Mosaic results after preimplantation genetic testing for aneuploidy may be accompanied by changes in global gene expression

Aneuploidy in preimplantation embryos is a major cause of human reproductive failure. Unlike uniformly aneuploid embryos, embryos diagnosed as diploid-aneuploid mosaics after preimplantation genetic testing for aneuploidy (PGT-A) can develop into healthy infants. However, the reason why these embryos achieve full reproductive competence needs further research. Current RNA sequencing techniques allow for the investigation of the human preimplantation transcriptome, providing new insights into the molecular mechanisms of embryo development. In this prospective study, using euploid embryo gene expression as a control, we compared the transcriptome profiles of inner cell mass and trophectoderm samples from blastocysts with different levels of chromosomal mosaicism. A total of 25 samples were analyzed from 14 blastocysts with previous PGT-A diagnosis, including five low-level mosaic embryos and four high-level mosaic embryos. Global gene expression profiles visualized in cluster heatmaps were correlated with the original PGT-A diagnosis. In addition, gene expression distance based on the number of differentially expressed genes increased with the mosaic level, compared to euploid controls. Pathways involving apoptosis, mitosis, protein degradation, metabolism, and mitochondrial energy production were among the most deregulated within mosaic embryos. Retrospective analysis of the duration of blastomere cell cycles in mosaic embryos revealed several mitotic delays compared to euploid controls, providing additional evidence of the mosaic status. Overall, these findings suggest that embryos with mosaic results are not simply a misdiagnosis by-product, but may also have a genuine molecular identity that is compatible with their reproductive potential.

O-073 Artificial intelligence (AI) based triage for preimplantation genetic testing (PGT); an AI model that detects novel features in the embryo associated with ploidy

Study question

Can an AI based triage system noninvasively detect aneuploidy in preimplantation embryos in a precise and valid manner?

Summary answer

Using a feature extraction approach to identify features in time-lapse images, an AI model was validated and found to noninvasively detect ploidy with unprecedented accuracy.

What is known already

Invasive PGT with trophectoderm biopsy is the gold standard for evaluating the genetic integrity of an embryo prior to transfer. Even so, its utility and diagnostic accuracy is debated due to concern of structural damage, sampling bias and viability after vitrification-warming. Though several noninvasive methods for evaluating ploidy have been developed, their main limitations lay in their accuracy. This study reports on the ongoing validation of an AI model that relies on feature extraction and thresholding techniques to distinguish between aneuploid and euploid embryos; the model is intended to be used in clinical settings for PGT triage and preferential transfer.

Study design, size, duration

In this single-center study, we used a retrospective dataset consisting of time-lapse images from 2,502 preimplantation embryos with known ploidy status to train and validate the AI model.

Participants/materials, setting, methods

The model utilized videos captured from time-lapse incubator (Embryoscope) up to 144 hours post-fertilization with chromosome analysis performed using next-generation sequence technology as ground truth labels. The data set was divided using an 70/15/15 training-validation-test split of the data. The AI model included convolutional neural network extracted features alongside spatial features based on several biological and clinical characteristics known to associate with ploidy, embryo behavior, and function. Performances were measured by validation and test-set accuracy.

Main results and the role of chance

Five feature modules were included in the AI model for ploidy evaluation. All modules were analyzed separately and combined: (I) automated detection of abnormal morphokinetic patterns (t2-t8, tM, tSB, tB, tHB) differentiated between the two classes (aneuploid and euploid) to predict aneuploidy with an accuracy of 52%, p < 0.05; (II) previously validated embryo grading classification algorithm demonstrated an association between A and C-grade embryos with euploidy and aneuploidy, respectfully, with an accuracy of 68%, p < 0.05; (III) differential cell division activity and compaction between the two classes predicted aneuploidy with an accuracy of 73%, p < 0.05; (IV): AI-based classification of mitochondrial DNA content, measured as 0.5 micron irregularities in time-lapse images, predicted aneuploidy with an accuracy of 77%, p < 0.05; blastocoelic contractions of more than 8 microns in diameter predicted aneuploidy with 56% accuracy, p < 0.05. Using our AI model, we were able to integrate all 5 features, thereby achieving an unprecedented 90% accuracy. Two features – detection of abnormal morphokinetic patterns and blastocoelic contractions – occur in a minority of embryos (in 3% and 20% of all embryos in the database, respectively). When they do occur, they independently predict aneuploidy with an accuracy of 90% and 82%, demonstrating the robustness of our multi-feature model.

Limitations, reasons for caution

Our AI model needs to be tested on a large, multi-centric dataset to ensure standardization and ability to be replicated in different settings. Even so, given our high degree of demonstrated accuracy, we conclude that our single-center dataset was sufficient for developing the initial validation of the model reported here.

Wider implications of the findings

The ‘explainability’ and implementation of our AI model enables more objective embryo quality assessment and improves the clinics’ ability to prioritize embryos for PGT and preferential transfer using a validated and trusted framework that reduce dramatically the chances of transferring an aneuploid embryo to our patients.

Trial registration number

not applicable

P–189 The transcriptional profile of arrested cleavage stage human embryos

Study question

What are the molecular pathways overactivated in arrested cleavage stage human embryos?

Summary answer

There is an upregulation of mitochondrial activity and cellular stress-related pathways in arrested cleavage embryos, which is in agreement with the “quiet hypothesis”.

What is known already

mtDNA content decreases during embryo development, however there is a high increase in mtDNA content in arrested cleavage embryos that may correspond to a response to intrinsic or extrinsic factor creating stress. This reasoning would be in agreement with stablished hypothesis showing that a basal metabolism with a moderate-low energy consumption is actually a sign of embryo health, so a viable embryo does not need to use an extra energy to accommodate to the environment (Leese, 2012). The study of the transcriptional profile during human embryo development will give further information about key molecular process involved in in-vitro embryonic competence.

