CD19 and acute lymphoblastic leukemia: Leukemic cells express various markers of differentiation that allow the distinction of at least three main subtypes: Early precursor B-ALL (pro-B-ALL, CD10−, CD19+, cCD79a+, cCD22+, TdT+), Common B-ALL (CD10+) and Precursor B-ALL (pre-B-ALL, cytoplasmic μ+, sIg−, CD10+/−) [5].