The effect of engineered del(7q) on induced pluripotent stem cells (iPSCs) derived from patients with Shwachman Diamond Syndrome (SDS).

Monosomy 7 or deletion of 7q (del(7q)) frequently arise in inherited and acquired bone marrow failure, and are associated with progression to high grade Myelodysplastic Syndrome (MDS) and acute leukemia. Current non-transplant approaches to treat marrow failure may be complicated by potential stimulation of clonal outgrowth. To study the biological consequences of del(7q) within the context of a failing marrow, we utilized induced pluripotent stem cells (iPSCs) derived from patients with Shwachman Diamond Syndrome (SDS) and genomically engineered a deletion of (7q). Deletion of 7q failed to confer a relative fitness advantage in either pluripotent SDS iPSC or in iPSC-derived SDS CD34+ cells. The TGF-beta pathway was the top differentially regulated pathway in transcriptome analysis with the TGF? pathway found activated in SDS-iPSCs, compared to SDS-del(7q) iPSCs. Increased phosphorylation of SMAD2 in SDS-iPSCs was reduced following del(7q) and increased upon restoration of 7q diploidy, in support of an effect of 7q dosage on the activation status of the TGF-beta pathway in SDS. Inhibition of the TGF-beta pathway rescued hematopoiesis in SDS-iPSCs and in primary bone marrow cells from SDS patients without improving hematopoiesis of the SDS-del(7q) cells. Together, these results utilizing an iPSC model of MDS in BMF identified a targetable vulnerability for potential therapeutic strategies to ameliorate bone marrow failure without promoting outgrowth of the del7q clone. Overall design: RNA-seq transcriptome profiling of triplicate iPSCs with and without deletion of chr7q. iPSCs were generated from bone marrow mononuclear cells of two patients with SDS that carried homozygous c.258+2T>C SBDS mutations. The long arm of chromosome 7 was deleted by targeted insertion of two inverted loxP sites into the long arm of chromosome 7 followed by transient expression of Cre-recombinase. iPSCs samples without chromosome 7q deletion were labeled SDS. iPSCs samples with chromosome 7q deletion were labeled SDS del(7q).