Possible approaches to vaccination strategies after CD19-targeted CAR–T-cell therapy. (A) Possible vaccination approach in CD19-targeted CAR–T-cell therapy recipients who have no history of prior HCT or who completed post-HCT vaccines. (B) Possible vaccination approach in CD19-targeted CAR–T-cell therapy recipients who have a history of prior HCT and did not complete post-HCT vaccines. ^aCheck serum IgG titers to S pneumoniae (23 serotypes), tetanus toxoid, hepatitis A virus, and HBVsAg. ^bA response is defined as achieving the following for all administered vaccines: for non–S pneumoniae vaccines: at least twofold increase in IgG from prevaccination to 1 to 2 months postvaccination or achieving a seroprotective IgG level at 1 to 2 months postvaccination⁷⁷ ; for the S pneumoniae vaccine (Prevnar 13): at least twofold increase in IgG from prevaccination to 1 month postvaccination, achieving an IgG >1.3 µg/mL for ≥50% of the Prevnar 13 serotypes,⁷⁷  or as defined by the testing laboratory. Ab, antibody. This figure was adapted from the Fred Hutchinson Cancer Research Center Standard Practice Manual.⁷⁸