De novo generation of RBCs for transfusion can be particularly important for specific patients, and time has come that in vitro generated RBCs enter clinical testing. Research that preceded this breakthrough was presented during the 22nd Congress of EHA, as was the improvement of platelet quality for transfusion, by enabling cold storage of platelets using pharmacological inhibition.
For RBC transfusions, we are dependent on blood donors. Besides this restriction, using donor blood forms a potential risk for allo-immunization or transmission of blood-borne diseases. The in vitro generation of RBCs would overcome these issues, which could especially be important for particular patients, such as those with rare blood group antigens. “Our aim is to develop an alternative red cell product for all those patients who require a specified blood group”, explained Dr Marie-José Claessen (Sanquin, Amsterdam, The Netherlands).
In her presentation, Claessen showed that they are able to in vitro produce mature RBCs that were GMP grade expanded and differentiated, are immortal and can be custom-made.1 She explained that PBMCs are stimulated with growth factors and cytokines to obtain 1012 erythroblasts (compares to 1 yield of transfusion unit) from 200 ml whole blood in 26 days. These cells are then stimulated for some additional days to further differentiate to mature RBCs. During this process, RBCs removed their nuclei with >90% efficiency, looked identical to original RBCs and possessed the hemoglobin, oxygen-binding, blood group and deformability features similar to endogenous RBCs. Using the CRISPR system, a genome editing technique, Claessen was also able to immortalize and differentiate erythroblasts, thereby enabling the production of a customized end product.
A clinical trial, called SCEVAT, will evaluate these in vitro generated RBCs in healthy volunteers. According to Claessen “this is a clinical phase 1 trial in healthy volunteers to test the safety, the absence of immune reactions and also the survival of RBCs in vivo.”
Hemorrhagic and thrombocytopenic patients require platelet transfusion to prevent or treat bleeding. The use of platelet transfusions has increased dramatically the last three decades. However, storage at refrigerator temperature induces complex molecular lesions in platelets, reducing their lifespan. These lesions expose platelets to host macrophages and hepatocyte-counter receptors for phagocytosis and clearance. However, as room temperature storage increases the risk for bacterial contaminations, Dr Shailaja Hegde (University of Cincinnati College of Medicine, Cincinnati, OH, USA) explored the possibility to increase shelf life of platelets at cold temperatures by using pharmacological RhoA and Rac inhibition.
Hegde noticed that molecular lesions caused activation of RhoA GTPases on platelets. To explore whether inhibition of these GPTases extended the lifespan of platelets, Hegde used in vitro assays as well as mice and primates undergoing xenogeneic or autologous transfusions, respectively, of manipulated platelets. Hedge said “our results demonstrate that the storage of platelets with reversible RhoA and Rac inhibitors prevents refrigerated platelet lesions in vivo, while it maintains the hemostatic activity in vitro and in vivo.” More specifically, reversible RhoA inhibition prevented platelet clearance of 7-day refrigerator-stored platelets through inhibiting the translocation of glycosyl-transferases and membrane Gplb clustering.
Next, these results need to be confirmed in human allogeneic transfusions.