Tumorigenicity of hMSC-EGFP cell transplants. Left side: histological assessment of tumour growth by hMSC-EGFP cell transplants in rat spinal cord between day 1 and week 2 post-transplantation in immune suppressed animals (+ cyclosporine A). Right side: histological assessment of tumour regression in rat spinal cord at week 4 post-transplantation upon withdrawal of immune suppression at week 2 post-transplantation (-cyclosporine A). First row: hematoxylin-eosin (HE) staining indicating localisation and general appearance of transplantation site. Second row: direct EGFP fluorescence indicating the presence or absence of EGFP positive hMSC-EGFP cell transplants. Third row: immuno-histochemical staining for EGFP indicating the presence or absence of EGFP positive hMSC-EGFP cell transplants. Fourth row: immuno-histochemical staining for CD68 indicating macrophage infiltration into the transplantation site. Representative pictures were chosen from multiple hMSC-EGFP cell transplanted spinal cords analysed 1 day (n = 4), 2 weeks (n = 3) and 4 weeks (n = 2) post-transplantation.