CD19 occupancy may drive CARs further

In this issue of Blood, Sakemura et al¹ report that treatment with the CD19-targeting monoclonal antibody tafasitamab followed by CD19-targeted chimeric antigen receptor T (CAR T) cells leads to reduced early CAR T-cell activation and apoptosis, with robust, but delayed, CAR T-cell expansion, resulting in improved efficacy, diminished tumor cell pyroptosis, and decreased severity of cytokine release syndrome (CRS) in preclinical models (see figure).

CD19 CAR T-cell therapy demonstrated high response rates in patients with relapsed and/or refractory large B-cell lymphoma (LBCL) and is now approved for the treatment of adults as early as second-line therapy. CD19 CAR T-cell activity is dependent on antigen density,² and lower pretreatment CD19 cell surface density was associated with progressive disease after CAR T-cell therapy in LBCL.³ Treatment with the CD3-CD19 bispecific T-cell engager blinatumomab before CD19 CAR T-cell therapy was associated with diminished or partial CD19 expression and worse outcomes.⁴ With the approvals of tafasitamab and loncastuximab terisine for patients with LBCL, whether the administration of these CD19-targeted antibodies before CD19 CAR T-cell therapy impacts its efficacy is a clinically relevant question.

Sakemura et al examined the impact of CD19 targeting with a monoclonal antibody on subsequent CD19 CAR T-cell therapy in preclinical models. They demonstrate that concomitant treatment with tafasitamab and CD19 CAR T cells inhibited T-cell effector function due to competition for CD19 binding. Conversely, prior treatment with tafasitamab improved the efficacy of CD19 CAR T cells due to delayed and robust CAR T-cell expansion. Sequential treatment with tafasitamab resulted in lower CD19 antigen availability and reduced early CAR T-cell activation and apoptosis. CAR T cells display tonic signaling, leading to impaired T-cell function and exhaustion,⁵ and are prone to activation-induced cell death.⁶ To enhance functionality, several approaches have been used to modulate CAR T-cell activation, including use of lower-affinity CAR,⁷ and transient inhibition of CAR signaling.⁸ The current study adds transient CD19 occupancy as another strategy. Of note, the effects of antigen modulation on CAR T-cell activation may be dependent on CD19-binding affinity, as reduced CAR T-cell activation and apoptosis were not observed with the CD19 monoclonal antibody clone used in blinatumomab, which has weaker binding affinity compared with tafasitamab.

Sequential therapy with tafasitamab and CD19 CAR T cells also decreased the severity of CRS in a CAR T-cell toxicity mouse model. The development of CRS is closely associated with CAR T-cell activation and proliferation, and the release of inflammatory cytokines from both the infused T cells and bystander immune cells, with preclinical data suggesting that monocytes/macrophages play a key role in the pathogenesis of CRS.⁹ Prior treatment with tafasitamab resulted in lower tumor burden at the time of CAR T-cell infusion, delayed CAR T-cell expansion with a modest increase in proinflammatory cytokines, and diminished tumor cell pyroptosis. Pyroptosis activates macrophages, resulting in the production of CRS-related cytokines,¹⁰ and, again, lower levels of pyroptosis-released factors were only observed after treatment with tafasitamab.

Treatment with tafasitamab did not result in copy number variations or focal deletions in the CD19 locus, and CD19 expression recovered within 3 days after stopping the drug. However, given CD19 expression heterogeneity in LBCL,² and potential clonal selection due to immune pressure and trogocytosis, studies to accurately evaluate CD19 expression, such as quantitative flow cytometry, on tumor cells from patients treated with CD19-targeting monoclonal antibodies are warranted. The results of such studies may influence the sequencing of these novel therapies. Furthermore, a better understanding of the antigen density threshold for CAR T-cell activity and efficacy will help inform the optimal time interval between CD19-targeting monoclonal antibody and CD19 CAR T-cell therapy. This study provides a proof of concept that sequential treatment with tafasitamab and CD19 CAR T cells may represent a clinically viable strategy to modulate CD19 antigen density and, therefore, CAR T-cell activation and tumor cell pyroptosis.

Conflict-of-interest disclosure: A.V.H. received research funding from Juno Therapeutics (a Bristol Myers Squibb company) and Nektar Therapeutics, and received honoraria from Bristol Myers Squibb. M.B. is an inventor on a patent describing HA-1 T-cell receptor therapy that was licensed to ElevateBio, received funding from ElevateBio/HighPassBio (an Elevate Portfolio company), was a scientific advisory board member of and had equity in HighPassBio, served on the scientific advisory board of Orca Bio, has given sponsored talks for Miltenyi Biotec, and leads a clinical trial that receives some research funding from Miltenyi Biotec.