The impact of estradiol supplementation on endometrial thickness and intrauterine insemination outcomes.

The impact of estrogen supplementation during the follicular/proliferative phase on the endometrial lining thickness (EMT) prior to intrauterine insemination (IUI) remains largely unstudied. Our study examined changes in EMT and rates of clinical pregnancy, miscarriage, and live birth for all patients who completed an IUI cycle at Stanford Fertility Center from 2017-2023 (n = 2281 cycles). Cycles with estradiol supplementation (n = 309) were compared to reference cycles without supplementation (n = 1972), with the reference cohort further categorized into cycles with a pre-ovulatory EMT of < 7 mm ("thin-lining", n = 536) and ≥ 7 mm ("normal-lining", n = 1436). The estradiol group had a statistically significant greater change in EMT from baseline to ovulation compared to the thin-lining reference groups (2.4 mm vs 1.9 mm, p < =0.0001). Similar rates of clinical pregnancy and live birth were observed. After adjusting for age, BMI, race/ethnicity, infertility diagnosis, and EMT at trigger, the estradiol cohort had a significantly increased odds of miscarriage versus the entire reference cohort (2.46, 95 % confidence interval [1.18, 5.14], p = 0.02). Thus, although estradiol supplementation had a statistically significant increase in EMT compared to IUI cycles with thin pre-ovulatory EMT (<7 mm), this change did not translate into improved IUI outcomes such as increased rates of clinical pregnancy and live birth or decreased rate of miscarriage. Our study suggests that supplemental estradiol does not appear to improve IUI outcomes.

Elevated body mass index in modified natural cycle frozen euploid embryo transfers is not associated with live birth rate.

PURPOSE: To assess the impact of elevated BMI on the success of modified natural cycle frozen embryo transfers (mNC-FET) of euploid embryos. METHODS: This retrospective cohort study at a single academic institution reviewed mNC-FET involving single euploid blastocysts from 2016 to 2020. Comparison groups were divided by pre-pregnancy BMI (kg/m2) category: normal weight (18.5-24.9), overweight (25-29.9) or obese (≥ 30). Underweight BMI (< 18.5) was excluded from the analysis. The primary outcome was live birth rate (LBR) and secondary outcome was clinical pregnancy rate (CPR), defined as presence of fetal cardiac activity on ultrasound. Absolute standardized differences (ASD) were calculated to compare descriptive variables and p-values and multivariable logistic regressions with generalized estimating equations (GEE) were used to compare pregnancy outcomes. RESULTS: 562 mNC-FET cycles were completed in 425 patients over the study period. Overall, there were 316 transfers performed in normal weight patients, 165 in overweight patients, and 81 in obese weight patients. There was no statistically significant difference in LBR across all BMI categories (55.4% normal weight, 61.2% overweight, and 64.2% obese). There was also no difference for the secondary outcome, CPR, across all categories (58.5%, 65.5%, and 66.7%, respectively). This was confirmed in GEE analysis when adjusting for confounders. CONCLUSION: While increased weight has commonly been implicated in poor pregnancy outcomes, the effect of BMI on the success of mNC-FET remains debated. Across five years of data from a single institution using euploid embryos in mNC-FET cycles, elevated BMI was not associated with reduced LBR or CPR.

Pregnancy and neonatal outcomes of letrozole versus natural cycle frozen embryo transfer of autologous euploid blastocyst.

PURPOSE: To investigate the pregnancy and neonatal outcomes of letrozole-stimulated frozen embryo transfer (LTZ-FET) cycles compared with natural FET cycles (NC-FET). METHODS: Our retrospective cohort included all LTZ-FET (n = 161) and NC-FET (n = 575) cycles that transferred a single euploid autologous blastocyst from 2016 to 2020 at Stanford Fertility Center. The LTZ-FET protocol entailed 5 mg of daily letrozole for 5 days starting on cycle day 2 or 3. Outcomes were compared using absolute standardized differences (ASD), in which a larger ASD signifies a larger difference. Multivariable regression models adjusted for confounders: maternal age, BMI, nulliparity, embryo grade, race, infertility diagnosis, and endometrial thickness. RESULTS: The demographic and clinical characteristics were overall similar. A greater proportion of the letrozole cohort was multiparous, transferred high-graded embryos, and had ovulatory dysfunction. The cohorts had similar pregnancy rates (67.1% LTZ vs 62.1% NC; aOR 1.31, P = 0.21) and live birth rates (60.9% LTZ vs 58.6% NC; aOR 1.17, P = 0.46). LTZ-FET neonates on average were born 5.7 days earlier (P < 0.001) and had higher prevalence of prematurity (18.6% vs. 8.0%NC, ASD = 0.32) and low birth weight (10.4% vs. 5.0%, ASD = 0.20). Both cohorts' median gestational ages (38 weeks and 1 day for LTZ; 39 weeks and 0 day for NC) were full term. CONCLUSION: There were similar rates of pregnancy and live birth between LTZ-FET and NC-FET cycles. However, there was a higher prevalence of prematurity and low birth weight among LTZ-FET neonates. Reassuringly, the median gestational age in both cohorts was full term, and while the difference in gestational length of almost 6 days does not appear to be clinically significant, this warrants larger studies.

