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T F Gajewski

Publications and source records attributed to T F Gajewski.

At least 37 records · Page 2Linked to original sources
PubMed1999

Polymyositis with respiratory muscle weakness requiring mechanical ventilation in a patient with metastatic thymoma treated with octreotide.

Although most patients with thymoma present with a mediastinal mass amenable to surgical resection, some patients develop metastatic disease requiring systemic therapy. The majority of thymomas express somatostatin receptors as demonstrated by octreotide scanning, an observation which has prompted the clinical use of octreotide in patients with this disease. Many patients with thymoma exhibit autoimmune paraneoplastic syndromes, most frequently myesthenia gravis. We report here the case of a patient with metastatic thymoma who developed a profound autoimmune polymyositis and lupus-like syndrome that flared following treatment with octreotide and was associated with a clinical response to this agent. No evidence for myesthenia gravis was discovered. The severity of the myopathy necessitated mechanical ventilation for 12 weeks. The natural history of thymoma, treatment options including recent combination chemotherapy regimens, and potential mechanisms for flaring of autoimmune paraneoplastic syndromes triggered by therapy of thymoma are discussed.

Acute Disease↗
PubMed1999

The immune system as anti-tumor sentinel: molecular requirements for an anti-tumor immune response.

The concept behind immune surveillance against cancer is that tumor cells continuously develop, but that there may not be clinical evidence of their presence because the immune system recognizes the cells as foreign and destroys them. A clear role for the immune system in preventing and/or eliminating tumors is emerging as insights into the molecular requirements for the induction and effector function of cytolytic T lymphocytes (CTL) have been gained. Using murine tumor rejection models, the role of particular molecular components of the immune system in controlling tumor growth has been defined. However, tumor rejection does not always occur spontaneously in vivo, indicating that defects in the generation or execution of an anti-tumor immune response may be common. Understanding defects when they arise should allow for development of new therapeutic approaches in tumor-bearing individuals. Many clinical studies are underway to test strategies to induce or heighten an antitumor immune response in cancer patients.

Animals↗
PubMed1998

B7.1 is a quantitatively stronger costimulus than B7.2 in the activation of naive CD8+ TCR-transgenic T cells.

Using a TCR transgenic mouse bred onto a recombinase-activating gene-2-deficient background, we have examined the influence of B7.1 and B7.2 on activation of naive, CD8+ T cells in vitro. We found that B7.1 was a more potent costimulus than B7.2 for induction of proliferation and IL-2 production by naive CD8+ T cells. This difference appeared to be quantitative in nature, as determined using transfectants expressing various defined levels of B7.1 or B7.2, or using purified B7.1 or B7.2 fusion proteins. In contrast to the quantitative differences seen in stimulation of naive T cells, B7.1 and B7.2 were comparable in their ability to costimulate responses in T cells previously primed in vitro. In addition, primed, but not naive, T cells were capable of proliferating and producing IL-2 in response to a TCR stimulus alone, apparently in the absence of B7 costimulation. Lastly, we found that B7.1 and B7.2 were equivalently capable of driving differentiation of naive CD8+ T cells into an IL-4-producing phenotype when exogenous IL-4 was added to the primary culture or to an IFN-gamma-producing phenotype in the presence of IL-12. These results indicate that signals generated by B7.1 and B7.2 are qualitatively similar, but that B7.1 is quantitatively stronger than B7.2. Further, our results indicate that the activation state of the responding T cell may influence the efficiency with which the T cell can respond to a costimulatory signal provided by either B7.1 or B7.2.

Animals↗
PubMed1998

Expression and function of CTLA-4 in Th1 and Th2 cells.

