have generated an immunodeficient LGMD2A mouse model by combining the CAPN3-KO mouse model with NOD/SCID and IL2Rg mutations. This mouse is ideal for studies on the transplantation of human cells. In summary, we have corrected the CAPN3 mutation in LGMD2A iPS cells for the first time, and ongoing transplantation studies with corrected iPS cells will provide proof-of-principal for a potential new cell therapy that can permanently restore CAPN3 function in all LGMD2A patients.