In patients with CVID and CLL with SID, a significantly increased expression of CD200 was observed on CD4+, CD8+, and CD19+ lymphocytes compared HV (p < 0.001), with the highest levels consistently found in CLL with SID (p < 0.001 vs. CVID for all subsets; Figure 1D–F). Here, CD4 is linked to B-cell chronic lymphocytic leukemia.