Tumor-infiltrating CD8+ T cell antitumor efficacy and exhaustion: molecular insights

Host immunity has an essential role in the clinical management of cancers. Therefore, it is advantageous to choose therapies that can promote tumor cell death and concurrently boost host immunity. The dynamic tumor microenvironment (TME) determines whether an antineoplastic drug will elicit favorable or disparaging immune responses from tumor-infiltrating lymphocytes (TILs). CD8+ T cells are one of the primary tumor-infiltrating immune cells that deliver antitumor responses. Here, we review the influence of various factors in the TME on CD8+ T cell exhaustion and survival, and possible strategies for restoring CD8+ T cell effector function through immunotherapy.

Immunotherapies: Exploiting the Immune System for Cancer Treatment

Cancer is a condition that has plagued humanity for thousands of years, with the first depictions dating back to ancient Egyptian times. However, not until recent decades have biological therapeutics been developed and refined enough to safely and effectively combat cancer. Three unique immunotherapies have gained traction in recent decades: adoptive T cell transfer, checkpoint inhibitors, and bivalent antibodies. Each has led to clinically approved therapies, as well as to therapies in preclinical and ongoing clinical trials. In this review, we outline the method by which these 3 immunotherapies function as well as any major immunotherapeutic drugs developed for treating a variety of cancers.

IL15 and T-cell Stemness in T-cell-Based Cancer Immunotherapy

Preclinical models revealed that the immune system can mediate rejection of established tumors, but direct evidence in humans has been limited to largely immunogenic tumors, such as melanoma. The recent success of immune checkpoint inhibitors and adoptive T-cell transfer immunotherapy in clinical trials has instilled new hope for the use of T-cell immunotherapy in the treatment of cancer. IL15, a potent immunostimulatory cytokine, both potentiates host T-cells and natural killer (NK) cell immune responses and promotes the generation of long-lived memory T cells with superior functional capacity, with potential use in adoptive T-cell transfer protocols. IL15 has been recently tested in the clinic and showed dramatic effects at the level of responding NK and CD8(+) memory T cells. The recent advances in the knowledge of IL15-dependent regulation of T-cell responses, gene expression, and metabolic adaptation have important implications for the use of IL15 in T-cell-based immunotherapy of cancer.

Potential of human γδ T cells for immunotherapy of osteosarcoma

Recurrent or metastatic osteosarcomas remain a challenging malignancy to treat. Therefore, development and testing of novel therapeutic strategies to target these patients are needed. Adoptive cellular therapy strategies are being evaluated intensively as a novel therapeutic strategy for cancer. Unlike αβ T cells requiring antigen processing and MHC-restricted peptide displayed by antigen-presenting cells, γδ T cells exhibit the potent MHC-unrestricted lytic activity against various tumors in vitro and in vivo. The recent considerable success of γδ T cell-based immunotherapy in lung metastasis of renal cell carcinoma warrants further efforts to apply this treatment to other cancers including osteosarcoma, especially recurrent and metastatic osteosarcomas. In this review, we summarize the available evidence on γδ T cell-based immunotherapy for osteosarcoma that has been achieved to date. More importantly, we discuss potential strategies of the combination of expanded γδ T cells and bisphosphonates, and modification and expansion of αβ TCR modified γδ T cells for improving its efficacy for the treatment of osteosarcoma.

Challenges in T cell receptor gene therapy

The function of T lymphocytes as orchestrators and effectors of the adaptive immune response is directed by the specificity of their T cell receptors (TCRs). By transferring into T cells the genes encoding antigen-specific receptors, the functional activity of large populations of T cells can be redirected against defined targets including virally infected or cancer cells. The potential of therapeutic T cells to traffic to sites of disease, to expand and to persist after a single treatment remains a major advantage over the currently available immunotherapies that use monoclonal antibodies. Here we review recent progress in the field of TCR gene therapy, outlining challenges to its successful implementation and the strategies being used to overcome them. We detail strategies used in the optimization of affinity and surface expression of the introduced TCR, the choice of T cell subpopulations for gene transfer, and the promotion of persistence of gene-modified T cells in vivo. We review the safety concerns surrounding the use of gene-modified T cells in patients, discussing emerging solutions to these problems, and describe the increasingly positive results from the use of gene-modified T cells in recent clinical trials of adoptive cellular immunotherapy. The increasing sophistication of measures to ensure the safety of engineered T cells is accompanied by an increasing number of clinical trials: these will be essential to guide the effective translation of cellular immunotherapy from the laboratory to the bedside.