Study design, size, duration

A prospective cohort study was performed with 11 MII oocytes (average age= 22,9 years), 10 non-arrested cleavage embryos (average age= 29,9 years), 5 arrested cleavage embryos (average age= 38,8 years) and 8 blastocysts (average age= 39,1 years). All specimens were warmed and sampled in PCR tubes with 2 μl of suitable reaction buffer for the RNA sequencing protocol.

Participants/materials, setting, methods

Specimens were analyzed by single-cell RNA sequencing (scRNA-seq). Correlation studies, principal component and differential expression analysis were performed with DESeq2 package. Differential gene expression analyses were done using the parametric Wald test, with Benjamini-Hochberg multiple test correction (padj). Finally, Fgsea algorithm was used for enrichment analysis on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene ontology (GO) terms.

Main results and the role of chance

We do not observe mitochondria-related activity pathways significantly (P>.05) deregulated between MII oocytes and non-arrested cleavage embryos considering GO and KEGG categories.

When comparing non-arrested cleavage embryos versus blastocysts, we observe several ATP production/consumption and cristae formation-related pathways significantly (P<.05) upregulated in blastocysts compared to non-arrested cleavage embryos considering GO and KEGG categories. This change in activity coincides with the metabolic activation event that occurs in the blastocyst stage.

However, when we analyze arrested cleavage embryos versus non-arrested cleavage embryos, we observe several ATP production related-pathways and mitochondria-related apoptosis pathways significantly (P<.05) upregulated in arrested cleavage embryos compared to non-arrested cleavage embryos considering GO categories. With KEGG categories, we notice a significant (P<.05) upregulation of oxidative phosphorylation in arrested cleavage embryos. On the other hand, when we analyze the differences between arrested cleavage embryos and blastocysts, taking into account the differences related to the change of embryo stage, we do not observe ATP production or consumption-related pathways significantly (P>.05) deregulated considering GO and KEGG categories. Then, human arrested embryos in parallel with the increase in mtDNA content, display an upregulation of mitochondrial activity and cellular stress which is in line with the expected overactive metabolism of non-viable embryos.

Limitations, reasons for caution

All analyzed blastocyst were aneuploid, so we are unable to determine what the results would be with euploid blastocysts. Also, although age can it be ruled out, no differences were observed between mean age from cleavage stage embryos (arrested and non-arrested ones) and blastocyst.

Wider implications of the findings: This study evidences the relation between extreme mtDNA content increase and the identification of the pathways involved in active metabolism and apoptosis in arrested cleavage stage human embryos.

Trial registration number

Not applicable

P–549 What trophectoderm cells from mosaic embryos tell us about embryonic competence at the transcriptional level

Study question

Does transcriptome of remaining trophectoderm (TE) reflect the developmental potential of mosaic blastocysts after preimplantation genetic testing for aneuploidy (PGT-A)? Summary answer: TE from low-degree mosaic (Low-mos) and high-degree mosaic (High-mos) blastocysts are transcriptionally equivalent, standing between euploid and aneuploid categories and displaying key deregulated developmental processes.

What is known already

Blastocysts classified as mosaic by PGT-A are associated with lower implantation and higher miscarriage rates than those classified as euploid, yet they still lead to healthy babies. Unveiling the true developmental identity of these embryos faces a dilemma: understanding to which extent they represent technical artefacts or whether they hold own potential to implant and give rise to normal pregnancies. Current RNA sequencing (RNA-seq) techniques allow for the determination of whole transcriptomic profiles even from single cells, which paves the way for the identification of new molecular keys of embryonic competence.

Study design, size, duration

Prospective study comparing RNA-seq data of remaining TE from blastocysts classified as euploid (n = 4), Low-mos (n = 5), High-mos (n = 4) and aneuploid (n = 6) by PGT-A. Participants were recruited between October 2018 and November 2019 at IVI-RMA Valencia.

Participants/materials, setting, methods

Chromosomal mosaicism was defined in the range 30%-<50% (Low-mos) and 50%-<70% (High-mos) using a next-generation sequencing (NGS) validated algorithm. Whole TE fractions were separately collected and processed for RNA-seq. Differentially expressed genes (DEGs) were calculated with DESeq2 package [Benjamini-Hochberg (BH)-adjusted p < 0.01 & abs(log2FoldChange)>2 significant]. Fgsea algorithm was used for enrichment analysis on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene Ontology (GO) terms (BH-adjusted p < 0.01 significant).

Main results and the role of chance

For comparisons, TE from euploid blastocysts were used as control. At the gene level, 15 DEGs were found in Low-mos, 20 DEGs in High-mos, and 64 DEGs in aneuploid blastocysts. To address the functional implications of these differences, pathways significantly deregulated according to KEGG and GO categories were identified. TE from aneuploid blastocysts displayed significant downregulation in up to 115 KEGG and GO processes directly involved in processing and integrity maintenance of nuclear and mitochondrial genomes, a reflection of their aberrant chromosomal identity. In addition, TE from High-mos and Low-mos were transcriptionally equivalent (0 DEGs between both groups), with 23 overlapping KEGG and GO processes significantly downregulated compared with control. Importantly, main significantly-affected processes included mitotic sister chromatid segregation, NIK NF-kB activity, regulation of apoptosis, and pathways related to the biosynthesis and metabolism of proteins, fatty acids, carbohydrates and steroid hormones. These findings indicate that mosaic embryos comprise a unique developmental entity, which swims between the euploid and aneuploid waterfronts and may regulate survival by diverse mechanisms, including cell proliferation and apoptosis.