CTLA-4 is expressed on T cells after activation and shares homology with the CD28 costimulatory receptor. In contrast to CD28, CTLA-4 is thought to be a negative regulator of T cell activation. Cross-linking of CTLA-4 during activation of peripheral T cells reduces IL-2 production and arrests T cells in G1. Much less is known about the function of CTLA-4 in differentiated T cells. We have investigated the expression and function of CTLA-4 in established Th1 and Th2 clones and in bulk populations of Th1 and Th2 cells freshly derived in vitro from TCR transgenic splenocytes. We found that CTLA-4 was induced under similar conditions and with similar kinetics following activation of both Th1 and Th2 clones. However, CTLA-4 expression was much higher in Th2 than Th1 clones and lines. This was confirmed by flow cytometry, confocal microscopy, and Northern blot analysis. The ratio of surface to intracellular expression of CTLA-4 and its rate of endocytosis were similar in Th1 and Th2 clones. Inhibition of binding of CTLA-4 to its ligands using soluble anti-CTLA-4 mAb during stimulation with Ag increased the production not only of IL-2 by Th1 clones, but also that of IL-3 and IFN-gamma by Th1 clones and of IL-3, IL-4, IL-5, and IL-10 by Th2 clones. In contrast, when anti-CTLA-4 was coimmobilized with anti-CD3 and anti-CD28 mAbs, a decrease in the production of multiple cytokines was observed. We conclude that CTLA-4 can function to suppress the production of cytokines produced by both Th1 and Th2 cells.

Abatacept↗
PubMed1998

B7-1 engagement of cytotoxic T lymphocyte antigen 4 inhibits T cell activation in the absence of CD28.

Ligation of cytotoxic T lymphocyte antigen 4 (CTLA4) appears to inhibit T cell responses. Four mechanisms have been proposed to explain the inhibitory activity of CTLA4: competition for B7-1 and B7-2 binding by CD28; sequestration of signaling molecules away from CD28 via endocytosis; delivery of a signal that antagonizes a CD28 signal; and delivery of a signal that antagonizes a T cell receptor (TCR) signal. As three of these potential mechanisms involve functional antagonism of CD28, an experimental model was designed to determine whether CTLA4 could inhibit T cell function in the absence of CD28. TCR transgenic/recombinase activating gene 2-deficient/CD28-wild-type or CD28-deficient mice were generated and immunized with an antigen-expressing tumor. Primed T cells from both types of mice produced cytokines and proliferated in response to stimulator cells lacking B7 expression. However, whereas the response of CD28+/+ T cells was augmented by costimulation with B7-1, the response of the CD28-/- T cells was strongly inhibited. This inhibition was reversed by monoclonal antibody against B7-1 or CTLA4. Thus, CTLA4 can potently inhibit T cell activation in the absence of CD28, indicating that antagonism of a TCR-mediated signal is sufficient to explain the inhibitory effect of CTLA4.

Abatacept↗
PubMed1998

Helper T cell differentiation is controlled by the cell cycle.

Helper T (Th) cell differentiation is highly regulated by cytokines but initiated by mitogens. By examining gene expression in discrete generations of dividing cells, we have delineated the relationship between proliferation and differentiation. Initial expression of IL-2 is cell cycle-independent, whereas effector cytokine expression is cell cycle-dependent. IFNgamma expression increases in frequency with successive cell cycles, while IL-4 expression requires three cell divisions. Cell cycle progression and cytokine signaling act in concert to relieve epigenetic repression and can be supplanted by agents that hyperacetylate histones and demethylate DNA. Terminally differentiated cells exhibit stable epigenetic modification and cell cycle-independent gene expression. These data reveal a novel mechanism governing Th cell fate that initially integrates proliferative and differentiative signals and subsequently maintains stability of the differentiated state.

Animals↗
PubMed1997

Antigen recognition and allogeneic tumor rejection in CD8+ TCR transgenic/RAG(-/-) mice.

