Gene therapy with a lentiviral vector expressing a chimeric antigen receptor with specificity for CD19 (CART19) has induced complete remission in 3 patients with chronic lymphocytic leukemia (CLL), according to research published simultaneously in the August 10 issues of The New England Journal of Medicine and Science Translational Medicine.
The research team, from the University of Pennsylvania, reported that the reinfused, modified T cells expanded to more than 1000 times the initial engraftment level. The patients’ remission was ongoing at 10 months after treatment.
The investigators believe the big difference between this genetically modified T cell and previous ones that had disappointing clinical activity is the addition of the CD137 (4-1BB) costimulatory signaling domain that significantly increases antitumor activity.
The team, led by Carl June, MD, described in the NEJM article the T-cell treatment of one of the patients with advanced, p53-deficient CLL.
A half year prior to enrolling in the trial, the 64-year-old patient’s T cells were collected and frozen. Before reinfusing the T cells into the patient, the investigators thawed the cells and transduced them with lentivirus expressing CD19-specific chimeric antigen receptor.
Four days prior to reinfusion, the patient received chemotherapy with pentostatin and cyclophosphamide to deplete his lymphocytes. After 3 days of chemotherapy, his bone marrow was hypercellular with approximately 40% involvement by CLL.
After 4 days of chemotherapy, the patient received an infusion of T cells, of which 5% were transduced, totaling 1.42 x 107 transduced cells, split into 3 consecutive daily infusions.
Two weeks after the infusion, the patient experienced chills, fever, and fatigue, which intensified over the subsequent days. He was diagnosed with tumor lysis syndrome on day 22 after infusion. On day 23 after the CART19-cell infusion, the patient had no evidence of CLL in the bone marrow, and by day 28, his adenopathy was not palpable.
In addition to tumor lysis syndrome, the only other grade 3/4 toxicity observed was lymphopenia.
The investigators did not expect that such a low dose of chimeric antigen receptor T cells would result in a clinically evident antitumor response. The dose was several orders of magnitude lower than that used in previous studies of modified T cells.
They speculated that the course of chemotherapy administered to the patient prior to the CART19-cell infusion may have been responsible for the increased engraftment and for “potentiating the ability of chimeric antigen receptor T cells to kill stressed tumor cells that would otherwise survive the chemotherapy.”
The researchers conclude that continued study of CD19-redirected T cells is warranted and plan to test the approach in other CD19-positive tumors, including non-Hodgkin lymphoma and acute lymphocytic leukemia.