Separately expressed T cell receptor alpha and beta chain transgenes exert opposite effects on T cell differentiation and neoplastic transformation

Effective Cytotoxicity of Dendritic Cells against Established T Cell Lymphomas in Mice

T cell lymphomas arise in mice that constitutively express a single TCR in the absence of NK cells. Upon TCR engagement these lymphomas are able to corrupt tumor surveillance by decreasing NK cell numbers. In this study, we investigate the outcome of interactions between these T cell lymphomas and dendritic cells. Bone marrow–derived dendritic cells mediated effective killing of T cell lymphomas after activation with IFN-γ and TLR ligands in culture. This cytotoxicity was independent of MHC compatibility. Cell lysis was reduced by the presence of the peroxynitrite inhibitors FeTTPS and L-NMMA, whereas inhibitors of apoptosis, death receptors, and degranulation were without effect, suggesting NO metabolites as the main mediators. When injected together with GM-CSF and R848 into lymphoma-bearing mice, in vitro–expanded bone marrow–derived dendritic cells caused significant survival increases. These data show that dendritic cell adaptive immunotherapy can be used as treatment against T cell lymphomas in mice.

Stimulated bone marrow–derived dendritic cells lyse T lymphoma target cells in vitro.

Dendritic cell–mediated cytotoxicity is dependent on peroxynitrite.

Dendritic cell transfers into T lymphoma-bearing mice show antitumor efficacy.

NK cells prevent T cell lymphoma development in T cell receptor-transgenic mice

Mice that express a single transgenic T cell receptor have a low incidence of T cell lymphoma development. We investigated whether this tumor development is restricted by surveillance mechanisms that are exerted by IL-15-dependent cells. Lymphoma incidence was increased to between 30 and 60% when TCR transgenes were expressed in IL-15-deficient mice. Mice in which NK cells had been depleted genetically or with neutralizing antibodies allowed lymphoma growth while the absence of CD8 T cells was without consequence. Half of the emerged T cell lymphomas carried Notch1 mutations. The distinct phenotype of the lymphomas involved expression of PD1, CD30, CD24, the stress receptor ligand Mult1 and MHC class I down-regulation. NK cells were able to directly lyse lymphoma cells, and neutralizations of Mult1 and class I expression prevented NK cell degranulation. Together these data support an involvement of NK cells in tumor surveillance of nascent T cell lymphomas.

The TCR/CD3 complex in leukemogenesis and as a therapeutic target in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) arises from T cell precursors and is characterized by expression of many lineage-specific proteins. While T-cell antigen receptor (TCR) signaling and its strength are central for thymocyte development, mature T cell homeostasis and immune responses, their roles in T-ALL remain undetermined. Indeed, in contrast to mouse models, in which absence of TCR or major histocompatibility complex binding does not impact on leukemogenesis, other mouse models suggest that basal or weak signaling drives leukemia development. However, recent reports indicate that strong TCR signaling can be detrimental to leukemic cells. Indeed, sustained/high level TCR signaling, stimulated by antigen or CD3 antibody, is strongly anti-leukemic in both murine T-ALL expressing endogenous or transgenic TCR and diagnostic T-ALL cases. As discussed, further work should address the efficacy of T-ALL therapeutic targeting with either TCR/CD3 antibodies or TCR-directed chimeric antigen receptor T cells.

Thymic expression of a T-cell receptor targeting a tumor-associated antigen coexpressed in the thymus induces T-ALL

T-cell receptors (TCRs) and chimeric antigen receptors recognizing tumor-associated antigens (TAAs) can now be engineered to be expressed on a wide array of immune effectors. Engineered receptors targeting TAAs have most commonly been expressed on mature T cells, however, some have postulated that receptor expression on immune progenitors could yield T cells with enhanced potency. We generated mice (survivin-TCR-transgenic [Sur-TCR-Tg]) expressing a TCR recognizing the immunodominant epitope (Sur20-28) of murine survivin during early stages of thymopoiesis. Spontaneous T-cell acute lymphoblastic leukemia (T-ALL) occurred in 100% of Sur-TCR-Tg mice derived from 3 separate founders. The leukemias expressed the Sur-TCR and signaled in response to the Sur20-28 peptide. In preleukemic mice, we observed increased cycling of double-negative thymocytes expressing the Sur-TCR and increased nuclear translocation of nuclear factor of activated T cells, consistent with TCR signaling induced by survivin expression in the murine thymus. β2M(-/-) Sur-TCR-Tg mice, which cannot effectively present survivin peptides on class I major histocompatibility complex, had significantly diminished rates of leukemia. We conclude that TCR signaling during the early stages of thymopoiesis mediates an oncogenic signal, and therefore expression of signaling receptors on developing thymocytes with specificity for TAAs expressed in the thymus could pose a risk for neoplasia, independent of insertional mutagenesis.

