International Journal of Pediatrics 3 Table 1: Panel of Monoclonal Antibodies used in this study for immunophenotypic acute leukemia characterization. First step Second step B-cell markers CD79a, CD19, CD22 cytIg, sIg T-cell markers sCD3, cyCD3, CD7 CD1a, CD4, CD5, CD8 Myeloid markers CD13, CD33, anti-MPO CD117, CD41, CD61, GlycoA No speciﬁc markers CD45 CD34, DR, TdT, CD10 sIg: surface immunoglobulin, cyIg: cytoplasmic immunoglobulin, sCD3: surface CD3, cyCD3: cytoplasmic CD3, MPO: myeloperoxidase, Glyco A: Glycophorin A, DR: HLA-DR: antigen, TdT: terminal deoxynucleotidyl transferase. 3.1. B-Cell-Lineage ALLs 3.1.1. Precursor B-Cell. 216 children with pB-cell phenotype were studied. There were 99 females and 117 males with a male/female ratio of 1.18 : 1 and median age of 6 years. All tested pB-cell-lineage ALLs expressed CD19. Almost all cases have cytoplasmic CD79a and surface CD22, the CD20 is present in more than one-half (54.2%) of cases tested for this antigen. CD10, terminal deoxynucleotidyl transferase (TdT), HLA-DR, and CD45 were detectable in 91.2%, 89.8%, 98.1%, and 87% of cases, respectively, and cells in more than 74% of cases express CD34. In 40% of CD34 positives cases, CD45 is negative or weak. CD13 and/or CD33 occur more frequently (57.4%). CD7 is also present in few cases (3.2%). Immunologic subclassiﬁcation of 58 pB cell ALLs cases tested for cytoplasmic and surface immunoglolobin since August 2006 revealed 40 early pre-B (69%), 16 pre-B (27.6%), and 2 transitional pre-B (3.4%). 3.1.2. B-Cell ALL. Four cases with L3 morphology by the FAB criteria were classiﬁed as B-cell ALL. All of them were males with ages 5, 6, 9, and 13 years. The blasts were CD19+, CD22+ in all cases and showed dimly expression of CD10. CD45 was bright, with HLA-DR positivity in all cases. The surface light chain immunoglobin expressed was Kappa in one case and lambda in 3 cases. The leukemic cells were CD34− and TdT− in all cases. 3.2. T-Cell-Lineage ALLs. Fifty nine children with T-cell ALL were studied. There were 44 male and 15 female (male/female ratio 2.93 : 1) with ages ranging from 0.5 to 17 years and median age of 9 years. Based on their reactivity with various anti-T-cell mon- oclonal antibodies (Table 3), all tested T-cell ALL cells have surface CD7 and cytoplasmic CD3 (cCD3) antigens. CD5 was found in 98.2% cases and 70.5% express TdT. CD1a, surface CD3, and CD4 are detected in about 80% to 83% of cases. CD10 was found in 10 cases (21.3%) and absent in 37 (78.7%) of 47 T-cell ALLs cases tested for CD10. Except for 2 cases, none of the B-cell associated antigens was expressed on any T-cell ALLs cases. Myeloid antigen expression CD13 and/or CD33 was examined, and 33.9% of cases tested positive for at least one of the two markers, more frequently CD13 than CD33, and two cases expressed the two myeloid antigens. The immunologic subtypes, deﬁned according to the expression of CD1a and CD3, were as follows: 3.6% pro-T, 80.4% common thymocyte, and 16.1% mature thymocyte. 3.3. CD10 Expression. The correlation of CD10 positivity with age, leukocyte count at presentation, gender, and FAB morphology at presentation was analyzed (Table 4). CD10 expression was found in 197 cases of pB-ALL (91.2%) and 10 cases of the T-ALL (21.3%). CD10 expression in pB-ALL was frequent in patients with age range 1–10 years and having low leukocyte count (P, not signiﬁcant). In contrast, children with pB-ALL CD10− phenotypes were more frequently older than 10 years and have a high leukocyte count (P, not signiﬁcant). CD10 positivity was less common in T cell lineage and was associated with female sex and lower leukocyte count. The lack of CD10 in cases of T cell ALL was signiﬁcantly (P = .038) associated with patients between 1 and 10 years. 3.4. Lineage Heterogeneity. Lineage heterogeneity was found in both B-cell and T-cell lineage ALL with 144 (52.4%) cases having one or two myeloid associated antigens (CD13, CD33) expressed on their blasts cells. Most of them were of pB lineage (n = 124), T-lineage about (n = 20). The most common antigen expressed was the CD13 marker which was present on 100/216 (46.3%) pB-cell ALL and 13/59 (22%) T-cell ALL cases. In nine cases (3.3%) lymphoid antigens (CD7, CD19, and CD22) were expressed. Two T-cell ALL patients’ cells expressed CD19 or CD22 and cells of seven pB-cell ALL cases expressed CD7. The leukemic blast of two pB-cell ALL cases expressed also CD13 and CD33 with CD7. 4. Discussion and Conclusion The present work gives the ﬁrst large series of unselected acute lymphoblastic Leukemia, providing an idea about the distribution of ALL subtype in Moroccan children. Almost the majority of children with ALL in Morocco are treated at pediatric centers (Onco-haematology-Pediatric services of University Hospital of Rabat and Casablanca) [6, 7], and about 92% had a three color cytometric immunophenotyp- ing performed at the National Hygiene Institute laboratory. Immunophenotyping was used in order to analyze retro- spectively 279 children with acute lymphoblastic leukemia. The panel of markers proposed considers two steps; it should lead to cost saving without loss of valuable information [9]. With the ﬁrst panel we were able to identify the lineage of over 97% of childhood acute leukemia. Only less than 3% were assigned to deﬁnite lineage after staining with the second panel.