Stem cell therapeutic possibilities: future therapeutic options for male-factor and female-factor infertility?

Modelling in vitro gametogenesis using induced pluripotent stem cells: a review

In vitro gametogenesis (IVG) has been a topic of great interest in recent years not only because it allows for further exploration of mechanisms of germ cell development, but also because of its prospect for innovative medical applications especially for the treatment of infertility. Elucidation of the mechanisms underlying gamete development in vivo has inspired scientists to attempt to recapitulate the entire process of gametogenesis in vitro. While earlier studies have established IVG methods largely using pluripotent stem cells of embryonic origin, the scarcity of sources for these cells and the ethical issues involved in their use are serious limitations to the progress of IVG research especially in humans. However, with the emergence of induced pluripotent stem cells (iPSCs) due to the revolutionary discovery of dedifferentiation and reprogramming factors, IVG research has progressed remarkably in the last decade. This paper extensively reviews developments in IVG using iPSCs. First, the paper presents key concepts from groundwork studies on IVG including earlier researches demonstrating that IVG methods using embryonic stem cells (ESCs) also apply when using iPSCs. Techniques for the derivation of iPSCs are briefly discussed, highlighting the importance of generating transgene-free iPSCs with a high capacity for germline transmission to improve efficacy when used for IVG. The main part of the paper discusses recent advances in IVG research using iPSCs in various stages of gametogenesis. In addition, current clinical applications of IVG are presented, and potential future applications are discussed. Although IVG is still faced with many challenges in terms of technical issues, as well as efficacy and safety, novel IVG methodologies are emerging, and IVG using iPSCs may usher in the next era of reproductive medicine sooner than expected. This raises both ethical and social concerns and calls for the scientific community to cautiously develop IVG technology to ensure it is not only efficacious but also safe and adheres to social and ethical norms.

Genetic association of vitamin D receptor gene with female infertility

BACKGROUND

Infertility is defined as failure to achieve a clinical pregnancy after 12 months of unprotected intercourse. It affects 15% of couples globally and 22% of couples within Pakistan. Female infertility can be caused by numerous genetic or environmental factors including hormone imbalances and exposure to chemicals or radiation. The prevalence of vitamin D deficiency among the adult population was reported to be 14-59% with a higher prevalence in Asian countries. Furthermore, the expression of Vitamin D receptor (VDR) can play a vital role in the reproductive organs of females. Hence, the aim of our present study was to check the association of VDR polymorphisms with infertile females. For this purpose, blood samples were collected for genotyping of four known VDR mutations [FokI (rs2228570), TaqI (rs731236), ApaI (rs7975232), and BsmI (rs1544410)] via PCR-based RFLP assay.

RESULTS

Genotyping indicated that FokI, TaqI, and ApaI are associated with infertility (p = 0.004*, p = 0.013*, and p = 0.033*, respectively). However, BsmI did not show any significance. Multinomial regression analysis indicated that FokI heterozygous genotypes increase the risk of infertility by 2.5 times (hetero: OR = 2.5, 95%, p = 0.001*) as compared to wild type. Heterozygous genotypes of TaqI and ApaI were found to play a protective role and reduce the risk of infertility by 58 and 52%, respectively [TaqI: OR = 0.42, 95%, p = 0.004*, ApaI: OR = 0.48, 95%, p = 0.01*, respectively] as compared to wild type. Multinomial logistic regression analysis was also performed for allelic data as well.

CONCLUSION

Thus, it could be summarized that among the studied polymorphisms of VDR, FokI SNP greatly increased the risk of infertility, while TaqI and ApaI genotypes protect from infertility. However, BsmI does not influence the risk of infertility in Pakistani females.

Cell therapy for the treatment of reproductive diseases and infertility: an overview from the mechanism to the clinic alongside diagnostic methods

Infertility is experienced by 8%-12% of adults in their reproductive period globally and has become a prevalent concern. Besides routine therapeutic methods, stem cells are rapidly being examined as viable alternative therapies in regenerative medicine and translational investigation. Remarkable progress has been made in understanding the biology and purpose of stem cells. The affected pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs) are further studied for their possible use in reproductive medicine, particularly for infertility induced by premature ovarian insufficiency and azoospermia. Accordingly, this study discusses current developments in the use of some kinds of MSCs such as adipose-derived stem cells, bone marrow stromal cells, umbilical cord MSCs, and menstrual blood MSCs. These methods have been used to manage ovarian and uterine disorders, and each technique presents a novel method for the therapy of infertility.

