Recurrence of melanoma following T cell treatment: continued antigen expression in a tumor that evades T cell recruitment.

Clinical therapy with T cells shows promise for cancer patients, but is currently challenged by incomplete responses and tumor relapse. The exact mechanisms that contribute to tumor relapse remain largely unclear. Here, we treated mouse melanomas with T cell receptor-engineered T cells directed against a human peptide-major histocompatibility complex antigen in immune-competent mice. T cells resulted in significant tumor regression, which was followed by relapse in about 80-90% of mice. Molecular analysis revealed that relapsed tumors harbored nonmutated antigen genes, not silenced by promoter methylation, and functionally expressed surface antigen at levels equal to nontreated tumors. Relapsed tumors resisted a second in vivo T cell treatment, but regained sensitivity to T cell treatment upon retransplantation in mice. Notably, relapsed tumors demonstrated decreased levels of CD8 T cells and monocytes, which were substantiated by downregulated expression of chemoattractants and adhesion molecules. These observations were confirmed when using T cells specific for a less immunogenic, endogenous mouse melanoma antigen. We conclude that tumors, when exposed to T cell treatment, can relapse without loss of antigen and develop a milieu that evades recruitment of effector CD8 T cells. Our findings support the concept to target the tumor milieu to aid T cell therapy in limiting tumor relapse.

Flow cytometric assessment of agonist-induced P-selectin expression as a measure of platelet quality in stored platelet concentrates.

BACKGROUND: Platelet (PLT) function in PLT concentrates declines during storage and is further affected by pathogen reduction treatment. Flow cytometric assessment of agonist-induced P-selectin expression can be used to assess PLT function in patients with thrombocytopenia. The aim of this study was to evaluate how this functional test relates to established in vitro measures of PLT function. STUDY DESIGN AND METHODS: Six units of PLTs in plasma and 6 units of riboflavin and ultraviolet (Mirasol, TerumoBCT)-treated PLTs in plasma were sampled on Days 2, 6, 8, and 10 after donation. PLT concentration, Annexin 5A staining, ThromboLUX (LightIntegra) thrombelastography, and P-selectin expression, both in unstimulated PLTs and in response to concentration series of adenosine diphosphate, collagen-related peptide, and thrombin receptor-activating peptide (TRAP), were measured. RESULTS: For PLTs in plasma Annexin 5A expression increased by 0.60% (95% confidence interval [CI], 0.40%-0.80%) and P-selectin expression increased by 1.2% (95% CI, 0.80%-1.6%) per day. Responsiveness to TRAP simultaneously decreased by 1.3% (95% CI, 0.80%-1.8%) per day. After Mirasol treatment ThromboLUX scores decreased 3.3 points (95% CI, 0.2-6.4 points) from 22 to 19 points, Annexin 5A expression increased by 4.8% (95% CI, 3.3%-6.2%), and P-selectin expression increased by 13% (95% CI, 10%-16%), all averaged over the entire storage period. Responsiveness to TRAP simultaneously decreased by 19% (95% CI, 17%-21%). CONCLUSIONS: Our results suggest flow cytometric measurement of agonist-induced P-selectin expression can measure PLT quality decline over the entire range encountered during 10-day storage of both standard PLTs and Mirasol-treated PLTs in plasma.

Design and use of conditional MHC class I ligands.

Major histocompatibility complex (MHC) class I molecules associate with a variety of peptide ligands during biosynthesis and present these ligands on the cell surface for recognition by cytotoxic T cells. We have designed conditional MHC ligands that form stable complexes with MHC molecules but degrade on command, by exposure to a defined photostimulus. 'Empty MHC molecules' generated in this manner can be loaded with arrays of peptide ligands to determine MHC binding properties and to monitor antigen-specific T-cell responses in a high-throughput manner. We document the value of this approach by identifying cytotoxic T-cell epitopes within the H5N1 influenza A/Vietnam/1194/04 genome.

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.

TCR gene therapy of spontaneous prostate carcinoma requires in vivo T cell activation.

Analogous to the clinical use of recombinant high-affinity Abs, transfer of TCR genes may be used to create a T cell compartment specific for self-Ags to which the endogenous T cell repertoire is immune tolerant. In this study, we show in a spontaneous prostate carcinoma model that the combination of vaccination with adoptive transfer of small numbers of T cells that are genetically modified with a tumor-specific TCR results in a marked suppression of tumor development, even though both treatments are by themselves without effect. These results demonstrate the value of TCR gene transfer to target otherwise nonimmunogenic tumor-associated self-Ags provided that adoptive transfer occurs under conditions that allow in vivo expansion of the TCR-modified T cells.

Prospects and limitations of T cell receptor gene therapy.

