Uncontrolled-rate freezing and storage at -80 degrees C, with only 3.5-percent DMSO in cryoprotective solution for 109 autologous peripheral blood progenitor cell transplantations

The tardigrade-derived mitochondrial abundant heat soluble protein improves adipose-derived stem cell survival against representative stressors

Human adipose-derived stem cell (ASC) grafts have emerged as a powerful tool in regenerative medicine. However, ASC therapeutic potential is hindered by stressors throughout their use. Here we demonstrate the transgenic expression of the tardigrade-derived mitochondrial abundant heat soluble (MAHS) protein for improved ASC resistance to metabolic, mitochondrial, and injection shear stress. In vitro, MAHS-expressing ASCs demonstrate up to 61% increased cell survival following 72 h of incubation in phosphate buffered saline containing 20% media. Following up to 3.5% DMSO exposure for up to 72 h, a 14-49% increase in MAHS-expressing ASC survival was observed. Further, MAHS expression in ASCs is associated with up to 39% improved cell viability following injection through clinically relevant 27-, 32-, and 34-gauge needles. Our results reveal that MAHS expression in ASCs supports survival in response to a variety of common stressors associated with regenerative therapies, thereby motivating further investigation into MAHS as an agent for stem cell stress resistance. However, differentiation capacity in MAHS-expressing ASCs appears to be skewed in favor of osteogenesis over adipogenesis. Specifically, activity of the early bone formation marker alkaline phosphatase is increased by 74% in MAHS-expressing ASCs following 14 days in osteogenic media. Conversely, positive area of the neutral lipid droplet marker BODIPY is decreased by up to 10% in MAHS-transgenic ASCs following 14 days in adipogenic media. Interestingly, media supplementation with up to 40 mM glucose is sufficient to restore adipogenic differentiation within 14 days, prompting further analysis of mechanisms underlying interference between MAHS and differentiation processes.

A Deeper Depth of Response After Salvage Therapy Improves Outcomes of Autologous Stem Cell Transplantation in Relapsed Lymphoma and the Feasibility of Non-controlled Rate Freezing of Peripheral Blood Stem Cells

Background High-dose chemotherapy followed by autologous stem cell transplantation is considered a standard treatment approach for patients with relapsed Hodgkin's lymphoma (HL) and non-Hodgkin lymphoma (NHL). The goal of autologous stem cell transplant in relapsed lymphoma is to achieve long-term disease control, i.e., cure, in contrast to disorders like multiple myeloma, where it only prolongs the duration of remission, progression-free survival, and improves the quality of life. Published outcomes of high-dose therapy and ASCT and the impact of different factors affecting survival in low- to middle-income countries are very limited. Our study analyzed all the autologous stem cell transplants performed in our center over a six-year period to ascertain engraftment, responses, outcomes, and variables that may have impacted transplant outcomes. Methods We conducted a retrospective study including 76 patients from January 2015 to December 2020. Data were retrieved from electronic medical records at Shaukat Khanum Memorial Cancer Hospital and Research Centre, Lahore, Pakistan. Results Out of a total of 82 autologous transplant patients, 76 were eligible for the study, out of which 50 (66%) had HL and 26 (34%) had NHL. The median age was 29 years (range 18-53) and 29 years (range 20-45) for HL and NHL, respectively. The male-to-female ratio was 5:2 and 4:1 for HL and NHL, respectively. The majority had advanced-stage disease, 85% in HL and 75% in NHL. The minimum cell dose infused was 2.5 million CD34+ cells/kg. Median days to platelets and ANC engraftment were 14 and 11 days, respectively. The 30-day transplant-related mortality was 8.9% and 7.4% in HL and NHL, respectively. The 100-day mortality was 15.2% and 11% in HL and NHL, respectively. The two-year disease-free survival (DFS) and overall survival (OS) were 83% and 83%, respectively, in HL patients. The two-year DFS and OS were 78% and 85%, respectively, in NHL patients. Conclusion High-dose therapy and autologous stem cell transplantation in low- to middle-income countries are limited to relatively younger patients, potentially curative conditions such as lymphoma, and predominantly after achieving a complete response to salvage therapy due to limited resources. Due to these factors, our study shows excellent response rates and survival outcomes compared to internationally published data. Engraftment was also excellent and comparable to published data despite the non-controlled rate freezing of peripheral blood stem cells.

Long-Term Cryopreservation of Peripheral Blood Stem Cell Harvest Using Low Concentration (4.35%) Dimethyl Sulfoxide with Methyl Cellulose and Uncontrolled Rate Freezing at -80 °C: An Effective Option in Resource-Limited Settings

Long-term cryopreservation of peripheral blood stem cells (PBSCs) is highly useful in the setting of tandem/multiple transplantations or treatment of relapse in the autologous hematopoietic stem cell transplantation (HSCT) setting. Even in allogeneic HSCT, donor lymphocyte infusions may be stored for months to years if excess stem cells are collected from donors. Cryopreservation is a delicate, complex, and costly procedure, and higher concentrations of dimethyl sulfoxide (DMSO), a commonly used cryoprotectant, can be toxic to cells and cause adverse effects in the recipient during infusions. In this study, we examined the effect of long-term cryopreservation using 4.35% DMSO (as final concentration) with methyl cellulose and uncontrolled rate freezing in a mechanical freezer (-80 °C) on the viability and colony-forming ability of CD34+ human PBSCs. For patients undergoing autologous HSCT, PBSCs were cryopreserved using DMSO (final concentration of 4.35%) with methyl cellulose. The post-thaw viability of PBSCs was determined using Trypan blue exclusion and flow cytometry-based 7-amino-actinomycin-D (FC-7AAD) methods. Concentrations of CD34+ stem cells and immune cell subsets in post-thaw PBSC harvest samples were assessed using multicolor flow cytometry, and the clonogenic potential of post-thaw stem cells was studied using a colony-forming unit (CFU) assay. CD34+ stem cell levels were correlated with the prestorage CD34 levels using the Pearson correlation test. The viability results in the Trypan blue dye exclusion method and the flow cytometry-based method were compared using Bland-Altman plots. We studied 26 PBSC harvest samples with a median cryopreservation duration of 6.6 years (range, 3.8 to 11.5 years). The median viability of post-thaw PBSCs was >80% using both methods, with a weak agreement between them (r = .03; P = .5). The median CD34+ stem cell count in the post-thaw samples was 9.13 × 106/kg (range, .44 to 26.27 × 106/kg). The CFU assay yielded a good proliferation and differentiation potential in post-thaw PBSCs, with a weak correlation between granulocyte macrophage CFU and CD34+ stem cell levels (r = .4; P = .05). Two samples that had been cryopreserved for >8 years showed low viability. Cryopreservation of PBSCs using 4.35% DMSO with methyl cellulose and uncontrolled freezing in a mechanical freezer at -80 °C allows the maintenance of long-term viability of PBSC for up to 8 years.