Three sources of help for the development of a CD8+ CTL response have been described: the CD4+ direct and indirect pathways and the CD8+ direct pathway. In an effort to understand the minimal requirements for the development of a CTL response in vivo, we have bred mice transgenic for the 2C TCR onto a RAG(-/-) background. The 2C T cells in this animal are exclusively CD8+ CTLs of a single specificity, and they exhibit altered thymic maturation compared with that of T cells from 2C TCR/RAG(+/+) mice. T cells from 2C TCR/RAG(-/-) mice can be activated to a high level in vivo by administration of a self-MHC-restricted antigenic peptide. The 2C TCR/RAG(-/-) mice are able to reject B7-negative allogeneic tumors bearing the appropriate peptide/MHC ligand p2C/Ld. These mice fail to reject syngeneic tumors, and their RAG(-/-) littermates lacking 2C T cells uniformly succumb to both allogeneic and syngeneic tumors. Moreover, blockade of B7 costimulatory molecules fails to prevent tumor rejection in the 2C TCR/RAG(-/-) mice, suggesting that allorejection is occurring independently of B7-mediated costimulation as well as in the absence of CD4+ T cells. CTLs isolated from the site of the tumor during the period of rejection express the activation marker CD25 and are able to mediate ex vivo cytolysis of tumor cells bearing the appropriate Ag. These results suggest that in this TCR transgenic model with a very high precursor frequency, CTL development can occur in the absence of B7:CD28 costimulation and without CD4+ help.

Animals↗
PubMed1997

The expression of mouse gene P1A in testis does not prevent safe induction of cytolytic T cells against a P1A-encoded tumor antigen.

Tumor antigen P815AB is recognized by cytolytic T lymphocytes (CTL) on mouse mastocytoma P815. This antigen is encoded by P1A, a gene activated in several tumors but silent in normal tissues except for testis and placenta. Notwithstanding the expression of P1A in testis, we found that male mice mounted P815AB-specific CTL responses as efficiently as females. The responding males remained fertile and no autoimmune lesions were observed in their testes. By immunohistochemistry with a rabbit antiserum directed against the P1A protein, we identified spermatogonia as the testicular cells expressing P1A. The absence of MHC class-I molecules on spermatogonia could be one of the mechanisms of protection against testicular autoimmunity, as the antigenic peptide should not be displayed at the cell surface. Human genes MAGE, BAGE and GAGE, which also code for tumor antigens recognized by autologous CTL, are not expressed in normal tissues other than testis. The results obtained in mice with antigen P815AB suggest that immunization of human males with such antigens will not generate autoimmune side-effects. Although P1A is strongly expressed in placenta, we also found that gestation did not prevent generation of CTL responses against antigen P815AB, and that such CTL responses did not affect gestation outcome. We identified labyrinthine trophoblasts as the placental cells expressing P1A. Again, the absence of MHC class-I molecules on these cells provides a plausible explanation for placental protection, although other mechanisms may also play a role.

Animals↗
PubMed1997

Antigen-specific regression of established tumors induced by active immunization with irradiated IL-12- but not B7-1-transfected tumor cells.

Transfection of modestly immunogenic tumors to express B7 family co-stimulator molecules results in their rejection by syngeneic mice, suggesting a possible clinical application in cancer patients. Immunization of naive mice with irradiated B7-1-transfected P1.HTR cells is sufficient to induce specific cytolytic T lymphocytes (CTL) and to protect against tumor challenge. However, patients to be treated will have an existing tumor burden; thus, preclinical models should examine therapeutic efficacy in an established tumor setting. Contrary to expectations, immunization of mice with irradiated B7-1-transfected P1.HTR cells had no impact on the growth of pre-established control-transfected tumors. Mice bearing control-transfected P1.HTR tumors successfully rejected living B7-1 transfectants on the contralateral flank, demonstrating the ability of tumor-bearing mice to respond to B7 co-stimulation. Inasmuch as IL-12 is another important factor for CTL maturation, P1.HTR transfectants expressing B7-1 and/or IL-12 were then constructed. Remarkably, regression of pre-established tumors was achieved following immunization with irradiated IL-12 transfectants, even without co-expression of B7-1. Rejection required a shared antigen with the tumor used for immunization, could not be reproduced with rIL-12 alone, depended on host T lymphocytes and correlated with a high IFN-gamma-producing T cell phenotype. In addition, IL-12-facilitated tumor rejection required co-operation with a CTLA-4 ligand provided by the host, and correlated with up-regulation of B7-1 and B7-2 on host antigen-presenting cells. Thus, active immunization in the established tumor setting is benefitted greatly by the provision of IL-12, which may recruit participation of sufficient B7 co-stimulation from the host that it need not be provided exogenously.

