Labeling of immune cells for in vivo monitoring of cell migration using magnetic resonance imaging and near-infrared imaging

In addition to macrophage localization, the opening of the blood brain barrier (BBB) as well as demyelination processes have been measured by MRI mapping gadolinium (Gd) related signal enhancement and magnetic transfer (MT), respectively. By successively applying this protocol at different time points during the EAE model progression, we were able to analyse the interdependence of immuno-cellular processes leading to axonal damage as well as the longitudinal evolution of pathological hallmarks of EAE.
Furthermore, these techniques have been used to validate and quantify the anti-inflammatory effect of EDG-1 inhibitor FTY720 on EAE symptoms. Repeated USPIO administrations and MRI measurements combining the analysis of MT ratios and Gd-enhancement have been performed on vehicle and FTY720 treated animals. This study demonstrates that FTY720 can prevent inflammatory events in EAE rats by sequestrating immune cells in lymphoid organs during acute inflammation episodes.
The third goal, was to translate the iron-labeling protocol from macrophages to T lymphocytes. As T-cells are initiators of the immune cascade leading to the occurence of symptoms in the EAE model, it would be highly relevant to visualize T lymphocytes prior to the onset of symptoms. Yet, as lymphocytes have no natural phagocytotic activity, in vivo tagging with CA was not feasible. We decided to label them in vitro with ferumoxides (FeO) and then, transfer iron-presenting cells adoptively to EAE animals intravenously. Different techniques have been used to evaluate the efficiency of lymphocytes labeling combining iron oxide particles with commonly available transfection agents (TAs) and the feasibility of labeling T lymphocytes in vitro has been demonstrated. However, the adoptive transfer of iron-tagged T-cells to EAE rats did not lead to the detection of these cells by MRI.
As MR detection of iron-tagged cell in vivo was unsuccessful probably due to the inherent lack of sensitivity of the MRI technique for molecular changes and the dilution of labeled cells in the blood, we decided to switch to a more sensitive technique. Thus, the goal of the last part of the thesis was to label primary cultured T lymphocytes with a fluorescent dye: cyanine 5.5 (Cy5.5). The Tat peptide from the HIV virus chemically has been bound to the Cy5.5 to cargo the dye across T-cells membrane. The ability of this probe to penetrate T-cells and its potential toxicity has been evaluated in vitro. Subsequently, Cy5.5-Tat labeled lymphocytes were transferred to EAE rats in order to monitor their bio-distribution during EAE. Prominent signals have been obtained from rat brain and histological experimentation using confocal microscopy analysis have been performed to confirm the localization of Cy5.5 within the brain parenchyma.