Timeline for antimicrobial prophylaxis in patients receiving CD19-targeted CAR–T-cell therapy. In patients meeting high-risk criteria, refer to Table 2 for additional recommendations for antimicrobial management and infection monitoring. Monitoring absolute CD4 T-cell counts can be considered for guidance regarding when to stop prophylaxis for herpesviruses and Pneumocystis jirovecii pneumonia (PCP), although the utility of this approach in cancer treatment–induced cytopenias is unclear. ^aDuring periods of severe neutropenia (ANC <0.5 × 10⁹/L).