Factors associated with response
Dr. Hill said a shortened manufacturing process may be associated with enhanced response, as all responders received CAR T cells produced via a shorter manufacturing process. The shortened process involves freezing cells on day 4-5 post transduction, as opposed to day 7.
“While the numbers are too small to make any definitive conclusions, this seems to correlate with less terminal differentiation, which might improve potency,” Dr. Hill said. “However, additional analyses are ongoing.”
Dr. Hill also pointed out that CAR T-cell expansion was observed in all patients, with higher peak levels observed at the higher dose. In addition, CAR T-cell persistence was durable at both dose levels.
“We have been able to detect the CAR transgene at all follow-up time points, out to 9 months for some patients,” Dr. Hill said. “While limited persistence may play a role in nonresponders, it does not appear to be the only factor.”
Safety
“Surprisingly, no selective ablation of normal T cells has been observed,” Dr. Hill said. “As CAR T cells dwindled [after infusion], we were able to see recovery of normal T cells, all of which expressed normal levels of CD5. This was observed in all patients on study, except for one patient who had prolonged pancytopenia.”
Cytopenias were the most common grade 3/4 adverse events, including neutropenia (n = 8), anemia (n = 7), and thrombocytopenia (n = 5). Other grade 3/4 events included elevated aspartate aminotransferase (n = 2), hypoalbuminemia (n = 1), hyponatremia (n = 1), hypophosphatemia (n = 1), and elevated alanine aminotransferase (n = 1). There were no grade 5 adverse events.
Two patients developed grade 1 CRS, and two had grade 2 CRS. Both patients with grade 2 CRS were treated with tocilizumab, and their symptoms resolved.
One patient developed grade 2 immune effector cell-associated neurotoxicity syndrome, but this resolved with supportive care.
One patient had a central line–associated bloodstream infection (coagulase-negative staphylococci), and one had cytomegalovirus and BK virus reactivation. There were no fungal infections.
“We have demonstrated that CD5 CAR T cells can be manufactured from heavily pretreated patients with T-cell malignancies, and therapy is well tolerated,” Dr. Hill said. “We have seen strong and promising activity in T-cell lymphoma, which we hope to be able to translate to T-ALL as well.”
Dr. Hill said she and her colleagues hope to improve upon these results with a higher dose level of CD5 CAR T cells (1 x 108), which the team plans to start testing soon. The researchers may also investigate other target antigens, such as CD7, as well as the use of donor-derived CAR T cells for patients who have relapsed after allogeneic HSCT.
Dr. Hill said she has no relevant disclosures. Baylor College of Medicine is sponsoring this trial.
SOURCE: Hill L et al. ASH 2019. Abstract 199.