Ten years later, the engineered cells are still killing leukemia

Researchers at the University of Pennsylvania reported in 2022 that two men infused with their own reprogrammed T cells in 2010 were still cancer free, with the cells still on patrol.

Two men in the summer of 2010

Bill Ludwig and Doug Olson had chronic lymphocytic leukemia, a cancer of B lymphocytes. Olson had been diagnosed in 1996, Ludwig in 2000. In the summer of 2010, at the University of Pennsylvania's Abramson Cancer Center, they became the first participants in a trial of T cells taken from their own blood, genetically altered to recognize the cancer, and returned to them by infusion.

The first report, by Porter, June and colleagues in the New England Journal of Medicine in August 2011, described a single patient with refractory disease. He received a low dose, approximately 150,000 engineered cells per kilogram of body weight. The cells expanded in his body to more than 1,000 times the initial engraftment level. He developed tumor lysis syndrome, a consequence of rapid cancer cell death, and then a complete remission. Engineered cells persisted at high levels in blood and bone marrow for six months and still expressed the receptor. Remission was ongoing at ten months.

How the cells were built

The receptor is a chimeric antigen receptor, or CAR. An antibody fragment that binds CD19, a protein on the surface of B cells and of most B-cell leukemias, is fused to two signalling domains: CD3-zeta, which triggers the T cell, and CD137, also called 4-1BB, a costimulatory domain that the Penn group credited with the cells' persistence. The gene for the receptor was delivered with a lentiviral vector.

A companion paper by Kalos and colleagues in Science Translational Medicine, published the same month, reported on three patients. All three had clinical responses; two had complete remissions. The cells expanded more than 1,000-fold, trafficked to bone marrow and kept expressing functional receptors for at least six months. The authors calculated that each infused CAR-expressing T cell eliminated at least 1,000 leukemia cells. Because CD19 is also on healthy B cells, the patients lost their normal B cells and the antibodies they produce, an expected and persistent side effect.

Fourteen patients

Mature results from the initial trial appeared in 2015, again in Science Translational Medicine. Fourteen patients with relapsed or refractory chronic lymphocytic leukemia had received doses ranging from 14 million to 1.1 billion cells. Eight of fourteen responded, a rate of 57 percent, with four complete and four partial remissions. In the first two patients to achieve complete remission, the CAR T cells persisted and remained functional beyond four years. No patient in complete remission had relapsed, and minimal residual disease was undetectable in those who achieved it. The degree to which the cells expanded in the body correlated with clinical response. All responders developed B-cell aplasia and cytokine release syndrome, the fever and inflammation that accompany the cells' proliferation.

The decade

In February 2022, J. Joseph Melenhorst, June and colleagues from Penn and Children's Hospital of Philadelphia published in Nature a study of those first two patients, both of whom had achieved complete remission in 2010. CAR T cells remained detectable in both more than ten years after a single infusion, with sustained remission in both. The cells had changed. The early response was dominated by CD8-positive killer T cells, and in one patient by a population of gamma delta CAR T cells. At the later time points a highly activated CD4-positive population dominated. According to Penn's release on the paper, CD4-positive cells made up 97.5 percent of the CAR T cells in one patient at 1.4 years and more than 99.6 percent from 3.4 to 9.3 years, and 97.6 percent in the other patient at 7.2 years. Single-cell profiling showed that these cells carried cytotoxic features along with ongoing activation and proliferation, and the clonal repertoire had stabilized around a small number of clones.

Ludwig died in early 2021 of complications of COVID-19, in remission from his leukemia. Olson, a former scientist, took up distance running after treatment and had completed six half marathons by the time the paper appeared. Melenhorst said the long-term remission was remarkable and called it a testament to the potency of a living drug.

From two adults to children, and to approval

The same receptor was moved into acute lymphoblastic leukemia, the most common childhood cancer. In 2013 Grupp and colleagues reported two children treated at Children's Hospital of Philadelphia: both entered complete remission, one ongoing at 11 months, while the other relapsed about two months later with leukemia cells that no longer expressed CD19. In 2014 Maude and colleagues reported 30 children and adults, of whom 27, or 90 percent, achieved complete remission. Event-free survival at six months was 67 percent. Every patient had cytokine release syndrome, severe in 27 percent and treated with the interleukin-6 receptor antibody tocilizumab.

On August 30, 2017, the U.S. Food and Drug Administration approved tisagenlecleucel, sold as Kymriah, for patients up to 25 years of age with B-cell precursor acute lymphoblastic leukemia that is refractory or in second or later relapse. It was the first gene therapy approved in the United States. The agency cited a National Cancer Institute estimate of about 3,100 new diagnoses a year in patients aged 20 and younger, of whom 15 to 20 percent relapse or fail initial treatment. In the trial supporting approval, 63 patients were treated and 83 percent were in remission within three months. The label carries a boxed warning for cytokine release syndrome and neurological events, and the drug is dispensed only through certified hospitals under a risk evaluation and mitigation strategy. The agency expanded tocilizumab's approval the same day for severe cytokine release syndrome after CAR T-cell treatment.

What the story does and does not show

The 2022 paper describes two patients with one disease, chronic lymphocytic leukemia. In the fourteen-patient series from which they came, 57 percent responded and four of fourteen achieved complete remission, so the decade-long outcome is the best case, not the typical one. Persistence was measured in blood. That the cells were still killing leukemia is an inference from their activated, cytotoxic profile and from the patients' continued remission and B-cell aplasia, not from direct observation of residual leukemia being destroyed; the authors note it is unclear whether leukemia cells remained to be killed.

The story says both men were still cancer free in 2022. Ludwig was in remission when he died of COVID-19 in early 2021, so the statement holds for the length of his life, not to the date of publication. Relapse through loss of CD19 was documented in the first pediatric cases and remains a known failure mode. Cytokine release syndrome affected every responder. What the sequence shows is a cell product that, in two people, remained alive, evolved, and continued to work for more than ten years after one infusion. How often that happens, and in which patients, is a question the first two cannot answer.

One infusion. Ten years. Still on patrol.