Taken together, functionally expressed hyper-IL-6 through i.v. delivered vaccinia virus optimized the combination therapy of the oncolytic virus GLV-1h90 and the chemotherapeutic agent mitomycin C. Besides the improved oncolytic effect, which also occurred with the parental strain GLV-1h68, GLV-1h90 was further able to significantly reduce thrombocytopenia, a negative side effect caused by the chemotherapeutic agent. Here, IL6 is linked to Thrombocytopenia.