Immunophenotyping of acute leukaemias has become an important diagnostic tool in haematology laboratories as it is now well recognised that the presence of certain surface markers has prognostic significance. In 1988, we experimented with the alkaline phosphatase anti-alkaline phosphatase (APAAP) method for immunophenotyping of leukaemic cells in our laboratory. 48 cases of peroxidase-negative acute leukaemias were studied. Our study showed that 2 peroxidase-negative cases carried myeloid surface markers, 44% were negative for the markers studied and 5% were unclassified due to technical problems. We concluded that the APAAP method is a useful technique for demonstrating cell markers in leukaemic cells as the reaction is reddish and usually intense. We failed to demonstrate surface markers in 44% of the cases probably because of the choice of a limited panel of monoclonal antibodies.
T cells undergo a series of complex phenotypic changes before achieving maturation. Discrete stages of T-cell differentiation are simplified to four stages (pro-, pre-, cortical and mature-T cell) and used in the classification of T-cell leukaemia. HLA-DR has been reported to be expressed in immature T-cell acute lymphoblastic leukemia (ALL) and also confer a poorer treatment outcome. Simultaneously, the genotype goes through distinct pattern changes due to rearrangement of T-cell receptor (TCR) genes. TCR gene rearrangement is important in the diagnosis of clonality and used as markers to detect minimal residual disease in lymphoproliferative disorders. We identified a subset within Pro-T and Pre-T cell cases distinguished by the expression of HLA-DR. These subgroups appeared to be more immature as rearrangement of the TCR-gamma gene was either at germline or involved only the first constant region (C1) unlike a more rearranged pattern in the HLA-DR-subgroups. We also observed a higher incidence of mediastinal mass (67%) in the HLA-DR-subgroup in the Pre-T stage. These characteristics may be useful as markers to further refine staging of T-cell ALL and determine prognosis.