Cryopreservation of hematopoietic and non-hematopoietic stem cells

Key quality parameter comparison of mesenchymal stem cell product cryopreserved in different cryopreservation solutions for clinical applications

Introduction

Cryopreservation is a critical process of cell products for achieving a commercial viability through wide scale adoption. By preserving cells in a lower temperature, cryopreservation enables a product to be off-the-shelf and ready for infusion. An optimized cryopreservation strategy can maintain the viability, phenotype, and potency of thawed mesenchymal stromal/stem cells (MSCs) while being regulatory compliant. We compared three clinical-ready formulations with one research cryopreservation solutions and evaluated key quality parameters of post thawed MSCs.

Method and result

MSCs were cryopreserved at 3, 6, and 9 million cells/mL (M/mL) in four different cryopreservation solutions: NutriFreez (10% dimethyl sulfoxide [DMSO]), Plasmalyte A (PLA)/5% human albumin (HA)/10% DMSO (PHD10), CryoStor CS5 (5% DMSO), and CryoStor CS10 (10% DMSO). To establish post thaw viability, cells were evaluated with no dilution of DMSO (from 3 M/mL), 1:1 dilution (from 6 M/mL), or 1:2 dilution (from 9 M/mL) with PLA/5% HA, to achieve uniform concentration at 3 M/mL. Cell viability was measured at 0-, 2-, 4-, and 6-h post thaw with Trypan blue exclusion and Annexin V/PI staining. Dilution (1:2) of final cell products from 9M/mL resulted in an improvement of cell viability over 6 h but showed a trend of decreased recovery. MSCs cryopreserved in solutions with 10% DMSO displayed comparable viabilities and recoveries up to 6 h after thawing, whereas a decreasing trend was noted in cell viability and recovery with CS5. Cells from all groups exhibited surface marker characteristics of MSCs. We further evaluated cell proliferation after 6-day recovery in culture. While cells cryopreserved in NutriFreez and PHD10 presented similar cell growth post thaw, MSCs cryopreserved in CS5 and CS10 at 3 M/mL and 6M/mL showed 10-fold less proliferative capacity. No significant differences were observed between MSCs cryopreserved in NutriFreez and PHD10 in their potency to inhibit T cell proliferation and improve monocytic phagocytosis.

Conclusion

MSCs can be cryopreserved up to 9 M/mL without losing notable viability and recovery, while exhibiting comparable post thaw potency with NutriFreez and PHD10. These results highlight the importance of key parameter testing for selecting the optimal cryopreservation solution for MSC-based therapy.

Cryopreservation of Human Bone Marrow Derived Mesenchymal Stem Cells at High Concentration Is Feasible

Introduction: For stem cell therapies to be adopted in mainstream health care, robust, reliable, and cost-effective storage and transport processes must be developed. Cryopreservation remains the best current platform for this purpose, and freezing cells at high concentration may have many benefits, including savings on cost and storage space, facilitating transport logistics, and reducing cryoprotectant volume. Cells, such as mesenchymal stem cells (MSCs), are typically frozen at 1 million cells per milliliter (mL), but the aim of this study is to examine the post-thaw attributes of human bone marrow derived MSCs (hBM-MSCs) frozen at 1, 5, and 10 million cells per mL. Methods: Thawed cells were assessed for their morphology, phenotypic marker expression, viability, apoptosis level, metabolic activity, proliferation, and osteogenic and adipogenic differentiation. Results: In this study, for the first time, it is shown that all assessed cells expressed the typical MSC markers (CD90, CD105, and CD73) and lacked the expression of CD14, CD20, CD34, CD45, and HLA-DR. In addition, all cells showed elongated fibroblastic morphology. Post-thaw viability was retained with no difference among the three concentrations. Moreover, no significant statistical difference was observed in the post-thaw apoptosis level, metabolic activity, proliferation, and osteogenic potential, indicating that these cells are amenable to cryopreservation at higher concentrations. Conclusion: The results of this study are of paramount importance to the development of manufacturing processes around a useful freezing concentration when cells are targeted to be stored for at least 6 months.

Vitrification with microinjection of single seminiferous tubules: an efficient cryopreservation approach for limited testicular tissue

RESEARCH QUESTION

Is vitrification with microinjection of single seminiferous tubules an efficient cryopreservation approach for limited testicular tissue?

DESIGN

Testicular tissue from 10 patients with normal spermatogenesis were assigned to a fresh control group or one of the following cryopreservation procedures: uncontrolled slow freezing (USF) using either 1.5 or 2.1 M DMSO combined with sucrose and vitrification with or without single seminiferous tubules microinjection.

RESULTS

Single seminiferous tubules microinjected with cryoprotective agents (CPA) enhanced the penetration of CPA compared with CPA-treated testicular tissue fragments. Microinjection of seminiferous tubules (VLP) maintained tubule structural integrity and germ cell numbers, and reduced spermatogonial apoptosis after cryopreservation compared with vitrification without microinjection (apoptosis rate: VLP versus vitrification without microinjection, P = 0.047; VLP versus USF, P= 0.049). Freezing of single seminiferous tubules using 0.25-ml straws and traditional sperm freezing methods protected sperm retrieval and recovery rates, and the progressive motility index.

CONCLUSIONS

Vitrification of single seminiferous tubule with microinjection of low CPA concentration is an effective approach to testicular cryopreservation.

Phenotypic Characterization of SLex+ and CLA+ CD4+ T Cells

Recent advances in high-resolution multiparametric flow cytometry enable ever deeper analysis of human lymphocyte subsets that require rigorous methodology development and optimization. Here, we detail methods to characterize glycosylated Sialyl-Lewis^X (SLe^X)- or cutaneous lymphocyte-associated antigen (CLA)-expressing CD4+ T cells using two separate multiparametric flow cytometry panels enabling the identification of memory subsets, Th subsets, and expression of diverse activation markers and chemokine receptors. The proposed protocol allows optimal resolution of the measured parameters while minimizing background in a 25-parameter experiment.

