Imaging CAR-NK cells targeted to HER2 ovarian cancer with human sodium-iodide symporter-based positron emission tomography.

Chimeric antigen receptor (CAR) cell therapies utilize CARs to redirect immune cells towards cancer cells expressing specific antigens like human epidermal growth factor receptor 2 (HER2). Despite their potential, CAR T cell therapies exhibit variable response rates and adverse effects in some patients. Non-invasive molecular imaging can aid in predicting patient outcomes by tracking infused cells post-administration. CAR-T cells are typically autologous, increasing manufacturing complexity and costs. An alternative approach involves developing CAR natural killer (CAR-NK) cells as an off-the-shelf allogeneic product. In this study, we engineered HER2-targeted CAR-NK cells co-expressing the positron emission tomography (PET) reporter gene human sodium-iodide symporter (NIS) and assessed their therapeutic efficacy and PET imaging capability in a HER2 ovarian cancer mouse model.NK-92 cells were genetically modified to express a HER2-targeted CAR, the bioluminescence imaging reporter Antares, and NIS. HER2-expressing ovarian cancer cells were engineered to express the bioluminescence reporter Firefly luciferase (Fluc). Co-culture experiments demonstrated significantly enhanced cytotoxicity of CAR-NK cells compared to naive NK cells. In vivo studies involving mice with Fluc-expressing tumors revealed that those treated with CAR-NK cells exhibited reduced tumor burden and prolonged survival compared to controls. Longitudinal bioluminescence imaging demonstrated stable signals from CAR-NK cells over time. PET imaging using the NIS-targeted tracer 18F-tetrafluoroborate ([18F]TFB) showed significantly higher PET signals in mice treated with NIS-expressing CAR-NK cells.Overall, our study showcases the therapeutic potential of HER2-targeted CAR-NK cells in an aggressive ovarian cancer model and underscores the feasibility of using human-derived PET reporter gene imaging to monitor these cells non-invasively in patients.

Anthropogenic particle concentrations and fluxes in an urban river are temporally variable and impacted by storm events.

Anthropogenic particles (AP), which include microplastics and other synthetic, semisynthetic, and anthropogenically modified materials, are pollutants of concern in aquatic ecosystems worldwide. Rivers are important conduits and retention sites for AP, and time series data on the movement of these particles in lotic ecosystems are needed to assess the role of rivers in the global AP cycle. Much research assessing AP pollution extrapolates stream loads based on single time point measurements, but lotic ecosystems are highly variable over time (e.g., seasonality and storm events). The accuracy of models describing AP dynamics in rivers is constrained by the limited studies that examine how frequent changes in discharge drive particle retention and transport. This study addressed this knowledge gap by using automated, high-resolution sampling to track AP concentrations and fluxes during multiple storm events in an urban river (Milwaukee River) and comparing these measurements to commonly monitored water quality metrics. AP concentrations and fluxes varied significantly across four storm events, highlighting the temporal variability of AP dynamics. When data from the sampling periods were pooled, there were increases in particle concentration and flux during the early phases of the storms, suggesting that floods may flush AP into the river and/or resuspend particles from the benthic zone. AP flux was closely linked to river discharge, suggesting large loads of AP are delivered downstream during storms. Unexpectedly, AP concentrations were not correlated with other simultaneously measured water quality metrics, including total suspended solids, fecal coliforms, chloride, nitrate, and sulfate, indicating that these metrics cannot be used to estimate AP. These data will contribute to more accurate models of particle dynamics in rivers and global plastic export to oceans. PRACTITIONER POINTS: Anthropogenic particle (AP) concentrations and fluxes in an urban river varied across four storm events. AP concentrations and fluxes were the highest during the early phases of the storms. Storms increased AP transport downstream compared with baseflow. AP concentrations did not correlate with other water quality metrics during storms.

Biofilms on plastic litter in an urban river: Community composition and activity vary by substrate type.

