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Abstract Autologous transplantation remains the standard of care for eligible multiple myeloma (MM) patients, yet optimal CD34+ cell dose remains unclear. We conducted a retrospective study on MM patients undergoing upfront transplant between 2005 and 2021 and divided them into low (≤2.5 × 106 cells/kg) and high (>2.5 × 106 cells/kg) CD34+ dose groups. We included 2479 patients, 95 in the low CD34+ group and 2384 in the high CD34+ group. Patients in the low CD34+ group were older (63.2 vs 61.1 years, p = 0.013), more often had R-ISS III (19% vs 9%, p = 0.014), received plerixafor (60% vs 35%, p 2.5 × 106 cells/kg. Multivariable analysis affirmed that CD34+ >2.5 × 106 cells/kg was associated with better PFS (HR 0.71, p = 0.008) and OS (0.59, p 2.5 × 106 cells/kg remained a predictor of better OS (0.42, p 2.5 × 106 cells/kg was associated with improved survival, without any additional benefit at incrementally higher doses.

Abstract Autologous stem cell transplantation (autoHCT) is considered standard of care for newly diagnosed multiple myeloma (MM). Although most patients eventually progress after autoHCT, a small proportion achieve a durable response. In this retrospective study we included 1576 patients, 244 (15%) of whom were long-term responders (LTR), defined as having a progression-free survival (PFS) of ≥8 years after transplant. Patients in the LTR group were younger than the non-LTR group (median age 58.4 vs. 59.5 years; p = 0.012), less likely to have high-risk cytogenetics (4% vs. 14%; p

Abstract The prognostic impact of additional copies of chromosome 1q (1q + ) on outcomes of newly-diagnosed multiple myeloma (NDMM) patients undergoing autologous transplantation (autoSCT) is unclear. We conducted a retrospective single-center analysis of NDMM patients with 1q21 gain/amplification (3 or ≥4 copies of 1q, respectively) that received autoSCT between 2008–2018. 213 patients were included (79% 1q gain; 21% 1q amplification). The most commonly used induction regimen was bortezomib, lenalidomide, and dexamethasone (41%). At day100 post-autoSCT and at best post-transplant response, 78% and 87% of patients achieved ≥VGPR, and 38% and 50% achieved MRD-negative ≥VGPR, respectively. Median PFS and OS for the entire cohort were 35.5 months and 81.4 months, respectively. On multivariable assessment for PFS, MRD negative ≥VGPR before autoSCT (HR 0.52, p = 0.013) was associated with superior PFS, whereas 1q amplification was associated with inferior PFS (2.03, p = 0.003). On multivariate analysis for OS, achieving MRD negative ≥VGPR at best post-transplant response was associated with superior survival (0.29, p

Abstract Oral corticosteroids (OCS) are commonly prescribed for acute, self‐limited conditions, despite studies demonstrating toxicity. Studies evaluating longitudinal OCS prescribing in the general population are scarce and do not compare use across countries. This study investigated and compared OCS prescription patterns from 2009 to 2018 in the general populations of the United States, Taiwan, and Denmark. This international population‐based longitudinal cohort study used nationwide claims databases (United States: Optum Clinformatics Data Mart; de‐identified; Taiwan: National Health Insurance Research Database; and Denmark: National Prescription and Patient Registries/Danish National Patient Registry) to evaluate OCS prescribing. We classified annual OCS duration as short‐term (1–29 days), medium‐term (30–89 days), or long‐term (≥90 days). Longitudinal change in annual prevalence of OCS use and physician prescribing patterns were reported. Among 54,630,437 participants, average annual percentage of overall OCS use was 6.8% in the United States, 17.5% in Taiwan, and 2.2% in Denmark during 2009–2018. Prevalence of OCS prescribing increased at an average annual rate of 0.1%–0.17%, mainly driven by short‐term prescribing to healthy adults. One‐quarter to one‐fifth of OCS prescribing was associated with a diagnosis of respiratory infection. Family practice and internal medicine physicians were among the highest OCS prescribers across countries and durations. Age‐ and sex‐stratified trends mirrored unstratified trends. This study provides real‐world evidence of an ongoing steady increase in OCS use in the general populations of the United States, Taiwan, and Denmark. This increase is largely driven by short‐term OCS prescribing to healthy adults, a practice previously viewed as safe but recently shown to incur substantial population‐level risk.

