Cu antibody-targeting of the T-cell receptor and subsequent internalization enables in vivo tracking of lymphocytes by PET

T cells are key players in inflammation, autoimmune diseases, and immunotherapy. Thus, holistic and noninvasive in vivo characterizations of the temporal distribution and homing dynamics of lymphocytes in mammals are of special interest. Herein, we show that PET-based T-cell labeling facilitates quantitative, highly sensitive, and holistic monitoring of T-cell homing patterns in vivo. We developed a new T-cell receptor (TCR)-specific labeling approach for the intracellular labeling of mouse T cells. We found that continuous TCR plasma membrane turnover and the endocytosis of the specific ⁶⁴Cu-monoclonal antibody (mAb)–TCR complex enables a stable labeling of T cells. The TCR–mAb complex was internalized within 24 h, whereas antigen recognition was not impaired. Harmful effects of the label on the viability, DNA-damage and apoptosis-necrosis induction, could be minimized while yielding a high contrast in in vivo PET images. We were able to follow and quantify the specific homing of systemically applied ⁶⁴Cu-labeled chicken ovalbumin (cOVA)-TCR transgenic T cells into the pulmonary and perithymic lymph nodes (LNs) of mice with cOVA-induced airway delayed-type hypersensitivity reaction (DTHR) but not into pulmonary and perithymic LNs of naüüöüüüïve control mice or mice diseased from turkey or pheasant OVA-induced DTHR. Our protocol provides consequent advancements in the detection of small accumulations of immune cells in single LNs and specific homing to the sites of inflammation by PET using the internalization of TCR-specific mAbs as a specific label of T cells. Thus, our labeling approach is applicable to other cells with constant membrane receptor turnover. Significance Noninvasive tracking of T cells is an important method to reveal basic mechanisms of T-cell–based immunotherapies. Herein, to our knowledge we show for the first time that intracellular labeling of mouse lymphocytes for in vivo PET can be achieved by targeting membranous T-cell receptors with specific ⁶⁴Cu-coupled antibodies because of a continuous plasma membrane turnover. This direct-labeling method provides impressive advantages compared with common radioactive labeling methods, like [ ⁶⁴Cu]PTSM or [ ¹¹¹In]oxin, with regard to minimized influences on the target cells, while providing a high labeling stability and contrast. Thus, in noninvasive in vivo cell-tracking PET studies, we could follow the specific homing of T cells into inflamed tissues. Consequently, this method is eas