In aquatic ecosystems, plastic litter is a substrate for biofilms. Biofilms on plastic and natural surfaces share similar composition and activity, with some differences due to factors such as porosity. In freshwaters, most studies have examined biofilms on benthic substrates, while little research has compared the activity and composition of biofilms on buoyant plastic and natural surfaces. Additionally, the influence of substrate size and successional stage on biofilm composition has not been commonly assessed. We incubated three plastics of distinct textures that are buoyant in rivers, low-density polyethylene (rigid; 1.7 mm thick), low-density polyethylene film (flexible; 0.0254 mm thick), and foamed polystyrene (brittle; 6.5 mm thick), as well as wood substrates (untreated oak veneer; 0.6 mm thick) in the Chicago River. Each material was incubated at three sizes (1, 7.5, and 15 cm2 ). Substrates were incubated at 2-10 cm depths and removed weekly for 6 weeks. On each substrate we measured chlorophyll concentration, biofilm biomass, respiration, and flux of nitrogen gas. We sequenced 16S and 23S rRNA genes at Weeks 1, 3, and 6 to capture biofilm community composition across successional stages. Chlorophyll, biomass, and N2 flux were similar across substrates, but respiration was greater on wood than plastics. Bacterial and algal richness and diversity were highest on foam and wood compared to polyethylene substrates. Bacterial biofilm community composition was distinct between wood and plastic substrates, while the algal community was distinct on wood and foam, which were different from each other and polyethylene substrates. These results indicate that polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban rivers. This study provides valuable insights into the effects of substrate on biofilm characteristics, and the ecological impacts of plastic pollution on urban rivers. PRACTITIONER POINTS: Plastic physical and chemical properties act as forces of selection for biofilm. Biofilm activity was similar among three different types of plastic. Community composition between plastic and wood was different.

Editorial Commentary: Surgical Videos on YouTube Are Not Peer Reviewed and Have Low Educational Value.

The rise of online platforms like YouTube for health information has prompted scrutiny over the quality of medical/surgical-related video content. Recent research on YouTube videos regarding anterior cruciate ligament reconstruction (ACLR) with quadriceps tendon autograft shows low educational quality and reliability using established assessment tools. Physicians primarily published content, with longer videos, and physician-generated videos, generally correlating with higher quality. However, YouTube's inadequacy as a reliable source for ACLR information underscores the need for alternative educational resources. Orthopaedic health care professionals must play a pivotal role in guiding patients toward credible sources and take aim at improving online content quality. Understanding patient preferences for online resources is essential for enhancing patient education, the patient-provider relationship, and decision-making in orthopaedic care.

The non to moderately dilated root in acute type A aortic dissection: outcomes of the PENN-BERN registry in young, non-syndromic patients.

OBJECTIVES: There is an ongoing debate regarding whether patients benefit more from root replacement compared to a reconstruction of the sinuses of Valsalva in acute type A aortic dissection (aTAAD). In those with known or suspected connective tissue disorders, root replacement is considered appropriate. However, there are currently no diameter-based guidelines regarding the best approach in patients with minimally to moderately dilated root and no connective tissue disorders. METHODS: From January 2005 to December 2022, a two-centre registry of aTAAD was created. Patients were included based on their age (≤60 years), the absence of root entry and dilatation >50 mm and the absence of syndromic hereditable aortic disease. Patients were divided into 2 groups based on the proximal procedure, root reconstruction and root replacement. Propensity score pair matching was performed based on preoperative characteristics. RESULTS: Cumulative incidence of reintervention at 10 years was slightly higher after root reconstruction 13% vs 3.9% in the matched group (P = 0.040). Survival at 10 years was not affected by the procedure independently of the matching 72.1% vs 71.4% (P = 0.2). Uni- and multivariate Cox regressions showed that a root diameter of >40 mm was associated with a hazard ratio of 7.7 (95% confidence interval 2.6-23) and 5.4 (7-17), respectively, for reoperation for aneurysm and pseudoaneurysm. CONCLUSIONS: Rate of reoperation due to proximal pseudoaneurysm and aneurysm could be significantly reduced with a lower threshold of 40 mm to replace the aortic root in aTAAD than in elective cases.

Non-inferior outcomes in lower urgency patients transplanted with extended criteria donor hearts.

