Recent insights highlight that CD4+ T cells can contribute to effective tumor immune defense but also participate in tissue homeostasis, regeneration and tumor promotion. The goal of A 27 is to better understand the molecular and cellular mechanisms regulating the phenotypes and effector functions of CD4+ T cells in tumor tissues in vivo. We will use adoptive T cell immunotherapy protocols in our experimental mouse melanoma models established in the laboratory. A focus of our work is the immunoregulatory role of neutrophils both locally in the tumor microenvironment as well as systemically.