In vivo cytokine production and recombinant interleukin 2 immunotherapy: an insight into the possible mechanisms underlying clinical responses.

Recombinant interleukin 2 (rIL-2), when given to patients with advanced malignant disease, induces a limited beneficial effect, with only 20-30% of patients with solid tumours responding. This present study has identified those patients with advanced colorectal cancer most likely to respond to rIL-2 therapy, by analysis of serum cytokine levels, prior to and during rIL-2 treatment, documented in responders and non-responders. Responders were found to have significantly lower pretreatment serum IL-6 and soluble IL-2 receptor levels (sIL-2R) than non-responders (P < 0.01 and P < 0.05 respectively). During rIL-2 infusion, responders developed high circulating levels of IL-6 and had low constant levels of prostaglandin E2 (PGE2). Non-responders failed to produce IL-6 and demonstrated elevated serum concentrations of PGE2, during infusions of rIL-2. Thus, an enhanced ongoing IL-6 and sIL-2R response, prior to therapy, was detrimental to subsequent treatment with rIL-2. Differential production and/or release of cytokines and prostaglandins, during therapy, further determined the likelihood of response to rIL-2.