In Vivo Tracking of Th1 Cells by PET Reveals Quantitative and Temporal Distribution and Specific Homing in Lymphatic Tissue

Although T cells can be labeled for noninvasive in vivo imaging, little is known about the impact of such labeling on T-cell function, and most imaging methods do not provide holistic information about trafficking kinetics, homing sites, or quantification. Methods: We developed protocols that minimize the inhibitory effects of Cu-64-pyruvaldehyde-bis(N4-methylthiosemicarbazone) (Cu-64-PTSM) labeling on T-cell function and permit the homing patterns of T cells to be followed by PET. Thus, we labeled ovalbumin (OVA) T-cell receptor transgenic interferon (IFN)-gamma-producing CD4(+) T (Th1) cells with 0.7-2.2 MBq of Cu-64-PTSM and analyzed cell viability, IFN-gamma production, proliferation, apoptosis, and DNA double-strand breaks and identified intracellular Cu-64 accumulation sites by energy dispersive x-ray analysis. To elucidate the fate of Th1 cell homing by PET, 107 Cu-64-OVA-Th1 cells were injected intraperitoneally or intravenously into healthy mice. To test the functional capacities of Cu-64-OVA-Th1 cells during experimental OVA-induced airway hyperreactivity, we injected 10(7) Cu-64-OVA-Th1 cells intraperitoneally into OVA-immunized or nonimmunized healthy mice, which were challenged with OVA peptide or phosphate-buffered saline or remained untreated. In vivo PET investigations were followed by biodistribution, autoradiography, and fluorescence-activated cell sorting analysis. Results: PET revealed unexpected homing patterns depending on the mode of T-cell administration. Within 20 min after intraperitoneal administration, Cu-64-OVA-Th1 cells homed to the perithymic lymph nodes (LNs) of naive mice. Interestingly, intravenously administered Cu-64-OVA-Th1 cells homed predominantly into the lung and spleen but not into the perithymic LNs. The accumulation of Cu-64-OVA-Th1 cells in the pulmonary LNs (6.8 +/- 1.1 percentage injected dose per cubic centimeter [%ID/cm(3)]) 24 h after injection was highest in the OVA-immunized and OVA-challenged OVA airway hyperreactivity-diseased littermates 24 h after intraperitoneal administration and lowest in the untreated littermates (3.7 +/- 0.4 %ID/cm(3)). As expected, Cu-64-OVA-Th1 cells also accumulated significantly in the pulmonary LNs of nonimmunized OVA-challenged animals (6.1 +/- 0.5 %ID/cm(3)) when compared with phosphate-buffered saline-challenged animals (4.6 +/- 0.5 %ID/cm(3)). Conclusion: Our protocol permits the detection of Th1 cells in single LNs and enables temporal in vivo monitoring of T-cell homing over 48 h. This work enables future applications for Cu-64-PTSM-labeled T cells in clinical trials and novel therapy concepts focusing on T-cell-based immunotherapies of autoimmune diseases or cancer.