Abatacept↗
PubMed1996

Induction of a cytolytic T-cell response in mice with a recombinant adenovirus coding for tumor antigen P815A.

We investigated the efficacy of a recombinant adenovirus in inducing a cytolytic T-lymphocyte (CTL) response in mice against tumor antigen P815A, which is present on mouse mastocytoma P815. The recombinant adenoviral vector (Adeno.PIA) contained the sequence coding for the antigenic nonapeptide which binds to the H-2.Ld molecule to form antigen P815A. We verified that murine cells infected in vitro with Adeno. PIA were lysed by an anti-P815A CTL clone. Mice then received a single intradermal injection of Adeno. PIA, and after a few weeks their spleen cells were stimulated in vitro with tumor cells expressing antigen P815A. An anti-P815A CTL response was observed with the spleen lymphocytes of nearly all the mice, providing the lymphocytes were re-stimulated in vitro with cells expressing both P815A and co-stimulatory molecule B7.1. When the stimulatory cells did not express B7.1, a specific CTL response was observed in only 45% of the mice, and it was less intense. The Adeno. P1A viral vector was unable to raise an anti-P815A response in mice that had been previously infected with a recombinant adenovirus carrying the beta-galactosidase gene or with a defective adenovirus. We conclude that adenoviral vectors may be very useful for the priming of cytolytic T-cell responses directed against human tumor antigens. Other modes of immunization may be necessary to boost the responses induced with adenoviral vectors.

Adenoviridae↗
PubMed1996

Tumor rejection requires a CTLA4 ligand provided by the host or expressed on the tumor: superiority of B7-1 over B7-2 for active tumor immunization.

Although transfection to express any of a multitude of immunomodulatory molecules can lead to the rejection of murine tumors in vivo, it is not clear which of these cofactors are truly important for the induction of tumor-specific CTL. Examination of the costimuli used by the host immune response during the normal rejection of immunogenic tumors should reveal critical cofactors for CTL differentiation in vivo. The involvement of a host B7 family costimulator molecule in the rejection of immunogenic tum- variants of the mastocytoma P815 was explored. Rejection of immunogenic P815 variants was prevented by mCTLA4 gamma 3, a fusion protein between the extracellular domain of murine CTLA4 and the Fc portion of a murine IgG3 Ab, indicating the importance of a CTLA4 ligand provided by the host in the rejection of B7- tumors. Tumor rejection also was prevented by mCTLA4 gamma 3 in the absence of CD4+ cells, suggesting that CD8+ lymphocytes may receive direct costimulation by B7 in vivo. Finally, although living transfectants of poorly immunogenic P1.HTR cells expressing B7-1 or B7-2 were equally rejected by syngeneic mice, if delivered as multiple injections of irradiated cells, only B7-1 transfectants successfully induced CTL activity and protected against living tumor challenge. Our results indicate that a CTLA4 ligand is normally involved in the generation of CD8+ CTL against tumor Ag and suggest that immunization with irradiated B7-1-transfected tumor cells may be superior to immunization with irradiated B7-2 transfectants as an approach to tumor Ag vaccination in patients.

Abatacept↗
PubMed1996

Blocked Ras activation in anergic CD4+ T cells.

