Evaluation of the cytokine stability in serum for the production of allogeneic serum eye drops.

Background Allogenic serum eye drops (SEDs) offer an alternative to autologous SEDs, especially in patients who do not tolerate frequent bloodletting. Production of autologous SEDs is well established at our hospital, but is limited by the availability of male blood donors with blood group AB. In this study we wanted to evaluate cytokine stability in donor serum stored at -40ºC for six months prior to SEDs production. Materials and methods Serum samples from 23 healthy male blood donors were analyzed for cytokines using a magnetic bead-based immunoassay (Luminex). Measurements were performed on fresh drawn serum, processed serum prior to freezing, and thawed serum after six months storage at -40ºC. Inter-plate variability was assessed using a bridge sample. Results High inter-plate variability was observed for all the measured cytokines among the 23 donors. Only TNF-α, and TGF-β isotypes were consistently measurable in over 40% of the individuals, and on every time point of the analysis. Significant differences in TGF-β levels were found between the individuals and across the time points, but the results are unreliable due to high inter-plate variability. Conclusion Luminex platform was not sufficiently robust for assessing changes in cytokine concentrations in donor serum samples under the investigated conditions. Due to these limitations, we were unable to reliably assess the temporal stability of the measured cytokines. Simpler and potentially more robust methods, such as ELISA, may be more suitable.