T-stem cell leukemia/lymphoma with both myeloid lineage conversion and T-specific δ recombination

We evaluated retrospectively the clinical and biological characteristics of six patients with CD7 + early T-acute lymphoblastic leukemia and lymphoma (T-ALL/LBL) originating from prothymocyte stage I (pro-T I) or II cells. Patients exhibited mediastinal mass (five of six) and lymphoadenopathy (five of six) but without leukocytosis and circulating blast cells (six of six). All patients achieved a complete remission. All but one had a relapse with a transformation to the mixed type (triphenotype—three cases, biphenotype—two cases) including myeloid features in three patients. The altered phenotypes were myeloperoxidase (MPO) + (three of five), CD13 + (four of five), CD33 + (three of five) and CD19 + (three of five). The difference for MPO-positivity were observed between the bone marrow (BM)- and lymph node (LN)-blast cells (three of three). On cytogenetic analysis, there is no common abnormality in these patients. Immunomolecular analysis revealed T-cell lineage specific δ gene rearrangements [Dδ2-Jδ1 (five of six) and Vδ1-Jδ1 (one of six)] in all cases. Furthermore, Dδ2-Jδ1 occurred even in the cases with the pro-T I phenotype. Rearrangements of TCR β, γ or immunoglobulin heavy chain genes occurred in three patients. The same rearranged band(s) appeared at both diagnosis and relapse, indicating the same originality of the pro-T leukemic cell clone (three of three). We suggest that this type of CD7 + early T-ALL/LBL was transformed from a pro-T I or II cell, such as T-stem cell leukemia/lymphoma, which is a subtype of CD7 + stem cell leukemia as defined by Kurtzberg et al. This study reveals that pro-T I and II cells might be capable of myeloid, T- and B-lymphoid differentiation, and T-cell lineage specific TCR δ recombination occurs.