Evaluation of four different methods for platelet freezing. In vitro and in vivo studies

Concentration of Human Hematopoietic Stem Cells in Bone Marrow Transplantation: Results of a Multicenter Study Using Baxter CS 3000 plus Cell Separator

Preliminary BM processing to produce an enriched MNC fraction from large BM volumes improves subsequent pharmacological and/or immunological “ex vivo” treatment and cryopreservation. We detail on a multicenter study (6 Transplant Centers) performed to establish an effective and reliable protocol using a CS 3000 continuous flow separator on a large series of BM processed for autologous (96) and allogeneic (12) transplantation. The reduction in volume was 78.6+7.2% while 28.9+12.4% of the original nucleated cells were found in the final product. A mean of 84.3+13.2% of the starting MNC was yielded in a fraction containing over 81% MNC. Cloning efficiency indicated than the final graft was highly enriched in progenitor cells committed to the granulocyte/macrophage pathway (> 100%) as assessed in vitro (CFU-GM). Removal of RBC and PLT was 98.3+1.1 and 37.7+14.6%, respectively. The mean dose of MNC and CFU-GM was 0.6+0.37 x 108 and 0.96+1 x 108 recipient weight. The entire process was accomplished in 87.5+20 min. We concluded that this automated device is a simple and reproducible method for BM processing suitable as first step for further “ex vivo” automated negative and/or positive cell selections.

Improved Cryopreservation of Human Umbilical Vein Endothelial Cells: A Systematic Approach

Cryopreservation of human umbilical vein endothelial cells (HUVECs) facilitated their commercial availability for use in vascular biology, tissue engineering and drug delivery research; however, the key variables in HUVEC cryopreservation have not been comprehensively studied. HUVECs are typically cryopreserved by cooling at 1 °C/min in the presence of 10% dimethyl sulfoxide (DMSO). We applied interrupted slow cooling (graded freezing) and interrupted rapid cooling with a hold time (two-step freezing) to identify where in the cooling process cryoinjury to HUVECs occurs. We found that linear cooling at 1 °C/min resulted in higher membrane integrities than linear cooling at 0.2 °C/min or nonlinear two-step freezing. DMSO addition procedures and compositions were also investigated. By combining hydroxyethyl starch with DMSO, HUVEC viability after cryopreservation was improved compared to measured viabilities of commercially available cryopreserved HUVECs and viabilities for HUVEC cryopreservation studies reported in the literature. Furthermore, HUVECs cryopreserved using our improved procedure showed high tube forming capability in a post-thaw angiogenesis assay, a standard indicator of endothelial cell function. As well as presenting superior cryopreservation procedures for HUVECs, the methods developed here can serve as a model to optimize the cryopreservation of other cells.

Review of in vivo studies of dimethyl sulfoxide cryopreserved platelets

A literature review was conducted to assess the efficacy and safety of dimethyl sulfoxide (DMSO) cryopreserved platelets for potential military use. In vivo DMSO cryopreserved platelet studies published between 1972 and June of 2013 were reviewed. Assessed were the methods of cryopreservation, posttransfusion platelet responses, prevention or control of bleeding, and adverse events. Using the Department of Defense's preferred 6% DMSO cryopreservation method with centrifugation to remove the DMSO plasma before freezing at -65°C and no postthaw wash, mean radiolabeled platelet recoveries in 32 normal subjects were 33% ± 10% (52% ± 12% of the same subject's fresh platelet recoveries), and survivals were 7.5 ± 1.2 days (89% ± 15% of fresh platelet survivals). Using a variety of methods to freeze autologous platelets from 178 normal subjects, mean radiolabeled platelet recoveries were consistently 39% ± 9%, and survivals, 7.4 ± 1.4 days. More than 3000 cryopreserved platelet transfusions were given to 1334 patients. There were 19 hematology/oncology patient studies, and, in 9, mean 1-hour corrected count increments were 11 100 ± 3600 (range, 5700-15 800) after cryopreserved autologous platelet transfusions. In 5 studies, bleeding times improved after transfusion; in 3, there was either no improvement or a variable response. In 4 studies, there was immediate cessation of bleeding after transfusion; in 3 studies, patients being supported only with cryopreserved platelets had no bleeding. In 1 cardiopulmonary bypass study, cryopreserved platelets resulted in significantly less bleeding vs standard platelets. In 3 trauma studies, cryopreserved platelets were hemostatically effective. No significant adverse events were reported in any study. In summary, cryopreserved platelets have platelet recoveries that are about half of fresh platelets, but survivals are only minimally reduced. The platelets appear hemostatically effective and have no significant adverse events.

