Clinical researchers have made remarkable progress toward one of science’s most important goals: finding novel ways to treat or even cure disease with our own immune systems.
Most of the medical advances we rely on — including things like antibiotics to conquer infection or organ transplants that replace essential biological functions — harness mechanisms that occur naturally. How do we kill a certain strain of bacteria, for example? By replicating the same weapons other bacteria have created to kill that strain through millions of years of evolution.
Scientists have long aimed to tackle one of our greatest medical foes, cancer, by taking advantage of the tremendously powerful built-in traits we already have in our immune system. These complex protection systems include the tools needed to kill cancer cells; in fact, every day our immune systems destroy rogue cells in our body that have the potential to become cancerous. What if we could give our immune system an extra boost when people already have cancer, and let it do what it does best?
That’s the concept behind a huge leap forward in cancer treatment known as CAR T therapy. (CAR stands for chimeric antigen receptor. “Chimera” refers to a combination of more than one genetic component which is used to selectively target a specific protein. “T” is for T-cells, a type of white blood cell that is altered using the CAR.)
And — spoiler alert — it’s working. Recently, some pioneering scientists in this field published a report in Nature showing that two of the first people to receive this kind of treatment, both leukemia patients who faced dwindling clinical options and grim prognoses, have now remained cancer-free for 10 years.
In a statement announcing this decade-long feat, scientist Joseph Melenhorst from the University of Pennsylvania said, “This long-term remission is remarkable, and witnessing patients living cancer-free is a testament to the tremendous potency of this ‘living drug’ that works effectively against cancer cells.”
Indeed, patients’ response to CAR T therapies has been so promising that scientists are now trying to expand its use to diseases beyond cancer. Here’s how it works: a simple blood draw is used to extract a patient’s own immune cells. In a lab, those T cells are genetically tweaked to more effectively target the cells that need to be destroyed (like specific cancer cells). The boosted cells are then injected back into the patient.
So far, CAR T therapies have been developed to target B cells, which often go awry in leukemias and lymphomas. Since people can live without B cells, the therapy can safely eradicate all cells carrying the characteristic B cell markers, to wipe out cancer. To date, the FDA has approved five CAR T therapies for clinical use. “All of these CARs have really worked incredibly well in patients whose disease was [resistant] to all other forms of therapy,” said Marcela Maus, a physician-scientist at Massachusetts General Hospital who spoke about CAR T therapies in a recent presentation for the Association for Molecular Pathology (AMP).
One of the reasons patients display such a long-term response to CAR T therapies is that the re-infused cells can persist for years with their cancer-killing precision intact. “This is a living therapy,” said Michael Milone, a scientist at the University of Pennsylvania, in another AMP presentation. “When these cells go into patients, they replicate and divide and maintain themselves over a long period of time.”
Milone is one of the scientists working to bring the promise of CAR T therapies to diseases beyond cancer. He focuses on autoimmune diseases and has adjusted the original approach to target only B cells expressing a certain antibody for a more specific effect. His team’s studies in cells and in mouse models were so successful that there are now clinical trials enrolling patients to determine whether these therapies are safe and effective for clinical use in autoimmune diseases such as pemphigus vulgaris and myasthenia gravis. The same approach may even be useful for other immune-mediated situations such as hemophilia and organ transplantation.
CAR T therapies are not perfect. They are very expensive and can trigger a number of toxicities and side effects, though scientists believe many of those effects can be managed with clinical intervention. But if these therapies continue to produce results as impressive as those seen in the leukemia patients treated 10 years ago, this will be a very important new class of treatments.