Innovative Approach in the Cryogenic Freezing Medium for Mesenchymal Stem Cells

The physical stresses during cryopreservation affect stem cell survival and further proliferation. To minimize or prevent cryoinjury, cryoprotective agents (CPAs) are indispensable. Despite the widespread use of 10% dimethyl sulfoxide (DMSO), there are concerns about its potential adverse effects. To bypass those effects, combinations of CPAs have been investigated. This study aimed to verify whether high-molecular-hyaluronic acid (HMW-HA) serves as a cryoprotectant when preserving human mesenchymal stem cells (hMSCs) to reduce the DMSO concentration in the cryopreservation medium. We studied how 0.1% or 0.2% HMW-HA combined with reduced DMSO concentrations (from 10% to 5%, and 3%) affected total cell count, viability, immunophenotype, and differentiation potential post-cryopreservation. Immediately after cell revival, the highest total cell count was observed in 10% DMSO-stored hMSC. However, two weeks after cell cultivation an increased cell count was seen in the HMW-HA-stored groups along with a continued increase in hMSCs stored using 3% DMSO and 0.1% HMW-HA. The increased total cell count corresponded to elevated expression of stemness marker CD49f. The HA-supplemented cryomedium did not affect the differential potential of hMSC. Our results will participate in producing a ready-to-use product for cryopreservation of mesenchymal stem cells.

Anti-thymocyte globulin and post-transplant cyclophosphamide predisposes to inferior outcome when using cryopreserved stem cell grafts

During 2020, the concurrent novel COVID-19 pandemic lead to widespread cryopreservation of allogeneic hematopoietic cell transplant grafts based on National Marrow Donor Program and European Society of Blood and Marrow Transplantation recommendations, in order to secure grafts before the start of conditioning chemotherapy. We sought to examine the impact of this change in practice on patient outcomes. We analyzed the outcomes of 483 patients who received hematopoietic stem cell transplantation (HSCT) between August 2017 and August 2020, at Princess Margaret Cancer Centre, Canada, in the retrospective study, comparing the outcomes between those who received cryopreserved or fresh peripheral blood stem cell grafts. Overall compared with those who received fresh grafts (n = 348), patients who received cryopreserved grafts (n = 135) had reduced survival and GRFS, reduced incidence of chronic graft-versus-host disease (GvHD), delay in neutrophil engraftment, and higher graft failure (GF), with no significant difference in relapse incidence or acute GvHD. However, recipients of cryopreserved matched-related donor HSCT showed significantly worse OS, NRM, GRFS compared with fresh grafts. Multivariable analysis of the entire cohort showed significant impact of cryopreservation on OS, relapse, cGvHD, GF, and GRFS. We conclude that cryopreservation was associated with inferior outcomes post-HSCT, possibly due to the combination of ATG and post-transplant cyclophosphamide impacting differential tolerance to cryopreservation on components of the stem cell graft; further studies are warranted to elucidate mechanisms for this observation.

Effects of storage media, supplements and cryopreservation methods on quality of stem cells

Despite a vast amount of different methods, protocols and cryoprotective agents (CPA), stem cells are often frozen using standard protocols that have been optimized for use with cell lines, rather than with stem cells. Relatively few comparative studies have been performed to assess the effects of cryopreservation methods on these stem cells. Dimethyl sulfoxide (DMSO) has been a key agent for the development of cryobiology and has been used universally for cryopreservation. However, the use of DMSO has been associated with in vitro and in vivo toxicity and has been shown to affect many cellular processes due to changes in DNA methylation and dysregulation of gene expression. Despite studies showing that DMSO may affect cell characteristics, DMSO remains the CPA of choice, both in a research setting and in the clinics. However, numerous alternatives to DMSO have been shown to hold promise for use as a CPA and include albumin, trehalose, sucrose, ethylene glycol, polyethylene glycol and many more. Here, we will discuss the use, advantages and disadvantages of these CPAs for cryopreservation of different types of stem cells, including hematopoietic stem cells, mesenchymal stromal/stem cells and induced pluripotent stem cells.

Reduced dimethyl sulfoxide concentrations successfully cryopreserve human hematopoietic stem cells with multi-lineage long-term engraftment ability in mice

BACKGROUND AIMS

The cryopreservation of hematopoietic stem cells (HSCs) in dimethyl sulfoxide (DMSO) is used widely, but DMSO toxicity in transplant patients and the effects of DMSO on the normal function of cryopreserved cells are concerns. To address these issues, in vitro and clinical studies have explored using reduced concentrations of DMSO for cryopreservation. However, the effect of reducing DMSO concentration on the efficient cryopreservation of HSCs has not been directly measured.

METHODS

Cryopreservation of human bone marrow using 10%, 7.5% and 5% DMSO concentrations was examined. Cell counting, flow cytometry and colony assays were used to analyze different cell populations. The recovery of stem cells was enumerated using extreme limiting dilution analysis of long-term multi-lineage engraftment in immunodeficient mice. Four different methods of analyzing human engraftment were compared to ascertain stem cell engraftment: (i) engraftment of CD33⁺ myeloid, CD19⁺ B-lymphoid, CD235a⁺ erythroid and CD34⁺ progenitors; (ii) engraftment of the same four populations plus CD41⁺CD42b⁺ platelets; (iii) engraftment of CD34⁺⁺CD133⁺ cells; and (iv) engraftment of CD34⁺⁺CD38^- cells.

RESULTS

Hematopoietic colony-forming, CD34^++/+, CD34⁺⁺CD133⁺ and CD34⁺⁺CD38^- cells were as well preserved with 5% DMSO as they were with the higher concentrations tested. The estimates of stem cell frequencies made in the xenogeneic transplant model did not show any significant detrimental effect of using lower concentrations of DMSO. Comparison of the different methods of gauging stem cell engraftment in mice led to different estimates of stem cell numbers, but overall, all measures found that reduced concentrations of DMSO supported the cryopreservation of HSCs.