For complete details on the use and execution of this protocol, please refer to Colomb et al. (2020).

•

25-parameter panels for glycosylated CD4+ T cell deep immune profiling

•

Characterization of memory subsets and Th profiles on CD4+ T cells

•

Quantification of expression levels of many activation markers and chemokine receptors

•

Optimal resolution and minimal background

Non-toxic freezing media to retain the stem cell reserves in adipose tissues

Subcutaneous adipose tissue is a rich source of stromal vascular fraction (SVF) and adipose-derived stromal/stem cells (ASCs) that are inherently multipotent and exhibit regenerative properties. In current practice, lipoaspirate specimens harvested from liposuction surgeries are routinely discarded as a biohazard waste due to a lack of simple, cost effective, and validated cryopreservation protocols. The aim of this study is to develop a xenoprotein-free cryoprotective agent cocktail that will allow for short-term (up to 6 months) preservation of lipoaspirate tissues suitable for fat grafting and/or stromal/stem cell isolation when stored at achievable temperatures (-20 °C or -80 °C). Lipoaspirates donated by three consenting healthy donors undergoing elective cosmetic liposuction surgeries were suspended in five freezing media (FM1: 10% DMSO and 35% BSA; FM2: 2% DMSO and 43% BSA; FM3: 10% DMSO and 35% lipoaspirate saline; FM4: 2% DMSO and 6% HSA; and FM5: 40% lipoaspirate saline and 10% PVP) all suspended in 1X DMEM/F12 and frozen using commercially available freezers (-20 °C or -80 °C) and stored at least for a 1 month. After 1 month of freezing storage, SVF cells and ASCs were isolated from the frozen-thawed lipoaspirates by digestion with collagenase type I. Cell viability was evaluated by fluorescence microscopy after staining with acridine orange and ethidium bromide. The SVF isolated from lipoaspirates frozen at -80 °C retained comparable cell viability with the tested freezing media (FM2, FM3, FM4) comparable with the conventional DMSO and animal serum media (FM1), whereas the FM5 media resulted in lower viability. In contrast, tissues frozen and stored at -20 °C did not yield live SVF cells after thawing and collagenase digestion. The surface marker expression (CD90, CD29, CD34, CD146, CD31, and CD45) of ASCs from frozen lipoaspirates at -80 °C in different cryoprotectant media were also evaluated and no significant differences were found between the groups. The adipogenic and osteogenic differentiation potential were studied by histochemical staining and gene expression by qRT-PCR. Oil Red O staining for adipogenesis revealed that the CPA media FM1, FM4 and FM5 displayed robust differentiation. Alizarin Red S staining for osteogenesis revealed that FM1 and FM4 media displayed superior differentiation in comparison to other tested media. Measurement of adipogenic and osteogenic gene expression by qRT-PCR provided similar outcomes and indicated that FM4 CPA media comparable with FM1 for adipogenesis and osteogenesis.

Cryopreservation of hematopoietic cells using a pre-constituted, protein-free cryopreservative solution with 5% dimethyl sulfoxide

BACKGROUND AIMS

Adequate cryopreservation techniques are critical to ensure optimal recovery of functional progenitor cells in hematopoietic cell (HC) transplantation, minimize risk of contamination and prevent infusion-related adverse events (irAEs). In this article, we provide graft function and infusion safety results observed by decreasing the concentration of dimethyl sulfoxide (DMSO) in cryopreservative media and by minimizing processor-dependent formulation.

METHODS

Ten HC products, collected after standard mobilization of multiple myeloma patients, were cryopreserved with PRIME-XV FreezIS (FreezIS) and compared with products previously cryopreserved with media formulated in-house to achieve a final DMSO concentration of 10% (Std10) and 5% (Std5). At infusion, HCs were analyzed for recovery of CD34+ cells and viability; irAEs and time to engraftment of neutrophils and platelets were also monitored.

RESULTS

Median CD34+ cell recovery for HC cryopreserved with Std10, Std5 and FreezIS was 38%, 78% and 68%, respectively (P = 0.0002). There were less frequent irAEs with Std5 and FreezIS (10%) compared with Std10 (80%) (P ≤ 0.0001). Median time to neutrophil engraftment was comparable (11 days) for all three groups, while platelet engraftment occurred at a median of 20, 19 and 17 days, respectively (p-values not significant).

CONCLUSIONS

FreezIS, a Good Manufacturing Practice-grade, pre-constituted cryopreservative with low DMSO content, maintains functional viability of the HC product while reducing the incidence of irAEs compared with 10% DMSO solutions. The pre-constituted nature of this agent also decreases processor-dependent handling, hence decreasing the risk of variability and infection.

Cell survival after cryopreservation of dissociated testicular cells from feline species

Testicular cell suspension (TCS) can be cryopreserved for male germ-line preservation and fertility restoration. We aimed to validate a cryopreservation protocol for TCS of domestic cat to be applied in endangered felids species. Testis tissue from adult domestic cats was enzymatically dissociated and spermatogenic cells were enriched. The resulting TCS was diluted in 7.5% or 15% Me2SO based medium. Slow and fast freezing methods were tested. We examined the effects of freezing approaches using two combinations of fluorescent dyes: Calcein-AM with Propidium iodide (C/PI) and SYBR14 with Propidium iodide (S/PI). Ploidy analysis of domestic cat fresh TCS revealed that the majority of testicular cells were haploid cells. Based on microscopic observation, two size populations (12.3 ± 2.3 μm and 20.5 ± 4 μm in diameter) were identified and presumed to be mainly spermatids and spermatocytes, respectively. Both evaluation methods proved higher viability of aggregated cells before and after cryopreservation compared with single cells, and superiority of low concentration of Me2SO (7.5%) in association with slow freezing to preserve viability of testicular cells. However, S/PI resulted in a more precise evaluation compared with the C/PI method. The combination of 7.5% Me2SO-based medium with slow freezing yielded post thaw viability of S/PI labeled aggregated (49.8 ± 20%) and single cells (31.5 ± 8.1%). Comparable results were achieved using testes of a Cheetah and an Asiatic golden cat. In conclusion, TCS from domestic cat can be successfully cryopreserved and has the potential to support fertility restoration of endangered felids species.