Objective: Examine the association between traditional Medicare (TM) vs. commercial insurance and the use of preventive care and potentially preventable hospitalization (PPH) among adults (18+) with disability [cerebral palsy/spina bifida (CP/SB); multiple sclerosis (MS); traumatic spinal cord injury (TSCI)] in the United States. Methods: Using 2008–2016 Medicare and commercial claims data, we compared adults with the same disability enrolled in TM vs. commercial insurance [Medicare: n = 21,599 (CP/SB); n = 7,605 (MS); n = 4,802 (TSCI); commercial: n = 11,306 (CP/SB); n = 6,254 (MS); n = 5,265 (TSCI)]. We applied generalized estimating equations to address repeated measures, comparing cases with controls. All models were adjusted for age, sex, race/ethnicity, and comorbid conditions. Results: Compared with commercial insurance, enrolling in TM reduced the odds of using preventive services. For example, adjusted odds ratios (OR) of annual wellness visits in TM vs. commercial insurance were 0.31 (95% confidence interval (CI): 0.28–0.34), 0.32 (95% CI: 0.28–0.37), and 0.19 (95% CI: 0.17–0.22) among adults with CP/SB, TSCI, and MS, respectively. Furthermore, PPH risks were higher in TM vs. commercial insurance. ORs of PPH in TM vs. commercial insurance were 1.50 (95% CI: 1.18–1.89), 1.83 (95% CI: 1.40–2.41), and 2.32 (95% CI: 1.66–3.22) among adults with CP/SB, TSCI, and MS, respectively. Moreover, dual-eligible adults had higher odds of PPH compared with non-dual-eligible adults [CP/SB: OR = 1.47 (95% CI: 1.25–1.72); TSCI: OR = 1.61 (95% CI: 1.35–1.92), and MS: OR = 1.80 (95% CI: 1.55–2.10)]. Conclusions: TM, relative to commercial insurance, was associated with lower receipt of preventive care and higher PPH risk among adults with disability.

Abstract Background Patients presenting to academic medical centers (AMC) typically receive primary care, specialty care, or both. Resources needed for each type of care vary, requiring different levels of care coordination. We propose a novel method to determine whether a patient primarily receives primary or specialty care to allow for optimization of care coordination. Objectives We aimed to define the concepts of a Lifer Patient and Destination Patient and analyze the current state of care utilization in those groups to inform opportunities for improving care coordination. Methods Using AMC data for a 36-month study period (FY17-19), we evaluated the number of unique patients by residence zip code. Patients with at least one primary care visit and patients without a primary care visit were classified as Lifer and Destination patients, respectively. Cohen’s effect sizes were used to evaluate differences in mean utilization of different care delivery settings. Results The AMC saw 35,909 Lifer patients and 744,037 Destination patients during the study period. Most patients were white, non-Hispanic females; however, the average age of a Lifer was seventy-two years whereas that of a Destination patient was thirty-eight. On average, a Lifer had three times more ambulatory care visits than a Destination patient. The proportion of Inpatient encounters is similar between the groups. Mean Inpatient length of stay (LOS) is similar between the groups, but Destination patients have more variance in LOS. The rate of admission from the emergency department (ED) for Destination patients is nearly double Lifers’. Conclusion There were differences in ED, ambulatory care, and inpatient utilization between the Lifer and Destination patients. Furthermore, there were incongruities between rate of hospital admissions and LOS between two groups. The Lifer and Destination patient definitions allow for identification of opportunities to tailor care coordination to these unique groups and to allocate resources more efficiently.

Objective: To compare the incidence of and adjusted hazards for serious and life-threatening morbidities among adults with traumatic spinal cord injury (TSCI) with and without type 2 diabetes (T2D). Participants and Methods: A retrospective longitudinal cohort study was conducted from September 1, 2022 to February 2, 2023, among privately insured beneficiaries if they had an International Classification of Diseases, 9th Revision or 10th Revision, Clinical Modification diagnostic code for TSCI (n=9081). Incidence estimates of serious and life-threatening morbidities, and more common secondary and long-term health conditions, were compared at 5 years of enrollment. Survival models were used to quantify unadjusted and adjusted hazard ratios for serious and life-threatening morbidities. Results: Adults living with TSCI and T2D had a higher incidence of all of the morbidities assessed as compared with nondiabetic adults with TSCI. Fully adjusted survival models reported that adults with TSCI and T2D had a greater hazard for most of the serious and life-threatening conditions assessed, including sepsis (hazard ratio [HR]: 1.65), myocardial infarction (HR: 1.63), osteomyelitis (HR: 1.9), and stroke or transient ischemic attack (HR: 1.59). Rates for comorbid and secondary conditions were higher for individuals with TSCI and T2D, such as pressure sores, urinary tract infections, and depression, even after controlling for sociodemographic and comorbid conditions. Conclusion: Adults living with TSCI and T2D have a significantly higher incidence of and risk of developing serious and life-threatening morbidities as compared with nondiabetic adults with TSCI.

