Responses to RhD protein by T cells from patients with CLL with AIHA when different PBMC populations are used as APCs. T cells were purified from PBMCs, and the remaining cells were fractionated by negative selection into putative APC types. Sequential depletion of CD14⁺, CD1a⁺/11c⁺, and CD5⁺ cells removes monocytes, dendritic cells, and CLL cells, respectively. The APC fractions were tested for the ability to stimulate T-cell proliferation in response to RhD protein. Proliferative responses in patients CLL+AIHA1 (A), CLL+AIHA4 (B-C), and CLL+AIHA5 (D) are inhibited by the depletion of CLL B cells, but they remain unaffected by the removal of other APC fractions. Significant differences between cultures stimulated using unfractionated and fractionated PBMCs as APCs are indicated (Student t test: *P < .05; **P < .01).