Six patients with BD type I (three LR and three NR) were recruited as well as four healthy control subjects (see Materials and Methods for further details). The B-lymphocytes from these patients and neurotypical controls were immortalized using EBV virus and reprogrammed into iPSCs using the Yamanaka episomal vector set described by Okita et al.53 (see Materials and Methods for more details). The iPSC clones that passed the quality controls described below in the Materials and Methods (Figure 1a–d) were differentiated into a primed neural progenitor cell population and subsequently into hippocampal DG granule-cell-like neurons using a protocol described previously55 (Figure 1e and f). Over 48% of the differentiated neurons expressed the Prox1 gene, which is a specific marker for dentate granule cells, and no significant difference was observed between controls and patients (average controls: 49.11 ± 6.30%; LR: 48.87 ± 5.23%; NR: 49.59 ± 6.37%, all errors given as s.e.m.) (Figure 1f). This demonstrates that reprogramming of EBV-immortalized B-lymphocytes into iPSCs was possible and that the differentiated cells could be used to obtain reliable data are important advances in the field because large collections of these cells are banked and readily accessible.
