WT1-targeted immunotherapy of leukaemia

T cell therapy targeting a public neoantigen in microsatellite instable colon cancer reduces in vivo tumor growth

T-cell receptor (TCR) transfer is an attractive strategy to increase the number of cancer-specific T cells in adoptive cell therapy. However, recent clinical and pre-clinical findings indicate that careful consideration of the target antigen is required to limit the risk of off-target toxicity. Directing T cells against mutated proteins such as frequently occurring frameshift mutations may thus be a safer alternative to tumor-associated self-antigens. Furthermore, such frameshift mutations result in novel polypeptides allowing selection of TCRs from the non-tolerant T-cell repertoire circumventing the problem of low affinity TCRs due to central tolerance. The transforming growth factor β Receptor II frameshift mutation (TGFβRII^mut) is found in Lynch syndrome cancer patients and in approximately 15% of sporadic colorectal and gastric cancers displaying microsatellite instability (MSI). The -1A mutation within a stretch of 10 adenine bases (nucleotides 709-718) of the TGFβRII gene gives rise to immunogenic peptides previously used for vaccination of MSI+ colorectal cancer patients in a Phase I clinical trial. From a clinically responding patient, we isolated a cytotoxic T lymphocyte (CTL) clone showing a restriction for HLA-A2 in complex with TGFβRII^mut peptide. Its TCR was identified and shown to redirect T cells against colon carcinoma cell lines harboring the frameshift mutation. Finally, T cells transduced with the HLA-A2-restricted TGFβRII^mut-specific TCR were demonstrated to significantly reduce the growth of colorectal cancer and enhance survival in a NOD/SCID xenograft mouse model.

Targeting c-MYC with T-cells

Over-expression of the proto-oncogene c-MYC is frequently observed in a variety of tumors and is a hallmark of Burkitt´s lymphoma. The fact that many tumors are oncogene-addicted to c-MYC, renders c-MYC a powerful target for anti-tumor therapy. Using a xenogenic vaccination strategy by immunizing C57BL/6 mice with human c-MYC protein or non-homologous peptides, we show that the human c-MYC protein, despite its high homology between mouse and man, contains several immunogenic epitopes presented in the context of murine H2^b haplotype. We identified an MHC class II-restricted CD4⁺ T-cell epitope and therein an MHC class I-restricted CD8⁺ T-cell epitope (SSPQGSPEPL) that, after prime/boost immunization, protected up to 25% of mice against a lethal lymphoma challenge. Lymphoma-rejecting animals contained MHC multimer-binding CD8⁺ cell within the peripheral blood and displayed in vivo cytolytic activity with specificity for SSPQGSPEPL. Taken together these data suggest that oncogenic c-MYC can be targeted with specific T-cells.

Structural and energetic evidence for highly peptide-specific tumor antigen targeting via allo-MHC restriction

Immunotherapies targeting peptides presented by allogeneic MHC molecules offer the prospect of circumventing tolerance to key tumor-associated self-antigens. However, the degree of antigen specificity mediated by alloreactive T cells, and their ability to discriminate normal tissues from transformed cells presenting elevated antigen levels, is poorly understood. We examined allorecognition of an HLA-A2-restricted Hodgkin's lymphoma-associated antigen and were able to isolate functionally antigen-specific allo-HLA-A2-restricted T cells from multiple donors. Binding and structural studies, focused on a prototypic allo-HLA-A2-restricted T-cell receptor (TCR) termed NB20 derived from an HLA-A3 homozygote, suggested highly peptide-specific allorecognition that was energetically focused on antigen, involving direct recognition of a distinct allopeptide presented within a conserved MHC recognition surface. Although NB20/HLA-A2 affinity was unremarkable, TCR/MHC complexes were very short-lived, consistent with suboptimal TCR triggering and tolerance to low antigen levels. These data provide strong molecular evidence that within the functionally heterogeneous alloreactive repertoire, there is the potential for highly antigen-specific "allo-MHC-restricted" recognition and suggest a kinetic mechanism whereby allo-MHC-restricted T cells may discriminate normal from transformed tissue, thereby outlining a suitable basis for broad-based therapeutic targeting of tolerizing tumor antigens.

Gene-modified T lymphocytes in the setting of hematopoietic cell transplantation: potential benefits and possible risks

INTRODUCTION

Allogeneic hematopoietic cell transplantation (HCT) is a consolidated treatment for several hematologic malignancies. Donor T lymphocytes can mediate a graft versus tumor (GVT) effect and control opportunistic infections but can also cause severe graft versus host disease (GVHD). Gene-transfer strategies are appealing tools to modulate T cell functions when infused after HCT.