T cells and their eons-old obsession with MHC

T cells bearing receptors made up of α and β chains (TCRs) usually react with peptides bound to major histocompatibility complex proteins (MHC). This bias could be imposed by positive selection, the phenomenon that selects thymocytes to mature into T cells only if the TCRs they bear react with low but appreciable affinity with MHC + peptide combinations in the thymus cortex. However, it is also possible that the polypeptides of TCRs themselves do not have random specificities but rather are biased toward reaction with MHC. Evolution would therefore have selected for a collection of TCR variable elements that are prone to react with MHC. If this were to be so, positive selection would act on thymocytes bearing a pre biased collection of TCRs to pick out those that react to some extent, but not too well, with self MHC + self-peptides. A problem with studies of this evolutionary idea is the fact that there are many TCR variable elements and that these differ considerably in the amino acids with which they contact MHC. However, recent experiments by our group and others suggest that one group of TCR variable elements, those related to the mouse Vβ8 family, has amino acids in their CDR2 regions that consistently bind a particular site on an MHC α-helix. Other groups of variable elements may use different patterns of amino acids to achieve the same goal. Mutation of these amino acids reduces the ability of T cells and thymocytes to react with MHC. These amino acids are present in the variable regions of distantly related species such as sharks and human. Overall the data indicate that TCR elements have indeed been selected by evolution to react with MHC proteins. Many mysteries about TCRs remain to be solved, including the nature of auto-recognition, the basis of MHC allele specificity, and the very nature and complexity of TCRs on mature T cells.

T-cell receptor-driven lymphomagenesis in mice derived from a reprogrammed T cell

The conversion of mature somatic cells into pluripotent stem cells, both by nuclear transfer and transduction with specific "reprogramming" genes, represents a major advance in regenerative medicine. Pluripotent stem cell lines can now be generated from an individual's own cells, facilitating the generation of immunologically acceptable stem cell-based therapeutics. Many cell types can undergo nuclear reprogramming, leading to the question of whether the identity of the reprogrammed cell of origin has a biological consequence. Peripheral blood, containing a mixture of T, B, NK, and myeloid cell types, represents one potential source of reprogrammable cells. In this study, we describe the unique case of mice derived from a reprogrammed T cell. These mice have prerearranged T-cell receptor (TCR) genes in all cells. Surprisingly, ≈50% of mice with prerearranged TCR genes develop spontaneous T cell lymphomas, which originate in the thymus. The lymphomas arise from developing T cells, and contain activated Notch1, similar to most human and mouse T-cell acute lymphoblastic lymphomas. Furthermore, lymphomagenesis requires the expression of both prerearranged TCRα and TCRβ genes, indicating a critical role for TCR signaling. Furthermore, inhibitors of multiple branches of TCR signaling suppress lymphoma growth, implicating TCR signaling as an essential component in lymphoma proliferation. The lymphomagenesis in mice derived from a reprogrammed T cell demonstrates the deleterious consequences of misregulation of the TCR rearrangement and signaling pathways and illustrates one case of cellular reprogramming where the identity of the cell of origin has profound consequences.

A Stat5b transgene is capable of inducing CD8+ lymphoblastic lymphoma in the absence of normal TCR/MHC signaling

