PROTECTION OF HERPES-SIMPLEX VIRUS THYMIDINE KINASE-TRANSDUCED CELLS FROM GANCICLOVIR-MEDIATED CYTOTOXICITY BY BYSTANDER CELLS - THE GOOD-SAMARITAN EFFECT

Although considerable attention has been directed in the field of gene therapy toward elucidating the mechanism by which a transduced cell c ould kill a bystander cell, little is known about how bystander cells may affect transduced cells. We hypothesized that bystander cells, par ticularly if they were capable of gap junctional communication, could protect cells transduced with the herpes simplex virus thymidine kinas e (HSV-TK) from ganciclovir (GCV)-induced cytotoxicity. To test this h ypothesis, me used a rat hepatocyte cell line (WB) that can carry out efficient gap junctional communication, a WB clone transduced with HSV -TK (WB-TK), and a communication-incompetent subclone of WB cells (aB1 ). We cocultured WB-TK cells with either WB or aB1 cells, treated them with GCV, and then plated the cells into selective media that permitt ed us to quantify independently the surviving fraction of WB-TK cells or bystander cells. We found that WB bystander cells conferred up to a 1000-fold protection on WB-TK cells treated with GCV. aB1 cells confe rred detectable, but significantly less, protection. These findings de monstrate that herpes simplex virus thymidine kinase-transduced cells can be significantly protected by bystander cells, particularly those that can carry out gap junctional communication. Whether this ''Good S amaritan'' effect improves the overall efficacy of gene therapy, by pr olonging the survival of the source of toxic metabolites, or decreases effectiveness by increasing the survival of transduced cells will nee d to be determined in vivo.