OBJECTIVES
We investigated the development of binding and neutralizing antibodies to GM-CSF in patients receiving prolonged therapy with GM-CSF as adjuvant therapy of melanoma and the impact of these antibodies on biologic effects.
METHODS
Fifty-three patients with high-risk melanoma which had been surgically excised were treated with GM-CSF, 125 µg/m2 daily for 14 days every 28 days for 1 year following surgical resection of disease. Serum samples for antibodies to GM-CSF were measured before treatment and on Study Days 155 and 351. Blood draws for testing biologic effects were keyed to GM-CSF administration: Days 0 (before), 15 (after 14 days on GM-CSF), 29 (after 14 days off GM-CSF), 155, and 351 (after 14 days on GM-CSF in the 6th and 13th cycle of treatment).
RESULTS
Of 53 patients enrolled, 43 were evaluable for the development of anti-GM-CSF antibodies. Of these, 93% developed binding antibodies and 42% developed both binding and neutralizing antibodies. The increase in the white blood cell (WBC) count, percent eosinophils, or neopterin levels engendered by GM-CSF administration, was abrogated or markedly decreased in patients with neutralizing antibodies but not in patients who developed only binding antibodies.
CONCLUSIONS
Ninety-three percent of patients with melanoma treated with GM-CSF as adjuvant therapy develop antibodies to GM-CSF. In those with neutralizing antibodies, a diminution of the biologic effects of GM-CSF was observed. The development of neutralizing antibodies might also abrogate the potential clinical benefit of this treatment and should be considered in the design of future clinical trials.