Objective: To evaluate the risk of potentially preventable hospitalizations (PPHs) among adults with sensory loss. We hypothesized a greater PPH risk among people with a sensory loss (hearing, vision, and dual) compared with controls. Patients and Methods: Using 2007-2016 Medicare fee-for-service claims, this retrospective, case-control study examined the risk of PPH among adults aged 65 years and older with hearing, vision, and dual sensory loss compared with their corresponding counterparts without sensory loss (between June 1, 2022, and February 1, 2023). We ran 3 step-in regression models for the 3 case and control cohorts examining PPH risk. Our generalized linear regression models controlled for age, sex, race, Elixhauser comorbidity count, rurality, neighborhood characteristics, and the number of primary care physicians and hospitals at the county level. Results: People with vision (adjusted odds ratio [aOR], 1.21; 95% CI, 0.84-0.87) and dual sensory loss (aOR, 1.26; 95% CI, 1.14-1.40) showed a higher PPH risks than their corresponding controls. For people with hearing loss, our unadjusted models showed a higher PPH risk (OR, 1.40; 95% CI, 1.38-1.43) but after adjustment, hearing loss showed a protective association against PPH risk (OR, 0.85; 95% CI, 0.84-0.87). Moreover, in all models, annual wellness visits reduced the PPH risk by about half (eg, aOR, 0.54; 95% CI, 0.52-0.55), whereas living in disadvantaged neighborhood increased the PPH risk (eg, aOR, 1.13; 95% CI, 1.10-1.15) for cases and controls. Conclusion: People with vision and dual sensory loss were at greater PPH risk. This study has important health policy implications in reducing PPH and is indicative of a need for more incentivized and systematic approaches to facilitating the use of preventive care, particularly among older adults living in a disadvantaged neighborhood.

Continuity of care is considered a key metric of quality healthcare. Yet, continuity of care in adults aging with congenital disability and the factors that contribute to care continuity are largely unknown. Using data from a national private administrative health claims database in the United States (2007–2018). we examined continuity of care in 8596 adults (mean age 48.6 years) with cerebral palsy or spina bifida. Logistic regression models analyzed how proximity to health care facilities, availability of care providers, and community socioeconomic context were associated with more continuous care. We found that adults aging with cerebral palsy or spina bifida saw a variety of different physician specialty types and generally had discontinuous care. Individuals who lived in areas with more hospitals and residential care facilities received more continuous care than those with limited access to these resources. Residence in more affluent areas was associated with receiving more fragmented care. Findings suggest that over and above individual factors, community healthcare resources and socioeconomic context serve as important factors to consider in understanding continuity of care patterns in adults aging with cerebral palsy or spina bifida.

Abstract Most patients with multiple myeloma (MM) undergoing autologous hematopoietic stem cell transplantation (autoHCT) eventually relapse, perhaps due to the presence of clonal plasma cells (CPC) in the autograft. We conducted a retrospective analysis to evaluate the impact of CPC in the autograft on the outcomes of high-risk chromosomal abnormalities (HRMM) patients undergoing autoHCT between 2008 and 2018. Patients were divided into CPC+ or CPC− in the autograft by next-generation flow cytometry (NGF). There were 75 CPC + autografts (18%) and 341 CPC− (82%). The CPC + group was less likely to achieve MRD-negative complete remission post-transplant (11% vs. 42%; p

