Leukaemia-associated immunophenotypes (LAIP) are observed in 90% of adult and childhood acute lymphoblastic leukaemia: detection in remission marrow predicts outcome

Analysis of differentiation antigens on leukaemic blasts is routinely done for diagnostic purposes, i.e. determination of stage of differentiation and lineage assignment. Acute lymphoblastic leukaemias are also frequently cha racterized by a leukaemia-associated immunophenotype (LAIP), either the coe xpression of differentiation antigens physiologically restricted to other s tages of differentiation (asynchronous LAIP) or cell lineages (aberrant LAI P). We defined LAIP in 241 consecutive unselected B-lineage (n = 193) and T -lineage (n = 48) ALL by three-colour now cytometry using directly conjugat ed monoclonal antibodies. The incidence of LAIP was found to be 91.7%. In 6 3% of patients two to six leukaemia-associated expression patterns were det ected, In order to study the specificity of LAIP in a therapy-relevant sett ing, remission bone marrow samples from patients with B-lineage ALL were an alysed for the expression of T-lineage-associated phenotypes on the normal bone marrow cells and vice versa. The frequency of ail T-lineage LAIP(+) ce lls and all aberrant B-lineage LAIP(+) cells was <1% in regenerating bone m arrow samples at different timepoints. The incidence and clinical significa nce of LAIP(+) cells was studied in 196 remission marrows of 70 ALL patient s (55 remaining in CCR, 14 with bone marrow relapse, one with isolated CNS relapse). The presence of >1% LAIP(+) at two consecutive timepoints predict ed 5/8 bone marrow relapses in B-lineage ALL. The occurrence of LAIP(+) cel ls >1% in T-lineage ALL after induction therapy predicted relapse in 7/7 ca ses. In conclusion, flow cytometric detection of LAIP(+) cells appears to b e a powerful tool for the prediction of outcome in ALL.