CD66 expression in acute leukaemia

Antibodies against CD66 identify antigens from the carcinoembryonic antigen (CEA) family of proteins, which belong to the immunoglobulin gene superfam ily. Despite being usually restricted to cells of myeloid or monocytic orig in, CD66 expression has also been reported in blasts from children with B-c ell Lineage acute lymphocytic leukaemia (ALL). An analysis of the CD66 expr ession was undertaken in a series of acute leukaemia patients. Antigenic ex pression was analysed using triple combinations of monoclonal antibodies (m Abs) in forty-five patients. The CD66 Kat4 fluorescein isothiocyanate clone was purchased from Dako (Glostrup, Denmark). CD66 was expressed in 2 of 29 patients with AML (acute myeloblastic leukemia) (6.8%) and in 8 of 12 pati ents with B-cell lineage ALL (66.7%; P<0.001); in blast crisis (BC) of chro nic myelocytic leukaemia (CML), CD66 was expressed in two patients with lym phoid BC but not in the two with myeloid BC. The co-expression of CD66 with other myeloid antigens was observed in all CD66+ ALL/ Ly-BC cases tested: CD 13 in six patients, CD33 in seven and CD117 in two patients. The CD66 ex pression is more frequent in ALL than in AML. Furthermore, we analysed mini mal residual disease (MRD) in eight patients in complete remission. CD66 ex pression was associated with an abnormal B-cell differentiation pattern and with increases in CD34/CD19+ cells in all but one case. These findings sug gest that an aberrant expression of CD66 could be used to investigate MRD i n ALL. The association between CD66 reactivity and bcr-abl in adult ALL rem ains to be investigated.