BACKGROUND: Recent work has suggested that outcomes among heart transplant patients listed at the lower-urgency (United Network for Organ Sharing Status 4 or 6) status may not be significantly impacted by donor comorbidities. The purpose of this study was to investigate outcomes of extended criteria donors (ECD) in lower versus higher urgency patients undergoing heart transplantation. METHODS: The United Network for Organ Sharing (UNOS) database was queried for all adult patients undergoing heart transplantation from October 18, 2018 through December 31, 2021. Patients were stratified by degree of urgency (higher urgency: UNOS 1 or 2 vs lower urgency: UNOS 4 or 6) and receipt of ECD hearts, as defined by donor hearts failing to meet established acceptable use criteria. Outcomes were compared using propensity score matched cohorts. RESULTS: Among 9,160 patients included, 2,320 (25.4%) were low urgency. ECD hearts were used in 35.5% of higher urgency (HU) patients and 39.2% of lower urgency (LU) patients. While ECD hearts had an impact on survival among high-urgency patients (p < 0.01), there was no difference in 1- and 2-year survival (p > 0.05) found among low urgency patients receiving ECD versus standard hearts. Neither ECDs nor individual ECD criteria were independently associated with mortality in low urgency patients (p > 0.05). CONCLUSIONS: Post-transplant outcomes among low urgency patients are not adversely affected by receipt of ECD vs. standard hearts. Expanding the available donor pool by optimizing use of ECDs in this population may increase transplant frequency, decrease waitlist morbidity, and improve postoperative outcomes for the transplant community at large.

Validation of the GERAADA score to predict 30-day mortality in acute type A aortic dissection in a single high-volume aortic centre.

OBJECTIVES: This study aimed to evaluate employing the German Registry of Acute Aortic Dissection Type A (GERAADA) score to predict 30-day mortality in an aortic centre in the USA. METHODS: Between January 2010 and June 2021, 689 consecutive patients underwent surgery for acute type A dissection at a single institution. Excluded were patients with missing clinical data (N = 4). The GERAADA risk score was retrospectively calculated via a web-based application. Model discrimination power was calculated with c-statistics from logistic regression and reported as the area under the receiver operating characteristic curve with 95% confidence intervals. The calibration was measured by calculating the observed versus estimated mortality ratio. The Brier score was used for the overall model evaluation. RESULTS: Included were 685 patients [mean age 60.6 years (SD: 13.5), 64.8% male] who underwent surgery for acute type A aortic dissection. The 30-day mortality rate was 12.0%. The GERAADA score demonstrated very good discrimination power with an area under the receiver operating characteristic curve of 0.762 (95% confidence interval 0.703-0.821). The entire cohort's observed versus estimated mortality ratio was 0.543 (0.439-0.648), indicating an overestimation of the model-calculated risk. The Brier score was 0.010, thus revealing the model's acceptable overall performance. CONCLUSIONS: The GERAADA score is a practical and easily accessible tool for reliably estimating the 30-day mortality risk of patients undergoing surgery for acute type A aortic dissection. This model may naturally overestimate risk in patients undergoing surgery in experienced aortic centres.

Chiropractic Manipulation Causing Anterior-Posterior Compression Type Pelvic Ring Injury: A Case Report.

CASE: We present a case of an anteroposterior compression (APC) type pelvic ring injury that occurred after chiropractic manipulation in a patient with a history of quadriplegia. Emergent surgical stabilization was undertaken, and he had an excellent outcome with no complications at 3.5-year follow-up. CONCLUSION: APC type pelvic ring injuries usually occur to high-energy mechanisms. We describe a case of a patient with quadriplegia and osteopenia that suffered a pelvic ring injury because of a unique mechanism. Practitioners performing pelvic manipulation should be aware of this type of injury in at-risk patients.

Placement of Temporary Left Ventricular Assist Device Using Monitored Anesthesia Care and Regional Anesthesia.

