Optimization of cryoprotectant loading into murine and human oocytes.

Loading of cryoprotectants into oocytes is an important step of the cryopreservation process, in which the cells are exposed to potentially damaging osmotic stresses and chemical toxicity. Thus, we investigated the use of physics-based mathematical optimization to guide design of cryoprotectant loading methods for mouse and human oocytes. We first examined loading of 1.5 M dimethyl sulfoxide (Me(2)SO) into mouse oocytes at 23°C. Conventional one-step loading resulted in rates of fertilization (34%) and embryonic development (60%) that were significantly lower than those of untreated controls (95% and 94%, respectively). In contrast, the mathematically optimized two-step method yielded much higher rates of fertilization (85%) and development (87%). To examine the causes for oocyte damage, we performed experiments to separate the effects of cell shrinkage and Me(2)SO exposure time, revealing that neither shrinkage nor Me(2)SO exposure single-handedly impairs the fertilization and development rates. Thus, damage during one-step Me(2)SO addition appears to result from interactions between the effects of Me(2)SO toxicity and osmotic stress. We also investigated Me(2)SO loading into mouse oocytes at 30°C. At this temperature, fertilization rates were again lower after one-step loading (8%) in comparison to mathematically optimized two-step loading (86%) and untreated controls (96%). Furthermore, our computer algorithm generated an effective strategy for reducing Me(2)SO exposure time, using hypotonic diluents for cryoprotectant solutions. With this technique, 1.5 M Me(2)SO was successfully loaded in only 2.5 min, with 92% fertilizability. Based on these promising results, we propose new methods to load cryoprotectants into human oocytes, designed using our mathematical optimization approach.

Self and microbiota-derived epitopes induce CD4+ T cell anergy and conversion into CD4+Foxp3+ regulatory cells.

The physiological role of T cell anergy induction as a key mechanism supporting self-tolerance remains undefined, and natural antigens that induce anergy are largely unknown. In this report, we used TCR sequencing to show that the recruitment of CD4+CD44+Foxp3-CD73+FR4+ anergic (Tan) cells expands the CD4+Foxp3+ (Tregs) repertoire. Next, we report that blockade in peripherally-induced Tregs (pTregs) formation due to mutation in CNS1 region of Foxp3 or chronic exposure to a selecting self-peptide result in an accumulation of Tan cells. Finally, we show that microbial antigens from Akkermansia muciniphila commensal bacteria can induce anergy and drive conversion of naive CD4+CD44-Foxp3- T (Tn) cells to the Treg lineage. Overall, data presented here suggest that Tan induction helps the Treg repertoire to become optimally balanced to provide tolerance toward ubiquitous and microbiome-derived epitopes, improving host ability to avert systemic autoimmunity and intestinal inflammation.

Probing lasting cryoinjuries to oocyte-embryo transcriptome.

Clinical applications of oocytes cryopreservation include preservation of future fertility of young cancer patients, substitution of embryo freezing to avoid associated legal and ethical issues, and delaying childbearing years. While the outcome of oocyte cryopreservation has recently been improved, currently used vitrification method still suffer from increased biosafety risk and handling issues while slow freezing techniques yield overall low success. Understanding better the mechanism of cryopreservation-induced injuries may lead to development of more reliable and safe methods for oocyte cryopreservation. Using the mouse model, a microarray study was conducted on oocyte cryopreservation to identify cryoinjuries to transcriptionally active genome. To this end, metaphase II (MII) oocytes were subjected to standard slow freezing, and then analyzed at the four-cell stage after embryonic genome activation. Non-frozen four-cell embryos served as controls. Differentially expressed genes were identified and validated using RT-PCR. Embryos produced from the cryopreserved oocytes displayed 200 upregulated and 105 downregulated genes, associated with the regulation of mitochondrial function, protein ubiquitination and maintenance, cellular response to stress and oxidative states, fatty acid and lipid regulation/metabolism, and cell cycle maintenance. These findings reveal previously unrecognized effects of standard slow oocyte freezing on embryonic gene expression, which can be used to guide improvement of oocyte cryopreservation methods.

Commensal epitopes drive differentiation of colonic Tregs.

