Interleukin-24 (IL-24) is a member of the IL-10 cytokine family. IL-24, also known as melanoma differentiation associated gene 7 (mda-7), is a unique cytokine in that it has cytokine properties and functions as a novel tumor suppressor gene. Studies by us and other investigators using viral and non-viral vectors have demonstrated IL-24 overexpression in human cancer cells inhibited tumor growth both in vitro and in vivo. A majority of these studies using immunodeficient animal models have focused on demonstrating the direct anticancer properties of IL-24. Very few studies have focused on studying the immunotherapeutic properties of IL-24 despite it being reported to function as a Th1 cytokine. A phase I clinical trial using an adenovirus vector expressing IL-24 (Ad-IL24/INGN241) reported Ad-IL24 treatment of cancer patients resulted in changes in cytokines and T cells. However, well-designed and detailed preclinical studies to support the clinical findings are warranted. Demonstrating immune modulation by IL-24 will provide a rationale for developing IL-24-based immunotherapeutic approaches for cancer treatment.In the present chapter, we provide experimental details for conducting IL-24-based immunotherapy studies. As it is not possible for the authors to cover all of the information the authors recommend reading other immunology-based literature and procedures for a better understanding of conducting preclinical studies.