Limitations, reasons for caution

This is a descriptive, single-center study with limited sample size. TE fractions were obtained by micromanipulation, which may have led to potential cross-contamination with the inner cell mass.

Wider implications of the findings: Transcriptomic equivalence between Low-mos and High-mos TE fractions questions the biological significance of inferring mosaicism degrees from single biopsies. Deregulated processes in these embryos support their reduced developmental and live birth potential, pointing to mechanisms that may mediate survival in the presence of aneuploid cells, as shown in the mouse.

Trial registration number

Not applicable

P-549 What trophectoderm cells from mosaic embryos tell us about embryonic competence at the transcriptional level

Study question

Does transcriptome of remaining trophectoderm (TE) reflect the developmental potential of mosaic blastocysts after preimplantation genetic testing for aneuploidy (PGT-A)?

Summary answer

TE from low-degree mosaic (Low-mos) and high-degree mosaic (High-mos) blastocysts are transcriptionally equivalent, standing between euploid and aneuploid categories and displaying key deregulated developmental processes.

What is known already

Blastocysts classified as mosaic by PGT-A are associated with lower implantation and higher miscarriage rates than those classified as euploid, yet they still lead to healthy babies. Unveiling the true developmental identity of these embryos faces a dilemma: understanding to which extent they represent technical artefacts or whether they hold own potential to implant and give rise to normal pregnancies. Current RNA sequencing (RNA-seq) techniques allow for the determination of whole transcriptomic profiles even from single cells, which paves the way for the identification of new molecular keys of embryonic competence.

Study design, size, duration

Prospective study comparing RNA-seq data of remaining TE from blastocysts classified as euploid (n = 4), Low-mos (n = 5), High-mos (n = 4) and aneuploid (n = 6) by PGT-A. Participants were recruited between October 2018 and November 2019 at IVI-RMA Valencia.

Participants/materials, setting, methods

Chromosomal mosaicism was defined in the range 30%- < 50% (Low-mos) and 50%- < 70% (High-mos) using a next-generation sequencing (NGS) validated algorithm. Whole TE fractions were separately collected and processed for RNA-seq. Differentially expressed genes (DEGs) were calculated with DESeq2 package [Benjamini-Hochberg (BH)-adjusted p < 0.01 & abs(log2FoldChange)>2 significant]. Fgsea algorithm was used for enrichment analysis on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene Ontology (GO) terms (BH-adjusted p < 0.01 significant).

Main results and the role of chance

For comparisons, TE from euploid blastocysts were used as control. At the gene level, 15 DEGs were found in Low-mos, 20 DEGs in High-mos, and 64 DEGs in aneuploid blastocysts. To address the functional implications of these differences, pathways significantly deregulated according to KEGG and GO categories were identified. TE from aneuploid blastocysts displayed significant downregulation in up to 115 KEGG and GO processes directly involved in processing and integrity maintenance of nuclear and mitochondrial genomes, a reflection of their aberrant chromosomal identity. In addition, TE from High-mos and Low-mos were transcriptionally equivalent (0 DEGs between both groups), with 23 overlapping KEGG and GO processes significantly downregulated compared with control. Importantly, main significantly-affected processes included mitotic sister chromatid segregation, NIK NF-kB activity, regulation of apoptosis, and pathways related to the biosynthesis and metabolism of proteins, fatty acids, carbohydrates and steroid hormones. These findings indicate that mosaic embryos comprise a unique developmental entity, which swims between the euploid and aneuploid waterfronts and may regulate survival by diverse mechanisms, including cell proliferation and apoptosis.

Limitations, reasons for caution

This is a descriptive, single-center study with limited sample size. TE fractions were obtained by micromanipulation, which may have led to potential cross-contamination with the inner cell mass.

Wider implications of the findings

Transcriptomic equivalence between Low-mos and High-mos TE fractions questions the biological significance of inferring mosaicism degrees from single biopsies. Deregulated processes in these embryos support their reduced developmental and live birth potential, pointing to mechanisms that may mediate survival in the presence of aneuploid cells, as shown in the mouse.

Trial registration number

Not applicable

Origin and composition of cell-free DNA in spent medium from human embryo culture during preimplantation development

STUDY QUESTION

What is the origin and composition of cell-free DNA in human embryo spent culture media?

SUMMARY ANSWER

Cell-free DNA from human embryo spent culture media represents a mix of maternal and embryonic DNA, and the mixture can be more complex for mosaic embryos.

WHAT IS KNOWN ALREADY

In 2016, ~300 000 human embryos were chromosomally and/or genetically analyzed using preimplantation genetic testing for aneuploidies (PGT-A) or monogenic disorders (PGT-M) before transfer into the uterus. While progress in genetic techniques has enabled analysis of the full karyotype in a single cell with high sensitivity and specificity, these approaches still require an embryo biopsy. Thus, non-invasive techniques are sought as an alternative.

