The use of Zymosan A and bacteria anchored to tumor cells for effective cancer immunotherapy: B16-F10 murine melanoma model

•Effective cancer immunotherapy based on stimulation of phagocytosis was described.•Phagocytosis stimulating ligands are directly attached to tumor cells surface.•The role of neutrophils and NK cells in therapy was evaluated.•Therapeutic approaches applicable for human cancer immunotherapy are proposed.

The idea of using killed microorganisms or their parts for a stimulation of immunity in the cancer immunotherapy is very old, but the question of interactions and binding of these preparations to tumor cells has not been addressed so far. The attachment of Zymosan A and both Gram-positive and Gram-negative bacteria to tumor cells was tested in in vivo experiments. This binding was accomplished by charge interactions, anchoring based on hydrophobic chains and covalent bonds and proved to be crucial for a strong immunotherapeutic effect. The establishment of conditions for simultaneous stimulation of both Toll-like and phagocytic receptors led to very strong synergy. It resulted in tumor shrinkage and its temporary or permanent elimination. The role of neutrophils in cancer immunotherapy was demonstrated and the mechanism of their action (frustrated phagocytosis) was proposed. Finally, therapeutic approaches applicable for safe human cancer immunotherapy are discussed. Heat killed Mycobacterium tuberculosis covalently attached to tumor cells seems to be promising tool for this therapy.