An autologous or allogeneic cell vaccine comprised of tumor cells which have been lethally irradiated and genetically modified to secrete granulocyte-macrophage colony stimulating factor (GM-CSF), a hormone which plays a key role in stimulating the body's immune response to vaccines. GM-CSF may stimulate the body's immune system against tumor cells by attracting and enhancing the activation of antigen-presenting cells (APCs), such as dendritic cells (DCs). This promotes antigen presentation to T-lymphocytes and induces a cytotoxic T-lymphocyte (CTL) response against cells expressing tumor-associated antigens (TAAs).