CCL2 and malignant glioma: MCP-1 was purified from the culture supernatants of not only activated peripheral blood mononuclear leukocytes [10] but also malignant glioma cells [11] and was subsequently found to be identical to the factor previously described as tumor cell-derived chemotactic factor (TDCF) [12], which is hypothesized to be responsible for the infiltration of blood monocyte-derived macrophages, the so-called tumor-associated macrophages (TAMs), into tumors.