In vivo 19F MRI for Cell Tracking

Summary

We describe a general protocol for in vivo cell tracking using MRI in a mouse model with ex vivo labeled cells. A typical protocol for cell labeling, image acquisition processing and quantification is included.

Abstract

In vivo ¹⁹F MRI allows quantitative cell tracking without the use of ionizing radiation. It is a noninvasive technique that can be applied to humans. Here, we describe a general protocol for cell labeling, imaging, and image processing. The technique is applicable to various cell types and animal models, although here we focus on a typical mouse model for tracking murine immune cells. The most important issues for cell labeling are described, as these are relevant to all models. Similarly, key imaging parameters are listed, although the details will vary depending on the MRI system and the individual setup. Finally, we include an image processing protocol for quantification. Variations for this, and other parts of the protocol, are assessed in the Discussion section. Based on the detailed procedure described here, the user will need to adapt the protocol for each specific cell type, cell label, animal model, and imaging setup. Note that the protocol can also be adapted for human use, as long as clinical restrictions are met.

Introduction

In vivo cell tracking is essential for the optimization and monitoring of cellular therapeutics¹. Due to its noninvasive nature, imaging offers excellent opportunities to monitor cells in vivo. Magnetic Resonance Imaging (MRI) is independent of ionizing radiation and allows a superior imaging resolution and intrinsic soft tissue contrast. MRI-based cell tracking has already been used clinically to follow dendritic cells in melanoma patients². Conventional clinical MRI is carried out on the ¹H nucleus, present in mobile water in tissues. It is also possible to carry out MRI on other active nuclei, such as ¹³....

Protocol

Note: All experiments and procedures involving animals must be carried out in accordance with relevant ethical guidelines and conform with standard animal care and humane requirements.

1. Cell Labeling (Standard Protocol with Coincubation)

1. Add ¹⁹F label⁸ to immature DCs at a concentration of 4 mg/10⁶ cells (in 2 ml medium). Swirl gently to mix.
2. Incubate the cells with the label for 3 days before maturing and harvesting the DCs.
3. Collect the DCs and remove excess label by washing at least 3x in PBS. Count the cells.
4. Resuspend in a small volume of PBS for injection or f....

Results

Here we show the typical results for a protocol involving the transfer of ¹⁹F-labeled cells homing to a draining lymph node. Figure 2 shows a ¹⁹F NMR spectrum of 10⁶ labeled cells using a TFA reference. The imaging setup was carried out as described in the protocol (Figure 3). For the in vivo imaging, we used a reference consisting of a sealed cylinder of the same label used for the cells placed between the feet of the mouse. A representative pro.......

Discussion

The protocol outlined here describes the general procedure for in vivo ¹⁹F MRI cell tracking. Despite the described co-incubation method, there are several different protocols for labeling cells with a ¹⁹F agent. However, the co-incubation is most often used and can be further optimized e.g. by addition of transfection agents⁶. The actual cell labeling protocol will depend on the cell type. Only key labeling steps are described in the protocol here. Generally, the label .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
REAGENTS
PBS	Sigma-Aldrich	MFCD00131855
TFA	Sigma-Aldrich	76-05-1
Ketamine (Ketavet)	Pfizer	778-551
Xylazine (Rompun)	Bayer	QN05 cm92
Ophtosan	Produlab Pharma	2702	eye ointment
Material name
MRI scanner	Bruker Biospec
NMR spectrometer	Bruker Biospec