Analysis of transgene-specific immune responses that limit the in vivo persistence of adoptively transferred HSV-TK–modified donor T cells after allogeneic hematopoietic cell transplantation

Abstract

IntroductionThe genetic modification of cells has the potential to improve upon current therapies for inherited and acquired diseases. For example, the introduction of a conditional suicide gene into T cells has been proposed as a strategy for enhancing the safety of adoptive T-cell therapy for cancer where the antigens targeted by transferred T cells are expressed on both normal and malignant cells [1][2][3][4][5][6] or where T cells are modified to confer novel functions that might improve antitumor efficacy but could cause toxicity. 7 However, a problem that is increasingly being recognized in clinical gene therapy is the development of immune responses to transgene-encoded proteins, and many of the suicide genes developed for clinical use are derived from pathogens and are potentially immunogenic. 8,9 The herpes simplex virus thymidine kinase (HSV-TK) gene has been used most extensively in the clinic for regulating cell survival, but data on its immunogenicity are conflicting, perhaps reflecting differences in the immunocompetence of treated patients and/or the assays used to analyze immune responses. [8][9][10][11][12][13][14][15] The first study to administer HSV-TK-modified T cells to patients used a retrovirus (HyTK) that encodes hygromycin phosphotransferase (Hy) and HSV-TK to transduce autologous HIV gag-specific CD8 ϩ T-cell clones that were infused into HIV-infected individuals to augment virus-specific immunity. There was rapid clearance of HyTKpositive T cells after repeated infusions, and the elimination of T cells coincided with the induction of CD8 ϩ cytotoxic T lymphocyte (CTL) responses directed against Hy and HSV-TK. 11 In contrast, studies in allogeneic hematopoietic cell transplantation (HCT) recipients in which transferred donor T cells were modified with HSV-TK and adoptively transferred to induce a graft versus leukemia (GVL) effect have suggested that immune recognition of gene-modified T cells may be less of an impediment. Bonini et al 12 used HSV-TK-modified donor lymphocyte infusion (DLI) to treat a small number of patients with Epstein-Barr virus (EBV) lymphoproliferative disease (LPD) or relapsed leukemia after allogeneic T-cell-depleted HCT. The transferred HSV-TK-positive T cells were detected for more than 12 months in vivo, exerted an antitumor effect, and could be eliminated by administration of ganciclovir (GCV). 12 Tiberghien et al administered HSV-TKpositive T cells with a T-cell-depleted graft to 12 HCT recipients and confirmed the persistence of HSV-TK-modified cells. 14 However, in a subsequent study in which HSV-TK-modified donor T cells were administered to patients with relapsed malignancies after unmodified allogeneic HCT, the gene-modified cells did not persist after transfer in most of the patients. 16 Studies to evaluate immune responses to HSV-TK were not performed; thus, it was unclear if the failure of gene-modified T cells to persist was due to immune rejection or to the in vitro culture conditions used to generate the cells. 16,17 Here we report the results o...

An Inducible Caspase 9 Safety Switch Can Halt Cell Therapy-Induced Autoimmune Disease

“…Furthermore, immunogenicity of the gene-modified cells is likely to be minimal, because of the lack of substantial amounts of nonhuman sequence. This offers a substantial advantage over the HSV-TK system, where the survival of gene-modified cells may be limited due the immunogenicity of the HSV-TK gene product (11), and where ganciclovir treatment of CMV infection can also lead to the untimely elimination of the infused cell population.…”

“…However, ganciclovir is also frequently used to treat CMV infections in patients who undergo allogeneic stem cell transplantation (allo-SCT), resulting in an unwanted elimination of the genetically modified cells. More importantly, unwanted elimination of the transferred T cells as a consequence of immune responses toward the HSV-TK gene product has been observed in a substantial fraction of patients, likely limiting the use of this safety switch to patients who are immune suppressed at the time of T cell infusion (11,12). As a first possible nonimmunogenic alternative safety switch, a human CD20 molecule has been validated in preclinical studies (13,14).…”

Harnessing autophagy for cell fate control gene therapy

“…First, the HSV-TK enzyme used in initial clinical efforts is highly immunogenic, thereby likely limiting the in vivo persistence and immune therapeutic efficacy of transgene-expressing T cells. 13,30 In a second approach, T cell expression of iCasp9 allowed dimerization of proapoptotic molecules thus resulting in rapid elimination of transgene-expressing T cells and subsequent reduction in GVHD; 15 however, the dimerizing agent prodrug is not FDA inhibits cytokine signaling and the cell cycle machinery required for T cell proliferation 35,36 one might hypothesize that T cells treated in vitro with rapamycin would be refractory to LV transduction. That is, LV is known for transducing many types of nondividing cells and also for promoting stable gene expression, but one limitation is its relative inability to infect resting T cells; 37 consistent with this point, in previous studies, T cell transduction in the setting of increased IL2 signaling was permissive for LV infection.…”

Chimeric antigen receptor modified T cell therapy for B cell malignancies

“…Suicide genes may be incorporated into CAR-encoding vectors. Thymidine kinase from HSV (HSV-TK) has been used as an effective suicide gene in transferred T cells, but its immunogenicity may limit its future utility in adoptive T cell transfer [58,63]. Recent studies demonstrated that administration of a small molecule dimerizer (AP1903) to allogeneic HCT recipients induced rapid amelioration of acute GVHD and elimination of transplanted T cells that were engineered to express an AP1903-inducible caspase [64].…”