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J P Allison

Publications and source records attributed to J P Allison.

At least 19 recordsLinked to original sources
PubMed1998

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) regulates the unfolding of autoimmune diabetes.

Evidence has been accumulating that shows that insulin-dependent diabetes is subject to immunoregulation. To determine whether cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is involved, we injected anti-CTLA-4 mAb into a TCR transgenic model of diabetes at different stages of disease. When injected into young mice, months before they would normally become diabetic, anti-CTLA-4 induced diabetes rapidly and essentially universally; this was not the result of a global activation of T lymphocytes, but did reflect a much more aggressive T cell infiltrate in the pancreatic islets. These effects were only observed if anti-CTLA-4 was injected during a narrow time window, before the initiation of insulitis. Thus, engagement of CTLA-4 at the time when potentially diabetogenic T cells are first activated is a pivotal event; if engagement is permitted, invasion of the islets occurs, but remains quite innocuous for months, if not, insulitis is much more aggressive, and diabetes quickly ensues.

Abatacept↗
PubMed1997

CD28/B7 interactions are required for sustaining the graft-versus-leukemia effect of delayed post-bone marrow transplantation splenocyte infusion in murine recipients of myeloid or lymphoid leukemia cells.

Graft-vs-leukemia (GVL) can reduce relapse rates after bone marrow transplantation (BMT). Delayed lymphocyte infusion (DLI) post-BMT can mediate a potent GVL effect with less graft-vs-host disease (GVHD) than would be observed if given early post-BMT. In vivo CD28/B7 blockade can reduce GVHD lethality, and B7 ligand expression can augment an antitumor immune response in mice. To examine the role of CD28/B7 interactions in DLI-mediated GVL, we established murine allogeneic BMT models in C57BL/6 (B6) recipients of C1498 (B6 acute myeloid leukemia) or EL4 (B6 acute T cell leukemia) that closely mimic human GVL. Recipients of C1498 and DLI had a marked reduction in relapse. GVL was blocked by anti-B7 mAb infusion. In contrast, recipients of EL4 cells and B10.BR DLI had a more modest GVL effect. The forced expression of B7-1 on EL4 cells markedly augmented the GVL effect of DLI, in contrast to the forced expression of B7-2 on EL4 cells. Relapse rates observed in recipients of C1498-B7-1 and DLI were significantly lower than in recipients of parental C1498 cells. We conclude that the administration of anti-B7 mAbs may impair the GVL effect of DLI and that the forced expression of B7-1 ligands stimulates a GVL effect without adversely affecting the GVHD lethality effect of DLI.

Adoptive Transfer↗
PubMed1997

Interaction of CTLA-4 with AP50, a clathrin-coated pit adaptor protein.

CTLA-4 plays a critical role in regulating the immune response. It is mainly located in cytoplasmic vesicles and is expressed only transiently on the surface after T cell activation. In this study, we demonstrate that CTLA-4 is associated with AP50, the medium chain of the clathrin-associated coated pit adaptor protein complex AP2. In a yeast two-hybrid screen, three individual cDNA clones that encode mouse AP50 were isolated, all of which can interact specifically with the cytoplasmic domain of mouse CTLA-4, but not with the cytoplasmic domain of mouse CD28. We have shown that CTLA-4 can bind specifically to AP50 when CTLA-4 and AP50 are cotransfected into human 293T cells. A Y201 to F201 mutation in the YVKM intracellular localization motif of the CTLA-4 cytoplasmic domain significantly diminished its binding to AP50. We also found that AP50 bound to a CTLA-4 peptide containing unphosphorylated Y201 but not to a peptide containing phosphorylated Y201. Conversely, the p85 subunit of phosphatidylinositol 3-kinase and, to a lesser extent, protein tyrosine phosphatase SYP (SHP-2) and SHP (SHP-1) bind only to the CTLA-4 peptide containing phosphorylated Y201. Therefore, the phosphorylation status of Y201 in the CTLA-4 cytoplasmic domain determines the binding specificity of CTLA-4. These results suggest that AP50 and the coated pit adaptor complex AP2 may play an important role in regulating the intracellular trafficking and function of CTLA-4.

Abatacept↗
PubMed1997

Thymocyte development is normal in CTLA-4-deficient mice.

