Much of what we'd like to know about cancer therapies takes a long time to emerge. Only now is the long term data available for the first CAR-T immunotherapies aimed at forms of leukemia in which cancerous cells are clearly and distinctly marked by characteristic surface features. The field has long since expanded, and researchers are at present trying to adjust CAR-T in order to apply this form of treatment to solid cancers. Long term remission is not the same as a cure, as cancer is a disease in which it remains challenging to say whether or not a few remnant cancer cells await a return at some future time. If one can make it ten years in remission, with no sign of cancer, however, that may well be a cure under the hood, the cancer gone and never to return.
The year was 2010, and Olson was one of the first people with chronic lymphocytic leukaemia to receive the treatment, called CAR-T cell therapy. When his doctors wrote the protocol for the clinical trial that Olson was involved in, they hoped that the genetically engineered cells might survive for a month in his body. They knew that cancer research could be heartbreaking; they didn't dare to expect a cure. But more than ten years later, the immune cells continue to patrol Olson's blood and he remains in remission. Doctors finally ready to admit what Olson suspected all along. "We can now conclude that CAR T cells can actually cure patients with leukaemia."
CAR-T cell therapies involve removing immune cells called T cells from a person with cancer, and genetically altering them so that they produce proteins - called chimeric antigen receptors, or CARs - that recognize cancer cells. The cells are then reinfused into the person, in the hope that they will seek out and destroy tumours. In the years since Olson's treatment, five CAR-T cell therapies have been approved by the US Food and Drug Administration, to treat leukaemias, lymphomas, and myelomas. It is estimated that tens of thousands of people have received CAR-T cell treatment.
But the therapy is expensive, risky and technically demanding. It remains a last resort, to be used when all other treatments have failed. Despite the treatment's success for Olson, not everyone experiences durable remission of their cancer. In the beginning, only about 25-35% of CAR-T cell recipients with chronic lymphocytic leukaemia experienced a complete remission of their cancer. With refinement, that percentage has increased over the years, he says, but some of these initial successes still lead to relapse. Tracking the treatment long-term could reveal clues as to what factors are important for lasting CAR-T cell success.