Classification of NK-Large Granular Lymphocytic Leukemia By CD56 Expression
Authors: Li Yuxi , Yuan Jingjing , Cui Rui , Yu Ying , Huang Yanshan , Yan Yuting , Sun Jingwen , Wang Tingyu , Lyu Rui , Wenjie Xiong , Wang Qi , LIU Wei , An Gang , Sui Weiwei , Xu Yan , Huang Wenyang , Zou Dehui , Zhang Fengkui , Wang Huijun , Qiu Lugui , Yi Shuhua 
Published: December 2024

Introduction
Large granular lymphocytic leukemia (LGLL) is a rare chronic lymphoproliferative disease of T cell and natural killer (NK) cell lineage. Less than 10% of cases are NK-large granular lymphocytic leukemia (NK-LGLL) (Zawit et al. 2021). Mature NK cells could be divided into two subsets, CD56dim and CD56bright. The CD56dim NK-cell subset exhibits a higher level of natural cytotoxic activity compared to the CD56bright NK-cell subset, which, in turn, is capable of producing abundant cytokines (Cooper, Fehniger, and Caligiuri 2001). In this study, we conducted an analysis of a large cohort with 47 NK-LGLL patients, finding that patients presenting CD56 dim or negative expression on NK-LGLs had more severe symptoms and worse outcomes.
Methods
Between January 2014 and July 2023, 47 patients diagnosed with NK-LGLL were collected from the Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College. All the patients met the recommended diagnostic criteria for LGLL(Lamy, Moignet, and Loughran 2017). NK subtype was defined by flow cytometry analysis using common surface markers showing CD3−/CD16+, or CD56+ pattern, and cells were considered antigen partial positive if CD56 antibody staining was between 20%-80%. To perform subgroup analysis, we incorporated partial CD56 positive into the negative group since mature NK cells are CD56-positive.
Results
With regards to clinical and biological features of the 47 NK-LGLL cases, more than half of the patients (61.7%) presented symptoms (including cytopenia and splenomegaly) at the time of visit, among which anemia was the primary clinical manifestations observed in 57.4%. Pure red cell aplasia (PRCA) was found in 14.0%. 23 of 37 (62.2%) did not exhibit any of the five assessed KIR, when the remaining (37.8%) showed a restrictive pattern, predominantly of CD158i (27.0%). The next generation sequencing was available for 32/47 (68.1%) patients, STAT3 (13/32, 40.6%) was the most frequently mutated gene. With a median follow-up of 56.2 months (range 6.7 to 112.3 months), more than half (27/47, 57.4%) of patients required treatment. The 5-year OS was 95.2%. The median number of treatment lines was 1 (range 1-4). MTX-based therapy and CsA-based therapy were delivered in 51.9% (14/27) patients and 29.6% of patients, respectively, as a first-line treatment, when no significant difference in response rate were found between the two therapies (ORR: 85.7% vs 87.5%, P = 1.000; CRR: 50.0% vs 37.5%, P = 0.675).
To further, we classified 47 patients into the CD56 diminished group (28/47, 59.6%) and CD56 normal group (19/47, 40.4%). Notably, we found that diminished CD56 patients displayed a skewed sex ratio of males (89.3% vs 31.6%, P &lt; 0.001), and a more aggressive clinical features encompassing neutropenia (67.9% vs 0, P &lt; 0.001), anemia (85.7% vs 15.8%, P &lt; 0.001), splenomegaly (42.9% vs 10.5%, P = 0.024), obvious fibrosis of bone marrow (92.3% vs 50.0%, P = 0.006), more frequent occurrence of STAT3 mutations (61.9% vs 0, P = 0.003) and a higher necessity for therapeutic intervention (89.3% vs 15.8%, P &lt; 0.001). None of the thirteen patients in the normal CD56 group showed indications for treatment at diagnosis compared to four patients in the diminished CD56 group. The 4-year time to first treatment TTFT was shorter in diminished CD56 group compared to normal CD56 group without significance, given the limited number of terminal events (66.7% vs 100.0%, HR = 0.02, 95%CI: 0.0001-1.69, P = 0.083). Furthermore, among the 23 patients treated with first-line immunosuppressors, the patients with diminished CD56 expression showed shorter PFS although without significant difference compared to normal CD56 expression group (median PFS: 26.3 months vs not reached, HR = 0.267, 95%CI: 0.05-1.36, P = 0.112).
Conclusion
In conclusion, our findings indicate an indolent course and excellent response to immunosuppressive therapies of NK-LGLL. To further we classify NK-LGLL by CD56 and highlight that diminished expression of CD56 correlates with a unique cluster of biological features, more symptomatic disease, and a more aggressive disease course. This research contributes significantly to the classification and deeper understanding of NK-LGLL, paving the way for more refined treatment strategies and a deeper exploration of the underlying mechanisms driving this complex disease.