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Chapter 081. Principles of Cancer Treatment (Part 24)

Immune Mediators of Antitumor Effects The very existence of a cancer in a person is testimony to the failure of the immune system to deal effectively with the cancer. Tumors have a variety of means of avoiding the immune system: (1) they are often only subtly different from their normal counterparts; (2) they are capable of downregulating their major histocompatibility complex antigens, effectively masking them from recognition by T cells; (3) they are inefficient at presenting antigens to the immune system; (4) they can cloak themselves in a protective shell of fibrin to minimize contact with surveillance mechanisms; and. | Chapter 081. Principles of Cancer Treatment Part 24 Immune Mediators of Antitumor Effects The very existence of a cancer in a person is testimony to the failure of the immune system to deal effectively with the cancer. Tumors have a variety of means of avoiding the immune system 1 they are often only subtly different from their normal counterparts 2 they are capable of downregulating their major histocompatibility complex antigens effectively masking them from recognition by T cells 3 they are inefficient at presenting antigens to the immune system 4 they can cloak themselves in a protective shell of fibrin to minimize contact with surveillance mechanisms and 5 they can produce a range of soluble molecules including potential immune targets that can distract the immune system from recognizing the tumor cell or can kill the immune effector cells. Some of the cell products initially polarize the immune response away from cellular immunity shifting from TH1 to TH2 responses Chap. 308 and ultimately lead to defects in T cells that prevent their activation and cytotoxic activity. Cancer treatment further suppresses host immunity. A variety of strategies are being tested to overcome these barriers. Cell-Mediated Immunity The strongest evidence that the immune system can exert clinically meaningful antitumor effects comes from allogeneic bone marrow transplantation. Adoptively transferred T cells from the donor expand in the tumor-bearing host recognize the tumor as being foreign and can mediate impressive antitumor effects graft-versus-tumor effects . Three types of experimental interventions are being developed to take advantage of the ability of T cells to kill tumor cells. 1. Allogeneic T cells are transferred to cancer-bearing hosts in three major settings in the form of allogeneic bone marrow transplantation as pure lymphocyte transfusions following bone marrow recovery after allogeneic bone marrow transplantation and as pure lymphocyte transfusions following .