Human oocyte cryopreservation

Acoustic Droplet Vitrification Method for High-Efficiency Preservation of Rare Cells

Cryopreservation is a key step for current translational medicine including reproductive medicine, regenerative medicine, and cell therapy. However, it is challenging to preserve rare cells for practical applications due to the difficulty in handling low numbers of cells as well as the lack of highly efficient and biocompatible preservation protocols. Here, we developed an acoustic droplet vitrification method for high-efficiency handling and preservation of rare cells. By employing an acoustic droplet ejection device, we can encapsulate rare cells into water-in-air droplets with a volume from ∼pL to ∼nL and deposit these cell-containing droplets into a droplet array onto a substrate. By incorporating a cooling system into the droplet array substrate, we can vitrify hundreds to thousands of rare cells at an ultrafast speed (about ∼2 s) based on the high surface to volume ratio of the droplets. By optimizing this method with three different cell lines (a human lung cancer cell line, A549 cells, a human liver cell line, L02 cells, and a mouse embryonic fibroblast cell line, 3T3-L1 cells), we developed an effective protocol with excellent cell viability (e.g., >85% for days, >70% for months), proliferation, and adhesion. As a proof-of-concept application, we demonstrated that our method can rapidly handle and efficiently preserve rare cells, highlighting its broad applications in species diversity, basic research, and clinical medicine.

Impact of vitrification on human oocytes before and after in vitro maturation: A systematic review and meta-analysis

OBJECTIVE

There are controversies regarding in vitro maturation (IVM) procedure, the time of storing frozen oocytes and maturation stage of vitrified oocytes and its impact on oocytes fertilization capability. The aim of this systematic review and meta-analysis was to evaluate the impact of vitrification on human oocytes during IVM procedure.

STUDY DESIGN

A systematic review with meta-analysis was undertaken. Main search terms were those related key words. We searched Medline, Embase, Scopus and ISI web of science to detect English-language studies. The final search was performed on 27 January 2018. The original articles which studied laboratory outcomes after vitrification of MII or GV oocytes before or after IVM were included. Exclusion criteria were animal trials and the studies that performed cryopreservation using slow-freeze method. Oocyte maturation, survival, fertilization and cleavage rates were assessed. Bias and quality assessments were applied.

RESULTS

2476 articles were screened and after duplicates removing together with application of inclusion and exclusion criteria, 14 studies assessed for eligibility. Finally 5 studies included for analysis. All studies compared laboratory outcomes between oocytes that vitrified at the GV stage and those which firstly matured in vitro, and then vitrified. Meta-analysis showed that vitrification of oocytes at GV stage had a negative impact on maturation rate (RR = 1.28, 95% CI: 0.96-1.70); but not on cleavage rate (RR = 1.07, 95% CI: 0.70-1.64); fertilization rate (RR = 0.99, 95% CI: 0.85-1.14) and survival rate(RR = 1.01, 95% CI: 0.96-1.06).

CONCLUSION

In general, Based on our results, oocyte vitrification decreases the maturation rate. In addition, survival, fertilization as well as cleavage rates did not significantly differ between the oocytes vitrified before IVM versus oocytes vitrified after IVM.

High throughput cryopreservation of cells by rapid freezing of sub-μl drops using inkjet printing--cryoprinting

We have successfully used inkjet printing to cryopreserve 3T3 mouse fibroblast cells and human neuroprogenitor cells (NPCs) derived from human embryonic stem cells (hESCs). Sessile drops of volume 114 nl were formed by printing cell suspensions containing dimethyl sulphoxide (DMSO) as a cryoprotection agent (CPA) at rates in the region 100 Hz-20 kHz, from individual droplets of 380 pl. After printing and a freeze/thaw cycle (with a minimum 24 hours hold period at liquid N2 temperature), 3T3 cells showed an average viability of >90% with CPA concentration <0.8 M at all drop deposition rates. This is a significantly lower CPA concentration than normally used with conventional cryopreservation methods. Cell viability shows a small variation with the polymer substrates used, with the best results obtained using a polyimide substrate. The viability of 3T3 cells after 2 months storage at liquid nitrogen temperature was slightly reduced compared to the cells held for 24 hours but there was no significant further deterioration after 4 or 6 months storage. The viability of NPCs after an identical freeze/thaw cycle were only 55% but this is comparable with conventional cryopreservation methods that use much higher CPA concentrations. A parallel series of experiments printing cells onto substrates held at 195 K or directly into liquid N2 showed considerable variation in cell survival rate with drop deposition rate. Cell suspensions required higher levels of CPA than when printing followed by freezing. At low deposition rates a combination of DMSO and polyethylene glycol (PEG) was needed to allow cell viability after freezing. These results show that inkjet printing provides a practical high throughput method for the cryopreservation of cells with lower CPA concentrations than are required for current low volume cryopreservation methods.

