J B Gurdon, S Yamanaka: stem cell research
The prize was "for the discovery that mature cells can be reprogrammed to become pluripotent" meaning that mature cells can be induced to become stem cells which have the potential to differentiate into any of the three derm layers: endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous system).