Directed cytokine expression in tumour cells in vivo using recombinant vaccinia virus

Athymic (Swiss nude) and euthymic (DBA) tumour-bearing mice were injected intravenously with various vaccinia virus (Copenhagen strain) recombinants. Several days after inoculation, tumour cells were found to be well infected with infective vaccinia particles, while organs such as liver, spleen, brain and bone marrow showed barely detectable levels or no signs at all of virus infection. Injection of tumour bearing mice with recombinant VV harbouring the cDNA for either huIL-2 or muIL-6 resulted in detectable lymphokine in the sera of injected animals. Injection of tumour-bearing nude mice with VV-IL-6, but not with VV-IL-2, resulted in significant reduction in growth rate of the tumour, and in some cases, complete rejection of the tumour. Tumour-bearing euthymic mice responded differently. Intravenous injection of VV-IL-2, but not VV-IL-6 resulted in reduced growth rate of 50% of tumours and complete rejection of 17% of tumours.