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Laurence A Turka

Publications and source records attributed to Laurence A Turka.

At least 19 recordsLinked to original sources
PubMed2006

The adaptor molecule MyD88 activates PI-3 kinase signaling in CD4+ T cells and enables CpG oligodeoxynucleotide-mediated costimulation.

While T cells respond directly to toll-like receptor (TLR) agonists, TLR-signaling pathways in T cells are poorly characterized. Here we demonstrate in CD4(+) T cells that CpG DNA directly enhances proliferation, prevents anergy, and augments humoral responses to a T cell-dependent antigen by a Myeloid differentiation primary-response protein 88 (MyD88) and Phosphatidylinositol 3-kinase (PI-3 kinase)-dependent pathway. PI-3 kinase activation required a putative Src-homology domain (SH2) binding motif in the MyD88 Toll-Like or IL-1 Receptor (TIR) domain. Reconstitution of MyD88-deficient primary T cells with a MyD88 transgene mutated in this motif abrogated association of PI-3 kinase with MyD88, phosphorylation of protein kinase B (Akt) and Glycogen Synthetase Kinase-3 (GSK-3), and interleukin-2 (IL-2) production. The MyD88 death domain, on the other hand, was required for NF-kB activation and survival. These studies identify a MyD88-dependent PI-3 kinase-signaling pathway in T cells that differentiates CpG DNA-mediated proliferation from survival and is required for an in vivo T cell-dependent immune response.

Animals↗
PubMed2006

Cutting edge: T cell requirement for CD28 costimulation is due to negative regulation of TCR signals by PTEN.

Recent studies suggest that the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) plays a critical role in the maintenance of self-tolerance. Using T cell-specific PTEN knockout mice (PTENDeltaT), we have identified a novel mechanism by which PTEN regulates T cell tolerance. We found that TCR stimulation alone, without CD28 costimulation, is sufficient to induce hyperactivation of the PI3K pathway, which leads to enhanced IL-2 production by naive PTENDeltaT T cells. Importantly, as a result of this increased response to TCR stimulation, PTENDeltaT CD4(+) T cells no longer require CD28 costimulation for in vitro or in vivo expansion. In fact, unlike wild-type T cells, PTENDeltaT CD4(+) T cells are not anergized by delivery of TCR stimulation alone. These data suggest that by negatively regulating TCR signals, PTEN imposes a requirement for CD28 costimulation, thus defining a novel mechanism for its role in self-tolerance.

Animals↗
PubMed2006

PTEN inhibits IL-2 receptor-mediated expansion of CD4+ CD25+ Tregs.

One of the greatest barriers against harnessing the potential of CD4+ CD25+ Tregs as a cellular immunotherapy is their hypoproliferative phenotype. We have previously shown that the hypoproliferative response of Tregs to IL-2 is associated with defective downstream PI3K signaling. Here, we demonstrate that targeted deletion of the lipid phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10) regulates the peripheral homeostasis of Tregs in vivo and allows their expansion ex vivo in response to IL-2 alone. PTEN deficiency does not adversely affect either the thymic development or the function of Tregs, which retain their ability to suppress responder T cells in vitro and prevent colitis in vivo. Conversely, reexpression of PTEN in PTEN-deficient Tregs as well as in activated CD4+ T cells inhibits IL-2-dependent proliferation, confirming PTEN as a negative regulator of IL-2 receptor signaling. These data demonstrate that PTEN regulates the "anergic" response of Tregs to IL-2 in vitro and Treg homeostasis in vivo and indicate that inhibition of PTEN activity may facilitate the expansion of these cells for potential use in cellular immunotherapy.

Animals↗
PubMed2006

Defective activation of protein kinase C and Ras-ERK pathways limits IL-2 production and proliferation by CD4+CD25+ regulatory T cells.