Patients with advanced cardiogenic shock requiring mechanical circulatory support are uniquely susceptible to clinical deterioration. Limiting physiologic perturbations via avoidance of general anesthesia and endotracheal intubation by awake Impella 5.5 placement is safe and may represent a novel strategy in mechanical circulatory support initiation among patients in cardiogenic shock. (Level of Difficulty: Intermediate.).

Outcomes of aortic valve repair with the reimplantation technique and maintenance of commissural orientation.

Background: Debate still persists on whether valve-sparing root reimplantation (VSRR) of a very asymmetric bicuspid aortic valve (BAV) should be completed such that the asymmetry of the native commissural orientation is retained, or if it should be made symmetric (180°-180°). Herein, we present our approach, in which the native asymmetry is preserved, and the valve is reimplanted in a 210°-150° orientation. Methods: A retrospective review was performed of 130 patients with BAV who underwent VSRR between January 1, 2004 and March 1, 2023 at a single institution. Of this total, 37 were reimplanted asymmetrically (210°-150°). The primary outcome was > moderate aortic insufficiency (AI). Secondary outcomes included severe aortic stenosis (AS), reintervention, and survival. Results: The included 37 patients were mostly male [94.6% (35/37)] with mean age of 46.3 years, and with low rates of comorbidities. At least moderate AI was present in 40.5% (15/37) prior to surgery. All BAV in this series were Sievers Type 1 with a mean commissural angle of 128.2°. Leaflet repair was required in 81.1% (30/37), most commonly involving central plication of the conjoined cusp [96.7% (29/30)] and raphe release [73.3% (22/30)]. There was no 30-day mortality or stroke. At 10 years, the cumulative incidences of > moderate AI, severe AS, and reintervention were 7.6% (0-17.2%), 7.1% (0-19.7%), and 5.3% (0.3-22%), respectively. There was no mortality for the entire duration of the study period. Conclusions: This series demonstrates excellent 10-year outcomes of maintaining commissural orientation in asymmetric BAV reimplantation procedures. However, further study with additional patients, longer follow-up, and direct comparison to symmetric reimplantation for similar BAV morphology is required.

Decreased survival of simultaneous heart-kidney transplant recipients in the new heart allocation era.

BACKGROUND: In 2018, the United Network for Organ Sharing (UNOS) modified their heart allocation policy to reduce waitlist mortality. The rates of simultaneous heart-kidney transplant (SHKT) have dramatically increased in recent years, despite increased rates of posttransplant renal failure in the new policy era. This study sought to investigate the impact of the new allocation system on waitlist and posttransplant outcomes of simultaneous heart-kidney transplantation. METHODS: Adult patients listed for SHKT between 2012 and 2021 were included. Patients were cross-validated across both Thoracic and Kidney UNOS databases to confirm accurate listing and transplant data. Patients were stratified according to listing era. The Fine and Gray model was used to assess waitlist outcomes and posttransplant renal graft function. Kaplan-Meier analysis and Cox regression were used to compare posttransplant survival. RESULTS: A total of 2,588 patients were included, of whom 1,406 (54.1%) were listed between 2012 and 2018 (era 1) and 1,182 (45.9%) between 2019 and 2021 (era 2). Era 2 was associated with increased likelihood of transplant (adjusted Sub-hazard ratios (aSHR): 1.52; p < 0.01) and decreased waitlist mortality (aSHR: 0.63; p < 0.01). Posttransplant survival at 2 years was decreased in era 2 (78.8% vs 86.9%; p < 0.01). Undersized hearts (hazard ratio [HR]: 2.02; p < 0.01), use of extracorporeal membrane oxygenation (HR: 2.67; p < 0.1), and transplants performed following the policy change (HR: 1.45; p = 0.03) were associated with increased mortality. Actuarial survival (combined waitlist and posttransplant) was significantly lower in the modern era (71.6% vs 62.2%; p = 0.02). CONCLUSIONS: The allocation policy change has improved waitlist outcomes in patients listed for SHKT but potentially at the cost of worsened posttransplant outcomes.

Ligamentum teres cardiopexy for post vertical sleeve gastrectomy gastroesophageal reflux.