Cryoprotectant-Free Freezing of Cells Using Liquid Marbles Filled with Hydrogel

Cryopreservation without cryoprotectant remains a significant challenge for the re-establishment of cell culture after freeze-thaw. Thus, finding an alternative and a simple cryopreservation method is necessary. Liquid marble (LM)-based digital microfluidics is a promising approach for cryoprotectant-free cryopreservation. However, the use of this platform to efficiently preserve samples with low cell density and well-controlled serum concentrations has not been investigated. We addressed this issue by embedding an agarose-containing fetal bovine serum (FBS) inside the LM. A low density of 500 cells/μL of murine 3T3 cells was selected for evaluating the postcryogenic survivability. The effects on the post-thaw cell viability of the concentration of agarose, the amount of FBS inside the agarose, and the volume of the LM were investigated systematically. This paper also presents an analysis on the changes in shape and crack size of post-thawed agarose. The results revealed that the embedded agarose gel serves as a controlled release mechanism of FBS and significantly improves cell viability. Post-thaw recovery sustains major cellular features, such as viability, cell adhesion, and morphology. The platform technology reported here opens up new possibilities to cryopreserve rare biological samples without the toxicity risk of cryoprotectants.

Alternatives to Dimethylsulfoxide for Serum-Free Cryopreservation of Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) have some favorable characteristics like high plasticity, multilineage differentiation potential, and comparably easy handling in vitro, making them of interest for many clinical and therapeutic approaches including cell therapy. For routine applications, these cells have to be stored over a certain period of time without loss of cell vitality and function. An easy way to preserve cells is to store them at temperatures between -80°C and -196°C (liquid nitrogen). To prevent cells from the damage caused by the cryopreservation process and to achieve high cell recovery and vitality, cryoprotectants are used. Typically dimethylsulfoxide, often in combination with serum, is used as a cryoprotectant. However, for clinical approaches, the use of dimethylsulfoxide and serum in patients is problematic for several reasons. Therefore, the cryopreservation of human mesenchymal stem cells for cell therapeutic applications without dimethylsulfoxide and serum demands investigation. In this work, non-toxic alternatives to dimethylsulfoxide such as glycerol or the compatible solutes, proline and ectoin, were analyzed in a serum-free cryomedium with respect to their cryoprotective properties. Different concentrations of the cryoprotectants (1–10% (w/v) ectoin or proline, respectively, or 5–20% (v/v) glycerol) and certain incubation times (0–60 minutes) were investigated with regard to post-thaw cell vitality and cell growth. Our results showed that, in general, cryopreservation with ectoin led to high post-thaw cell survival of up to 72% whereas after cryopreservation with glycerol and proline, the hMSC cells were completely dead (glycerol) or had only poor cell survival (proline, 22%). Moreover, the morphology of the hMSC cells changed to a large and flat phenotype after cryopreservation with proline. These results indicate that glycerol and proline are not suitable for cryopreservation of hMSC. In contrast, ectoin has the potential to replace dimethylsulfoxide as a cryoprotectant in a serum-free cryomedium.

A method for transplantation of human HSCs into zebrafish, to replace humanised murine transplantation models

Haematopoietic stem cell (HSC) transplantation is a critical therapy for haematopoietic malignancies and immune disorders. Incomplete or delayed engraftment of HSCs in the host results in increased risk of infection and morbidity. The mechanisms of HSC engraftment are poorly understood and understanding these processes will increase transplantation success on many levels. Current animal models are immunocompromised 'humanised' mice transplanted with human HSCs. Harmful procedures include genetic manipulations and irradiation to ablate the mouse immune system, and opaque mouse tissues make visualisation of the early steps of HSC engraftment impossible. There is a need for new models to offer alternatives to humanised mice in the study of HSC transplantation. Here we described a detailed method for transplantation of human HSCs into zebrafish, before the onset of adaptive immunity. Human HSCs were purified from whole blood by enrichment of the CD34 cell population using a positive magnetic selection and further purified using an anti-CD34 antibody and cell sorting. Sorted CD34 cells were transplanted into the blood stream of 52 hour old zebrafish larvae. Human HSCs home into the zebrafish haematopoietic niche, where they engage with endothelial cells and undergo cell division. Our model offers the opportunities to image in vivo human HSC engraftment in a transparent organism, without the myeloablative strategies used in mice, and provides a unique system to understand the dynamic process of engraftment and replace current murine models. This technique can be applied to current engraftment protocols to validate the viability and efficiency of cryofrozen HSC grafts. This humanised zebrafish model will be instrumental to develop the 3Rs values in stem cell transplantation research and our detailed protocol will increase the chances of uptake of this zebrafish model by the mouse community.

The Relative Functionality of Freshly Isolated and Cryopreserved Human Adipose-Derived Stromal/Stem Cells

The capability of multipotent mesenchymal stem cells to maintain cell viability, phenotype and differentiation ability upon thawing is critical if they are to be banked and used for future therapeutic purposes. In the present study, we examined the effect of 9-10 months of cryostorage on the morphology, immunophenotype, colony-forming unit (CFU) and differentiation capacity of fresh and cryopreserved human adipose-derived stromal/stem cells (ASCs) from the same donors. Cryopreservation did not reduce the CFU frequency and the expression levels of CD29, CD73, CD90 and CD105 remained unchanged with the exception of CD34 and CD45; however, the differentiation capacity of cryopreserved ASCs relative to fresh cells was significantly reduced. While our findings suggest that future studies are warranted to improve cryopreservation methods and agents, cryopreserved ASCs retain sufficient features to ensure their practical utility for both research and clinical applications.