The Effect of Human Growth Hormone on Endometrial Growth in Controlled Ovarian Hyperstimulation Cycles.

This study aims to compare endometrial growth before and after the addition of human growth hormone (hGH) in controlled ovarian hyperstimulation (COH) cycles. A 5-year retrospective cohort study of patients treated with hGH to improve oocyte development during COH cycles was conducted. Each patient's cycle without hGH immediately preceding cycle(s) with hGH was used for patients to serve as their own controls. Primary outcome was absolute growth in endometrial thickness from pre-stimulation start to day of hCG trigger. Mixed-model regression analysis controlled for patient correlation over repeat cycles and potential confounders. 80 patients were included. Mean age was 39.7 years; mean BMI was 23.8 kg/m2. Majority of patients were nulliparous, non-smoking, and White or Asian. Most common diagnosis was diminished ovarian reserve. Endometrial growth was compared between 159 COH cycles with hGH and 80 COH control cycles; mean increase was 4.5 mm and 3.9 mm, respectively-an unadjusted difference of 0.6 mm (95% CI: 0.2−1.1, p = 0.01). After adjusting for demographic/clinical factors, hGH was associated with 0.9 mm greater endometrial growth (0.4−1.4, p < 0.01). Absolute increase in endometrial thickness was higher in COH cycles that included hGH. Further prospective studies in embryo transfer cycles are needed.

The impact of euploid blastocyst morphology and maternal age on pregnancy and neonatal outcomes in natural cycle frozen embryo transfers.

PURPOSE: To evaluate whether morphology impacts the pregnancy and neonatal outcomes of euploid blastocysts, and whether maternal age still affects outcomes when top-graded, euploid blastocysts are used. METHODS: This retrospective cohort study included all natural-cycle frozen embryo transfers (NC-FET) using an autologous, euploid blastocyst from June 2016 to June 2020 (n = 610). There were five groups based on embryo grade: AA, AB, BA, BB, and "any C". For analysis of only AA-graded embryos, there were three maternal age groups: < 35, 35-39, and 40 + years. The main outcomes measured were clinical pregnancy and live birth rates, while the secondary outcomes included neonatal outcomes such as gestational age at delivery and birthweight. Multivariable logistic regression models were performed to adjust for confounders. RESULTS: Euploid blastocysts with poorer morphology had lower odds of pregnancy and live birth; specifically, embryos with inner cell mass (ICM) graded as "C" had statistically significant decreased odds of pregnancy (aOR 0.33, p = 0.04) and live birth (aOR 0.32, p = 0.03) compared with ICM grade "A". The differences in pregnancy rate between trophectoderm grades were not statistically significant. Even in cycles that transferred a top-graded (AA) euploid embryo, maternal age at transfer was independently associated with outcomes. Embryo grade and maternal age, however, did not significantly impact neonatal outcomes such as prematurity and birthweight. CONCLUSION: The morphology of euploid blastocysts and maternal age at NC-FET both independently impact pregnancy outcomes. Neonatal outcomes were similar across embryo morphology and maternal age groups, suggesting that lower morphology euploid embryos not be discounted as viable options for transfer.

The impact of estradiol on pregnancy outcomes in letrozole-stimulated frozen embryo transfer cycles.