T-cell receptor gene therapy targeting melanoma-associated antigen-A4 inhibits human tumor growth in non-obese diabetic/SCID/γcnull mice

Adoptive cell therapy with lymphocytes that have been genetically engineered to express tumor-reactive T-cell receptors (TCR) is a promising approach for cancer immunotherapy. We have been exploring the development of TCR gene therapy targeting cancer/testis antigens, including melanoma-associated antigen (MAGE) family antigens, that are ideal targets for adoptive T-cell therapy. The efficacy of TCR gene therapy targeting MAGE family antigens, however, has not yet been evaluated in vivo. Here, we demonstrate the in vivo antitumor activity in immunodeficient non-obese diabetic/SCID/γc(null) (NOG) mice of human lymphocytes genetically engineered to express TCR specific for the MAGE-A4 antigen. Polyclonal T cells derived from human peripheral blood mononuclear cells were transduced with the αβ TCR genes specific for MAGE-A4, then adoptively transferred into NOG mice inoculated with MAGE-A4 expressing human tumor cell lines. The transferred T cells maintained their effector function in vivo, infiltrated into tumors, and inhibited tumor growth in an antigen-specific manner. The combination of adoptive cell therapy with antigen peptide vaccination enhanced antitumor activity, with improved multifunctionality of the transferred cells. These data suggest that TCR gene therapy with MAGE-A4-specific TCR is a promising strategy to treat patients with MAGE-A4-expressing tumors; in addition, the acquisition of multifunctionality in vivo is an important factor to predict the quality of the T-cell response during adoptive therapy with human lymphocytes.

Immunogenicity of a recombinant influenza virus bearing both the CD4+ and CD8+ T cell epitopes of ovalbumin

Recombinant influenza viruses that bear the single immunodominant CD8+ T cell epitope OVA_257−264 or the CD4+ T cell epitope OVA_323−339 of the model antigen ovalbumin (OVA) have been useful tools in immunology. Here, we generated a recombinant influenza virus, WSN-OVA_I/II, that bears both OVA-specific CD8+ and CD4+ epitopes on its hemagglutinin molecule. Live and heat-inactivated WSN-OVA_I/II viruses were efficiently presented by dendritic cells in vitro to OT-I TCR transgenic CD8+ T cells and OT-II TCR transgenic CD4+ T cells. In vivo, WSN-OVA_I/II virus was attenuated in virulence, highly immunogenic, and protected mice from B16-OVA tumor challenge in a prophylactic model of vaccination. Thus, WSN-OVA_I/II virus represents an additional tool, along with OVA TCR transgenic mice, for further studies on T cell responses and may be of value in vaccine design.

T cell receptor gene therapy for cancer

T cell-based adoptive immunotherapy has been shown to be a promising treatment for various types of cancer. However, adoptive T cell therapy currently requires the custom isolation and characterization of tumor-specific T cells from each patient-a process that can be not only difficult and time-consuming but also often fails to yield high-avidity T cells, which together have limited the broad application of this approach as a clinical treatment. Employing T cell receptor (TCR) gene therapy as a component of adoptive T cell therapy strategies can overcome many of these obstacles, allowing autologous T cells with a defined specificity to be generated in a much shorter time period. Initial studies using this approach have been hampered by a number of technical difficulties resulting in low TCR expression and acquisition of potentially problematic specificities due to mispairing of introduced TCR chains with endogenous TCR chains. The last several years have seen substantial progress in our understanding of the multiple facets of TCR gene therapy that will have to be properly orchestrated for this strategy to succeed. Here we outline the challenges of TCR gene therapy and the advances that have been made toward realizing the promise of this approach.

Genetic redirection of T cells for cancer therapy

Adoptive immunotherapy can induce dramatic tumor regressions in patients with melanoma or viral-induced malignancies, but extending this approach to many common cancers has been hampered by a lack of naturally occurring tumor-specific T cells. In this review, we describe recent advances in the genetic modification of T cells using genes encoding cell-surface receptors specific for tumor-associated antigen. Using genetic modification, the many functional properties of T cells, including cytokine secretion and cytolytic capacity, are redirected from their endogenous specificity toward the elimination of tumor cells. Advances in gene design, vectors, and cell production are discussed, and details of the progress in clinical application of this approach are provided.

