Hematotoxicity represents a frequent chimeric antigen receptor (CAR) T-cell related adverse event and remains poorly understood. In this multicenter analysis, we studied patterns of hematopoietic reconstitution and evaluated potential predictive markers in 258 patients receiving Axicabtagene ciloleucel (Axi-cel) or Tisagenlecleucel (Tisa-cel) for relapsed/refractory large B-cell lymphoma. We observed profound (ANC<100/µl) and prolonged (≥day 21) neutropenia in 72 and 64% of patients respectively. The median duration of severe neutropenia (ANC<500/µl) was 9 days. We aimed to identify predictive biomarkers of hematotoxicity using the duration of severe neutropenia until day +60 as the primary endpoint. In the training cohort (n=58), we observed a significant correlation with baseline thrombocytopenia (r= -0.43, P=0.001) and hyperferritinemia (r=0.54, P<0.0001) on uni- and multivariate analysis. Incidence and severity of CRS, ICANS and peak cytokine levels were not associated with the primary endpoint. We calculated the CAR-HEMATOTOX model, which included markers associated with hematopoietic reserve (e.g. platelet count, hemoglobin and ANC) and baseline inflammation (e.g. C-reactive-protein, ferritin). This model was validated in two independent cohorts from Europe (n=91) and the USA (n=109), and discriminated patients with severe neutropenia ≥/<14 days (pooled validation: AUC=0.89, Sensitivity 89%, Specificity 68%). A high CAR-HEMATOTOX score resulted in a longer duration of neutropenia (12 vs. 5.5 days, P<0.001), and a higher incidence of severe thrombocytopenia (87% vs. 34%, P<0.001) and anemia (96% vs. 40%, P<0.001). The score implicates pre-CART bone marrow reserve and inflammatory state as key features associated with delayed cytopenia and will be useful for risk-adapted management of hematotoxicity.
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