Phenotypic and genotypic characteristics of human early T-cell differentiation: the T-cell acute lymphoblastic leukaemia model

Flow cytometry immunophenotyping evaluation in acute lymphoblastic leukemia: correlation to factors affecting clinic outcome

The authors conducted a flow cytometry immunophenotyping study in patients with acute lymphoblastic leukemia (ALL) from Natal, Rio Grande do Norte, Brazil. The patients (n = 126) were newly diagnosed using a panel of monoclonal antibodies: CD1a, CD2, CD3, CD4, CD7, CD8, CD10, CD13, CD33, CD14, CD19, CD22, CD79a, CD117, CD34, anti-IgM, anti-TdT, anti-HLA-Dr, and anti-human kappa and lambda light chains. Additional data, such as patients' age and gender, clinical and laboratory findings such as presence of tumor masses, lymphadenopathy, hepatomegaly, splenomegaly, leukemic infiltration in the central nervous system (CNS) were also investigated. Results showed that 56.7% of the cases were B-lineage ALL and 55% were T-cell ALL. Also, we found that males were more affected by the disease, regardless of immunological classification. The correlation between age and immunological subtypes showed that the B-lineage ALL occurred more frequently in patients aged under 15 while the T-cell ALL subtype was more frequent in adults. Immunophenotypic profiles and morphological subtypes showed a direct correlation between L3 subtype and B-lineage ALL, while L1 and L2 subtypes correlated more often with B-cell lineage and T-cell ALL, respectively. Correlation analysis between immunophenotypic and clinical profiles showed that T-cell ALL was more associated with a higher incidence of lymphadenopathy, hepatomegaly, splenomegaly and CNS leukemic infiltration, also showing a greater blast cell count in peripheral blood than the other subgroups. The presented data suggest that immunophenotyping is an important method in the diagnosis, monitoring and prognostic assessment in determining the pathological mechanisms of evolution of ALL.

The C-MYB locus is involved in chromosomal translocation and genomic duplications in human T-cell acute leukemia (T-ALL), the translocation defining a new T-ALL subtype in very young children

The C-Myb transcription factor is essential for hematopoiesis, including in the T-cell lineage. The C-Myb locus is a common site of retroviral insertional mutagenesis, however no recurrent genomic involvement has been reported in human malignancies. Here, we identified 2 types of genomic alterations involving the C-MYB locus at 6q23 in human T-cell acute leukemia (T-ALL). First, we found a reciprocal translocation, t(6;7)(q23;q34), that juxtaposed the TCRB and C-MYB loci (n = 6 cases). Second, a genome-wide copy-number analysis by array-based comparative genomic hybridization (array-CGH) identified short somatic duplications that include C-MYB (MYB(dup), n = 13 cases of 84 T-ALL, 15%). Expression analysis, including allele-specific approaches, showed stronger C-MYB expression in the MYB-rearranged cases compared with other T-ALLs, and a dramatically skewed C-MYB allele expression in the TCRB-MYB cases, which suggests that a translocation-driven deregulated expression may overcome a cellular attempt to down-regulate C-MYB. Strikingly, profiling of the T-ALLs by clinical, genomic, and large-scale gene expression analyses shows that the TCRB-MYB translocation defines a new T-ALL subtype associated with a very young age for T-cell leukemia (median, 2.2 years) and with a proliferation/mitosis expression signature. By contrast, the MYB(dup) alteration was associated with the previously defined T-ALL subtypes.

Characterization of a progenitor cell population in childhood T-cell acute lymphoblastic leukemia

A significant proportion of children with T-cell acute lymphoblastic leukemia (T-ALL) continue to fail therapy. Consequently, characterization of the cells that proliferate to maintain the disease should provide valuable information on the most relevant therapeutic targets. We have used in vitro suspension culture (SC) and nonobese diabetic-severe combined immune deficient (NOD/SCID) mouse assays to phenotypically characterize and purify T-ALL progenitor cells. Cells from 13 pediatric cases were maintained in vitro for at least 4 weeks and expanded in 8 cases. To characterize the progenitors, cells were sorted for expression of CD34 and CD4 or CD7 and the subfractions were evaluated in vitro and in vivo. The majority of cells capable of long-term proliferation in vitro were derived from the CD34+/CD4- and CD34+/CD7- subfractions. Moreover, the CD34+/CD4- or CD7- cells were the only subfractions capable of NOD/SCID engraftment. These T-ALL cells successfully repopulated secondary and tertiary recipients with equivalent levels of engraftment, demonstrating self-renewal ability. The immunophenotype and genotype of the original leukemia cells were preserved with serial passage in the NOD/SCID mice. These data demonstrate the long-term repopulating ability of the CD34+/CD4- and CD34+/CD7- subfractions in T-ALL and suggest that a cell with a more primitive phenotype was the target for leukemic transformation in these cases.

