The current state of platelet and granulocyte cryopreservation

Generation of Platelet Microparticles after Cryopreservation of Apheresis Platelet Concentrates Contributes to Hemostatic Activity

OBJECTIVE

In the last decade, substantial evidence has accumulated about the use of cryopreserved platelet concentrates, especially in trauma. However, little reference has been made in these studies to the morphological and functional changes of platelets. Recently platelets have been shown to be activated by cryopreservation processes and to undergo procoagulant membrane changes resulting in the generation of platelet-derived microparticles (PMPs), platelet degranulation, and release of platelet-derived growth factors (PDGFs). We assessed the viabilities and the PMP and PDGF levels of cryopreserved platelets, and their relation with thrombin generation.

MATERIALS AND METHODS

Apheresis platelet concentrates (APCs) from 20 donors were stored for 1 day and cryopreserved with 6% dimethyl sulfoxide. Cryopreserved APCs were kept at -80 °C for 1 day. Thawed APCs (100 mL) were diluted with 20 mL of autologous plasma and specimens were analyzed for viabilities and PMPs by flow cytometry, for thrombin generation by calibrated automated thrombogram, and for PDGFs by enzyme-linked immunosorbent assay testing.

RESULTS

The mean PMP and PDGF levels in freeze-thawed APCs were significantly higher (2763±399.4/µL vs. 319.9±80.5/µL, p<0.001 and 550.9±73.6 pg/mL vs. 96.5±49 pg/mL, p<0.001, respectively), but the viability rates were significantly lower (68.2±13.7% vs. 94±7.5%, p<.001) than those of fresh APCs. The mean endogenous thrombin potential (ETP) of freeze-thawed APCs was significantly higher than that of the fresh APCs (3406.1±430.4 nM.min vs. 2757.6±485.7 nM.min, p<0.001). Moreover, there was a significant positive poor correlation between ETP levels and PMP levels (r=0.192, p=0.014).

CONCLUSION

Our results showed that, after cryopreservation, while levels of PMPs were increasing, significantly higher and earlier thrombin formation was occurring in the samples analyzed despite the significant decrease in viability. Considering the damage caused by the freezing process and the scarcity of evidence for their in vivo superiority, frozen platelets should be considered for use in austere environments, reserving fresh platelets for prophylactic use in blood banks.

In vitro thromboelastometric evaluation of the efficacy of frozen platelet transfusion

BACKGROUND

Although frozen platelets are extensively used in remote locations and military environments, scientific evidence of their efficacy is scarce. The objective of this study was to evaluate the in vitro hemostatic efficacy of frozen versus fresh platelet transfusions by rotational thromboelastometry (ROTEM) to ascertain whether the freezing and thawing process impaired platelet contribution to clot strength.

METHODS

An experimental study was performed using platelet in vitro transfusions. Blood samples were collected from 12 patients with non-autoimmune thrombocytopenia. The samples were each transfused with one of 6 pairs of fresh platelet concentrates and platelet concentrates frozen with dimethylsulfoxyde. Optical platelet counts, coagulation studies and ROTEM (EXTEM and FIBTEM) were performed for the baseline and the post-transfusion samples.

RESULTS

Only fresh platelet transfusions significantly increased the EXTEM maximum clot firmness (MCF) and maximum clot elasticity (MCE) over baseline (p<0.001), achieving values within the normal range. The frozen platelet contribution to MCE was negligible. However, the EXTEM clotting time (CT) was significantly (p<0.001) shorter after the frozen platelet transfusion compared with the fresh platelet transfusion. The EXTEM clot formation time (CFT) was significantly shortened after the transfusion of fresh platelets (p=0.002).

CONCLUSION

The ROTEM analysis assessment indicates a dual effect in frozen platelet transfusion: it produces a hypercoagulable state (shortening of CT), and a second, more predominant effect of frozen platelets' functionality impairment compared with fresh platelets (shorter MCF/MCE and longer CFT).

Freezing human platelets with 6 percent dimethyl sulfoxide with removal of the supernatant solution before freezing and storage at -80 degrees C without postthaw processing

BACKGROUND

Platelets (PLTs) can be frozen with 6 percent dimethyl sulfoxide (DMSO) at -80 degrees C for up to 2 years. This method has been modified by concentrating the PLTs and removing the supernatant before freezing.