Improved expression and reactivity of transduced tumor-specific TCRs in human lymphocytes by specific silencing of endogenous TCR

Adoptive T-cell therapy using lymphocytes genetically engineered to express tumor antigen-specific TCRs is an attractive strategy for treating patients with malignancies. However, there are potential drawbacks to this strategy: mispairing of the introduced TCR alpha/beta chains with the endogenous TCR subunits and competition of CD3 molecules between the introduced and endogenous TCRs can impair cell surface expression of the transduced TCR, resulting in insufficient function and potential generation of autoreactive T cells. In addition, the risk of tumor development following the infusion of cells with aberrant vector insertion sites increases with the vector copy number in the transduced cells. In this study, we developed retroviral vectors encoding both small interfering RNA constructs that specifically down-regulate endogenous TCR and a codon-optimized, small interfering RNA-resistant TCR specific for the human tumor antigens MAGE-A4 or WT1. At low copy numbers of the integrated vector, the transduced human lymphocytes exhibited high surface expression of the introduced tumor-specific TCR and reduced expression of endogenous TCRs. In consequence, the vector-transduced lymphocytes showed enhanced cytotoxic activity against antigen-expressing tumor cells. Therefore, our novel TCR gene therapy may open a new gate for effective immunotherapy in cancer patients.

The Lewis-Y carbohydrate antigen is expressed by many human tumors and can serve as a target for genetically redirected T cells despite the presence of soluble antigen in serum

In this study we aimed to determine the suitability of the Lewis-Y carbohydrate antigen as a target for immunotherapy using genetically redirected T cells. Using the 3S193 monoclonal antibody and immunohistochemistry, Lewis-Y was found to be expressed on a range of tumors including 42% squamous cell lung carcinoma, 80% lung adenocarcinoma, 25% ovarian carcinoma, and 25% colorectal adenocarcinoma. Expression levels varied from low to intense on between 1% and 90% of tumor cells. Lewis- was also found in soluble form in sera from both normal donors and cancer patients using a newly developed enzyme-linked immunosorbent assay. Serum levels in patients was often less than 1 ng/mL, similar to normal donors, but approximately 30% of patients had soluble Lewis-Y levels exceeding 1 ng/mL and up to 9 ng/mL. Lewis-Y-specific human T cells were generated by genetic modification with a chimeric receptor encoding a single-chain humanized antibody linked to the T-cell signaling molecules, T-cell receptor-zeta, and CD28. T cells responded against the Lewis-Y antigen by cytokine secretion and cytolysis in response to tumor cells. Importantly, the T-cell response was not inhibited by patient serum containing soluble Lewis-Y. This study demonstrates that Lewis-Y is expressed on a large number of tumors and Lewis-Y-specific T cells can retain antitumor function in the presence of patient serum, indicating that this antigen is a suitable target for this form of therapy.

TCR transgenes and transgene cassettes for TCR gene therapy: status in 2008

The genetic introduction of T cell receptor genes into T cells has been developed over the past decade as a strategy to induce defined antigen-specific T cell immunity. With the potential value of TCR gene therapy well-established in murine models and the feasibility of infusion of TCR-modified autologous T cells shown in a first phase I trial, the next key step will be to transform TCR gene transfer from an experimental technique into a robust clinical strategy. In this review, we discuss the different properties of the TCR transgene and transgene cassette that can strongly affect both the efficacy and the safety of TCR gene transfer.

Alpha beta T cell receptor transfer to gamma delta T cells generates functional effector cells without mixed TCR dimers in vivo

The successful application of T cell-based immunotherapeutic applications depends on the availability of large numbers of T cells with the desired Ag specificity and phenotypic characteristics. Engineering of TCR-transferred T lymphocytes is an attractive strategy to obtain sufficient T cells with an Ag specificity of choice. However, the introduction of additional TCR chains into T cells leads to the generation of T cells with unknown specificity, due to the formation of mixed dimers between the endogenous and introduced TCR chains. The formation of such potentially autoaggressive T cells may be prevented by using gammadelta T cells as recipient cells, but the in vivo activity of such TCR-engineered gammadelta T cells has not been established. In the present study, we have investigated the in vivo functionality of TCR-transduced gammadelta T cells, in particular their Ag specific proliferative capacity, Ag specific reactivity, in vivo persistence, and their capacity to mount recall responses. The results demonstrate that alphabeta TCR engineering of gammadelta T cells forms a feasible strategy to generate Ag-specific effector T cells that do not express mixed TCR dimers. In view of increasing concerns on the potential autoimmune consequences of mixed TCR dimer formation, the testing of alphabeta TCR engineered gammadelta T cells in clinical trials seems warranted.