The present invention discloses cell lines and recombinant growth factor receptors useful in adoptive cell therapy (ACT), wherein the recombinant growth factor receptor can act as a molecular switch enabling cells expressing the rGFR protein to be expanded in-vitro or in- vivo. Thus the invention provides a T or NK cell, comprising a recombinant growth factor receptor (rGFR) comprising: (i) an extracellular (EC) domain； (ii) a thrombopoietin receptor transmembrane (TM) domain； and (iii) a growth factor receptor intracellular (IC) domain.
