T-Cell Prolymphocytic Leukemia: Diagnosis, Pathogenesis, and Treatment

T-cell prolymphocytic leukemia (T-PLL) is a rare and aggressive neoplasm of mature T-cells. Most patients with T-PLL present with lymphocytosis, anemia, thrombocytopenia, and hepatosplenomegaly. Correct identification of T-PLL is essential because treatment for this disease is distinct from that of other T-cell neoplasms. In 2019, the T-PLL International Study Group (TPLL-ISG) established criteria for the diagnosis, staging, and assessment of response to treatment of T-PLL with the goal of harmonizing research efforts and supporting clinical decision-making. T-PLL pathogenesis is commonly driven by T-cell leukemia 1 (TCL1) overexpression and ATM loss, genetic alterations that are incorporated into the TPLL-ISG diagnostic criteria. The cooperativity between TCL1 family members and ATM is seemingly unique to T-PLL across the spectrum of T-cell neoplasms. The role of the T-cell receptor, its downstream kinases, and JAK/STAT signaling are also emerging themes in disease pathogenesis and have obvious therapeutic implications. Despite improved understanding of disease pathogenesis, alemtuzumab remains the frontline therapy in the treatment of naïve patients with indications for treatment given its high response rate. Unfortunately, the responses achieved are rarely durable, and the majority of patients are not candidates for consolidation with hematopoietic stem cell transplantation. Improved understanding of T-PLL pathogenesis has unveiled novel therapeutic vulnerabilities that may change the natural history of this lymphoproliferative neoplasm and will be the focus of this concise review.

T-cell large granular lymphocyte leukemia of donor origin after allogeneic bone marrow transplantation

A 39-year-old man with chronic myeloid leukemia in accelerated phase underwent allogeneic bone marrow transplantation (BMT). At 6 months after BMT, lymphocytosis (WBC count, 23,100/microL [23.1 x 10(9)/L]; 80% (0.80) large granular lymphocytes [LGLs]) occurred. The LGLs were CD3+CD4-CD8+, with clonally rearranged T-cell receptor gamma gene, and of donor origin, as shown by analysis of polymorphic microsatellite markers. Epstein-Barr virus was not present. The diagnosis, therefore, was consistent with T-cell large granular lymphocytic (T-LGL) leukemia. Corticosteroids controlled the LGL count, but progressive pancytopenia led to death 4 months later. Retrospective analysis showed that the T-LGL leukemia apparently had arisen as early as 3 months after BMT. The distinguishing features of this case included donor origin, neoplastic nature, and the aggressive fatal outcome.