CALM-AF10 is a common fusion transcript in T-ALL and is specific to the TCR-γδ lineage

The t(10;11)(p13-14;q14-21) associated with CALM-AF10 is considered to be rare and associated with a variety of acute lymphoid and myeloid leukemias. Twelve (9%) of 131 unselected T-cell acute lymphoid leukemias (T-ALLs) expressed CALM-AF10 by reverse transcription-polymerase chain reaction or fluorescence in situ hybridization (or both), including 8% of children and 10% of adults, of whom only half demonstrated a t(10;11) by classical cytogenetics. CALM-AF10 was not found in T-cell-receptor alphabeta (TCRalphabeta) lineage T-ALLs, as defined by expression of TCRalphabeta, cytoplasmic TCRbeta, or TCRbeta VDJ rearrangement in immature cytoplasmic TCRbeta(-) cases, compared with 19% of TCRgammadelta T-ALLs and 33% of immature delta/gamma T-ALLs. The latter differed from their CALM-AF10(-) immature counterparts by a CD5(+)/CD2(-) phenotype, as found in TCRgammadelta but not TCRalphabeta T-ALLs and in their TCRgamma and TCRdelta configurations, altogether suggesting that CALM-AF10(+) immature delta/gamma T-ALLs are TCRgammadelta precursors and that, within T-ALL, CALM-AF10 is specific for this lineage. Nine of 12 immature CALM-AF10 T-ALLs demonstrated 3' fusion transcripts, whereas 6 of 7 TCRgammadelta T-ALLs demonstrated 5' fusion transcripts. The latter retain the AF10 extended LAP/PHD domain necessary for homo-oligomerization. All 8 patients with CALM-AF10(+) TCRgammadelta T-ALLs are alive, compared with only 3 of 12 with immature CALM-AF10(+) T-ALLs. Six CALM-AF10(+) non-T acute leukemias all expressed CD7 and demonstrated T-restricted TCRdelta rearrangements, suggesting that they may also be related to the TCRgammadelta lineage. CALM-AF10 is therefore the most common fusion protein in T-ALL. It requires molecular and immunophenotypic characterization for appropriate prognostic evaluation and should be included in diagnostic screening panels of T-ALL and immature acute leukemias. Analysis of immature CALM-AF10(+) leukemias will also facilitate analysis of the early stages of development of the TCRgammadelta lineage.