PURPOSE: Vertical sleeve gastrectomy (VSG) evolved in the early 2000s into the standalone weight loss procedure we see today. While numerous studies highlight VSG's durability for weight loss, and improvements co-morbidities such as type 2 diabetes mellitus and cardiovascular disease, patients with gastroesophageal reflux disease (GERD) have been counseled against VSG due to the concern for worsening reflux symptoms. When considering anti-reflux procedures, VSG patients are unable to undergo traditional fundoplication due to lack of gastric cardia redundancy. Magnetic sphincter augmentation lacks long-term safety data and endoscopic approaches have undetermined longitudinal benefits. Until recently, the only option for patients with a history of VSG with medically refractory GERD has been conversion to roux en Y gastric bypass (RNYGB), however, this poses other risks including marginal ulcers, internal hernias, hypoglycemia, dumping syndrome, and nutritional deficiencies. Given the risks associated with conversion to RNYGB, we have adopted the ligamentum teres cardiopexy as an option for patients with intractable GERD following VSG. METHODS: A retrospective chart review was conducted of patients who had prior laparoscopic or robotic VSG and subsequently GERD symptoms refectory to pharmacological management who underwent ligamentum teres cardiopexy between 2017 and 2022. Pre-operative GERD disease burden, intraoperative cardiopexy characteristics, post-operative GERD symptomatology and changes in H2 blocker or PPI requirements were reviewed. RESULTS: Of the study's 60 patients the median age was 50 years old, and 86% were female. All patients had a diagnosis of GERD through pre-operative assessments and were taking antisecretory medication. Of the 36 patients who have completed their one year follow up, 81% of patients had either a decrease in dosage or cessation of the antisecretory medication at one year following ligamentum teres cardiopexy. CONCLUSION: Ligamentum teres cardiopexy is a viable alternative to RNYGB in patients with a prior vertical sleeve gastrectomy with medical refractory GERD.

Midterm Results of an Algorithmic 3-Pronged Approach to Bicuspid Aortic Valve Repair.

BACKGROUND: This study evaluated midterm outcomes of a 3-pronged algorithm for bicuspid aortic valve (BAV) repair. Valve-sparing root reimplantation (VSRR) was performed for patients with aortic root dilatation. In those without a root aneurysm, external subannular ring (ESAR) was performed for annuli ≥28 mm and subcommissural annuloplasty (SCA) for annuli <28 mm. METHODS: This was a retrospective review of prospectively collected data of 242 patients undergoing primary BAV repair from April 29, 2004, to March 1, 2023, at a single institution. Primary end points were mortality, structural valve degeneration (SVD), which was defined as a composite of more than moderate aortic insufficiency or severe aortic stenosis, and reintervention. RESULTS: The algorithm was used to treat 201 patients; of these, 130 underwent VSRR, 35 had ESAR, and 36 underwent SCA. Most were men with mean age of 43.8 years (SD, 12.0 years), which was similar between groups. Preoperative aortic insufficiency more than moderate was more common for ESAR compared with VSRR and SCA (74.3% vs 37.7% vs 44.4%, P < .001). At 30 days, mortality was 0.8% (n = 1) for VSRR and 0% for ESAR and SCA. At 6 years, overall Kaplan-Meier survival was 98.9% (95% CI, 97.3%-100%), with no differences between groups (P = .5). The cumulative incidence of SVD was 4.7% (95% CI, 0.1%-9.2%) for VSRR, 6.4% (95% CI, 0%-14.6%) for ESAR, and 0% for SCA (P = .4). Similarly, the cumulative incidence of reintervention with all-cause mortality as a competing risk was 2.2% (95% CI, 0.4%-6.9%), 6.1% (95% CI, 1%-17.9%), and 0% for VSRR, ESAR, and SCA, respectively (P = .506). CONCLUSIONS: A 3-pronged algorithmic approach to BAV repair results in excellent survival and freedom from reoperation at 6 years.

Comparison of Intraaortic Balloon Pump and Impella 5.5 as Heart Transplant Bridging Strategies.

