“Hematotoxicity after CAR T is common and clinically relevant, but it also remains poorly understood [with] a high degree of heterogeneity in terms of grading its clinical management,” said first author Kai Rejeski, MD, in presenting on the findings at the 6th European CAR T-cell Meeting, held in Spain and jointly sponsored by the European Society for Blood and Marrow Transplantation (EBMT) and the European Hematology Association (EHA).
“We hope that this novel grading system helps with this by enabling harmonized reporting using the same nomenclature and allowing the comparison of the expected incidence rates of grade 3 or higher [hematological toxicities] across several disease entities and CAR T products,” said Dr. Rejeski, of the Adult BMT (Blood Marrow Transplant) and Cellular Therapy Service, Memorial Sloan Kettering Cancer Center, New York City.
ICAHT Grading System
In a recent meta-analysis, Dr. Rejeski and his team found that infections are the cause of as many as 49% of non–relapse related deaths after CAR T-cell therapy, representing the most common cause of death and numbering significantly more than the more prominent causes of cytokine release syndrome (CRS) or immune effector cell–associated neurotoxicity (ICANS), which paradoxically have been the focus of significantly more research. In addition, the authors have reported substantial inconsistency among CAR T centers in the grading and management of the post–CAR T cytopenias that can cause those infections, underscoring the need for better guidelines.
“The narrative around CAR T toxicity has long centered on CRS and ICANS as novel and prototypical side effects with distinct management protocols,” Dr. Rejeski said in an interview. “However, it is cytopenias and the associated infections that drive nonrelapse mortality after CAR T.”
To address the need, the EHA and EBMT established the grading system for Immune Effector Cell–Associated HematoToxicity (ICAHT) that is applicable across disease types, indications, and treatment settings.
The details of the grading system were published in September 2023 in the journal Blood. The new system, which specifically focuses on neutrophil count and timing, importantly addresses the biphasic nature of ICAHT by distinguishing “early” ICAHT, occurring within 30 days of the CAR T administration, and “late” ICAHT, occurring more that 30 days following the treatment.
By contrast, conventional grading scales for CAR T–related cytopenias, such as the Common Terminology Criteria for Adverse Events (CTCAE) scale, “neither reflect the unique quality of post–CAR T neutrophil recovery, nor do they reflect the inherent risk of infections due to protracted neutropenia,” the authors report in the study.
Real-World Evaluation
To assess the ICAHT grading system’s relevance in a real-world clinical setting of CAR T-cell therapy recipients, Dr. Rejeski and colleagues conducted a multicenter observational study, published in January 2024 in Blood Advances.
The study involved 549 patients at 12 international CAR T centers treated with BCMA- or CD19- directed CAR T therapy for relapsed/refractory B-cell malignancies.
Of the patients, 112 were treated for multiple myeloma (MM), 334 for large B cell lymphoma (LBCL), and 103 for mantle cell lymphoma (MCL).
Using the grading system, grade 3 (severe) or 4 (life-threatening) ICAHT (n = 125), was found to be strongly associated with key factors including a cumulative duration of severe neutropenia (P < .0001), the presence of multilineage cytopenias, such as severe thrombocytopenia (90%, compared with 46% in nonsevere ICAHT) and severe anemia (92% vs 49%; both P < .001), as well as the use of platelet and red blood cell transfusions.
Grade 3 or higher ICAHT was more common in patients with MCL (28%), compared with LBCL (23%) and MM (15%).
Key factors at baseline that were independently associated with severe ICAHT after multivariate adjustment included the presence of bone marrow infiltration, increased serum LDH levels, elevated CAR-HEMATOTOX scores (all P < .001), and receipt of CD28z costimulatory domain products, including axi-cel or brexu-cel (P = .01).
Those with grade 3 or higher ICAHT scores had a significantly higher rate of severe infections, compared with lower ICAHT scores (49% vs 13%; P < .0001), as well as increased nonrelapse mortality (14% vs 4.5%; P < .0001), primarily attributable to fatal infections.
Survival outcomes were also worse with grade 3 or higher ICAHT, including significantly lower rates of 1-year progression-free survival (35% vs 51%) and 1-year overall survival (52% vs 73%; both P < .0001).
Grade 3 or higher ICAHT was also significantly associated with prolonged hospital stays (median 21 vs 16 days; P < .0001).
However, contrary to findings from some previous studies, the current study showed no association between ICAHT severity and the prior administration of autologous stem cell transplant.
The number of prior treatment lines was not associated with grade 3 or higher ICAHT. However, grade 3 or higher CRS was more common as a cotoxicity (15% vs 5% without severe ICAHT), as was severe ICANS (26% vs 13%; both P < .001).
Notably, ICAHT grading showed superiority in the prediction of severe infections, compared with CTCAE grading (c-index 0.73 vs 0.55, P < .0001 vs nonsignificant).
While mild to moderate toxicity after CAR T-cell therapy has been associated with more favorable outcomes, the poor survival rates associated with severe ICAHT “underscore that high-grade toxicity and inferior treatment outcomes often go hand-in-hand,” the authors write.
Conversely, “the patients with grade 1 or 2 ICAHT exhibited excellent treatment outcomes in our study,” they point out.
