Optimizing platelet transfusions:

In utero exposure to alloantigens primes alloimmunization to platelet transfusion in mice

BACKGROUND

Platelet transfusions remain a mainstay of treatment for many patients with thrombocytopenia, but can lead to alloantibodies to Human Leukocyte Antigens (anti-HLA) resulting in inadequate responses to subsequent platelet transfusions (refractoriness), as well as complicate transplantation. Despite substantial decreases in alloimmunization with the implementation of leukoreduction, a significant percentage of patients still become alloimmunized following platelet transfusions. It remains unclear why some patients make anti-HLA antibodies, but others do not make anti-HLA antibodies even with chronic transfusion. Antecedent pregnancy correlates with risk of alloimmunization due to platelet transfusion in humans - however, isolation of pregnancy as a single variable is not possible in human populations.

STUDY DESIGN AND METHODS

A tractable murine model of pregnancy and transfusion was engineered by breeding C57BL/6 (H-2b ) dames with BALB/c (H-2d ) sires. After pregnancy, female mice were transfused with leukoreduced platelets from F1 (H-2b/d ) donors that expressed the same paternal major histocompatibility complex (MHC) H-2d alloantigens as the sires. Control groups allowed isolation of pregnancy or transfusion alone as independent variables. Alloimmunization was determined by testing serum for antibodies to H-2d MHC alloantigens.

RESULTS

No alloantibodies were detected after pregnancy alone, or in response to transfusion of platelets alone; however, significant levels of alloantibodies were detected when pregnancy was followed by transfusion.

CONCLUSIONS

These findings isolate antecedent pregnancy as a causal contribution to increased frequencies of alloimmunization by subsequent platelet transfusion in mice and provide a platform for ongoing mechanistic investigation.

Fluids of the Future

Fluids are a vital tool in the armament of acute care clinicians in both civilian and military resuscitation. We now better understand complications from inappropriate resuscitation with currently available fluids; however, fluid resuscitation undeniably remains a life-saving intervention. Military research has driven the most significant advances in the field of fluid resuscitation and is currently leading the search for the fluids of the future. The veterinary community, much like our civilian human counterparts, should expect the fluid of the future to be the fruit of military research. The fluids of the future not only are expected to improve patient outcomes but also be field expedient. Those fluids should be compatible with military environments or natural disaster environments. For decades, military personnel and disaster responders have faced the peculiar demands of austere environments, prolonged field care, and delayed evacuation. Large scale natural disasters present field limitations often similar to those encountered in the battlefield. The fluids of the future should, therefore, have a long shelf-life, a small footprint, and be resistant to large temperature swings, for instance. Traumatic brain injury and hemorrhagic shock are the leading causes of preventable death for military casualties and a significant burden in civilian populations. The military and civilian health systems are focusing efforts on field-expedient fluids that will be specifically relevant for the management of those conditions. Fluids are expected to be compatible with blood products, increase oxygen-carrying capabilities, promote hemostasis, and be easy to administer in the prehospital setting, to match the broad spectrum of current acute care challenges, such as sepsis and severe systemic inflammation. This article will review historical military and civilian contributions to current resuscitation strategies, describe the expectations for the fluids of the future, and describe select ongoing research efforts with a review of current animal data.

A comparison of platelet quality between platelets from healthy donors and hereditary hemochromatosis donors over seven-day storage

BACKGROUND

Therapeutic phlebotomy is the standard treatment of hereditary hemochromatosis (HH), the most common genetic disease in people of Northern European descent. Red cell concentrates from HH donors have been reported safe for transfusion, but little data is available on the storage properties of platelet concentrates from HH donors.

STUDY DESIGN AND METHODS

Whole blood was collected from 10 healthy individuals and 10 newly diagnosed HH patients with elevated serum ferritin. Platelet-rich plasma (PRP) was prepared and split into four 20-mL units. Platelet quality tests were performed on days 0, 1, 3, 5, and 7 of storage, including platelet aggregation (ADP, arachidonic acid, collagen, and epinephrine agonists), blood gas analysis, flow cytometry (CD41, CD42b, and CD62P expression), and ELISA (sCD40L and sCD62p in supernatant).

RESULTS

Mean serum ferritin levels were higher in HH patients than in controls (847.5 vs 45.8 ng/mL, P < .001). Overall, no difference in quality test results was observed between the two study groups over 7-day storage (P > .05), including blood gas analysis, platelet aggregation, and expression of surface (CD62p and CD42b) and secreted (sCD62P and sCD40L) activation markers. Expected alterations in metabolic (CO₂ and glucose decrease, O₂ and lactate increase, P < .001) and platelet activation markers (CD42b decrease, CD62P increase, P < .05) over time were observed in both groups.

CONCLUSION

Although these findings indicate that platelets of individuals with HH are comparable to platelets from healthy donors, more extensive studies are needed before definite conclusions can be drawn.