CONCLUSION

Cryopreservation of HSCs in DMSO concentrations as low as 5% is effective.

No Detectable Alteration of Inorganic Allogeneic Bone Matrix Colonizing Mesenchymal Cells: A Step Towards Personalized Bone Grafts

Background

During major bone substance loss, secured allogeneic bone matrix (ABM) is normally utilized for bone repair. Here, we propose a method to colonize ABM using autologous mesenchymal cells (MCs) to improve their integration. Moreover, in this study, the consequences of in vitro colonization on MCs have been evaluated.

Methods

After in vitro propagation of MCs, their proliferation kinetics on ABM pre-coated with gelatin, fibronectin, collagen IV and human serum (HS) was monitored, and they were compared with cells cultured without ABM for 8 weeks. The effect of ABM on cell phenotype was also assessed. Lastly, the ability of ABM-colonizing MCs to perform hematopoiesis, a function normally preserved in selected culture conditions, and their differentiation towards osteoblastic lineage were evaluated.

Results

MC and colony-forming unit-fibroblast proliferated 930- and 590-fold, respectively. The proliferation rate of the expanded MCs was higher, forming a 3-dimensional structure in all ABMs. Pre-coating with HS was the most efficient treatment of ABMs to increase the initial adherence of MCs, and it partly explains the reason for the higher propagation of MCs. Flow cytometry analyses revealed subtle alterations in ABM-colonizing cells; however, the ability of MCs to maintain long-term culture initiating cells proliferation and differentiate into osteoblastic lineage was preserved.

Conclusions

In this study, the in vitro biocompatibility of bone marrow (BM) MCs with ABMs, the role of HS in scaffold coating, and the possibility of initially using a small BM sample for this approach were demonstrated.

Intracellular delivery of trehalose renders mesenchymal stromal cells viable and immunomodulatory competent after cryopreservation

Trehalose is a nontoxic disaccharide and a promising cryoprotection agent for medically applicable cells. In this study, the efficiency of combining trehalose with reversible electroporation for cryopreservation of two types of human mesenchymal stromal cells was investigated: adipose-derived stromal cells, and umbilical-cord-derived stromal cells. Comparable results to standard dimethyl sulfoxide cryopreservation protocols were achieved, even without extensive electroporation parameters and protocol optimization. The presence of high extracellular trehalose resulted in comparable cell viabilities without and with electroporation. According to the determination of trehalose concentrations, 250 mM extracellular trehalose resulting in, 20 mM to 50 mM intracellular trehalose were sufficient for successful cryopreservation of cells. With electroporation, higher (i.e. 50 mM to 90 mM) intracellular trehalose was achieved after cryopreservation, although cell survival was not improved significantly. To evaluate the impact of electroporation and cryopreservation on cells, stress and immune-activation-related gene expression were analyzed. Electroporation and/or cryopreservation resulted in increased SOD2 and HSPA1A expression. Despite the increased stress response, the high up-regulation by mesenchymal stromal cells of immunomodulatory genes in the inflammatory environment was not affected. Highest expression was seen for the IDO1 and TSG6 genes. In conclusion, cryopreservation of mesenchymal stromal cells in trehalose results in comparable characteristics to their cryopreservation using dimethyl sulfoxide.

Cryopreservation of peripheral blood mononuclear cells using uncontrolled rate freezing

Peripheral blood mononuclear cells are widely used as source material for anticancer immunotherapies. The conventional cryopreservation method for peripheral blood mononuclear cells is time-consuming and expansive, which involves controlled rate freezing followed by storage in liquid nitrogen. Instead, the convenient uncontrolled rate freezing cryopreservation method had been reported successfully in peripheral blood hematopoietic stem cells and peripheral blood progenitor cells. Therefore, we hypothesized that uncontrolled rate freezing cooling method maybe also applied to peripheral blood mononuclear cells cryopreservation. In this study, we evaluated the performance of uncontrolled rate freezing and controlled rate freezing cooling methods through cell recovery rate, viability, differentiation potential into cytokine-induced killer cells and the cellular properties of the cultured cytokine-induced killer cells. The results showed similar post-thaw viability and recovery rate in both controlled rate freezing and uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells. Importantly, the uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells exhibited higher growth ratio and earlier cell clustering during ex-vivo cytokine-induced killer cell culture than the controlled rate freezing ones. These two groups of expanded cytokine-induced killer cells also exhibited similar effector cell subset ratio and tumoricidal activity. In general, the performance of cryopreserved peripheral blood mononuclear cells using uncontrolled rate freezing cooling method, with the commercial cryoprotective agent CellBanker 2, was equal or better than the controlled rate freezing method. Our study implied that the combined use of cryoprotective agent CellBanker 2 and uncontrolled rate freezing could be a convenient cryopreservation method for peripheral blood mononuclear cells.

Dimethyl sulfoxide-free cryopreservation for cell therapy: A review

Cell-based therapeutics promise to transform the treatment of a wide range of diseases including cancer, genetic and degenerative disorders, or severe injuries. Many of the commercial and clinical development of cell therapy products require cryopreservation and storage of cellular starting materials, intermediates and/or final products at cryogenic temperature. Dimethyl sulfoxide (Me₂SO) has been the cryoprotectant of choice in most biobanking situations due to its exceptional performance in mitigating freezing-related damages. However, there is concern over the toxicity of Me₂SO and its potential side effects after administration to patients. Therefore, there has been growing demand for robust Me₂SO-free cryopreservation methods that can improve product safety and maintain potency and efficacy. This article provides an overview of the recent advances in Me₂SO-free cryopreservation of cells having therapeutic potentials and discusses a number of key challenges and opportunities to motivate the continued innovation of cryopreservation for cell therapy.