AREAS COVERED

The current and potential future applications of T cell gene-transfer approaches to HCT. This review is not limited to GVHD control but covers the issues of GVT and immune reconstitution. Clinical data are used to discuss more general issues, perspectives and concerns common to gene-modification of T cells. An overview of the results and limitations emerging from clinical trials with herpes simplex virus-thymidine kinase (HSV-TK) engineered lymphocytes is provided. The review provides perspectives on additional gene-transfer strategies, currently at preclinical level or that have just entered clinical trials, to increase the efficacy and safety of HCT.

EXPERT OPINION

Gene-transfer can positively interfere with T cell functions after HCT. TK-lymphocytes have proven effective in controlling GVHD while retaining an acceptable GVT effect. Strategies exploiting new suicide molecules or engineered T cell receptors (TCRs) should be further explored to address current limitations with TK-lymphocytes and augment the efficacy and specificity of GVT and antiviral activity.

WT1 immunoreactivity in breast carcinoma: selective expression in pure and mixed mucinous subtypes

Current literature suggests that strong WT1 expression in a carcinoma of unknown origin virtually excludes a breast primary. Our previous pilot study on WT1 expression in breast carcinomas has shown WT1 expression in approximately 10% of carcinomas that show mixed micropapillary and mucinous morphology (Mod Pathol 2007;20(Suppl 2):38A). To definitively assess as to what subtype of breast carcinoma might express WT1 protein, we examined 153 cases of invasive breast carcinomas. These consisted of 63 consecutive carcinomas (contained 1 mucinous tumor), 20 cases with micropapillary morphology (12 pure and 8 mixed), 6 micropapillary 'mimics' (ductal no special type carcinomas with retraction artifacts), 33 pure mucinous carcinomas and 31 mixed mucinous carcinomas (mucinous mixed with other morphologic types). Overall, WT1 expression was identified in 33 carcinomas, that is, 22 of 34 (65%) pure mucinous carcinomas and in 11 of 33 (33%) mixed mucinous carcinomas. The non-mucinous component in these 11 mixed mucinous carcinomas was either a ductal no special type carcinoma (8 cases) or a micropapillary component (3 cases). WT1 expression level was similar in both the mucinous and the non-mucinous components. The degree of WT1 expression was generally weak to moderate (>90% cases) and rarely strong (<10% cases). None of the breast carcinoma subtype unassociated with mucinous component showed WT1 expression.

Listeriolysin O expressed in a bacterial vaccine suppresses CD4+CD25high regulatory T cell function in vivo

CD4(+)CD25(high) regulatory T cells (Treg) protect the host from autoimmune diseases but are also obstacles against cancer therapies. An ideal cancer vaccine would stimulate specific cytotoxic responses and reduce/suppress Treg function. In this study, we showed that Escherichia coli expressing listeriolysin O and OVA (E. coli LLO/OVA) demonstrated remarkable levels of protection against OVA-expressing tumor cells. By contrast, E. coli expressing OVA only (E. coli OVA) showed poor protection. High-avidity OVA-specific CTL were induced in E. coli LLO/OVA-vaccinated mice, and CD8(+) depletion--but not NK cell depletion, abolished the antitumor activity of the E. coli LLO/OVA vaccine. Phenotypic analysis of T cells following vaccination with either vaccine revealed preferential generation of CD44(high)CD62L(low) CD8(+) effector memory T cells over CD44(high)CD62L(high) central memory T cells. Unexpectedly, CD4(+) depletion turned E. coli OVA into a vaccine as effective as E. coli LLO/OVA suggesting that a subset of CD4(+) cells suppressed the CD8(+) T cell-mediated antitumor response. Further depletion experiments demonstrated that these suppressive cells consisted of CD4(+)CD25(high) regulatory T cells. We therefore assessed these vaccines for Treg function and found that although CD4(+)CD25(high) expansion and Foxp3 expression within this population was similar in all groups of mice, Treg cells from E. coli LLO/OVA-vaccinated animals were unable to suppress conventional T cells proliferation. These findings provide the first evidence that LLO expression affects Treg cell function and may have important implications for enhancing antitumor vaccination strategies in humans.

Immunomodulation against leukemias and lymphomas: a realistic future treatment?

Immunotherapy offers the potential for cure of malignancy without the side effects too commonly seen with conventional chemotherapy. The efficacy of allogenic transplantation and monoclonal antibodies in hematological malignancies illustrate this principle and are now part of routine care. Newer cell based and molecular approaches aimed at stimulating cytotoxic activity against host derived tumor associated antigens are able to 'boost' anti-tumor immunity as judged by immunological assays in vitro. Although clinically meaningful responses were originally less evident, more promising results are now being reported. Our growing understanding of tumor immunology provide rationales for further improvements in the field.

