“We can now conclude that CAR T cells can actually cure patients with leukemia based on these results,” said senior author Carl H. June, MD, in a press briefing on the study published in Nature.
Dr. Carl H. June
“The major finding from this paper is that, 10 years down the road, you can find these [CAR T] cells,” Dr. June, director of the Center for Cellular Immunotherapies, University of Pennsylvania, Philadelphia, added. “The cells have evolved, and that was a big surprise ... but they are still able to kill leukemia cells 10 years after infusion.”
CAR T-cell therapy, in which patients’ own T cells are removed, reprogrammed in a lab to recognize and attack cancer cells, and then infused back into the patients, has transformed treatment of various blood cancers and shows often-remarkable results in achieving remissions.
While the treatment has become a routine therapy for certain leukemias, long-term results on the fate and function of the cells over time has been highly anticipated.
In the first published observations of a 10-year follow-up of patients treated with CAR T cells, Dr. June and colleagues described the findings for two patients, both with CLL, who back in 2010 were among the first to be treated with this groundbreaking therapy at the University of Pennsylvania.
A decade later, the CAR T cells are found to have remained detectable in both patients, who achieved complete remission in their first year of treatment, and both have sustained that remission.
Notably, the cells have evolved over the years – from initially being dominated by killer T cells to being dominated primarily by proliferative CD4-positive CAR T cells – with one of the patients exclusively having CD4-positive cells at year 9.3.
Dr. J. Joseph Melenhorst
“The killer T cells did the initial heavy lifting of eliminating the tumor, “ first author J. Joseph Melenhorst, PhD, said in an interview.
“Once their job was done, those cells went down to very low levels, but the CD4-positive population persisted,” said Dr. Melenhorst, who established the lab at the University of Pennsylvania to follow patients treated with CAR T-cell therapy. “[This] delayed phase of immune response against cancer is a novel insight, and we were surprised to see it.”
Dr. Melenhorst noted that the clonal makeup of the CD4-positive cells importantly stabilized and became dominated by a small number of clones, suggesting further sustainability.
When one of the two patients, Doug Olson, who participated in the press conference, donated his cells back to the center after 9.3 years, the researchers found that his cells were still capable of destroying leukemia cells in the lab.
“Ten years [post infusion], we can’t find any of the leukemia cells and we still have the CAR T cells that are on patrol and on surveillance for residual leukemia,” Dr. June said.
One challenge of the otherwise desirable elimination of leukemia cells is that some aspects of sustaining CAR T-cell activity become problematic.
“The aspect of how the remission is maintained [is] very hard to study in a patient when there is no leukemia at all,” Dr. June explained. “It could be the last cell was gone within 3 weeks [of treatment], or it could be that the [cancer cells] are coming up like whack-a-moles, and they are killed because these CAR T cells are on patrol.”
Sadly, the other CLL patient, Bill Ludwig, who was first to receive the CAR T-cell treatment, died in 2021 from COVID-19.