Alemtuzumab levels and immune reconstitution. (A) Day 0 alemtuzumab levels were measured in 26 subjects. The median alemtuzumab concentration was 0.58 μg/mL (range, 0-2.82 μg/mL) at day 0. (B-D) Subjects with alemtuzumab above the median had lower absolute CD3, CD4, and CD8 counts at 30 and 60 days posttransplantation compared with subjects with alemtuzumab levels below the median. *P < .05; **P < .01.