[Successful treatment of pure red cell aplasia with cyclosporin in a patient with T-cell large granular lymphocytic leukemia harboring the STAT3 D661V mutation].

T-cell large granular lymphocyte (T-LGL) leukemia is a chronic T-cell monoclonal disease that is occasionally associated with pure red cell aplasia (PRCA). A 71-year-old previously healthy man complained of physical fatigue and exhibited anemia (hemoglobin, 10.5 g/dl) with lymphocytosis (76%) showing LGL. The LGL cells expressed CD3, CD7, CD8, and T-cell receptor (TCR) -α/β. TCR-β/γ gene rearrangement was positive. He was thus diagnosed with CD8＋ T-LGL leukemia. Anemia progressed with low reticulocyte count (0.11%), and the patient became blood transfusion-dependent, but no distinct abnormality caused the anemia. Bone marrow aspiration revealed an increase in lymphocytes (33.6%) and a decrease in erythroblasts (M/E ratio, 6.1). He was thus diagnosed with T-LGL-associated PRCA. Oral cyclosporin A administration resulted in prompt improvement of anemia, suggesting its high sensitivity. Whole-exome sequencing of his peripheral blood DNA revealed somatic mutations in 33 genes, including the STAT3 gene, implying their roles in T-LGL leukemia.