RAG1 and acute lymphoblastic leukemia: TLX1+ T-ALL samples exhibit a predominantly CD1+CD3- surface phenotype with high levels of TCR recombination activating gene (RAG1) expression and TCRβ rearrangement on at least one allele; but they often lack cytoplasmic and surface TCRβ expression, suggesting that the onset of malignant transformation occurs before β-selection [32-36].