Potent influence of bovine serum proteins in experimental dendritic cell-based vaccination protocols

Typically autologous dendritic cells (DCs) intended for vaccination are generated from bone marrow derived stem cells or blood monocytes, loaded with antigen and introduced into the organism. However, addition of serum to DC culture medium is often necessary. Thus, serum proteins will be taken up and presented by the DCs together with other antigens. If heterologous serum is used, some of the serum proteins might be antigenic and thus induce a strong immune response when introduced in the recipient. We used the murine model of malignant melanoma, B16, to investigate the consequences of addition of fetal calf serum (FCS) to the medium for culturing murine DCs. The results showed that vaccination of mice with DCs cultured in vitro in the presence of FCS but in the absence of extraneous tumour antigens, protected the mice from challenge with B16 tumour cells similarly cultured in FCS. This protection could not be elicited by vaccination with FCS alone. Interestingly, the protective effect of DC vaccination was abolished when the challenging B16 tumour cells were free of serum proteins. Thus, these results show that DCs grown in the presence of FCS are able to induce immunity, which may be mistaken to be tumour immunity.