Prevalence and Clinical Characterization of CD20 and CD22 Expression in Pediatric Precursor B-Cell Acute Lymphoblastic Leukemia

Abstract Immunophenotypic classification of leukemia has important therapeutic and prognostic implications. In B-cell malignancies, CD20 and CD22 also represent therapeutic targets. CD20 expression in adult patients with B lineage ALL has been associated with a poor prognosis. The data are conflicting in the pediatric population and may be impacted by the type of therapy employed. A recent study of pediatric patients treated in consecutive St Jude Children’s Research Hospital Total Therapy ALL regimens observed excellent outcomes and no prognostic significance for CD20 expression (Jeha et al. Blood2006, 108:3302–3304). We retrospectively analyzed 50 consecutive patients aged 4 months to 28 years with precursor-B ALL treated with contemporary risk-adapted BFM-based ALL regimens for whom flow cytometric, genetic, and early response data were available. Cases were defined as positive for CD20 and/or CD22 expression if surface expression was identified in more than 20% of leukemic blasts. We found that CD22 was expressed at high levels (68–99%) in all patients evaluated. CD20 expression was positive in 27 (54%) of patients. CD20 expression did not correlate with known NCI prognostic features, including presenting white blood count or age. All 3 patients with BCR-ABL translocation ALL were CD20 positive. Consistent with previously published data, neither of the 2 patients with MLL-AF4 translocation were CD20 positive. There was no association of CD20 expression with trisomy 4/10/17 or TEL-AML1 status. We did not observe an association between CD20 expression and rapid early bone marrow response to therapy at day 8 or 15; 47/50 patients were in remission at day 29. At a median follow-up time of 48 months 46/50 patients were alive without relapse. These limited data do not suggest a strong association between CD20 expression and known prognostic features or early treatment response in pediatric precursor-B ALL treated with contemporary BFM therapy platforms. However, our findings of frequent expression of CD22 on precursor-B ALL blasts from children supports its consideration as a target for immunotherapy approaches in high risk or relapsed disease.