Use of hollow fiber membrane filtration for the removal of DMSO from platelet concentrates

Cryopreserved platelets washed with a dialysis machine for dimethyl sulphoxide removal

BACKGROUND AND OBJECTIVES

Cryopreserved platelets (cPLTs) can be stored for years and are mainly used in military settings. However, the commonly used cryoprotectant dimethyl sulphoxide (DMSO) has toxic side effects when utilized in high quantities. We developed a novel method to aseptically remove DMSO from thawed cPLTs by dialysis.

MATERIALS AND METHODS

One unit of platelets (N = 6) was mixed with 75 mL of 27% DMSO within 4 days after collection and stored at -80°C for 1 week. The platelet counts, platelet distribution width, mean platelet volume (MPV), platelet activity, platelet release, platelet aggregation, platelet metabolism indicators and platelet ultrastructural features (determined by electron microscopy) of the samples at the pre-freeze, post-thaw wash (post-TW) and 24 h post-thaw wash (24-PTW) stages were determined and compared.

RESULTS

The DMSO clearance rate from the post-TW platelets was 95.56 ± 1.3%, and the platelet recovery rate after washing was 74.66 ± 6.34%. The total count, activity, release factors, aggregation and thrombolytic ability of the post-TW platelets were lower, whereas the MPV and apoptosis rates were higher compared with those of the pre-freeze platelets. The lactic acid, glucose and potassium ions released from the platelets during washing were filtered away by the dialyser, which significantly reduced their concentration. However, 24-PTW platelets were metabolically active, resulting in a decrease in pH and glucose content and an increase in lactic acid content. The level of potassium ions remained low after 24 h of storage and washing. The pre-freeze platelets maintained their normal disc shape and exhibited an open canalicular system (OCS) and a dense tubular system. The cPLTs appeared irregular after washing, with protruding pseudopodia and an extensive OCS, which increased the release of their contents.

CONCLUSION

We developed a novel dialysis method to effectively remove DMSO from cPLTs under aseptic conditions and maintain platelet quality. The clinical efficacy of our method remains to be determined. However, the function of the platelets declined 24 h after washing, making them unsuitable for transfusion.

A novel method for processing adipose-derived stromal stem cells using a closed cell washing concentration device with a hollow fiber membrane module

Cell-assisted lipotransfer (CAL) is an advanced lipoinjection method that uses autologous lipotransfer with addition of a stromal vascular fraction (SVF) containing adipose-derived stromal stem cells (ASCs). The CAL procedure of manual isolation of cells from fat requires cell processing to be performed in clean environment. To isolate cells from fat without the need for a cell processing center, such as in a procedure in an operation theater, we developed a novel method for processing SVF using a closed cell washing concentration device (CCD) with a hollow fiber membrane module. The CCD consists of a sterilized closed circuit, bags and hollow fiber, semi-automatic device and the device allows removal of >99.97% of collagenase from SVF while maintaining sterility. The number of nucleated cells, ASCs and viability in SVF processed by this method were equivalent to those in SVF processed using conventional manual isolation. Our results suggest that the CCD system is as reliable as manual isolation and may also be useful for CAL. This approach will help in the development of regenerative medicine at clinics without a cell processing center.

Dimethyl sulfoxide: a central player since the dawn of cryobiology, is efficacy balanced by toxicity?

Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice for most animal cell systems since the early history of cryopreservation. It has been used for decades in many thousands of cell transplants. These treatments would not have taken place without suitable sources of DMSO that enabled stable and safe storage of bone marrow and blood cells until needed for transfusion. Nevertheless, its effects on cell biology and apparent toxicity in patients have been an ongoing topic of debate, driving the search for less cytotoxic cryoprotectants. This review seeks to place the toxicity of DMSO in context of its effectiveness. It will also consider means of reducing its toxic effects, the alternatives to its use and their readiness for active use in clinical settings.

