Experimental methods to preserve male fertility and treat male factor infertility

Abstract

Infertility is a prevalent condition that has insidious impacts on the infertile individuals, their families, and society, which extend far beyond the inability to have a biological child. Lifestyle changes, fertility treatments, and assisted reproductive technology (ART) are available to help many infertile couples achieve their reproductive goals. All of these technologies require that the infertile individual is able to produce at least a small number of functional gametes (eggs or sperm). It is not possible for a person who does not produce gametes to have a biological child. This review focuses on the infertile man and describes several stem cell-based methods and gene therapy approaches that are in the research pipeline and may lead to new fertility treatment options for men with azoospermia.

Keywords: Fertility; azoospermia; culture; de novo testicular morphogenesis; gene therapy; grafting; infertility; stem cells; transplantation.

Figure 1. Human spermatogonial stem cells and spermatogenesis

(A) Spermatogenesis occurs inside the seminiferous tubules of the testis. (B) Cut-out of the basement membrane of the seminiferous Tubule. (B and C) The basement membrane of the seminiferous epithelium contains undifferentiated (A_dark and A_pale) spermatogonia and differentiating Type B spermatogonia. Type B spermatogonia give rise to primary spermatocytes that enter meiosis and migrate off the basement membrane. Subsequent meiotic divisions and spermiogenesis give rise to secondary spermatocytes, spermatids and the terminally differentiated spermatozoa that are released into the lumen of the seminiferous tubules. Figure reprinted from Valli et al., 2014 with permission from Elsevier. Artwork is by Dr. Bart Phillips, National Institute of Environmental Health Sciences.

Figure 2. Standard and experimental options to treat male infertility

(A) Sperm obtained from ejaculated semen or by testicular sperm extraction (TESE) of infertile men, can be used to achieve pregnancy by intrauterine insemination (IUI), in vitro fertilitzation (IVF) or IVF with intracytoplasmic sperm injection (ICSI). (B) When it is not possible to obtain sperm, testicular tissue containing spermatogonial stem cells (SSCs) can be obtained by biopsy. Testicular tissue can be digested with enzymes to produce a cell suspension from which SSCs can be expanded in culture and/or transplanted into the testes of the patient. This method has the potential to regenerate spermatogenesis and possibly natural fertility. Heterogeneous testicular cell suspensions also have the potential undergo de novo testicular morphogenesis with seminiferous tubules and a polarized epithelium surrounded by a basement membrane with germ cells inside and interstitial cells outside the tubules. Sperm generated in the “rebuilt” testes can be used to fertilize eggs by ICSI. Intact testicular tissues from prepubertal animals can be grafted or xenografted under the skin or in the scrotum and produce mature sperm that can be used to fertilize eggs by ICSI. Sperm can also be generated when immature testicular tissues are maintained in organ culture and used to fertilize eggs by ICSI. (C) Patient-specific induced pluripotent stem (iPS) cells can be derived from patient somatic tissues (e.g., skin or blood) and differentiated into germline stem cells (GSCs) to be transplanted into patient testes. This method may have the potential to regenerate spermatogenesis and natural fertility. It may also be possible to differentiate iPS cells into sperm that can be used to fertilize eggs by ICSI.