Active specific immunotherapy against occult brain metastasis

We determined whether lyophilized High Five (H5) insect cells engineered to produce IFN-β (H5BVIFN-β) could induce systemic immunity against occult brain metastases. C3H/HeN mice were injected s.c with syngeneic UV-2237M fibrosarcoma or K-1735M2 melanoma cells. Intralesional injection of 2 × 10⁶ lyophilized H5BVIFN-β cells produced complete regression of the s.c. tumors. Six weeks later, UV-2237M fibrosarcoma cells or K-1735M2 melanoma cells were injected into the internal carotid artery of naive or treated mice. UV-2237M brain metastases developed in naive mice or mice cured of K-1735M2 tumors but not in mice cured of UV-2237M tumors. Similarly, K-1735M2 brain metastases developed in naive mice or mice cured of UV-2237M fibrosarcomas but not in mice cured of K-1735M2 melanoma. In the next set of studies, mice were injected s.c. with UV-2237M fibrosarcoma cells. On day 7, UV-2237M fibrosarcoma cells or K-1735M2 cells were implanted into the internal carotid artery, and on day 10, the s.c. tumors were injected with lyophilized H5BVIFN-β. Both the s.c. tumors and the occult brain metastases produced from carotid injections were eradicated in a tumor-specific manner. The regression of the brain metastases was abrogated by depletion of CD4⁺ or CD8⁺ cells from immunized mice. These results demonstrate that specific systemic immunity can be induced by lyophilized H5BVIFN-β and that the resultant immune response can eliminate established brain metastasis.