Gamma delta T cells as novel immunotherapeutic tool to cure drug-resistant viral infections in transplanted pediatric patients: development and validation of procedures for a new ATMP (advanced therapy medicinal product)

Background & Aim Viral infections remain a leading cause of morbidity and mortality after transplantation. Although prophylactic pharmacotherapy is effective in reducing the risk for some viral infections, therapeutic options for breakthrough infections are still unsatisfactory. Conventional pharmacologic agents against Adenovirus (AdV) and Epstein-Barr virus (EBV) have limited efficacy and relevant toxicity, whereas in the case of cytomegalovirus (CMV) are documented better response rates, but toxicity and reactivation after treatment stop are frequent. T-cell reconstitution is a key requirement for effective antiviral control following transplantation, and factors that influence the speed of T-cell recovery impact also the risk of viral infection in this period. The use of lymphocyte infusions derived from seropositive donors is an effective salvage therapy for viral infections in transplanted recipients prior to T-cell recovery, but the risk of severe graft-versus-host disease (GVHD) is a critical concern. Thus, we propose a novel immunotherapeutic approach based on gd T cells specific for AdV, CMV and EBV. Many studies highlighted the importance of gd T cells in antiviral immunity, uniquely combining conventional adaptive features with rapid, innate-like responses. These lymphocytes are effector cells that: i) recognize target cells in a MHC-independent manner, thus do not cause GvHD; ii) participate CMV and EBV responses, particularly when conventional adaptive immunity is insufficient to clear the viral infection; iii) may develop memory responses, and iv) cross-talk with other immune cells, including NK lymphocytes, alfa beta T cells and dendritic cells. These features render gd T cells extremely appealing for clinical purposes. We believe that an ATMP containing Vd1 and Vd2 gd T cells will be the ideal immunotherapeutic approach to prevent and treat viral infections after transplantation. Methods, Results & Conclusion To this end, we are developing a new method to obtain a cell product containing expanded Vd1 and Vd2 gd T cells using exclusively GMP-graded reagents, including zoledronic acid, cytokines, viral peptides (related to AdV, CMV and EBV) and ab depletion techniques. Such cell product has been tested for i) phenotype, ii) allo-reactivity, iii) cytotoxicity and iv) specificity. Our preliminary results strongly support the feasibility for development of new immunotherapeutic protocols using gd T cells, with the aim of preventing and treating viral infections after transplantation.