Cryopreservation of Human Mesenchymal Stem Cells for Clinical Applications: Current Methods and Challenges

Mesenchymal stem cells (MSCs) hold many advantages over embryonic stem cells (ESCs) and other somatic cells in clinical applications. MSCs are multipotent cells with strong immunosuppressive properties. They can be harvested from various locations in the human body (e.g., bone marrow and adipose tissues). Cryopreservation represents an efficient method for the preservation and pooling of MSCs, to obtain the cell counts required for clinical applications, such as cell-based therapies and regenerative medicine. Upon cryopreservation, it is important to preserve MSCs functional properties including immunomodulatory properties and multilineage differentiation ability. Further, a biosafety evaluation of cryopreserved MSCs is essential prior to their clinical applications. However, the existing cryopreservation methods for MSCs are associated with notable limitations, leading to a need for new or improved methods to be established for a more efficient application of cryopreserved MSCs in stem cell-based therapies. We review the important parameters for cryopreservation of MSCs and the existing cryopreservation methods for MSCs. Further, we also discuss the challenges to be addressed in order to preserve MSCs effectively for clinical applications.

Preserving human cells for regenerative, reproductive, and transfusion medicine

Cell cryopreservation maintains cellular life at sub-zero temperatures by slowing down biochemical processes. Various cell types are routinely cryopreserved in modern reproductive, regenerative, and transfusion medicine. Current cell cryopreservation methods involve freezing (slow/rapid) or vitrifying cells in the presence of a cryoprotective agent (CPA). Although these methods are clinically utilized, cryo-injury due to ice crystals, osmotic shock, and CPA toxicity cause loss of cell viability and function. Recent approaches using minimum volume vitrification provide alternatives to the conventional cryopreservation methods. Minimum volume vitrification provides ultra-high cooling and rewarming rates that enable preserving cells without ice crystal formation. Herein, we review recent advances in cell cryopreservation technology and provide examples of techniques that are utilized in oocyte, stem cell, and red blood cell cryopreservation.

A nano-stripe based sensor for temperature measurement at the submicrometer and nano scales

Submicrometer dual-stripe temperature sensors made from a single piece of metal thin film (e.g., Pd) are developed. With the narrowest sensor being 900 nm in width, they show sensitivity of 1-2 μV/K for the full range of 10-300 K. The results confirm the size effect in Seebeck coefficient previously observed in microstripe sensors of the same device configuration.

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.

Bone marrow processing for transplantation using Cobe Spectra cell separator

Concentration of bone marrow aspirates is an important prerequisite prior to infusion of ABO incompatible allogeneic marrow and prior to cryopreservation and storage of autologous marrow. In this paper we present our experience in processing 15 harvested bone marrow for ABO incompatible allogeneic and autologous bone marrow (BM) transplantation using Cobe Spectra® cell separator. BM processing resulted in the median recovery of 91.5% CD34+ cells, erythrocyte depletion of 91% and volume reduction of 81%. BM processing using cell separator is safe and effective technique providing high rate of erythrocyte depletion and volume reduction, and acceptable recovery of the CD34+ cells.

Bioprocessing of cryopreservation for large-scale banking of human pluripotent stem cells

Human pluripotent stem cell (hPSC)-derived cell therapy requires production of therapeutic cells in large quantity, which starts from thawing the cryopreserved cells from a working cell bank or a master cell bank. An optimal cryopreservation and thaw process determines the efficiency of hPSC expansion and plays a significant role in the subsequent lineage-specific differentiation. However, cryopreservation in hPSC bioprocessing has been a challenge due to the unique growth requirements of hPSC, the sensitivity to cryoinjury, and the unscalable cryopreservation procedures commonly used in the laboratory. Tremendous progress has been made to identify the regulatory pathways regulating hPSC responses during cryopreservation and the development of small molecule interventions that effectively improves the efficiency of cryopreservation. The adaption of these methods in current good manufacturing practices (cGMP)-compliant cryopreservation processes not only improves cell survival, but also their therapeutic potency. This review summarizes the advances in these areas and discusses the technical requirements in the development of cGMP-compliant hPSC cryopreservation process.

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.

Transfusion issues in cancer patients

Allogeneic blood transfusion (ABT) therapy plays a major role in the case of patients with cancer. Packed red blood cells (PRBC) are given for increased oxygen-carrying capacity, platelets concentrates (PC) and fresh frozen plasma (FFP) for the cessation and prevention of bleeding due to thrombocytopenia and other defects of hemostasis associated with neoplasia. All these blood components can induce complications and/or adverse reactions in cancer patients including transfusion-associated graft versus host disease (TA-GVHD), transfusion transmitted diseases, alloimmunization to blood cell antigens, pulmonary decompensation, immunomodulation. Therefore, specific modifications such as leukocyte-reduction and irradiation of the blood components to be transfused in cancer patients should be introduced to reduce the risk of these complications. Patients undergoing hematopoietic progenitor cell (HPC) transplantation are a unique group and present complex concerns related to transfusion, including major and minor ABO incompatibility and chimeric blood cells. Therefore, transfusion for patients undergoing treatment with cellular therapies requires careful blood component selection. The process of HPC infusion itself carries many risks including DMSO toxicity and hemolytic reactions. In all areas of transfusion therapy, new advances such as pathogen inactivation and synthetic alternatives to blood components should help to increase the safety and tolerance of transfusion in cancer patients.

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.

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.

An efficient, economical slow-freezing method for large-scale human embryonic stem cell banking

Human embryonic stem cells (hESCs) are one of the most interesting cell types for tissue engineering, cell therapy, basic scientific research, and drug screening. Fast advancement in these areas requires the availability of large amounts of safe and well-characterized hESCs from hESC banks. Therefore, optimized freezing protocols, allowing the cryopreservation of large amounts of hESC without direct contact with liquid nitrogen, need to be established. In this study, 6 different cryoprotector combinations [dimethylsulfoxide (DMSO), ethylene glycol, and hydroxyethylstarch (HES)] combined with 2 different application methods were screened with the VUB01 cell line, to establish a new slow-freezing protocol with high recovery rates and a good expansion capacity. Our best conditions were confirmed in 4 other hESC lines: H1, H9, 181, and UGent2. To our knowledge, this is the first time that HES is evaluated as a cryoprotector for hESCs. The use of 5% DMSO+5% HES combined with a new detachment protocol leads to efficient hESC cryopreservation. This protocol involves treating the hESC colonies with cell dissociation solution, a mild dissociation solution uncommonly used for hESC culture. A recovery ratio ranging from 45.5% to 168.2% was obtained, and these were significantly different from the other tested conditions (Student's t-test, P<0.05). The cryopreserved hESCs were morphologically comparable to control cells, exhibited a good expansion profile, were positive for pluripotent expression markers, and could still differentiate into the 3 germ layers. This new protocol allows efficient and economical hESC cryopreservation, ideal for hESC banking.

