Suicide gene therapy of graft-versus-host disease: immune reconstitution with transplanted mature T cells

Abstract

After allogeneic hematopoietic stem cell transplantation (HSCT), mature transplanted T cells play a major role in restoration of the immune system. However, they can also induce a life-threatening complication: graftversus-host disease (GVHD). Suicide gene therapy of GVHD aims to selectively eliminate alloreactive T cells mediating GVHD while sparing nonalloreactive T cells that should contribute to immune reconstitution. It was demonstrated previously that treatment with ganciclovir (GCV) can control GVHD in mice by killing donor T cells engineered to express the thymidine kinase (TK) suicide gene. TK allows phosphorylation of nontoxic GCV into triphosphate GCV, which is selectively toxic for dividing cells. Thus, in the TK-GCV system, the specificity of cell killing depends on the cycling status of TK T cells rather than allogeneic recognition. This is a potential drawback because in recipients of lymphopenic allogeneic HSCT, alloreactive and homeostatic signals drive the proliferation of donor T cells. It is shown here that the onset of alloreactive T-cell division occurs earlier than that of nonalloreactive T cells, thus establishing a time frame for GCV administration. A 7-day GCV treatment initiated at the time of HSCT allowed efficient prevention of GVHD, while sparing a pool of nondividing donor TK T cells. These cells later expanded and contributed to the replenishment of the recipient immune system with a diversified T-cell receptor repertoire. These results provide a rationale for designing the therapeutic scheme when using TK-GCV suicide gene therapy in allogeneic HSCT. IntroductionThe prognosis for a patient who undergoes allogeneic hematopoietic stem cell transplantation (HSCT) is influenced by the presence in the recipient of postthymic peripheral donor T cells that improve engraftment 1 and T-cell reconstitution 2 and that provide a graft-versusleukemia (GVL) effect. 3 In adult patients, such T cells mainly arise from the persistence and expansion of infused donor T cells. 2,4 Indeed, the differentiation of donor HSCs in the adult recipient thymus is inefficient, as illustrated by the observation that adults grafted with T-cell-depleted (TCD) bone marrow (BM) often remain immunodeficient for several months after transplantation. 4 In addition to the beneficial effects of infused donor T cells, activation of those specific for recipient alloantigens often results in a life-threatening complication: graft-versus-host disease (GVHD). 5 Thus, a major challenge of allogeneic HSCT is to achieve good T-cell reconstitution without GVHD.A strategy for genetic immunosuppression based on conditional elimination of dividing donor T cells expressing the herpes simplex type 1 thymidine kinase (TK) suicide gene was recently developed (for review, see Cohen et al). 6 TK allows phosphorylation of the nontoxic prodrug ganciclovir (GCV) into triphosphate GCV, which, by blocking DNA elongation, is toxic for dividing cells. Hence, on activation and division, TK T cells become sensitive to GCV. 7,8 We previously vali...

Tumor Vaccination after Allogeneic Bone Marrow Cell Reconstitution of the Nonmyeloablatively Conditioned Tumor-Bearing Murine Host

“…According to our findings, GVT reactivity appears late, even if the graft is not T cell depleted, and is predominantly mediated by newly appearing donor-derived T cells that matured in the allogeneic host (39). Reports describing that a selective depletion of alloreactive T cells does not necessarily reduce GVT reactivity could well be in line with our findings (29,31,36,49). In addition, several reports confirm that even in the adult, T cells will be newly generated, i.e., passage through the host thymus (50 -53).…”

Functional impairment of human T-lymphocytes following PHA-induced expansion and retroviral transduction: implications for gene therapy

“…Evidence from HSVtk transgenic murine models, 10,11 and from protocols of transduction based on antigen-specific or allogeneic stimulation, 3,27,28 suggests that ex vivo expansion with polyclonal stimuli is a major contributing factor to the functional outcome of transduction protocols. Nevertheless, polyclonal expansion continues to be a prerequisite for the majority of protocols of retroviral transduction of primary T cells.…”

“…In fact, there is evidence to suggest that the expansion process rather than the integration or expression of the transgene may have the largest effect on the function of GM T cells in vitro and in animal models. 2,4,6,[9][10][11][12][13] In humans, although the data available are still limited, a number of trials showed that GM T cells can have reduced function in vivo. [14][15][16] Phytohemagglutinin (PHA) is a common polyclonal stimulus used in protocols of retroviral transduction.…”

Effect of combined cytostatic cyclosporin A and cytolytic suicide gene therapy on the prevention of experimental graft-versus-host disease

“…Indeed, in a murine model of GVHD, we have already shown that a 7-day GCV treatment initiated at the time of transplantation is fully protective against GVHD, 9 and allows an efficient immune reconstitution. 9,[19][20][21] We also previously showed that the TK/GCV system more efficiently prevents than cures GVHD. 20 Whether or not this preventive treatment should be associated with the classical preventive treatment based on CsA in future clinical trials was the aim of this study.…”