Storage-Induced Micro-Erythrocytes Are Rapidly Cleared from Recipient Circulation and Predict Transfusion Recovery

Background Hypothermic storage of red blood cell (RBC) concentrates for up to 42 days is associated with biochemical, molecular, morphological, and mechanical modifications. This “storage lesion” increases with storage duration and is associated with increased clearance of transfused storage-damaged RBCs from the recipient's circulation in the first few hours post-transfusion. This rapid clearance reduces transfusion efficacy, but how it occurs is not fully elucidated. RBCs with reduced surface area called “storage-induced micro-erythrocytes” (SMEs) were recently described. Their proportion increases from 2% to 23% during storage. Their reduced surface-to-volume ratio is expected to induce rapid mechanical clearance by the spleen. We aimed to evaluate whether SMEs can be used as a marker of transfusion efficacy, if this subpopulation of RBCs is preferentially cleared by the spleen after transfusion, and if so, by which mechanisms. Methods We evaluated the proportion of SMEs in stored RBC concentrates in vitro using ImageStream and correlated it to the 51Chromium-labeled 24h post-transfusion recovery (24hPTR) in vivo in 31 healthy human volunteers. We then investigated the fate of SMEs during 8 ex vivo perfusions of human spleens (16 RBC concentrates stored for 35-42 days). Finally, we developed a mouse transfusion model to assess the fate of SMEs in vivo and determine their main mechanisms of clearance. Results The proportion of SMEs in RBC concentrates at day 42 of storage correlated negatively with 24hPTR in healthy volunteers (r=-0.42, P5 passages through the spleen). The percentage of SMEs correlated with splenic retention rate ex vivo (r=0.46, p