Human platelet lysate stimulates high-passage and senescent human multipotent mesenchymal stromal cell growth and rejuvenation in vitro

Background aims. Multipotent mesenchymal stromal cells (MSCs) are clinically useful because of their immunomodulatory and regenerative properties, but MSC therapies are limited by the loss of self-renewal and cell plasticity associated with ex vivo expansion culture and, on transplantation, increased immunogenicity from xenogen exposure during culture. Recently, pooled human platelet lysate (hPL) has been used as a culture supplement to promote MSC growth; however, the effects of hPL on MSCs after fetal bovine serum (FBS) exposure remain unknown. Methods. MSCs were cultured in medium containing FBS or hPL for up to 16 passages, and cell size, doubling time and immunophenotype were determined. MSC senescence was assessed by means of a fluorometric assay for endogenous beta-galactosidase expression. MSCs cultured with FBS for different numbers of passages were switched to hPL conditions to evaluate the ability of hPL to "rescue" the proliferative capacity of MSCs. Results. hPL culture resulted in more rapid cell proliferation at earlier passages (passage 5 or earlier) than remove PBS; by day 4, hPL (5%) yielded an MSC doubling time of 1.28 days compared with 1.52 days in 16% FBS. MSCs cultured first in FBS and switched to hPL proliferated more and demonstrated less beta-galactosidase production and smaller cell sizes than remove MSCs continuously propagated in FBS. Conclusions. hPL enables rapid expansion of MSCs without adversely affecting immunophenotype. hPL culture of aged and senescent MSCs demonstrated cellular rejuvenation, reflected by decreased doubling time and smaller cell size. These results suggest that expansion of MSCs in hPL after FBS exposure can enhance cell phenotype and proliferative capacity.