Current methods to manufacture human platelet lysates (HPLs) for cell therapy and tissue engineering: possible trends in product safety and standardisation

Human platelet lysates (HPLs), obtained from therapeutic‐grade platelet concentrates (PC), are rich in growth factors and other bioactive molecules. HPL is increasingly evaluated as a substitute for foetal bovine serum (FBS), to likely become the next ‘gold standard’ supplement of growth media for clinical‐grade ex vivo propagation of human cells. HPL avoids the risks of immunological reactions against xenoproteins. HPL quality and safety benefit from the pathogen safety measures in place for producing PC for transfusion. Numerous studies support that HPL‐expanded mesenchymal stromal cells show improved proliferation and decreased doubling time than when using FBS‐supplemented media and maintain characteristic immunophenotype, differentiation capacity and T‐cell immunosuppressive effect. Several methods are used to prepare HPL; they differ in the selection and formulation of the starting PC, the consideration or not for blood groups, the pool size, the membrane lysis procedure, the depletion of fibrinogen, and the implementation or not of a pathogen inactivation step on PC materials or during manufacture. Allogeneic ‘off‐the‐shelf’ pooled HPLs, made from approximately fifty, or more, PC, are currently produced by blood establishments and/or available through commercial suppliers. Improved HPL standardization and safety profile, through larger pools and dedicated viral inactivation and removal treatments, is expected in the next few years, broadening applications in cell therapy and regenerative medicine. Systematic studies of the impact of the mode of production of HPL on the isolation and expansion of various human cell types should be encouraged.