Researchers reported Wednesday that after ten years of getting a therapy that changes a patient's own immune cells to combat cancer, two patients with a kind of blood cancer exhibit no indications of the disease.

The treatment, CAR-T therapy, is a highly expensive form of treatment, but promising, according to researchers. The remissions can be indicative of how long its effects may last in certain patients.

Of the three patients who underwent the therapy at the University of Pennsylvania in 2010 as part of a clinical trial evaluating the treatment's safety and efficacy, two went into complete remission that year.

CAR-T treatment entails extracting T cells — a kind of immune cell — from a patient's blood, altering the cells so they contain a receptor that identifies and subsequently destroys cancer cells, growing the T cells and reinfusing them into the patient's blood.

The therapy has been approved by the FDA to treat leukemia, lymphoma, and multiple myeloma. The therapy is not without risks and can cause the development of cytokine release syndrome and neurological downsides.

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In a press briefing this week, Carl June, an immunologist and oncologist at the University of Pennsylvania and an author of the paper published Wednesday in Nature, said, "We can now conclude CAR-T cells can cure patients with leukemia based on these results," adding that there needs to be more follow-up with other patients.

As a result of the therapy, the cells also developed in the patients in the same way that regular T cells do: they transitioned from active killer T cells to another sort of immune cell called helper T cells, which are bystanders but may still destroy cancer cells.

According to the researchers, remission may be difficult to study. It is unknown to them whether the cancer cell has been completely eradicated or if they come back and keep getting defeated by the cells from therapy.

June emphasized that "clinically he is cured because 10 years down the line there is no leukemia."

Although promising, the downside is that the therapy does not work for all types of cancers as the majority cause solid tumors that are surrounded by proteins and cells that CAR-T cells find difficult to penetrate. It does, however, provide insight into how CAR-T cells can be more effective. 

J. Joseph Melenhorst, an immunologist at the University of Pennsylvania and another author of the study, noted that "the deep learning into these trials is key."