Efficacy Study on the Strategy of HSV-Tk Engineering Donor Lymphocytes to Treat Patients With High Risk Acute Leukemia

Delayed immune-reconstitution remains one of the main limitation of haploidentical stem cell transplantation. The risk of severe infections remains high for several months and CD3+ reconstitution could take more than 10 months. The low number of lymphocytes infused with the graft, the degree of HLA (Human Leukocyte Antigen) disparity, and a reduced thymic function in adults and differences in host/donor antigen presenting cells are contributing causes. The infusions of HSV-TK engineered lymphocytes may represent a significant therapeutic improvement in haploidentical HCT (hematopoietic cell transplantation), because it remarkably may enhance both GvL (Graft versus Leukemia) activity, thus reducing the occurrence of disease relapse, and post-transplant immune reconstitution in the absence of chronic immune suppression, thus decreasing the rate of both post-transplant opportunistic infections and transplant-related mortality. Furthermore, the efficient control of GvHD achieved via the suicide mechanism allows also the multiple infusion of HSV-TK-treated donor lymphocytes, when needed, that might further improve post-transplant host immune reconstitution, and survival in patients receiving haplo-HCT. Finally, this therapeutic approach can become a valuable option for all candidates, including patients with advanced disease and older age. The proposed clinical trial represents an innovative therapeutic treatment for patients affected by high risk acute leukemia, who have undergone haploidentical stem cell transplantation.