Durable remissions have been obtained in around 30%-40% of relapsed/refractory large B-cell lymphomas (BCL) through the use of CD19-directed chimeric antigen receptor-modified T-cell (CAR T-cell) therapy. However, T cell exhaustion and/or an immunosuppressive tumor environment may contribute to CAR T cell failure and BCL relapse.
To counter this failure, researchers assessed the use PD1 blockade with pembrolizumab after CD19-directed CAR T-cell therapy. Such treatment appeared safe and was able to achieve clinical responses in some patients with B-cell lymphomas refractory to or relapsed after CAR T-cell therapy, according to the results of a small study (NCT02650999) reported in Blood.
Success for some
Twelve patients with BCL who were either refractory to (nine patients) or relapsed after (three patients) CD19-directed CAR T-cell therapy were treated with pembrolizumab at 200 mg IV every 3 weeks, according to Elise A. Chong, MD, of the University of Pennsylvania, Philadelphia, and colleagues.
Overall, 3 of the 12 patients showed a response after pembrolizumab: One complete response; two partial responses. In addition, 1 patient had stable disease; thus, 4 of the 12 patients showed clinical benefit, according to the researchers. After pembrolizumab, these four patients with clinical benefit showed an increase in the percentage of CAR T cells as assessed by mass cytometry, and three out of the four also showed increases in CAR19 transgene levels as determined by qPCR. In addition, immune profiling using mass cytometry revealed increased CAR T-cell activation and proliferation and less T-cell exhaustion in these clinical responders.
In terms of safety, pembrolizumab appeared to be well tolerated and the only ≥ grade 3 adverse events related to pembrolizumab were neutropenia in three patients, the researchers added.
Looking forward
“Although patient numbers are small, these data suggest potential differences in the biology of CAR T cells or in the overall immune landscape of responders and nonresponders that influence the clinical efficacy of PD-1 blockade administered in this setting. Future work aimed at improving immune health after CAR T-cell infusion, as well as work aimed at decreasing CD8+ CAR T-cell exhaustion in CAR T-cell products, may serve as potential platforms for enhancing the efficacy of immune checkpoint blockade in patients treated with CAR T cells,” the researchers concluded.
The study was sponsored by the Abramson Cancer Center of the University of Pennsylvania. The authors reported serving on advisory boards and receiving research funding from a variety of pharmaceutical and biotechnology companies.