Objective: To compare the prevalence and incidence of, and adjusted hazards for comorbidities among adults with traumatic spinal cord injuries (TSCIs) across insurance types (private vs governmental insurance) in the United States. Patients and Methods: Privately insured (N=9081) and Medicare (N=7645) beneficiaries with a diagnosis of TSCI were included. Prevalence and incidence estimates of common psychological, cardiometabolic, and musculoskeletal morbidities were compared at baseline and at 4-years after index diagnosis, respectively. Survival models were used to quantify hazard ratios (HRs) for outcomes, controlling for insurance type, sociodemographic characteristics, and other comorbidities. Sensitivity analyses were conducted to determine the effects of insurance and race/ethnicity. Results: Adults with TSCIs on Medicare had a higher prevalence of any psychological (54.7% vs 35.4%), cardiometabolic (74.7% vs 70.1%), and musculoskeletal (72.8% vs 66.3%) morbidity than privately insured adults with TSCIs. Similarly, the 4-year incidences of most psychological (eg, depression: 37.6% [Medicare] vs 24.2% [private]), cardiometabolic (eg, type 2 diabetes: 22.5% [Medicare] vs 12.9% [private], and musculoskeletal (eg, osteoarthritis: 42.1% [Medicare] vs 34.6% [private]) morbidities were considerably higher among adults with TSCIs on Medicare. Adjusted survival models found that adults with TSCIs on Medicare had a greater hazard for developing psychological (HR, 1.40; 95% CI, 1.31-1.50) and cardiometabolic (HR, 1.21; 95% CI, 1.10-1.33) morbidities compared with privately insured adults with TSCI. There was evidence of both insurance and racial disparities. Conclusion: Adults with TSCIs on Medicare had significantly higher prevalence and risk for developing common physical and mental health comorbidities, compared with privately insured adults with TSCIs.

Objective: To compare the incidence of and adjusted hazard ratios for common cardiometabolic diseases, musculoskeletal disorders, and psychological morbidities among adults with and without multiple sclerosis (MS). Patients and Methods: Beneficiaries were included if they had an International Classification of Diseases, Ninth Revision, Clinical Modification diagnostic code for MS (n=9815) from a national private insurance claims database (Clinformatics Data Mart; OptumInsight). Adults without MS were also included (n=1,474,232) as a control group. Incidence estimates of common cardiometabolic diseases, musculoskeletal disorders, and psychological morbidities were compared at 5 years of continuous enrollment. Survival models were used to quantify unadjusted and adjusted hazard ratios for incident morbidities. Results: Adults with MS had a higher incidence of any common cardiometabolic disease (51.6% [2663 of 5164] vs 36.4% [328,690 of 904,227]), musculoskeletal disorder (68.8% [3411 of 4959] vs 47.5% [512,422 of 1,077,737]), and psychological morbidity (49.4% [3305 of 6691] vs 30.8% [380,893 of 1,235,388]) than adults without MS, and differences were clinically meaningful (all P

Abstract Health and environmental hazards related to high pollution concentrations have become a serious issue from public policy perspectives and human health. Using Machine Learning (ML) approach, this research aims to improve the estimation of grid‐wise PM2.5, a criteria pollutant, by reducing systematic bias from speciation provided by MERRA‐from the Modern‐Era Retrospective analysis for Research and Applications version 2 (MERRA‐2). The ML model was trained using various meteorological parameters and aerosol species simulated by MERRA‐2 and ground measurements from Environmental Protection Agency (EPA) air quality system stations. The ML approach significantly improved performance and reduced mean bias in the 0–10 μg m−3 range. We also used the Random Forest ML model for each EPA region using 1 year of collocated data sets. The resulting ML models for each EPA region were validated, and the aggregate data set has a Spearman Rank correlation (SR) of 0.73 (RMSE = 4.8 μg m−3) and 0.69 (RMSE = 5.8 μg m−3) for training and testing, respectively. The SR (and RMSE in μg m−3) increased to 0.81 (3.9), 0.89 (1.6), and 0.90 (1.1) for daily, monthly, and yearly averages, respectively. The results from the initial implementation of the ML model for the global region are encouraging. Still, they require more research and development to overcome challenges associated with data gaps in many parts of the world.

The current global platelet supply is often insufficient to meet all the transfusion needs of patients, in particular for those with alloimmune thrombocytopenia. To address this issue, we have developed a strategy employing a combination of approaches to achieve more efficient production of functional megakaryocytes (MKs) and platelets collected from cord blood (CB)-derived CD34+ hematopoietic cells. This strategy is based on ex-vivo expansion and differentiation of MKs in the presence of bone marrow niche-mimicking mesenchymal stem cells (MSCs), together with two other key components: (1) To enhance MK polyploidization, we used the potent pharmacological Rho-associated coiled-coil kinase (ROCK) inhibitor, KD045, resulting in liberation of increased numbers of functional platelets both in-vitro and in-vivo; (2) To evade HLA class I T-cell-driven killing of these expanded MKs, we employed CRISPR-Cas9-mediated β-2 microglobulin (β2M) gene knockout (KO). We found that coculturing with MSCs and MK-lineage-specific cytokines significantly increased MK expansion. This was further increased by ROCK inhibition, which induced MK polyploidization and platelet production. Additionally, ex-vivo treatment of MKs with KD045 resulted in significantly higher levels of engraftment and donor chimerism in a mouse model of thrombocytopenia. Finally, β2M KO allowed MKs to evade killing by allogeneic T-cells. Overall, our approaches offer a novel, readily translatable roadmap for producing adult donor-independent platelet products for a variety of clinical indications.