STUDY DESIGN AND METHODS

High-yield leukoreduced PLTs stored at 22 degrees C for up to 5 days were divided into three equal volumes: one was frozen with 6 percent DMSO at -80 degrees C, thawed, washed, and resuspended in plasma (old method with DMSO); the second was treated with 6 percent DMSO, concentrated to remove the supernatant DMSO, frozen at -80 degrees C, thawed, and diluted with 0.9 percent NaCl (new method with DMSO); and the third was treated with 0.9 percent NaCl without DMSO, concentrated to remove the supernatant solution, frozen at -80 degrees C, thawed, and diluted with 0.9 percent NaCl (new method without DMSO).

RESULTS

Freeze-thaw-wash recovery of PLTs frozen by the old method with DMSO was 74 +/- 2 percent with 5 percent PLT microparticles. Freeze-thaw recovery was 94 +/- 2 percent with 7 percent PLT microparticles (new method with DMSO) and 69 +/- 9 percent with 15 percent PLT microparticles (new method without DMSO). Total DMSO in washed PLTs was 400 and 600 mg in PLTs concentrated before freezing. In vivo recovery of PLTs frozen by the new method with DMSO and transfused into normal volunteers was 30 percent and the life span was 7 days.

CONCLUSION

Concentrating PLTs before freezing simplified the procedure by eliminating postthaw washing. PLTs frozen by this method had more PLTs with reduced GPIb and increased annexin V binding than those frozen by the old method.

Effect of WBC reduction and storage temperature on PLTs frozen with 6 percent DMSO for as long as 3 years

BACKGROUND

PLTs frozen with 6 percent DMSO can be stored at -80 degrees C for 2 years, while those frozen with 5 percent DMSO at -150 degrees C can be stored for at least 3 years. The more rapid deterioration seen in PLTs frozen at -80 degrees C may be due to the presence of granulocytes. The effects of storage temperature and WBC reduction on PLTs frozen with DMSO and the breakage of the PVC plastic bags stored at -80 and -135 degrees C were assessed.

STUDY DESIGN AND METHODS

Apheresed PLT-rich plasma (PRP) was either divided into two equal volumes where one volume was WBC-reduced and the other volume was not or filtered or not and then divided into two equal volumes. PLTs frozen with 6 percent DMSO were stored in PVC plastic bags at either -80 or -135 degrees C for as long as 3 years.

RESULTS

After 2 years of storage at -80 degrees C, the PLTs exhibited satisfactory freeze-thaw-wash values regardless of whether or not they were WBC-reduced, but after 2 to 3 years of storage at -80 degrees C, the PLTs had significantly reduced freeze-thaw-wash values. Freeze-thaw-wash values were not reduced in PLTs stored at -135 degrees C for up to 3 years.

CONCLUSIONS

WBC reduction did not improve freeze-thaw-wash recovery values in PLTs stored at -80 or -135 degrees C for up to 3 years, but reducing the storage temperature from -80 to -135 degrees C did. Breakage of PVC plastic bags stored at -135 degrees C was excessive.

Comparison of the effects of transfusions of cryopreserved and liquid-preserved platelets on hemostasis and blood loss after cardiopulmonary bypass

OBJECTIVE

The aim of the study was to compare the clinical effects and hemostatic efficiency of transfusions of platelets preserved in the frozen state for as long as 2 years with transfusions of platelets preserved in the conventional manner for as long as 5 days in patients undergoing cardiopulmonary bypass.

METHODS

Seventy-three patients were prospectively randomly assigned to receive transfusions of cryopreserved or liquid-preserved platelets. Nonsurgical blood loss was measured during and after the operation. Bleeding time, hematologic variables, and the bleeding time site shed blood were assayed before cardiopulmonary bypass and at 30 minutes and 2, 4, and 24 hours after transfusion. In vitro platelet function tests were conducted on platelets obtained from healthy volunteers.

RESULTS

No adverse sequelae of the transfusions were observed. Blood loss and the need for postoperative blood product transfusions were lower in the group receiving cryopreserved platelets. Lower posttransfusion platelet increments and a tendency toward decreased platelet survival were observed in patients receiving cryopreserved platelets. Hematocrit and plasma fibrinogen were significantly higher in this group, and the duration of intubation was shorter. In vitro, cryopreserved platelets demonstrated less aggregation, lower pH, and decreased response to hypotonic stress but generated more procoagulant activity and thromboxane.