STUDY DESIGN, SIZE, DURATION

This study was based on a total of 113 human embryos undergoing trophectoderm biopsy as part of PGT-A analysis. For each embryo, the spent culture media used between Day 3 and Day 5 of development were collected for cell-free DNA analysis. In addition to the 113 spent culture media samples, 28 media drops without embryo contact were cultured in parallel under the same conditions to use as controls. In total, 141 media samples were collected and divided into two groups: one for direct DNA quantification (53 spent culture media and 17 controls), the other for whole-genome amplification (60 spent culture media and 11 controls) and subsequent quantification. Some samples with amplified DNA (N = 56) were used for aneuploidy testing by next-generation sequencing; of those, 35 samples underwent single-nucleotide polymorphism (SNP) sequencing to detect maternal contamination. Finally, from the 35 spent culture media analyzed by SNP sequencing, 12 whole blastocysts were analyzed by fluorescence in situ hybridization (FISH) to determine the level of mosaicism in each embryo, as a possible origin for discordance between sample types.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Trophectoderm biopsies and culture media samples (20 μl) underwent whole-genome amplification, then libraries were generated and sequenced for an aneuploidy study. For SNP sequencing, triads including trophectoderm DNA, cell-free DNA, and follicular fluid DNA were analyzed. In total, 124 SNPs were included with 90 SNPs distributed among all autosomes and 34 SNPs located on chromosome Y. Finally, 12 whole blastocysts were fixed and individual cells were analyzed by FISH using telomeric/centromeric probes for the affected chromosomes.

MAIN RESULTS AND THE ROLE OF CHANCE

We found a higher quantity of cell-free DNA in spent culture media co-cultured with embryos versus control media samples (P ≤ 0.001). The presence of cell-free DNA in the spent culture media enabled a chromosomal diagnosis, although results differed from those of trophectoderm biopsy analysis in most cases (67%). Discordant results were mainly attributable to a high percentage of maternal DNA in the spent culture media, with a median percentage of embryonic DNA estimated at 8%. Finally, from the discordant cases, 91.7% of whole blastocysts analyzed by FISH were mosaic and 75% of the analyzed chromosomes were concordant with the trophectoderm DNA diagnosis instead of the cell-free DNA result.

LIMITATIONS, REASONS FOR CAUTION

This study was limited by the sample size and the number of cells analyzed by FISH.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to combine chromosomal analysis of cell-free DNA, SNP sequencing to identify maternal contamination, and whole-blastocyst analysis for detecting mosaicism. Our results provide a better understanding of the origin of cell-free DNA in spent culture media, offering an important step toward developing future non-invasive karyotyping that must rely on the specific identification of DNA released from human embryos.

STUDY FUNDING/ COMPETING INTEREST

This work was funded by Igenomix S.L. There are no competing interests.

Smoking habits of parents and male: female ratio in spermatozoa and preimplantation embryos

BACKGROUND

Previous observations have addressed a decreased male:female ratio associated with smoking. Our aim was to assess whether this effect is observed at the spermatozoa or at the early embryo development.

METHODS

We retrospectively assessed smoking intake habits of 56 couples included in our preimplantation genetic diagnosis (PGD) program. Three groups were established according to male or female cigarette consumption per day: non-smokers, smokers (1-19 cigarettes per day) and heavy smokers (> or =20 cigarettes per day). Fluorescence in-situ hybridization (FISH) was performed on ejaculated sperm samples to analyse chromosomes X and Y. On day 3, embryos were also analysed. Additionally, sperm samples from four heavy smoking and four non-smoking donors were prospectively analysed before and after capacitation.

RESULTS

FISH on spermatozoa revealed no statistical differences in the Y:X ratio between the three groups. However, in the PGD study, in male heavy smokers, the XY:XX embryo ratio was decreased compared with non-smokers (22:47 versus 80:71; P = 0.0057). The smoking condition of the female partner had no significant effect on embryo XY:XX ratio, but for non-smoking females with a heavy smoking partner, the ratio was decreased (P = 0.0018) compared with non-smoking males. In heavy smoking donors a decreased of Y:X ratio was observed after swim-up with a statistically significant difference of ratios (P = 0.021).

CONCLUSIONS

Smoking habits of males do not have an effect on the percentage of X- and Y-bearing spermatozoa on ejaculated samples. However, male heavy smokers produce an increased incidence of female embryos that could be related to an enrichment of X spermatozoa after swim-up in patients with high tobacco consumption.

Implantation Rates after Two, Three, or Five Days of Embryo Culture

Extended embryo culture together with amelioration of embryo selection methods and embryo culture conditions have allowed a substantial increase on both pregnancy and implantation rates. However, uterine embryo transfers are still performed after 2 to 6 days of egg retrieval. In this paper, we show the results of two studies, one prospective study comparing IVF outcome of day 2 and day 3 embryo transfers, and a retrospective study looking at blastocyst transfers versus day 3 embryo transfers in our egg donation program. Also, we test the predictive value of the presence of three or more seven cell-stage embryos on day 3 of development on blastocyst formation and pregnancy rates. No significant differences were found between day 2 and day 3 embryo transfers in terms of pregnancy, ongoing pregnancy, and implantation rates, as well as in multiple and in high order pregnancy. In general, day 6 embryo transfers resulted in significantly higher ongoing pregnancy and implantation rates compared with day 3 embryo transfers (41.1 per cent and 23.6 per cent versus 50.1 per cent and 38.1 per cent, respectively). No differences were found in terms of multiple gestations despite transferring significantly more embryos on day 3 compared with day 6 transfers. When less than three 7-cell embryos were present in the embryo cohort, day 6 embryo transfers did not improve the rates of ongoing pregnancy with regards to day 3 embryo transfer, although significant high implantation rates were obtained on the group of blastocyst transfer. The presence of three or more 7 cell-stage embryos improved significantly both ongoing pregnancy and rates on blastocyst transfers compared to day 3 embryo transfers (65.6 per cent versus 50.6 per cent and 37.4 per cent vs 24.7 per cent, respectively). In conclusion, at least in egg donation, day 3 embryo transfers do not improve either pregnancy or implantation rates when compared to day 2 transfers. Generally speaking blastocyst transfers give significantly higher chance of pregnancy and implantation rates per cycle and per transfer than early cleavage stage transfers. However, the absence of a good embryo cohort, that is having less than three 7 cell-stage embryos on day 3, blastocyst transfers will improve implantation rates but not ongoing pregnancy rates.