Traditional and emerging technologies for washing and volume reducing blood products

Millions of blood components including red blood cells, platelets, and granulocytes are transfused each year in the United States. The transfusion of these blood products may be associated with adverse clinical outcomes in some patients due to residual proteins and other contaminants that accumulate in blood units during processing and storage. Blood products are, therefore, often washed in normal saline or other media to remove the contaminants and improve the quality of blood cells before transfusion. While there are numerous methods for washing and volume reducing blood components, a vast majority utilize centrifugation-based processing, such as manual centrifugation, open and closed cell processing systems, and cell salvage/autotransfusion devices. Although these technologies are widely employed with a relatively low risk to the average patient, there is evidence that centrifugation-based processing may be inadequate when transfusing to immunocompromised patients, neonatal and infant patients, or patients susceptible to transfusion-related allergic reactions. Cell separation and volume reduction techniques that employ centrifugation have been shown to damage blood cells, contributing to these adverse outcomes. The limitations and disadvantages of centrifugation-based processing have spurred the development of novel centrifugation-free methods for washing and volume reducing blood components, thereby causing significantly less damage to the cells. Some of these emerging technologies are already transforming niche applications, poised to enter mainstream blood cell processing in the not too distant future.

Fatigue damage to pig erythrocytes during repeated swelling and shrinkage

During the removal of cryoprotectants from cryopreserved-thawed blood with the dialysis-based or dilution-filtration method, due to the change in the extracellular osmolality, erythrocytes usually undergo repeated swelling and shrinkage. However, the erythrocyte fatigue damage induced by this repeated volume change has not yet been studied. In this work, by successively loading hypotonic and hypertonic solutions, we mimicked the repeated swelling and shrinkage of pig erythrocytes and then examined the effect of the number of cycle loops on the steady-state volume and the mortality of the pig erythrocytes. The results suggest that because of cell leakage in the swelling process, the steady-state volume of the pig erythrocytes after one cycle is smaller than the volume before the cycle, even though the cell performs a self-protective regulatory procedure. If the number of cycle loops is increased, the repeated swelling and shrinkage will cause a continuous decrease in the steady-state volume, and the ability of the pig erythrocytes to resist osmotic damage will decrease; as a result, the mortality of the pig erythrocytes increases as the number of cycle loops increases. The viability of the cells is also affected by the hypotonic and isotonic processing times: a short processing time may contribute to a decrease in the mortality of the pig erythrocytes. This work is of significance to optimizing the process of removing cryoprotectants.

Effect of the polydispersity of RBCs on the recovery rate of RBCs during the removal of CPAs

In the process of removing cryoprotectants from cryopreserved blood, the theoretically optimal operating condition, which is based on the assumption that the distribution of red blood cells is uniform, is often used to reduce or even avoid the hypotonic damage to cells. However, due to the polydispersity of cells, the optimal condition is actually not reliable. In this study, based on the discrete concept developed in our previous work, the effect of the polydispersity on the recovery rate of cells in the dilution-filtration system was statistically investigated by assigning three random parameters, isotonic cell volume, cell surface area, and osmotically inactive cell volume, to cells in small units of blood. The results show that, due to the polydispersity, the real recovery rate deviates from the ideal value that is based on uniform distribution. The deviation significantly increases with the standard errors of cell parameters, and it can be also magnified by high cryoprotectant concentrations. Under the effect of polydispersity, the uniform distribution-based optimized blood or diluent flow rate is not perfect. In practice, one should adopt a more conservative blood or diluent flow rate so that the hypotonic damage to cells can be further reduced.

