CD33 and acute myeloid leukemia: On AML bulk cells, we found varying degrees of surface antigen density both at initial diagnosis and at relapse, hereafter quantified as median MFI ratios (Fig. 1a, Supplemental Table 1; negative: < 1.5; low: 1.5–5; medium: 5–15; high: > 15): High expression was found for CD33 (Initial diagnosis: 27.1/Relapse: 34.1) and CD244 (18.9/35.8).