CD83 CAR T overcome CD19 antigen loss in B cell malignancies after CD19-directed therapy

Abstract Chimeric antigen receptor T cells (CAR T) targeting CD19 can cure approximately a third of patients with aggressive B cell malignancies, but relapse due to CD19 antigen loss and serious infections resulting from B cell aplasia remain major causes of death following CD19 CAR T. Here, we demonstrate that CD83 is a clinically relevant target for CAR T therapy in patients with B cell malignancies and that CD83 CAR T can effectively kill tumors even in the context of CD19 antigen loss. CD83 was highly expressed on B cell acute lymphoblastic leukemia (ALL; n=40, 43% of lymphoblasts CD83+), mantle cell lymphoma (MCL; n=5, 69% of lymphoma cells CD83+), and diffuse large B cell lymphoma (DLBCL; n=2, 80% of lymphoma cells CD83+), yet low on healthy B cells (16% of B cells CD83+; n=9 healthy donors). In contrast, CD19 was expressed on B cell malignancies and circulating B cells alike (96-100% of leukemia/lymphoma or B cells CD19+). Focusing on ALL, CD83 antigen density was 10 times lower than CD19 (1051 vs 10882 MESF, ANOVA, P=0.0001), but similar to CD20 or CD22. Therefore, CD83 CAR T therapy for B cell leukemia or lymphoma carries a low risk for B cell aplasia and related infectious complications, otherwise observed with CD19 CAR T. In a cohort of B ALL patients treated with CD19-directed therapy (n=6, including brexucabtagene autoleucel or blinatumomab), CD19 antigen expression on lymphoblasts was significantly reduced upon relapse. Conversely, CD83 antigen was well expressed on B ALL lymphoblasts at diagnosis and relapse (99% to 24% of lymphoblasts CD19+, P=0.0012; 30% to 48% of lymphoblasts CD83+, P=0.3918, mixed-effects analysis). B ALL CD19 expression is susceptible to selective pressure when subjected to anti-CD19 therapy, like CAR T or bispecific engagers. The persistent expression of CD83 on B ALL lends itself toward a form of targeted rescue therapy. CD83 CAR T effectively killed Raji (94.1% of cells CD83+) and Nalm6 (99.4% of cells CD83+) cell lines, often outperforming CD19 CAR T, especially against CD19 knock-out Raji targets. When cocultured with Raji target cells, CD83 CAR T produced more IFNγ (2665 v 3319 pg/ml, P=0.0001) and less IL-6 (53 v 20 pg/ml, P=0.0001) than CD19 CAR T. Thus, the target cell-stimulated CD83 CAR T displayed a cytokine profile favoring potency over toxicity, compared to CD19 CAR T. The CD83 CAR T product consisted of a rich central memory population and expressed significantly less PD-1, suggesting a propensity toward durable persistence and resistance to exhaustion. In NSG mice bearing luciferase-transduced Raji tumors, CD19 or CD83 CAR T monotherapy significantly extended survival compared to untreated mice (n=7-8 mice per group, median survival 24 vs 51.5 [P=0.0003] or 40.5 [P=0.0035] days, respectively). To mimic the expected clinical scenario of using CD83 CAR T in an era of commercial cell products, we tested the sequential use of CD83 CAR T after the initial infusion of CD19 CAR T in the Raji model. The sequential CD19=>CD83 CAR T approach resulted in superior mouse survival compared to either cell product alone (median survival undefined at 60 days, with 75% of mice alive, P=0.03, Log-rank test). Sequential CD19=>CD83 CAR T cleared the tumor burden in treated mice by day +48. Our preclinical evidence justifies further translational investigation of CD83 CAR T in B cell leukemia and lymphoma, as a strategy to overcome the complications of B cell aplasia and CD19 antigen loss.