Myeloproliferative neoplasms (MPNs) are clonal hematopoietic cell diseases characterized by gain-of-function mutations in the JAK2, CALR, and MPL genes [1, 2]. CALR is a chaperone protein that resides primarily in the endoplasmic reticulum and is involved in various cellular processes, including cell adhesion. CALR mutations in exon 9 are the second most frequently detected mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) [1, 2]. Mutant CALR enables pathogenic binding with MPL, leading to ligand-independent activation of the MPL signaling pathway [3,4,5]. Therefore, the mutant CALR/MPL complex is regarded as an important target for controlling CALR-mutated MPNs [1]. JAK2 mutations are the most frequently detected in MPNs [1, 2]. Cell line models harboring JAK2 mutations, such as HEL 92.1.7 (HEL), not only mimic MPNs in in vitro experiments, but also serve as a useful resource in developing therapeutics targeting mutant JAK2 [6]. MARIMO is a unique cell line that expresses a mutant CALR [7, 8]. However, MARIMO cells do not express MPL, which is accompanied by inactivation of its downstream signaling pathway, including JAK/STAT/ERK. Therefore, MARIMO cells may not be suitable for studying oncogenic functions of mutant CALR [7, 8]. To the best of our knowledge, no other cell lines have been described as ideal models for oncogenic functions of mutant CALR. Here, we report a patient-derived megakaryocytic leukemia cell line, designated ELC52, which is driven by a mutant CALR, and is a potentially useful model for investigating megakaryocyte biology.

We established a leukemia cell line designated ELC52 (ET-overt Leukemia cells with a CALR 52-bp deletion). ELC52 cells were obtained from bone marrow of a 67-year-old male patient. The patient was initially diagnosed with an ET. After a stable phase of 26 years of treatment with hydroxycarbamide or busulfan, myeloid leukemia transformation occurred. The patient was admitted because of fever, fatigue, and priapism. A full blood count showed a hemoglobin level of 8.0 g/dL, platelet count of 14.2 × 10⁹/L, and white blood cell count of 18.6 × 10⁹/L, of which myeloperoxidase-positive blasts accounted for 37%. Bone marrow samples for in vitro culture, in which immature blasts accounted for 68.8% after five months of leukemia transformation, were collected under protocols approved by the institutional review board of Fujita Health University and with written, informed consent in accordance with the Declaration of Helsinki.

骨髓增生性肿瘤 （MPN） 是一种克隆性造血细胞疾病，其特征是 JAK2、CALR 和 MPL 基因的功能获得性突变 [1， 2]。CALR 是一种伴侣蛋白，主要存在于内质网中，参与各种细胞过程，包括细胞粘附。外显子 9 中的 CALR 突变是原发性血小板增多症 （ET） 和原发性骨髓纤维化 （PMF） 中第二常见的突变 [1， 2]。突变型 CALR 能够与 MPL 发生致病性结合，导致 MPL 信号通路的配体非依赖性激活 [3,4,5]。因此，突变型 CALR/MPL 复合物被视为控制 CALR 突变型 MPN 的重要靶标 [1]。JAK2 突变在 MPN 中最常检测到 [1， 2]。携带 JAK2 突变的细胞系模型，如 HEL 92.1.7 （HEL），不仅在体外实验中模拟 MPN，而且可作为开发靶向突变 JAK2 的疗法的有用资源 [6]。MARIMO 是一种表达突变 CALR 的独特细胞系 [7， 8]。然而，MARIMO 细胞不表达 MPL，MPL 伴随着其下游信号通路的失活，包括 JAK/STAT/ERK。因此，MARIMO 细胞可能不适合研究突变体 CALR 的致癌功能 [7， 8]。据我们所知，没有其他细胞系被描述为突变 CALR 致癌功能的理想模型。在这里，我们报告了一种患者来源的巨核细胞白血病细胞系，命名为 ELC52，它由突变体 CALR 驱动，是研究巨核细胞生物学的潜在有用模型。

我们建立了一种命名为 ELC52 的白血病细胞系（具有 CALR 52 bp 缺失的 ET 显性白血病细胞）。ELC52 细胞取自一名 67 岁男性患者的骨髓。患者最初被诊断为 ET。在用羟基脲或白消安治疗 26 年的稳定期后，发生了髓系白血病转化。患者因发热、疲劳和异常勃起入院。全血细胞计数显示血红蛋白水平为 8.0 g/dL，血小板计数为 14.2 × 10⁹/L，白细胞计数为 18.6 × 10⁹/L，其中髓过氧化物酶阳性原始细胞占 37%。用于体外培养的骨髓样本，其中白血病转化 5 个月后未成熟原始细胞占 68.8%，根据藤田医科大学机构审查委员会批准的方案收集，并根据赫尔辛基宣言获得书面知情同意。