Naturally occurring CD4+CD25+ regulatory T cells (Tregs), which play an important role in the maintenance of self-tolerance, proliferate poorly and fail to produce IL-2 following stimulation in vitro with peptide-pulsed or anti-CD3-treated APCs. When TCR proximal and distal signaling events were examined in Tregs, we observed impairments in the amplitude and duration of tyrosine phosphorylation when compared with the response of CD4+CD25- T cells. Defects were also seen in the activity of phospholipase C-gamma and in signals downstream of this enzyme including calcium mobilization, NFAT, NF-kappaB, and Ras-ERK-AP-1 activation. Enhanced stimulation of diacylglycerol-dependent pathways by inhibition of diacylglycerol metabolism could overcome the "anergic state" and support the ability of Tregs to up-regulate CD69, produce IL-2, and proliferate. Our results demonstrate that Tregs maintain their hyporesponsive state by suppressing the induction and propagation of TCR-initiated signals to control the accumulation of second messengers necessary for IL-2 production and proliferation.

Animals↗
PubMed2006

Constitutive activation of STAT5 supersedes the requirement for cytokine and TCR engagement of CD4+ T cells in steady-state homeostasis.

The transcription factor STAT5 is one of several signaling mediators activated via common gamma-chain cytokine receptors. As such, it plays an important role in lymphocyte survival and proliferation during normal homeostasis as well as under lymphopenic conditions. Transgenic mice expressing a constitutively activated form of STAT5b have been shown previously to contain increased numbers of peripheral CD4+CD25- T cells. To define the mechanism(s) for this occurrence, we have used adoptive transfer studies to examine the effects of STAT5 activity on steady-state CD4+ T cell homeostasis. We observed that constitutive STAT5 signaling induced 4- to 7-fold increased levels of basal steady-state proliferation, which was accompanied by a comparable increase in T cell recovery. Most strikingly, steady-state CD4 T cell proliferation occurred independently of both MHC class II and IL-15. These observations demonstrate that the STAT5-driven pathway is important to lymphocyte homeostasis and can supersede the need for both TCR engagement and cytokine stimulation. This suggests that the need for TCR stimulation to induce common gamma-chain cytokine receptor expression, and thus STAT5 activation, is a key factor in maintaining normal CD4+ T cell homeostasis.

Adoptive Transfer↗
PubMed2006

TRAF6 is a T cell-intrinsic negative regulator required for the maintenance of immune homeostasis.

TRAF6 has a key role in the regulation of innate immune responses by mediating signals from both TNF receptor and interleukin-1 receptor/Toll-like receptor superfamilies. Here we show that T cell-specific deletion of TRAF6 unexpectedly results in multiorgan inflammatory disease. TRAF6-deficient T cells exhibit hyperactivation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway compared with wild-type T cells and, as a result, become resistant to suppression by CD4+ CD25+ regulatory T cells. These data identify a previously unrecognized role for TRAF6 in the maintenance of peripheral tolerance, and suggest the presence of a T cell-intrinsic control mechanism to render responder T cells susceptible to tolerizing signals.

Animals↗
PubMed2006

Adeno-associated virus-mediated CTLA4Ig gene transfer protects MHC-mismatched renal allografts from chronic rejection.

Short-term results of renal transplantation have improved considerably in the past 20 yr; however, similar improvements in long-term outcome have not been achieved. The primary cause of late graft loss is chronic rejection that might be treated by gene therapeutic approaches. Ideally, one would like to impair locally the contact between transplant antigen and the host immune system without compromising the generalized immune competence of the recipient. This can be achieved by local expression of the therapeutic protein in the site of interest using gene therapy. Here it is shown that chronic allograft rejection can be prevented effectively by local delivery of recombinant adeno-associated virus (AAV) vectors that encode the CTLA4Ig immunosuppressant protein to the donor kidney in a fully MHC-mismatched rat strain combination. AAV CTLA4Ig prevented progressive proteinuria and protected transplant kidneys from renal structural injury. A population of anergic T cells with regulatory activity, which eventually were responsible for the induction of tolerance, were found in recipient lymph nodes and in the graft as long as 120 d after transplantation. These data indicate that AAV-mediated CTLA4Ig gene transfer to donor graft represents a promising tool to prevent the onset of chronic rejection and circumvent the unwanted systemic adverse effects of the administration of immunomodulatory protein.