Stem cells: Haemobiology and clinical data summarising: A critical review

Stem cells (SC) are the unique and "key-cells" in the human body "working" as a source of producing a large number (proliferation) of mature (differentiation) cells inside different tissues ("cytopoiesis") - while at the same time maintaining the ability to "reproduce" themselves (self-renewal). These events are balanced by interactive signals from the extracellular matrix, as well as microenvironment provided by stromal cells. On the other hand, SC plasticity (so-called "inter-systemic plasticity") is the ability of the most "primitive" (immature) adult SCs to switch to novel identities. The phrase SC plasticity also involves phenotypic potential of these cells, broader than spectrum of phenotypes of differentiated cells in their original tissues. Recent increasing clinical use of cell-mediated therapeutic approaches has resulted in enlarged needs for both, higher quantity of SCs and improved operating procedures during extracorporeal manipulations. The aim of harvesting procedures is to obtain the best SC yield and viability. The goal of optimised cryopreservation is to minimise cellular thermal damages during freeze/thaw process (cryoinjury). Despite the fact that different SC collection, purification and cryopreservation protocols are already in routine use - a lot of problems related to the optimal SC extracorporeal manipulations are still unresolved. The objective of this paper is to provide an integral review of early haemobiological and cryobiological research in the unlimited "SC-field" with emphasis on their entities, recent cell-concepts, extracorporeal manipulative and "graft-engineering" systems. Their therapeutic relevance and efficacy in "conventional" SC transplants or regenerative medicine will be briefly summarised. Finally, in this paper original results will not be pointed out - related to neither SC transplants nor regenerative medicine - but a light will be shed on some of them.

Adverse reactions of dimethyl sulfoxide in humans: a systematic review

Background: Dimethyl sulfoxide (DMSO) has been used for medical treatment and as a pharmacological agent in humans since the 1960s. Today, DMSO is used mostly for cryopreservation of stem cells, treatment of interstitial cystitis, and as a penetrating vehicle for various drugs. Many adverse reactions have been described in relation to the use of DMSO, but to our knowledge, no overview of the existing literature has been made. Our aim was to conduct a systematic review describing the adverse reactions observed in humans in relation to the use of DMSO. Methods: This systematic review was reported according to the PRISMA-harms (Preferred Reporting Items for Systematic reviews and Meta-Analysis) guidelines. The primary outcome was any adverse reactions occurring in humans in relation to the use of DMSO. We included all original studies that reported adverse events due to the administration of DMSO, and that had a population of five or more. Results: We included a total of 109 studies. Gastrointestinal and skin reactions were the commonest reported adverse reactions to DMSO. Most reactions were transient without need for intervention. A relationship between the dose of DMSO given and the occurrence of adverse reactions was seen. Conclusions: DMSO may cause a variety of adverse reactions that are mostly transient and mild. The dose of DMSO plays an important role in the occurrence of adverse reactions. DMSO seems to be safe to use in small doses. Registration: PROSPERO CRD42018096117.

Adverse reactions of dimethyl sulfoxide in humans: a systematic review

Background: Dimethyl sulfoxide (DMSO) has been used for medical treatment and as a pharmacological agent in humans since the 1960s. Today, DMSO is used mostly for cryopreservation of stem cells, treatment of interstitial cystitis, and as a penetrating vehicle for various drugs. Many adverse reactions have been described in relation to the use of DMSO, but to our knowledge, no overview of the existing literature has been made. Our aim was to conduct a systematic review describing the adverse reactions observed in humans in relation to the use of DMSO.

Methods: This systematic review was reported according to the PRISMA-harms (Preferred Reporting Items for Systematic reviews and Meta-Analysis) guidelines. The primary outcome was any adverse reactions occurring in humans in relation to the use of DMSO. We included all original studies that reported adverse events due to the administration of DMSO, and that had a population of five or more.

Results: We included a total of 109 studies. Gastrointestinal and skin reactions were the commonest reported adverse reactions to DMSO. Most reactions were transient without need for intervention. A relationship between the dose of DMSO given and the occurrence of adverse reactions was seen.

Conclusions: DMSO may cause a variety of adverse reactions that are mostly transient and mild. The dose of DMSO plays an important role in the occurrence of adverse reactions. DMSO seems to be safe to use in small doses.

Registration: PROSPERO CRD42018096117.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.

Outcome of 51 autologous peripheral blood stem cell transplants after uncontrolled-rate freezing ("dump freezing") using -80°C mechanical freezer

BACKGROUND AND OBJECTIVE:

Controlled-rate freezing is a complicated, expensive, and time-consuming procedure. Therefore, there is a growing interest in uncontrolled-rate freezing (UCF) with −80°C mechanical freezers for cryopreservation of hematopoietic stem cells. This is a retrospective analysis of efficiency of UCF and outcome of autologous peripheral hematopoietic stem cell (PBSC) transplants at our center from December 2011 to June 2016.

MATERIALS AND METHODS:

Cryoprotectant solutions used included 5% dimethyl sulfoxide and 5% albumin with 2% hydroxyethyl starch and stored at −80°C mechanical freezer till transplant. Evaluation of cryopreservation was studied by analyzing the variation in cellularity, viability, and CD34+ stem cell dose recovery as well as clinical follow-up with engraftment.

RESULTS:

A total of 51 patients (23 females and 28 males) underwent autologous PBSC transplantations with a median age of 31 years (range: 3–60 years) for both hematological and nonhematological indications. Mean recovery post by UCF at −80°C mechanical was 92.9% ± 15.5% for nucleated cells, 86.6% ± 15.5% for viability, and 80% ± 21.5% in CD34+ dose. The median day to neutrophil engraftment was 10 (range 5–14 days) and platelets engraftment was 15 (range 8–45 days). The cryopreserved products were stored at −80°C for median 7 days (range 2-41 day) before transplant.

DISCUSSION/CONCLUSION:

Our analysis shows that PBSC can be successfully cryopreserved with mechanical uncontrolled rate freezing. This is a cheap and simple method to freeze the stem cells for a short period in resource-constrained setting.

