Adenovirus transduction and culture conditions affect the immunogenicity of murine dendritic cells

Adenovirus vectors encoding carcinoembryonic antigen (Ad-CEA) or costimulatory molecules CD80, intercellular adhesion molecule-1 (ICAM-1) and leucocyte function-associated antigen-3 (LFA-3) (Ad-STIM) were used to transduce murine bone marrow-derived dendritic cells (BMDC). BMDC were characterized for expression of activation markers and for their ability to elicit protective immunity against MC38-CEA tumours in wildtype and CEA-transgenic (CEA-tg) mice. To determine optimal culture conditions, studies were conducted using BMDC cultured in heterologous bovine serum or autologous mouse serum. Transduction of cells grown in presence of heterologous serum increased the expression of costimulatory molecules, major histocompatibility complex class II, of IL-6 and IL-12. Upon vaccination, tumour protection was not specific and was observed also with untransduced cells. Transduced BMDC cultured in the presence of autologous serum showed low expression of the activation markers, did not express IL-6 and had reduced ability to stimulate T-cell proliferation. Nonetheless, CEA-specific CD8+ T-cell response was enhanced upon coinfection of Ad-STIM and Ad-CEA in both mouse strains, although this immune response was not sufficient to protect CEA-tg mice from tumour challenge. These studies support the use of BMDC transduced with Ad vectors encoding tumour antigens for cancer immunotherapy and demonstrate that culture conditions greatly affect the immunological properties of these cells.