Stat5 proteins are critical signaling molecules activated by many cytokines. Within the immune system, Stat5 plays important roles related to the development of thymocytes and proliferation of T cells. Stat5 has been implicated in malignant transformation, and moreover, the activated tyrosine phosphorylated form of Stat5 is frequently observed in human lymphomas. We previously demonstrated the oncogenic potential of Stat5, with thymic lymphoblastic lymphomas developing in a significant proportion of transgenic (TG) mice overexpressing Stat5a or Stat5b in lymphocytes. In addition, immunization or expression of a T-cell receptor (TCR) transgene augmented the rate of tumor formation. Here, we investigate the mechanism of Stat5-mediated lymphomagenesis by exploring the contributions of major histocompatibility complex (MHC)/TCR and pre-TCR signals. We present data demonstrating that Stat5b TG mice unexpectedly develop CD8(+) lymphoma even in the absence of either pre-TCR signaling or normal thymic selection. Indeed, acceleration of Stat5b transgene-mediated lymphoma occurred on TCRalpha(-/-) and pre-TCRalpha(-/-) backgrounds. In light of these data, we propose a model in which alterations in T-cell development at the double-negative/double-positive (DN/DP) stages cooperate with cytokine-mediated pathways in immature thymocytes to give rise to lymphoblastic T-cell lymphomas in Stat5b TG mice.

Early TCR expression and aberrant T cell development in mice with endogenous prerearranged T cell receptor genes

The factors that regulate the rate of production of T cells by the thymus remain incompletely defined. To test whether generation of functional T cell receptors limits the rate of thymic T cell export, we made use of a line of mice, LN3alphabeta, that have endogenously prerearranged TCR genes. The prerearranged TCR genes were expressed abnormally early in hemopoietic development, indicating that RAG-mediated recombination, rather than transcription factor expression, is the key determinant of the initiation of robust TCR transcription. Thymic T cell export rates were similar between wild-type (wt) and LN3alphabeta mice, indicating that T cell maturation rates in these mice are determined by factors other than TCR gene rearrangement. In competitive bone marrow chimeras, however, LN3alphabeta thymocytes were out-competed by wt cells and failed to develop beyond the double-negative 4 stage. Furthermore, wt progenitors transplanted intrathymically into LN3alphabeta mice proliferated excessively, suggesting that increased proliferative signals in the LN3alphabeta thymus compensate for faulty T cell development driven by early TCR expression.

Transgenic Mice as an In Vivo Model of Lymphomagenesis

This review covers multiple data obtained on genetically modified mice that help to elucidate various intricate molecular mechanisms of lymphomagenesis in humans. We are in a "golden age" of mouse genetics. The mouse is by far the most accessible mammalian system physiologically similar to humans. Transgenic mouse models have illuminated how different genes contribute to human lymphomagenesis. Multiple experiments with transgenic mice have not only confirmed the data obtained for human lymphomas but also gave additional evidence for the role of some genes and cooperative participation of their products in the development of human lymphomas. Genes and gene networks detected on transgenic mice can successfully serve as molecular targets for tumor therapy. This review demonstrates the extraordinary possibilities of transgenic technology, which is presently one of the readily available, efficient, and accurate tools to solve the problem of cancer.

Overexpression of murine TSLP impairs lymphopoiesis and myelopoiesis

The role of thymic stromal cell-derived lymphopoietin (TSLP) in regulating hematopoiesis is poorly characterized, so we investigated its regulatory effects in vivo using TSLP transgenic mice. Overexpression of TSLP disrupted hematopoietic homeostasis by causing imbalances in lymphopoiesis and myelopoiesis. Mice harboring a TSLP transgene had 5- to 700-fold fewer B and T precursors and no detectable pre-B lymphocyte colonyforming activity in the marrow or spleen. Conversely, TSLP transgenic mice possessed 15 to 20 times more splenic myeloid precursors than their littermates, and progenitor activity of the granulocyteerythrocyte-macrophage-megakaryocyte colony-forming units was significantly elevated. The arrest in lymphopoiesis and the expansion of myeloid progenitor cells in TSLP transgenic mice suggest that TSLP has negative and positive regulatory effects on lymphoid and myeloid development, respectively.

Human invariant V alpha 24-J alpha Q TCR supports the development of CD1d-dependent NK1.1+ and NK1.1- T cells in transgenic mice