T cell anergy is a state of functional unresponsiveness characterized by the inability to produce interleukin-2 (IL-2) upon T cell receptor stimulation. The mitogen-activated protein kinases ERK-1 and ERK-2 and the guanosine triphosphate-binding protein p21ras were found to remain unactivated upon stimulation of anergic murine T helper cell 1 clones. The inability to activate the Ras pathway did not result from a defect in association among Shc, Grb-2, and murine Son of Sevenless, nor from a defect in their tyrosine phosphorylation. This block in Ras activation may lead to defective transactivation at activator protein 1 sites in anergic cells and may enable T cells to shut down IL-2 production selectively during anergy.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Endogenous IL-12 is necessary for rejection of P815 tumor variants in vivo.

Although murine tumor cells have been transfected to express a multitude of different cytokines and shown to be rejected in vivo, it is unclear which of these factors might be useful to facilitate tumor Ag immunization schemes. A study of the normal immune mechanisms involved in tumor rejection when it naturally occurs should reveal critical signals for generation of antitumor CTL in vivo. The highly transfectable variant of P815, P1.HTR, was found to be rejected in the hind footpads by approximately one-third of syngeneic DBA/2 mice. Analysis of draining popliteal lymph nodes revealed a large influx of CD4+ and CD8+ T lymphocytes in all mice, indicating that a failure to reject was not due to the complete absence of an inflammatory response. However, although IL-2 and IL-3 were produced by lymph node cells from all mice, only approximately one-third generated a high IFN-gamma response. IL-4 was not detected. To explore a role for IL-12 in the induction of the IFN-gamma-producing phenotype, a histidine-tagged IL-12 fusion protein was expressed in mammalian cells and purified by nickel-chelate chromatography, and a rabbit antiserum was produced. Neutralization of IL-12 in vivo eliminated the high IFN-gamma response and prevented rejection of P1.HTR tumors and also of a more immunogenic tum- variant of P815, P198. Conversely, exogenous IL-12 delivered early during challenge with P1.HTR cells induced high IFN-gamma production and resulted in tumor rejection in most mice. Therefore, endogenous IL-12 is vital for the rejection of these tumors when it naturally occurs, supporting a role for exogenous administration of this cytokine to favor a Th1-like phenotype in the immunotherapy of cancer.

Animals↗
PubMed1996

B7-1 but not B7-2 efficiently costimulates CD8+ T lymphocytes in the P815 tumor system in vitro.

We recently have developed a method to generate primary P815-specific CTL in vitro from normal syngeneic splenocytes by employing transfection of B7-1 combined with exogenous IL-12 and IL-6. Surprisingly, when the homologous costimulator molecule B7-2 was substituted for B7-1 in this system, no specific CTL activity was obtained. Similarly, B7-1- but not B7-2-transfected P815 cells generated alloantigen-specific CTL activity from C57BL/6, accessory cell- and CD4(+)-depleted splenocytes, and costimulated proliferation of CD8+ lymphocytes in the presence of low doses of anti-CD3 mAb. In all systems, combined expression of both B7-1 and B7-2 costimulated as effectively as B7-1 alone, arguing against delivery of a dominant negative signal by B7-2. Proliferation of allogeneic, CD4(+)-depleted splenocytes in response to P815 cells, which relies on costimulation by normal accessory cells, was inhibited by anti-B7-1 but not anti-B7-2 mAbs. Finally, indirect evidence suggested a higher avidity of B7-1+ cells than B7-2+ cells for CTLA4. Thus, at least in the context of primary stimulation by irradiated P815 transfectants, B7-1 appears to be superior to B7-2 at costimulation of CD8+ T lymphocytes.

Abatacept↗
PubMed1996

Control of T lymphocyte signal transduction through clonal anergy.

