Bacterial Peptides as Immunotherapy Targets

Bacterial peptides that exist on tumor cells may be immunotherapy targets. Research has shown that protein fragments from bacteria that invade tumor cells may be on the surface of the tumor cell, and the immune system may recognize those protein fragments. This discovery may advance certain cancer immunotherapies.

Microorganisms colonize on human tumors. These colonies are called the tumor microbiota, which impacts the microenvironment of the tumor like causing local immunosuppression or inflammation. This may alter how the body’s immune system responds to the tumor, which in turn may change responses to treatment. But, are the bacteria within a tumor recognized by the immune system? New research suggests that bacterial protein fragments known as peptides may exist on the surface of tumor cells. Immune cells called T cells recognize these peptides. This discovery may lead to advancements in cancer immunotherapeutics.

Identification of Bacteria-Derived HLA-Bound Peptides

Molecules known as tumor antigens enable the immune system to differentiate healthy cells from tumor cells. Each cell has antigen-producing mechanisms, which present antigen-derived peptides to be presented to the immune system via molecules called human leukocyte antigens (HLAs). These specialized molecules are called epitopes.

Tumor antigens fall into two primary categories: tumor-associated and tumor-specific. Tumor-associated antigens are found in normal tissue in addition to tumors. Hence, they do not trigger an immune response. But if an immune response does initiate, there is a risk of harmful autoimmune reactions against the normal tissues that have the tumor-associated antigen.

Because these tumor-associated antigens are found in many types of cancer tumors, they may be effective targets for immunotherapies. In contrast, tumor-specific antigens are found only in tumor cells, which makes them targets for specific immune attacks against the tumor.