Recombinant herpes simplex virus (HSV)-1 capable of selectively replicating in alternative lengthening of telomeres (ALT)-dependent tumor cells are described. The recombinant HSV-1 are ICP0-deficient, such as by complete deletion of the ICP0 gene, or mutation of the ICP0 gene sufficient to diminish or eliminate E3 ubiquitin ligase activity of ICP0. In some cases, the recombinant HSV-1 further include additional gene deletions or mutations, such as those that render the virus glycoprotein C (gC) deficient, or include a heterologous gene, such as a gene encoding an immunostimulatory molecule. Methods of treating ALT-dependent cancer, and methods of selectively killing ALT-dependent tumor cells are also described.
