Molecular analysis of T-cell receptor (TCR) rearranging genes has been used for assessing clonality of lymphoproliferative disorders and for tracking the persistence of minimal residual disease in those cases where a clonality marker (i.e. cytogenetic translocations) was not available.

Fifty four pediatric patients with acute lymphoblastic leukemia (ALL) have been studied at the onset of the disease. We analyzed TCR δ and γ genes because of the high percentage of rearrangements reported in B lineage ALL and for the relative low number of germline V, D, J gene segments.

DNA was isolated from bone marrow, digested with different restriction enzymes (ECORI, HINDIII, BGLII) and, after Southern blot analysis, TCR δ locus was studied using TCRDJ1 probe. PCR with specific primers allowed to define exactly the gene segments involved in the rearrangement.

In B lineage ALL we found only incomplete rearrangements with a high prevalence of the type Vδ2Dδ3 (65%) and Dδ2Dδ3 (19% of the rearranged cases), whereas in T-lineage ALL the most common rearrangement found was complete VJ.

TCR γ rearrangements were analyzed by PCR, using different combinations of Vγ and Jγ primers. Rearrangement monoclonality was assessed after running the PCR products on polyacrylamide gels followed by silver staining. The most common rearrangements involved the Vγl family(52% of rearranged cases). Moreover, 26 cases were sequenced (directly or after cloning) and in all of them it was possible to identify a clonospecific probe. The hypervariable region ranged from 3 to 10 bases in Vδ2Dδ3 rearrangements and from 10 to 18 bases in Vγl cases. The patient specific probe obtained is useful to monitor the persistence of blasts in remission samples.