Background and objectives: Administration of virus-specific T cells (VSTs) is a viable antiviral treatment strategy after allogeneic HSCT, even if conventional therapies fail. Third-party donors are often chosen for the generation of the VST product. The eligibility of the donor has to be tested in a rigorous donor screening procedure, since the isolation technology only targets pre-existing VSTs. Materials and methods: In a period of 3 years, we performed 32 VST treatments for 28 patients. Targeting four different viruses, 284 healthy individuals underwent 417 donor screening procedures. VSTs were counted by flow cytometry detecting interferon-gamma (IFN-γ) producing T cells. Generation of the VSTs was performed from leukapheresis products in a fully automated and closed system using magnetic cell separation. Results: The mean circulating VST frequencies ranged from 0·006% to 0·328%. The average yield of viable VSTs in the product was 1·83·106 cells, while the average VST dose calculated for the patient's body weight was 4·63·104/kg. The mean purity – percentage of VSTs within the T cells – of all T-cell products was 62·9%. Correlation was identified between the frequency of the VSTs in the peripheral blood of the donor and the VST numbers of the end product; the strongest correlation was seen for CMV. Conclusion: This paper focuses on the T-cell donors, highlighting some key points on the donor selection process. Based on the findings in connection with the CMV therapies, peripheral VST seems to be the best predictor of the VST content of the final product administered to the patient.
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