By: Ameena Qadri PharmD Candidate c/o 2027

Advancements in reproductive technology have considerably enhanced fertility treatments, with in-vitro fertilization (IVF) serving as the primary method for many years. IVF facilitates external fertilization of oocytes, offering a solution to infertility. However, this method has presented limitations due to its inability to produce viable gametes and its reduced success rates in older individuals.⁵ In contrast, in-vitro gametogenesis (IVG), a method that saw its first signs of success in animal trials in 2016, is now being studied as an alternative with the potential to address these limitations by generating functional gametes from pluripotent stem cells. Human gametogenesis involves the differentiation of germ cells into oocytes and spermatozoa, they combine to form a diploid zygote, initiating embryogenesis. At its core, human gametogenesis is the maintenance of totipotency during fertilization. Totipotency is the ability of a single cell to develop into an entire organism. IVG aims to replicate human gametogenesis in vitro, using stem cells to produce functional gametes.

Totipotent cells have the ability to form all cell types in an organism whereas pluripotent cells, such as Embryonic Stem Cells (ESCs) and Induced Pluripotent Stem Cells (iPSCs), can differentiate into all cell types except extraembryonic tissue.¹ IVG utilizes advanced stem cell technologies to create functional gametes in vitro. The primary types of stem cells used in IVG are Embryonic Stem Cells (ESCs) and Induced Pluripotent Stem Cells (iPSCs). Understanding these stem cells is crucial for comprehending the potential of IVG. Using two different types of stem cells creates two different potential methods when performing IVG. The first method, using Embryonic Stem Cells (ESCs), requires a pre-existing embryo; ESCs are extracted from the inner cell mass of a blastocyst. The Embryonic Stem Cells (ESCs) extracted from the embryo can then be cultured to form primordial germ cell-like cells (PGCLCs). These PGCLCs, can then be guided through the meiosis process and can then form viable gametes. This method allows for the creation of oocytes or sperm cells from these stem cells, which can then be used for fertilization to form embryos. Although this process is helpful for patients who are unable to produce more than one embryo from their pre-existing egg and sperm cells, this method does not help improve the conception rate for patients who are unable to produce any embryos on their own.

Pluripotent Stem Cells (iPSCs) offer an alternative to Embryonic Stem Cells (ESCs) by providing an ethical method for generating pluripotent cells since they do not require a preexisting embryo. Pluripotent stem-cell lines may be obtained through the reprogramming of somatic cells from different tissues and species by the expression of specific factors.² Since this process derives embryos from an individual’s own cells, it significantly reduces the risk of immune rejection and providing a safer and personalized approach to reproductive technologies. Like the IVG Embryonic Stem Cells (ESCs) method, Pluripotent Stem Cells (iPSCs) are used to generate PGCLCs, which are then cultured in an environment replicative to that of natural gametogenesis to produce haploid gametes. IVG uses either 46XX or 46XY somatic cells to make an oocyte or sperm cell from those lab based somatic cells and fertilize them with gametes of the opposite biological sex to make an embryo. This method has been demonstrated to effectively replicate critical aspects of meiosis, including chromosomal synapsis and recombination, with studies showing that “intracytoplasmic injection of the resulting spermatid-like cells into oocytes produced viable and fertile offspring.”³

IVG has the potential to significantly enhance the accessibility and the success rate for fertility treatments by enabling the production of gametes from somatic cells, eliminating the need for viable gametes from the patient. This is particularly beneficial for individuals with non-functional gametes. Additionally, a study shows that “age-related fertility decline is a significant issue, with studies showing that fecundability decreases as women age, particularly after 35 years. By 40–44 years, half of women experience impaired reproductive capacity due to reduced ovarian reserve and oocyte quality.”⁴ IVG creates a potential solution by generating gametes from somatic cells, which eliminates the issue of the lack of natural gametes due to age-related decline. IVG also allows for the generation of gametes in vitro, which can be screened for genetic abnormalities before fertilization. This could reduce the incidence of genetic disorders, offering a more precise approach to managing genetic risks compared to traditional IVF.

Despite its life changing impact, IVF has limitations, notably in older women. Research indicates that the failure rate for IVF cycles increases significantly with age. In a study conducted in 2023 involving women aged 41 and older, “211 started cycles, and 169 reached the oocyte pickup stage, resulting in a cancellation rate of 20%, compared to 10% in the overall IVF group.”⁴ These high failure rates reflect the difficulties of IVF in older women, who have decreased ovarian reserve and poorer oocyte quality. Moreover, IVF often requires multiple cycles, which can often cause significant physical, emotional, and financial burdens on patients. IVG may offer a more cost-effective and emotionally manageable option by hypothetically reducing the number of cycles needed and addressing infertility issues more efficiently and effectively.

While IVG holds immense potential, it faces several challenges. The technology is still in its early stages and still requires extensive research to ensure the safety and efficacy of IVG-derived gametes. Currently achieving complete meiosis and maintaining the genetic stability of the gametes produced pose as the most significant challenges. The long-term health effects of using IVG-derived gametes on offspring are also unknown, requiring further investigation to understand possible risks and ensure the safety and efficacy of the IVG process. Ongoing research is needed to address these issues and validate the reliability of IVG as a feasible reproductive technology. Despite the significant technical hurdles, in-vitro gametogenesis is a hopeful development in reproductive technology. IVG carries the potential to offer more inclusive and effective solutions for individuals facing infertility. While IVF has significantly impacted fertility treatments, the advancements offered by IVG may address some of IVF’s limitations, specifically regarding gamete viability and age-related fertility decline. Extensive research will be pivotal in eliminating current challenges and realizing the full potential of IVG.

References

1. Chen G, Gulbranson DR, Hou Z, et al. Chemically defined conditions for human iPSC derivation and culture. Nature Methods. 2011;8(5):424-429. doi:https://doi.org/10.1038/nmeth.1593
2. González F, Boué S, Belmonte JCI. Methods for making induced pluripotent stem cells: reprogramming à la carte. Nature Reviews Genetics. 2011;12(4):231-242. doi:https://doi.org/10.1038/nrg2937
3. Wesevich VG, Arkfeld C, Seifer DB. In Vitro Gametogenesis in Oncofertility: A Review of Its Potential Use and Present-Day Challenges in Moving toward Fertility Preservation and Restoration. Journal of Clinical Medicine. 2023;12(9):3305. doi:https://doi.org/10.3390/jcm12093305
4. Zhou Q, Wang M, Yuan Y, et al. Complete Meiosis from Embryonic Stem Cell-Derived Germ Cells In Vitro. Cell Stem Cell. 2016;18(3):330-340. doi:https://doi.org/10.1016/j.stem.2016.01.017
5. von Wolff, M., Schwartz, A. K., Bitterlich, N., Stute, P., & Fäh, M. (2019). Only women’s age and the duration of infertility are the prognostic factors for the success rate of natural cycle IVF. Archives of gynecology and obstetrics, 299, 883-889.