Only 5 cases (4 IM, 1 TCRαβ) expressed CD13 and CD33.

Five cases were classified as noninformative for pTα and 16 for RAG-1, including 2 IM, 6 pre-αβ, 6 TCRαβ, and 4 TCRγδ. pTα and RAG-1 expression were closely correlated, with each expressed in 57% of cases overall; 47 expressed both transcripts, and 37 expressed neither. pTα expression in the absence of RAG-1 was only seen in 2 IM, and isolated RAG-1 expression was seen in 2 IMβ and 1 DN TCRαβ. pTα and RAG-1 negativity was restricted to IM, TCRγδ, and TCRαβ SP/DN T-ALLs.

TCRδ configurations refer to T-ALL cases unless specified as (rearranged) alleles. GL indicates germline; R, rearranged; Del, deleted. TCRδ rearrangement on at least one allele was seen by Southern blot analysis in 75% of cases. In total, it was possible to identify 108 TCRδ rearrangements in 85 T-ALLs. These were classified as non–T-restricted VD ior DD, immature DJ, or complete V(D)J rearrangements.

Four pre-αβ, 3 TCRαβ, and 1 TCRγδ were TCRδ multiplex PCR negative and were not analyzed by Southern blot, thus preventing distinction between a germline, bilateral deletion, and an unidentified rearranged profile.

Because the TCRγ locus does not contain D segments, we classified T-ALLs as demonstrating an immature TCRγ recombination if a rearrangement involving Vγ9, Vγ10, Vγ11, JP, and/or JP1/2 (3′Vγ-5′Jγ) was observed on at least one allele, and as demonstrating end-stage if only Vγf1-Jγ1/2 rearrangements (5′Vγ-3′Jγ) were observed. TCRγ rearrangement on at least one allele was seen in 89% of cases. Most rearranged TCRγ alleles involved the Vγf1-Jγ1/2 (60%), Vγ10, and Vγ11 pseudogenes (22%), and Vγ9 (18%). Twenty-six JP1/2 and 2 JP (Vγf1) rearrangements were identified.

These cases probably correspond to a failure of the Vβ family-specific primers to recognize the functional rearrangement, corresponding to a 9% false-negative rate.