Statistical estimation of red blood cell osmotic damage during cryoprotective agent removal from cryopreserved blood

Statistical estimation of the osmotic damage of red blood cells (RBCs) during the removal of cryoprotective agents (CPAs) from cryopreserved blood has been a very difficult issue. In this paper, the discrete mass transfer model developed in our previous work is modified to study the volume variation of individual RBCs and thereby to estimate the osmotic damage of all RBCs statistically during CPA removal by the dilution-concentration method we proposed recently. The model is validated with respect to the experimental results either with or without RBCs. Then, it is used to investigate the effects of blood volume, hematocrit, blood and diluent flow rates on the osmotic damage of RBCs, as well as the washing time of CPAs. Our results show that both the increase of blood flow rates and the decrease of diluent flow rates can bring about a reduction in osmotic damage of RBCs; however, only the former can cause a decrease in the washing time of CPAs. The blood volume could also affect the osmotic damage of RBCs. For a given flow condition, there could exist an optimal blood volume range for the dilution-concentration system. The effect of blood volume could be alleviated by an increase in the dilution region volume. In addition, the osmotic damage of RBCs decreases as the hematocrit decreases. Therefore, in practice, the increase of blood flow rates is the best solution to reduce both the osmotic damage of RBCs and the washing time of CPAs simultaneously. A lower hematocrit in the cryopreserved blood and/or longer tubing in the dilution region are also recommended to achieve better performance for the dilution-concentration method.

Theoretical optimization of the removal of cryoprotective agents using a dilution-filtration system

Background

In the cryopreservation of blood, removing cryoprotectants from the cryopreserved blood safely and effectively is always being focused on. In our previous work, a dilution-filtration system was proposed to achieve the efficient clearance of cryoprotectants from the cryopreserved blood.

Method

In this study, a theoretical method is presented to optimize the diluent flow rate in the system to further reduce the osmotic damage to red blood cells (RBCs) and shorten the washing time necessary to remove cryoprotective agents (CPAs), based on a discrete mass transfer concept. In the method, the diluent flow rate is automatically adjusted by a program code in each cycle to maximize the clearance of CPAs, whereas the volume of RBCs is always maintained below the upper volume tolerance limit.

Results

The results show that the optimized diluent flow rate can significantly decrease the washing time of CPAs. The washing time under the optimized diluent flow rate can be reduced by over 50%, compared to the one under the fixed diluent flow rate. In addition, the advantage of our method becomes more significant when the blood flow rate is lower, the dilution region volume is larger, the initial CPA concentration is higher, or the cell-swelling limit set by the system is smaller.

Conclusion

The proposed method for the dilution-filtration system is an ideal solution for not only guaranteeing the volume safety of RBCs but also shortening the washing time of CPAs. In practice, the optimization strategies provided here will be useful in the rapid preparation of cryopreserved blood for clinical use.

Advancing the preservation of cellular therapy products

Cell therapies are typically collected in one location, processed in a second location, and then administered in a third location. The ability to preserve the cells is critical to their clinical application. It improves patient access to therapies by increasing the genetic diversity of cells available. In addition, the ability to preserve cells improves the "manufacturability" of a cell therapy product by permitting the cells to be stored until the patient is ready for administration of the therapy, permitting inventory control of products, and improving management of staffing at cell therapy facilities. Finally, the ability to preserve cell therapies improves the safety of cell therapy products by extending the shelf life of a product and permitting completion of safety and quality control testing before release of the product for use. The support of the National Blood Foundation has been critical to our work on improving the quality of frozen and thawed cell therapy products through the development of a microfluidic device to remove dimethlysulfoxide (DMSO). We are also involved in research to replace DMSO with other agents that are less toxic to cells and patients. Finally, the need to advance the preservation of cell therapies was a driving force behind the development of the Biopreservation Core Resource (http://www.biocor.net), a national resource in biopreservation. New interest in translation of cell therapies from the bench to the patient's bedside has the potential to drive the transformation of preservation science, technology, and practice.