A validation study of new cryopreservation bags for implementation in a blood and marrow transplant laboratory

BACKGROUND

A new cryopreservation bag for hematopoietic cell transplantation requires validation as a safe alternative to the bag currently being used in the laboratory.

STUDY DESIGN AND METHODS

The new bag was validated using both laboratory and clinical criteria. Laboratory validation proceeded using paired samples of mononuclear cells processed using standard procedures. Cells cryopreserved in the new and old bags were compared for viability, cell counts, CD34 enumeration, colony-forming unit assays, and bag integrity. After completion of laboratory investigations, engraftment with the new bags was followed and compared to historical engraftment using the old bags.

RESULTS

There were no significant differences between the old and new bags detected using laboratory studies. Bag integrity was equivalent. The validation data suggested impaired cell function after cryopreservation in the new bags, but there were no significant differences in engraftment potential using either material. Days to engraftment was longer using the new bags, but statistical analysis revealed an association with CD34 dose and not with cryopreservation bag type.

CONCLUSION

The new bags were noninferior to the old bags. A change in cryopreservation bag type may appear to affect cell function and potentially affect engraftment. Multiple analyses may be needed to understand the effect of cell processing changes.

Effect of dimethyl sulfoxide (DMSO) on cryopreservation of porcine mesenchymal stem cells (pMSCs)

Dimethyl sulfoxide (DMSO), a commonly used cryoprotectant in cryopreservation procedures, is detrimental to viability of cells. In this view point, a comparative study was carried out to evaluate the effect of DMSO on porcine mesenchymal stem cells (pMSCs). We compared the viability, colony forming unit-fibroblast (CFU-F) assay, expression of Bak and Bcl2 genes, Bcl2 protein antigen, and CD90 in pMSCs cryopreserved with 5%, 10%, and 20% DMSO. pMSCs isolated from bone marrow were characterized by alkaline phosphatase activity and the expression of transcription factors, such as Oct 3/4, Nanog, and Sox2. The cells were then cryopreserved by cooling at a rate of -1°C/min in a programmable freezer and stored in liquid nitrogen. The results of survival of pMSCs cryopreserved at 5% DMSO were comparable to control group (fresh pMSCs). The survival and the number of colonies formed in cryopreserved pMSCs were inversely proportional to the concentration of DMSO. The number of colonies formed in pMSCs cryopreserved with all concentrations of DMSO was significantly (p < 0.05) lower than the control group. An increased tendency for Bak and Bcl2 gene expression was noticed in cryopreserved pMSCs at 3 h postthawing compared to control group. There was a close resemblance in higher level of expression of CD90 between control and cryopreserved pMSCs. Because there was no considerable difference in the results of pMSCs cryopreserved at 5% and 10% DMSO, this study strongly suggests the use of 5% DMSO in cryopreservation of pMSCs as an alternative to conventional 10% DMSO.

Management of fertility preservation in prepubertal patients: 5 years' experience at the Catholic University of Louvain

BACKGROUND Since prepubertal boys cannot benefit from sperm banking, a potential alternative strategy for fertility preservation involves immature testicular tissue (ITT) banking aimed at preservation of spermatogonial stem cells. Survival of spermatogonia has been demonstrated after ITT freezing, which is considered ethically acceptable. We report the results of a pilot program set up for fertility preservation in prepubertal boys. METHODS All boys undergoing ITT cryobanking from May 2005 were identified from our clinical register. Data were collected from medical files. RESULTS Testicular tissue was retrieved from 52 prepubertal patients under 12 years of age and 10 peripubertal patients aged between 12 and 16 years, in whom no spermatozoa were identified in testicular biopsies. Malignant disease accounted for 80.6% of cases; the remaining patients suffered from benign disorders requiring gonadotoxic treatments. Mean ages, Tanner stages and occurrence rates of urogenital pathology were 6.43 ± 3.32 and 14 ± 1.23 years, I and I-IV, and 13.5 and 20% for pre- and peripubertal patients, respectively. Mean volumes of removed tissue were 20.1 ± 8.6 and 42.4 ± 15.6 mm(3) for pre- and peripubertal patients, respectively. No complications occurred during or after tissue retrieval and 93.5% of referred patients accepted ITT storage. The presence of spermatogonia, and thus the potential for later tissue use, was established in all of these patients. CONCLUSIONS The majority of cryopreserved samples showed reproductive potential. Storage was accepted by most parents. All parents and children considered this fertility preservation strategy a positive approach.

Comparison of biological features of C3A and L-02 hepatocytes undergoing subzero nonfreezing storage for use in bioartificial liver support system

AIM: To evaluate the biological features of C3A and L-02 hepatocytes undergoing subzero nonfreezing storage in University of Wisconsin (UW) solution for use in bioartificial liver support systems (BALSS).

METHODS: C3A and L-02 hepatocytes were cultured, digested with 0.25% trypsin, prepared into a cell suspension, adjusted to a density of 2 × 10⁶/mL, and stored in UW solution. After 0, 24, 48 and 72 h of hypothermic storage (-0.8 ℃), cell viability and apoptosis, LDH and AST release, and urea synthesis and albumin secretion were measured.

