Reconsideration of the safety and effectiveness of human oocyte cryopreservation

Mature oocyte cryopreservation (OC) has become increasingly common since the American Society for Reproductive Medicine declared OC to no longer be experimental. Utilization of the open vitrification protocol has led to a marked improvement in the efficacy of oocyte cryopreservation. However, the safety and effectiveness of this cryopreservation method remain controversial. A previous report stated that among all initiated recipient cycles, the live-birth rate among recipients of all ages was significantly higher when using fresh donor oocytes (FDOs) rather than cryopreserved donor oocytes (CDOs). Confounding patient characteristics were noted as possible causes. OC stands as an acceptable elective medical intervention for preserving fertility in women. To further understand the effects of OC on the live birth rate resulting from fresh versus cryopreserved donor oocytes, reported data from the Society for Assisted Reproductive Technology from 2013 to 2020 were analyzed. The mean of the mean live-birth rate in all ages resulting from FDOs was 49.0% (44.6-53.3%) versus 41.0% (39.1-43.2%) for CDOs (difference, 8.0% [95% confidence interval, 5.35-10.57%], p value < 0.001). The lower live-birth rate observed for CDOs versus FDOs has been consistent throughout past decades. While there has been no reported increase in the aneuploidy rate for CDOs compared to FDOs, differences in the nondisjunction separation rate among different chromosomes were described in a recent report. Open vitrification culture medium usually contains high concentrations of cryoprotectants, such as 15% dimethyl sulfoxide (DMSO) and 15% ethylene glycol (EG). Recent studies showed that tissue culture with 0.1% DMSO or 10% EG resulted in deregulation of gene expression, disruption of epigenetic imprints, and accumulation of reactive oxygen species. The addition of melatonin, which can remove reactive oxygen species from vitrification medium, was shown to improve CDOs qualities and functions to conditions similar to those of FDOs; however, there were insufficient data to conclude that melatonin could improve the lower live-birth rate. These factors that affect live birth rates, birth defects, birth weights and developmental health cannot be ignored and perhaps need to be studied again and followed when evaluating the true effectiveness of human oocyte cryopreservation.

Subpopulations of human embryonic stem cells with distinct tissue-specific fates can be selected from pluripotent cultures

Directed differentiation of human embryonic stem cells (hESCs) has generated much interest in the field of regenerative medicine. While subpopulations of hESCs within pluripotent cultures have been identified based on expression of specific surface antigens, their significance and fates are not well understood. To determine whether such subpopulations indicate specific tissue fates or represent stochastic antigen distributions within proliferating cultures, we isolated CD133(+) or CD135(+) hESCs from proliferating cultures constitutively expressing enhanced green fluorescent protein (GFP), and co-cultured these with unselected GFP(-) hESCs. After passage in culture, GFP(+) hESCs reanalyzed for the persistence of CD133 or CD135 expression, as well as other surface antigens (Tra-1-60, SSEA-4, FGFR-1), demonstrated that these two subpopulations continued to express CD133 or CD135 over serial passage, and that CD133(+) hESCs were enriched for SSEA-4 expression as well. Upon differentiation in vitro, CD133(+)GFP(+) hESCs gave rise solely to ectoderm, as detected by expression of nestin. Tissues representing endoderm (alpha-fetoprotein(+)) and mesoderm (smooth muscle actin(+)) were not seen among GFP(+) tissues. In contrast, selection against CD133 gave rise almost exclusively to mesoderm and endoderm. In contrast, CD135(+)GFP(+) hESCs gave rise to tissues representing all three embryonic germ layers, and were virtually indistinguishable from CD135(-)-derived tissues. Similar results were obtained by in vivo differentiation in teratomas. These data establish that subpopulations of proliferating hESCs whose tissue fate is predetermined exist, and challenge the notion that all cells within proliferating hESC cultures are truly "pluripotent." This co-culture approach also will enable identification of other distinct hESC subpopulations, and selection for these should prove valuable in generating tissue-specific reagents for cell-based therapy.

Frizzled 9 knock-out mice have abnormal B-cell development

The binding of frizzled (Fzd) receptors by their Wnt ligands results in the inhibition of beta-catenin degradation and subsequent transcription of beta-catenin/LEF-inducible genes. The beta-catenin pathway is known to be involved in development, tumorigenesis, and stem cell self-renewal. In humans, the FZD9 gene lies in the region of chromosome 7q11.23 deleted in the neurodevelopmental disorder, Williams-Beuren syndrome (WBS). Fzd9-/- mice show no obvious features of WBS, but reveal a role for Fzd9 in lymphoid development and maturation. Fzd9-/- mice show pronounced splenomegaly, thymic atrophy, and lymphadenopathy with age, with accumulation of plasma cells in lymph nodes. There is a depletion of developing B cells in the bone marrow (BM), particularly in the pre-B stage where immunoglobulin heavy chains are expressed and the cells are undergoing clonal expansion prior to light chain rearrangement. The pre-B defect is partially intrinsic to the hematopoietic system; as in competitive BM reconstitution studies, Fzd9-/- -derived BM exhibits defective B-cell development when implanted into a wild-type host. Mature B cells are present in normal numbers in lymph node and spleen. These findings suggest a role for Fzd9 signaling in lymphoid development, particularly at points where B cells undergo self-renewal prior to further differentiation.