Efficacy of different targeting agents in the photolysis of interleukin-2 receptor bearing cells

The multichain interleukin-2 receptor (IL-2R) has been proposed as a target for immunotherapy in the treatment of certain cancers including adult T-cell leukemia and cutaneous T-cell lymphoma as well as certain autoimmune diseases. The IL-2R is abnormally expressed on cells associated with each of these diseases; while normal, non-activated T-cells do not express the receptor. This report describes the selective photolysis of activated and non-activated IL-2R expressing cells using several immunoconjugates synthesized with one of two photosensitizers, hematoporphyrin (HP) or chlorin-e6 (Ce6), covalently linked to IL-2 or an anti-IL-2R antibody. Destruction of IL-2R bearing cells was achieved after photosensitizer internalization and irradiation using all tested photosensitizer conjugates. Chlorin containing conjugates were more effective, by a factor of 4 or more, than HP containing conjugates. Conjugates made with IL-2 were up to 30 times more effective than conjugates that used a monoclonal antibody against the IL-2R for targeting. Activation of the cells to increase IL-2R expression decreased the internalization time required for optimal therapeutic efficacy; however, stimulation of the cell to increase IL-2 secretion greatly reduced conjugate effectiveness. This work could lead to the development of more effective strategies to treat T-cell diseases.