Lineage restricted dominant reprogramming of human lymphocytes by embryo-derived stem cells. The reprogramming activity of embryonic stem (ES), trophectoderm stem (TS) and extra-embryonic endoderm (XEN) cells was assessed by heterokaryon formation with human B-lymphocytes (hB). Relative expression levels of human stem cell-specific genes in interspecies heterokaryons were detected by quantitative reverse transcriptase polymerase chain reaction analysis. The transcript levels of ES (OCT4, NANOG, CRIPTO, REX1), TS (CDX2, HAND1) and XEN-specific (GATA6, FOXA2 and HNF4) genes were measured 1 to 3 days after fusion and normalized to GAPDH expression. The constitutively expressed gene HPRT was included as a control. Values shown are the mean from two independent experiments and error bars indicate standard deviations.