Hybrid cell vaccines of autologous tumour cells fused with allogenic dendritic cells (DC) combine the tumour's antigenicity with the immune-stimulatory capacity of mature dendritic cells and allogenic MHC class II molecules to activate T cell help and induce tumour-specific cytotoxic T cells. This concept was tested in a clinical trial with melanoma stage III and IV patients. Seventeen patients were evaluated: one experienced complete, one partial response and six stable disease with long survival times. Eleven of fourteen patients, clinical responders and non-responders alike, mounted high-frequency T cell responses to various tumour-associated antigens. Failing clinical responses correlated with loss of antigenicity.