Induction of lymphokine-activated killing with reduced secretion of interleukin-1β, tumor necrosis factor-α, and interferon-γ by interleukin-2 analogs

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Abstract
Background: Interleukin-2 (IL-2)-based immunotherapy has been shown to effect clinical responses in 15–35% of patients with metastatic renal cell carcinoma or melanoma. Despite its clinical efficacy, many clinicians refrain from using IL-2 because of the associated toxicity. This toxicity is believed to be mediated by such secondary cytokines as IL-1, tumor necrosis factor (TNF), and interferon (IFN)-γ, which are produced by the patient's IL-2-stimulated peripheral blood mononuclear cells (PBMCs). Methods: Human PBMCs were stimulated with 1 nM wild-type recombinant IL-2 (rIL-2) or IL-2 analogs (R38A or F42K) that preferentially bind to the intermediate affinity IL-2 receptor (IL-2R). PBMCs were activated for lymphokine-activated killer (LAK) activity in 4-h51Cr-release assays, using Daudi target cells. Cytokine content in the culture supernatants was determined by enzyme-linked immunosorbent assay. Results: Both R38A and F42K were capable of generating substantial LAK activity. Maximal specific lysis was 54% for PBMCs activated by R38A and 52% for F42K-stimulated cells, in contrast to 64% for rIL-2. In addition, analog-stimulated PBMCs secreted 59% of the IL-1β, 25% of the TNF-α, and only 8% of the IFN-γ produced in response to rIL-2 (allpConclusions: IL-2 analogs that preferentially bind the intermediate-affinity IL-2R retain the capacity to induce substantial LAK activity despite a greatly reduced secondary cytokine production. Therefore, such IL-2 analogs may provide an effective, yet less toxic means of cancer immunotherapy.

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