Small-Molecule Ice Recrystallization Inhibitors Improve the Post-Thaw Function of Hematopoietic Stem and Progenitor Cells

The success of hematopoietic stem cell transplantation depends in part on the number and the quality of cells transplanted. Cryoinjuries during freezing and thawing reduce the ability of hematopoietic stem and progenitor cells (HSPCs) to proliferate and differentiate after thawing. Up to 20% of the patients undergoing umbilical cord blood (UCB) transplant experience delayed or failed engraftment, likely because of the inadequate hematopoietic potency of the unit. Therefore, the optimization of cryopreservation protocols, with an emphasis on the preservation of HSPCs, is an important issue. Current protocols typically utilize a 10% dimethyl sulfoxide cryoprotectant solution. This solution ensures 70-80% post-thaw cell viability by diluting intracellular solutes and maintaining the cell volume during cryopreservation. However, this solution fails to fully protect HSPCs, resulting in the loss of potency. Therefore, a new class of cryoprotectants (N-aryl-d-aldonamides) was designed and assessed for the ability to inhibit ice recrystallization and to protect HSPCs against cryoinjury. Several highly active ice recrystallization inhibitors were discovered. When used as additives to the conventional cryoprotectant solution, these nontoxic small molecules improved the preservation of functionally divergent hematopoietic progenitors in the colony-forming unit and long-term culture-initiating cell assays. By contrast, structurally similar compounds that did not inhibit ice recrystallization failed to improve the post-thaw recovery of myeloid progenitors. Together, these results demonstrate that the supplementation of cryopreservation solution with compounds capable of controlling ice recrystallization increases the post-thaw function and potency of HSPCs in UCB. This increase may translate into reduced risk of engraftment failure and allow for greater use of cryopreserved cord blood units.

Long-term effects of cryopreservation on clinically prepared hematopoietic progenitor cell products

BACKGROUND AIMS

The question of how long hematopoietic progenitor cells (HPCs) destined for clinical applications withstand long-term cryopreservation remains unanswered. To increase our basic understanding about the stability of HPC products over time, this study focused on characterizing long-term effects of cryopreservation on clinically prepared HPC products.

METHODS

Cryovials (n = 233) frozen for an average of 6.3 ± 14.2 years (range, 0.003-14.6 years) from HPC products (n = 170) representing 75 individual patients were thawed and evaluated for total nucleated cells (TNCs), cell viability, viable CD34+ (vCD34+) cells and colony-forming cells (CFCs). TNCs were determined by use of an automated cell counter, and cell viability was measured with the use of trypan blue exclusion. Viable CD34 analysis was performed by means of flow cytometry and function by a CFC assay.

RESULTS

Significant losses in TNCs, cell viability, vCD34+ cells and CFC occurred on cryopreservation. However, once frozen, viable TNCs, vCD34+ cells and CFC recoveries did not significantly change over time. The only parameter demonstrating a change over time was cell viability, which decreased as the length of time that an HPC product was stored frozen increased. A significant negative correlation (correlation coefficient = -0.165) was determined between pre-freeze percent granulocyte content and post-thaw percent viability (n = 170; P = 0.032). However, a significant positive correlation was observed between percent viability at thaw and pre-freeze lymphocyte concentration.

CONCLUSIONS

Once frozen, HPC products were stable for up to 14.6 years at <-150°C. Post-thaw viability was found to correlate negatively with pre-freeze granulocyte content and positively with pre-freeze lymphocyte content.

Cryopreserved ECP-treated lymphocytes maintain apoptotic response and anti-proliferative effect

BACKGROUND

The ability to cryopreserve a portion of the cells treated during extracorporeal photopheresis (ECP) would improve therapy logistics, particularly for pediatric patients, by allowing multiple therapeutic doses to be collected from a single apheresis session. However, the effect of cryopreservation on ECP-treated cells is unknown (e.g., ECP-induced lymphocyte apoptosis and inhibition of proliferation).

STUDY DESIGN AND METHODS

Mononuclear cell (MNC) apheresis products collected from healthy subjects were ECP-treated using offline methods. Fresh samples of ECP-treated and control cells were placed immediately in culture. The remainder of the cells were frozen in cryovials (n = 8) or cryobags (n = 8) at -80°C. After 1 week of -80°C storage, ECP-treated and control cells were thawed rapidly and samples were placed in culture. Lymphocyte apoptosis was assessed by phosphatidylserine exposure using Annexin V/7-AAD labeling. Lymphocyte proliferation after 3 days culture was measured using the carboxyfluorescein succinimidyl ester labeling technique.

RESULTS

On Day 0, apoptosis levels were <5% in fresh ECP-treated and control cells and approximately 20% on thawing of cryopreserved ECP-treated and control cells. Apoptosis levels were comparable between the two cryopreserved groups immediately on thawing, indicating that ECP-treated cells were no more sensitive to the cryopreservation process than control cells. During 72-h culture, apoptosis levels increased to >80% in fresh and cryopreserved ECP-treated cells but remained near constant in both control groups. Inhibition of lymphocyte proliferation was >95% in all ECP-treated cells with no significant difference between fresh and cryopreserved cells (P = 0.12).

CONCLUSION

Cryopreservation did not impair the apoptotic response or anti-proliferative effect of ECP-treated lymphocytes, thereby demonstrating early feasibility of this approach.

Storage of human biospecimens: selection of the optimal storage temperature

Millions of biological samples are currently kept at low tempertures in cryobanks/biorepositories for long-term storage. The quality of the biospecimen when thawed, however, is not only determined by processing of the biospecimen but the storage conditions as well. The overall objective of this article is to describe the scientific basis for selecting a storage temperature for a biospecimen based on current scientific understanding. To that end, this article reviews some physical basics of the temperature, nucleation, and ice crystal growth present in biological samples stored at low temperatures (-20°C to -196°C), and our current understanding of the role of temperature on the activity of degradative molecules present in biospecimens. The scientific literature relevant to the stability of specific biomarkers in human fluid, cell, and tissue biospecimens is also summarized for the range of temperatures between -20°C to -196°C. These studies demonstrate the importance of storage temperature on the stability of critical biomarkers for fluid, cell, and tissue biospecimens.