OBJECTIVE: To assess the impact of low estradiol (E2) levels in letrozole-stimulated frozen embryo transfer (FET) cycles on pregnancy and neonatal outcomes. DESIGN: Retrospective cohort. SETTING: University-affiliated fertility center. PATIENTS: All patients who underwent letrozole-stimulated FET cycles from January 2017 to April 2020 (n = 217). The "Low E2" group was defined as those with E2 serum levels on the day of trigger <10th percentile level (E2 <91.16 pg/mL, n = 22) and the "Normal E2" group was defined as those with E2 serum levels ≥10th percentile level (E2 ≥91.16 pg/mL, n = 195). INTERVENTIONS: None. MAIN OUTCOME MEASURES: Pregnancy outcomes including rates of clinical pregnancy, clinical miscarriage, and live birth. Neonatal outcomes including gestational age at delivery, birth weight, and Apgar score. RESULTS: The mean ± SD estradiol level was 66.8 ± 14.8 pg/mL for the "Low E2" group compared with 366.3 ± 322.1 pg/mL for the "Normal E2" group. There were otherwise no substantial differences in cycle characteristics such as endometrial thickness on the day of ovulation trigger and progesterone levels in early pregnancy. The "Low E2" group had a significantly higher clinical miscarriage rate (36.4% vs. 8.8%, adjusted odds ratio 8.06) and lower live birth rate (31.8% vs. 57.9%, adjusted odds ratio 0.28). Neonatal outcomes such as gestational age at delivery, mean birth weight, Apgar scores, and incidence of newborn complications were not clinically different between the groups. CONCLUSION: Low E2 levels were associated with a significantly higher miscarriage rate and lower live birth rate, suggesting that E2 levels in the follicular phase may have an effect on cycle outcomes. Given the rise in use of FET, further studies are needed to confirm our findings and understand the mechanisms.

The obstetrical research landscape: a cross-sectional analysis of clinical trials from 2007-2020.

Background: Obstetrical complications affect more than a third of women globally, but are underrepresented in clinical research. Little is known about the comprehensive obstetrical clinical trial landscape, how it compares with other fields, or factors associated with the successful completion of obstetrical trials. Objective: This study aimed to characterize obstetrical clinical trials registered on ClinicalTrials.gov with the primary objective of identifying features associated with early discontinuation and results reporting. Study Design: This is a cross-sectional study with descriptive, logistic regression and Cox regression analyses of clinical trials registered on ClinicalTrials.gov. Our primary exposure variables were trial focus (obstetrical or nonobstetrical) and trial funding (industry, United States government, or academic). We conducted additional exploratory analyses of other trial features including design, enrollment, and therapeutic focus. We examined the associations of exposure variables and other trial features with 2 primary outcomes: early discontinuation and results reporting. Results: We downloaded data for all studies (N=332,417) registered on ClinicalTrials.gov from October 1, 2007, to March 9, 2020, from the Aggregate Analysis of ClinicalTrials.gov database. We excluded studies with a noninterventional design (n=63,697) and those registered before October 1, 2007 (n=45,209). A total of 4276 obstetrical trials (1.9%) (ie, interventional studies) and 219,235 nonobstetric trials (98.1%) were compared. Among all trials, 2.8% of academic-funded trials, 1.9% of United States government-funded trials, and 0.4% of industry-funded trials focused on obstetrics. The quantity of obstetrical trials increased over time (10.8% annual growth rate). Compared with nonobstetrical trials, obstetrical trials had a greater risk of early discontinuation (adjusted hazard ratio, 1.40; 95% confidence interval, 1.21-1.62; P<.0001) and similar odds of results reporting (adjusted odds ratio, 0.89; 95% confidence interval, 0.72-1.10; P=.19). Among obstetrical trials funders after controlling for confounding variables, United States government-funded trials were at the lowest risk of early discontinuation (United States government, adjusted hazard ratio, 0.23; 95% confidence interval, 0.07-0.69; P=.009; industry reference; academic, adjusted hazard ratio, 1.04; 95% confidence interval, 0.62-1.74; P=.88). Academic-funded trials had the lowest odds of results reporting after controlling for confounding variables (academic institutions, adjusted odds ratio, 0.39; 95% confidence interval, 0.22-0.68; P=.0009; industry reference; United States government, adjusted odds ratio, 1.06; 95% confidence interval, 0.53-2.09; P=.87). Conclusion: Obstetrical trials represent only 1.9% of all clinical trials in ClinicalTrials.gov and have comparatively poor completion. All stakeholders should commit to increasing the number of obstetrical trials and improving their completion and dissemination to ensure clinical research reflects the obstetrical burden of disease and advances maternal health.