Recent studies indicate that CTLA-4 interaction with B7 ligands transduces an inhibitory signal to T lymphocytes. Mice homozygous for a null mutation in CTLA-4 have provided the most dramatic example of the functional importance of CTLA-4 in vivo. These animals develop a fatal lymphoproliferative disorder and were reported to have an increase in CD4(+) and CD8(+) thymocytes and CD4(-)CD8(-) thymocytes, and a decrease in CD4(+)CD8(+) thymocytes. Based on these observations, it was proposed that CTLA-4 is necessary for normal thymocyte development. In this study, CTLA-4-deficient mice carrying an insertional mutation into exon 3 of the ctla-4 gene were generated. Although these mice display a lymphoproliferative disorder similar to previous reports, there was no alteration in the thymocyte profiles when the parathymic lymph nodes were excluded from the thymi. Further, thymocyte development was normal throughout ontogeny and in neonates, and there was no increase in thymocyte production. Finally, T cell antigen receptor signaling, as assessed by proximal and distal events, was not altered in thymocytes from CTLA-4(-/-) animals. Collectively, these results clearly demonstrate that the abnormal T cell expansion in the CTLA-4-deficient mice is not due to altered thymocyte development and suggest that the apparent altered thymic phenotype previously described was due to the inclusion of parathymic lymph nodes and, in visibly ill animals, to the infiltration of the thymus by activated peripheral T cells. Thus it appears that CTLA-4 is primarily involved in the regulation of peripheral T cell activation.

Abatacept↗
PubMed1997

Manipulation of T cell costimulatory and inhibitory signals for immunotherapy of prostate cancer.

The identification of potentially useful immune-based treatments for prostate cancer has been severely constrained by the scarcity of relevant animal research models for this disease. Moreover, some of the most critical mechanisms involved in complete and proper antitumoral T cell activation have only recently been identified for experimental manipulation, namely, components involved in the costimulatory pathway for T cell activation. Thus, we have established a novel syngeneic murine prostate cancer model that permits us to examine two distinct manipulations intended to elicit an antiprostate cancer response through enhanced T cell costimulation: (i) provision of direct costimulation by prostate cancer cells transduced to express the B7.1 ligand and (ii) in vivo antibody-mediated blockade of the T cell CTLA-4, which prevents T cell down-regulation. In the present study we found that a tumorigenic prostate cancer cell line, TRAMPC1 (pTC1), derived from transgenic mice, is rejected by syngeneic C57BL/6 mice, but not athymic mice, after this cell line is transduced to express the costimulatory ligand B7.1. Also, we demonstrated that in vivo antibody-mediated blockade of CTLA-4 enhances antiprostate cancer immune responses. The response raised by anti-CTLA-4 administration ranges from marked reductions in wild-type pTC1 growth to complete rejection of these cells. Collectively, these experiments suggest that appropriate manipulation of T cell costimulatory and inhibitory signals may provide a fundamental and highly adaptable basis for prostate cancer immunotherapy. Additionally, the syngeneic murine model that we introduce provides a comprehensive system for further testing of immune-based treatments for prostate cancer.

Abatacept↗
PubMed1997

Itk negatively regulates induction of T cell proliferation by CD28 costimulation.

CD28 is a cell surface molecule that mediates a costimulatory signal crucial for T cell proliferation and lymphokine production. The signal transduction mechanisms of CD28 are not well understood. Itk, a nonreceptor protein tyrosine kinase specifically expressed in T cells and mast cells, has been implicated in the CD28 signaling pathway because of reports that it becomes phosphorylated on tyrosines and associates with CD28 upon cross-linking of the cell surface molecule. To determine whether Itk plays a functional role in CD28 signaling, we compared T cells from Itk-deficient mice and control mice for their responses to CD28 costimulation. T cells defective in Itk were found to be fully competent to respond to costimulation. Whereas the CD3-mediated proliferative response was severely compromised in the absence of Itk, the calcineurin-independent CD28-mediated response was significantly elevated when compared with cells from control animals. The augmented proliferation was not due to increased production of interleukin-2. The results suggest that Itk has distinct roles in the CD3 versus the CD28 signaling pathways. By negatively regulating the amplitude of signaling upon CD28 costimulation, Itk may provide a means for modulating the outcome of T cell activation during development and during antigen-driven immune responses.

Animals↗
PubMed1997

Specific blockade of CTLA-4/B7 interactions results in exacerbated clinical and histologic disease in an actively-induced model of experimental allergic encephalomyelitis.

