In 2017, the first immuno-oncology cell therapies, known as chimeric antigen receptor T cells, or CAR T, were approved by the U.S. Food and Drug Administration. Immuno-oncology cell therapy is a field that leverages the immune system by modifying, and thereby enhancing, immune cells to target cancer. It accomplishes this by interdicting pathways that maintain checks and balances on cellular elements of the immune system, thereby disrupting the tolerance of the body to the growth and spread of cancer.
CAR-T therapies have had an unprecedented success in blood cancers, such as certain leukemias and lymphomas. They have shown high response rates and redefined the treatment of patients who have exhausted other options. The therapeutic success relies on an antibody fragment that binds to a surface protein on leukemias and lymphomas; the protein is known as CD19. The antibody fragment is linked to stimulatory and signaling molecules that fire upon binding of the antibody with the CD19 molecule, thereby activating the T cells and making them destroy the cancer cell.
SOLID TUMOR CHALLENGES
CAR T therapies have shown limited success in solid tumors, since they do not typically express a molecule on their surface that is unique to the solid tumor and not to normal tissue. This, coupled with the complex matrix in which cancer cells grow, makes it challenging to develop cellular therapies for solid tumors.
One way to overcome this challenge is to target proteins expressed inside the cell rather than large cell surface proteins. This sort of immune response involves the activation of T cells against a portion of an internal protein that the T cell sees as foreign. These protein fragments, known as peptides, dock with protein structures known as major histocompatibility antigens (MHC) on the cell surface, which is the cellular network that governs the presentation of self versus non-self peptides and lets T cells distinguish friend from foe.
T cells are some of the “surveyors and assassins” of the immune system. They have T cell receptors (TCR) on their surface, and they circulate through the body, binding foreign peptides on the surface of cells that are infected by foreign organisms such as viruses and bacteria. When a cell is infected, bits of that organism’s protein make it to the surface, docking with the right MHC. Surveying T cells can see these proteins through their TCRs and kill them to prevent propagation of the infection.
However, cancer cells have proteins that look similar to the body’s own, not like foreign proteins, which creates an ability to evade the immune system. This makes it difficult to effectively target tumors with our body’s own naturally occurring TCRs. When cancer cells develop mutations, they may present novel aberrant peptides, but often the malignant cell and other elements of the tumor dampen the T cell response by interfering with the molecular network that regulates how the T cell functions. The unraveling of some of the proteins that regulate T cell function against tumor cells resulted in two scientists sharing the 2018 Nobel Prize in Physiology or Medicine..
THE POTENTIAL OF ENHANCED RECEPTORS
Companies are now exploring how to enhance the body’s naturally occurring TCRs to target solid tumors. Engineering TCRs to have optimal affinity to the docking peptide enables the receptors to more easily identify proteins from cancer cells that would have otherwise not be recognized as foreign.
These engineered TCRs can be put into a patient’s own T cells and then returned to the patient. These newly enhanced T cells can kill tumors, multiply and attack more cancer cells than a patient’s naturally occurring T cells.
At Adaptimmune, we utilize our unique SPEAR (specific peptide enhanced affinity receptor) T cell platform to engineer TCRs so that they can recognize cancer proteins on solid tumors. Adaptimmune’s SPEAR T cell therapy targeting a protein called NY-ESO, now transitioned to GlaxoSmithKline, has shown efficacy in two unique sarcoma types—both very difficult-to-treat solid tumors.
There is still more to come from the immuno-oncology cell therapy field with respect to utilizing TCRs, since many solid tumors recur and become incurable. This is why Adaptimmune is conducting clinical trials with multiple engineered TCRs across a broad range of solid tumors. The company is also investigating next-generation TCRs armed with molecules to further improve the engineered T-cells’ ability to target and destroy solid tumors. These enhanced approaches will likely lead to longer-lasting antitumor responses.
Patients in dire need of novel treatment options are the driving force behind the impetus of Adaptimmune and many companies in the life sciences industry to continue the quest to eradicate metastatic cancer. The field has come a long way, and its potential appears boundless as scientists unravel the intricate interplay between cancer and anticancer immunity.