The influence of antigen density on CD19 and BAFF-R CAR T cells. Bulk BAFF-R CAR T cells were stimulated with Nalm-6 BAFF-R–high (WT), BAFF-R–low, or BAFF-R–deficient (control) target cells for 5 hours at an E:T of 1:2. CD4⁺ and CD8⁺ T cells were enriched and then loaded onto microchips for secretomic evaluation. (A) FACS showing the proportion of EGFR⁺ BAFF-R CAR T cells. Polyfunctionality was analyzed either as (B) the percentage of single cells that released >2 cytokines or as (C) PSI. Bulk CD19 CAR T cells were stimulated with Raji-CD19⁺–high (WT), Raji-CD19⁺–low, or Raji-CD19–deficient (control) target cells as described above. CD4⁺ and CD8⁺ T cells were enriched and then loaded onto microchips for secretomic evaluation. (D) FACS plots showing the proportion of EGFR⁺ CD19 CAR T cells. Polyfunctionality was analyzed either as (E) the percentage of single cells that released >2 cytokines, or as (F) PSI.