(P-CB-7) Cold Storage Effects on Platelet Activation and Immune Markers: Preliminary Comparison of Whole Blood vs. Apheresis Platelets

The renewed interest in cold-stored platelets highlights the need for a deeper understanding of their integrity. Platelets play a crucial role in immune responses by mediating inflammation and upregulating receptors to recognize pathogens, significant in trauma transfusion settings. During storage, platelets undergo transformations such as the release of microparticles and contents from α and β granules. However, data on the stability of immune functions during cold storage remain scarce. This study investigates the variability in platelet marker expression important for activation and immune responses at various time points during 4°C storage for apheresis platelets and those isolated from whole blood.

Study

Design/Methods: Two healthy donors consented to donate both apheresis platelets and whole blood for this study. Fourteen days after donating platelet apheresis in plasma, each donor returned to donate whole blood, which was leukoreduced with a platelet-sparing filter before cold storage. After two hours at 21°C, the apheresis platelets were stored at 4°C (CS-AP). Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) were separated from the cold-stored whole blood (CS-PRP) at each time point. Flow cytometry was conducted at baseline (Day 0) and on Days 2, 7, 14, and 21 of cold storage, analyzing the frequency of markers CD61, CD62P, CD61/CD41, CD154, CD284, and CD107a (Figure A).

Results/Findings:

The comparative analysis of surface glycoproteins showed that over 90% of CS-PRP exhibited high levels of CD41/CD61 at baseline and day 2, indicating early activation. In contrast, CS-AP platelets gradually reached 90% CD41/CD61 positivity between day 2 and day 7. CD154 expression remained stable in CS-PRP, while steadily increasing in CS-AP. Similarly, CD284 was upregulated throughout the cold-storage period in CS-AP.

Our secondary analysis revealed notable early activation in CS-PRP, with about 17% (range: 4-30%) forming a distinct subset of activated platelets between day 2 and day 7, characterized by elevated CD154 (20%) and CD284 (30%), suggesting CS-PRP engenders a more heterogeneous activation pattern.

Conclusions:

Our results support the hypothesis that platelets from CS-AP and CS-PRP exhibit distinct activation patterns. These differences may be attributed to the specific methods used during the collection of whole blood and/or the processing of PRP, potentially leading to early activation in CS-PRP. Furthermore, the increased expression of CD154 and CD284 in CS-AP, along with the presence of a distinct sub-population of activated platelets in CS-PRP, necessitates further investigation. This additional research should focus on elucidating the mechanisms underlying these variations, which could have implications for optimizing the storage and clinical use of platelets.