Immune response to reovirus (REO) in phase I study with chemotherapy in patients with KRAS mutant metastatic colorectal cancer (mCRC).

Abstract

217 Background: Viruses are well known immune sensitizing agents. The therapeutic efficacy of oncolytic reovirus in combination with chemotherapy is underway in a phase 1 study of mCRC. This study evaluates the nature of immune response by determining the distribution of antigen presenting cells (APCs) and activated T lymphocytes along with the cytokine expression pattern in peripheral circulation. Methods: REO was administered as a 60-minute intravenous infusion for 5 consecutive days every 28 days, at a tissue culture infective dose (TCID50) of 3x106. Serum was collected pre- and post- REO on days 1, pre REO on days 2-5, and days 8, 15, 22, and 29. Peripheral blood mononuclear cells (PBMC) were isolated and stained with fluorophore labelled antibodies against CD4, CD8, CD56, CD70, and CD123. Stained cells were fixed and evaluated by flow cytometry. The expression profile of 25 cytokines in plasma was assessed (post PBMC isolation) on an EMD Millipore multiplex Luminex platform. Results: Patients mount a robust immune response with dendritic cell maturation at 48 hrs (p < 0.01) followed by activation of cytotoxic T (CD8+) cells at Day 8 (p < 0.01). Cytokine assay indicated upregulation of Interleukin 1 beta (IL-1β; p = 0.004), Granulocyte-macrophage colony-stimulating factor (GM-CSF; p = 0.05), the chemokine Macrophage Inflammatory Proteins (MIP-1β; p = 0.05) at day 15. Furthermore, consistent upregulation of inflammatory cytokine IL-6 was seen from days 3 through 8 (p < 0.05), and decrease in IL-8 at 72 hrs (p = 0.03) was observed. Conclusions: REO induces strong immune response in patients with mCRC. APCs are stimulated within 48 hrs and activated (CD8+ CD70+) T cells within 168 hrs. Cytokine profiling indicates stimulation for maturation of APCs, chemotactic induction for macrophages and activation of T cells as highlighted by release of IL-1β, GM-CSF and MIP-1β respectively. Sustained increased expression of IL-6 (triggering lymphocyte maturation) and downregulation of IL-8 (pro-angiogenic cytokine) is also observed. REO thus functions bimodally as an oncolytic agent causing lysis of tumor cells, and facilitator of immune-mediated recognition and destruction of tumor cells. Clinical trial information: NCT01274624.