One of the first researchers who suggested the leading role of the immune system in antitumor resistance was Paul Ehrlich - the founder of the humoral theory of immunity . Therefore, the first attempts to study the immune system in malignant tumors were aimed at finding specific tumor antigens that could be used to immunize and obtain specific sera for the diagnosis and treatment of cancer patients. This methodical approach was widely used in immunology until the mid-60s, and in some cases, it is used in the present.