hematology and oncology
Host Response to Tumors
Failure of Host Defenses
Although some tumors are eliminated by the immune system (and thus are never detected) others continue to grow despite immune surveillance. Several mechanisms are proposed to explain this deficient host response to the cancer, including the following: Specific immunologic tolerance to TAAs in a process that involves antigen-presenting cells and suppressor T cells, possibly secondary to prenatal exposure to the antigen Suppression of immune response by chemical, physical, or viral agents (eg, helper T-cell destruction by human immunodeficiency virus [HIV]) Suppression of the immune response by cytotoxic drugs or radiation Suppression of the immune response by the tumor itself through various complex mechanisms that cause various problems, including decreased T-cell, B-cell, and antigen-presenting cell function, decreased IL-2 production, generation of exhausted T cells, and increased circulating soluble IL-2 receptors (which bind and inactivate IL-2) Presence and activity of TAM-2 (M2) polarized cells, myeloid-derived suppressor cells, and regulatory T cells, promoting tolerance 