Treatment of human embryos with the TGFβ inhibitor SB431542 increases epiblast proliferation and permits successful human embryonic stem cell derivation

Study question: Is there an effect of the TGFb inhibitor SB431542 (SB) on the epiblast compartment of human blastocysts, and does it affect subsequent human embryonic stem cell (hESC) derivation? Summary answer: SB increases the mean number of NANOG-positive cells in the inner cell mass (ICM), and allows for subsequent hESC derivation. What is known already: It is known that inhibition of TGFb by SB has a positive effect on mouse ESC self-renewal, while active TGFb signalling is needed for self-renewal of primed ESC. Study design, size, duration: From December 2011 until March 2012, 263 donated spare embryos were used from patients who had undergone IVF/ICSI in our centre. Participants/materials, setting, methods: Donated human embryos were cultured in the presence of SB or Activin A, and immunocytochemistry was performed on Day 6 blastocysts for NANOG and GATA6. Moreover, blastocysts were used for the derivation of hESC, with or without exposure to SB. Mmain results and the role of chance: Immunocytochemistry revealed a significantly higher number of NANOG-positive ICM cells in the SB group compared with the control (12.0+5.9 versus 6.1+4.7), while no difference was observed in the Activin A group compared with other groups (6.7+3.7). The number of GATA6-positive ICM cells did not differ between the SB, Activin A and control group (8.8+4.3, 8.0+4.6 and 7.2+4.0, respectively). Blocking TGFb signalling did not prevent subsequent hESC line derivation. Limitations, reasons for caution: The number of human blastocysts available for this study was too low to reveal if the observed increase in NANOG-positive epiblast cells after exposure to SB affected the efficiency of hESC derivation (12.5% compared with 16.7%). Wider implications of the findings: This work can contribute to the derivation of naive hESC lines in the future