Fertility preservation in young females with non-gynaecologic malignancy: an emerging speciality

BACKGROUND

As new treatment and research advances continue to improve the prognosis of cancer patients, oncologists and surgeons are increasingly faced with the issue of fertility protection and preservation. Cancer patients are frequently exposed to gonadotoxic chemotherapy and radiation therapy as a component of their treatment regimens. There are currently various anticipatory techniques available to women who wish to retain future reproductive ability, the most successful of which involves oocyte retrieval followed by in vitro fertilisation and embryo cryopreservation. Innovative methods include oocyte cryopreservation, ovarian follicle cryopreservation and oophoropexy.

AIM

The aim of this study was to examine our combined experiences at Mayo General Hospital of treating female patients (<30 years) with non-gynaecologic malignancy and requiring referral to the HARI Unit during a 6-year period (2007-2012). Emphasis was placed on reviewing the fertility-preservation options available.

METHODS

The hospital inpatient enquiry system was inspected for all cases of non-gynaecologic malignancy referred for fertility preservation from 2007 to 2012.

RESULTS

Three cases of non-gynaecologic malignancy in young females, with an intention to protect and preserve future fertility were identified. The primary treatment plan did not initially incorporate input from a gynaecology or fertility specialist. It was after concerted inquiry and reflection by both physician and patient that oncofertility consultation was sought.

CONCLUSION

The responsibility is on both physicians and surgeons to consider a more holistic approach to cancer care in young female patients, which focuses not only on the elimination of malignancy but also on preservation of fertility and quality of life.

Female fertility loss and preservation: threats and opportunities

BACKGROUND

Ovarian aging and cytotoxic treatments are the most common causes for fertility loss in women. With increasing numbers of young female survivors following cytotoxic cancer treatments, the issue of fertility preservation has assumed greater importance.

METHODS

We review the literature on the causes of female fertility loss as well as the recent advances in fertility preservation options and strategies that might be of interest to oncologists. Currently, several methods and techniques exist for fertility preservation of female patients with cancer including embryo freezing, ovarian protection techniques, oocyte cryopreservation, ovarian tissue cryopreservation followed by autotransplantation, and recently in vitro culture of ovarian tissue, follicles, and oocytes. Each method or technique has advantages and disadvantages related to current success rate, required delay in cancer treatment, sperm requirement, and risk of reintroducing cancer cells.

RESULTS

To date, embryo freezing is the only established method successfully and widely used for fertility preservation of female patients with cancer. The other methods are promising but still considered experimental.

CONCLUSION

Patient awareness, physician knowledge, early counseling, costs management, international registry, interdisciplinary networks, and research development are necessary to improve the current care in the field of female fertility preservation.

Emerging technologies in medical applications of minimum volume vitrification

Cell/tissue biopreservation has broad public health and socio-economic impact affecting millions of lives. Cryopreservation technologies provide an efficient way to preserve cells and tissues targeting the clinic for applications including reproductive medicine and organ transplantation. Among these technologies, vitrification has displayed significant improvement in post-thaw cell viability and function by eliminating harmful effects of ice crystal formation compared to the traditional slow freezing methods. However, high cryoprotectant agent concentrations are required, which induces toxicity and osmotic stress to cells and tissues. It has been shown that vitrification using small sample volumes (i.e., <1 µl) significantly increases cooling rates and hence reduces the required cryoprotectant agent levels. Recently, emerging nano- and micro-scale technologies have shown potential to manipulate picoliter to nanoliter sample sizes. Therefore, the synergistic integration of nanoscale technologies with cryogenics has the potential to improve biopreservation methods.

In-vitro maturation of human oocytes: before or after vitrification?

PURPOSE

This study aims to determine if in-vitro maturation (IVM) of human immature oocytes should be performed before or after vitrification.

