KINETICS OF RETROVIRUS-MEDIATED GENE-TRANSFER - THE IMPORTANCE OF INTRACELLULAR HALF-LIFE OF RETROVIRUSES

Gene therapy is a new therapeutic modality that holds vast potential f or the treatment of genetic disorders. Retroviruses are used as a vehi cle for the transfer of genes into mammalian cells. The process of gen e transfer has been shown to depend on the cell cycle status of target cells. We constructed a mathematical model that integrates the kineti cs of gene transfer with cell cycle kinetics. We define three cell pop ulations: uninfected cells, cells with the virus in their cytoplasm, b ut not integrated, and infected cells, in which the viral DNA has inte grated in their genome. Our model predicts that the stability of the v iral particles after internalization in the cellular cytoplasm, limits the process of gene transfer. Intracellular viral half-life also limi ts the usefulness of synchronization experiments, used to detect cell cycle dependence of the gene transfer process. We use the predictions of our model to propose a new experimental method for the detection of cell cycle dependence of retrovirus mediated gene transfer. It is bas ed on the maturity distributions of the infected cells, and it is inde pendent of viral intracellular stability. Despite the importance of th e viral intracellular half-life this quantity still remains unknown. A n extended version of the model is used to simulate a novel experiment al method that measures the intracellular retroviral half-life. Analyt ical solutions of a simplified model confirm our numerical results and reveal the key dimensionless groups that characterize the process of gene transfer. Knowledge of the intracellular half-life of retroviral vectors is of particular importance for the design of new vectors, esp ecially for slowly growing target cells, such as the stem cells of the hematopoietic system. (C) 1996 Academic Press Limited