SEVERE HEMATOLOGICAL TOXICITY FOLLOWING CD19 CAR‐T FOR RELAPSED/REFRACTORY LBCL IS ASSOCIATED WITH SUPPRESSIVE IMMUNE DYSREGULATION AND LIMITED CAR‐T EXPANSION

Abstract

Background: Hematological toxicity represents the most frequent high-grade toxicity of CD19 CAR-T, but remains poorly understood. We recently proposed a classification system for CAR-T-related hematotoxicity, defining three unique phenotypes of neutrophil recovery: quick [“Q”] versus intermittent [“I”] versus aplastic [“A”]. Quick: sustained neutrophil recovery without a second dip below an ANC <1000/µL. Intermittent: neutrophil recovery (ANC > 1500/µL) followed by a second dip with an ANC < 1000/µL after day 21. Aplastic: continuous severe neutropenia (ANC < 500/µL) ≥14 days. Multivariable binary logistic regression was applied to analyze clinical metadata. CAR T-cell expansion dynamics were studied during the first 4 months post-CAR-T infusion. The plasma proteome was explored in 58 patients across four time points (day 0, 4, 14, 28) using a 92-protein multiplex proximity extension assay (Olink Bioscience). Progression-free (PFS) and overall survival (OS) were studied via Kaplan-Meier estimates. Results: The distribution of phenotypes was 18%, 42%, and 40% (A vs. I vs. Q). As expected, ‘aplastic’ patients displayed prolonged severe neutropenia (A vs. I vs. Q: 28 vs. 10 vs. 5 days, p < 0.001) and a higher rate of severe infections (40% vs. 22% vs. 18%). On multivariable regression of baseline risk factors (n = 344), the aplastic phenotype was independently associated with the presence of BM infiltration (p = 0.004), low ANC (p = 0.002), and increased ferritin (p = 0.039). When comparing CAR-T expansion among phenotypes, ‘intermittent’ patients displayed the greatest CAR T-cell expansion over time (Figure 1A). Conversely, ‘aplastic’ patients displayed low expansion with an unfavorable relationship between CAR-T expansion and baseline tumor burden (Figure 1B). Serum proteomics revealed higher markers of T-cell suppression, endothelial dysfunction, inflammatory cytokines, and macrophage activation in the ‘aplastic’ phenotype group (Figure 1C). Notably, both PFS and OS was poor in the ’aplastic’patients (1-yr PFS 26%, 1-yr OS 46%). On the other hand, the ‘intermittent’ phenotype, characterized by recurrent neutrophil dips, was associated with superior survival outcomes (1-yr PFS 51%, 1-yr OS 46%). Keywords: aggressive B-cell non-Hodgkin lymphoma, cellular therapies, basic and translational science – Basic and Translational Science - Other Conflicts of interests pertinent to the abstract K. Rejeski Consultant or advisory role: BMS/CELGENE Honoraria: Novartis, BMS/CELGENE Research funding: Kite/Gilead Travel grants: Kite/Gilead