BACKGROUND: Temporary mechanical circulatory support is increasingly utilized as a bridge to heart transplantation. The Impella 5.5 (Abiomed) has achieved anecdotal success as a bridge since receiving US Food and Drug Administration approval. The purpose of the current study was to compare waitlist and posttransplant outcomes of patients bridged with intraaortic balloon pumps (IABPs) to those receiving Impella 5.5 therapy. METHODS: Patients listed for heart transplantation between October 2018 and December 2021 who received IABP or Impella 5.5 at any time during waitlist course were identified from the United Network for Organ Sharing database. Propensity-matched groups of recipients with each device were created. Competing-risks regression for mortality, transplantation, and removal from waitlist for illness was performed according to the method of Fine and Gray. Posttransplant survival was censored at 2 years. RESULTS: Overall, 2936 patients were identified, of whom 2484 (85%) were supported with IABP and 452 (15%) received Impella 5.5. Patients with Impella 5.5 support had more functional impairment, higher wedge pressures, higher rates of preoperative diabetes and dialysis, and more ventilator support (all P < .05). Waitlist mortality was significantly worsened in the Impella group and transplantation was less frequent (P < .001). However, survival at 2 years after transplant was similar in both complete (90% vs 90%, P = .693) and propensity-matched cohorts (88% vs 83%, P = .874). CONCLUSIONS: Patients bridged with Impella 5.5 were sicker than IABP-bridged patients and less frequently transplanted; however, posttransplant outcomes were similar in propensity-matched cohorts. The role of these bridging strategies in patients listed for heart transplantation should be continually assessed with future allocation system changes.

macroH2A2 antagonizes epigenetic programs of stemness in glioblastoma.

Self-renewal is a crucial property of glioblastoma cells that is enabled by the choreographed functions of chromatin regulators and transcription factors. Identifying targetable epigenetic mechanisms of self-renewal could therefore represent an important step toward developing effective treatments for this universally lethal cancer. Here we uncover an epigenetic axis of self-renewal mediated by the histone variant macroH2A2. With omics and functional assays deploying patient-derived in vitro and in vivo models, we show that macroH2A2 shapes chromatin accessibility at enhancer elements to antagonize transcriptional programs of self-renewal. macroH2A2 also sensitizes cells to small molecule-mediated cell death via activation of a viral mimicry response. Consistent with these results, our analyses of clinical cohorts indicate that high transcriptional levels of this histone variant are associated with better prognosis of high-grade glioma patients. Our results reveal a targetable epigenetic mechanism of self-renewal controlled by macroH2A2 and suggest additional treatment approaches for glioblastoma patients.

Mitogen-induced defective mitosis transforms neural progenitor cells.

BACKGROUND: Chromosome instability (CIN) with recurrent copy number alterations is a feature of many solid tumors, including glioblastoma (GBM), yet the genes that regulate cell division are rarely mutated in cancers. Here, we show that the brain-abundant mitogen, platelet-derived growth factor-A (PDGFA) fails to induce the expression of kinetochore and spindle assembly checkpoint genes leading to defective mitosis in neural progenitor cells (NPCs). METHODS: Using a recently reported in vitro model of the initiation of high-grade gliomas from murine NPCs, we investigated the immediate effects of PDGFA exposure on the nuclear and mitotic phenotypes and patterns of gene and protein expression in NPCs, a putative GBM cell of origin. RESULTS: NPCs divided abnormally in defined media containing PDGFA with P53-dependent effects. In wild-type cells, defective mitosis was associated with P53 activation and cell death, but in some null cells, defective mitosis was tolerated. Surviving cells had unstable genomes and proliferated in the presence of PDGFA accumulating random and clonal chromosomal rearrangements. The outcome of this process was a population of tumorigenic NPCs with recurrent gains and losses of chromosomal regions that were syntenic to those recurrently gained and lost in human GBM. By stimulating proliferation without setting the stage for successful mitosis, PDGFA-transformed NPCs lacking P53 function. CONCLUSIONS: Our work describes a mechanism of transformation of NPCs by a brain-associated mitogen, raising the possibility that the unique genomic architecture of GBM is an adaptation to defective mitosis that ensures the survival of affected cells.