Research Advances in Gametogenesis and Embryogenesis Using Pluripotent Stem Cells

The previous studies of human gametogenesis and embryogenesis have left many unanswered questions, which hinders the understanding of the physiology of these two vital processes and the development of diagnosis and treatment strategies for related diseases. Although many results have been obtained from animal studies, particularly mouse research, the results cannot be fully applied to humans due to species differences in physiology and pathology. However, due to ethical and material limitations, the direct study of human gametes and embryos is very difficult. The emergence and rapid development of organoids allow the construction of organoid systems that simulate gametogenesis and embryogenesis in vitro, and many studies have successfully established organoid systems for some parts of or even the entire processes of gametogenesis and embryogenesis. These studies typically start with the establishment of mouse models and then modify these models to obtain human organoid models. These organoid models can be used to obtain a better understanding of the signaling pathways, molecular mechanisms, genetics, and epigenetic changes involved in gametogenesis and embryogenesis and could also be applied to clinical applications, such as drug screening. Here, we discuss the formation of primordial stem cell-like cells (PGCLCs), and in vitro-induced gametes and embryoids using pluripotent stem cells (PSCs). We also analyze their applications and limitations.

Decidualization Potency and Epigenetic Changes in Human Endometrial Origin Stem Cells During Propagation

Human endometrium derived mesenchymal stem cells (hEndSCs) offer a great promise for regenerative medicine and reproductive system disorders treatment methods based on cell therapy due to their broad differentiation potential and highly efficient proliferation. In our study, we investigated the characteristics of hEndSCs that were isolated from two sources: endometrium and menstrual blood, which both contain endometrial origin stem cells. Changes in gene and protein expression levels during long-term cultivation and decidualization potential were examined in endometrial stem cells (EndSCs) and menstrual blood stem cells (MenSCs). The decidualization process was induced on early and late passages of hEndSCs using dibutyryl cyclic-AMP (db-cAMP) and medroxyprogesterone acetate (MPA) agents. We demonstrated that after long-term cultivation of hEndSCs the expression of typical mesenchymal stromal cell surface markers such as CD44, CD73, CD90, CD105 and perivascular marker CD146 remains at a similar level throughout long-term cultivation. Additionally, hematopoietic and endothelial markers CD34, CD45 were also tested, they were negative in all cases. Analyzed stem cells gene markers, such as OCT4, SOX2, NANOG, KLF4, showed similar expression in all passages of hEndSCs. RT-qPCR results demonstrated that the expression of cell cycle control associated genes - CDK2, CCNA2, CCNE2, p21, p53 and Rb, among all groups was very similar. Expression of genes associated with senescence (ATM, JUND, TOP2A, MYC) was maintained at a similar level throughout passaging. In addition, Western blot analysis was used to assess changes in proteins’ levels associated to epigenetics (EZH2, SUZ12, H3K27me3) and cell cycle control (cyclinE1, p53) during long-term cultivation. The levels of proteins associated with epigenetic changes were fluctuated slightly depending on the patient. Also, we demonstrated that in all induced hEndSCs the expression of decidualization markers Prolactin (PRL), IGFBP1 and WNT4 was upregulated. In conclusion, we demonstrated successful decidualization of stem cells derived from two reproductive system resources: endometrium and menstrual blood by using db-cAMP and MPA regardless of the length of the stem cell passaging. According these findings, we suppose that endometrium derived stem cells and menstrual blood derived stem cells could have a potency not only for endometrium tissue regeneration, but could also become a successful therapy for reproductive system disorders, including infertility or recurrent pregnancy loss.