Adoptive transfer of antigen-specific T cells is an attractive means to provide cancer patients with immune cells of a desired specificity and the efficacy of such adoptive transfers has been demonstrated in several clinical trials. Because the T cell receptor is the single specificity-determining molecule in T cell function, adoptive transfer of TCR genes into patient T cells may be used as an alternative approach for the transfer of tumor-specific T cell immunity. On theoretical grounds, TCR gene therapy has two substantial advantages over conventional cellular transfer, as it can circumvent the demanding process of in vitro generation of large numbers of specific immune cells and it allows the use of a set of particularly effective TCR genes in large patient groups. Conversely, TCR gene therapy may be associated with a number of specific problems that are not confronted during classical cellular therapy. Here we review our current understanding of the potential and possible problems of TCR gene therapy, as based on in vitro experiments and mouse model systems. Furthermore, we discuss the prospects of clinical application of this gene therapy approach, and the possible barriers on the route towards clinical use.

An Altered gp100 Peptide Ligand with Decreased Binding by TCR and CD8α Dissects T Cell Cytotoxicity from Production of Cytokines and Activation of NFAT.

Altered peptide ligands (APLs) provide useful tools to study T cell activation and potentially direct immune responses to improve treatment of cancer patients. To better understand and exploit APLs, we studied the relationship between APLs and T cell function in more detail. Here, we tested a broad panel of gp100280-288 APLs with respect to T cell cytotoxicity, production of cytokines, and activation of Nuclear Factor of Activated T cells (NFAT) by human T cells gene-engineered with a gp100-HLA-A2-specific TCRαß. We demonstrated that gp100-specific cytotoxicity, production of cytokines, and activation of NFAT were not affected by APLs with single amino acid substitutions, except for an APL with an amino acid substitution at position 3 (APL A3), which did not elicit any T cell response. A gp100 peptide with a double amino acid mutation (APL S4S6) elicited T cell cytotoxicity and production of IFNγ, and to a lesser extent TNFα, IL-4, and IL-5, but not production of IL-2 and IL-10, or activation of NFAT. Notably, T cell receptor (TCR)-mediated functions showed decreases in sensitivities for S4S6 versus gp100 wild-type (wt) peptide, which were minor for cytotoxicity but at least a 1000-fold more prominent for the production of cytokines. TCR-engineered T cells did not bind A3-HLA-A2, but did bind S4S6-HLA-A2 although to a lowered extent compared to wt peptide-HLA-A2. Moreover, S4S6-induced T cell function demonstrated an enhanced dependency on CD8α. Taken together, most gp100 APLs functioned as agonists, but A3 and S4S6 peptides acted as a null ligand and partial agonist, respectively. Our results further suggest that TCR-mediated cytotoxicity can be dissected from production of cytokines and activation of NFAT, and that the agonist potential of peptide mutants relates to the extent of binding by TCR and CD8α. These findings may facilitate the design of APLs to advance the study of T cell activation and their use for therapeutic applications.

T-cell receptor gene therapy in human melanoma-bearing immune-deficient mice: human but not mouse T cells recapitulate outcome of clinical studies.

Adoptive cell therapy using T-cell receptor (TCR)-engineered T cells is a clinically feasible and promising approach to target tumors, but is currently faced with compromised antitumor efficacies in patients. Here, we extensively validated immune-deficient mice to facilitate further development of the therapeutic potential of TCR-engineered T cells. Treatment of human melanoma-bearing SCID or NSG mice with high doses of human T cells transduced with an hgp100/HLA-A2-specific TCR did not result in antitumor responses irrespective of chemotherapeutic preconditioning. Imaging of human green fluorescent protein-labeled T cells demonstrated significant T-cell accumulation in intratumoral vasculature directly upon T-cell transfer, which was followed by loss of T cells within 72 hr. Peripheral persistence of human T cells was highly compromised and appeared related to T-cell differentiation. On the contrary, adoptive transfer (AT) of relatively low numbers of hgp100/HLA-A2 TCR-transduced mouse T cells resulted in rapid clearance of large established human melanomas. Unexpectedly and in contrast to reported studies with chimeric antibody receptor-engineered T cells, antitumor activity and homeostatic expansion of T cells were independent of TCR transgene as evidenced in two SCID strains and using two different human melanoma cell lines. Interestingly, the xeno-reactive melanoma response of mouse T cells appeared to be dictated by CD4(+) tumor-infiltrating lymphocytes and did not require in vitro T-cell activation, retroviral gene transfer, or subcutaneous interleukin-2 support. Taken together, AT of human but not mouse T cells in human melanoma-bearing immune-deficient mice is in close accordance with clinical studies.

Prospects and limitations of T cell receptor gene therapy.

Adoptive transfer of antigen-specific T cells is an attractive means to provide cancer patients with immune cells of a desired specificity and the efficacy of such adoptive transfers has been demonstrated in several clinical trials. Because the T cell receptor is the single specificity-determining molecule in T cell function, adoptive transfer of TCR genes into patient T cells may be used as an alternative approach for the transfer of tumor-specific T cell immunity. On theoretical grounds, TCR gene therapy has two substantial advantages over conventional cellular transfer. First, it circumvents the demanding process of in vitro generation of large numbers of specific immune cells. Second, it allows the use of a set of particularly effective TCR genes in large patient groups. Conversely, TCR gene therapy may be associated with a number of specific problems that are not confronted during classical cellular therapy. Here we review our current understanding of the potential and possible problems of TCR gene therapy, as based on in vitro experiments, mouse model systems and phase I clinical trials. Furthermore, we discuss the prospects of widespread clinical application of this gene therapy approach for the treatment of human cancer.

