The two major subtypes of diffuse large B cell lymphoma (DLBCL)--activated B cell-like (ABC) and germinal center B cell-like (GCB)--arise by distinct mechanisms, with ABC selectively acquiring mutations that target the B cell receptor (BCR), fostering chronic active BCR signaling. The ABC subtype has a ∼40% cure rate with currently available therapies, which is worse than the rate for GCB DLBCL, and highlights the need for ABC subtype-specific treatment strategies. We hypothesized that ABC, but not GCB, DLBCL tumors would respond to ibrutinib, an inhibitor of BCR signaling. In a phase 1/2 clinical trial that involved 80 subjects with relapsed or refractory DLBCL, ibrutinib produced complete or partial responses in 37% (14/38) of those with ABC DLBCL, but in only 5% (1/20) of subjects with GCB DLBCL (P = 0.0106). ABC tumors with BCR mutations responded to ibrutinib frequently (5/9; 55.5%), especially those with concomitant myeloid differentiation primary response 88 (MYD88) mutations (4/5; 80%), a result that is consistent with in vitro cooperation between the BCR and MYD88 pathways. However, the highest number of responses occurred in ABC tumors that lacked BCR mutations (9/29; 31%), suggesting that oncogenic BCR signaling in ABC does not require BCR mutations and might be initiated by non-genetic mechanisms. These results support the selective development of ibrutinib for the treatment of ABC DLBCL.

A B S T R A C T PurposeSurvival and progression of mature B-cell malignancies depend on signals from the B-cell antigen receptor, and Bruton tyrosine kinase (BTK) is a critical signaling kinase in this pathway. We evaluated ibrutinib (PCI-32765), a small-molecule irreversible inhibitor of BTK, in patients with B-cell malignancies. Patients and MethodsPatients with relapsed or refractory B-cell lymphoma and chronic lymphocytic leukemia received escalating oral doses of ibrutinib. Two schedules were evaluated: one, 28 days on, 7 days off; and two, once-daily continuous dosing. Occupancy of BTK by ibrutinib in peripheral blood was monitored using a fluorescent affinity probe. Dose escalation proceeded until either the maximumtolerated dose (MTD) was achieved or, in the absence of MTD, until three dose levels above full BTK occupancy by ibrutinib. Response was evaluated every two cycles. ResultsFifty-six patients with a variety of B-cell malignancies were treated over seven cohorts. Most adverse events were grade 1 and 2 in severity and self-limited. Dose-limiting events were not observed, even with prolonged dosing. Full occupancy of the BTK active site occurred at 2.5 mg/kg per day, and dose escalation continued to 12.5 mg/kg per day without reaching MTD. Pharmacokinetic data indicated rapid absorption and elimination, yet BTK occupancy was maintained for at least 24 hours, consistent with the irreversible mechanism. Objective response rate in 50 evaluable patients was 60%, including complete response of 16%. Median progression-free survival in all patients was 13.6 months. ConclusionIbrutinib, a novel BTK-targeting inhibitor, is well tolerated, with substantial activity across B-cell histologies. J Clin

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Autologous chimeric antigen receptor (CAR) T-cell therapies targeting CD19 have high efficacy in large B-cell lymphomas (LBCL), but long-term remissions are observed in less than half the patients and treatment-associated adverse events such as immune effector cell-associated neurotoxicity syndrome (ICANS) are a clinical challenge. We performed single-cell RNA sequencing with capture-based cell identification on autologous axicabtagene ciloleucel (axi-cel) anti-CD19 CAR T-cell infusion products to identify transcriptomic features associated with efficacy and toxicity in 24 patients with LBCL. Patients that achieved a complete response by PET/CT at their 3-month follow-up had 3-fold higher frequencies of CD8 T-cells expressing memory signatures compared to patients with partial response or progressive disease. Molecular response measured by cell-free DNA (cfDNA) sequencing at day 7 post-infusion was significantly associated with clinical response (p=0.008), and a signature of CD8 T-cell exhaustion was associated (q=2.8×10 −149 ) with a poor molecular response. Furthermore, a rare cell population *