Abstract Background: Reactivation of CMV and EBV negatively impacts on outcome after allogeneic stem cell transplantation (aSCT). Specific antiviral therapy is only available for CMV. With the exception of ganciclovir all drugs are being used off-label. 40-50% of patients reactivate CMV following aSCT. For the 20-30% of patients reactivating EBV, only rituximab is available to control EBV. Rituximab leads to long term B-cell depletion requiring frequent administration of immunoglobulins. To cover the unmet medical need of CMV and EBV control after aSCT, we investigate a somatic cell therapy approach by means of CMV- and EBV-specific peptide-stimulated T cells. We have set up a prospective randomized controlled phase I/IIa multi-center clinical trial to evaluate the preventive and preemptive adoptive transfer of this ATMP in patients after aSCT (EudraCT number 2012-004240-30). The multi-center trial is currently recruiting. Methods: For manufacturing of the cell product two peptide pools (CMV and EBV) each covering 17 well-defined HLA class I and class II epitopes for stimulation of donor derived PBMC are used. PBMC collected by leukapheresis of mobilized or non-mobilized donors can be used as starting material. To avoid a second leukapheresis of the donor, CMV- and EBV-specific T cells are preferentially expanded from a small fraction of the stem cell graft. A strong expansion of virus-specific T cells could be observed in the cell products as determined by HLA class I multimer analysis. Reconstitution and cell counts of leukocytes after aSCT are monitored for both treatment and control group. To obtain further insights in the expansion of transferred T cells, the TCR beta (TCRb) repertoire of the T-cell product before and after adoptive transfer in the patient is monitored by high throughput sequencing. Specificities of TCRb sequences can be assigned by determining the repertoire of HLA/peptide-multimer-sorted CD8+ T cells. New virus-specific TCRb sequences can be identified thereby. Furthermore, TCR sequences within the T-cell product can be tracked in the patient. Study design: After recruitment patients are randomized in intervention or control group. Patients of the intervention group receive three applications of virus specific T cells (5x10e4/kg bodyweight) starting the first adoptive transfer 30 days after allogeneic stem cell transplantation. Cells are transferred as preventive, preemptive, or also as therapeutic treatment. Patients are monitored for occurrence of GvHD, for viral load, as well as for immune reconstitution, especially of virus-specific T cells. Results: So far, 10 patients have been randomized. The reconstitution of virus-specific T cells of treated patients looks encouraging after transfer so far. The immunomonitoring of six included patients is completed. New CMV- and EBV-specific TCRb sequences could be identified and tracked. Conclusion: Our first observations show promising results regarding feasibility and efficacy of our approach under clinical trial conditions. Disclosures Hennig: HS Diagnomics GmbH: Employment, Equity Ownership.