Abstract

The TCL1 (T-cell leukemia/lymphoma1) oncogene is a coactivator of the AKT oncoprotein, an essential molecule in the transduction of antiapoptotic signals in T and B cells. Eμ-TCL transgenic mice with B cells with high TCL1 expression develop the aggressive phenotype of chronic lymphocytic leukemia (CLL). Studies in human CLL have found that expression of TCL1 correlates with high expression of ZAP-70 and use of unmutated IgVH genes. The expression of TCL1 may be regulated in part by microRNA, miR-29 and miR-181, which map to chromosome 11(11q). Because aberrations at 11q have been associated with poor prognosis in CLL, we interrogated the relationship between deletions at 11q and expression of TCL1 and ZAP-70. We used a direct immunophenotyping method to investigate the relative co-expression levels of TCL1 and ZAP-70 within CLL cells and examined the relationship between such levels and the proportion of leukemia cells within the CLL population bearing 11q deletions, as detected by FISH analysis. Direct staining of intracellular TCL1 protein was performed by using the monoclonal anti-TCL1 antibody (clone 1–21) labeled with Alexa647 in combination with the established ZAP-70 protocol (

NEJM
2004
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351
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893
) together with mAb directed against CD5 and B cell surface antigens. Negative staining levels were set using isotype control antibodies. FISH was performed on interphase nuclei by using uniform and cross-validated procedures at all CRC sites using the CLL-panel from Vysis. Chromosomal abnormalities were detected in 76% (520) of the 680 CLL samples analyzed. Sixteen percent of the patients had leukemia cells with monoalleleic deletions at 11q. We performed flow cytometry for intracellular co-expression TCL1 and ZAP-70 on cryopreserved samples obtained from 25 CLL patient samples with varying proportions of cells with the 11q deletion (10% to 98% abnormal cells with 11q deletion, mean 70%) and 30 CLL samples lacking any chromosomal abnormalities. We detected significantly higher levels of TCL1 in CLL cells that expressed ZAP-70 and/or unmutated IgVH genes. The ZAP-70pos cases (39/55) had a median percent of TCL1pos cells of 34% compared to 15% for the ZAP-70neg cases. The cases using unmutated IgVH genes (43/55) had a median percent of TCL1pos cells of 31%, which was greater than the 19% median observed for cases that used mutated IgVH genes. Multiparameter analyses revealed that the ZAP-70 positive fraction of each CLL clone had significantly higher levels of TCL1 than did the ZAP-70 negative cells (mean=45% versus 29%, respectively, p=0.002). We observed a significant difference between the expression levels of TCL1 for CLL cells that had deletions in 11q relative to that of CLL cells lacking any chromosomal abnormalities (mean=41% versus 18%, respectively p=0.0002). In addition, we observed a relationship between the levels of TCL1 expressed in leukemia cell populations and the relative proportion of leukemia cells with deletions at 11q. This study reveals a relationship between the levels of TCL1 expression in CLL leukemia-cell expression of ZAP-70, and the relative proportions of leukemia cells having deletions at 11q. Studies are in progress to define whether these relationships can be explained by altered expression of microRNA that map to 11q, which might also account for the noted adverse prognosis of CLL that has deletions at 11q.

Author notes

Disclosure: No relevant conflicts of interest to declare.