The Role of Stem Cells and Their Derived Extracellular Vesicles in Restoring Female and Male Fertility

Infertility is a globally recognized issue caused by different reproductive disorders. To date, various therapeutic approaches to restore fertility have been attempted including etiology-specific medication, hormonal therapies, surgical excisions, and assisted reproductive technologies. Although these approaches produce results, however, fertility restoration is not achieved in all cases. Advances in using stem cell (SC) therapy hold a great promise for treating infertile patients due to their abilities to self-renew, differentiate, and produce different paracrine factors to regenerate the damaged or injured cells and replenish the affected germ cells. Furthermore, SCs secrete extracellular vesicles (EVs) containing biologically active molecules including nucleic acids, lipids, and proteins. EVs are involved in various physiological and pathological processes and show promising non-cellular therapeutic uses to combat infertility. Several studies have indicated that SCs and/or their derived EVs transplantation plays a crucial role in the regeneration of different segments of the reproductive system, oocyte production, and initiation of sperm production. However, available evidence triggers the need to testify the efficacy of SC transplantation or EVs injection in resolving the infertility issues of the human population. In this review, we highlight the recent literature covering the issues of infertility in females and males, with a special focus on the possible treatments by stem cells or their derived EVs.

Infertility cell therapy and epigenetic insights

Recent advances in assisted reproductive technology (ART) have allowed couples with severe infertility to conceive, but the methods are not effective for all cases. Stem cells as undifferentiated cells which are found in different stages of embryonic, fetal and adult life are known to be capable of forming different cell types, tissues, and organs. Due to their unlimited resources and the incredible power of differentiation are considered as potential new therapeutic biological tools for treatment of infertility. For reproductive medicine, stem cells are stimulated in vitro to develop various specialized functional cells including male and female gametes. The epigenetic patterns can be modified in the genome under certain drugs exposure or lifestyle alterations. Therefore, epigenetics-related disorders may be treated if the nature of the modifications is completely admissible. It is proved that our understanding of epigenetic processes and its association with infertility would help us not only to understand the etiological factors but also to treat some type of male infertilities. Exploration of both genetic and epigenetic variations in the disease development could help in the identification of the interaction patterns between these two phenomena and possible improvement of therapeutic methods.

Application of Stem Cell Therapy for Infertility

Infertility creates an immense impact on the psychosocial wellbeing of affected couples, leading to poor quality of life. Infertility is now considered to be a global health issue affecting approximately 15% of couples worldwide. It may arise from factors related to the male (30%), including varicocele, undescended testes, testicular cancer, and azoospermia; the female (30%), including premature ovarian failure and uterine disorders; or both partners (30%). With the recent advancement in assisted reproduction technology (ART), many affected couples (80%) could find a solution. However, a substantial number of couples cannot conceive even after ART. Stem cells are now increasingly being investigated as promising alternative therapeutics in translational research of regenerative medicine. Tremendous headway has been made to understand the biology and function of stem cells. Considering the minimum ethical concern and easily available abundant resources, extensive research is being conducted on induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSC) for their potential application in reproductive medicine, especially in cases of infertility resulting from azoospermia and premature ovarian insufficiency. However, most of these investigations have been carried out in animal models. Evolutionary divergence observed in pluripotency among animals and humans requires caution when extrapolating the data obtained from murine models to safely apply them to clinical applications in humans. Hence, more clinical trials based on larger populations need to be carried out to investigate the relevance of stem cell therapy, including its safety and efficacy, in translational infertility medicine.

Histological Study on the Protective Effect of Endogenous Stem Cell Mobilization in Busulfan-Induced Testicular Injury in Albino Rats

BACKGROUND

Testicular damage is one of the most hazardous effects of chemotherapy as it is frequently associated with oligozoospermia and azoospermia.

AIM OF THE WORK

This study aimed at evaluating the protective effect of hematopoietic stem cell mobilization by granulocyte colony-stimulating factor (G-CSF) in a rat model of busulfan-induced testicular injury.

MATERIALS AND METHODS

Twenty-four adult albino rats were divided into four groups: group I, the control, Group II: rats received two doses of busulfan (each 15 mg/kg) intraperitoneally (IP) with 14 days interval, Group III: rats received busulfan and left untreated, and Group IV received busulfan IP then G-CSF (70 μg/kg/day) subcutaneously for 5 consecutive days. Testicular sections were stained with H and E and immunohistochemically for CD34, proliferating cell nuclear antigen (PCNA) and caspase-3, and semithin sections were stained with toluidine blue.

RESULTS

Groups II and III showed loss of the normal histological architecture of the testis and spermatogenic cells, with increased apoptosis confirmed by significantly increased caspase-3 and significantly decreased PCNA immunoexpression. While Group IV revealed improved testicular histology, decreased apoptosis, and increased proliferative capacity of spermatogenic cells. This was confirmed by significantly decreased caspase-3 immunoexpression and increased PCNA immunoreaction.