The gut microbiome is the largest source of intrinsic non-self-antigens that are continuously sensed by the immune system but typically do not elicit lymphocyte responses. CD4+ T cells are critical to sustain uninterrupted tolerance to microbial antigens and to prevent intestinal inflammation. However, clinical interventions targeting commensal bacteria-specific CD4+ T cells are rare, because only a very limited number of commensal-derived epitopes have been identified. Here, we used a new approach to study epitopes and identify T cell receptors expressed by CD4+Foxp3+ (Treg) cells specific for commensal-derived antigens. Using this approach, we found that antigens from Akkermansia muciniphila reprogram naïve CD4+ T cells to the Treg lineage, expand preexisting microbe specific Tregs, and limit wasting disease in the CD4+ T cell transfer model of colitis. These data suggest that the administration of specific commensal epitopes may help to widen the repertoire of specific Tregs that control intestinal inflammation.

Comparison and avoidance of toxicity of penetrating cryoprotectants.

The objective of this study was to elucidate the toxicity of widely used penetrating cryoprotective agents (CPAs) to mammalian oocytes. To this end, mouse metaphase II (M II) oocytes were exposed to 1.5 M solutions of dimethylsulfoxide (DMSO), ethylene glycol (EG), or propanediol (PROH) prepared in phosphate buffered saline (PBS) containing 10% fetal bovine serum. To address the time- and temperature-dependence of the CPA toxicity, M II oocytes were exposed to the aforementioned CPAs at room temperature (RT, ∼23°C) and 37°C for 15 or 30 minutes. Subsequently, the toxicity of each CPA was evaluated by examining post-exposure survival, fertilization, embryonic development, chromosomal abnormalities, and parthenogenetic activation of treated oocytes. Untreated oocytes served as controls. Exposure of MII oocytes to 1.5 M DMSO or 1.5 M EG at RT for 15 min did not adversely affect any of the evaluated criteria. In contrast, 1.5 M PROH induced a significant increase in oocyte degeneration (54.2%) and parthenogenetic activation (16%) under same conditions. When the CPA exposure was performed at 37°C, the toxic effect of PROH further increased, resulting in lower survival (15%) and no fertilization while the toxicity of DMSO and EG was still insignificant. Nevertheless, it was possible to completely avoid the toxicity of PROH by decreasing its concentration to 0.75 M and combining it with 0.75 M DMSO to bring the total CPA concentration to a cryoprotective level. Moreover, combining lower concentrations (i.e., 0.75 M) of PROH and DMSO significantly improved the cryosurvival of MII oocytes compared to the equivalent concentration of DMSO alone. Taken together, our results suggest that from the perspective of CPA toxicity, DMSO and EG are safer to use in slow cooling protocols while a lower concentration of PROH can be combined with another CPA to avoid its toxicity and to improve the cryosurvival as well.

Cryobanking of embryoid bodies to facilitate basic research and cell-based therapies.

Pluripotent stem cells offer unique opportunities for curing debilitating diseases. However, further comprehensive research is needed to better understand cell signaling during the differentiation of pluripotent cells into different cell lineages and accordingly to develop clinically applicable protocols. One of the limiting steps for differentiation studies is proper culture and expansion of pluripotent stem cells, which is labor intensive, expensive, and requires a great deal of expertise. This limiting step can be overcome by successful banking and distribution of embryoid bodies (EBs), which are aggregates of pluripotent stem cells and typically the starting point of differentiation protocols. The objective of this study was to investigate the feasibility of EB banking by studying survival and functionality of cryopreserved EBs. To this end, EBs were formed by culturing mouse 129 embryonic stem (ES) cells in the absence of leukemia inhibitory factor (LIF) in hanging drops and then subjected to different cryopreservation protocols. In a series of experiments, we first tested the postthaw survival of EBs as a function of dimethylsulfoxide (DMSO) and extracellular trehalose concentrations and cooling rates. Next, we studied the functionality of cryopreserved EBs by assessing their postthaw attachment, growth, and differentiation into various cell types. Higher (≥5%) DMSO concentrations alone or in combination with trehalose (0.1 M and 0.2 M) yielded good postthaw survival rates of >80%, whereas cooling of EBs at 1°C/min in the presence of 5% DMSO +0.1 M trehalose gave the best attachment and growth rates, with differentiation into cell lineages of three germ layers. Taken together, our results suggest that EBs are tolerant to cryopreservation-associated stresses and retain their differentiation potential after freezing and thawing. Furthermore, our experiments with dissociated EB cells and nondissociated EBs suggest that the extracellular matrix may play a beneficial role in the cryotolerance of EBs. Overall, our data support the feasibility of EB banking, which would facilitate advancement of cell-based therapies.