This disclosure relates to a combination therapy of chemotherapeutics and/or radiosensitizing agents with a replication competent viral vectors for treating cell proliferative disorders and chemotherapeutic treatments. The disclosure further relates to the use of such replication competent viral vectors for delivery and expression of a heterologous nucleic acid in normal and diseased tissues and methods and compositions that facilitate such delivery and expression to tissues in vivo and in vitro. The disclosure further relates to replication competent retroviral vectors for these uses and in conjunction with methods and compositions that facilitate in vivo therapeutics.