The present invention provides a combination therapy which relies on a small molecule immune stimulator—cyclic-di-nucleotide (CDN)—that activates DCs via a recently discovered cytoplasmic receptor known as STING (Stimulator of Interferon Genes) formulated with allogeneic human tumor cell lines engineered to secrete high amounts of GM-CSF. This combination therapy can provide an ideal synergy of multiple tumor associated antigens, DC recruitment and proliferation, coupled with a potent DC activation stimulus.