可溶性 CD26 (sCD26) 是一种具有二肽基肽酶 (DPP4) 酶活性的糖蛋白，有助于结直肠癌和晚期腺瘤的早期诊断，并且已在各种其他类型的癌症和疾病中进行了研究，包括用于预后目的。该领域的最新研究证实，大多数（尽管不是全部）血清/血浆 sCD26 与炎症有关。不同免疫细胞的 sCD26 脱落和/或分泌正在研究中，并且血液 DPP4 活性水平与蛋白质滴度没有很强的相关性。该酶的一些主要底物是参与免疫细胞迁移的关键趋化因子，可溶性和细胞表面 CD26 都可以结合腺苷脱氨酶 (ADA)，腺苷脱氨酶是一种参与免疫抑制剂细胞外腺苷代谢的酶。值得注意的是，T 细胞富含 CD26 表达，并且在小鼠肿瘤模型中，肿瘤浸润淋巴细胞表现出与肿瘤消退相关的 CD26 百分比升高。我们在结直肠癌根治性切除术后的随访中采用 sCD26 作为生物标志物，以早期检测肿瘤复发。在类风湿性关节炎中也观察到了使用不同的生物疾病缓解抗风湿药物（包括 Ig-CTLA4）治疗后的变化。最近，在使用人源化抗 CD26 抗体进行癌症免疫治疗的 I 期试验后，血清可溶性 CD26/DPP4 滴度变异被提议作为潜在的预后生物标志物。我们建议，除了众所周知的炎症生物标志物（例如已用作免疫检查点免疫治疗信息的 CRP）之外，动态监测 sCD26/DPP4 变化可能表明治疗后续步骤中的耐药或反应。由于表达 CD26 的肿瘤细胞也可以产生 sCD26，因此讨论了从非免疫系统来源的 sCD26 中分选免疫来源的 sCD26 的可能性。

Soluble CD26 (sCD26), a glycoprotein with dipeptidyl peptidase (DPP4) enzymatic activity, can contribute to early diagnosis of colorectal cancer and advanced adenomas and has been studied, including for prognostic purposes, across various other types of cancer and disease. The latest research in this field has confirmed that most, though not all, serum/plasma sCD26 is related to inflammation. The shedding and/or secretion of sCD26 from different immune cells are being investigated, and blood DPP4 activity levels do not correlate very strongly with protein titers. Some of the main substrates of this enzyme are key chemokines involved in immune cell migration, and both soluble and cell-surface CD26 can bind adenosine deaminase (ADA), an enzyme involved in the metabolism of immunosuppressor extracellular adenosine. Of note, there are T cells enriched in CD26 expression and, in mice tumor models, tumor infiltrating lymphocytes exhibited heightened percentages of CD26+ correlating with tumor regression. We employed sCD26 as a biomarker in the follow-up after curative resection of colorectal cancer for the early detection of tumor recurrence. Changes after treatment with different biological disease-modifying antirheumatic drugs, including Ig-CTLA4, were also observed in rheumatoid arthritis. Serum soluble CD26/DPP4 titer variation has recently been proposed as a potential prognostic biomarker after a phase I trial in cancer immunotherapy with a humanized anti-CD26 antibody. We propose that dynamic monitoring of sCD26/DPP4 changes, in addition to well-known inflammatory biomarkers such as CRP already in use as informative for immune checkpoint immunotherapy, may indicate resistance or response during the successive steps of the treatment. As tumor cells expressing CD26 can also produce sCD26, the possibility of sorting immune- from non-immune-system-originated sCD26 is discussed.