Image-guided In Vivo Tracking of Transplanted Distal Lung Epithelial Progenitor Cells for Pulmonary Fibrosis Using Magnetic Particle Imaging

Summary

Cell therapy offers a promising intervention for pulmonary fibrosis by using progenitor cells to repair damaged tissue and improve lung function. As imaging plays a pivotal role in tracking cell integration, herein, we describe magnetic particle imaging-guided in vivo tracking of cell therapy for pulmonary fibrosis in a mouse model.

Abstract

Pulmonary fibrosis (PF) is a progressive and chronic lung disease characterized by repeated alveolar epithelial injury that leads to excessive extracellular matrix deposition, resulting in tissue thickening, scarring, and impaired gas exchange, leading to respiratory dysfunction. In the United States, around 50,000 new cases are reported annually, with patients facing serious complications such as pneumothorax, pulmonary hypertension, respiratory failure, and an increased risk of lung cancer. Current therapeutic options are limited in efficacy and primarily aim to slow disease progression. Cell therapy has emerged as a promising intervention, offering the potential to regenerate damaged lung tissue, modulate inflammation, and improve pulmonary function. However, the effectiveness of these therapies depends significantly on the ability to monitor the distribution, survival, and integration of transplanted cells within the host lungs.

Magnetic Particle Imaging (MPI) is a novel, non-invasive, preclinical imaging modality that utilizes superparamagnetic iron oxide nanoparticles (SPIONs) as tracers. MPI offers high sensitivity, specificity, and no background signal, allowing for real-time and quantitative tracking of labeled cells in vivo. In this study, we investigated the use of MPI for monitoring human distal lung epithelial progenitor cells transplanted into the lungs of immunocompromised mice. Cells were labeled with varying SPION concentrations to optimize the signal, confirmed by immunostaining and iron quantification. After intratracheal instillation, 2D MPI scans were acquired to track the spatial distribution of transplanted cells. Longitudinal imaging over 2 weeks enabled visualization of cell integration and retention within lung tissue. Successful instillation exhibited MPI signals in both left and right lungs, which decreased (~65%) over time. Mice were subsequently sacrificed for histological validation. This study demonstrates the utility of MPI for noninvasive, longitudinal tracking of cell therapy in pulmonary fibrosis, and pivots around the intricate techniques utilized during the procedures.

Introduction

Cell therapy^1,2 offers regenerative potential, promoting tissue repair, reducing inflammation, and improving outcomes in chronic diseases like leukemia and lymphoma^3,4 (hematopoietic stem cells), osteoarthritis^5,6 (mesenchymal stem cells), type 1 diabetes⁷ (islet cell transplantation), spinal cord injuries^8,9, neurodegenerative diseases^10,11,

Protocol

All procedures involving animal subjects have been approved by the Michigan State University Institutional Animal Care and Use Committee (IACUC) and involving human subjects have been approved by Corewell Health IRB no. 2017-198. All patients provided written informed consent prior to participation in the study.

Human lung explant samples from Idiopathic Pulmonary Fibrosis (IPF) patients undergoing lung transplantation were collected from Corewell Health. Prior to the transplantation procedure, all patients met the diagnostic criteria for idiopathic pulmonary fibrosis (IPF), characterized by hypoxemia, dyspnea, and reduced lung volume

Results

The pilot study was undertaken with six mice. Out of these, only one mouse died before the completion of the study, at day 10. 2D MPI signal intensities for different labeling concentrations were assessed as a function of the number of cells (Figure 1A). It was observed that the signal intensity was directly proportional to the concentration of the iron oxide tracer. Therefore, the concentration of 250 µg/mL was considered as the optimal labeling concentration and used for subsequent studies.......

Discussion

Intratracheal instillation in mice is a precise technique for delivering substances directly into the lungs. Careful attention is required during multiple critical steps throughout this procedure. Starting with ensuring proper depth of anesthesia to prevent discomfort and movement and positioning the mouse supine with the neck extended to align the airway for clear access to the tracheal opening. Use of a tongue depressor may help keep the airway open. Make sure that the catheter is carefully inserted and the substances .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1.7 mL microcentrifuge tube	DOT Scientific	RN1700-GMT	For cell collection and prepraring BLM dilutions
Anti-Dextran antibdoy	STEMCELL Technologies	60026	Primary Antibody
BD Luer-Lok Syringe	Becton, Dickinson	309628	For air injections during intratracheal instillation
Cytospin 3	Thermo Shandon	74010121GB
DNase I	Millipore-Sigma	10104159001
Dulbecco's phosphate-buffered saline (DPBS -/-)	Gibco	14190250
Fetal Bovine Serum	ThermoFisher Scientific	A5670701
Gentamicin	Gibco	15750060
Goat anti-Mouse IgG (H+L) Cross-Adsorbed Secondary Antibody, Alexa Fluor™ 568	ThermoFisher Scientific	A-11004	Secondary Antibody
Goat Serum	Millipore-Sigma	G9023
Isoflurane	Covetrus	11695067772	Gas anesthesia
Isoflurane vaporizer	SOMNI Scientific	VS6002	Anethesia apparatus
Momentum	Magnetic Insight Inc		Preclinical Magnetic Particle Imaging (MPI) scanner
Mouse intubation kit	OHAN	Ohan-201	Complete intubation kit with all the required accessories
NOD/SCID Mice	Jackson Laboratory	RRID:IMSR_JAX:001303	Immunocompromised mouse model
Penicillin/Streptomycin	Gibco	15140122
PneumaCult-Ex Plus Medium	STEMCELL Technologies	5040
ProLong Diamond Antifade Mountant with DAPI	Invitrogen	P36962	Mounting medium for immunostained slides
Protease from Streptomyces griseus	Millipore-Sigma	P5147
Surgical kit			Blunt-end forceps used for holding tongue of the. Mouse
Tris-Buffered Saline with Tween20 (TBST)	ThermoFisher Scientific	28360
TrypLE Express Enzyme	ThermoFisher Scientific	12604021
VivoTrax Plus	Magnetic Insight	MIVTP01	Iron oxide tracer for cell labeling in vitro and subsequent MPI