RAF1 and systemic lupus erythematosus: LEFTY1 gene encodes a secreted ligand of the TGF‐beta superfamily.49 Interestingly, inhibition of the Ras/Raf/Mek/Erk pathway dramatically enhances TGF‐mediated Lefty1 up‐regulation.50 Thus, the up‐regulation of LEFTY1 could be explained by the low levels of pErk in the hiPSCs‐SLE.