Treatment of CLL patients with BTKi enhances the cytotoxic effector function of autologous and allogeneic T cells in response to CD19/CD3 bsAb. (A) Tumor cell killing in response to the CD19/CD3 bsAb was tested in PBMCs obtained from the same CLL patients before starting therapy (baseline), and again on BTKi therapy (BTKi) mixed at a 1:1 ratio. VPD staining was used to identify the source of the sample in the mixing experiments. CLL cell killing was assessed in the VPD-negative population. (B) CLL-specific killing after culture with CD19/CD3 bsAb; tested were PBMC samples from 4 patients obtained at baseline (gray circles), on BTKi therapy (blue circles) tested were PBMC samples were alone (dotted circles) or mixed containing 50% baseline and 50% BTKi-treated PBMCs (plain circles). Each dot represents 1 patient; lines connect samples obtained from the same patient. (C) To test whether CLL cells affect normal T-cell function, we mixed PBMCs from a healthy donor with CLL cells purified from baseline samples (gray circles) or during BTKi therapy (blue circles) at 1:10 T cells:CLL cell ratios (n = 8). CLL-specific killing after 3 days of culture with the CD19/CD3 bsAb is shown. Each dot represents 1 patient; lines connect samples obtained from the same patient. Statistical significance by Wilcoxon matched-pair signed-rank test. **P < .01.