RESULTS: Hypothermic storage decreased cell viability, urea synthesis and albumin secretion, but increased apoptosis and AST and LDH release in both C3A and L-02 hepatocytes. After 72 h of hypothermic storage, C3A hepatocytes had higher viability (86.49% ± 2.80% vs 70.17% ± 2.82%, P < 0.001) and albumin secretion (2 060 mg/L ± 220 mg/L vs 9.04 mg/L ± 0.53 mg/L, P < 0.001) but lower apoptosis rate (1.26% ± 0.84% vs 5.73% ± 1.68%, P < 0.001), LDH and AST release (4.61 U/L ± 0.43 U/L vs 6.22 U/L ± 0.65 U/L, P < 0.001; 86.10 U/L ± 11.10 U/L vs 113.88 U/L ± 5.64 U/L, P < 0.001) and urea synthesis (1.01 mmol/L ± 0.14 mmol/L vs 0.60 mmol/L ± 0.06 mmol/L, P < 0.001) than L-02 hepatocytes.

CONCLUSION: Both C3A and L-02 hepatocytes could be stored for more than 72 h in UW solution. C3A hepatocytes are more probably suitable for BALSS for management of liver failure with hepatic encephalopathy, while L-02 hepatocytes are more probably suitable for BALSS for management of liver failure with low albuminemia.

Bioequivalence comparison of a new freezing bag (CryoMACS(®)) with the Cryocyte(®) freezing bag for cryogenic storage of human hematopoietic progenitor cells

BACKGROUND AIMS

We investigated two different plastic freezing bags, namely the most recently U.S. Food and Drug Administration (FDA)-approved CryoMACS(®) freezing bag (200-074-402) from Miltenyi Biotec and the familiar Cryocyte(®) freezing bag (R4R9955) from (Baxter Healthcare, Deerfield, IL, United States) for the cryogenic storage of human hematopoietic progenitor cells (HPC).

METHODS

The study material consisted of 12 frozen HPC pairs (= 24 transplant units) that were no longer needed for autologous treatment of patients. After thawing, one unit of a pair was transferred into the Miltenyi (M) bag; the other unit remained in the original Baxter (B) bag. After refreezing both units, all units were stored again under cryogenic conditions either partially immersed in liquid nitrogen (n = 22) or in the vapor phase over liquid nitrogen, n = 2, <-170°) before thawing.

RESULTS

The correlation coefficients (r) between the results obtained from the two bag types were high for white blood cells (WBC) content (r = 0.98), mononuclear cells (MNC) (r = 0.97), lymphocytes (r = 0.98), monocytes (r = 0.96), membrane integrity (r = 0.93), concentration of 'free' hemoglobin (r = 0.97) and hemolysis rate (r = 0.95). With regard to clonogenicity, there were no significant differences (Student's paired t-test) for the three parameters investigated [i.e. total number of colonies, including the numbers of burst-forming units-erythroid (BFU-E) and colony-forming units-granulocyte-macrophage (CFU-GM) colonies, respectively).

CONCLUSIONS

The CryoMACS freezing bag 200-074-402 is bioequivalent to the Cryocyte freezing container R4R9955. An advantageous feature of the CryoMACS is that its double-sterile wrapping provides additional safety regarding potential cross-contamination during cryogenic storage.

Evaluation of polyvinylpyrrolidone as a cryoprotectant for adipose tissue-derived adult stem cells

The objective of this study was to test the hypothesis that human adipose tissue-derived adult stem cells (ASCs) can be effectively cryopreserved and stored in liquid nitrogen using a freezing medium containing a high-molecular-weight polymer, polyvinylpyrrolidone (PVP), as the cryoprotective agent (CPA) instead of dimethylsulfoxide (DMSO). To this end we investigated the postfreeze/thaw viability and apoptotic behavior of passage 1 ASCs cryopreserved in 15 different media: (i) the traditional media containing Dulbecco's modified Eagle's medium (DMEM) with 80% fetal calf serum (FCS) and 10% DMSO; (ii) DMEM with 80% human serum (HS) and 10% DMSO; (iii) DMEM with various concentrations (1%, 5%, 10%, 20%, and 40%) of PVP as the sole CPA; (iv) DMEM with PVP (5%, 10%, and 20%) and HS (10%); (v) DMEM with PVP (5%, 10%, and 20%) and FCS (10%); and (vi) DMEM with PVP (10%) and FCS (40% and 80%). Approximately 1 mL (10(6) cells/mL) of passage 1 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 six-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 significantly increases the fraction of apoptotic and/or necrotic ASCs. However, the percentage of viable cells obtained with 10% PVP and DMEM was comparable with that obtained in freezing media with DMSO and serum (HS or FCS), that is, approximately 70% + or - 8% and approximately 83% + or - 8%, respectively. Slightly enhanced cell viability was observed with the addition of serum (either HS or FCS) to the freezing media containing PVP as the CPA. Adipogenic and osteogenic differentiation behaviors of the frozen thawed cells were also assessed using histochemical staining and optical density measurements and the expression of adipogenic-associated genes was analyzed using reverse transcription-polymerase chain reaction. Our results suggest that after thawing, ASC viability and adipogenic and osteogenic differentiation abilities can be maintained even when ASCs are frozen in the absence of serum but with 10% PVP in DMEM.