Abatacept↗
PubMed2006

Accelerated memory cell homeostasis during T cell depletion and approaches to overcome it.

Partial T cell depletion is used in solid organ transplantation as a valuable strategy of peritransplant induction immunosuppression. Using a murine cardiac allograft model, we recently demonstrated that this led to lymphopenia-induced (homeostatic) proliferation among the residual nondepleted lymphocytes. Rather than promoting tolerance, peritransplant T cell-depleting Abs actually resulted in resistance to tolerance induction by costimulatory blockade. In this study we show that memory T cells predominate shortly after subtotal lymphodepletion due to two distinct mechanisms: relative resistance to depletion and enhanced homeostatic proliferation. In contrast, regulatory cells (CD4+ CD25+ Foxp3+) are depleted as efficiently as nonregulatory cells and exhibit reduced homeostatic expansion compared with memory cells. The resistance to tolerance induction seen with subtotal T cell depletion can be overcome in two different ways: first, by the adoptive transfer of additional unprimed regulatory cells at the time of transplant, and second, by the adjunctive use of nondepleting anti-CD4 and anti-CD8 mAbs, which effectively block homeostatic expansion. We conclude that the resistance to tolerance induction seen after subtotal lymphocyte depletion can be attributed to alterations in the balance of naive, memory, and regulatory T cells. These data have clinically relevant implications related to the development of novel strategies to overcome resistance to tolerance.

Adoptive Transfer↗
PubMed2006

Critical, but conditional, role of OX40 in memory T cell-mediated rejection.

Memory T cells can be a significant barrier to the induction of transplant tolerance. However, the molecular pathways that can regulate memory T cell-mediated rejection are poorly defined. In the present study we tested the hypothesis that the novel alternative costimulatory molecules (i.e., ICOS, 4-1BB, OX40, or CD30) may play a critical role in memory T cell activation and memory T cell-mediated rejection. We found that memory T cells, generated by either homeostatic proliferation or donor Ag priming, induced prompt skin allograft rejection regardless of CD28/CD154 blockade. Phenotypic analysis showed that, in contrast to naive T cells, such memory T cells expressed high levels of OX40, 4-1BB, and ICOS on the cell surface. In a skin transplant model in which rejection was mediated by memory T cells, blocking the OX40/OX40 ligand pathway alone did not prolong the skin allograft survival, but blocking OX40 costimulation in combination with CD28/CD154 blockade induced long-term skin allograft survival, and 40% of the recipients accepted their skin allograft for >100 days. In contrast, blocking the ICOS/ICOS ligand and the 4-1BB/4-1BBL pathways alone or combined with CD28/CD154 blockade had no effect in preventing skin allograft rejection. OX40 blockade did not affect the homeostatic proliferation of T cells in vivo, but markedly inhibited the effector functions of memory T cells. Our data demonstrate that memory T cells resisting to CD28/CD154 blockade in transplant rejection are sensitive to OX40 blockade and suggest that OX40 is a key therapeutic target in memory T cell-mediated rejection.

4-1BB Ligand↗
PubMed2006

Specificity of CD4+CD25+ regulatory T cell function in alloimmunity.

CD4+CD25+ regulatory T cells (TRegs) are critical for the acquisition of peripheral allograft tolerance. However, it is unclear whether TRegs are capable of mediating alloantigen-specific suppressive effects and, hence, contributing to the specificity of the tolerant state. In the current report we have used the ABM TCR transgenic (Tg) system, a C57BL/6-derived strain in which CD4+ T cells directly recognize the allogeneic MHC-II molecule I-A(bm12), to assess the capacity of TRegs to mediate allospecific effects. In these mice, 5-6% of Tg CD4+ T cells exhibit conventional markers of the TReg phenotype. ABM TRegs are more effective than wild-type polyclonal TRegs at suppressing effector immune responses directed against I-A(bm12) alloantigen both in vitro and in vivo. In contrast, they are incapable of suppressing responses directed against third-party alloantigens unless these are expressed in the same allograft as I-A(bm12). Taken together, our results indicate that in transplantation, TReg function is dependent on TCR stimulation, providing definitive evidence for their specificity in the regulation of alloimmune responses.