Vascular Health of Children Conceived via In Vitro Fertilization.

OBJECTIVE: To evaluate whether in vitro fertilization (IVF) has an effect on the cardiovascular health of offspring. STUDY DESIGN: This was a cross-sectional pilot study. We performed vascular health assessment for 17 children aged 10-14 years who were conceived via IVF with autologous oocytes at Stanford University. Carotid artery ultrasound evaluated intima-media thickness and stiffness, carotid-femoral pulse wave velocity determined segmental arterial stiffness, and endothelial pulse amplitude testing assessed endothelial function. We compared IVF offspring with control adolescents assessed in the same laboratory, with all comparisons adjusted for age, sex, and race/ethnicity. RESULTS: All participants had normal body mass index and blood pressure. Compared with controls, IVF children had thicker common carotid artery intima-media thickness (0.44 ± 0.03 mm vs 0.38 ± 0.03 mm; P < .01), higher elastic modulus (395.29 ± 185.33 mm Hg vs 242.79 ± 37.69 mm Hg; P = .01), higher ßstiffness (2.65 ± 0.38 vs 2.28 ± 0.23; P < .01), and higher peak velocity (142.29 ± 31.62 cm/s vs 117.71 ± 32.69 cm/s; P = .04). The mean endothelial pulse amplitude testing reactive hyperemia index was not significantly different between IVF and controls. The mean pulse wave velocity was 4.69 ± 0.51 m/s compared with the controls 4.60 ± 0.57 m/s (P = .11), with 8 (47%) having abnormal values. CONCLUSION: In an assessment of endothelial function and arterial properties of children conceived via IVF, we found that children conceived via IVF seem to have evidence of abnormal vascular health. Further studies with larger sample size and long-term follow-up are warranted.

Maternal and neonatal outcomes associated with trophectoderm biopsy.

OBJECTIVE: To assess whether pregnancies achieved with trophectoderm biopsy for preimplantation genetic testing (PGT) have different risks of adverse obstetric and neonatal outcomes compared with pregnancies achieved with IVF without biopsy. DESIGN: Observational cohort. SETTING: University-affiliated fertility center. PATIENT(S): Pregnancies achieved via IVF with PGT (n = 177) and IVF without PGT (n = 180) that resulted in a live birth. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Maternal outcomes including preeclampsia and placenta previa and neonatal outcomes including birth weight and birth defects. RESULT(S): There was a statistically significant increase in the risk of preeclampsia among IVF+PGT pregnancies compared with IVF without PGT pregnancies, with an incidence of 10.5% versus 4.1% (adjusted odds ratio [aOR] = 3.02; 95% confidence interval [95% CI], 1.10, 8.29). The incidence of placenta previa was 5.8% in IVF+PGT pregnancies versus 1.4% in IVF without PGT pregnancies (aOR = 4.56; 95% CI, 0.93, 22.44). Similar incidences of gestational diabetes, preterm premature rupture of membranes, and postpartum hemorrhage were observed. IVF+PGT and IVF without PGT neonates did not have a significantly different gestational age at delivery or rate of preterm birth, low birth weight, neonatal intensive care unit admission, neonatal morbidities, or birth defects. All trends, including the significantly increased risk of preeclampsia in IVF+PGT pregnancies, persisted upon stratification of analysis to only singleton live births. CONCLUSION(S): To date, this is the largest and most extensively controlled study examining maternal and neonatal outcomes after trophectoderm biopsy. There was a statistically significant three-fold increase in the odds of preeclampsia associated with trophectoderm biopsy. Given the rise in PGT use, further investigation is warranted.

Prolonged survival of transplanted stem cells after ischaemic injury via the slow release of pro-survival peptides from a collagen matrix.

Stem-cell-based therapies hold considerable promise for regenerative medicine. However, acute donor-cell death within several weeks after cell delivery remains a critical hurdle for clinical translation. Co-transplantation of stem cells with pro-survival factors can improve cell engraftment, but this strategy has been hampered by the typically short half-lives of the factors and by the use of Matrigel and other scaffolds that are not chemically defined. Here, we report a collagen-dendrimer biomaterial crosslinked with pro-survival peptide analogues that adheres to the extracellular matrix and slowly releases the peptides, significantly prolonging stem cell survival in mouse models of ischaemic injury. The biomaterial can serve as a generic delivery system to improve functional outcomes in cell-replacement therapy.

