Mice with fibrosarcoma or colorectal carcinoma were treated with a peptide vaccine (AH1, a murine retrovirus-derived peptide) alone or in combination with F8-TNF (murine TNF fused to an scFv of the F8 antibody, targeting fibronectin in the tumor extracellular matrix). AH1 alone modestly slowed down tumor growth, while the combination treatment led to a complete response in some mice by inducing tumor necrosis and increasing the density of AH1-specific CD8+ T cells in the TDLN and the tumor. AH1-specific CD8+ T cells had a predominantly effector phenotype and expressed markers of exhaustion (PD-1, LAG-3, TIM-3).
PURPOSE: There is a growing interest in the use of tumor antigens for therapeutic vaccination strategies. Unfortunately, in most cases, the use of peptide vaccines in patients does not mediate shrinkage of solid tumor masses. EXPERIMENTAL DESIGN: Here, we studied the opportunity to boost peptide vaccination with F8-TNF, an antibody fusion protein that selectively delivers TNF to the tumor extracellular matrix. AH1, a model antigen to investigate CD8(+)T cell immunity in BALB/c mice, was used as vaccine. RESULTS: Peptide antigens alone exhibited only a modest tumor growth inhibition. However, anti-cancer activity could be substantially increased by combination with F8-TNF. Analysis of T cells in tumors and in draining lymph nodes revealed a dramatic expansion of AH1-specific CD8(+)T cells, which were strongly positive for PD-1, LAG-3 and TIM-3. The synergistic anti-cancer activity, observed in the combined use of peptide vaccination and F8-TNF, was largely due to the ability of the fusion protein to induce a rapid hemorrhagic necrosis in the tumor mass, thus leaving few residual tumor cells. While the cell surface phenotype of tumor-infiltrating CD8(+)T cells did not substantially change upon treatment, the proportion of AH1-specific T cells was strongly increased in the combination therapy group, reaching more than 50% of the CD8(+)T cells within the tumor mass. CONCLUSIONS: Since both peptide vaccination strategies and tumor-homing TNF fusion proteins are currently being studied in clinical trials, our study provides a rationale for the combination of these two regimens for the treatment of patients with cancer.