765. Suicide Gene Therapy by Central Memory Human T Lymphocytes
Authors: Shin Kaneko, Sara Mastaglio, Attilio Bondanza, Maurilio Ponzoni, Luca Aldrighetti, Salvatore Toma, Marina Radrizzani, Simona La Seta, Fabio Ciceri, Claudio Bordignon, Chiara Bonini
Journal: Molecular Therapy (2006)

Adoptive immunotherapy represents a powerful therapeutic approach for the treatment of cancer and infectious diseases. A compelling example is represented by donor lymphocytes infusions (DLI) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although alloreactive donor lymphocytes are very powerful in mediating malignant-cell killing (graft-versus-leukemia-GVL), recognition of host antigens by donor cells often results in a life-threatening event called graft versus host disease (GVHD). To solve this double bind, we investigated the therapeutic potential of donor lymphocytes retrovirally transduced to express the suicide gene thymidine kinase of Herpes Simplex virus (TK) in high-risk patients affected by hematologic malignancies. Donor TK+ lymphocytes are sensitive to the pro-drug ganciclovir (GCV) and can thus be safely infused to patients after allo-HSCT. Preclinical and clinical studies have substantiated the concept that a time-wise infusion of GCV can fully control life-threatening GVHD and may separate GVHD form GVL. The efficacy of the suicide machinery suggests that an increase in the alloreactive potential of TK+ cells may boost the anti-tumor effect, while allowing the selective control of GvHD. The clinical efficacy of T-cell based therapy relies not only on the ability of T cells to mediate an anti-tumor response (effector phase), but also in the ability of T cells to persist and expand in vivo, thus providing a long-term protection from disease relapse (memory phase). In this study, we tackled the rules governing the generation and expansion of memory T cells, by exploiting the positive effects of the IL-7 homeostatic cytokine on memory cells, to increase the potency of the TK-based T cell therapy. We showed that polyclonal stimulation with anti-CD3 antibodies (aCD3) and culture in the presence of high doses of IL-2 generates mainly CD45RA-CCR7-effector memory (EM) cells, with a mixed phenotype in regard to CD28/CD27 co-expression and a limited ability to engraft and persist in vivo. On the contrary, polyclonal stimulation by anti-CD3/CD28 conjugated cell sized beads and culture in the presence of low doses of IL-7 result in the generation of TK+ cells with a central memory (CM) phenotype, CD45RA+CCR7+, CD28+CD27+, that produce high levels of IL-2 upon restimulation, and express sustained high levels of IL-7R alpha, a receptor required for the generation and survival of memory T-cells. In mixed lymphocytes cultures performed with CFSE-labeled TK+ cells we observed that CM TK+ cells display a higher proliferative alloreactive activity than EM TK+ cells. Finally, when infused in conditioned NOD/scid mice EM TK+ cells displayed a limited ability to engraft and cause xenogeneic-GvHD, while CM TK+ lymphocytes persistently engrafted and caused lethal GvHD in a significant fraction of mice. GvHD was successfully treated by GCV administration.