Purpose: A reason that the immune system may fail to reject tumors is that T cells encounter tumor antigen derived peptides on the surface of tumor cells in a tolerizing rather than activating context since tumor cells do not express T cell co-stimulatory molecules such as B7-1 (CD80). In preclinical models over expression of B7-1 on the surface of tumor cells has been shown to activate T cells which kill tumor cells. We conducted a phase I clinical trial testing this approach in patients with metastatic renal cell carcinoma.
Materials and methods: Resected tumors from 15 patients were disaggregated and adapted to tissue culture, transduced with the B7-1 gene and injected subcutaneously as a vaccine. The dose of the vaccine was escalated in 3 separate cohorts of patients, and systemic interleukin-2 (IL-2) was administered as an adjuvant designed to enhance the proliferation of the vaccine activated T cells.
Results: Of the 15 patients 9 had measurable disease, 2 had a partial response and 2 had stable disease. Perivascular T cell infiltrates at autologous tumor delayed type hypersensitivity skin test sites developed in 3 of the 4 patients with stable disease or partial response. Although the patients experienced the usual and expected toxicity from the IL-2, there was no significant toxicity observed with the vaccine.
Conclusions: The B7-1 gene modified autologous tumor cell vaccine is safe and can be combined with systemic IL-2 with acceptable toxicity. Immunological and clinical responses were observed in some of the patients. A phase II trial is reasonable to determine the efficacy of this approach.