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Abstract
To evaluate the clinical implications of CD45 expression in acute childhood lymphoblastic leukemia (ALL), we measured the CD45 expression of blast cells from 133 untreated patients with childhood B-precursor ALL (n=118) or T-ALL (n=15). CD45 expression (≥20%) was detected in all 15 cases (100%) of T-ALL, and 101 cases (86%) of B-precursor ALL. In 122 cases, the fluorescence intensity of the CD45 expression was measured as a relative value; the ratio of average linear values (RALV) of CD45 on the blasts to that on CD3-positive T-lymphocytes from the same specimen. The expression was more intense in the T-ALL cases than in the B-precursor ALL cases (RALV, mean ± SE: T-ALL 0.230 ± 0.04 vs. pro-B ALL 0.150 ± 0.012/pre-B ALL 0.153 ± 0.019, p < 0.05). However, the intensity of the CD10, CD19, CD20 and CD34 antigen immunoreactivity did not correlate with the CD45 expression. Patients with hyperdiploidy (chromosome number >50) showed significantly lower levels of CD45 expression than patients with t(1;19) or normal karyotypes (RALV, mean ± SE: 0.081 ± 0.022 vs. 0.133 ± 0.03/0.143 ± 0.019, p < 0.05). Other clinical features such as age, gender and WBC count did not correlate with CD45 expression. The prognostic implications of CD45 expression were studied in non-high-risk (low-risk + intermediate-risk) (n=60) and high-risk patients (n=52) with B-precursor ALL who had been treated with the risk-directed protocol of ALL-941 trial. Although CD45 expression did not correlate with the event-free survival (EFS) of the non-high-risk patients, there was a significant correlation between the expression levels and the EFS of the high-risk patients: the 3-year EFS rate of the CD45lowgroup (n=26, RALV=0.017 - 0.132) was 88 ± 7% versus the CD45highgroup (n=26, RALV=0.133 - 0.450) at 34 ± 24% (p < 0.05). These results show that the levels of expression of the CD45 antigen on leukemic lymphoblasts are significantly correlated with the clinical features and prognosis of childhood ALL.