Intracellular magnetic labeling of lymphocytes for in vivo trafficking studies

Area of Science:

• Biomedical Imaging
• Cell Biology
• Nanotechnology

Background:

• Observing lymphocyte adhesion and trafficking in vivo over extended periods presents significant challenges.
• Current methods for tracking lymphocytes lack the resolution and non-invasive capabilities required for dynamic in vivo studies.

Purpose of the Study:

• To develop and validate a method for magnetically labeling lymphocytes using superparamagnetic particles.
• To assess the feasibility of using magnetic resonance imaging (MRI) to detect and track these labeled lymphocytes in vitro and in vivo.
• To evaluate the impact of the labeling process on lymphocyte viability, function, and biodistribution.

Main Methods:

• Developed a lymphocyte labeling technique utilizing fluid-phase endocytosis of biocompatible superparamagnetic nanoparticles.
• Quantified particle uptake per cell and assessed cell viability and retention of the label for up to 3 days.
• Evaluated the effect of labeling on lymphocyte adhesion to endothelial cells and assessed particle-mediated cytotoxicity.
• Determined the MRI detection threshold for labeled lymphocytes in phantom experiments.
• Administered labeled lymphocytes intravenously to rats and tracked their biodistribution using MRI, comparing it to unlabeled cells.

Main Results:

• Lymphocyte labeling achieved a maximum uptake of 0.11 ng Fe/cell (5 x 10^6 particles/lymphocyte) with stable label retention and full viability for at least 3 days.
• Labeled lymphocytes exhibited adhesion to endothelial cells comparable to unlabeled cells, indicating no alteration in adhesion protein expression.
• No particle-mediated cytotoxicity was observed.
• The MRI detection limit was 2.5 x 10^6 cells/30 microL.
• In vivo studies showed labeled lymphocytes accumulated in spleen, lymph nodes, and liver similarly to unlabeled cells, with spleen accumulation being detectable by MRI.

Conclusions:

• Intracellular lymphocyte labeling with superparamagnetic particles is a feasible technique.
• The labeling process does not adversely affect lymphocyte viability or their natural biodistribution.
• MRI can successfully detect magnetically labeled lymphocytes in vivo, enabling non-invasive tracking of lymphocyte trafficking.