In VivoDelivery of Interleukin-4 by a Recombinant Vaccinia Virus Prevents Tumor Development in Mice

Abstract

To study the immunotherapeutic potential of interleukin-4 (IL-4) delivered in vivo via a recombinant vaccinia virus, a thymidine kinase-negative (TK¯) vaccinia virus that expressed the murine IL-4 gene (VV1/IL-4) was constructed. When mice were inoculated with 10⁷ plaque-forming units (pfu) of VV1/IL-4 subcutaneously (s.c.), 10⁵ pfu/cm² were found in skin, and smaller numbers in liver and kidney between 1 and 7 days after infection; few viral pfu were found in spleen and lung, or in any organ after intravenous infection. This suggested that recombinant vaccinia viruses might be most efficient at delivery of cytokine genes to the skin. Because IL-4 has recently been found to have potent anti-tumor activity, the effect of recombinant virus infection on the development of s.c. tumors was studied. A single s.c. inoculation with VV1/IL-4 delayed the development of NCTC 2472 tumors, but when VV1/IL-4 was inoculated s.c. weekly for 8 weeks, tumor development was completely prevented in 93% of mice. Similarly, the development of M-3 melanoma tumors was also prevented by weekly s.c. inoculations of VV1/IL-4. About 40% of mice treated with control VV2/βgal by the same regimen also failed to develop tumors. Weekly virus treatment did not prevent NCTC 2472 tumor development in athymic nu/nu mice, suggesting that mature T cells are required for expression of VV1/IL-4 induced antitumor activity. Thus, recombinant vaccinia viruses may be especially well suited for convenient therapeutic delivery of immunomodulator genes to skin-related sites. DNA viruses such as vaccinia, adenovirus, and herpes viruses are being studied as vectors for safe, short-term gene therapy; these do not integrate into cellular DNA, can infect nondividing cells, and have the capacity to express large eukaryotic genes. Here we demonstrate that s.c. inoculated vaccinia virus preferentially replicates in the skin of mice, and thus may be ideally suited for local delivery of therapeutic genes to skin-related diseases such as melanomas. In fact, a single s.c. inoculation with a TK¯ recombinant vaccinia virus expressing the murine IL-4 gene delayed the development of the s.c. transplantable tumors in mice. Furthermore, when recombinant virus was inoculated s.c. weekly for 8 weeks, tumor development was completely prevented in the overwhelming majority of animals.