Ovarian cortex tissue egg-producing portion can be cryopreserved and transplanted later to make pregnancy possible in different mammalian species
(Andersen et al., 2012; Mohammed 2018a,
2019). Cryopreservation of ovarian tissue is mainly used in girls and women facing a gonadotoxic treatment for fertility preservation. Transplanted ovarian tissues regain ovarian functions in almost all patients (
Yding Andersen et al., 2019). Ovarian tissues’ transplantation and cryopreservation offer fascinating opportunities for mammalian species
(Aljubran et al., 2023; Mohammed 2019). The auto-grafting and xeno-grafting of ovarian cortex tissue demonstrate potential advancement of cyopreservation
(Aljubran et al., 2023; Mohammed 2019). The cryopreserved ovarian tissue has been transplanted in different animal species and humans resulting in the birth of normal young
[Demirci et al., 2003, Donnez et al., 2004). Such techniques of ovarian tissue transplantation and cryopreservation in females who suffer from cancer present the elixir of life through ovariectomy and cryopreservation before chemotherapy and radiation treatments followed by re-transplantation after recovery. Therefore, ovarian tissue cryopreservation and transplantation is a noble goal for humanity and preserving the genetic materials of superior animal species. Premature ovarian failure upon autotransplantation of cryopreserved ovarian tissue in women exposed to chemotherapy
(Schmidt et al., 2012).
Modulation of gonadal tissues is essential for conservation of species, increase productivity, fertility treatments of mammalian species
(Ali et al., 2021; Al Masruri et al., 2022; Mohammed and Al-Suweigh 2023;
Al Mufarji et al., 2023). Various treatments have been recently applied for enhancing the purpose of ovarian transplantation (Table 1).
They include treatments for enhancement of blood vascularization, inhibition of ovarian follicle degeneration in addition to stimulation of ovarian follicle growth and development (
Mohammed 2019;
Oktay and Marin 2023). In addition, ovarian cryopreservation and transplantation processes and the resulting outcomes in addition to the factors effecting cryopreservation and transplantation are indicated in the following figure (Fig 1).
Furthermore, cumulus-enclosed germinal vesicle oocytes could be aspirated from the transplanted ovarian tissues and used for
in vitro embryo production
(Mohammed et al., 2005; Sánchez et al., 2015;
Báez et al., 2022). Ovarian tissue cryopreservation and transplantation results in a 76.0% spontaneous pregnancy live baby rate in humans
(Silber et al., 2022). Therefore, the current review was carried out to collect, consolidate and highlight the ovarian tissue cryopreservation and transplantation.
The current review was designed according to the procedure approved by Scientific Research Deanship, King Faisal University of Saudi Arabi from November to March 2024. The articles concerning ovarian tissue collection and processing, ovarian tissues cryopreservation, ovarian transplantation process, the assisted reproductive techniques used after ovarian transplantation were collected form PubMed, science direct and google scholar in addition to our articles related to ovarian transplantation for writing the current review.
Ovarian tissue collection and processing
Ovarian tissue collection for transplantation involves removing a small piece of ovarian tissue through laparoscopy procedure
(Beckmann et al., 2016; Fabbri et al., 2022). The removed ovaries are divided into small pieces and either transplanted or cryopreserved. The cryopreserved ovarian tissues can be stored for several years in liquid nitrogen tank (-196.0°C) especially storage facilities where samples are carefully monitored and preserved.
Practical aspects of freezing ovarian tissue
Ovarian tissue cryopreservation (OTC) has developed from being an experimental procedure to being a standard method of fertility preservation since the late 1990s. The necessitate of ovarian tissue cryopresevation includes the urgent need for chemotherapy, which indicates no time for ovarian superovulation and egg aspiration protocol (
Macklon 2020;
Shapira et al., 2020). Fifty percent of the women had ovarian tissue transplantation achieved pregnancies and 28.4-42.0% of them delivered an infant
(Shapira et al., 2020; Oktay et al., 2015).
Transportation of ovarian tissues prior to fresh transplantation or freezing
The transportation standard procedure of ovarian tissue is necessitated for both human and animals. The OT transportation procedure has been shown to be valuable in clinical practices
(Kyono et al., 2017). The transportation time should be minimized as much as possible. The ideal temperature for transporting ovarian tissues is around 4°C to minimize ischemic damage caused by a lack of blood flow. Ovarian tissues are transported in sterile containers designed to maintain the cool temperature. These containers typically contain a transport medium as buffer solution.
In human patients, the procedure is required where the ovarian tissue is surgically removed and other lab performing the cryopreservation
(Duncan et al., 2016, Kyono et al., 2017). In animals, the circumstances that need ovarian tissue transportation (OTT) might include sudden or accidental death of superior animals in addition to OTT form slaughterhouses. Loss of ovarian follicles during transportation is minimal as recently shown where follicle survival of frozen and thawed tissues transported was similar to that of fresh and frozen tissues
(Kristensen et al., 2018).
