Abstract
Regenerative medicine uses the patient own stem cells to regenerate damaged tissues. Molecular imaging techniques are commonly used to image the transplanted cells, either right after surgery or at a later time. However, few techniques are fast or straightforward enough to label cells intraoperatively. Adipose tissue-derived stem cells (ADSCs) were harvested from knee joints of minipigs. The cells were labeled with PET contrast agent by flowing mechanoporation using a microfluidic device. While flowing through a series of microchannels, cells are compressed repeatedly by micro-ridges, which open transient pores in their membranes and induce convective transport, intended to facilitate the transport of 68Ga-labeled and lipid-coated mesoporous nanoparticles (MSNs) into the cells. This process enables cells to be labeled in a matter of seconds. Cells labeled with this approach were then implanted into cartilage defects, and the implant was imaged using positron emission tomography (PET) post-surgery. The microfluidic device can efficiently label millions of cells with 68Ga-labeled MSNs in as little as 15 min. The method achieved labeling efficiency greater than 5 Bq/cell on average, comparable to 30 min-long passive co-incubation with 68Ga-MSNs, but with improved biocompatibility due to the reduced exposure to ionizing radiation. Labeling time could also be accelerated by increasing throughput through more parallel channels. Finally, as a proof of concept, ADSCs were labeled with 68Ga-MSNs and quantitatively assessed using clinical PET/MR in a mock transplant operation in pig knee joints. MSN-assisted mechanoporation is a rapid, effective and straightforward approach to label cells with 68Ga. Given its high efficiency, this labeling method can be used to track small cells populations without significant effects on viability. The system is applicable to a variety of cell tracking studies for cancer therapy, regenerative therapy, and immunotherapy.
Highlights
Regenerative medicine uses the patient own stem cells to regenerate damaged tissues
We demonstrated that harvested Adipose tissue-derived stem cells (ADSCs) could be co-labeled with iron oxide nanoparticles and 18F-FDG through a novel microfluidic device, allowing for nearly instantaneous cell labeling and tracking using positron emission tomography (PET)/MRI14
We quantified the uptake of mesoporous nanoparticles (MSNs) by ADSCs and found that labeled cells had 87% higher green fluorescence compared to unlabeled cells (Fig. 2d), indicating that use of the microfluidics procedure enables efficient transport of MSNs into cells
Summary
Regenerative medicine uses the patient own stem cells to regenerate damaged tissues. Molecular imaging techniques are commonly used to image the transplanted cells, either right after surgery or at a later time. Regardless of the labeling method, labeled cells can be transplanted and imaged non-invasively in living subjects using fluorescence, bioluminescence, single-photon emission computed tomography (SPECT), positron emission tomography (PET), or magnetic resonance imaging (MRI)[7]. Among all these modalities, PET is unique due to its exceptional sensitivity, sufficient to detect picomolar level of probe in humans. MSNs can efficiently ferry large amounts of molecular cargo, including drug and small biogenic molecules, into cells[20,21] Using this property, we previously used MSNs to efficiently label cells with radiometals such as 68Ga and 89Zr through passive incubation and thereby achieve single-cell sensitivity in vivo[10]. This approach was relatively slow and could result in detectable toxicity due to the long incubation with radioactive compounds during the incubation phase
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