Deleterious effects of freezing on osteogenic differentiation of human adipose-derived stromal cells in vitro and in vivo

Human adipose-derived stromal cells (hASCs) represent a multipotent stromal cell type with a proven capacity to undergo osteogenic differentiation. Many hurdles exist, however, between current knowledge of hASC osteogenesis and their potential future use in skeletal tissue regeneration. The impact of frozen storage on hASC osteogenic differentiation, for example, has not been studied in detail. To examine the effects of frozen storage, hASCs were harvested from lipoaspirate and either maintained in standard culture conditions or frozen for 2 weeks under standard conditions (90% fetal bovine serum, 10% dimethyl sulfoxide). Next, in vitro parameters of cell morphology (surface electron microscopy [EM]), cell viability and growth (trypan blue; bromodeoxyuridine incorporation), osteogenic differentiation (alkaline phosphatase, alizarin red, and quantitative real-time (RT)-polymerase chain reaction), and adipogenic differentiation (Oil red O staining and quantitative RT-polymerase chain reaction) were performed. Finally, in vivo bone formation was assessed using a critical-sized cranial defect in athymic mice, utilizing a hydroxyapatite (HA)-poly(lactic-co-glycolic acid) scaffold for ASC delivery. Healing was assessed by serial microcomputed tomography scans and histology. Freshly derived ASCs differed significantly from freeze-thaw ASCs in all markers examined. Surface EM showed distinct differences in cellular morphology. Proliferation, and osteogenic and adipogenic differentiation were all significantly hampered by the freeze-thaw process in vitro (*P < 0.01). In vivo, near complete healing was observed among calvarial defects engrafted with fresh hASCs. This was in comparison to groups engrafted with freeze-thaw hASCs that showed little healing (*P < 0.01). Finally, recombinant insulin-like growth factor 1 or recombinant bone morphogenetic protein 4 was observed to increase or rescue in vitro osteogenic differentiation among frozen hASCs (*P < 0.01). The freezing of ASCs for storage significantly impacts their biology, both in vitro and in vivo. The ability of ASCs to successfully undergo osteogenic differentiation after freeze-thaw is substantively muted, both in vitro and in vivo. The use of recombinant proteins, however, may be used to mitigate the deleterious effects of the freeze-thaw process.

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.

Hypothermic storage of hepatocytes used for bioartificial liver support system: current status and recent advances

The problem that high-quality hepatocytes are difficult to obtain restricts the use of bioartificial liver support system (BLASS) in clinical practice. Finding an effective way to preserve hepatocytes and constructing a "ready-to-use" hepatocyte bank would efficiently promote the development of the BLASS. Nowadays, the methods for hypothermic storage of hepatocytes could be classified into two types: conventional hypothermic storage at 4 °C or subzero nonfreezing storage, and cryopreservation at -80 °C or -196 °C. Each type of hypothermic storage method has its advantages and disadvantages. Many factors may affect the effect of hypothermic storage (cryopreservation), such as storage solution and cryoprotective agent. Although the precise mechanism underlying the death of hepatocytes during hypothermic storage is not well understood, numerous studies have indicated that apoptosis plays an important role in hypothermic storage injury.

Subzero nonfreezing storage of C3A hepatocytes for use in bioartificial liver support systems

AIM: To investigate whether subzero nonfreezing storage (-0.8 °C) is superior to conventional cold storage in preservation of C3A hepatocytes for use in bioartificial liver support systems.

METHODS: C3A hepatocytes suspended in University of Wisconsin (UW) solution were divided into three groups: subzero nonfreezing group (-0.8 °C), zero nonfreezing group (0 °C) and control group (4 °C). After 24, 48 and 72 hours of hypothermic storage, cell viability and apoptosis were detected by flow cytometry; intracellular adenosine triphosphate (ATP) content, lactate dehydrogenase (LDH) release, lactic acid production, urea synthesis and albumin secretion were determined; and cell morphological changes were observed.

RESULTS: Compared to the zero nonfreezing group and the control group, after 72 hours of hypothermic storage, the percentage of viable C3A hepatocytes was significantly higher (86.49% ± 2.80% vs 81.50% ± 2.83% and 77.83% ± 3.40%, respectively; both P < 0.05), and cell apoptosis rate was significantly lower (1.26% ± 0.84% vs 5.34% ± 1.20% and 9.16% ± 1.99%, respectively; both P < 0.05) in the subzero nonfreezing group. Lactic acid and LDH production was more significantly suppressed (lactic acid: 10.38 μg/10⁶ cells ± 1.40 μg/10⁶ cells vs 12.02 μg/10⁶ cells ± 1.64 μg/106 cells and 17.41 μg/10⁶ cells ± 2.40 μg/10⁶ cells; LDH: 80.10 U/L ± 11.10 U/L vs 120.04 U/L ± 14.32 U/L and 148.98 U/L ± 15.37 U/L, respectively; all P < 0.05), and the ability of hepatocytes to synthesize urea and secrete albumin was better maintained in the subzero nonfreezing group (both P < 0.05). Moreover, cells in the subzero nonfreezing storage group had lower death rate and better cellular morphology. A burr-like structure around the cell membrane and an intracellular vacuole-like structure were found in cells in the zero nonfreezing group and the control group, but not in the subzero nonfreezing group.

CONCLUSION: Subzero nonfreezing storage (-0.8 °C) of hepatocytes to construct a "ready-to-use" hepatocyte bank like the "blood bank" will efficiently promote the development of bioartificial liver support systems.

Long-term storage of peripheral blood stem cells frozen and stored with a conventional liquid nitrogen technique compared with cells frozen and stored in a mechanical freezer

BACKGROUND

Cryopreservation of hematopoietic progenitor cells using liquid nitrogen and controlled-rate freezing requires complex equipment and highly trained staff and is expensive. We compared the liquid nitrogen method with methods using a combination of dimethyl sulfoxide (DMSO) and hydroxyethyl starch (HES) for cryopreservation followed by storage in mechanical freezers.

STUDY DESIGN AND METHODS

Peripheral blood stem cells (PBSCs) were collected from normal donors by apheresis and allocated to one of four preservation and storage conditions: 1) 10% DMSO with freezing in liquid nitrogen and storage in liquid nitrogen, 2) 5% DMSO and 6% HES with freezing and storage in a -80 degrees C mechanical freezer, 3) 5% DMSO and 6% HES with freezing in a -80 degrees C mechanical freezer and storage in a -135 degrees C mechanical freezer, or 4) 5% DMSO and 6% HES with freezing and storage both in a 135 degrees C mechanical freezer. Cells were stored for 5 years during which total nucleated cells (TNCs), cell viability, CD34+ cell content, and colony-forming unit-granulocyte-macrophage content were determined.

RESULTS

There were some significant differences in the variables measured during freezing and the 5 years of storage compared to the values before freezing and storage; however, these differences were not consistent and do not favor one protocol over the others. Samples stored for 24 hours before cryopreservation showed a significant decrease in TNCs, but no other significant changes during the 5 years.

