Novel adoptive T-cell immunotherapy using a WT1-specific TCR vector encoding silencers for endogenous TCRs shows marked antileukemia reactivity and safety

Abstract

Adoptive T-cell therapy for malignancies using redirected T cells genetically engineered by tumor antigen-specific T-cell receptor (TCR) gene transfer is associated with mispairing between introduced and endogenous TCR chains with unknown specificity. Therefore, deterioration of antitumor reactivity and serious autoimmune reactivity are major concerns. To address this problem, we have recently established a novel retroviral vector system encoding siRNAs for endogenous TCR genes (siTCR vector). In this study, to test the clinical application of siTCR gene therapy for human leukemia, we examined in detail the efficacy and safety of WT1-siTCR-transduced T cells. Compared with conventional WT1-TCR (WT1-coTCR) gene-transduced T cells, these cells showed significant enhancement of antileukemia reactivity resulting from stronger expression of the introduced WT1-specific TCR with inhibition of endogenous TCRs. Notably, WT1-siTCR gene-transduced T cells were remarkably expandable after repetitive stimulation with WT1 peptide in vitro, without any deterioration of antigen specificity. WT1-siTCR gene-transduced T cells from IntroductionRecent identification of various tumor-associated antigens has encouraged the clinical development of cell-mediated immunotherapy for leukemia targeting leukemia-associated antigens. 1,2 Among various kinds of immunotherapy, adoptive tumor-specific T-cell therapy using ex vivo expansion of autologous tumorresponsive T cells seems to be an attractive option. Indeed, patients with advanced metastatic melanoma have been treated successfully with melanoma-specific T cells obtained from tumor-infiltrating T cells. [3][4][5] Although adoptive transfer of tumor-specific tumorinfiltrating T cells is a promising strategy, its general application for therapy would appear to be unlikely because of the complex procedures and difficulties involved in the timely preparation of sufficient numbers of tumor-specific cytotoxic T lymphocytes (CTLs) with adequate therapeutic quality. 6,7 To address these problems, an innovative approach involving substituting redirected T cells using predefined tumor antigen-specific T-cell receptor (TCR) gene transfer has been developed. In recent clinical trials, melanoma antigen-specific TCR gene-transferred T cells have been used for treatment of patients with advanced melanoma. 8,9 However, the clinical efficacy of TCR gene-engineered T cells is still not satisfactory, and serious autoimmune responses have been observed in some melanoma patients. In addition, adoptive immunotherapy using tumor antigen-specific TCR gene-transferred T cells targeting malignancies other than melanoma still remains in its infancy. Therefore, the development of TCR gene-immunotherapy targeting universal tumor-associated antigens is essential to popularize this strategy for cancer treatment.Wilms tumor gene product 1 (WT1) is one of the zinc-finger transcriptional regulators that is abundantly expressed in the vast majority of acute leukemias, but not in normal cells. 10,11 In addition, the exp...

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