Platelet cryopreservation using a trehalose and phosphate formulation

Long-term storage of platelets is infeasible due to platelet activation at low temperatures. In an effort to address this problem, we evaluated the effectiveness of a formulation combining trehalose and phosphate in protecting platelet structure and function following cryopreservation. An annexin V binding assay was used to quantify the efficacy of the trehalose and phosphate formulation in suppressing platelet activation during cryopreservation. Of the platelets cryopreserved with the trehalose plus phosphate formulation, 23% +/- 1.2% were nonactivated, compared with 9.8% +/- 0.26% nonactivated following cryopreservation with only trehalose. The presence of both trehalose and phosphate in the cryopreservation medium is critical for cell survival and preincubation in trehalose plus phosphate solutions further enhances viability. The effectiveness of trehalose plus phosphate in preserving platelets in a nonactivated state is comparable to 6% dimethyl sulfoxide (Me(2)SO). Measurements of platelet metabolic activity using an alamarBlue assay also established that trehalose plus phosphate is superior to trehalose alone. Finally, platelets protected by the trehalose plus phosphate formulation exhibit similar aggregation response upon thrombin addition as fresh platelets, but an increase of cytosolic calcium concentration upon thrombin addition was not observed in the cryopreserved platelets. These results suggest that trehalose and phosphate protect several aspects of platelet structure and function during cryopreservation, including an intact plasma membrane, metabolic activity, and aggregation in response to thrombin, but not intracellular calcium release in response to thrombin.

Effects of high platelet concentration in collecting and freezing dry platelets concentrates

OBJECTIVE

To evaluate, in vitro, the effects of collecting and cryopreserving fresh dry platelet concentrates (PCs).

MATERIAL AND METHODS

Standard and dry PCs were collected in the same apheresis procedure. PCs were evaluated by mean platelet volume (MPV), pH, glucose and LDH levels. Activation was examined by flow cytometry using anti-CD41, anti-CD42 and anti-CD62p monoclonal antibodies and annexin binding assay. Platelet function was assessed by aggregation using ADP, collagen and arachidonic acid as agonists. Dry PCs were compared to standard PCs and to cryopreserved dry PCs. We also compared the use of ThromboSol to 5% DMSO as cryoprotectives.

RESULTS

Dry PCs presented a significantly reduced pH and glucose (p<0.001), increased LDH levels and CD62p expression (p<0.001) and diminished aggregation response to ADP (p<0.001). Platelet cryopreservation was associated with platelet lysis, activation and loss of function. Dry PCs cryopreserved with TS were associated with statistically higher LDH levels (p<0.001) and a higher percentage of annexin binding (p=0.005), in addition to a lower number of CD42 positive platelets (p=0.01).

CONCLUSION

Dry PCs should be rapidly frozen after collection to avoid a fall in pH and platelet activation. 5% DMSO performed better than TS to cryopreserve dry PCs.

Platelet cryopreservation using a combination of epinephrine and dimethyl sulfoxide as cryoprotectants

Current methods of platelet storage are unsatisfactory because of the short shelf life of platelets and the rapid loss of platelet viability. We have developed a cryopreservation method that results in less damage from freezing and higher recovered function of platelets. Platelets were cryopreserved using a combination of epinephrine (EPN) and dimethyl sulfoxide (Me(2)SO) as cryoprotectants. The response of platelets to agonists was studied by flow cytometry and aggregation tests. Cryopreserving platelets with Me(2)SO decreased platelet annexin V binding due to freezing. The combination of EPN with Me(2)SO enhanced Me(2)SO cryoprotection and decreased platelet microparticle generation, suggesting that cryopreserving platelets using this combination is associated with increased platelet integrity. Platelet cryopreservation with an Me(2)SO/EPN combination also increased platelet aggregability, which was demonstrated by decreasing the lag phase and increasing the aggregation density to 66.39% +/- 6.6 that of fresh platelet-rich plasmas. We conclude that adding EPN as a combined cryoprotectant improves the quality of Me(2)SO-frozen platelets. As a method of aggregation of cryopreserved platelets, this method is comparable to that of normal fresh platelets and may improve the conditions for platelet transfusion.