METHODS

A total of 184 immature oocytes were randomly divided into two different groups: 100 were vitrified at metaphase II (MII) stage 24 h-48 h after IVM (group 1) and 84 were immediately vitrified at germinal vesicle (GV) or metaphase I (MI) stages and in vitro matured after warming (group 2).

RESULTS

Survival rate after warming was similar in both groups (86.9% versus 84.5%). However, oocyte maturation rate per collected oocyte was significantly higher for oocytes matured before vitrification (group 1, 46%) than for oocytes vitrified before IVM (group 2, 23.8%) (p < 0.01). Consequently, the number of MII oocytes inseminated per oocyte collected was significantly higher for group 1 (40%) than for group 2 (23.8%) (p < 0.05).

CONCLUSION

IVM procedure is more efficient when it is performed before oocyte vitrification.

Oocyte cryostorage to preserve fertility in oncological patients

Thanks to the progress in oncostatic treatments, young women affected by cancer have a fairly good chance of surviving the disease and leading a normal post-cancer life. Quite often, however, polychemiotherapy and/or radiotherapy can induce ovarian damage and significantly reduce the content of follicles and oocytes inside the ovary, thus predisposing the patient to menstrual disorders, infertility, and precocious menopause. Several techniques have been proposed to preserve fertility in these patients; among them oocyte collection and cryopreservation prior to the oncostatic treatment has been widely applied in the last decade. The proper indications, the permitting conditions, the available hormonal stimulation protocols, as well as the effectiveness and limits of this option will be discussed herein, with a comprehensive and up-to-date review of the two techniques commonly used to cryostore oocytes, the slow-freezing technique and the vitrification technique.

Nanoliter droplet vitrification for oocyte cryopreservation

AIM

Oocyte cryopreservation remains largely experimental, with live birth rates of only 2-4% per thawed oocyte. In this study, we present a nanoliter droplet technology for oocyte vitrification.

MATERIALS & METHODS

An ejector-based droplet vitrification system was designed to continuously cryopreserve oocytes in nanoliter droplets. Oocyte survival rates, morphologies and parthenogenetic development after each vitrification step were assessed in comparison with fresh oocytes.

RESULTS

Oocytes were retrieved after cryoprotectant agent loading/unloading, and nanoliter droplet encapsulation showed comparable survival rates to fresh oocytes after 24 h in culture. Also, oocytes recovered after vitrification/thawing showed similar morphologies to those of fresh oocytes. Additionally, the rate of oocyte parthenogenetic activation after nanoliter droplet encapsulation was comparable with that observed for fresh oocytes. This nanoliter droplet technology enables the vitrification of oocytes at higher cooling and warming rates using lower cryoprotectant agent levels (i.e., 1.4 M ethylene glycol, 1.1 M dimethyl sulfoxide and 1 M sucrose), thus making it a potential technology to improve oocyte cryopreservation outcomes.

Vitrification of in vitro matured oocytes collected from antral follicles at the time of ovarian tissue cryopreservation

BACKGROUND

In the past few years, cryopreservation of ovarian tissue has become an established procedure proposed in many centers around the world and transplantation has successfully resulted in full-term pregnancies and deliveries in human. This prospective study aims to evaluate the feasibility of vitrifying in vitro matured oocytes (IVM) isolated at the time of ovarian tissue cryopreservation to improve the efficiency of fertility preservation programs.

METHODS

Oocyte-cumulus complexes were retrieved from freshly collected ovarian cortex by aspirating antral follicular fluid, and were matured in vitro for 24-48 h prior to vitrification. Oocytes were matured in an IVM commercial medium (Copper Surgical, USA) supplemented with 75 mIU/ml FSH and 75 mIU/ml LH and vitrified using a commercial vitrification kit (Irvine Scientific, California) in high security vitrification straws (CryoBioSystem, France). Oocyte collection and IVM rates were evaluated according to the age, the cycle period and the amount of tissue collected.

RESULTS

Immature oocyte retrieval from ovarian tissue was carried out in 57 patients between 8 and 35 years of age, undergoing ovarian tissue cryopreservation. A total of 266 oocytes were isolated, 28 of them were degenerated, 200 were at germinal vesicle stage (GV), 35 were in metaphase I (MI) and 3 displayed a visible polar body (MII). The number of oocytes collected was positively correlated with the amount of tissue cryopreserved (p < 0.001) and negatively correlated with the age of the patients (p = 0.005). Oocytes were obtained regardless of menstrual cycle period or contraception. A total maturation rate of 31% was achieved, leading to the vitrification of at least one mature oocyte for half of the cohort.

