Procalcitonin as a biomarker for predicting bacterial infection in chimeric antigen receptor T-cell therapy recipients

Background: It is unknown whether serum procalcitonin (PCT) concentration monitoring can differentiate between bacterial infection or cytokine release syndrome (CRS) when chimeric antigen receptor T-cell (CAR-T) recipients present with a constellation of signs and symptoms that may represent both complications. Objective: The objective of the study was to assess the utility of serum PCT concentrations as a biomarker of bacterial infection in CAR-T recipients. Study design: This single-center, retrospective, medical record review evaluated patients prescribed CAR-T therapy until death or 30 days after infusion. Logistic regression modeling determined the association between elevated serum PCT concentrations within 48 h of fever onset and microbiologically confirmed infection. Secondary outcomes included clinically suspected infection, CAR-T toxicity rates, and broad-spectrum antibiotic usage. Predictive performance of PCT was assessed by area under the receiver operating characteristic curve (AUC). Results: The 98 included patients were a median age of 63 (IQR: 55–69) years old, 47 (48%) were male, and 87 (89%) were Caucasian. Baseline demographics and clinical characteristics were similar between patients with and without a bacterial infection. Serum PCT >0.4 ng/mL within 48 h of fever was significantly associated with a microbiologically confirmed bacterial infection (OR: 2.75 [95% CI: 1.02–7.39], p = 0.045). Median PCT values in patients with and without confirmed infections were 0.40 ng/mL (IQR: 0.26, 0.74) and 0.26 ng/mL (IQR: 0.13, 0.47), respectively. The AUC for PCT to predict bacterial infection was 0.62 (95% CI 0.48–0.76). All patients experienced CRS of some grade, with no difference in CRS severity based on elevated PCT. Broad-spectrum antibiotics were used for a median of 45% and 23% of days in those with and without confirmed infection, respectively (p = 0.075). Conclusion: Elevated serum PCT concentrations above 0.4 ng/mL at time of first fever after CAR-T infusion was significantly associated with confirmed bacterial infection. Furthermore, rigorous, prospective studies should validate our findings and evaluate serial PCT measurements to optimize antimicrobial use after CAR-T therapy.