Inflammatory Biomarkers and Outcomes in Multiple Myeloma Patients after CAR T-Cell Therapy

Introduction: CAR T-cell therapy is an effective tool for the treatment of multiple myeloma but produces a systemic inflammatory response which can manifest as cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS) and other neurologic toxicities, and hyperferritinemia. Understanding the factors associated with these complications can help clinicians better evaluate their patients' candidacy for CAR T-cell therapy. In this study, we assessed whether baseline values of inflammatory biomarkers were associated with outcomes after CAR T-cell therapy.

Methods: We retrospectively reviewed multiple myeloma patients who underwent CAR T-cell therapy with commercial products or on clinical trials at The Mount Sinai Hospital between 2017 and 2023. We gathered data on lab parameters that we felt were indicative of patients' baseline inflammatory status including C-reactive protein (CRP), ferritin, D-dimer, fibrinogen, absolute lymphocyte count (ALC), and absolute neutrophil count (ANC). Baseline data were collected prior to lymphodepletion. Outcomes of interest were occurrence and maximum grade of CRS and ICANS, occurrence of delayed neurotoxicity, attainment of peak ferritin ≥5000 within 30 days of infusion, progression-free survival (PFS), and overall survival (OS). Univariate logistic regression was used to assess the association between baseline labs and CRS, ICANS, delayed neurotoxicity, and peak ferritin ≥5000. Ordinal logistic regression was used to assess the baseline labs' association with maximum grade of CRS and ICANS, while proportional cox regression was used to assess their association with OS and PFS. The percentage of bone marrow plasma cells pre-CAR T, which we used as a surrogate for tumor burden, was included as a covariate on multivariable analyses.

Results: A total of 101 patients treated with CAR T cells were included - 45 with ciltacabtagene autoleucel, 37 with idecabtagene vicleucel, and 19 with other products on clinical trials. Median age was 63 (range 37-82), median baseline marrow plasma cells percentage was 5% (range 0%-95%), and median follow-up was 11.9 months. Patients had a median (IQR) CRP of 4.0 mg/L (1.8, 11.8), ferritin of 174 ng/mL (68, 364), D-dimer of 0.6 mcg/L (0.4, 1.2), fibrinogen of 397.0 mg/dL (334.0, 477.5), ALC of 0.8 x10 ³/µL (0.5, 1.1), and ANC of 2.7 x10 ³/µL (1.9, 3.6). CRS occurred in 88.2% of patients (3.9% grade ≥3), ICANS in 15.7% (all grade <3), and delayed neurotoxicity in 5.9% (all grade <3).

Increased baseline fibrinogen and ferritin were significantly associated with inferior OS even after adjusting for covariates (p-values 0.031 and 0.010, respectively). Every 143 mg/dL increase in fibrinogen increased the hazard of death by 83.7%, while every 500 ng/mL increase in ferritin increased the hazard of death by 27.5%. Patients with higher baseline CRP had a trend towards inferior OS (30.2% increased hazard of death per 20 mg/L CRP increase, p = 0.055). Baseline CRP, D-dimer, fibrinogen, ferritin, ALC, and ANC were not associated with PFS.

Higher baseline ALC was associated with both increased odds of ICANS (110.2% increased odds of ICANS for every 0.5 x10 ³/µL increase in ALC, p = 0.019 on multivariable analysis) and increased grade of ICANS (p = 0.023 on multivariable analysis). None of the assessed biomarkers were associated with peak ferritin ≥5000 (aside from baseline ferritin), occurrence of CRS, maximum grade of CRS, or delayed neurotoxicity.

Conclusion: Although CAR T-cell therapy is a highly effective treatment option for patients with multiple myeloma, outcomes of infused patients can be highly variable. Serologic biomarkers like fibrinogen and ferritin are routinely assessed in patients undergoing CAR T-cell therapy and could offer value as predictors of outcomes. We found that higher fibrinogen and ferritin values at baseline were associated with inferior OS after CAR T-cell therapy, even after controlling for tumor burden. Higher baseline ALC was also associated with higher risk of ICANS and higher grade of ICANS, an important toxicity to consider for patients receiving CAR T. Baseline fibrinogen, ferritin, and ALC may be incorporated into assessments of the risk of CAR T-cell therapy for multiple myeloma patients.