Acute graft-vs.-host (GVHD) disease remains a common complication of allogeneic stem cell transplantation with very poor outcomes once the disease becomes steroid refractory. Mesenchymal stem cells (MSCs) represent a promising therapeutic approach for the treatment of GVHD, but so far this strategy has had equivocal clinical efficacy. Therapies using MSCs require optimization taking advantage of the plasticity of these cells in response to different microenvironments. In this study, we aimed to optimize cord blood tissue derived MSCs (CBti MSCs) by priming them using a regimen of inflammatory cytokines. This approach led to their metabolic reprogramming with enhancement of their glycolytic capacity. Metabolically reprogrammed CBti MSCs displayed a boosted immunosuppressive potential, with superior immunomodulatory and homing properties, even after cryopreservation and thawing. Mechanistically, primed CBti MSCs significantly interfered with glycolytic switching and mTOR signaling in T cells, suppressing T cell proliferation and ensuing polarizing toward T regulatory cells. Based on these data, we generated a Good Manufacturing Process (GMP) Laboratory protocol for the production and cryopreservation of primed CBti MSCs for clinical use. Following thawing, these cryopreserved GMP-compliant primed CBti MSCs significantly improved outcomes in a xenogenic mouse model of GVHD. Our data support the concept that metabolic profiling of MSCs can be used as a surrogate for their suppressive potential in conjunction with conventional functional methods to support their therapeutic use in GVHD or other autoimmune disorders.

Natural killer (NK) cells are innate lymphocytes recognized for their important role against tumor cells. NK cells expressing chimeric antigen receptors (CARs) have enhanced effector function against various type of cancer and are attractive contenders for the next generation of cancer immunotherapies. However, a number of factors have hindered the application of NK cells for cellular therapy, including their poor in vitro growth kinetics and relatively low starting percentages within the mononuclear cell fraction of peripheral blood or cord blood (CB). To overcome these limitations, we genetically-engineered human leukocyte antigen (HLA)-A− and HLA-B− K562 cells to enforce the expression of CD48, 4-1BBL, and membrane-bound IL-21 (mbIL21), creating a universal antigen presenting cell (uAPC) capable of stimulating their cognate receptors on NK cells. We have shown that uAPC can drive the expansion of both non-transduced (NT) and CAR-transduced CB derived NK cells by >900-fold in 2 weeks of co-culture with excellent purity (>99.9%) and without indications of senescence/exhaustion. We confirmed that uAPC-expanded research- and clinical-grade NT and CAR-transduced NK cells have higher metabolic fitness and display enhanced effector function against tumor targets compared to the corresponding cell fractions cultured without uAPCs. This novel approach allowed the expansion of highly pure GMP-grade CAR NK cells at optimal cell numbers to be used for adoptive CAR NK cell-based cancer immunotherapy.

Abstract Background Several systemic treatments have been shown to increase survival for patients with metastatic castration-resistant prostate cancer. This study sought to characterize variation in use of the six “focus drugs” (docetaxel, abiraterone, enzalutamide, sipuleucel-T, radium-223, and cabazitaxel) that have been approved by the Food and Drug Administration for the treatment of metastatic castration-resistant prostate cancer during the years 2010–2015. We hypothesized that the use of these treatments would vary over time and by region of the country. Methods We used Clinformatics DataMart™ Database (OptumInsight, Eden Prairie, MN), a de-identified claims database from a national insurance provider. Our sample included patients with prostate cancer who received any of the six drugs. We describe changes in usage patterns over time and geographic region of the United States via detailed descriptive statistics. We explore both patterns of first line therapy and sequence of treatments in our database. Results Our final analysis included 4275 patients with a mean age of 74 years. Docetaxel was the most commonly used first-line therapy in 2010 (97%), 2011 (66%), and 2012 (49%). Abiraterone was the most commonly used first-line therapy in 2013 (56%), 2014 (46%), and 2015 (34%). Approximately 14% of our study cohort received ≥3 of the 6 drugs throughout their disease course. There was marked geographic variation in use of each of the drugs. Conclusion Variation in treatment patterns were found with respect to both time and geographic location. Prescription rates of abiraterone outpaced docetaxel as the most commonly prescribed drug after 2013 when it became widely available. However, some regions of the country still lagged behind and prescribed less than would be expected.

