When I first met the immunology researcher James P. Allison in 2014, he was just becoming an icon. Columbia University had brought him to its campus to present him with the Louisa Gross Horwitz Prize for the new type of cancer therapy he had developed. Instead of trying to burn, poison or surgically remove malignant cells from the body, his treatment mobilized a patient’s immune system to destroy them.

During his talk at the award ceremony, Allison explained that three years earlier, the Food and Drug Administration had approved the antibody drug he had developed, ipilimumab, for use against late-stage metastatic melanoma, which is among the deadliest of cancers. Some of the terminal patients who had participated in earlier trials, he reported, had gained a decade of life. As he described how his drug had changed the prognosis for some of these patients — it was effective for about 20% of them — tears came to his eyes.

In all my years on a science beat, I’d never seen a researcher cry. Allison, with his long gray hair and his loose-fitting clothes, struck me as among the most interesting figures in the scientific world. Speaking with him later, I sensed that he was someone deeply original, extremely confident of his intellectual powers and unafraid to go where they took him — the exact qualities it takes to invent a paradigm-shifting cancer treatment.

Allison’s drug wasn’t the first or only form of immunotherapy; scientists have worked on anticancer vaccines, for example, for decades. What made Allison’s “immune checkpoint therapy” unique was that it used antibodies to unlock the immune system’s potential to kill cancer cells.

This approach is the culmination of Allison’s highly accomplished immunology career. In the early 1980s, he identified the receptor that allows the immune system’s T cells to recognize the antigens of infected or abnormal cells. A decade later, he showed that T cells also need a signal from a “costimulatory” molecule to launch their attacks. Then Allison and his colleagues discovered that a molecule called cytotoxic T lymphocyte antigen-4 (CTLA-4) acts as a checkpoint, or built-in brake, on T cells. They could remove the brake and set T cells loose against cancer cells with an antibody — ipilimumab — that inhibited the CTLA-4 checkpoint.

Work on immunotherapy has become a major trend in biotech research in the past decade. Variants and extensions of immune checkpoint therapy, often in combination with other drugs, are the basis for many treatments under development for cancers of the brain, lung, bladder and kidneys. None of these immunotherapy drugs are yet effective for all patients or all cancers, but when patients respond — as many metastatic melanoma patients do — their longevity is significantly improved.

Allison, now 71, was emphatic in his assessment of those outcomes when I spoke with him in his office at the University of Texas MD Anderson Cancer Center, where he is the chairman of the department of immunology and the executive director of its Immunotherapy Platform. “You don’t just get an increase in median survival,” he said. Thousands of patients treated with immunotherapy have lived cancer-free for 10 or more years. “These people have been cured.”

Such results have brought Allison not a few honors, including the Paul Ehrlich and Ludwig Darmstaedter Prize and the Lasker-DeBakey Clinical Medical Research Award in 2015 and the Wolf Prize in Medicine and the Balzan Prize in 2017. Then, in 2018, Allison shared the big one with Tasuku Honjo of Kyoto University: the Nobel Prize in Physiology or Medicine (Honjo had independently found a different cancer checkpoint).

At MD Anderson, Allison’s colleagues were so thrilled that they held a victory parade for him. In Houston, Allison has become a major celebrity: a sought-after guest at fundraising galas, an advocate with the Texas legislature for research dollars, and the target of countless autograph hounds and selfie seekers. It hasn’t hurt his celebrity standing that on occasion he also plays harmonica on stage with Willie Nelson and that a documentary about him and his work, Jim Allison: Breakthrough, was released last year.

Allison and I spoke in person and over the phone, and also corresponded by email in the course of this reporting. The interview has been condensed and edited for clarity.