CONCLUSION

Mobilization of stem cells with G-CSF was found to improve the testicular histology following busulfan chemotherapy in albino rats.

Human amniotic mesenchymal stem cells improve ovarian function in natural aging through secreting hepatocyte growth factor and epidermal growth factor

Background

Although many reports show that various kinds of stem cells have the ability to recover function in premature ovarian aging, few studies have looked at stem cell treatment of natural ovarian aging (NOA). We designed this experimental study to investigate whether human amniotic mesenchymal stem cells (hAMSCs) retain the ability to restore ovarian function, and how hAMSCs work in this process.

Methods

To build the NOA mouse model, the mice were fed for 12–14 months normally with young fertile female mice as the normal control group (3–5 months old). Hematoxylin and eosin staining permitted follicle counting and showed the ovarian tissue structure. An enzyme-linked immunosorbent assay was used to detect the serum levels of the sex hormones estradiol (E2), anti-mullerian hormone (AMH), and follicle-stimulating hormone (FSH). The proliferation rate and marker expression level of human ovarian granule cells (hGCs) (ki67, AMH, FSH receptor, FOXL2, and CYP19A1) were measured by flow cytometry (FACS). Cytokines (growth factors) were measured by a protein antibody array methodology. After hepatocyte growth factor (HGF) and epidermal growth factor (EGF) were co-cultured with hGCs, proliferation (ki67) and apoptosis (Annexin V) levels were analyzed by FACS. After HGF and EGF were injected into the ovaries of natural aging mice, the total follicle numbers and hormone levels were tested.

Results

After the hAMSCs were transplanted into the NOA mouse model, the hAMSCs exerted a therapeutic activity on mouse ovarian function by improving the follicle numbers over four stages. In addition, our results showed that hAMSCs significantly promoted the proliferation rate and marker expression level of ovarian granular cells that were from NOA patients. Meanwhile, we found that the secretion level of EGF and HGF from hAMSCs was higher than other growth factors. A growth factor combination (HGF with EGF) improved the proliferation rate and inhibited the apoptosis rate more powerfully after a co-culture with hGCs, and total follicle numbers and hormone levels were elevated to a normal level after the growth factor combination was injected into the ovaries of the NOA mouse model.

Conclusions

These findings provide insight into the notion that hAMSCs play an integral role in resistance to NOA. Furthermore, our present study demonstrates that a growth factor combination derived from hAMSCs plays a central role in inhibiting ovarian aging. Therefore, we suggest that hAMSCs improve ovarian function in natural aging by secreting HGF and EGF.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0781-9) contains supplementary material, which is available to authorized users.

The Regenerative Effect of Bone Marrow-Derived Stem Cells in Spermatogenesis of Infertile Hamster

BACKGROUND

Infertility is a serious social problem in advanced nations, with male factor in half of all cases of infertility. This study was conducted to determine the regenerative effect of bone marrow-derived stem cells in spermatogenesis of infertile hamster.

METHODS

Twelve adult male hamsters were equally divided into azoospermic and control groups. Busulfan was intraperitoneally used for induction of azoospermia, while the right testis was treated with bone marrow-derived stem cells (10⁶ BM-SCs), labeled with sterile trypan blue, 35 days after busulfan injection. The left testis served as positive control for azoospermia. Sixty days after cell transplantation, the animals were euthanized and both testes were removed and evaluated histologically.

RESULTS

BM-SCs were spindle-shaped, adherent to the culture flasks and had positive expression of CD29 and CD73 and negative expression of CD45. Alcian blue staining confirmed differentiation of BM-SCs into chondrocytes. Karyotyping denoted to stability of chromosomes. Treatment with busulfan in seminiferous tubules resulted into distruption of spermatogenesis. After two months in busulfan treatment group, seminiferous tubular atrophy and germinal epitheliums degenerations were noticed with no spermatozoa in epididymis. After treatment of busulfan group with BM-SCs, spermatogonia, primary spermatocytes, spermatids and sperms were present in seminiferous tubules.

CONCLUSION

As cell transplantation in seminiferous tubules resulted into a rapid repair of pathological changes, BM-SCs can be recommended an effective treatment measure in azoospermia. It seems that more studies are necessary to confirm the use of this technique in treatment of azoospermia and infertility in human.