The role of endothelial cells in the pathogenesis of ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of treatment with fertility drugs. Using human lung microvascular endothelial cells (HUMEC-L) as an in-vitro model of OHSS, we have tested the hypothesis that the endothelium is a target of HCG in the pathogenesis of OHSS. Since OHSS is characterized by increased capillary permeability, we have investigated the production and action of vasoactive agents. When HUMEC-L were cultured with high doses of estradiol (E(2)), no significant changes were observed in the secretion of vascular endothelial growth factor (VEGF), interleukin (IL)-6 or IL-1 beta. However, the addition of HCG resulted in a significant increase in the secretion of VEGF and IL-6. Time-course experiments showed that VEGF was secreted within minutes of HCG addition, whereas IL-6 was significantly increased only after 48 h in culture. The secretion of IL-1 beta was unchanged by these hormonal conditions. The presence of HCG receptors was demonstrated in HUMEC-L in basal conditions as well as after the addition of E(2). The expression of VEGF receptors was also investigated. High doses of E(2) were unable to increase the expression of KDR, flt-1 and sfl-t, but the addition of HCG significantly upregulated the KDR concentration in endothelial cells, while no change was observed for flt. Permeability assays demonstrated that while E(2) alone did not change the arrangement of HUMEC-L in vitro, the presence of HCG caused changes in the actin fibres corresponding to increased capillary permeability. Anti-human VEGF antibodies were able to overcome these changes. In conclusion, these experiments show that the endothelium may be a primary target of HCG, causing an acute release of VEGF and a significant increase in IL-6 and resulting in an autocrine-paracrine action that may increase vascular permeability.

An analysis of spontaneous hatching in a human endometrial epithelial coculture system: is assisted hatching justified?

PURPOSE

To evaluate spontaneous embryo hatching in an endometrial epithelial coculture system, and compare it with cases where coculture was performed because of maternal age, previous repeated implantation failures, or both. To clarify in which cases assisted hatching would be appropriate.

METHODS

Individual human embryos were cocultured on an endometrial epithelial cell monolayer until Day 6.

RESULTS

Blastocyst hatching rate at Day 6, depending on maternal age, was 9.1% (age <37 years) and 3.4% (age > or = 37 years). However, blastocyst hatching rates depending on number of previous IVF failures were similar.

CONCLUSIONS

Maternal age and previous implantation failures are factors affecting the ability of human embryos to reach the blastocyst stage in coculture. However, assisted hatching is not justified in these populations because of the absence of hatching rate differences between blastocysts obtained from these two groups and the control group.

Leptin and leptin receptor are expressed in the human endometrium and endometrial leptin secretion is regulated by the human blastocyst

Embryonic implantation is a crucial event for the human reproductive function. Cytokines and paracrine molecules have been proposed as putative local regulators of this process. The leptin or the OB protein has been linked to the reproductive function and inflammatory response. In the present study, we describe for the first time the expression of leptin and leptin receptor (long form) in the secretory endometrium and that endometrial leptin secretion is regulated in vitro by the human blastocyst. Leptin and leptin receptor messenger RNA and protein were identified in secretory endometrium and in cultured endometrial epithelial cells (EECs) by RT-PCR, Western blot, and immunohistochemistry. The concentrations of immunoreactive leptin secreted by human embryos alone or cocultured with EECs were also assessed. We found that human blastocysts secrete significantly higher levels of leptin than arrested embryos. In contrast, leptin concentrations secreted by arrested embryos cocultured with EECs were significantly higher than blastocysts cocultured with EECs. These findings suggest that the human endometrium is a site for local production and a target tissue for circulating leptin. Expression of leptin and its functional receptor in the endometrium and regulation of endometrial leptin secretion by the human embryo suggests that the leptin system may be implicated in the human implantation process.

Clinical experience employing co-culture of human embryos with autologous human endometrial epithelial cells

Attempts to improve the outcome in IVF and related techniques has drawn our attention to the development of culture systems that can grow embryos up to the blastocyst stage. We have developed a co-culture system with autologous human endometrial epithelial cells (EEC) that retained many features of the endometrium. In this review, we analyse our experience over the last 4 years; in particular, we address the question of whether the system would be safe and useful in cases of IVF and oocyte donation with previous implantation failure, and which factors may contribute to the failure of human embryos to develop in vitro up to the blastocyst stage. In all, 168 IVF cycles were carried out in 127 patients with 3.8+/-0.2 previous implantation failure, and 80 cycles in 57 women having oocyte donation with 3.0+/-0.2 previous implantation failure. In 168 IVF cycles, a 48.9% blastocyst formation rate was recorded; 2.3+/-0.1 blastocysts were transferred per cycle and 30 clinical pregnancies obtained (11.9% implantation and 19.6% pregnancy rates). A total of 20 IVF and 15 oocyte donation patients with three previous implantation failures in whom a day 2 embryo transfer was performed were the controls. In 88% of oocyte donation cycles, a 61.0% blastocyst formation rate was observed; 2.3+/-0.1 blastocysts were transferred per cycle and resulted in 38 clinical pregnancies (32.7% implantation and 54.3% pregnancy rates). In all, 15 cycles were cancelled (9%). In oocyte donation patients with implantation failure undergoing day 2 embryo transfer, implantation and pregnancy rates were significantly lower (4.5 and 13.3%; P < 0.01) than with co-culture; however, in IVF patients with implantation failure with day 2 transfer, results (10.7 and 35%) were similar to those with co-culture. A second question addressed was whether chromosomal abnormalities may contribute to the failure of human embryos to develop in vitro. We observed the performance of human embryos from our preimplantation diagnosis programme, which were biopsied and subsequently cultured in EEC before transfer. Out of 68 chromosomally normal embryos, 37 reached the blastocyst stage (54.4%) compared with 35 out of 104 abnormal embryos (33.6%). The present study demonstrates that co-culture of human embryos with EEC and blastocyst transfer is safe, effective, and may be a new approach to improve implantation in patients with implantation failure undergoing oocyte donation, but not in IVF patients. The system shows that abnormal embryos can also grow to the blastocyst stage, although to a lower rate. Prospective randomized studies are needed to confirm the preliminary conclusion that co-culture is an acceptable system to select good quality embryos, and the endometrium is a limiting factor in implantation that needs to be carefully managed.