Sensing of dangerous DNA.

The presence of damaged and microbial DNA can pose a threat to the survival of organisms. Cells express various sensors that recognize specific aspects of such potentially dangerous DNA. Recognition of damaged or microbial DNA by sensors induces cellular processes that are important for DNA repair and inflammation. Here, we review recent evidence that the cellular response to DNA damage and microbial DNA are tightly intertwined. We also discuss insights into the parameters that enable DNA sensors to distinguish damaged and microbial DNA from DNA present in healthy cells.

The DNA Structure-Specific Endonuclease MUS81 Mediates DNA Sensor STING-Dependent Host Rejection of Prostate Cancer Cells.

Self-DNA is present in the cytosol of many cancer cells and can promote effective immune rejection of tumor cells, but the mechanisms leading to the presence of cytosolic DNA are unknown. Here, we report that the cleavage of genomic DNA by DNA structure-specific endonuclease MUS81 and PARP-dependent DNA repair pathways leads to the accumulation of cytosolic DNA in prostate cancer cells. The number of nuclear MUS81 foci and the amount of cytosolic dsDNA increased in tandem from hyperplasia to clinical stage II prostate cancers and decreased at stage III. Cytosolic DNA generated by MUS81 stimulated DNA sensor STING-dependent type I interferon (IFN) expression and promoted phagocytic and T cell responses, resulting in type I and II IFN-mediated rejection of prostate tumor cells via mechanisms that partly depended on macrophages. Our results demonstrate that the tumor suppressor MUS81 alerts the immune system to the presence of transformed host cells.

Costimulation-adhesion blockade is superior to cyclosporine A and prednisone immunosuppressive therapy for preventing rejection of differentiated human embryonic stem cells following transplantation.

RATIONALE: Human embryonic stem cell (hESC) derivatives are attractive candidates for therapeutic use. The engraftment and survival of hESC derivatives as xenografts or allografts require effective immunosuppression to prevent immune cell infiltration and graft destruction. OBJECTIVE: To test the hypothesis that a short-course, dual-agent regimen of two costimulation-adhesion blockade agents can induce better engraftment of hESC derivatives compared to current immunosuppressive agents. METHODS AND RESULTS: We transduced hESCs with a double fusion reporter gene construct expressing firefly luciferase (Fluc) and enhanced green fluorescent protein, and differentiated these cells to endothelial cells (hESC-ECs). Reporter gene expression enabled longitudinal assessment of cell engraftment by bioluminescence imaging. Costimulation-adhesion therapy resulted in superior hESC-EC and mouse EC engraftment compared to cyclosporine therapy in a hind limb model. Costimulation-adhesion therapy also promoted robust hESC-EC and hESC-derived cardiomyocyte survival in an ischemic myocardial injury model. Improved hESC-EC engraftment had a cardioprotective effect after myocardial injury, as assessed by magnetic resonance imaging. Mechanistically, costimulation-adhesion therapy is associated with systemic and intragraft upregulation of T-cell immunoglobulin and mucin domain 3 (TIM3) and a reduced proinflammatory cytokine profile. CONCLUSIONS: Costimulation-adhesion therapy is a superior alternative to current clinical immunosuppressive strategies for preventing the post-transplant rejection of hESC derivatives. By extending the window for cellular engraftment, costimulation-adhesion therapy enhances functional preservation following ischemic injury. This regimen may function through a TIM3-dependent mechanism.

The role of SIRT6 protein in aging and reprogramming of human induced pluripotent stem cells.

Aging is known to be the single most important risk factor for multiple diseases. Sirtuin 6, or SIRT6, has recently been identified as a critical regulator of transcription, genome stability, telomere integrity, DNA repair, and metabolic homeostasis. A knockout mouse model of SIRT6 has displayed dramatic phenotypes of accelerated aging. In keeping with its role in aging, we demonstrated that human dermal fibroblasts (HDFs) from older human subjects were more resistant to reprogramming by classic Yamanaka factors than those from younger human subjects, but the addition of SIRT6 during reprogramming improved such efficiency in older HDFs substantially. Despite the importance of SIRT6, little is known about the molecular mechanism of its regulation. We show, for the first, time posttranscriptional regulation of SIRT6 by miR-766 and inverse correlation in the expression of this microRNA in HDFs from different age groups. Our results suggest that SIRT6 regulates miR-766 transcription via a feedback regulatory loop, which has implications for the modulation of SIRT6 expression in reprogramming of aging cells.