T cell receptor (TCR) gene therapy to treat melanoma: lessons from clinical and preclinical studies.

IMPORTANCE OF THE FIELD: Adoptive T cell therapy (ACT) with tumour infiltrating lymphocytes is currently the best treatment option for metastatic melanoma. Despite its clinical successes, ACT has limitations in availability and generation of therapeutic T cells for a larger group of patients. Introduction of tumour-specific T cell receptors into T cells, termed TCR gene therapy, can provide an alternative for ACT that is more widely applicable and might be extended to other types of cancer. AREAS COVERED IN THIS REVIEW: The current status of TCR gene therapy studies including clinical challenges, such as on-target toxicity, compromised anti-tumour T cell responses, compromised T cell persistence and potential immunogenicity of receptor transgenes. Strategies to address these challenges are covered. WHAT THE READER WILL GAIN: A listing and discussion of strategies that aim at improving the efficacy and safety of TCR gene therapy. Such strategies address antigen choice, TCR mis-pairing, functional avidity and persistence of T cells, immune responses towards receptor transgenes, and combination of ACT with other therapies. TAKE HOME MESSAGE: To ensure further clinical development of TCR gene therapy, it is necessary to choose safe T cell target antigens, and implement (combinations of) strategies that enhance the correct pairing of TCR transgenes and the functional avidity and persistence of T cells.

T cell receptor gene therapy: strategies for optimizing transgenic TCR pairing.

T cell receptor (TCR) gene therapy provides patients with autologous T cells that are genetically engineered with TCRalphabeta chains and constitutes a promising approach for the treatment of tumors and virus infections. Among the current challenges of TCR gene therapy is the optimization of TCRalpha and beta transgene pairing to enhance the functional avidity of therapeutic T cells. Recently, various genetically modified TCRs have been developed that enhance TCR pairing and minimize mispairing, i.e. pairing between transgenic and endogenous TCR chains. Here, we classify such receptors according to their CD3-dependence for surface expression and review their abilities to address functional T cell avidity. In addition, we discuss the anticipated clinical value of these and other strategies to generate high-avidity T cells.

Long-term functionality of TCR-transduced T cells in vivo.

To broaden the applicability of adoptive T cell therapy to cancer types for which tumor-specific T cells cannot routinely be isolated, an effort has been made to develop the transfer of tumor-specific TCR genes into autologous T cells as a novel immunotherapeutic approach. Although such TCR-modified T cells have been shown to react to Ag encounter and can be used to break tolerance to defined self-Ags, the persistence and capacity for renewed expansion of TCR-modified T cells has not been analyzed. To establish whether TCR-transduced T cells can provide recipients with long-term Ag-specific immune protection, we analyzed long-term function of TCR transduced T cells in mouse model systems. We demonstrate that polyclonal populations of T cells transduced with a class I restricted OVA-specific TCR are able to persist in vivo and respond upon re-encounter of cognate Ag as assessed by both proliferation and cytolytic capacity. These experiments indicate that TCR gene transfer can be used to generate long-term Ag-specific T cell responses and provide a useful model system to assess the factors that can promote high-level persistence of TCR-modified T cells.

Targeting self-antigens through allogeneic TCR gene transfer.

Adoptive transfer of T-cell receptor (TCR) genes has been proposed as an attractive approach for immunotherapy in cases where the endogenous T-cell repertoire is insufficient. While there are promising data demonstrating the capacity of TCR-modified T cells to react to foreign antigen encounter, the feasibility of targeting tumor-associated self-antigens has not been addressed. Here we demonstrate that T-cell receptor gene transfer allows the induction of defined self-antigen-specific T-cell responses, even when the endogenous T-cell repertoire is nonreactive. Furthermore, we show that adoptive transfer of T-cell receptor genes can be used to induce strong antigen-specific T-cell responsiveness in partially MHC-mismatched hosts without detectable graft versus host disease. These results demonstrate the feasibility of using a collection of "off the shelf" T-cell receptor genes to target defined tumor-associated self-antigens and thereby form a clear incentive to test this immunotherapeutic approach in a clinical setting.

The impact of self-tolerance on the polyclonal CD8+ T cell repertoire.

TCRs possess considerable cross-reactivity toward structurally related Ags. Because the signaling threshold for negative selection is lower than that required for activation of mature T cells, the question arises as to which extent thymic deletion of self-specific T cells affects T cell responsiveness toward foreign peptides. In this study we show, in three different mouse models systems, that the polyclonal CD8(+) T cell repertoire has a marked ability to react against the majority of Ags related to self despite self-tolerance, even in cases where self and foreign differ only marginally at a single TCR-contact residue. Thus, while individual T cells are markedly cross-reactive, the ability to distinguish between closely related Ags is introduced at the polyclonal T cell level.