The Yin and Yang of CAR T-cell Therapy: Lessons to Be Learned from Noninvasive Profiling

Chimeric antigen receptor (CAR) T-cell therapy has transformed the management of chemotherapy-refractory large B-cell lymphoma (LBCL) and is an effective treatment option for several other B-cell malignancies. Despite the enthusiasm, more than half of patients treated with CAR T-cell therapy will ultimately experience disease progression. Outcomes can be dismal for these patients. Substantial efforts are underway to explore mechanisms of resistance and develop strategies to enhance efficacy. Though incompletely characterized, resistance to CAR T-cell therapy has been described in general categories such as antigen loss, T-cell fitness, or protumor microenvironments. More should be done to improve our understanding of the mechanisms of resistance to inform patient selection, next-generation cellular therapy, and optimal treatment sequencing.

Sworder and colleagues leverage their expertise in noninvasive profiling of circulating tumorderived cell-free DNA (ctDNA), using targeted sequencing (CAncer Personalized Profiling by deep Sequencing [CAPP-seq]) to molecularly profile the tumor and detect measurable residual disease. They also profiled cell-free CAR19 retroviral fragments and cell-free T-cell receptor rearrangements in patients with LBCL treated with axicabtagene ciloleucel (axi-cel), which allowed them to characterize both tumor-intrinsic and -extrinsic factors concurrently. A total of 708 serial blood and tissue samples from 65 subjects in the independent discovery cohort and 73 subjects in the independent validation cohort were profiled. There was no significant difference in the outcomes among these two cohorts, with more than half in each group experiencing progression following axi-cel (discovery, 55%; validation, 58%).

Both pretreatment and dynamic ctDNA levels were predictive of outcomes following axi-cel, with ctDNA assessment at four weeks after treatment being the strongest predictor in multivariable models. Investigators also demonstrated that CAR19 expansion and functional persistence can be quantified from cell-free DNA and fragment length may correlate with trafficking. CD19 mutations and decreased CD19 membrane expression were observed but were relatively uncommon mechanisms of resistance. Alterations in multiple genes were associated with inferior event-free survival, including TMEM30A, P2RY8, IRF8, DTX1, PAX5, and TP53, which include classes associated with B-cell identity, immune checkpoints, and the microenvironment. Finally, the authors reported that CAR19 T cells may play a reciprocal role in shaping the tumor genotype and phenotype.