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Rationale: Patients receiving an allogeneic stem cell graft from cytomegalovirus (CMV) seronegative donors are particularly prone to CMV reactivation with a high risk of disease and mortality. Therefore we developed and manufactured a novel vaccine and initiated a clinical phase I trial with a CMV phosphoprotein 65 (CMVpp65)-derived peptide. Methods: Ten patients after allogeneic stem cell transplantation received four vaccinations at a biweekly interval. All patients were monitored for CMVpp65 antigenemia. Flow cytometry for CMV-specific CD8 + and γδ T cells as well as neutralizing anti-CMV antibodies were correlated to clinical parameters. Results: The vaccination was well tolerated. Seven of nine patients cleared CMVpp65 antigenemia after four vaccinations and are still free from antigenemia to this day. Two patients with CMV reactivation showed persisting CMV antigenemia. One patient received prophylactic vaccination and did not develop antigenemia. An increase of up to six-fold in frequency of both CMV-specific CD8 + T cells and/or Vδ2negative γδ T cells was detected. Titers of neutralizing antibodies increased up to the tenfold. Humoral and cellular immune responses correlated with clearance of CMV. Conclusion: In summary, CMVpp65 peptide vaccination for patients after allogeneic stem cell transplantation at high risk for CMV reactivation was safe, well tolerated and clinically encouraging. A study in solid-organ transplant patients is ongoing., Competing Interests: Competing Interests: J.K. is inventor of multiple patents dealing with γδ TCRs and co-founder as well as chief scientific officer (CSO) of Gadeta (http://www.gadeta.nl/). The other authors have declared that no competing interest exists.

Flow cytometry, as a powerful tool for immunomonitoring and quality control of peripheral blood mononuclear cells (PBMCs), is routinely used in clinical studies. However, flow cytometry based assays for cryopreserved peripheral blood mononuclear cells (cPBMCs) constitute a challenge. Down-regulation of surface and intracellular markers, as well as impairment of cell function might result from cryopreservation. Furthermore, protocols for resting cPBMCs are available but diverse. Therefore, we performed a standardization of the resting process concerning resting position, cell concentration, resting period and material of cell culture tubes as well as culture media. We further investigated the influence of resting on the phenotype and functionality of T cells comparing fresh PBMCs as gold standard to rested and non-rested cPBMCs. Polychromatic flow cytometry staining, peptide-MHC class I restricted tetramer staining and intracellular cytokine staining as major methods were used. Our results revealed that a horizontal position, a cell concentration of 2 to 5 × 10(6) cells/ml and an overnight resting phase is beneficial to eliminate dead or dying cells in cPBMCs with a mean cell loss of 14% overall cell populations. In addition, the quality and quantity of regulatory T cells and antigen specific T cells recovered upon resting. For multifunctional T cells a decrease of activation threshold in the way of a twofold mean fluorescence intensity (MFI) and increase of degranulation marker CD107a, co-stimulatory marker CD28, adhesion molecule CD62L as well as the ability to secrete antiviral cytokines like interferon gamma (IFN-γ), tumor necrosis factor (TNF), and interleukin 2 (IL-2) comparable to fresh PBMCs were observed. However, based upon our data resting is not helpful for the flow cytometric analyses of myeloid-derived suppressor cells (MDSCs) and large/intermediate size lymphocytes which rather decreased/vanished ex vivo. Therefore, we developed an algorithm to indicate for which cell population and for which type of analyses the resting process is useful or not., (© 2016 International Society for Advancement of Cytometry.)