A Dilution-Filtration System for Removing Cryoprotective Agents

In most cryopreservation applications, the final concentrations of cryoprotective agents (CPAs) must be reduced to biocompatible levels. However, traditional methods for removing CPAs usually have disadvantages of operation complexity, time consumption, and ease of contamination, especially for the applications involving large volumes of cell suspensions. A dilution-filtration system, which involves pure ultrafiltration for separation, was developed for continuous, automatic, and closed process of removing CPAs. To predict the optimal protocols under given experimental conditions, a theoretical model was established first. Cell-free experiments were then conducted to investigate the variation in CPA concentration during the process, and the experimental data were compared with the theoretical values for the validation of the model. Finally, ten units (212.9 ml/unit±9.5 ml/unit) of thawed human red blood cells (cryopreserved with 40% (w/v) glycerol) were deglycerolized using the theoretically optimal operation protocols to further validate the effectiveness and advantage of the system. In the cell-free experiments, glycerol was continuously removed and the concentration variations fitted the simulated results quite well. In the in-vitro experiments, glycerol concentration in RBC suspension was reduced to 5.57 g/l±2.81 g/l within an hour, and the cell count recovery rate was 91.19%±3.57%, (n=10), which proves that the system is not only safe for removing CPAs, but also particularly efficient for processing large-scale samples. However, the operation parameters must be carefully controlled and the optimal protocols should be specialized and various from case to case. The presented theoretical model provides an effective approach to find out the optimal operation protocols under given experimental conditions and constrains.

A steady-state mass transfer model of removing CPAs from cryopreserved blood with hollow fiber modules

Hollow fiber modules are commonly used to conveniently and efficiently remove cryoprotective agents (CPAs) from cryopreserved cell suspensions. In this paper, a steady-state model coupling mass transfers across cell and hollow fiber membranes is theoretically developed to evaluate the removal of CPAs from cryopreserved blood using hollow fiber modules. This steady-state model complements the unsteady-state model, which was presented in our previous study. The steady-state model, unlike the unsteady-state model, can be used to evaluate the effect of ultrafiltration flow rates on the clearance of CPAs. The steady-state model is validated by experimental results, and then is compared with the unsteady-state model. Using the steady-state model, the effects of ultrafiltration flow rates, NaCl concentrations in dialysate, blood flow rates and dialysate flow rates on CPA concentration variation and cell volume response are investigated in detail. According to the simulative results, the osmotic damage of red blood cells can easily be reduced by increasing ultrafiltration flow rates, increasing NaCl concentrations in dialysate, increasing blood flow rates, or decreasing dialysate flow rates.

Microprocessor-controlled vs. "dump-freezing" platelet and lymphocyte cryopreservation: A quantitative and qualitative comparative study

Background/Aim. Thermodynamical and cryobiological parameters responsible for cell damages during cryopreservation (cryoinjuries) have not yet been completely explained. Thus, freezing procedures should be revised, exactly optimized to obtain an enhanced structural and functional recovery of frozen- thawed cells. The aim of this study was to compare microprocessor- controlled (controlled-rate) with the compensation of the released fusion heat and ?dump-freezing? (uncontrolled- rate) of the platelet and lymphocyte cryopreservation efficacy. Methods. Platelet quantitative recovery (post-thaw vs. unfrozen cell count), viability (using hypotonic shock response - HSR), morphological score (PMS), ultrastructural (electron microscopy) properties and expression of different surface antigens were investigated. In lymphocyte setting, cell recovery and viability (using trypan blue exclusion test) as well as functionality (by plant mitogens) were determined. Controlled- rate freezing and uncontrolled-rate cryopreservation were combined with 6% (platelets) and 10% (lymphocytes) dimethyl sulfoxide (DMSO). Results. Platelet recovery and functionality were superior in the controlled-rate system. The majority of surface antigen expression was reduced in both freezing groups vs. unfrozen cells, but GP140/CD62p was significantly higher in controlled-rate vs. uncontrolled-rate setting. Controlled- rate freezing resulted with better lymphocyte recovery and viability (trypan blue-negative cell percentage). In mitogen-induced lymphocyte proliferative response no significant intergroup difference (controlled-rate vs. uncontrolled-rate) were found. Conclusion. The data obtained in this study showned the dependence of cell response on the cryopreservation type. Controlled-rate freezing provided a superior platelet quantitative and functional recovery. Lymphocyte recovery and viability were better in the controlled-rate group, although only a minor intergroup difference for cell proliferative response was obtained.