Histomorphometric evaluation of treatment of rat azoosper-mic seminiferous tubules by allotransplantation of bone marrow-derived mesenchymal stem cells

OBJECTIVES

Bone marrow-derived mesenchymal stem cells (BM-MSCs) potentials make them appropriate for cell therapy including ability of differentiation and release of anti-inflammatory cytokines and growth factors secreta. For treatment of azoospermia to induce proliferation and differentiation of germ cells, MSCs transplantation has been introduced. The aim of the present experimental case-control study was to histomorphometric evaluation of the germinal cells in seminiferous tubules of azoospermic rats before and after BM-MSCs allotransplantation.

MATERIALS AND METHODS

In the present study, BM-MSCs were isolated from six male rats and confirmed. Their testes also served as intact negative controls. The recipient rats (n=6) were received two doses of 10 mg/kg of busulfan with 21 days interval to induce azoospermia. After cessation of spermatogenesis, the rats were allotransplanted with the BM-MSCs into efferent duct of right testes. Thirty-five days later, the right cell-treated testes were compared to left azoospermic ones.

RESULTS

Histomorphometric analyses showed that the seminiferous tubules treated with BM-MSCs had normal morphology in comparison with azoospermic testes, which were without germinal layer. In most BM-MSCs-treated seminiferous tubules, spermatogenesis was observed.

CONCLUSION

The allotransplanted BM-MSCs could induce spermatogenesis in seminiferous tubules of azoospermic rats.

Induction of Spermatogenesis by Bone Marrow-derived Mesenchymal Stem Cells in Busulfan-induced Azoospermia in Hamster

Background

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have potential of differentiation and they secrete anti-inflammatory cytokines and growth factors which make them appropriate for cell therapy.

Aim of the Work

Were to evaluate the healing effect of BM-MSCs transplantation on germinal cells of busulfan-induced azoospermic hamsters.

Material and Methods

In the present experimental case control study, BM-MSCs were isolated from bone marrow of donor albino hamsters. Five mature male recipient hamsters received two doses of 10 mg/kg of busulfan with 21 days interval to stop endogenous spermatogenesis. After induction of azoospermia, right testis of hamsters was injected with 10⁶ BM-MSCs via efferent duct and the left one remained as azoospermia control testis. Five normal mature hamsters were selected as normal intact control. After 35 days, testes and epididymis of three groups were removed for histological evaluation.

Results

Histomorphological analyses of BM-MSCs treated testes and epididymis showed the epithelial tissue of seminiferous tubules had normal morphology and spermatozoa were present in epididymis tubes. Spermatogenesis was observed in most cell-treated seminiferous tubules. The untreated seminiferous tubules were empty.

Conclusion

Transplanted BM-MSCs could successfully induce spermatogenesis in seminiferous tubules of azoospermic hamster. Therefore, BM-MSCs can be an attractive candidate in cell transplantation of azoospermia.

Retracted article: In vitro derivation of mammalian germ cells from stem cells and their potential therapeutic application

Pluripotent stem cells (PSCs) are a unique type of cells because they exhibit the characteristics of self-renewal and pluripotency. PSCs may be induced to differentiate into any cell type, even male and female germ cells, suggesting their potential as novel cell-based therapeutic treatment for infertility problems. Spermatogenesis is an intricate biological process that starts from self-renewal of spermatogonial stem cells (SSCs) and leads to differentiated haploid spermatozoa. Errors at any stage in spermatogenesis may result in male infertility. During the past decade, much progress has been made in the derivation of male germ cells from various types of progenitor stem cells. Currently, there are two main approaches for the derivation of functional germ cells from PSCs, either the induction of in vitro differentiation to produce haploid cell products, or combination of in vitro differentiation and in vivo transplantation. The production of mature and fertile spermatozoa from stem cells might provide an unlimited source of autologous gametes for treatment of male infertility. Here, we discuss the current state of the art regarding the differentiation potential of SSCs, embryonic stem cells, and induced pluripotent stem cells to produce functional male germ cells. We also discuss the possible use of livestock-derived PSCs as a novel option for animal reproduction and infertility treatment.

