A CYTOTOXIC ANTIBODY AGAINST HUMAN EMBRYONIC STEM CELLS

Abstract

Human embryonic stem cells (hESCs) hold immense potential for regenerative medicine as they possess the dual properties of proliferating indefinitely and differentiating into cells from the 3 germ layers. However, there are safety concerns because residual undifferentiated hESC after differentiation carry the risk of teratoma formation, thus it is essential to remove them prior to transplantation.

A panel of monoclonal antibodies (mAbs) was generated and characterized against cell surface markers on undifferentiated hESC. One of the antibodies, mAb 84 was found not only to bind but also kill undifferentiated hESC/iPS cells but not the differentiated progenitors. By mass spectrometry, the antigen target of mAb 84 was identified as Podocalyxin-like protein 1 (PODXL-1)

Mechanistically, mAb 84 kills hESC by oncosis. This mAb 84-mediated cell death is preceded by cell aggregation and pore formation on the cell surface of hESC. Additionally, treatment of hESC with mAb 84 resulted in the degradation of several cytoskeleton-associated proteins and aggregation of PODXL-1 on the cell surface.

In vivo, SCID mice injected with mAb 84-treated hESC did not form teratomas compared to the untreated control or hESC treated with other antibodies, where teratomas were observed after 7 weeks post-injection.

This is the first study on antibody-mediated oncosis which utilizes hESCs as a model. The significance of these findings is that this antibody can be used to eliminate contaminating hESCs or iPS cells from the differentiated cell population prior to clinical applications because teratoma formation in vivo would severely compromise the success of the transplant. This ¿clean-up¿ step prior to transplantation will increase the safety of this procedure and alleviate concerns over the use of hESCs and iPS cells as the starting cell population for cell therapy.