A recombinant oncolytic adenovirus encoding the immunohematopoietic cytokine granulocyte-macrophage colony stimulating factor (GM-CSF) with potential antineoplastic activity. Upon administration, the oncolytic adenovirus selectively infects and replicates in tumor cells, which may result in tumor cells lysis. Synergistically, GM-CSF (sargramostim) expressed by the oncolytic adenovirus may promote a cytotoxic T cell response against tumor cells harboring the oncolytic adenovirus, resulting in an immune-mediated tumor cell death.