A transgene for endowing human quiescent cells from primary cultures with exogenously inducible telomere length homeostasis and cell cycle traverse is described. The transgene includes at least three promoter sequences; a G1-specific RNA interference sequence which is operably linked downstream of a first promoter sequence; a telomere length maintenance gene sequence which is operably linked downstream to a second promoter sequence; a Scaffold/Matrix attachment region (S/MAR) element positioned downstream in frame with said telomere length maintenance gene sequence and an exogenously-inducible transcriptional regulation system. The transgene is useful to immortalize human quiescent cells from primary cultures.