Thomas Tousseyn

JAK3 mutants transform hematopoietic cells through JAK1 activation, causing T-cell acute lymphoblastic leukemia in a mouse model

JAK3 is a tyrosine kinase that associates with the common γ chain of cytokine receptors and is recurrently mutated in T-cell acute lymphoblastic leukemia (T-ALL). We tested the transforming properties of JAK3 pseudokinase and kinase domain mutants using in vitro and in vivo assays. Most, but not all, JAK3 mutants transformed cytokine-dependent Ba/F3 or MOHITO cell lines to cytokine-independent proliferation. JAK3 pseudokinase mutants were dependent on Jak1 kinase activity for cellular transformation, whereas the JAK3 kinase domain mutant could transform cells in a Jak1 kinase-independent manner. Reconstitution of the IL7 receptor signaling complex in 293T cells showed that JAK3 mutants required receptor binding to mediate downstream STAT5 phosphorylation. Mice transplanted with bone marrow progenitor cells expressing JAK3 mutants developed a long-latency transplantable T-ALL-like disease, characterized by an accumulation of immature CD8(+) T cells. In vivo treatment of leukemic mice with the JAK3 selective inhibitor tofacitinib reduced the white blood cell count and caused leukemic cell apoptosis. Our data show that JAK3 mutations are drivers of T-ALL and require the cytokine receptor complex for transformation. These results warrant further investigation of JAK1/JAK3 inhibitors for the treatment of T-ALL.

Severe acute kidney injury as presentation of Burkitt's lymphoma

We discuss a case of acute kidney injury (AKI) at a very young age caused by primary lymphomatous renal infiltration due to Burkitts lymphoma and analyse the literature on this rare condition. At presentation, clinical examination showed impressive bilateral nephromegaly and hypertension. Blood analysis indicated severe AKI, mild anaemia and normal serum electrolytes. There were no signs of tumour lysis syndrome. Urine sediment was normal, with neither haematuria nor proteinuria. Abdominal ultrasound demonstrated bilateral renal enlargement (+12 SD), with increased corticomedullar differentiation. MRI demonstrated the presence of a homogenous renal enlargement with features of an infiltrative lesion. Ultimately, microscopic and immunohistochemical analysis of the renal biopsy confirmed the diagnosis of Burkitts lymphoma. Early and aggressive therapy is the key to ensure a good outcome.