CONCLUSIONS

(1) Cryopreserved platelet transfusions are superior to liquid-preserved platelets in reducing blood loss and the need for blood product transfusions after cardiopulmonary bypass. (2) The reduction in blood loss in the patients receiving cryopreserved platelet transfusions after cardiopulmonary bypass probably reflects improved in vivo hemostatic function of cryopreserved platelets. (3) Some in vitro measures of platelet quality (aggregation, pH, hypotonic stress) may not reflect in vivo quality of platelet transfusions after cardiopulmonary bypass, whereas other in vitro measures (platelet procoagulant activity and thromboxane) do.

Cryopreservation of human platelets and bone marrow and peripheral blood totipotential mononuclear stem cells

Human platelets in sufficient numbers for a therapeutic transfusion can be collected for preservation either by pooling ABO- and Rh-compatible platelets or by apheresis procedures using mechanical cell-separating machines. Human platelets have been frozen successfully with 5 or 6% dimethyl sulfoxide (DMSO) and stored at -150 or -180 degrees C, respectively. Platelets frozen with 5% DMSO have been stored at -150 degrees C for at least 3 years, and platelets frozen with 6% DMSO have been stored at -80 degrees C for at least 2 years. Approximately 95% of the DMSO usually is removed by washing the platelets after thawing, and the residual DMSO produces no untoward effects. Washed platelets resuspended in plasma can be stored at room temperature for 6 to 8 hr before transfusion. Platelets thus frozen have freeze-thaw-wash recovery values of about 80%. In vivo survival values are only about 50% those seen with fresh platelets, and it is necessary to transfuse twice as many to achieve comparable results. Studies have shown that these platelets have satisfactory circulation, reduce clinical bleeding, and shorten the prolonged bleeding times associated with thrombocytopenia. Studies are now being made on human bone marrow and peripheral blood, from which totipotential cells devoid of immunocompetent cells can be isolated and frozen.

Cryopreservation of human platelets using 6% dimethyl sulfoxide and storage at -80 degrees C. Effects of 2 years of frozen storage at -80 degrees C and transportation in dry ice

Platelet studies were done in healthy male volunteers and in thrombocytopenic patients. Some of the platelets used in the study were isolated by mechanical apheresis using either the Haemonetics blood processor 30, the IBM blood processor 2997 or the Fenwal CS-3000 blood processor before freezing. Other platelets were isolated from individual units of whole blood and pooled before freezing. The platelets were frozen with a 6% cryoprotectant (DMSO) in a polyvinylchloride (PVC) plastic bag or a polyolefin plastic bag at -80 degrees C in a mechanical freezer and stored for as long as 3 years. Some of the frozen platelets were transported in dry ice in polystyrene foam containers to determine whether they would be adversely affected by such treatment. Platelet recovery after freezing, thawing and washing was about 75%. In the healthy male volunteers, in vivo recovery of autologous platelets 1-2 h after transfusion was about 33%, and the life span was about 8 days. In the thrombocytopenic patients, in vivo recovery values were 50% of those from fresh platelets. The transfusion of previously frozen washed platelets reduced clinical bleeding in the thrombocytopenic patients with bleeding. There was no evidence of quality deterioration in platelets after storage at -80 degrees C for at least 2 years, as determined from in vivo recovery and in vivo survival values, nor was there any adverse effect as a result of shipment of the frozen platelets in dry ice in polystyrene foam containers from one facility to another.

Studies of cell separation: a comparison of the osmotic response of human lymphocytes and granulocyte-monocyte progenitor cells

The feasibility of using hypo- or hypertonic stress to selectively destroy lymphocytes while sparing stem cells was investigated. Lymphocytes were isolated from peripheral blood and exposed to Hanks' balanced salt solutions ranging in concentration from 66 to 2700 mOsm. The Boyle-van't Hoff plot of cell volume versus reciprocal osmolality was linear. Following osmotic stress, viabilities of the lymphocytes and the granulocyte-monocyte progenitor cells (CFUc) were determined. Lymphocyte viability was assessed by tritiated thymidine incorporation following mitogen stimulation. CFUc viability was measured with the soft agar colony assay. Both types of cells were found to possess high osmotic tolerances compared to other blood cells. While progenitor cells in general appeared to survive anisotonic exposure somewhat better than lymphocytes, significant statistical differences were not established for most situations. The highest degree of CFUc enrichment was twofold, but there was a concomitant 50% drop in CFUc survival. These results suggest that osmotic stress is not a useful procedure for the separation of peripheral blood lymphocytes and stem cells.