Coculture of human embryos with autologous human endometrial epithelial cells in patients with implantation failure

We have developed a coculture system with autologous human endometrial epithelial cells (AEEC) that retained many features of human endometrial epithelium. Implantation failure (IF; >3 previous cycles failed with 3-4 good quality embryos transferred) is a distressing condition in which 2-day embryo transfer repetition is the routine option. The objective of this study was to investigate the basics and to evaluate prospectively the clinical value of embryo coculture on AEEC and blastocyst transfer with their own oocytes [in vitro fertilization (IVF) patients] or with donated oocytes (oocyte donation patients) compared to a routine day 2 embryo transfer for patients with IF. Scanning electron microscopy and mouse embryo assays demonstrate that EEC from fertile and IF patients were morphologically and functionally similar; similar findings were observed in EEC obtained from fresh or frozen endometria. Clinically, 168 IVF cycles were performed in 127 patients with 3.8+/-0.2 previously failed cycles, and 80 cycles were performed in 57 patients undergoing oocyte donation with 3.0+/-0.2 previously failed cycles. Twenty IVF patients and 15 ovum donation patients with 3 previously failed cycles in whom a 2-day embryo transfer was performed were used as controls. In 88% of ovum donation cycles, at least 2 blastocysts were available for transfer, with 60.1% blastocyst formation; 2.2+/-0.1 blastocysts were transferred/cycle, and 36 pregnancies (determined by fetal cardiac activity) were obtained (32.7% implantation and 54.5% pregnancy rates). In 168 IVF cycles, 8.1+/-0.2 embryos/cycle started coculture, resulting in 49.2% blastocyst formation; 2.3+/-0.2 blastocysts were transferred/cycle, and 29 clinical pregnancies were obtained (11.8% implantation and 20.2% pregnancy rates). Fifteen cycles were canceled (9%). In oocyte donation patients with IF undergoing 2-day embryo transfer, implantation and pregnancy rates were significantly lower (4.5% and 13.3%; P < 0.01) than with coculture; however, in IVF patients with IF, results with day 2 transfer (10.7% and 35%) were similar to those with coculture. The present study demonstrates that coculture of human embryos with AEEC and blastocyst transfer is safe, ethical, and effective and constitutes a new approach to improve implantation in patients with IF undergoing ovum donation, but not in IVF patients.

Maturation in vitro of human oocytes from unstimulated cycles: selection of the optimal day for ovum retrieval based on follicular size

The potential use of immature oocytes for in-vitro fertilization (IVF) requires the conditions for successful maturation to be defined. This study focused on the day of oocyte retrieval. The selection of a dominant follicle may induce endocrine changes in the remaining cohort that may be detrimental to their subsequent fertilization and embryonic development. Natural cycles in volunteer donors were followed by measurement of serum oestradiol and by vaginal ultrasound, starting on day 3 of the cycle. Cycles were randomly allocated to one of two groups: group 1 (n = 10), in which follicles were aspirated before the leading follicle was 10 mm in diameter; and group 2 (n = 9), in which follicles were aspirated when a dominant follicle was clearly visible with diameter >10 mm. Oocytes were cultured in vitro to metaphase II (MII) stage, donated, and inseminated by intracytoplasmic sperm injection (ICSI) with husband's spermatozoa. Those that became fertilized within 24 h were further co-cultured in autologous endometrial epithelial cells up to the blastocyst stage, and cryopreserved. There was a significantly (P < 0.05) increased rate of oocyte retrieval in group 1 (70.8% of aspirated follicles) compared with group 2 (50.5%). Maturation to MII and fertilization were similar between the groups. However, development to blastocyst stage was significantly (P < 0.05) higher in group 1 embryos (56.5%) compared with group 2 (35.7%). There was a positive correlation (r2 = 0.1978) between the appearance of the cumulus cells and the ability to develop to blastocyst stage when both parameters were analysed in group 1, whereas no such correlation was found in group 2. In conclusion, our data suggest the importance of retrieving immature oocytes before follicular selection, and define the conditions for the first stage in the use of immature oocytes. Further stages must be defined before this technique can be used clinically.

The pathogenesis of ovarian hyperstimulation syndrome: in vivo studies investigating the role of interleukin-1beta, interleukin-6, and vascular endothelial growth factor

OBJECTIVE

To evaluate systemic and ovarian changes in levels of interleukin (IL)-1beta, IL-6, and vascular endothelial growth factor (VEGF) in response to hCG administration to determine which may be the potential initiator of vascular effects and to identify the main source of the substance; to evaluate serum and follicular fluid levels of these cytokines as markers of ovarian hyperstimulation syndrome (OHSS), and to compare levels of these cytokines under basal conditions in women with normal ovulation and those with polycystic ovary syndrome (PCOS).

DESIGN

Prospective controlled study.

