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