Stimulation of interleukin-2 producing T lymphocytes via the T cell receptor (TCR) complex in the absence of other costimulatory factor results paradoxically not in activation but in an unresponsive state termed clonal anergy. T cell anergy appears to be a mechanism by which potentially autoreactive T lymphocytes are inactivated in the periphery, thus maintaining tolerance to self antigens. The breakdown of such tolerance may result in autoimmune diseases. In contrast, induction of peripheral tolerance is the ultimate goal in organ transplantation and is a potential mechanism by which a growing tumor evades immune destruction. The anergic state is characterized by an inability to secrete interleukin-2 and proliferate following restimulation via the TCR even in the presence of constimulatory factors. Recent studies have demonstrated a specific block in Ras activation in anergic T lymphocytes. This defect is correlated with a failure to activate the downstream effectors Erk and Jnk and a lack of activation of the AP-1 transcription factor complex, offering a plausible mechanism for the inability to initiate interleukin-2 gene transcription in the anergic state.

Cell Differentiation↗
PubMed1995

Costimulation with B7-1, IL-6, and IL-12 is sufficient for primary generation of murine antitumor cytolytic T lymphocytes in vitro.

The requirements for generating CD8+ CTLs against the mastocytoma P815 were first defined by using an allogeneic mixed lymphocyte tumor culture (MLTC). Both the expansion of effector lymphocytes and the acquisition of lytic activity were dependent on the presence of accessory cells, but not CD4+ lymphocytes. Several factors were examined for their ability to replace accessory cell function. Expression of B7-1 by P815 was sufficient to induce IL-2 production by CD8+ cells, but substantial proliferation was achieved only if IL-6 was provided as well. Although IL-12 had little effect on the net proliferation of developing effector cells, it increased specific lytic activity 10-fold, acted synergistically with B7-1 in induction of IFN-gamma production during primary stimulation, and resulted in a shift toward a Th1 cytokine profile following secondary stimulation. These costimulatory factors were then studied in a primary syngeneic MLTC by using splenocytes from nonimmunized DBA/2 mice, an approach that had never before succeeded in generating specific CTLs. The combination of B7-1, IL-6, and IL-12 was sufficient to induce P815-specific CTL activity after a 5-day MLTC, which was expanded optimally following secondary stimulation in the presence of B7-1, IL-2, and IL-7. The irrelevant syngeneic tumor L1210, constructed to express B7-1 and the P815-derived tumor Ag gene P1A, also generated CTLs that lysed the parental P815. The combination of B7-1, IL-6, and IL-12 should be useful in the derivation of other tumor-specific CTLs in vitro, and may constitute the optimal stimuli for rapid proliferation and differentiation of helper-independent, tumor-specific CTLs in vivo.

Animals↗
PubMed1995

Induction of the increased Fyn kinase activity in anergic T helper type 1 clones requires calcium and protein synthesis and is sensitive to cyclosporin A.

Several alterations in T cell receptor-associated signal transduction have been observed following induction of anergy of T helper type 1 (Th1) clones, including a modified intracellular free calcium ([Ca2+]i) response and increased kinase activity associated with the protein tyrosine kinase p59fyn. In the current study, we demonstrate that, although the kinetics of acquisition of both of these signaling alterations correlated with the generation of anergy, a normal calcium response returned within 48 h after removal from the anergizing stimulus, whereas the increased p59fyn activity persisted and the cells remained hyporesponsive. Generation of both the anergic state and the increased p59fyn activity was prevented in the presence of calcium-free medium, cycloheximide (CHX), or cyclosporin A (CsA), and could be mimicked by the calcium ionophore ionomycin. In contrast, the altered calcium response was inhibited by stimulation in the presence of calcium-free medium or CsA, but not CHX. Thus, surprisingly, these data suggest that a chronic elevation of [Ca2+]i is proximal to and necessary for the increase in p59fyn-associated kinase activity observed in anergic Th1 clones. Increased p59fyn activity, but not the altered calcium response, correlates with maintenance of the anergic state.

Animals↗