Intravenous administration of synthetic platelets (SynthoPlate) in a mouse liver injury model of uncontrolled hemorrhage improves hemostasis

BACKGROUND

Clinical resuscitative treatment of traumatic hemorrhage involves transfusion of RBC, platelets and plasma in controlled ratios. However, use of such blood components, especially platelets, present many challenges including availability, portability, contamination risks, and short shelf-life, which limit the use of platelet transfusions outside of large trauma centers such as remote civilian hospitals and austere prehospital settings. This has prompted significant research in platelet substitutes that may resolve the above issues while providing platelet-mimetic hemostatic action. In this framework, we have developed a synthetic platelet surrogate, SynthoPlate, by integrative decoration of platelet function mimetic peptides on a biocompatible lipid nanovesicle platform. We have previously demonstrated hemostatic capability of SynthoPlate in correcting tail-bleeding time in thrombocytopenic mice. Building on this, we hypothesized that SynthoPlate transfusion would decrease bleeding in a murine model of acute hemorrhagic shock.

METHODS

A validated model of uncontrolled intraperitoneal hemorrhage, via liver laceration was used to induce hemorrhagic shock in mice. SynthoPlate, control (unmodified) particles, and normal saline were administered as pretreatment and recue infusions to mice undergoing liver laceration and evaluated for hemostatic benefit by determining differences in blood loss and monitoring real-time hemodynamic data.

RESULTS

Pretreatment SynthoPlate transfusion resulted in significant reduction of blood loss following hemorrhage, compared with control particles or normal saline treatment (0.86 ± 0.16 g control particles [CP] vs. 0.84 ± 0.13 g normal saline [NS] vs. 0.68 ± 0.09 g SynthoPlate, p < 0.005). SynthoPlate transfused mice demonstrated improved hemodynamics taking significantly longer to develop post-injury hypotension (168.3 ± 106.6 seconds CP vs. 137 ± 58 seconds NS vs. 546.7 ± 329.8 seconds SynthoPlate, p < 0.05). SynthoPlate infusion following liver laceration, that is, rescue transfusion, also resulted in a significant decrease in blood loss (0.89 ± 0.17 g CP vs. 0.92 ± 0.19 g NS vs. 0.69 ± 0.18 g SynthoPlate, p < 0.05).

CONCLUSION

Transfusion of SynthoPlate particles reduces blood loss in a murine model of liver injury, and SynthoPlates may represent a viable transfusion product for the mitigation of blood loss in acute, severe hemorrhagic shock.

Ultraviolet-Based Pathogen Inactivation Systems: Untangling the Molecular Targets Activated in Platelets

Transfusions of platelets are an important cornerstone of medicine; however, recipients may be subject to risk of adverse events associated with the potential transmission of pathogens, especially bacteria. Pathogen inactivation (PI) technologies based on ultraviolet illumination have been developed in the last decades to mitigate this risk. This review discusses studies of platelet concentrates treated with the current generation of PI technologies to assess their impact on quality, PI capacity, safety, and clinical efficacy. Improved safety seems to come with the cost of reduced platelet functionality, and hence transfusion efficacy. In order to understand these negative impacts in more detail, several molecular analyses have identified signaling pathways linked to platelet function that are altered by PI. Because some of these biochemical alterations are similar to those seen arising in the context of routine platelet storage lesion development occurring during blood bank storage, we lack a complete picture of the contribution of PI treatment to impaired platelet functionality. A model generated using data from currently available publications places the signaling protein kinase p38 as a central player regulating a variety of mechanisms triggered in platelets by PI systems.

Factors influencing platelet transfusion refractoriness in patients undergoing allogeneic hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation has been considered a risk factor for development of platelet transfusion refractoriness. The objective of this study was to assess the platelet transfusion refractoriness rate in patients undergoing allogeneic hematopoietic stem cell transplantation from different sources. We retrospectively reviewed the charts and transfusion records of patients who underwent allogeneic stem cell transplantation at our institution between 2013 and 2015. The evaluation of post-transfusion platelet count was assessed for each transfusion given, from day of progenitor infusion to day 30 after transplantation. Of 167 patients included in this study, 101 received peripheral blood stem cell transplantation (PBSCT) and 66 received umbilical cord blood transplantation (UCBT). Overall, the percentage of platelet transfusions with a 14-h CCI lower than 5000 was 59.3%, being these data significantly higher for UCBT (67.6%) than for PBSCT (31.0%). Seventy-eight percent of patients underwent UCBT become refractory, while 38.6% of patients who received PBSCT were refractory. Factors associated to platelet refractoriness were lower CD34+ cell dose infused, higher number of antibiotics used, presence of anti-HLA I antibodies, and reduced-intensity conditioning regimen. Platelet refractoriness is a frequent and complex adverse event and remains a therapeutic challenge in the management of patients undergoing HSCT. There is a higher rate of platelet refractoriness in patients who received UCBT as compared to patients who received PBSCT.