Artificial Gametogenesis and In Vitro Spermatogenesis: Emerging Strategies for the Treatment of Male Infertility

Abstract

Male-factor infertility accounts for approxiamately half of all infertility cases globally, yet therapeutic options remain limited for individuals with no retrievable spermatozoa, such as those with non-obstructive azoospermia (NOA). In recent years, artificial gametogenesis has emerged as a promising avenue for fertility restoration, driven by advances in two complementary strategies: organotypic in vitro spermatogenesis (IVS), which aims to complete spermatogenesis ex vivo using native testicular tissue, and in vitro gametogenesis (IVG), which seeks to generate male gametes de novo from pluripotent or reprogrammed somatic stem cells. To evaluate the current landscape and future potential of these approaches, a narrative, semi-systematic literature search was conducted in PubMed and Scopus for the period January 2010 to February 2025. Additionally, landmark studies published prior to 2010 that contributed foundational knowledge in spermatogenesis and testicular tissue modeling were reviewed to provide historical context. This narrative review synthesizes multidisciplinary evidence from cell biology, tissue engineering, and translational medicine to benchmark IVS and IVG technologies against species-specific developmental milestones, ranging from rodent models to non-human primates and emerging human systems. Key challenges-such as the reconstitution of the blood-testis barrier, stage-specific endocrine signaling, and epigenetic reprogramming-are discussed alongside critical performance metrics of various platforms, including air-liquid interface slice cultures, three-dimensional organoids, microfluidic "testis-on-chip" devices, and stem cell-derived gametogenic protocols. Particular attention is given to clinical applicability in contexts such as NOA, oncofertility preservation in prepubertal patients, genetic syndromes, and reprocutive scenarios involving same-sex or unpartnered individuals. Safety, regulatory, and ethical considerations are critically appraised, and a translational framework is outlined that emphasizes biomimetic scaffold design, multi-omics-guided media optimization, and rigorous genomic and epigenomic quality control. While the generation of functionally mature sperm in vitro remains unachieved, converging progress in animal models and early human systems suggests that clinically revelant IVS and IVG applications are approaching feasibility, offering a paradigm shift in reproductive medicine.

Keywords: ethical considerations; in vitro gametogenesis; in vitro spermatogenesis; male infertility; organoids; pluripotent stem cells.

Figure 1

Anatomical localization and functional roles of Sertoli cells in the seminiferous tubule. Schematic overview of the testis and a representative seminiferous tubule shown in cross- and longitudinal views. SC extend from the basement membrane to the lumen, forming TJ that constitute the BTB. They nurture GC, secrete key trophic factors—GDNF, SCF, ABP, inhibin B—respond to FSH and testosterone, phagocytose residual bodies, and sustain immune privilege. The bottom panel summarizes these principal functions. Abbreviations: ABP, androgen-binding protein; BTB, blood–testis barrier; FSH, follicle-stimulating hormone; GC, germ cell; GDNF, glial cell line-derived neurotrophic factor; Inhibin B, inhibin beta; PMC, peritubular myoid cell; SC, Sertoli cell; SCF, stem cell factor; TJ, tight junction. Created in BioRender. Kaltsas, A. (2025) https://BioRender.com/1m0mbsy, accessed on 18 July 2025.

Figure 2

Milestones in Pluripotent Stem Cell Research and In Vitro Gametogenesis. Chronological overview of key experimental breakthroughs in the development of human and murine in vitro gametogenesis (IVG) platforms. Each event is color-coded according to its thematic focus, including pluripotent stem cell derivation, germline commitment, PGCLC differentiation, and maturation to functional haploid gametes. Created in BioRender. Kaltsas, A. (2025) https://BioRender.com/j9i2j9n, accessed on 18 July 2025 [95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110].

Figure 3

IVS/IVG Development Pipeline. A proposed pipeline from laboratory to clinic for artificial gametogenesis. This infographic illustrates the sequential steps from obtaining patient tissue or cells (e.g., testis biopsy or skin/blood for iPSC reprogramming), through in vitro culture and differentiation (including use of bioengineered scaffolds and growth factors), to the generation of sperm cells and their use in assisted reproduction (e.g., IVF/ICSI). This figure underscores the translational vision, integrating the advances reviewed into a cohesive roadmap. Created in BioRender. Kaltsas, A. (2025), https://BioRender.com/zsmhj1h, accessed on 18 July 2025.