Introduction: Cytokines play important roles in regulating immune responses. Interleukin-2 (IL-2) has usually been used as an adjuvant to enhance antitumour immune responses. However, its crucial role in activation-induced cell death, inhibition of homeostatic proliferation of CD8+ memory T cells and its notable biological side effects impair its prospect of application. IL-15 has several similar functions to IL-2 and shows potential advantages over IL-2, and is being investigated to enhance antitumour dendritic cell (DC) vaccine strategies in our ongoing studies.
Objective: In this preliminary study, we evaluated the ability of IL-15, compared with IL-2, to act as an adjuvant to enhance T-cell responses activated by DCs in vitro.
Materials and methods: Bone marrow-derived DCs (BMDCs) were pulsed with tumour antigens and used to stimulate lymphocyte responses in the presence of IL-15 or IL-2. The activated T lymphocytes were examined by flow cytometric analysis, and interferon-γ (IFN-γ) enzyme-linked immunospot and cytotoxicity assays.
Results: IL-15 was observed to activate lymphocytes with comparable phenotype characteristics of activated/memory CD8+ lymphocytes, compared with IL-2. Both in primary and secondary stimulation with DCs, when using IL-15 as an adjuvant, activated lymphocytes showed higher proportions of IFN-γ-secreting subsets. In secondary stimulation with BMDCs in the presence of IL-15, the activated lymphocytes showed a stronger cytotoxicity to antigen-specific tumour target cells.
Conclusions: Our study suggested that IL-15 might be a prospective adjuvant for a DC vaccine strategy against cancers. The further observation that IL-15 acts as an adjuvant for an antitumour DC vaccine strategy is worth investigating.