Immuno–positron emission tomography (PET), a noninvasive imaging modality, can provide a dynamic approach for longitudinal assessment of cell populations of interest. Transformation of mAbs into single-chain variable fragment (scFv)–based PET imaging agents would allow noninvasive tracking in vivo of a wide range of possible targets. We used sortase-mediated enzymatic labeling in combination with PEGylation to develop an anti-mouse CD4 scFv–based PET imaging agent constructed from an anti-mouse CD4 mAb. This anti-CD4 scFv can monitor the in vivo distribution of CD4⁺ T cells by immuno-PET. We tracked CD4⁺ and CD8⁺ T cells in wild-type mice, in immunodeficient recipients reconstituted with monoclonal populations of OT-II and OT-I T cells, and in a B16 melanoma model. Anti-CD4 and -CD8 immuno-PET showed that the persistence of both CD4⁺ and CD8⁺ T cells transferred into immunodeficient mice improved when recipients were immunized with OVA in CFA. In tumor-bearing animals, infiltration of both CD4⁺ and CD8⁺ T cells increased as the tumor grew. The approach described in this study should be readily applicable to convert clinically useful Abs into the corresponding scFv PET imaging agents.

免疫正电子发射断层扫描 (PET) 是一种无创成像方式，可以为感兴趣的细胞群的纵向评估提供动态方法。将 mAb 转化为基于单链可变片段 (scFv) 的 PET 显像剂将允许在体内对各种可能的靶标进行无创跟踪。我们使用分选酶介导的酶标记结合 PEG 化来开发由抗小鼠 CD4 mAb 构建的基于抗小鼠 CD4 scFv 的 PET 显像剂。这种抗 CD4 scFv 可以通过免疫 PET监测 CD4 ^{+ T 细胞的体内分布。}我们跟踪了 CD4 ⁺和 CD8 ⁺野生型小鼠中的 T 细胞、用 OT-II 和 OT-I T 细胞的单克隆群重建的免疫缺陷受体中的 T 细胞，以及 B16 黑色素瘤模型中的 T 细胞。抗 CD4 和 -CD8 免疫 PET 表明，当用 CFA 中的 OVA 免疫受体时，转移到免疫缺陷小鼠中的 CD4 ⁺和 CD8 ^{+ T 细胞的持久性得到改善。}在荷瘤动物中，CD4 ⁺和 CD8 ⁺ T 细胞的浸润随着肿瘤的生长而增加。本研究中描述的方法应该很容易适用于将临床有用的 Abs 转化为相应的 scFv PET 显像剂。