A trial has been running in leukemia patients using immune cells modified to express a variety of chimeric antigen receptors. This allows the immune cells to recognize and attack cancer cells with a high degree of specificity, and the early results in the trial were impressive. Here is a more recent update:
The blood cells of cancer patients, reprogrammed by doctors to attack their leukemia and re-infused back into the patients' veins, led to complete remissions in 27 of 30 people. That's especially exciting because those patients had failed all conventional treatments. Not all of the remissions lasted. Nineteen patients in the study remain in remission 2 to 24 months later, and 15 of them didn't need any additional treatment. Seven patients relapsed between 6 months and 9 months after their infusion; those included three people whose cancers spread beyond the blood cells the new treatment targets. Five patients left the study for alternative therapy. The numbers are remarkable because these patients had cancer return as many as four times before they joined the study, including some whose cancer had returned after stem cell transplants.
For this method, the researchers harvest a patient's T cells using a process like blood transfusion. Then the lab [performs] a gene transfer, to teach the T cells to target a protein found on the surface of B cells, another type of blood cell that's affected in leukemia. The T cells are then transplanted back into the patient, where they hunt and kill anything with the protein attached to it. That means all B cells, not just the cancerous ones, are killed. Tests of all treated patients showed that their normal B cells had been killed along with the tumors. Because B cells are responsible for creating antibodies, which hunt any viruses or bacteria circulating in the blood stream, the solution isn't ideal; patients usually receive immunoglobulin replacement to help boost their immune systems to healthy levels. Living without B cells isn't perfect, but it's better than dying of cancer.
Absence of B cells is a situation that should be possible to fix with today's cell technologies. In past years researchers have destroyed and recreated the immune system in patients with autoimmune disease, so repopulating B cells should be a very plausible goal.