Hematopoietic SCT with cryopreserved grafts: adverse reactions after transplantation and cryoprotectant removal before infusion

Transplantation of hematopoietic stem cells (HSCs) has been successfully developed as a part of treatment protocols for a large number of clinical indications, and cryopreservation of both autologous and allogeneic sources of HSC grafts is increasingly being used to facilitate logistical challenges in coordinating the collection, processing, preparation, quality control testing and release of the final HSC product with delivery to the patient. Direct infusion of cryopreserved cell products into patients has been associated with the development of adverse reactions, ranging from relatively mild symptoms to much more serious, life-threatening complications, including allergic/gastrointestinal/cardiovascular/neurological complications, renal/hepatic dysfunctions, and so on. In many cases, the cryoprotective agent (CPA) used-which is typically dimethyl sulfoxide (DMSO)-is believed to be the main causal agent of these adverse reactions and thus many studies recommend depletion of DMSO before cell infusion. In this paper, we will briefly review the history of HSC cryopreservation, the side effects reported after transplantation, along with advances in strategies for reducing the adverse reactions, including methods and devices for removal of DMSO. Strategies to minimize adverse effects include medication before and after transplantation, optimizing the infusion procedure, reducing the DMSO concentration or using alternative CPAs for cryopreservation and removing DMSO before infusion. For DMSO removal, besides the traditional and widely applied method of centrifugation, new approaches have been explored in the past decade, such as filtration by spinning membrane, stepwise dilution-centrifugation using rotating syringe, diffusion-based DMSO extraction in microfluidic channels, dialysis and dilution-filtration through hollow-fiber dialyzers and some instruments (CytoMate, Sepax S-100, Cobe 2991, microfluidic channels, dilution-filtration system, etc.) as well. However, challenges still remain: development of the optimal (fast, safe, simple, automated, controllable, effective and low cost) methods and devices for CPA removal with minimum cell loss and damage remains an unfilled need.

Manufacturing and banking of mesenchymal stem cells

INTRODUCTION

Mesenchymal stem cells (MSC) and MSC-like cells hold great promise and offer many advantages for developing effective cellular therapeutics. Current trends indicate that the clinical application of MSC will continue to increase markedly. For clinical applications, large numbers of MSC are usually required, ideally in an off-the-shelf format, thus requiring extensive MSC expansion ex vivo and subsequent cryopreservation and banking.

AREAS COVERED

To exploit the full potential of MSC for cell-based therapies requires overcoming significant cell-manufacturing, banking and regulatory challenges. The current review will focus on the identification of optimal cell source for MSC, the techniques for production scale-up, cryopreservation and banking and the regulatory challenges involved.

EXPERT OPINION

There has been considerable success manufacturing and cryopreserving MSC at laboratory scale. Surprisingly little attention, however, has been given to translate these technologies to an industrial scale. The development of cost-effective advanced technologies for producing and cryopreserving commercial-scale MSC is important for successful clinical cell therapy.

Clinical grade adult stem cell banking

There has been a great deal of scientific interest recently generated by the potential therapeutic applications of adult stem cells in human care but there are several challenges regarding quality and safety in clinical applications and a number of these challenges relate to the processing and banking of these cells ex-vivo. As the number of clinical trials and the variety of adult cells used in regenerative therapy increases, safety remains a primary concern. This has inspired many nations to formulate guidelines and standards for the quality of stem cell collection, processing, testing, banking, packaging and distribution. Clinically applicable cryopreservation and banking of adult stem cells offers unique opportunities to advance the potential uses and widespread implementation of these cells in clinical applications. Most current cryopreservation protocols include animal serum proteins and potentially toxic cryoprotectant additives (CPAs) that prevent direct use of these cells in human therapeutic applications. Long term cryopreservation of adult stem cells under good manufacturing conditions using animal product free solutions is critical to the widespread clinical implementation of ex-vivo adult stem cell therapies. Furthermore, to avoid any potential cryoprotectant related complications, reduced CPA concentrations and efficient post-thaw washing to remove CPA are also desirable. The present review focuses on the current strategies and important aspects of adult stem cell banking for clinical applications. These include current good manufacturing practices (cGMPs), animal protein free freezing solutions, cryoprotectants, freezing & thawing protocols, viability assays, packaging and distribution. The importance and benefits of banking clinical grade adult stem cells are also discussed.

Hematologic, immunologic reconstitution, and outcome of 342 autologous peripheral blood stem cell transplantations after cryopreservation in a -80°C mechanical freezer and preserved less than 6 months

BACKGROUND

Controlled-rate freezing and storage in nitrogen is the standard technique for cryopreservation of peripheral hematopoietic progenitor cells (PHPCs) but presents high cost and dimethyl sulfoxide (DMSO) toxicity. Cryopreservation at -80°C, by uncontrolled rate freezing with only 3.5% DMSO, preserves the functional capacities of PHPCs, produces successful engraftment, and reduces toxicity during infusion.

STUDY DESIGN AND METHODS

Long-term hematopoietic and immunologic reconstitution for 342 autografts (311 adults, 31 children) after PHPCs were cryopreserved at -80°C was studied at 3, 6, and 12 months. The median (range) storage time of PHPCs cryopreserved was 1.7 (0.1-5.99) months.

RESULTS

Hemoglobin (Hb), white blood cells, and platelets (PLTs) reach normal values to trilineage at 12 months for 39% patients. Multivariate analysis shows a significant impact on CD34+ infused and on conditioning regimen for PLTs. Hb was influenced by growth factor administration at 3 months. Long-term recovery is also highly dependent on blood counts (Hb, PLT, and neutrophil) at start of high-dose chemotherapy. Only 43% of patients had reached normal lymphocyte values at 12 months after transplant, and a profound CD4+ T-lymphocyte deficit remained, as others reported.

CONCLUSION

Transplantation with PHPCs cryopreserved at -80°C for no more than 6 months is satisfactory for long-term hematopoietic and immunologic reconstitution, even if a profound CD4+ T lymphocyte deficit persists at 1 year. This easier and cheaper cryopreservation method also leads to successful engraftment.

Relative recovery of haematopoietic stem cell products after cryogenic storage of up to 19 years

There is an increasing trend towards long-term frozen storage of haematopoietic stem cells. For such stem cells, harvested from peripheral blood (PB) or BM, it is not known if stem cell viability decreases with time. In this study, 31 separate bags of stem cell product (SCP) stored for 11-19 years (median 15 years) were assessed for total nucleated cell (TNC) count, colony forming unit-granulocyte/macrophage (CFU-GM), CD34⁺ cell count and cell viability. The results were compared with the initial results obtained for the products at the time of stem cell harvest, and the percentage recovery of each parameter was plotted against time. Recovery of TNC, CD34⁺ cell count and cell viability decreased with time (P=<0.01) but CFU-GM did not. This study shows that SCPs harvested from PB and BM do deteriorate with long-term storage. This could have an impact on rates of engraftment.

