Patients immunosuppressed by antineoplastic or immunosuppressive treatments, those undergoing HPT and congenital or acquired immunodeficiencies are especially susceptible to cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections, among others. Its GLOBAL INCIDENCE ranges between 40 and 100 % according to the series and, in cases that do not respond to pharmacological treatment, mortality is close to 100 %. In addition, infections with some EBVs have been related to the INCIDENCE of Certain TYPES OF TUMORES such as nasopharyngeal carcinoma, Burkitt’s lymphoma, Hodgkin’s disease, B lymphoma in transplanted patients (both TPH and TOS), and HIV-infected patients. In these cases, long-term survival does not exceed 50 %. Taking into account the figures of transplants performed in Spain, the magnitude of the problem described is, at the very least, disturbing. An effective strategy for the treatment of viral infections after allogeneic TPH has been shown to be to TRANSFER T-CELLS OF VIRUS (VSTs) providing immediate and long-term protection; response rates of up to 80 % are presented in reference publications. The need to generate a specific cell product for each patient makes this approach not feasible for widespread or urgent use, or when the donor is seronegative. The alternative is the partially compatible healthy VST VST DEVELOPMENT, or third party donors, making it possible to infuse the most compatible and active line against the target virus with the advantages of immediate availability, urgent use (eventually outpatient), efficacy when donors are seronegative, persistence in circulation, overall response rates in more than 2/3 of cases, absence of side effects and lower cost compared to antiviral pharmacological treatment. The main objective of this project is to DOT TO THE PUBLIC HEALTH SYSTEM OF A NATIONAL BANK OF SPECIFIC T-LINFOCITIES FOR IMMEDIATE USE IN ONCHHEmatological ENFERMEDADES and to demonstrate its clinical efficacy. For this purpose, a cooperative research group has been created that includes a large part of the NATIONAL REFERENTS IN THE DEVELOPMENT OF DONATION STRATEGIES AND CELULARY BANKS, Immunobiology and TRASPANTS. The project will be developed in three phases with differentiated objectives: a) RETROSPECTIVE ANALYSIS of transplants and donor identification, studying patients who have developed severe CMV or EBV infections to identify which HLA alleles are involved and define the HLA profile of donors to increase the likelihood that the cells obtained are restricted to these HLAs. A selection algorithm will be developed and donors will be classified according to combinations of alleles that maximise compatibility with susceptible patients. b) Preclinical VALIDATION AND OPTIMISATION of cell expansion protocol. The approach we consider most appropriate has been selected according to our human, structural, technological and financial capacity. A work plan has been established that allows to carry out, under preclinical conditions, the safety and efficacy tests of the different steps of cell expansion T. c) CREATION OF VSTs BANK suitable for clinical use. After preclinical validation of the expansion protocol, it will be adapted to GMP conditions. After the evaluation of the obtained cell product, it must comply with the established criteria that guarantee safety and potential clinical efficacy. Finally, after the approval by the AEMPS and CEIC, the cell lines will be manufactured and a bank of VSTs for CMV and another for EBV will be created according to Phase I data, the data of which will be recorded in a single database accessible to any patient who needs it.