We have previously demonstrated that cystatin E/M (CST6), elevated in a subset of multiple myeloma (MM) patients lacking osteolytic lesions (OL), suppresses MM bone disease by blocking osteoclast differentiation and function. CST6 is a secreted type 2 cystatin, a cysteine protease inhibitor that regulates lysosomal cysteine proteases and the asparaginyl endopeptidase legumain. We have developed B cell maturation antigen (BCMA)-CST6-chimeric antigen receptor (CAR) T cells, which lyse MM cells and release CST6 proteins. Our in vitro studies show that these CAR-T cells suppress differentiation and formation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts. Using xenografted MM mice, bioluminescence images show that both BCMA-CAR-T and BCMA-CST6-CAR-T cells inhibit MM growth to a similar extent. Reconstructed micro-computed tomography (µCT) images reveal that BCMA-CST6-CAR-T cells, but not BCMA-CAR-T cells, prevent MM-induced bone damage and decrease osteoclast numbers. Our results provide a CAR-T strategy that targets tumor cells directly and delivers an inhibitor of bone resorption.

中文翻译：

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BCMA 和 CST6 特异性 CAR T 细胞裂解多发性骨髓瘤细胞并抑制小鼠溶骨性病变。

我们之前已经证明，胱抑素 E/M (CST6) 在缺乏溶骨性病变 (OL) 的多发性骨髓瘤 (MM) 患者亚群中升高，通过阻断破骨细胞分化和功能来抑制 MM 骨病。CST6 是一种分泌型 2 型胱抑素，一种半胱氨酸蛋白酶抑制剂，可调节溶酶体半胱氨酸蛋白酶和天冬酰胺酰内肽酶 legumain。我们开发了 B 细胞成熟抗原 (BCMA)-CST6-嵌合抗原受体 (CAR) T 细胞，可裂解 MM 细胞并释放 CST6 蛋白。我们的体外研究表明，这些 CAR-T 细胞可抑制抗酒石酸酸性磷酸酶 (TRAP) 阳性破骨细胞的分化和形成。使用异种移植的 MM 小鼠，生物发光图像显示 BCMA-CAR-T 和 BCMA-CST6-CAR-T 细胞抑制 MM 生长的程度相似。重建的微计算机断层扫描 (μCT) 图像显示，BCMA-CST6-CAR-T 细胞（而非 BCMA-CAR-T 细胞）可以预防 MM 诱导的骨损伤并减少破骨细胞数量。我们的研究结果提供了一种直接靶向肿瘤细胞并提供骨吸收抑制剂的 CAR-T 策略。