Risk Factors and Outcomes for Hematotoxicity Following Tisagenlecleucel for Pediatric B-Acute Lymphoblastic Leukemia

Background:

Hematotoxicity following chimeric antigen receptor (CAR) T-cell therapy is increasingly recognized as a distinct adverse event. The CAR-HEMATOTOX score has been developed as a prognostic tool for subsequent development of prolonged cytopenias in adults with lymphoma. However, risk factors in children and young adults (CAYA) with B-acute lymphoblastic leukemia (B-ALL) receiving CAR T cell therapy are less well-defined. We sought to describe incidence, outcomes, and risk factors for prolonged severe neutropenia in CAYA treated with tisagenlecleucel.

Methods:

This was a multi-institutional retrospective study involving CAYA ≤26 years of age with B-ALL treated with tisagenlecleucel who underwent leukapheresis and manufacturing between August 2017 and March 2020, with data collected through the Pediatric Real World CAR Consortium (PRWCC). Of 185 patients infused, 41 patients were excluded from analysis due to missing data (n=10), refractory disease/death from leukemia (n=27) or non-relapse mortality (n=4) prior to day 35 post-CAR T. Severe prolonged neutropenia was defined as absolute neutrophil count (ANC) <500 cells/mm³ for ≥30 days. For those with severe neutropenia pre-CAR T, day 0 of severe neutropenia was considered the day of CAR T-cell infusion. Statistical analyses included comparisons using Mann-Whitney and Fisher’s exact tests, receiver operating characteristic (ROC) curves to determine cut points with optimal sensitivity and specificity, univariate logistic regression, Kaplan-Meier curves for recovery from neutropenia, overall survival (OS) and relapse free survival (RFS).

Results:

Of 144 patients, 23 (15.9%) met the definition of severe prolonged neutropenia and 121 (84%) did not. For lymphodepleting chemotherapy, 139 (96.5%) received standard fludarabine (30mg/m²/dose x 4) and cyclophosphamide (500mg/m² x 2). Pre- and post-infusion characteristics are shown in Table 1. Pre-infusion, higher pre-infusion C-reactive protein (CRP), ferritin, bone marrow disease burden, and lower ANC and platelet counts were associated with severe prolonged neutropenia. Post-infusion, any grade cytokine release syndrome (CRS), severe CRS, CRS with hemophagocytic lymphohistiocytosis (HLH)-like manifestations, any grade neurotoxicity, peak CRP and ferritin, use of tocilizumab and steroids, and presence of infections within 30 days were associated with severe prolonged neutropenia. With univariate logistic regression, pre-infusion inflammatory markers, cytopenias, and bone marrow disease burden associated with severe prolonged neutropenia and of these, disease burden >15% had the highest odds ratio (Figure 1). Post-infusion infections and inflammatory toxicities, particularly CRS with HLH-like toxicities, as well as peak CRP, and peak ferritin, were associated with severe prolonged neutropenia. Peak ferritin >3800 ng/ml had the highest odds ratio. In patients with severe prolonged neutropenia, OS was inferior (p<0.0001) and RFS trended towards being inferior (p=0.052), compared to those without. Groups with or without severe prolonged neutropenia were also subdivided into >15% or ≤15% pre-infusion bone marrow disease burden subgroups. OS was similar between patients without severe prolonged neutropenia that had >15% or ≤15% pre-infusion disease burden, but patients with severe prolonged neutropenia and >15% disease burden had inferior OS, suggesting prolonged severe neutropenia may have independent prognostic value. Conversely, RFS was inferior in patients in the subgroups with >15% disease burden compared to those with ≤15%, regardless of occurrence of severe prolonged neutropenia.

Discussion/Conclusions:

We describe incidence, risk factors and outcomes for the development of severe prolonged neutropenia in CAYA with B-ALL following tisagenlecleucel. While there are similarities in risk factors with the CAR-HEMATOTOX score that has been validated in adults, in CAYA with B-ALL high disease burden pre-infusion and severe inflammation post-infusion were identified as the strongest risk factors for prolonged neutropenia. Identification of risk factors unique to the CAYA B-ALL population allows for tailored risk mitigation in higher risk patients and may help improve outcomes in CAYA at increased risk of prolonged severe neutropenia following tisagenlecleucel.