In addition to an antigen-specific signal, T cell activation requires an antigen-independent costimulatory signal provided by interaction of CD28 with B7 (CD80 and CD86) on the APC. By blocking B7 interactions, previous studies demonstrated the requirement for costimulation in the induction of experimental allergic encephalomyelitis (EAE). Recent studies suggest that unlike CD28, CTLA-4 (a second B7 ligand) delivers an inhibitory signal. To address the regulatory role of CTLA-4 in EAE, we used an antibody directed against CTLA-4 administered at the time of disease induction. This resulted in a significantly more severe clinical course and more inflammatory and demyelinating lesions in the CNS of anti-CTLA-4-treated mice. These data suggest that CTLA-4-mediated inhibitory signals can regulate the clinical severity and histologic parameters of neuroautoimmune disease.

Abatacept↗
PubMed1997

Co-stimulation in T cell responses.

Antigen-specific T cell responses have primarily been considered in terms of activation signals delivered through the TCR and the co-stimulatory molecule CD28. In the past few years, studies have demonstrated the critical importance of inhibitory signals for regulating lymphocyte activation. CD28 and its homologue cytotoxic T lymphocyte antigen-4 (CTLA-4) share the same counter-receptors on antigen-presenting cells, but recent experiments have shown that CD28 and CTLA-4 have opposite effects on T cell activation. The mechanisms responsible for integrating these activation and inhibitory signals at the cellular and molecular levels are just beginning to be elucidated.

Abatacept↗
PubMed1997

T cell-mediated elimination of B7.2 transgenic B cells.

Transgenic mice were generated to explore the effects on lymphoid development and immune function of constitutive expression of murine B7.2 on B and T cells. The number of B lymphocytes in primary and secondary lymphoid tissues is normal in B7.2 transgenic lines expressing low levels of B7.2 on B cells, but markedly reduced in transgenic lines expressing moderate to high levels of the transgene on B cells. This reduction is not due to an intrinsic abnormality of the transgenic B cells, but is rather the consequence of an elimination by an immune mechanism requiring the engagement of CD28 on T cells. Interestingly, during cognate antigen-specific interaction with T cells in vivo, B7.2 transgenic B cells are not eliminated, but proliferate and differentiate normally. Our findings suggest that, in the absence of high affinity ligand for the TCR, the CD28-B7.2 system participates in the regulation of B cell homeostasis.

Animals↗
PubMed1997

Lymphoproliferation in CTLA-4-deficient mice is mediated by costimulation-dependent activation of CD4+ T cells.

CTLA-4-deficient animals develop a fatal lymphoproliferative disorder. The cellular mechanism(s) responsible for this phenotype have not been determined. Here, we show that there is a preferential expansion of CD4+ T cells in CTLA-4(-/-) mice, which results in a skewing of the CD4/CD8 T cell ratio. In vivo antibody depletion of CD8+ T cells from birth does not alter the onset or the severity of the CD28-dependent lymphoproliferative disorder. In contrast, CD4+ T cell depletion completely prevents all features characteristic of the lymphoproliferation observed in CTLA-4-deficient mice. These results demonstrate that CD4+ T cells initiate the phenotype in the CTLA-4(-/-) mice. Further, these results suggest that the role of CTLA-4 in peripheral CD4+ versus CD8+ T cell homeostasis is distinct.

Abatacept↗
PubMed1996

CTLA-4 engagement inhibits IL-2 accumulation and cell cycle progression upon activation of resting T cells.

While interactions between CD28 and members of the B7 family costimulate and enhance T cell responses, recent evidence indicates that the CD28 homologue CTLA-4 plays a downregulatory role. The mechanism by which this occurs is not clear, but it has been suggested that CTLA-4 terminates ongoing responses of activated T cells, perhaps by induction of apoptosis. Here we demonstrate that CTLA-4 engagement by antibody cross-linking or binding to B7 inhibits proliferation and accumulation of the primary T cell growth factor, IL-2, by cells stimulated with anti-CD3 and anti-CD28. This inhibition is not a result of enhanced cell death. Rather it appears to result from restriction of transition from the G1 to the S phase of the cell cycle. Our observation that upregulation of both the IL-2R alpha chain and the CD69 activation antigen are inhibited by CTLA-4 engagement supplies further evidence that CTLA-4 restricts the progression of T cells to an activated state. Together this data demonstrates that CTLA-4 can regulate T cell activation in the absence of induction of apoptotic cell death.

Abatacept↗
PubMed1996

Enhancement of antitumor immunity by CTLA-4 blockade.

