Joan Hunt Senior award lecture: New tools to shed light on the 'black box' of pregnancy

Ethical considerations for advancing research using organoid models derived from the placenta

BACKGROUND

The advent of organoid culture systems has revolutionized our ability to model and study complex tissues in vitro. The placenta is one of the last human organs to have a functional organoid model developed: trophoblast organoids. These 3-dimensional structures, derived from placental tissue, offer researchers a valuable tool for studying previously inaccessible processes that occur within the womb and play a significant role in determining the health of the offspring. While primarily used for research, trophoblast organoids hold promise for clinical applications, including prenatal diagnostics and therapeutic interventions, both of which may have commercial interest. However, to ensure that research with organoid models derived from the placenta is conducted responsibly, the relevant ethics of these models need to be addressed.

OBJECTIVE AND RATIONALE

Ethical considerations related to organoid models derived from the placenta, such as trophoblast organoids are important but remain unexplored in literature. Therefore, the goal of this review is to explore the ethical considerations related to trophoblast organoids.

SEARCH METHODS

Since there is no ethical research specifically addressing organoid models of the placenta to date, we have based our findings on discussions related to other organoid models and research involving fetal tissue, placenta, or umbilical cord blood. We employed a scoping review method to search PubMed, Embase, Medline (all), Bioethics Research Library, and Google Scholar for research articles, books, or other correspondence on ethical issues regarding these indicated topics, with no date limits.

OUTCOMES

Ethical considerations related to trophoblast organoids can be divided into three distinct categories. First, there is a need to assess the moral value of trophoblast organoids, including their potential relational and symbolic dimensions. Second, it is important to understand ethical issues associated with ownership and commercialization of trophoblast organoids. Last, there are considerations related to appropriate informed consent procedures. It is worth noting that these three categories are interconnected, with the second and third being largely dependent on the moral value attributed to trophoblast organoids. Future research should assess the perspectives of various stakeholders, including parents who may donate placental tissue for organoid research.

WIDER IMPLICATIONS

This review offers valuable insights into the ethical landscape surrounding the derivation of tissues or products from pregnancies, and their further application, highlighting areas that require attention and discussion within both the scientific community and the broader society.

REGISTRATION NUMBER

N/A.

Organoid generation from trophoblast stem cells highlights distinct roles for cytotrophoblasts and stem cells in organoid formation and expansion

BACKGROUND

Organoids are stem-cell derived, self-organised, three-dimensional cultures that improve in vitro recapitulation of tissue structure. The generation of trophoblast organoids using primary placental villous digests (containing cytotrophoblasts and trophoblast stem cells (TSC)) improved high-throughput assessment of early trophoblast differentiation. However, the relative contributions of cytotrophoblasts and TSCs to trophoblast organoid growth and differentiation remain unclear, with implications for model interpretation. Here we sought to generate organoids from side-population trophoblasts (SpTSCs) to better understand the contribution of TSC to trophoblast organoid formation.

METHODS

Methods were adapted from Haider et al., 2018 to generate organoids from Okae TSCs (OkTSCs) or SpTSCs. Organoid growth was compared with primary villous trophoblast organoids and cellular composition interrogated by immunohistochemistry.

RESULTS

Organoids can be derived from first-trimester SpTSCs that exhibit similar architecture to those from primary villous trophoblast. However, organoids established from pure TSC populations (OkTSC or SpTSC) have different growth dynamics to primary placental villous digest-derived organoids - with OkTSCs developing faster and spontaneously generating migratory cells, whilst SpTSC organoids grow more slowly. Importantly, depletion of SpTSC from first-trimester villous digests ablates organoid formation. Finally, the capacity of the side-population technique to isolate late-gestation TSC enabled the generation of trophoblast organoids from term placentae, although these were significantly smaller than their first-trimester SpTSC counterparts.

DISCUSSION

Together, this work highlights the requirement of TSC for organoid formation, and the functional distinction between TSC and cytotrophoblasts. Proof-of-principle data demonstrating organoid generation from late gestation TSC isolated directly from the placenta lays the groundwork for future disease models.

Pathologic maternal and neonatal outcomes associated with programmed embryo transfer: potential etiologies and strategies for prevention

PURPOSE

In the first of two companion papers, we comprehensively reviewed the recent evidence in the primary literature, which addressed the increased prevalence of hypertensive disorders of pregnancy, late-onset or term preeclampsia, fetal overgrowth, postterm birth, and placenta accreta in women conceiving by in vitro fertilization. The preponderance of evidence implicated frozen embryo transfer cycles and, specifically, those employing programmed endometrial preparations, in the higher risk for these adverse maternal and neonatal pregnancy outcomes. Based upon this critical appraisal of the primary literature, we formulate potential etiologies and suggest strategies for prevention in the second article.

METHODS

Comprehensive review of primary literature.

RESULTS

Presupposing significant overlap of these apparently diverse pathological pregnancy outcomes within subjects who conceive by programmed autologous FET cycles, shared etiologies may be at play. One plausible but clearly provocative explanation is that aberrant decidualization arising from suboptimal endometrial preparation causes greater than normal trophoblast invasion and myometrial spiral artery remodeling. Thus, overly robust placentation produces larger placentas and fetuses that, in turn, lead to overcrowding of villi within the confines of the uterine cavity which encroach upon intervillous spaces precipitating placental ischemia, oxidative and syncytiotrophoblast stress, and, ultimately, late-onset or term preeclampsia. The absence of circulating corpus luteal factors like relaxin in most programmed cycles might further compromise decidualization and exacerbate the maternal endothelial response to deleterious circulating placental products like soluble fms-like tyrosine kinase-1 that mediate disease manifestations. An alternative, but not mutually exclusive, determinant might be a thinner endometrium frequently associated with programmed endometrial preparations, which could conspire with dysregulated decidualization to elicit greater than normal trophoblast invasion and myometrial spiral artery remodeling. In extreme cases, placenta accreta could conceivably arise. Though lower uterine artery resistance and pulsatility indices observed during early pregnancy in programmed embryo transfer cycles are consistent with this initiating event, quantitative analyses of trophoblast invasion and myometrial spiral artery remodeling required to validate the hypothesis have not yet been conducted.

CONCLUSIONS

Endometrial preparation that is not optimal, absent circulating corpus luteal factors, or a combination thereof are attractive etiologies; however, the requisite investigations to prove them have yet to be undertaken. Presuming that in ongoing RCTs, some or all adverse pregnancy outcomes associated with programmed autologous FET are circumvented or mitigated by employing natural or stimulated cycles instead, then for women who can conceive using these regimens, they would be preferable. For the 15% or so of women who require programmed FET, additional research as suggested in this review is needed to elucidate the responsible mechanisms and develop preventative strategies.

Modelling human placental villous development: designing cultures that reflect anatomy

The use of in vitro tools to study trophoblast differentiation and function is essential to improve understanding of normal and abnormal placental development. The relative accessibility of human placentae enables the use of primary trophoblasts and placental explants in a range of in vitro systems. Recent advances in stem cell models, three-dimensional organoid cultures, and organ-on-a-chip systems have further shed light on the complex microenvironment and cell-cell crosstalk involved in placental development. However, understanding each model's strengths and limitations, and which in vivo aspects of human placentation in vitro data acquired does, or does not, accurately reflect, is key to interpret findings appropriately. To help researchers use and design anatomically accurate culture models, this review both outlines our current understanding of placental development, and critically considers the range of established and emerging culture models used to study this, with a focus on those derived from primary tissue.