Intranuclear terminal deoxyribo-nucleotidyl transferase (TdT) expression in acute lymphoblastic leukimia : a flow cytometric analysis in bone marrow aspirate fixed permeabilized cells

Abstract

BACKGROUND. Despite advances in the understanding of the biology and characterization of acute lymphoblastic leukemia (ALL), evidence of utility of novel diagnostic techniques based on these developments is lacking in our setup. This is against a background of increased case reporting and rising incidence of this disease. OBJECTIVE. The aim of this study was to qualitatively and quantitatively detect the presence and level of TdT expression in cell isolates obtained from bone marrow aspirates in patients with ALL. ** DESIGN. This was a cross sectional descriptive study that was carried out for three months between June and August 2003. Consecutive cases of qualifying patients were recruited. They were stratified into cases (for those with ALL) and controls for other diagnostic entities. ** SETTING. This was a laboratory-based study carried out in the departments of Haematology and Blood Transfusion and KAVllaboratories at the University of Nairobi's Faculty of Medicine. Patients were recruited from the selected health care cielivery points within the KNH. Two cases were recruited from two private hospitals (one case each) within Nairobi. ** SUBJECTS. Thirty-two patients (eleven ALL and twenty one controls) were recruited over the study period. ** INTERVENTIONS. Peripheral blood and a bone marrow aspirate were obtained from each patient selected to participate in the study. These were used for the morphological diagnosis of ALL and other pathologies. BMAs were further used for flow cytometric analysis of TdT. ** MAIN OUTCOME MEASURES. For cases and controls, positivity or negativity for TdT expression was analyzed. Levels of expression were presented as a percentage of the total acquired events and the absolute numbers of positive events. Comparisons between the cases and controls were made. ** RESULTS. The cases to controls ratio were 1 :1.9. There were more males than females (1.8:1) in the ALL cluster. The median age for this group was nine years (range 3-13). Only three of these eleven had not received chemotherapy at the time of recruitment. Of the nine cases on treatment, only one was in morphologic complete remission. There was a strong positive correlation between the visual blasts cell counts and the absolute number of acquired events by FCM (r=O.99) a weaker association was exhibited by the controls (r=0.474). The frequency of TdT expression was higher in ALL (63.6%) than in controls (38.1 %). The cases of ALL on treatment had a TdT frequency of 66%. ** CONCLUSION. This study has demonstrated that TdT may be useful in the characterization of ALL. The revelation that the number of positive events has significance at either spectrum of blast cell counts suggests that TdT is useful in diagnosis and follow up of patients who are on chemotherapy. However, more work needs to be done with a larger sample size and more markers for instance CD 19, CD 10, CD 13, surface membrane immunoglobulin and cytoplasmic immunoglobulin.