A sizable fraction of T cells expressing the NK cell marker NK1.1 (NKT cells) bear a very conserved TCR, characterized by homologous invariant (inv.) TCR V alpha 24-J alpha Q and V alpha 14-J alpha 18 rearrangements in humans and mice, respectively, and are thus defined as inv. NKT cells. Because human inv. NKT cells recognize mouse CD1d in vitro, we wondered whether a human inv. V alpha 24 TCR could be selected in vivo by mouse ligands presented by CD1d, thereby supporting the development of inv. NKT cells in mice. Therefore, we generated transgenic (Tg) mice expressing the human inv. V alpha 24-J alpha Q TCR chain in all T cells. The expression of the human inv. V alpha 24 TCR in TCR C alpha(-/-) mice indeed rescues the development of inv. NKT cells, which home preferentially to the liver and respond to the CD1d-restricted ligand alpha-galactosylceramide (alpha-GalCer). However, unlike inv. NKT cells from non-Tg mice, the majority of NKT cells in V alpha 24 Tg mice display a double-negative phenotype, as well as a significant increase in TCR V beta 7 and a corresponding decrease in TCR V beta 8.2 use. Despite the forced expression of the human CD1d-restricted TCR in C alpha(-/-) mice, staining with mCD1d-alpha-GalCer tetramers reveals that the absolute numbers of peripheral CD1d-dependent T lymphocytes increase at most by 2-fold. This increase is accounted for mainly by an increased fraction of NK1.1(-) T cells that bind CD1d-alpha-GalCer tetramers. These findings indicate that human inv. V alpha 24 TCR supports the development of CD1d-dependent lymphocytes in mice, and argue for a tight homeostatic control on the total number of inv. NKT cells. Thus, human inv. V alpha 24 TCR-expressing mice are a valuable model to study different aspects of the inv. NKT cell subset.

Early TCRalpha expression generates TCRalphagamma complexes that signal the DN-to-DP transition and impair development

Clonotypic T cell receptor (TCR) genes undergo ordered rearrangement and expression in the thymus with the result that TCRalpha and TCRgamma proteins are not expressed in the same cell at the same time. Such "TCRalpha/gamma exclusion" is a feature of normal thymocyte differentiation, but it is abrogated in TCR-transgenic mice, which prematurely express transgenic TCRalpha proteins in early double-negative (DN) thymocytes. We report here that early expression of TCRalpha proteins results in the formation of TCRalphagamma complexes that efficiently signal the differentiation of DN into double-positive thymocytes independently of pre-TCR and TCRbeta expression. Thus, abrogation of TCRalpha/gamma exclusion by early TCRalpha expression results in the formation of isotypically mixed TCRalphagamma complexes whose in vivo signals circumvent TCRbeta selection and redirect thymocyte development along an aberrant developmental pathway.

A molecular marker for thymocyte-positive selection: selection of CD4 single-positive thymocytes with shorter TCRB CDR3 during T cell development

The generation of the naive T cell repertoire is a direct result of maturation and selection events in the thymus. Although maturation events are judged predominantly on the expression of surface markers, molecular markers, more intimately involved in the selection process, can be informative. We have identified a molecular marker for selection in later stages of maturation in humans. Thymocytes are selected for the expression of TCR beta-chains with shorter CDR3 at the double-positive to single-positive (SP) transition. Here we extend these studies to the mouse and show that the selection phenotype is not related to alpha-chain pairing but is a function of the MHC haplotype. Interestingly, the selection is much more apparent in CD4 SP thymocytes than in CD8 SP cells. This is in contrast to human thymocytes, where the selection is equally apparent in both lineages. The involvement of MHC in the process argues that this is a positive selection stage. The difference in the extent of this selection between the two SP lineages may indicate a class difference in the nature of the TCR-MHC interaction, the role of coreceptors in the selection process, or both.

Activation of Vbeta8 T cells affects spontaneous EAE in MBP TCR transgenic mice

Two strains of transgenic (Tg) mice (Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2) have T cell receptors (TCR) that recognize the NAc1-11 immunodominant epitope of the myelin basic protein (MBP). Spontaneous experimental autoimmune encephalomyelitis (sEAE) readily develops in Valpha2.3/Vbeta8.2 mice. T cells in Valpha2.3/Vbeta8.2 mice demonstrate increased levels of CD69, CD44(high) and decreased CD45RB relative to Valpha4/Vbeta8.2 mice. Increased proliferative responses to MBP and high levels of TNF-alpha are seen in Valpha2.3/Vbeta8.2 mice. High IL-4 and TGF-beta production is observed in Valpha4/Vbeta8.2 mice. CC chemokines (macrophage inflammatory protein-1 alpha (MIP-1alpha), RANTES and monocyte chemotactic protein 1 (MCP-1)) are increased in the central nervous system (CNS) of Valpha2.3/Vbeta8.2 mice. Thus, activated Th1 cells in the periphery of Valpha2.3/Vbeta8.2 mice may traffic to the CNS in response to CC chemokines, influencing sEAE.