Adoptive Transfer↗
PubMed2006

CTLA4Ig: bridging the basic immunology with clinical application.

After a very long and windy road, in December of 2005 the FDA approved CTLA4Ig for the treatment of rheumatoid arthritis. Orencia is the first-in-class antagonist of CD28 costimulation. In this perspective, we discuss the science that led to CTLA4Ig development and the clinical challenges in bringing the drug from the bench to the bedside.

Abatacept↗
PubMed2005

Murine vascular endothelium activates and induces the generation of allogeneic CD4+25+Foxp3+ regulatory T cells.

Unlike graft-resident donor-derived hemopoietic APCs, which decrease in number over time after transplantation, vascular endothelial cells are lifelong residents of a vascularized allograft. Endothelial cells are potent APCs for allogeneic CD8+ T lymphocytes but are unable to induce proliferation of allogeneic CD4+ T lymphocytes. Although the reason for this differential response has been poorly understood, here we report that alloantigen presentation by vascular endothelium to CD4+ T lymphocytes activates and induces CD4+25+Foxp3+ regulatory T cells, which can inhibit proliferation of alloreactive T cells both in vitro and in vivo. This process occurs independently of B7.1 costimulation but is dependent on programmed death ligand 1 (B7-H1). This finding may have important implications for tolerance induction in transplantation.

Animals↗
PubMed2005

Hypoxia inducible factor 1 alpha regulates T cell receptor signal transduction.

Low oxygen pressures exist in many solid tissues, including primary and secondary lymphoid organs. One key element in cellular adaptation to hypoxia is induced expression of hypoxia inducible factor (Hif) 1alpha. Here, we have examined the effect of Hif-1alpha, isolated from the myriad other effects of hypoxia, on T cell receptor (TCR) signaling in thymocytes. Because pVHL (von Hippel-Lindau protein) directs the proteolysis of Hif-1alpha under "normoxic" conditions, we achieved constitutive stabilization of Hif-1alpha through thymic deletion of Vhlh and reversed Hif-1alpha stabilization with double deletion of Vhlh and Hif-1alpha. We found that constitutive activity of Hif-1alpha resulted in diminished Ca(2+) response upon TCR crosslinking despite equivalent activation of phospholipase C(gamma1), normal intracellular Ca(2+) stores, and normal entry of Ca(2+) across the plasma membrane. Altered Ca(2+) response was instead due to accelerated removal of Ca(2+) from the cytoplasm into intracellular compartments, which occurred in association with Hif-1alpha-dependent overexpression of the calcium pump SERCA2 (sarcoplasmic/endoplasmic reticulum calcium ATPase 2). These data suggest a unique mechanism for control of TCR signaling through Hif-1alpha, which may be operative at the physiologic oxygen tensions seen in solid lymphoid organs.

Animals↗
PubMed2005

Homeostatic T cell proliferation as a barrier to T cell tolerance.

The maintenance of T cell numbers in the periphery is mediated by distinct homeostatic mechanisms that ensure the proper representation of naïve and memory T cells. Homeostatic proliferation refers to the process by which T cells in lymphopenic hosts divide in the absence of cognate antigen to reconstitute the peripheral lymphoid compartment. During this process T cells acquire effector-memory like properties, including the ability to respond to low doses of antigen in the absence of CD28 costimulation. Furthermore, this capacity is retained long after proliferation has ceased. Accumulating data implicates homeostatic proliferation in autoimmune diseases and transplant rejection, and suggests that it may represent a barrier to tolerance in protocols that use T cell depletion. Implementing combination therapies that aim to promote the development and expansion of regulatory T cell populations while specifically targeting alloresponsive T cells may be the soundest approach to attaining allograft tolerance in the aftermath of T cell depletion and homeostatic proliferation.

Cell Differentiation↗
PubMed2005

Role of the programmed death-1 pathway in regulation of alloimmune responses in vivo.