SETTING

In vitro fertilization program at the Instituto Valenciano de Infertilidad, Valencia, Spain.

PATIENT(S)

Women undergoing IVF, in whom the first two study objectives were analyzed, and women with normal ovulation and patients with PCOS undergoing retrieval of immature oocytes in natural cycles or cycles stimulated for IUI but cancelled during induction of ovulation, in whom the third study objective was analyzed.

INTERVENTION(S)

Serum was collected before and after hCG administration, and follicular fluid was collected at ovum pick-up.

MAIN OUTCOME MEASURE(S)

Serum and follicular fluid levels of IL-1beta, IL-6, and VEGF.

RESULT(S)

There was a significant increase in serum VEGF levels after hCG administration in patients who were at risk for OHSS compared with those who were not at risk for OHSS. Significantly lower VEGF levels were found in the follicular fluid of patients who were at risk; this decrease was the only useful marker to discriminate between the two groups. Moreover, both groups had similar cytokine production under basal conditions. An increase in serum E2 occurred coincident with a decrease in IL-1beta, IL-6, and VEGF in patients with PCOS.

CONCLUSION(S)

Vascular endothelial growth factor seems to be the mediator of hCG on the vascular tree. There was an early systemic increase in VEGF that may have significance in the development of OHSS. A decrease in the follicular fluid VEGF concentration is a valid marker to identify women in whom OHSS will develop. The pattern of cytokine release in patients with PCOS under basal conditions was not different from that in women with normal ovulation.

The follicular and endocrine environment in women with endometriosis: local and systemic cytokine production

OBJECTIVE

To assess the endocrine, paracrine, and autocrine milieu in patients with endometriosis on the basis of the measurement of several cytokines in serum and follicular fluid (FF) and in vitro culture of granulosa luteal cells.

DESIGN

Case-control study.

SETTING

In vitro fertilization program at the Instituto Valenciano de Infertilidad.

PATIENT(S)

Twenty patients with laparoscopically documented endometriosis and 18 controls. Fifteen subjects were studied in a natural cycle and 23 were investigated in a stimulated cycle while undergoing IVF.

INTERVENTION(S)

Individual follicle aspiration, oocyte isolation, FF storage, and preparation of luteinized granulosa cell cultures. Diagnostic laparoscopy in natural cycles.

MAIN OUTCOME MEASURE(S)

Serum (day of ovum pick-up or laparoscopy) and FF measurement of interleukin (IL)-1beta, IL-6, and vascular endothelial growth factor (VEGF). Secretion of IL-1beta, IL-6, and VEGF in the cell-conditioned medium. Results were compared between patients with endometriosis and controls.

RESULT(S)

Interleukin-6 levels in serum were increased in the natural cycles of patients with endometriosis and modulated by ovarian stimulation, showing a significant decrease in hMG- and FSH-stimulated cycles and a significant increase after hCG administration. In addition, IL-6 levels were increased in the FF of patients with endometriosis and released in higher amounts by their granulosa luteal cells. Vascular endothelial growth factor was accumulated in lesser concentrations in the FF of patients with endometriosis. Interleukin-1beta levels did not show significant changes. Implantation rates were decreased significantly in patients with endometriosis who were undergoing IVF.

CONCLUSION(S)

The data demonstrate that cytokines are regulated differently in patients with endometriosis, who have increased IL-6 production, and suggest that fine hormonal modulation of this cytokine occurs at the systemic and local (ovarian) levels. These changes show that the endocrine, paracrine, and autocrine milieu is different in patients with endometriosis and may be related to their lower implantation rates.

Embryonic regulation of integrins beta 3, alpha 4, and alpha 1 in human endometrial epithelial cells in vitro

In the present study, we examined the embryonic regulation of beta 3 integrin in human endometrial epithelial cells (EEC) at the protein level and analyzed putative embryonic factors responsible for this regulation. The model employed is based on a clinical in vitro fertilization program in which single human embryos were cocultured with EEC until blastocyst stage and then transferred back to the uterus. After embryo transfer, EEC wells were divided according to the embryonic status reached: EEC with embryos that achieved the blastocyst stage, EEC with arrested embryos, and EEC without embryos. Immunostaining for beta 3 was positive in plasma membrane of EEC. Flow cytometry showed a mean percentage of beta 3-stained cells of 24.1 +/- 5.7 in EEC cocultured with embryos that achieved the blastocyst stage (n = 13) vs. 9.5 +/- 1.6 (P < 0.05) in those EEC cultured with arrested embryos (n = 12). Immunostaining for alpha 1 and alpha 4 integrins was negative in EEC monolayers studied, regardless of the presence or absence of embryos, and these findings were confirmed by flow cytometry. The possibility that the embryonic IL-1 system and leukemia inhibitory factor were involved in the endometrial beta 3 up-regulation was investigated by neutralizing experiments demonstrating a significant inhibition of beta 3-stained cells when EEC monolayers were cultured in the presence of EEC/blastocyst-conditioned media with (n = 4) vs. without (n = 8) antihuman interleukin (IL)-1 alpha + IL-1 beta (1.65% vs. 14.6%; P < 0.05). Dose-response experiments further demonstrated an up-regulation of beta 3 positive cells when IL-1 alpha + IL-1 beta were added to the medium at a concentration of 10 pg/mL compared with control medium without added cytokines (40% vs. 20%, n = 4). The functional relevance of the EEC beta 3 up-regulation was tested using a mouse blastocyst adhesion assay. More mouse blastocysts attached to EEC previously in contact with human blastocyst (72.7%) compared with those EEC previously in contact with arrested embryos (40%). Our results demonstrate the selective effect of a developing human embryo on EEC expression of beta 3, which is maximal when a human blastocyst instead of an arrested embryo is considered. Furthermore, the embryonic IL-1 system seems to be involved in the EEC beta 3 up-regulation, reinforcing the concept of precise paracrine cross-talk between blastocyst and endometrial epithelium during embryonic implantation.