Effects of the addition of second-messenger effectors to platelet concentrates separated from whole-blood donations and stored at 4 degrees C or -80 degrees C

BACKGROUND

Platelet concentrates (PCs) are currently stored at 22 degrees C under continuous agitation. Because of the potential risk of the overgrowth of bacteria in case of contamination, PC shelf life is limited to 5 days. A mixture of second-messenger effectors is being evaluated to determine if it has benefits for cold liquid storage and cryopreservation of platelets.

STUDY DESIGN AND METHODS

PCs separated from whole-blood donations by the buffy coat method were randomly assigned (n = 6 each) to be stored for 5 days at 22 degrees C under continuous agitation or at 4 degrees C after treatment with a platelet storage medium (ThromboSol, LifeCell Corp. ). PCs were also cryopreserved with 6-percent DMSO (final concentration) or with ThromboSol plus 2-percent DMSO (final concentration) (TC). After storage, platelets were analyzed by flow cytometry, transmission electron microscopy, and aggregation and perfusion techniques.

RESULTS

Cold liquid storage of ThromboSol-treated platelets resulted in a lower binding of coagulation factor Va on the platelet surface than on platelets stored at 22 degrees C. In transmission electron microscopy, a conversion to spherical morphology was seen in the case of cold liquid storage. No difference between ThromboSol-treated platelets stored at 4 degrees C and platelets stored at 22 degrees C was seen in perfusion studies. Cryopreservation in the presence of TC prevented the reduction in glycoprotein Ib and IV expression on platelet surface that is seen in 6-percent DMSO-cryopreserved platelets. Platelets cryopreserved in TC covered, by thrombus, a significantly greater percentage of the perfused surface after the freezing and thawing process.

CONCLUSION

ThromboSol-treated PCs separated from whole-blood donations by the buffy coat method, stored at 4 degrees C for 5 days, or cryopreserved in the presence of TC, maintained in vitro functional activity comparable to that achieved by current methods of storage, although discoid morphology was not preserved during cold liquid storage with ThromboSol.

Platelets: preparations, transfusion, modifications, and substitutes

OBJECTIVE

To summarize current knowledge and recent progress pertaining to platelet concentrate preparations, modifications, and future prospects for platelet substitutes.

METHODS

Current publications identified through a search of an electronic literature database were evaluated and reviewed. Relevant data were abstracted into this article. Abstractions of the data were made depending on their relevance. This review starts with standard methods of platelet preparation and goes on to describe different modifications intended to optimize the product and increase its safety. The article concludes with a discussion of the use of hematopoietic growth factors and novel kinds of platelet components for future use.

CONCLUSIONS

Many modifications in the preparation of platelet transfusions have occurred in recent years. Platelets prepared by standard techniques contain significant numbers of donor leukocytes, which are responsible for several adverse effects. Awareness of this problem has lead to the development of effective means for their removal. Several methods to reduce the risk of viral and bacterial transmission through platelet transfusions are emerging. New technologies in the use of platelet substitutes have attempted to prolong the platelet storage potential and prevent the development of recipient alloimmunization. As the biological activities of growth factors become better understood, the clinical applications of novel recombinant products may redefine the concept of future platelet transfusions. It is important that research continues into the optimal methods for the preparation and use of platelet transfusions to provide maximal clinical benefits with minimal risk of complications.