Gamete derivation from embryonic stem cells, induced pluripotent stem cells or somatic cell nuclear transfer-derived embryonic stem cells: state of the art

Generating gametes from pluripotent stem cells (PSCs) has many scientific justifications and several biomedical rationales. Here, we consider several strategies for deriving gametes from PSCs from mice and primates (human and non-human) and their anticipated strengths, challenges and limitations. Although the 'Weismann barrier', which separates the mortal somatic cell lineages from the potentially immortal germline, has long existed, breakthroughs first in mice and now in humans are artificially creating germ cells from somatic cells. Spermatozoa with full reproductive viability establishing multiple generations of seemingly normal offspring have been reported in mice and, in humans, haploid spermatids with correct parent-of-origin imprints have been obtained. Similar progress with making oocytes has been published using mouse PSCs differentiated in vitro into primordial germ cells, which are then cultured after xenografting reconstructed artificial ovaries. Progress in making human oocytes artificially is proving challenging. The usefulness of these artificial gametes, from assessing environmental exposure toxicity to optimising medical treatments to prevent negative off-target effects on fertility, may prove invaluable, as may basic discoveries on the fundamental mechanisms of gametogenesis.

Adipose tissue-derived mesenchymal stem cells repair germinal cells of seminiferous tubules of busulfan-induced azoospermic rats

CONTEXT:

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) are less invasive than bone marrow mesenchymal stem cells to obtain for cell therapy.

AIMS:

The aims of this study were to evaluate the germinal cells characteristics and repairs in seminiferous tubules of busulfan-induced azoospermic rats after AT-MSCs transplantation.

SETTINGS AND DESIGN:

Experimental case-control study.

MATERIALS AND METHODS:

In the present experimental study, donors AT-MSCs were isolated from subcutaneous adipose tissue of two Sprague-Dawley rats. The recipients (n = 5) were received two doses of 10 mg/kg of busulfan with 21 days interval to stop endogenous spermatogenesis. After induction of azoospermia by busulfan, rats were injected with the AT-MSCs into the efferent duct of right testes. After 60 days, the right testes were injected AT-MSCs were compared to left azoospermic testes. Five untreated male rats served as negative control.

STATISTICAL ANALYSIS USED:

Stereological indices were analyzed by one-way ANOVA and LSD post-hoc test. The spermatogenesis index was compared using Mann–Whitney U test.

RESULTS:

After stereological analyses, the seminiferous tubules treated with AT-MSCs had normal morphology. The untreated seminiferous tubules were empty. Spermatogenesis was observed in most cell-treated seminiferous tubules.

CONCLUSIONS:

The testis of busulfan-induced azoospermic rats accepted transplanted AT-MSCs. The transplanted AT-MSCs could induce spermatogenesis in seminiferous tubules of the rat.

Stem cells as new agents for the treatment of infertility: current and future perspectives and challenges

Stem cells are undifferentiated cells that are present in the embryonic, fetal, and adult stages of life and give rise to differentiated cells that make up the building blocks of tissue and organs. Due to their unlimited source and high differentiation potential, stem cells are considered as potentially new therapeutic agents for the treatment of infertility. Stem cells could be stimulated in vitro to develop various numbers of specialized cells including male and female gametes suggesting their potential use in reproductive medicine. During past few years a considerable progress in the derivation of male germ cells from pluripotent stem cells has been made. In addition, stem cell-based strategies for ovarian regeneration and oocyte production have been proposed as future clinical therapies for treating infertility in women. In this review, we summarized current knowledge and present future perspectives and challenges regarding the use of stem cells in reproductive medicine.

Adult somatic cells to the rescue: nuclear reprogramming and the dispensability of gonadal germ cells

With advances in cancer therapies, survival rates in prepubescent patients have steadily increased. However, a number of these surviving patients have been rendered sterile owing to their rigorous oncologic treatment regimens. In addition to cancer treatments, men and women, who are genetically fertile, can become infertile owing to immune suppression treatments, exposure to environmental and industrial toxicants, and injury. Notwithstanding the great emotional burden from an inability to conceive a child with their partner, the financial burdens for testing and treatment are high, and successful treatment of these patients' sterility is rare. Recent advances in pluripotent stem cell differentiation and the generation of patient-specific, induced pluripotent stem cells indicate that stem cell replacement therapies or in vitro differentiation followed by IVF may be on the horizon. Here we discuss these recent advances, their relevance to treating male-factor and female-factor infertility, and what experimental procedures must be carried out in animal models before these exciting new treatments can be used in a clinical setting. The goal of this research is to generate functional gametes from no greater starting material than a mere skin biopsy.