A Mouse Model of CD19 CAR - T Cell Therapy Reveals Mechanism of Cytopenia

• Published in: Blood 2023-11, Vol.142 (Supplement 1), p.3460-3460
• Main Authors: Grzywacz, Bartosz, Tilahun, Ashenafi, Wilson, Irena, Welk, Kevin, Blazar, Bruce R, Pennell, Christopher A
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-190175

Immunotherapy with Chimeric Antigen Receptor (CAR) T cells against CD19 can cure patients with refractory B cell lymphoma and leukemia. However, complications of CAR-T cell therapy can cause morbidity. Among the complications of CAR-T cell therapy is cytopenia, i.e. decreased peripheral blood counts of platelets, leukocytes and / or erythrocytes. The exact mechanism of this side - effect is not known, retrospective analysis showed it affects 10-20% of patients and is linked with the severity of cytokine release syndrome (Juluri et al, PMID34666344). We have previously developed a mouse model of CAR-T cell therapy using C56BL/6 mouse expressing human CD19 under a B- Cell specific promoter (Pennell et al, PMID29735365). The recipient mice are heterozygous for human hCD19 on CD45.2 background. Congenic C56BL/6 CD45.1 mice served as T cell donors. The aim of this study was to investigate if the mouse model recapitulates cytopenia seen in patients after CAR-T cell therapy. C56BL/6 recipient mice were treated with lymphodepleting chemotherapy (Cyclophosphamide (CY) 300 mg/kg) and infused with 1) no T cells 2) control T cells transfected with hEGFR 3) T cells transfected with CD19 CAR with hCD137 and hCD3zeta signaling domains. The chosen dose of infused T cells at 0.3E+6 per animal was low, approximately 10x below the lethal dose and 3x less than IC50 dose, to reduce early mortality. The animals were weighed and examined regularly, and appearance and activity were scored from 0 (healthy) to 8 (moribund). Total of 30 animals per group were harvested at 5 time points, 6 mice each, on days 5, 12, 26, 40 and 54. Peripheral blood counts were measured using HemaVet CBC counter. Flow cytometry was performed on blood and bone marrow. Spleens, long bones (femur, tibia) and sternum were harvested for histopathologic assessment. Multiparametric immunohistochemistry (IHC) was performed using Codex (Phenocycler, Akoya). The mice receiving CAR-19 T cells showed significant, but transient loss of weight and transient increase in morbidity score during the first 2 weeks. Mortality was not significantly different between groups: 0, 1 and 2 deceased animals in CY, control T and CAR-T cell groups, respectively. We observed transient significant cytopenia in the CAR-T cell treated mice, with significantly lower platelet counts on day 5 (p