Combining cytokine-induced killer cells with vaccination in cancer immunotherapy: more than one plus one?

The immune system can be harnessed to fight cancer by active (stimulating the patient's intrinsic immune response to cancer) and by passive (transfer of active humoral or cellular immunity) immunotherapy. While for each strategy proof-of-principle was provided, clinical benefit was limited likely due to malfunction of lymphocytes. Increasing knowledge of both the mechanism of vaccination through dendritic cells (DCs) and the potency of a subset of natural killer T lymphocytes termed cytokine-induced killer (CIK) cells led to new strategies through combining adoptive and passive immunotherapy. This review summarizes most recent clinical trials indicating that CIK cells can substantially enhance the effect of tumor vaccines and discusses the potential therapeutic benefit in the long-term control of tumor progression.