Expression of Transmembrane Adaptors Is Specific in Distinct Childhood Acute Lymphoblastic Leukaemia Subgroups and Indicates Early Treatment Response in T-ALL.

Transmembrane adaptor proteins could play an important role in the development of ALL. They are key mediators of signalisation cascades controlling development and proliferation of lymphocytes. In animal model, variation in expression status of adaptor proteins can induce a malignant-like transformation. We analysed expression of membrane adaptor molecules LAT, NTAL and LIME at the mRNA level by real-time quantitative reverse-transcriptase polymerase chain reaction. In our study we assessed the expression levels in 33 patients with B-cell precursor ALL (BCP-ALL) and 36 patients with T-ALL at the time of diagnosis. Sorted and unsorted bone marrow/peripheral blood samples of volunteer donors were used as controls. To determine the expression levels in normal immature thymocytes we analysed sorted cells from the normal thymuses taken from children undergoing heart surgery. We used various differentiation markers of both B- (CD10, CD19, and CD20) and T-lineage (CD1a, CD3, CD4, CD7, CD8) for cell-sorting to compare the leukaemic samples with the most adequate control in terms of maturation status of the cells. Informed consents were obtained from all volunteer donors or their guardians. We divided the BCP-ALL cases into 4 subgroups (MLL+ infant ALL (n=5), TEL/AML1+ ALL (n=12), hyperdiploid ALL (n=8) and diploid/fusion gene negative ALL (n=8)). Within these subgroups, TEL/AML1 leukaemias show a distinct pattern of adaptor molecules expression. Compared to the hyperdiploid cases, which should be the closest ALL subtype in terms of the differentiation status, maturity of the blasts, biological and prognostic features, the TEL/AML1 patients present with significantly higher expression of LAT and LIME (p=0.04 and p=0.03, respectively) and significantly lower NTAL levels (p=0.001). In T-ALL the expression level of NTAL clearly separates patients into 2 distinct groups - with low and high NTAL expression. The two groups are not distinguishable using other variables (immunophenotype, cytogenetics, age at diagnosis, initial leukocyte count). However, the NTAL-high and -low groups differ in an early response to chemotherapy. While half of the patients (5/10) with low NTAL expression respond poorly to initial treatment (= prednisone poor responders), vast majority (18/21) of the NTAL-high group show good prednisone response and the NTAL expression in the prednisone poor vs. good responders reaches borderline statistical significance (p=0.05). As NTAL is a putative tumour suppressor gene acting probably through competitive inhibition of LAT and thus decreasing the phosphorylation level of Src-kinases, the differences in NTAL expression could explain the early treatment response variability. Our data show that expression of membrane adaptor molecules on leukaemic blasts is specific in some ALL subgroups - particularly in TEL/AML1+ ALL. Moreover, we demonstrate that the variable expression may play an important role in early treatment response in T-ALL. In addition to the ALL data, we show for the first time a detailed analysis of adaptor molecules expression dynamics during normal human lymphocyte differentiation.