The interleukin-1 system and human implantation

PROBLEM

Cytokines and growth factors are increasingly implicated in embryonic implantation. In the present study, we focus on the interleukin-1 system as an example of local regulator in human implantation.

METHOD

Three different approaches are considered. First, we present evidence demonstrating its presence, regulation, and relevance on the human endometrium. Second, we demonstrate the presence of IL-1 system in the human embryo and the selective IL-1 release only when embryos were co-cultured with human endometrial epithelial cells (EEC) or EEC-conditioned media, indicating an obligate role of the endometrium in the regulation of the embryonic IL-1 system. Finally, we show data regarding the presence, hormonal regulation, and endometrial origin of IL-1 alpha, IL-beta, and IL-1ra levels in the endometrial fluid inside the endometrial cavity. Specifically, we present the IL-1 intracavitary microenvironment surrounding the human embryo at the apposition phase.

RESULTS

This work suggests that the IL-1 system seems to be relevant for human endometrial and embryonic physiology. Furthermore, this family of molecules must be considered as a relevant paracrine language displayed by both partners that may be important to endometrial and embryonic crosstalk during embryonic implantation.

Hormonal regulation of serum and endometrial IL-1 alpha, IL-1 beta and IL-1ra: IL-1 endometrial microenvironment of the human embryo at the apposition phase under physiological and supraphysiological steroid level conditions

We have investigated serum and intracavitary levels of IL-1 alpha, IL-1 beta and IL-1ra from agonadal women undergoing mock cycles (n = 20) of oocyte donation as a clinical model of controlled hormonal stimulation. Further, we compared the intracavitary IL-1 alpha, IL-1 beta and IL-1ra levels in the microenvironment of the human embryo at the apposition phase, day 5 after progesterone (P) administration using two different clinical models: oocyte donation (n = 20) which provides physiological steroid levels and a higher implantation rate per embryo, and in vitro fertilization (n = 6) with supraphysiological hormonal levels and a lower implantation rate.

Cytokines-adhesion molecules-invasive proteinases. The missing paracrine/autocrine link in embryonic implantation?

How implantation is regulated and brought about remains an enigma. The objective of the present review is to propose a hypothetical model based on our actual knowledge of the role of cytokines, adhesion molecules and invasive proteinases in the adhesion and invasion phases of embryonic implantation. For the purpose of clarity we will describe first what is known about the presence of these molecules in the endometrium and embryo in animal models and their relevance in embryonic implantation. Secondly, since human implantation is unique the presence of these factors in the human endometrium and embryo and their possible clinical relevance is considered separately. Finally, the link between cytokines, adhesion molecules and invasive proteinases as well as their endocrine/paracrine/autocrine regulation is put forward as a possible model that could lead us to a better understanding of the implantation process in humans.

Role of endometrial factors in regulating secretion of components of the immunoreactive human embryonic interleukin-1 system during embryonic development

In the study reported here, we localized at the protein level the major components of the interleukin (IL)-1 system in the human embryo, and we investigated the endometrial factors influencing their secretion during embryonic development. To localize these components, we performed immunohistochemical experiments in 44 oocytes and 78 embryos. The following primary antibodies were used: monoclonal mouse anti-human IL-1 receptor type I (IL-1R tl), monoclonal mouse anti-human IL-1 beta, and polyclonal rabbit anti-human IL-1 receptor antagonist (IL-1ra). For embryo culture, human embryos at different developmental stages were cultured in 100-microliters drops of Ham's F-10 medium + 4 mg/ml BSA (n = 33), in 100-microliters drops of Menezo B2 culture medium (n = 18), or in wells with 1 ml of Menezo B2 culture medium (n = 8). For embryo coculture, endometrial stromal cells (ESC) and endometrial epithelial cells (EEC) were isolated from human secretory endometrium and cultured until confluence in 75% Dulbecco's Modified Eagle's Medium and 25% MCDB-105 containing antibiotics and supplemented with 10% charcoal-Dextran-treated fetal bovine serum. Individual human embryos were cocultured with experimental EEC and ESC (n = 23 and n = 4, respectively) for 5 days in 600-microliters drops of Menezo B2 medium, and conditioned medium was removed every 24 h. Human embryos were also cultured with EEC-conditioned medium (n = 9). IL-1 alpha, IL-1 beta, and IL-1ra levels were determined by ELISA in the 24-h culture- or coculture-conditioned media. Immunostaining confirmed the presence of IL-1 beta, IL-1ra, and IL-1R tl in oocytes and embryos in all stages analyzed, with no statistical differences. IL-1 alpha, IL-1 beta, and IL-1ra were absent in conditioned media of cultured embryos and embryos cocultured with ESC. However, when human embryos were cocultured with EEC or with EEC-conditioned medium alone, two different populations of embryos were observed: IL-1 producers (57% and 56%) and IL-1 nonproducers (43% and 44%, respectively). Finally, the IL-1 profile of a single human embryo cocultured with maternal EEC which successfully implanted and developed is presented, this pattern being similar to that described in the IL-1 producer population. These results demonstrate the presence of the IL-1 system in the human embryo. However, the selective release of IL-1 only when embryos were cocultured with EEC or EEC-conditioned medium indicates an obligatory role of the endometrium in the regulation of the embryonic IL-1 system. Furthermore, the differential embryonic production of IL-1 may be related to the implantation capability of the embryos.