Platelet cryopreservation using a reduced dimethyl sulfoxide concentration and second-messenger effectors as cryopreserving solution

Cryopreservation of platelets is of great interest since it could extend to years the shelf life of therapeutic platelet concentrates (PCs) and facilitate stockpiling and inventory control in blood banking. We have compared the cryopreservation of PCs by the standard method using 6% Me(2)SO as cryoprotectant with the method of freezing employing low concentrations of Me(2)SO (2%) plus ThromboSol, a mixture of second-messenger effectors that protect platelets from cold damage. PC pools were treated either with 6% Me(2)SO or with ThromboSol and 2% Me(2)SO and then placed directly in a -80 degrees C freezer or in the vapor phase of a liquid nitrogen freezer (-120 degrees C). After storage for 1 week or for 3 months, samples were removed, thawed, and analyzed. Measurements included cell recovery, biochemical parameters, membrane glycoproteins (GPs), platelet aggregation, and binding of radiolabeled von Willebrand factor (vWF) and fibrinogen. PCs cryopreserved with ThromboSol and 2% Me(2)SO displayed a platelet recovery (90%) equivalent to those frozen with 6% Me(2)SO. Following either cryopreservation procedure, platelets showed increased surface expression of P-selectin and moderate loss of GP Ibalpha in comparison to fresh platelets. The aggregatory response to ristocetin and the binding of vWF were similar in platelets frozen by either procedure. Finally, both methods promoted comparable impairment of the reactivity of platelets to thrombin, aggregation and binding of fibrinogen and vWF, compared to that of fresh platelets. In summary, cryopreservation of PCs using reduced Me(2)SO concentration and ThromboSol yields platelets with in vitro functional characteristics equivalent to those of cells frozen with the conventional method using 6% Me(2)SO.

Determination of human platelet membrane permeability coefficients using the Kedem-Katchalsky formalism: estimates from two- vs three-parameter fits

Attempts to cryopreserve human blood platelets have resulted in poor postthaw survival rates and have been inadequate for routine clinical application. As a result, most blood banks maintain platelets in nonfrozen solutions. Using this approach, platelets can be stored for only about 5 days and are then discarded. This situation greatly limits the use of platelet transfusion in clinical practice. Information regarding fundamental cryobiological characteristics can be applied to predict platelet response to cryoprotective agent (CPA) addition/removal and to cooling/warming. Methods can then be engineered to optimize cryopreservation procedures, thereby minimizing platelet damage and maximizing postthaw recovery. It was therefore the purpose of this study to determine some of the necessary biophysical parameters required for this process: (i) plasma membrane hydraulic conductivity (Lp), (ii) cryoprotectant solute permeability coefficient (Ps), (iii) the associated reflection coefficient (sigma), and (iv) their activation energies. The CPAs studied included dimethyl sulfoxide (Me2SO) and propylene glycol at 1.5 M concentration. Permeability was measured at 22, 10, and 4 degrees C using a modified Coulter counter in conjunction with a water-jacketed beaker system for temperature regulation. The Kedem-Katchalsky formalism was used to estimate the parameters using: (1) a three-parameter fit and (2) a two-parameter fit in which a noninteracting value of sigma was calculated. Two-parameter estimates were in closer agreement with previously published values, and these were used in a model to simulate addition and removal of 0.64 M (5%) and 1.0 M (7.8%) Me2SO, the most common CPA currently used in empirically determined platelet cryopreservation protocols.

Frozen/thawed platelets: importance of osmotic tolerance and platelet subpopulations

Me2SO cryopreserved platelets circulate in vivo, reduce bleeding time, and have hemostatic properties but their functional recovery is only half that of the fresh material. Poor osmotic response is often reported as the cause of the freezing injury. Osmotic excursions on 1- and 5-day-old platelets have been studied. Platelets stored for 5 days have a lesser capability to regulate their volume particularly after an initial swelling. This is attributed to the reduction of discoid cell number, 80% vs 62% for 1-day-old and 5-day-old platelets, respectively. After freezing, hypotonic stress response is reduced from 86 to 39% for 1-day-old and 73 to 31% for 5-day-old platelets. This reduction in function is supported by a similar reduction of discoid cells from 80 to 40% for 1-day-old and 62 to 32% for 5-day-old platelets. The integrity of the cytoskeleton is critical for the osmotic response. Freezing recovery is significantly lowered in the presence of propylene glycol, which alters actin. This contrasts with the recovery of platelets treated with anti-aggregating agents. Platelets show a greater viability after freezing and thawing when PGI2 is added. It is postulated that freshly collected platelets, which are heterogeneous, contain populations of cells that are more sensitive to freezing than others. More tolerant cells remain discoid after freezing and are also less susceptible to storage lesions. Therefore, the maintenance of the integrity of the membrane and the cytoskeleton should be considered for the development of preservation methodologies.