Ovarian tissues cryopreservation
Ovarian tissues cryopreservation has been performed since more than two decades. Several technical aspects for freezing ovarian tissue should be taken into consideration including the method of freezing, the type of cryoprotectants, the size of the ovarian tissue. The most common cryoprotectants are ethylene glycol, DMSO and propylene glycol
(Jadoul et al., 2017; Gook, 2017). These molecules are capable of penetrating cell membrane and are always combined with a sucrose that facilitates a further reduction in intracellular water activity (
Jain and Paulson, 2006). The cryoprotectants may be used either through freezing or vitrification process and discussed in many papers
(Suzuki et al., 2015).
It is so difficult to evaluate the efficiency of cryopreservation procedures through fertility potential upon OT or grafting as ovarian restoring function (follicle morphology, hormone production and gene expression), children born from the procedure and the duration of ovarian tissue function following transplantation. Dying
in vitro test through vital dye neutral red that evaluates follicles survival following freezing and thawing ovarian tissues was evaluated
(Kristensen et al., 2018). Living follicles were shown in intense red staining whereas nonviable follicles remained unstained
(Morewood et al., 2017, Kristensen et al., 2018). The benefit of OTC instead of follicle survival could be confirmed through tissue transplantation. Therefore, the procedures to improve ovarian tissue transplantation include enhancement of revascularization, supply of oxygen and nutrients and reduce apoptosis.
The ovarian tissue freezing protocol includes dissecting ovarian tissue into small pieces, exposing the tissues to a solution containing cryoprotectants (
e.g. glycerol, dimethyl sulfoxide and ethylene glycol) in a stepwise manner, the tissues are subjected to a controlled cooling curve process using a programmable freezer and the frozen tissues are stored in liquid nitrogen tank (-196°C)
(Isachenko et al., 2012; Rivas Leonel et al., 2019). There are different cooling curves as -2°C/min to -8°C, manual seeding, “0.3°C/min to -40°C and -30°C/min to -140°C
(Donnez et al., 2004). The vitrification is a rapid freezing technique includes dissecting ovarian tissue into small pieces, exposing the tissues to multiple solutions with increasing cryoprotectant concentration (
Seki and Mazur, 2008). The freezed or vitrified ovarian tissues are stored in liquid nitrogen for long-term preservation (
Rivas Leonel et al., 2019).
Small versus large pieces of ovarian tissues
Restoration of ovarian activity upon transplantation are indicated through ovarian follicle development, ovulation, embryo development and children born (Fig 2). The sizes of the transplanted ovarian cortical tissues are a factor effect on the total number of surviving follicles following transplantation. The too small pieces (< 1-3 mm
3) complicate their positioning and if they are left free they may move as the woman becomes physically active. This leads to disruption of revascularization and reduce follicle survival. The large ovarian cortical tissue (around 5.0 × 5.0 × 1.0 mm) are easy to position and fix in the right place. This accelerate revascularisation, nutrients and oxygen supply leading to enhancement of follicles survival (
Meirow et al., 2005).
Social reasons for ovarian tissue cryopreservation
Many well-educated women in many western countries are delaying childbearing, preserving their fertility potential by freezing good quality oocytes to find the right partner and focus on their careers. The usage rate of stored oocytes range 3.0-9.0% (
Ben-Rafael 2018), which indicates the need for alternative solution represented by OTC and transplantation. Such OTC and grafting procedure is a scenario for fertility and endocrine purposes. This unproven suggestion needs further investigation concerning the sizes of excised ovarian tissues and its side effect on the residual ovarian reserve. In the future, women undergoing C-section parturition may want to have a small ovarian biopsy and have it frozen for future use.
In vitro maturation of oocytes upon ovarian transplantation
In vitro maturation (IVM) of human oocytes last 24 h whereas IVM of ruminant oocytes, rodent oocytes, pig and camel oocytes last 24 h, 17 h and 42-48 h, respectively (
Gordon 2003;
Mohammed et al., 2005, 2008,
2010,
2019a,
2022).
In vitro maturation of oocytes is the most important step for further embryonic development
(Mohammed et al., 2005, 2022). Nuclear and cytoplasmic changes occur in oocytes for successful fertilization and early embryonic development
(Mohammed et al., 2005). Hjorth et al., (2020) investigated reproductive outcomes after
in vitro fertilization upon transplantation of cryopreserved ovarian tissue. The conclusion of such study that the women of advanced age have a poor ovarian reserve, resulting in a poor reproductive outcome. Several factors effect on efficiency of oocyte maturation and further embryonic development as species, follicle sizes, oestrous or menstrual stage, age, maturation media and supplements (
Mohammed 2014a,
b;
Mohammed et al., 2008, 2010,
2019b,
2020,
2022)
. The quality of oocytes, cumulus cells inclusion, follicular fluid or fetal calf supplementation effected on oocyte maturation rates and embryo cleavage and blastocyst and hatched rate
(Mohammed et al., 2005, 2022)
. Additionally, nutrition and feed additives have been shown to stimulate ovarian follicles and embryo development (
Mohammed 2018b;
Mohammed and Attaai 2011;
Mohammed et al., 2012a,b, 2019b,
2020,
2023)
.