Autologous Hematopoietic Stem Cell Transplantation for Multiple Myeloma without Cryopreservation

High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation is considered the standard of care for multiple myeloma patients who are eligible for transplantation. The process of autografting comprises the following steps: control of the primary disease by using a certain induction therapeutic protocol, mobilization of stem cells, collection of mobilized stem cells by apheresis, cryopreservation of the apheresis product, administration of high-dose pretransplant conditioning therapy, and finally infusion of the cryopreserved stem cells after thawing. However, in cancer centers that treat patients with multiple myeloma and have transplantation capabilities but lack or are in the process of acquiring cryopreservation facilities, alternatively noncryopreserved autologous stem cell therapy has been performed with remarkable success as the pretransplant conditioning therapy is usually brief.

Hydroxyethylstarch in cryopreservation - mechanisms, benefits and problems

As the progress of regenerative medicine places ever greater attention on cryopreservation of (stem) cells, tried and tested cryopreservation solutions deserve a second look. This article discusses the use of hydroxyethyl starch (HES) as a cryoprotectant. Charting carefully the recorded uses of HES as a cryoprotectant, in parallel to its further clinical use, indicates that some HES subtypes are a useful supplement to dimethysulfoxide (DMSO) in cryopreservation. However, we suggest that the most common admixture ratio of HES and DMSO in cryoprotectant solutions has been established by historical happenstance and requires further investigation and optimization.

Storage of hemopoietic stem cells

BACKGROUND

Autologous, and in some cases allogeneic, hemopoietic stem cells (HSC) are stored for varying periods of time prior to infusion. For periods of greater than 48 h, storage requires cryopreservation. It is essential to optimize cell storage and ensure the quality of the product for subsequent reinfusion.

METHODS

A number of important variables may affect the subsequent quality of infused HSC and therapeutic cells (TC). This review discusses these and also reviews the regulatory framework that now aims to ensure the quality of stem cells and TC for transplantation.

RESULTS

Important variables included cell concentration, temperature, interval from collection to cryopreservation, manipulations performed. They also included rate of freezing and whether controlled-rate freezing was employed. Parameters studied were type of cryoprotectant utilized [dimethyl sulphoxide (DMSO) is most commonly used, sometimes in combination with hydroxyethyl starch (HES)]; and storage conditions. It is also important to assess the quality of stored stem cells. Measurements employed included the total cell count (TNC), mononuclear cell count (MNC), CD34+ cells and colony-forming units - granulocyte macrophage (CFU-GM). Of these, TNC and CD34+ are the most useful. However, the best measure of the quality of stored stem cells is their subsequent engraftment. The quality systems used in stem cell laboratories are described in the guidance of the Joint Accreditation Committee of ISCT (Europe) and the EBMT (JACIE) and the EU Directive on Tissues and Cells plus its supporting commission directives. Inspections of facilities are carried out by the appropriate national agencies and JACIE.

CONCLUSION

For high-quality storage of HSC and TC, processing facilities should use validated procedures that take into account critical variables. The quality of all products must be assessed before and after storage.

5% dimethyl sulfoxide (DMSO) and pentastarch improves cryopreservation of cord blood cells over 10% DMSO

BACKGROUND

Cell number and viability are important in cord blood (CB) transplantation. While 10% dimethyl sulfoxide (DMSO) is the standard medium, adding a starch to freezing medium is increasingly utilized as a cytoprotectant for the thawing process. Similar to hetastarch, pentastarch has the advantages of faster renal clearance and less effect on the coagulation system.

STUDY DESIGN AND METHODS

We compared a lower DMSO concentration (5%) containing pentastarch with 10% DMSO and performed cell viability assay, colony-forming units (CFUs), and transplantation of CB cells in NOD/SCID IL2Rγ(null) mice.

RESULTS

CB cells in 5% DMSO/pentastarch had similar CD34+, CD3+, and CD19+ cell percentages after thawing as fresh CB cells. CB cells in 5% DMSO/pentastarch had higher viability (83.3±9.23%) than those frozen in 10% DMSO (75.3±11.0%, p<0.05). We monitored cell viability postthaw every 30 minutes. The mean loss in the first 30 minutes was less in the 5% DMSO/pentastarch group. At the end of 3 hours, the viability decreased by a mean of 7.75% for the 5% DMSO/pentastarch and 17.5% for the 10% DMSO groups. CFUs were similar between the two cryopreserved groups. Frozen CB cells engrafted equally well in IL2Rγ(null) mice compared to fresh CB cells up to 24 weeks, and CB cells frozen in 5% DMSO/pentastarch engrafted better than those in 10% DMSO.

CONCLUSION

Our data indicate that the lower DMSO concentration with pentastarch represents an improvement in the CB cryopreservation process and could have wider clinical application as an alternate freezing medium over 10% DMSO.

Preservation of differentiation and clonogenic potential of human hematopoietic stem and progenitor cells during lyophilization and ambient storage

Progenitor cell therapies show great promise, but their potential for clinical applications requires improved storage and transportation. Desiccated cells stored at ambient temperature would provide economic and practical advantages over approaches employing cell freezing and subzero temperature storage. The objectives of this study were to assess a method for loading the stabilizing sugar, trehalose, into hematopoietic stem and progenitor cells (HPC) and to evaluate the effects of subsequent freeze-drying and storage at ambient temperature on differentiation and clonogenic potential. HPC were isolated from human umbilical cord blood and loaded with trehalose using an endogenous cell surface receptor, termed P2Z. Solution containing trehalose-loaded HPC was placed into vials, which were transferred to a tray freeze-dryer and removed during each step of the freeze-drying process to assess differentiation and clonogenic potential. Control groups for these experiments were freshly isolated HPC. Control cells formed 1450+/-230 CFU-GM, 430+/-140 BFU-E, and 50+/-40 CFU-GEMM per 50 microL. Compared to the values for the control cells, there was no statistical difference observed for cells removed at the end of the freezing step or at the end of primary drying. There was a gradual decrease in the number of CFU-GM and BFU-E for cells removed at different temperatures during secondary drying; however, there were no significant differences in the number of CFU-GEMM. To determine storage stability of lyophilized HPC, cells were stored for 4 weeks at 25 degrees C in the dark. Cells reconstituted immediately after lyophilization produced 580+/-90 CFU-GM ( approximately 40%, relative to unprocessed controls p<0.0001), 170+/-70 BFU-E (approximately 40%, p<0.0001), and 41+/-22 CFU-GEMM (approximately 82%, p = 0.4171), and cells reconstituted after 28 days at room temperature produced 513+/-170 CFU-GM (approximately 35%, relative to unprocessed controls, p<0.0001), 112+/-68 BFU-E (approximately 26%, p<0.0001), and 36+/-17 CFU-GEMM ( approximately 82%, p = 0.2164) These studies are the first to document high level retention of CFU-GEMM following lyophilization and storage for 4 weeks at 25 degrees C. This type of flexible storage stability would potentially permit the ability to ship and store HPC without the need for refrigeration.