CONCLUSIONS

The study showed that a significant number of immature oocytes can be collected from excised ovarian tissue whatever the menstrual cycle phases and the age of the patients, even for prepubertal girls.

Correlation of oocyte morphometry parameters with woman's age

PURPOSE

Aim of this study was to evaluate morphometric parameters of metaphase II oocytes, including cytoplasm diameter (CD), zona pellucida thickness (ZPT) and width of the perivitelline space (PS), in relation with zona pellucida birefringence, spindle presence and age of the woman.

METHODS

Oocytes were classified into groups according to zona birefringence (low or high zona birefringence, LZB and HZB, respectively) and presence or absence of a visible spindle (SP and aSP, respectively).

RESULTS

HZB oocytes showed a thicker zona (17.7 ± 0.3 μm) than LZB oocytes (16.7 ± 0.3 μm, p < 0.01). Moreover, PS was narrower in HZB and SP oocytes than in LZB (p < 0,001) and aSP (p < 0,05) oocytes. Finally, we found that CD and ZPT linearly decrease with age of the woman (CD r = 0.028: p < 0.01; ZPT r = 0.050: p < 0.0001).

CONCLUSION

Our results evidence an association in human oocytes between zona pellucida and spindle birefringence and defined morphometric parameters and a decrease of oocyte size and ZPT as a function of women's age.

In vitro maturation and fertilization of vitrified immature human oocytes, subsequent vitrification of produced embryos, and embryo transfer after thawing

OBJECTIVE

To report on the capability of vitrified immature human oocytes to undergo in vitro maturation, fertilization, and embryo development, and to report on the post-thaw survival of vitrified embryos.

DESIGN

Case report.

SETTING

University-based IVF unit.

PATIENT(S)

Two women (34 and 36 years old) undergoing IVF therapy.

INTERVENTION(S)

Immature oocytes, retrieved after ovarian stimulation, were vitrified. Post-thaw, they underwent in vitro maturation and fertilization by intracytoplasmic sperm injection (ICSI). The produced embryos were vitrified at day 2. In one case, the embryos were thawed and transferred.

MAIN OUTCOME MEASURE(S)

Post-thaw survival of vitrified immature oocytes, capability for in vitro maturation, fertilization, embryo development; post-thaw survival of vitrified embryos.

RESULT(S)

In the first case, six immature oocytes survived after thawing and matured after in vitro maturation. Five of them underwent ICSI, four fertilized, and three cleaved. The embryos were vitrified for future use. In the second case, two out of three immature oocytes survived after thawing. They were normally fertilized and cleaved, and the embryos were vitrified. Later, the embryos were thawed and transferred to the patient.

CONCLUSION(S)

These cases demonstrate that vitrified immature oocytes can undergo post-thaw in vitro maturation and fertilization. The produced embryos are capable to undergo vitrification and thawing.

Current results with slow freezing and vitrification of the human oocyte

The past decade has witnessed renewed interest in human oocyte cryopreservation (OCP). This article reviews the two general methods used for OCP, slow freezing and vitrification, compares the outcomes associated with each technique and discusses the factors that might influence success with OCP (such as oocyte selection or day of transfer). Based on available data, OCP offers a reliable, reproducible method for preservation of the female gamete and will find increasing application in assisted reproductive technology. Oocyte cryopreservation can provide a number of advantages to couples undergoing assisted reproduction or to women interested in fertility preservation. Two methods, slow freezing and vitrification, have been used successfully for oocyte cryopreservation. This article reviews and compares these methods, and discusses various factors that can impact upon success of oocyte cryopreservation.

Cryopreservation of human genetic material

Up-to-date cryopreservation is a central component of contemporary human-assisted reproduction and fertility preservation technologies. Presently, the preservation of seminal and testicular spermatozoa, embryos, and oocytes can be readily achieved with a high functional survival rate. Preservation of the ovarian cortex containing a greater number of female germ cells is an experimental procedure under extensive investigation in many centers. All these techniques are used for various purposes like optimization of assisted reproduction, provision of donor gametes, fertility preservation for cancer patients and aging women, and posthumous reproduction. Here, we present a comprehensive review of the various applications of gamete, embryo, and ovarian tissue cryopreservation and discuss their basic biological principles, practical applicability, and limitations.