The availability of an agent that prevents IL-2-induced hypotension without adversely affecting the therapeutic mechanism of IL-2, would markedly facilitate IL-2 administration and at a minimum, would maximize the number of patients who could receive the full regimen of IL-2. The reduction in IL-2 toxicity may also enable higher doses and/or more frequent dosing of IL-2 to be used, with the potential of higher success of tumor response. Because M40403 may decrease the toxicity of IL-2, co-administration of M40403 may make it possible to broaden the clinical use of IL-2 to conditions where it is not currently indicated.