An innovative prototype sensor containing A36 carbon steel as a capacitor was explored to monitor early-stage corrosion. The sensor detected the changes of the surface- rather than the bulk- property and morphology of A36 during corrosion. Thus it was more sensitive than the conventional electrical resistance corrosion sensors. After being soaked in an aerated 0.2 M NaCl solution, the sensor’s normalized electrical resistance (R/R0) decreased continuously from 1.0 to 0.74 with the extent of corrosion. Meanwhile, the sensor’s normalized capacitance (C/C0) increased continuously from 1.0 to 1.46. X-ray diffraction result indicates that the iron rust on A36 had crystals of lepidocrocite and magnetite.

New therapeutic modalities are needed for ovarian cancer, the most lethal gynecologic malignancy. Recent clinical trials have demonstrated the impressive therapeutic potential of adoptive therapy using chimeric antigen receptor (CAR)-redirected T cells to target hematological cancers, and emerging studies suggest a similar impact may be achieved for solid cancers. We sought determine whether genetically-modified T cells targeting the CE7-epitope of L1-CAM, a cell adhesion molecule aberrantly expressed in several cancers, have promise as an immunotherapy for ovarian cancer, first demonstrating that L1-CAM was highly over-expressed on a panel of ovarian cancer cell lines, primary ovarian tumor tissue specimens, and ascites-derived primary cancer cells. Human central memory derived T cells (TCM) were then genetically modified to express an anti-L1-CAM CAR (CE7R), which directed effector function upon tumor antigen stimulation as assessed by in vitro cytokine secretion and cytotoxicity assays. We also found that CE7R+ T cells were able to target primary ovarian cancer cells. Intraperitoneal (i.p.) administration of CE7R+ TCM induced a significant regression of i.p. established SK-OV-3 xenograft tumors in mice, inhibited ascites formation, and conferred a significant survival advantage compared with control-treated animals. Taken together, these studies indicate that adoptive transfer of L1-CAM-specific CE7R+ T cells may offer a novel and effective immunotherapy strategy for advanced ovarian cancer.

Mesenchymal stem cells (MSCs) are currently being widely investigated both in the lab and in clinical trials for multiple disease states. The differentiation, trophic, and immunomodulatory characteristics of MSCs contribute to their therapeutic effects. Another often overlooked factor related to efficacy is the degree of engraftment. When reported, engraftment is generally low and transient in nature. MSC delivery methods should be tailored to the lesion being treated, which may be local or systemic, and customized to the mechanism of action of the MSCs, which can also be local or systemic. Engraftment efficiency is enhanced by using intra-arterial delivery instead of intravenous delivery, thus avoiding the “first-pass” accumulation of MSCs in the lung. Several methodologies to target MSCs to specific organs are being developed. These cell targeting methodologies focus on the modification of cell surface molecules through chemical, genetic, and coating techniques to promote selective adherence to particular organs or tissues. Future improvements in targeting and delivery methodologies to improve engraftment are expected to improve therapeutic results, extend the duration of efficacy, and reduce the effective (MSC) therapeutic dose.

Human mesenchymal stem cells (hMSCs) can be engineered to express specific genes, either for their use in cell-based therapies or to track them in vivo over long periods of time. To obtain long-term expression of these genes, a lentivirus- or retrovirus-mediated cell transduction is often used. However, given that the efficiency with these viruses is typically low in primary cells, additives such as polybrene are always used for efficient viral transduction. Unfortunately, as presented here, exposure to polybrene alone at commonly used concentratons (1-8 µg/mL) negatively impacts hMSC proliferation in a dose-dependent manner as measured by CyQUANT, EdU incorporation, and cell cycle analysis. This inhibition of proliferation was observable in culture even 3 weeks after exposure. Culturing the cells in the presence of FGF-2, a potent mitogen, did not abrogate this negative effect of polybrene. In fact, the normally sharp increase in hMSC proliferation that occurs during the first days of exposure to FGF-2 was absent at 4 µg/mL or higher concentrations of polybrene. Similarly, the effect of stimulating cell proliferation under simulated hypoxic conditions was also decreased when cells were exposed to polybrene, though overall proliferation rates were higher. The negative influence of polybrene was, however, reduced when the cells were exposed to polybrene for a shorter period of time (6 hr vs 24 hr). Thus, careful evaluation should be done when using polybrene to aid in lentiviral transduction of human MSCs or other primary cells, especially when cell number is critical.