One reason for the poor immunogenicity of many tumors may be that they cannot provide signals for CD28-mediated costimulation necessary to fully activate T cells. It has recently become apparent that CTLA-4, a second counterreceptor for the B7 family of costimulatory molecules, is a negative regulator of T cell activation. Here, in vivo administration of antibodies to CTLA-4 resulted in the rejection of tumors, including preestablished tumors. Furthermore, this rejection resulted in immunity to a secondary exposure to tumor cells. These results suggest that blockade of the inhibitory effects of CTLA-4 can allow for, and potentiate, effective immune responses against tumor cells.

Abatacept↗
PubMed1996

Generation of primary tumor-specific CTL in vitro to immunogenic and poorly immunogenic mouse tumors.

This study investigated the generation of primary tumor-specific CTL activity in vitro to several mouse tumors. We report that the development of optimal primary tumor-specific CTL to the P815 mastocytoma, the EL4 thymoma, and the Lewis lung carcinoma is dependent on tumor Ags, on enhancement of T cell costimulation by B7.1, and on exogenous T helper activity in the form of IL-2 and IL-4. A relatively low concentration of IL-2 and IL-4 was required to limit the induction of lymphokine-activated killer cells. In the case of P815, the CTL were directed toward molecularly defined tumor rejection Ags. These primary cultures yielded long term T cell lines that were heterogeneous in fine tumor Ag specificity and in cytokine production.

Animals↗
PubMed1996

The role of tyrosine phosphorylation and PTP-1C in CTLA-4 signal transduction.

Recently, there has been increasing interest in the inhibitory regulators of lymphocyte activation, and in particular, the role of CD28 homologue CTLA-4 in the regulation of T cell responses. Interaction of CTLA-4 with B7 ligands inhibits T cell responses, including T cell proliferation and interleukin-2 (IL-2) secretion. The mechanism(s) responsible for CTLA-4 signal transduction are unknown, but it has been suggested that tyrosine phosphorylation is involved. Here we demonstrate that phorbol ester phorbol 12-myrislate 13-acetate (PMA), which increases tyrosine phosphorylation by stimulating protein kinase C and p21ras, can overcome the CTLA-4-mediated inhibition of T cell proliferation. This provides the first functional evidence that tyrosine phosphorylation is involved in CTLA-4 signal transduction. Most interestingly, CTLA-4-mediated inhibition of IL-2 secretion was not influenced by the presence of PMA. Further, we demonstrate that CTLA-4 cross-linking inhibits proliferation and IL-2 secretion of T cells from motheaten mice. These mice lack PTP-1C, a tyrosine phosphatase which mediates in a number of lymphocyte inhibitory responses, indicating that PTP-1C is not essential for CTLA-4 signaling. Collectively, these results demonstrate that regulation of tyrosine phosphorylation plays a pivotal role in CTLA-4 function, and that the inhibition of the transition from G0/G1 to the S phase of the cell cycle and the inhibition of IL-2 secretion require distinct signaling pathways. These experiments provide a useful model system which can be used to elucidate the signaling pathways involved in CTLA-4 function and to understand how CTLA-4, CD28 and Tcell receptor-mediated signals are integrated in T cell responses to antigen.

Abatacept↗
PubMed1996

Superantigen responses and co-stimulation: CD28 and CTLA-4 have opposing effects on T cell expansion in vitro and in vivo.

Co-stimulation via the CD28/CTLA-4 system appears critical for T cell proliferation to peptide antigens presented in association with MHC. In this study, we examine the roles of CD28 and CTLA-4 in the response of murine T cells to the superantigen staphylococcal enterotoxin B (SEB). In vitro, antibodies against B7-1/B7-2 or Fab fragments of anti-CD28 antibodies significantly inhibit the response of splenocytes to SEB. Conversely, Fab fragments of anti-CTLA-4 antibodies augment the proliferative response. Further, addition of blocking antibodies directed against B7-1/B7-2 augment proliferation co-stimulated by intact anti-CD28 antibodies. These data support the hypothesis that CD28 and CTLA-4 exert opposing effects upon early T cell activation. In vivo, intact anti-CD28 antibodies and non-stimulatory Fab fragments of anti-CD28 appear to have similar inhibitory effects upon the expansion of V beta 8+ T cells. In contrast, both intact and Fab fragments of anti-CTLA-4 appear to amplify this expansion. We conclude that the SEB response is significantly augmented by CD28-derived signaling and this in turn may be attenuated by signals through CTLA-4.

Abatacept↗