Somatic cells, such as skin fibroblasts or PBMCs, from healthy control subjects (n = 3) and RA patients with MTX-induced hepatotoxicity (n = 3) were induced to form iPSCs with Sendai virus expressing the Yamanaka factors (Oct4, Sox2, KLF4, c-Myc). The gene discussed is POU5F1; the disease is rheumatoid arthritis.