Genome editing of human embryonic stem cells and induced pluripotent stem cells with zinc finger nucleases for cellular imaging.

RATIONALE: Molecular imaging has proven to be a vital tool in the characterization of stem cell behavior in vivo. However, the integration of reporter genes has typically relied on random integration, a method that is associated with unwanted insertional mutagenesis and positional effects on transgene expression. OBJECTIVE: To address this barrier, we used genome editing with zinc finger nuclease (ZFN) technology to integrate reporter genes into a safe harbor gene locus (PPP1R12C, also known as AAVS1) in the genome of human embryonic stem cells and human induced pluripotent stem cells for molecular imaging. METHODS AND RESULTS: We used ZFN technology to integrate a construct containing monomeric red fluorescent protein, firefly luciferase, and herpes simplex virus thymidine kinase reporter genes driven by a constitutive ubiquitin promoter into a safe harbor locus for fluorescence imaging, bioluminescence imaging, and positron emission tomography imaging, respectively. High efficiency of ZFN-mediated targeted integration was achieved in both human embryonic stem cells and induced pluripotent stem cells. ZFN-edited cells maintained both pluripotency and long-term reporter gene expression. Functionally, we successfully tracked the survival of ZFN-edited human embryonic stem cells and their differentiated cardiomyocytes and endothelial cells in murine models, demonstrating the use of ZFN-edited cells for preclinical studies in regenerative medicine. CONCLUSION: Our study demonstrates a novel application of ZFN technology to the targeted genetic engineering of human pluripotent stem cells and their progeny for molecular imaging in vitro and in vivo.

Imaging cardiac stem cell therapy: translations to human clinical studies.

Stem cell therapy promises to open exciting new options in the treatment of cardiovascular diseases. Although feasible and clinically safe, the in vivo behavior and integration of stem cell transplants still remain largely unknown. Thus, the development of innovative non-invasive imaging techniques capable of effectively tracking such therapy in vivo is vital for a more in-depth investigation into future clinical applications. Such imaging modalities will not only generate further insight into the mechanisms behind stem cell-based therapy, but also address some major concerns associated with translational cardiovascular stem cell therapy. In the present review, we summarize the principles underlying three major stem cell tracking methods: (1) radioactive labeling for positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging, (2) iron particle labeling for magnetic resonance imaging (MRI), and (3) reporter gene labeling for bioluminescence, fluorescence, MRI, SPECT, and PET imaging. We then discuss recent clinical studies that have utilized these modalities to gain biological insights into stem cell fate.

Effects of ionizing radiation on self-renewal and pluripotency of human embryonic stem cells.

Human embryonic stem cells (hESC) present a novel platform for in vitro investigation of the early embryonic cellular response to ionizing radiation. Thus far, no study has analyzed the genome-wide transcriptional response to ionizing radiation in hESCs, nor has any study assessed their ability to form teratomas, the definitive test of pluripotency. In this study, we use microarrays to analyze the global gene expression changes in hESCs after low-dose (0.4 Gy), medium-dose (2 Gy), and high-dose (4 Gy) irradiation. We identify genes and pathways at each radiation dose that are involved in cell death, p53 signaling, cell cycling, cancer, embryonic and organ development, and others. Using Gene Set Enrichment Analysis, we also show that the expression of a comprehensive set of core embryonic transcription factors is not altered by radiation at any dose. Transplantation of irradiated hESCs to immune-deficient mice results in teratoma formation from hESCs irradiated at all doses, definitive proof of pluripotency. Further, using a bioluminescence imaging technique, we have found that irradiation causes hESCs to initially die after transplantation, but the surviving cells quickly recover by 2 weeks to levels similar to control. To conclude, we show that similar to somatic cells, irradiated hESCs suffer significant death and apoptosis after irradiation. However, they continue to remain pluripotent and are able to form all three embryonic germ layers. Studies such as this will help define the limits for radiation exposure for pregnant women and also radiotracer reporter probes for tracking cellular regenerative therapies.