Evaluation of methylcellulose and dimethyl sulfoxide as the cryoprotectants in a serum-free freezing media for cryopreservation of adipose-derived adult stem cells

Developing effective techniques for the cryopreservation of human adipose-derived adult stem cells (ASCs) could increase the usefulness of these cells in tissue engineering and regenerative medicine. To this end, we investigated the post-freeze/thaw viability and apoptotic behavior of Passage 1 (P1) adult stem cells (ASCs) in 11 different media: (i) the traditional media containing Dulbecco's modified Eagle's medium (DMEM) with 80% fetal calf serum (FCS) and 10% dimethyl sulfoxide (DMSO), (ii) DMEM with 80% human serum (HS) and 10% DMSO, (iii) DMEM with 1% methyl cellulose (MC) and 10% of either HS or FCS or DMSO, and (iv) DMEM with 0%, 2%, 4%, 6%, 8%, or 10% DMSO. Approximately 1 mL (10(6) cells/mL) of P1 ASCs were frozen overnight in a -80 degrees C freezer and stored in liquid nitrogen for 2 weeks before being rapidly thawed in a 37 degrees C water bath (1-2 min of agitation), resuspended in culture media, and seeded in separate wells of a 6-well plate for a 24-h incubation period at 37 degrees C. After 24 h, the thawed samples were analyzed by bright-field microscopy and flow cytometry. The results suggest that the absence of DMSO (and the presence of MC) significantly increases the fraction of apoptotic and/or necrotic ASCs. However, the percentage of viable cells obtained with 2% DMSO and DMEM was comparable with that obtained in freezing media with 10% DMSO and 80% serum (HS or FCS), that is, approximately 84% +/- 5% and approximately 84% +/- 8%, respectively. Adipogenic and osteogenic differentiation behavior of the frozen thawed cells was also assessed using histochemical staining. Our results suggest that post-thaw ASC viability, adipogenic and osteogenic differentiability can be maintained even when they are frozen in the absence of serum but with a minimal concentration of 2% DMSO in DMEM.

Cryopreservation of mononuclear cells before extracorporeal photochemotherapy does not impair their anti-proliferative capabilities

BACKGROUND AIMS

The clinical benefits of extracorporeal photochemotherapy (ECP) are well recognized, but its clinical use is limited by logistical difficulties, especially because of the need to perform repeated aphereses. The cryopreservation of mononuclear cells could allow maintenance of the ECP schedule while reducing the number of aphereses. The aim of this work was to assess whether previous cryopreservation impairs the immunomodulatory function of ECP-treated peripheral blood mononuclear cells (PBMC).

METHODS

Fresh or previously cryopreserved PBMC were exposed to ECP and added on day 0 into a mixed leukocyte reaction. Proliferation of alloreactive lymphocytes was measured by carboxyfluorescein succinimidyl ester (CFSE) dye dilution. Apoptosis was quantified by annexin-7AAD staining.

RESULTS

ECP-induced apoptosis was slightly increased in cryopreserved cells but the kinetics of apoptosis were similar to fresh cells. Lymphocytes stimulated in the presence of ECP-treated PBMC displayed a significant decrease in proliferation. The suppression was enforced when ECP-treated cells had been activated previously by allogeneic stimulation. Cryopreservation before ECP exposure did not impact apoptosis triggering or anti-proliferative properties of ECP-treated cells.

CONCLUSIONS

Cryopreservation before ECP does not impair the immunomodulatory effects of treated cells. These data warrant investigation of the clinical use of cryopreserved PBMC for ECP.

Optimization of cryopreservation condition for hematopoietic stem cells from umbilical cord blood

The conditions for cryopreservation of CD34(+) hematopoietic stem cells (HSC) from umbilical cord blood (UCB) were optimized with a new cryo-medium containing 10% ethylene glycol (EG) and 2% dimethyl sulfoxide (Me(2)SO) using a controlled-rate freezing (CRF) method. After the cryopreservation of mononuclear cells (MNC) from UCB, recoveries of MNC, CD34(+) cells, and total colony-forming units (CFU) were significantly improved compared to those in the control cryo-medium containing 10% Me(2)SO and 2% Dextran-40 (P<0.05). This study shows that the new cryo-medium and CRF method provide better recoveries of MNC, HSC and total CFU than the control cryo-medium and isopropylalcohol freezing (IPA) method. Therefore, this cryo-medium, combined with the CRF method, is valuable for optimizing cryopreservation conditions for HSC from UCB to obtain satisfactory HSC recovery.

Freeze-drying of mononuclear cells derived from umbilical cord blood followed by colony formation

BACKGROUND

We recently showed that freeze-dried cells stored for 3 years at room temperature can direct embryonic development following cloning. However, viability, as evaluated by membrane integrity of the cells after freeze-drying, was very low; and it was mainly the DNA integrity that was preserved. In the present study, we improved the cells' viability and functionality after freeze-drying.

METHODOLOGY/PRINCIPAL FINDINGS

We optimized the conditions of directional freezing, i.e. interface velocity and cell concentration, and we added the antioxidant EGCG to the freezing solution. The study was performed on mononuclear cells (MNCs) derived from human umbilical cord blood. After freeze-drying, we tested the viability, number of CD34(+)-presenting cells and ability of the rehydrated hematopoietic stem cells to differentiate into different blood cells in culture. The viability of the MNCs after freeze-drying and rehydration with pure water was 88%-91%. The total number of CD34(+)-presenting cells and the number of colonies did not change significantly when evaluated before freezing, after freeze-thawing, and after freeze-drying (5.4 x 10(4)+/-4.7, 3.49 x 10(4)+/-6 and 6.31 x 10(4)+/-12.27 cells, respectively, and 31+/-25.15, 47+/-45.8 and 23.44+/-13.3 colonies, respectively).

CONCLUSIONS

This is the first report of nucleated cells which have been dried and then rehydrated with double-distilled water remaining viable, and of hematopoietic stem cells retaining their ability to differentiate into different blood cells.