SAN DIEGO – Checkpoint inhibition can be used safely and effectively with CD19-directed chimeric antigen receptor (CAR) T-cell therapy in children with relapsed B-cell acute lymphoblastic leukemia (ALL), and it may bolster CAR T-cell effects and persistence, suggest the findings in a series of 14 patients at the Children’s Hospital of Philadelphia.
Combined programmed death-1 (PD-1) blockade and CAR T-cell therapy appeared to have particular benefit in patients with early B-cell recovery and in those with bulky extramedullary disease,, PhD, reported during a press conference at the annual meeting of the American Society of Hematology.
The patients, aged 4-17 years with heavily pretreated relapsed B-ALL (13 patients) or B lymphoblastic lymphoma (1 patient), were treated with CD19-directed CAR T-cell therapy, including CTL019 in 4 patients and CTL119 in 10 patients, followed by pembrolizumab (in 13 patients) or nivolumab (in 1 patient).
Six patients received the combination therapy because of early B-cell recovery after initial CAR T-cell infusion, four patients had relapsed or refractory (R/R) bulky extramedullary disease, and four patients had failed to respond or relapsed after initial CAR T-cell therapy.
Three of the six with poor persistence of response reestablished B-cell aplasia (a reflection of CAR T-cell function) after reinfusion of the CAR T-cell product followed by infusion with PD-1 blockade, and they have “sustained CR [complete response] with B-cell aplasia, showing continued persistence of their CAR T cells,” said Dr. Maude, an attending physician in the Cancer Center at Children’s Hospital of Philadelphia.
Of the four patients with R/R bulky extramedullary disease, two patients had a partial response and two patients had CR, she said, explaining that it was hypothesized that the “PD-1 checkpoint pathway may be activated through the microenvironment in that extramedullary situation.”
However, all four patients who had partial or no response to initial CAR T-cell therapy progressed after PD-1 administration, she said, noting that “in one patient, this progression was marked by reduced CD19 expression, which was probably the mode of escape from CD19 CAR T cells.”
Prior studies have shown that patients who respond to CAR T-cell therapy have persistence of CD19 CAR T cells, whereas those with loss of CD19 CAR T cells within 6 months of infusion have a higher rate of relapse, Dr. Maude explained.
“Our hypothesis was that T cells, upon activation, may become exhausted through activation of immune checkpoint pathways, that one such pathway – PD-1 – may be involved in early loss of CD19 CAR T cells and therefore that the combination [of CD19 CAR T-cell therapy] with PD-1 checkpoint blockade may improve the function of the CAR T cells and their persistence,” she said.
The combined approach was well tolerated in this study, she said, noting that mild cytokine release syndrome symptoms and fever typical of CAR T-cell proliferative responses were observed in three patients within 2 days of starting pembrolizumab.
Other adverse effects associated with PD-1 inhibition, including acute pancreatitis, hypothyroidism, arthralgias, and urticaria, occurred in one patient each. There were four cases of grade 3-4 cytopenias that were deemed tolerable or reversible upon discontinuation.
“We show that PD-1 checkpoint inhibitors can be safely combined with CD19 CAR T-cell therapy and that this mechanism may be useful to improve CAR T-cell persistence,” Dr. Maude said.
These findings, which showed particular benefit in patients with poor persistence marked by early B-cell recovery and in those with R/R bulky extramedullary disease, should help inform future use of checkpoint inhibitors after CAR T-cell therapy, she added.
Dr. Maude reported financial ties to Novartis.
SOURCE: Li AM et al. ASH 2018, .