When Hela cells were transfected with the HSV-tk gene, and were then put in a culture with nontransfected cells, only the HSV-tk transfected Hela cells were killed by the granciclovir, leaving the nonviral cells unharmed.[1] The Hela cells were transfected with the encoding for the gap junction protenin connexin 43 (Cx43) to provide a channel that permits ions and other molecules to move between neighboring cells. Both Hela cells with the HSV-tk and without the HSV-tk were destroyed. This result has led to the evidence needed to state that the bystander effect in the HSV-tk gene therapy is possibly due to the Cx-mediated GJIC.