Premature TCR alpha beta expression and signaling in early thymocytes impair thymocyte expansion and partially block their development

In thymocyte ontogeny, Tcr-a genes rearrange after Tcr-b genes. TCR alpha beta transgenic (Tg) mice have no such delay, consequently expressing rearranged TCR alpha beta proteins early in the ontogeny. Such mice exhibit reduced thymic cellularity and accumulate mature, nonprecursor TCR(+)CD8(-)4(-) thymocytes, believed to be caused by premature Tg TCR alpha beta expression via unknown mechanism(s). Here, we show that premature expression of TCR alpha beta on early thymocytes curtails thymocyte expansion and impairs the CD8(-)4(-) --> CD8(+)4(+) transition. This effect is accomplished by two distinct mechanisms. First, the early formation of TCR alpha beta appears to impair the formation and function of pre-TCR, consistent with recently published results. Second, the premature TCR alpha beta contact with intrathymic MHC molecules further pronounces the block in proliferation and differentiation. These results suggest that the benefit of asynchronous Tcr-a and Tcr-b rearrangement is not only to minimize waste during thymopoiesis, but also to simultaneously allow proper expression/function of the pre-TCR and to shield CD8(-)4(-) thymocytes from TCR alpha beta signals that impair thymocyte proliferation and CD8(-)4(-) --> CD8(+)4(+) transition.

TCR v(beta) repertoire restriction and lack of CDR3 conservation implicate TCR-superantigen interactions in promoting the clonal evolution of murine thymic lymphomas

Thymic lymphoma development is a multistage process in which genetic and epigenetic events cooperate in the emergence of a malignant clone. The notion that signaling via TCR-ligand interactions plays a role in promoting the expansion of developing neoplastic clones is a matter of debate. To investigate this issue, we determined the TCR V(beta) repertoire of thymic lymphomas induced in AKR/J mice by either endogenous retroviruses or the carcinogen, N-methyl-N-nitrosourea (MNU). Both spontaneous and MNU-induced lymphomas displayed restricted V(beta) repertoires. However, whereas V(beta)6, V(beta)8 and V(beta)9 were expressed by a greater than expected frequency of MNU-induced lymphomas, V(beta)8, V(beta)7, V(beta)13 and V(beta)14 were over-represented on spontaneous lymphomas. The dissimilar TCR V(beta) profiles indicate that different endogenous ligands promote neoplastic clonal expansion in untreated and MNU-treated mice. Although the nature of these ligands is not clear, the lack of conservation in TCR beta chain CDR3 regions among lymphomas that express the same V(beta) segment suggests that endogenous superantigens (SAG), as opposed to conventional peptide ligands, are likely to be involved in the selection process. The biased representation of lymphomas expressing V(beta)6-, V(beta)7- and V(beta)9-containing TCRs that recognize endogenous SAG is consistent with this hypothesis. The finding that Bcl-2 is expressed at high levels in spontaneous and MNU-induced lymphomas suggests that preneoplastic thymocytes may be resistant to SAG-induced clonal deletion. A working model is presented in which preneoplastic clones expressing TCRs that recognize endogenous SAG are selectively expanded as a consequence of sustained TCR-mediated signaling.

Gammadelta T-cell precursor-derived CD4- CD8- alphabeta T cells retain gammadelta cell function

We have previously shown that some of the DN alphabeta+ T cells arising in TcR alpha-chain transgenic mice are of gammadelta T cell origin, based on phenotypic data and on their status of TcR gene rearrangements. In the present report we investigated the impact of alphabeta TcR expression on the functional programme of the mature gammadelta precursor-derived DN alphabeta+ T cells. Our results demonstrate that both their proliferative capacity and their cytokine production profile are similar to that of gammadelta T cells. Furthermore, both transgenic DN alphabeta+ T cells and DN gammadelta+ T cells up-regulate CD8alpha expression after activation, but, in contrast to CD4+ alphabeta T cells, are unable to induce proliferation of naive B cells. Thus, our results suggest that the effector functions of mature T cells are determined independently of the TcR isotype, probably at an early stage of differentiation, and thereby have important implications for current models of T-cell lineage commitment.