CONCLUSION

In vitro measurements indicate that PBSCs can be successfully frozen and stored using a combination of DMSO and HES providing smaller amounts of DMSO and allowing simplified freezing and storage conditions.

Emerging concepts in biomarker discovery; the US-Japan Workshop on Immunological Molecular Markers in Oncology

Supported by the Office of International Affairs, National Cancer Institute (NCI), the "US-Japan Workshop on Immunological Biomarkers in Oncology" was held in March 2009. The workshop was related to a task force launched by the International Society for the Biological Therapy of Cancer (iSBTc) and the United States Food and Drug Administration (FDA) to identify strategies for biomarker discovery and validation in the field of biotherapy. The effort will culminate on October 28th 2009 in the "iSBTc-FDA-NCI Workshop on Prognostic and Predictive Immunologic Biomarkers in Cancer", which will be held in Washington DC in association with the Annual Meeting. The purposes of the US-Japan workshop were a) to discuss novel approaches to enhance the discovery of predictive and/or prognostic markers in cancer immunotherapy; b) to define the state of the science in biomarker discovery and validation. The participation of Japanese and US scientists provided the opportunity to identify shared or discordant themes across the distinct immune genetic background and the diverse prevalence of disease between the two Nations. Converging concepts were identified: enhanced knowledge of interferon-related pathways was found to be central to the understanding of immune-mediated tissue-specific destruction (TSD) of which tumor rejection is a representative facet. Although the expression of interferon-stimulated genes (ISGs) likely mediates the inflammatory process leading to tumor rejection, it is insufficient by itself and the associated mechanisms need to be identified. It is likely that adaptive immune responses play a broader role in tumor rejection than those strictly related to their antigen-specificity; likely, their primary role is to trigger an acute and tissue-specific inflammatory response at the tumor site that leads to rejection upon recruitment of additional innate and adaptive immune mechanisms. Other candidate systemic and/or tissue-specific biomarkers were recognized that might be added to the list of known entities applicable in immunotherapy trials. The need for a systematic approach to biomarker discovery that takes advantage of powerful high-throughput technologies was recognized; it was clear from the current state of the science that immunotherapy is still in a discovery phase and only a few of the current biomarkers warrant extensive validation. It was, finally, clear that, while current technologies have almost limitless potential, inadequate study design, limited standardization and cross-validation among laboratories and suboptimal comparability of data remain major road blocks. The institution of an interactive consortium for high throughput molecular monitoring of clinical trials with voluntary participation might provide cost-effective solutions.

Characteristics and function of cryopreserved bone marrow-derived endothelial progenitor cells

BACKGROUND

This study examined ex vivo expansion of bone marrow-derived endothelial progenitor cell (EPC) from cryopreserved bone marrow-derived mononuclear cells, and evaluated proliferation and migration function of the cryopreserved EPC (Cryo-EPC).

METHODS

Bone marrow samples were taken from swine iliac bone (n = 6). Isolated bone marrow-derived mononuclear cells were cultured or cryopreserved at -80 degrees C for 2 to 3 months. After cell culture for 4 days, attached cells, EPCs with or without cryopreservation, were collected. Direct fluorescent staining by acetylated low-density lipoprotein, isolectin B4, and 4',6-diamidino-2-phenylindole were performed to confirm the attached cells as EPC. Endothelial progenitor cell proliferation by vascular endothelial growth factor was evaluated by the tetrazolium method. Endothelial progenitor cell migration in response to stromal-derived factor-1alpha was also evaluated by using a Boyden chamber assay.

RESULTS

The percentage of cells positively stained by direct fluorescent staining by acetylated low-density lipoprotein and isolectin B4 was similar between fresh and Cryo-EPC (EPC = 96.0 +/- 0.42 versus Cryo-EPC = 95.2 +/- 1.2; p = 0.21). Vascular endothelial growth factor increased proliferation activity in fresh and Cryo-EPC (p < 0.01). Stromal-derived factor-1alpha increased migration activity in fresh and Cryo-EPC (p < 0.01). There was no difference in proliferation and migration activity between fresh and Cryo-EPC.

CONCLUSIONS

Ex vivo expansion by cell culture was a useful method for collection of bone marrow-derived EPC from cryopreserved mononuclear cells. Proliferation and migration function of EPC is preserved after cryopreservation.

Numerical characterization of diffusion-based extraction in cell-laden flow through a microfluidic channel

Cells are routinely cryopreserved in dimethyl sulfoxide (DMSO), a cryoprotective agent, for medical applications. Infusion of a DMSO-laden cell suspension results in adverse patient reactions, but current DMSO extraction processes result in significant cell losses. A diffusion-based numerical model was employed to characterize DMSO extraction in fully developed channel flow containing a wash stream flowing parallel to a DMSO-laden cell suspension. DMSO was allowed to diffuse across cell membranes as well as across the channel depth. A variety of cases were considered with the ultimate goal of characterizing the optimal geometry and flow conditions to process clinical volumes of cell suspension in a reasonable time (2-3 ml/min). The results were dependent on four dimensionless parameters: depth fraction of the DMSO-laden stream, Peclet number, cell volume fraction in the DMSO-laden stream, and cell membrane permeability parameter. Smaller depth fractions led to faster DMSO extraction but channel widths that were not practical. Higher Peclet numbers led to longer channels but smaller widths. For the Peclet values and channel depths considered (>or=500 microm) and appropriate permeability values, diffusion across cell membranes was significantly faster than diffusion across the channel depth. Cell volume fraction influenced the cross-stream diffusion of DMSO by limiting the fluid volume fraction available in the contaminant stream but did not play a significant role in channel geometry or operating requirements. The model was validated against preliminary experiments in which DMSO was extracted from suspensions of B-lymphoblast cells. The model results suggest that a channel device with practical dimensions can remove a sufficient level of contaminant within a mesoscale volume of cells in the required time.