Cancer immunotherapy targeting Wilms' tumor gene WT1 product

The Wilms' tumor gene WT1 is expressed at high levels in leukemic blast cells in most acute myeloid and lymphoblastic leukemias. In myelodysplastic syndrome, WT1 mRNA expression levels increase along with disease progression; thus, WT1 mRNA is a tumor marker for leukemic blast cells. WT mRNA is also expressed at high levels in various types of solid cancers, including cancers of the lung, breast, colon and pancreas. Patients with WT1-expressing tumors produce antibodies and cytotoxic T-lymphocytes against WT1 protein, indicating that WT1 protein is highly immunogenic and a promising tumor antigen. Major histocompatibility complex class I-restricted cytotoxic T-lymphocyte and class II-restricted helper epitopes of WT1 protein were identified, and clinical studies of cancer immunotherapy using these cytotoxic T-lymphocyte epitope peptides were performed without significant adverse effect and with clinical results promising enough to encourage further clinical trials. The clinical efficacy of cancer immunotherapy targeting the WT1 protein should be clarified by a large-scale clinical study.

In vitro generation of tumor specific T cells that recognize a shared antigen of AML: molecular characterization of TCR genes

The identification of immunologically relevant tumor antigens is hampered by the difficulty of generating tumor-specific cytotoxic T cells (CTL). We present data demonstrating in vitro induction of autologous acute myelogenous leukemia (AML)-specific CTL. The specific T cell receptor has been identified and cloned. The CTL demonstrated specific lysis to autologous tumor blasts, but not to autologous BLCL or the NK-sensitive target K562. The clone secreted GM-CSF, TNFa, and IFNg when stimulated with AML blasts from 3 of 11 patients or cell lines tested, but not with K562 or autologous B-LCL. These three AML samples share a single HLA Class I antigen, HLA-A24. The T cell receptor genes identified by molecular methods are Vbeta7.9-J2.3-Cbeta2 and Valpha17-J49-Calpha.

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.

Antigen-specific cellular immunotherapy of leukemia

Advances in cellular and molecular immunology have led to the characterization of leukemia-specific T-cell antigens and to the development of strategies for effective augmentation of T-cell immunity in leukemia patients. While several leukemia-related antigens have been identified, this review focuses on the Wilms' tumor 1 (WT1) antigen and the proteinase 3 (Pr3) antigen that are overexpressed in leukemic cells and are already being used in the clinical setting. Moreover, WT1 is also overexpressed in a vast number of nonhematological solid tumors, thereby expanding its use as a promising target for cancer vaccines. Examples of spontaneous immune responses against WT1 and Pr3 in leukemia patients are presented and the potential of WT1 and Pr3 for adoptive T-cell immunotherapy of leukemia is discussed. We also elaborate on the use of professional antigen-presenting cells loaded with mRNA encoding WT1 exploiting the advantage of broad HLA coverage for therapeutic vaccination purposes. Finally, the summarized data underscore the potential of WT1 for the manipulation of T-cell immunity in leukemia and in cancer in general, that will likely pave the way for the development of more effective and generic cancer vaccines.

Direct recognition and lysis of leukemia cells by WT1-specific CD4+ T lymphocytes in an HLA class II-restricted manner

Wilms tumor gene 1 product (WT1) has been recognized as an attractive target antigen of immunotherapy for various malignancies including leukemia. Because tumor-associated antigen-specific CD4+ T lymphocytes undoubtedly play an important role in the induction of an antitumor immune response, we attempted to generate WT1-specific CD4+ T lymphocytes in vitro and examined their antileukemia functions. A CD4+ T-cell line, designated NIK-1, which proliferated and produced Th1 cytokines specifically in response to stimulation with the WT1-derived peptide, WT1337-347 LSHLQMHSRKH, in an HLA-DP5-restriced manner was established. NIK-1 exhibited cytotoxicity against HLA-DP5-positive, WT1-expressing leukemia cells but did not lyse HLA-DP5-negative, WT1-expressing leukemia cells or HLA-DP5-positive, WT1-negative cells. NIK-1 did not inhibit colony formation by normal bone marrow cells of HLA-DP5-positive individuals. This is the first report to describe WT1-specific and HLA class II-restricted CD4+ T lymphocytes possessing direct cytotoxic activity against leukemia cells. (Blood. 2005;106: 1415-1418)