Dendritic cells enhance the activity of human MUC1-stimulated mononuclear cells against breast cancer

Dendritic cells (DCs) are among the most potent antigen-presenting cells (APCs), stimulating peripheral blood mononuclear cells (PBMCs) to generate antigen-specific cytotoxic T lymphocytes (CTLs). The objectives of this study were to determine if interleukin (IL)-4 is beneficial or detrimental for the generation of human DCs in vitro and to understand whether DCs generated in vitro in the presence or absence of IL-4 stimulate the killing of adenocarcinoma cells by CTLs in vivo. Mucin 1 (MUC1), a glycoprotein found on the surface of adenocarcinoma cells was used to load DCs. MUC1-loaded DCs generated in the absence of IL-4 were superior to their counterparts produced with IL-4 in stimulating PBMCs to kill human breast cancer MCF-7 cells in vitro. A corollary in vivo protection experiment was performed by injecting immunodeficient NOD-SCID mice with MCF-7 cells s.c. and MUC1-loaded CTLs, PBMCs, or DCs generated in the absence of IL-4, i.p. Mice that received CTLs and MUC1-loaded DCs on days 0, 2, 4, 9, 14 and 19 were completely protected against the development of MCF-7-derived tumors, while other schedules conferred lower protection. Therefore, tumor antigen-loaded DCs enhance the efficacy of adoptive CTL transfer, and should thus be considered for combinatorial immunotherapeutic regimens.