Programmed death-1 (PD-1), an inhibitory receptor up-regulated on activated T cells, has been shown to play a critical immunoregulatory role in peripheral tolerance, but its role in alloimmune responses is poorly understood. Using a novel alloreactive TCR-transgenic model system, we examined the functions of this pathway in the regulation of alloreactive CD4+ T cell responses in vivo. PD-L1, but not PD-1 or PD-L2, blockade accelerated MHC class II-mismatched skin graft (bm12 (I-Abm12) into B6 (I-Ab)) rejection in a similar manner to CTLA-4 blockade. In an adoptive transfer model system using the recently described anti-bm12 (ABM) TCR-transgenic mice directly reactive to I-Abm12, PD-1 and PD-L1 blockade enhanced T cell proliferation early in the immune response. In contrast, at a later time point preceding accelerated allograft rejection, only PD-L1 blockade enhanced T cell proliferation. In addition, PD-L1 blockade enhanced alloreactive Th1 cell differentiation. Apoptosis of alloantigen-specific T cells was inhibited significantly by PD-L1 but not PD-1 blockade, indicating that PD-1 may not be the receptor for the apoptotic effect of the PD-L1-signaling pathway. Interestingly, the effect of PD-L1 blockade was dependent on the presence of CD4+ CD25+ regulatory T cells in vivo. These data demonstrate a critical role for the PD-1 pathway, particularly PD-1/PD-L1 interactions, in the regulation of alloimmune responses in vivo.

Adoptive Transfer↗
PubMed2005

Alloreactive T cell responses and acute rejection of single class II MHC-disparate heart allografts are under strict regulation by CD4+ CD25+ T cells.

Skin but not vascularized cardiac allografts from B6.H-2bm12 mice are acutely rejected by C57BL/6 recipients in response to the single class II MHC disparity. The underlying mechanisms preventing acute rejection of B6.H-2bm12 heart allografts by C57BL/6 recipients were investigated. B6.H-2bm12 heart allografts induced low levels of alloreactive effector T cell priming in C57BL/6 recipients, and this priming was accompanied by low-level cellular infiltration into the allograft that quickly resolved. Recipients with long-term-surviving heart allografts were unable to reject B6.H-2bm12 skin allografts, suggesting potential down-regulatory mechanisms induced by the cardiac allografts. Depletion of CD25+ cells from C57BL/6 recipients resulted in 15-fold increases in alloreactive T cell priming and in acute rejection of B6.H-2bm12 heart grafts. Similarly, reconstitution of B6.Rag(-/-) recipients with wild-type C57BL/6 splenocytes resulted in acute rejection of B6.H-2bm12 heart grafts only if CD25+ cells were depleted. These results indicate that acute rejection of single class II MHC-disparate B6.H-2bm12 heart allografts by C57BL/6 recipients is inhibited by the emergence of CD25+ regulatory cells that restrict the clonal expansion of alloreactive T cells.

Acute Disease↗
PubMed2005

Distinct temporal programming of naive CD4+ T cells for cell division versus TCR-dependent death susceptibility by antigen-presenting macrophages.

Naive T cells become programmed for clonal expansion and contraction during the early hours of antigenic signaling. Recent studies support an 'autopilot' model, wherein the commitment to proliferate and the magnitude of the proliferative response are simultaneously determined during a single, brief period of antigen exposure. Here, we have examined whether the proliferation of naive CD4+ T cells must occur on 'autopilot', or whether extended periods of antigenic signaling can impact primary proliferative responses to antigen-presenting macrophages (macrophage APC). We found that a single exposure to antigen (18 h) simultaneously committed T cells to (1) up-regulate surface TCR above the level expressed on naive T cells, (2) undergo minimal cell division, and (3) acquire susceptibility to TCR-dependent activation-induced cell death. However, continued antigenic signaling between 18 and 72 h was required to amplify the number of daughter cells derived from the already committed T cells. Thus, a discrete commitment time was followed by a 'tuning' period, where extended antigenic signaling determined the volume of the proliferative response. We conclude that T cell commitment to full clonal expansion versus TCR-dependent death susceptibility represent two separate programming events whose timing can be segregated by macrophage APC.

Animals↗