Cyclin D2 dysregulation by chromosomal translocations to TCR loci in T-cell acute lymphoblastic leukemias

Strong expression of at least one of the three D-type cyclins is common in human cancers. While the cyclin D1 and D3 genes (CCND1 and CCND3) are recurrently involved in genomic rearrangements, especially in B-cell lymphoid neoplasias, no clear involvement of the cyclin D2 gene (CCND2) has been reported to date. Here, we identified chromosomal translocations targeting the CCND2 locus at 12p13, and the T-cell receptor beta (TCRB) or the TCRA/D loci in T-cell acute lymphoblastic leukemias (T-ALLs). Expression analysis demonstrated dramatic cyclin D2 overexpression in the translocated cases (n=3) compared to other T-ALLs (total, n=89). In order to evaluate dysregulation in T-ALL with respect to normal T-cell differentiation, we analyzed CCND2 expression in normal purified human thymic subpopulations. CCND2 levels were downregulated through progression from the early stages of human T-cell differentiation, further suggesting that the massive and sustained expression in the CCND2-rearranged T-ALL cases was oncogenic. Association with other oncogene expression (TAL1, HOXAs, or TLX3/HOX11L2), NOTCH1 activating mutations, and/or CDKN2A/p16/ARF deletion, showed that cyclin D2 dysregulation could contribute to multi-event oncogenesis in various T-ALL groups. This report is the first clear evidence of a direct involvement of cyclin D2 in human cancer due to recurrent somatic genetic alterations.

Age-related phenotypic and oncogenic differences in T-cell acute lymphoblastic leukemias may reflect thymic atrophy

Postnatal thymic involution occurs progressively throughout the first 3 decades of life. It predominantly affects T-cell receptor (TCR) alphabeta-lineage precursors, with a consequent proportional increase in multipotent thymic precursors. We show that T-acute lymphoblastic leukemias (T-ALLs) demonstrate a similar shift with age from predominantly TCR expressing to an immature (IM0/delta/gamma) stage of maturation arrest. Half demonstrate HOX11, HOX11L2, SIL-TAL1, or CALM-AF10 deregulation, with each being associated with a specific, age-independent stage of maturation arrest. HOX11 and SIL-TAL represent alphabeta-lineage oncogenes, whereas HOX11L2 expression identifies an intermediate alphabeta/gammadelta-lineage stage of maturation arrest. In keeping with preferential alphabeta-lineage involution, the incidence of SIL-TAL1 and HOX11L2 deregulation decreased with age. In contrast, HOX11 deregulation became more frequent, suggesting longer latency. TAL1/LMO1 deregulation is more frequent in alphabeta-lineage T-ALL, when it is predominantly due to SIL-TAL1 rearrangements in children but to currently unknown mechanisms in adolescents and adults. LMO2 was more frequently coexpressed with LYL1, predominantly in IM0/delta/gamma adult cases, than with TAL1. These age-related changes in phenotype and oncogenic pathways probably reflect progressive changes in the thymic population at risk of malignant transformation.

Analysis of TCR, pT alpha, and RAG-1 in T-acute lymphoblastic leukemias improves understanding of early human T-lymphoid lineage commitment

T-acute lymphoblastic leukemias (T-ALLs) derive from human T-lymphoid precursors arrested at various early stages of development. Correlation of phenotype and T-cell receptor (TCR) status with RAG-1 and pT alpha transcription in 114 T-ALLs demonstrated that they largely reflect physiologic T-lymphoid development. Half the TCR alpha beta lineage T-ALLs expressed a pre-TCR, as evidenced by RAG-1, pT alpha, and cTCR beta expression, absence of TCR delta deletion, and a sCD3(-), CD1a(+), CD4/8 double-positive (DP) phenotype, in keeping with a population undergoing beta selection. Most TCR gamma delta T-ALLs were pT alpha, terminal deoxynucleotidyl transferase (TdT), and RAG-1(lo/neg), double-negative/single-positive (DN/SP), and demonstrated only TCR beta DJ rearrangement, whereas 40% were pT alpha, TdT, and RAG-1 positive, DP, and demonstrated TCR beta V(D)J rearrangement, with cTCR beta expression in proportion. As such they may correspond to TCR alpha beta lineage precursors selected by TCR gamma delta expression, to early gamma delta cells recently derived from a pT alpha(+) common alpha beta/gamma delta precursor, or to a lineage-deregulated alpha beta/gamma delta intermediate. Approximately 30% of T-ALLs were sCD3/cTCR beta(-) and corresponded to nonrestricted thymic precursors because they expressed non-T-restricted markers such as CD34, CD13, CD33, and CD56 and were predominantly DN, CD1a, pT alpha, and RAG-1 low/negative, despite immature TCR delta and TCR gamma rearrangements. TCR gene configuration identified progressive T-lymphoid restriction. T-ALLs, therefore, provide homogeneous expansions of minor human lymphoid precursor populations that can aid in the understanding of healthy human T-cell development.