PANX3 Channels Regulate Architecture, Adhesion, Barrier Function, and Inflammation in the Skin.

The channel-forming glycoprotein PANX3 functions in cutaneous wound healing and keratinocyte differentiation, but its role in maintaining skin homeostasis through aging is not yet understood. We found that PANX3 is absent in newborn skin but becomes upregulated with age. We characterized the skin of global Panx3-knockout (KO) mice and found that KO dorsal skin showed sex differences at different ages but generally had reduced dermal and hypodermal areas compared with age-matched controls. Transcriptomic analysis of the KO epidermis revealed reduced E-cadherin stabilization and Wnt signaling compared with that of wild-type, consistent with the inability of primary KO keratinocytes to adhere in culture and diminished epidermal barrier function in KO mice. We also observed increased inflammatory signaling in the KO epidermis and a higher incidence of dermatitis in aged KO mice compared with that in wild-type controls. These findings suggest that during skin aging, PANX3 is critical in the maintenance of dorsal skin architecture, keratinocyte cell-cell and cell-matrix adhesion, and inflammatory skin responses.

Complementary early-phase magnetic particle imaging and late-phase positron emission tomography reporter imaging of mesenchymal stem cells in vivo.

Stem cell-based therapies have demonstrated significant potential in clinical applications for many debilitating diseases. The ability to non-invasively and dynamically track the location and viability of stem cells post administration could provide important information on individual patient response and/or side effects. Multi-modal cell tracking provides complementary information that can offset the limitations of a single imaging modality to yield a more comprehensive picture of cell fate. In this study, mesenchymal stem cells (MSCs) were engineered to express human sodium iodide symporter (NIS), a clinically relevant positron emission tomography (PET) reporter gene, as well as labeled with superparamagnetic iron oxide nanoparticles (SPIOs) to allow for detection with magnetic particle imaging (MPI). MSCs were additionally engineered with a preclinical bioluminescence imaging (BLI) reporter gene for comparison of BLI cell viability data to both MPI and PET data over time. MSCs were implanted into the hind limbs of immunocompromised mice and imaging with MPI, BLI and PET was performed over a 30-day period. MPI showed sensitive detection that steadily declined over the 30-day period, while BLI showed initial decreases followed by later rapid increases in signal. The PET signal of MSCs was significantly higher than the background at later timepoints. Early-phase imaging (day 0-9 post MSC injections) showed correlation between MPI and BLI data (R2 = 0.671), while PET and BLI showed strong correlation for late-phase (day 10-30 post MSC injections) imaging timepoints (R2 = 0.9817). We report the first use of combined MPI and PET for cell tracking and show the complementary benefits of MPI for sensitive detection of MSCs early after implantation and PET for longer-term measurements of cell viability.

Dual Magnetic Particle Imaging and Akaluc Bioluminescence Imaging for Tracking Cancer Cell Metastasis.

Magnetic particle imaging (MPI) provides hotspot tracking and direct quantification of superparamagnetic iron oxide nanoparticle (SPIO)-labelled cells. Bioluminescence imaging (BLI) with the luciferase reporter gene Akaluc can provide complementary information on cell viability. Thus, we explored combining these technologies to provide a more holistic view of cancer cell fate in mice. Akaluc-expressing 4T1Br5 cells were labelled with the SPIO Synomag-D and injected into the mammary fat pads (MFP) of four nude mice. BLI was performed on days 0, 6 and 13, and MPI was performed on days 1, 8 and 14. Ex vivo histology and fluorescence microscopy of MFP and a potential metastatic site was conducted. The BLI signal in the MFP increased significantly from day 0 to day 13 (p < 0.05), mirroring tumor growth. The MPI signal significantly decreased from day 1 to day 14 (p < 0.05) due to SPIO dilution in proliferating cells. Both modalities detected secondary metastases; however, they were visualized in different anatomical regions. Akaluc BLI complemented MPI cell tracking, allowing for longitudinal measures of cell viability and sensitive detection of distant metastases at different locations. We predict this multimodal imaging approach will help to evaluate novel therapeutics and give a better understanding of metastatic mechanisms.