A Low-Toxicity IL-2―Based Immunocytokine Retains Antitumor Activity Despite Its High Degree of IL-2 Receptor Selectivity

The goal of the study was to engineer a form of interleukin 2 (IL-2) that, when delivered as a tumor-specific antibody fusion protein, retains the ability to stimulate an antitumor immune response via interaction with the high-affinity IL-2 receptor but has lower toxicity because of the reduced activation of the intermediate-affinity IL-2 receptor. We investigated changes in the proposed toxin motif of IL-2 by introducing a D20T mutation that has little effect on the activity of free IL-2. We expressed this IL-2 variant as a fusion protein with an antibody (NHS76) that targets the necrotic core of tumors and characterized this molecule (NHS-IL2LT) in vitro and in vivo. NHS-IL2LT was shown to have near normal biological activity in vitro by using T-cell lines expressing the high-affinity IL-2 receptor, but little or no activity by using cell lines expressing only the intermediate IL-2 receptor. Relative to the control antibody fusion protein containing wild-type IL-2, NHS-IL2LT retained antitumor activity against established neuroblastoma and non-small cell lung cancer metastases in syngeneic mouse tumor models but was much better tolerated in immune-competent mice and in cynomolgus monkeys. The qualities of low toxicity and single-agent efficacy shown suggest that NHS-IL2LT is a good candidate for therapeutic approaches combining standard cytotoxic and immune therapies. In fact, this molecule (also known as Selectikine or EMD 521873) is currently in phase I clinical trial.