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Publications and source records attributed to A M Krensky.
Although much is understood about the induction of genes expressed early (within 24 h) after T-cell activation, little is known about the regulation of expression of genes expressed 'late' (three or more days) post-stimulation. A better understanding of transcriptional regulation at this important stage of T-cell maturation may yield new insights into T-cell development and new immunotherapeutic targets.
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Over the past decade the use of synthetic peptides corresponding to linear sequences of HLA molecules has progressed from a concept to a reality. These peptides are currently being evaluated in clinical trials. In animal models these peptides, given over 1 week with cyclosporin alone, induced long-term immunological tolerance (Figure 3). They may similarly induce tolerance in humans. The next major hurdle for such tolerogenic drugs, however, is to prove efficacy in clinical circumstances. Many of the drugs used to treat transplant patients today (steroids, cyclosporin, azathioprine, mycophenolate mofetil) may actually inhibit the 'active' processes of induction and maintenance of immunological tolerance. Demonstration that new drugs induce tolerance will require efficacy studies in other immune-mediated diseases in which monotherapy is feasible (such as psoriasis), before further advances can be made in the induction of transplant tolerance. In addition, rapid assays of rejection must be developed in order to reverse tolerance induction failures without graft damage or loss. Lastly, it will require heroic physicians, surgeons, and patients to make immunological tolerance a reproducible clinical reality.
Understanding of the molecular basis of organ allograft rejection has increased tremendously in the past decade. Insight into the nature of the alloantigen and the mechanisms underlying T cell recognition, activation, and differentiation provide novel targets for immunotherapy. Appreciation of the role that peptides present in the human leukocyte antigen groove play in allorecognition provides a new target for synthetic peptide therapy. Elucidation of signal transduction pathways downstream from the T-cell receptor helps to explain the mechanism of action of immunosuppressive agents and impacts the design of new drugs. An understanding of the role of costimulatory molecules, such as CD28, has given rise to new therapies, such as CTLA4-Ig. Information about the mechanisms of cytotoxicity, chemoattraction, and vascular biology similarly has provided new targets for rational drug design. This article highlights new insights into the mechanism of allograft rejection relevant to the design of new immunotherapies.
Human leukocyte antigens (HLA) restrict immune responses by binding antigenic peptides and presenting them in the context of self to T lymphocytes. In transplantation, a vigorous T cell response, termed alloreactivity, is caused by recognition of non-self HLA. The major histocompatibility complex (MHC) encodes two major classes of HLA molecules, designated I and II. In general, HLA class I molecules present peptides derived by proteolysis of intracellular proteins (the endogenous pathway), while HLA class II molecules present peptides sampled from the extracellular body fluids (the exogenous pathway). The dichotomy between class I and class II antigens is reflected in the T cells in that the CD8 cell surface glycoprotein is expressed by cytotoxic T lymphocytes and recognizes HLA class I, while CD4 is expressed on helper T cells and recognizes HLA class II. Although the two classes of HLA molecules are thought to have originated from a common ancestral gene, they have evolved specific structures and intracellular trafficking compartments that account for their functions. The class I proteins bind short peptides of eight to nine amino acids that are tightly anchored at their ends. The class II proteins bind longer peptides that are more heterogeneous in size (12 to 28 amino acids) and have ragged ends. The class I peptides are generated by proteasomes and other mechanisms in the cytosol and translocated from the cytosol into the endoplasmic reticulum (ER). In the ER, functional HLA class I complexes are formed and then transported to the cell surface for presentation. HLA class II molecules are assembled without antigenic peptide. An "invariant chain" promotes the assembly of the class II molecule and protects its groove from binding peptides in the ER. In an endosomal compartment, antigens that have entered the cell via pinocytosis or via receptor-mediated internalization are processed, the invariant chain is degraded, and antigenic peptides bind to the HLA class II molecule. This mature complex is transported to the cell surface for presentation. Alloreactivity is the special case of antigen presentation responsible for transplant rejection.
The RANTES chemokine is a T cell-expressed, proinflammatory cytokine recently implicated as a suppressive agent of HIV replication. We have identified tandem kappaB-like sequences within the promoter for RANTES that are critical for RANTES promoter-reporter gene activity in both the T cell tumor line Hut78 and in PHA-activated PBL. This region binds not only Rel family members (including p50-p65 heterodimers and p50-p50 homodimers) but also non-Rel factors up-regulated in PBL 3 to 5 days following activation. The expression of these "late" expressed nuclear factors correlates with an up-regulation of RANTES message found at this point in T cell activation. These factors are also constitutively expressed in functionally mature CD8+ T cells. We hypothesize that these apparently novel proteins are responsible in part for the temporal regulation of RANTES seen in peripheral blood T cells and represent a component of transcriptional regulatory machinery newly expressed at this "late" stage of peripheral T cell development.
Patients with non-Hodgkin's B-cell lymphoma who received an antitumor vaccine of idiotypic ig protein showed humoral and proliferative immune responses. Because immunity to some antigens, including tumor antigens and human pathogenic viruses, may be better correlated with the cytolytic cellular immune response, we evaluated 16 non-Hodgkin's lymphoma patients immunized with autologous idiotypic ig molecules for changes in tumor-specific cytotoxic T-lymphocyte precursor (CTLp) frequency using limiting dilution analysis. Eleven patients had a significant increase in tumor-specific CTLp. Eight of these 11 patients remain without evidence of disease or with stable minimal disease. In contrast, all five patients who did not have a significant change in tumor-specific CTLp have developed progressive disease. Patient vaccination with tumor associated protein antigens can increase tumor-specific CTLp frequencies. The correlation of increased tumor specific CTLp with freedom from progression is significant at P = .002. This study indicates that measurement of CTLp frequencies are relevant to the clinical evaluation of human tumor vaccines and suggests that cell-mediated cytolytic immune responses may be an important determinant of vaccine efficacy.
Synthetic peptides corresponding to sequences of HLA class I molecules have inhibitory effects on T cell function. The peptides investigated in this study have sequences corresponding to the relatively conserved region of the alpha 1 helix of HLA class I molecules that overlaps the "public epitope" Bw4/Bw6. These HLA-derived peptides exhibit inhibitory effects on T lymphocytes and have beneficial effects on the survival of allogenic organ transplants in mice and rats. Peptides corresponding to the Bw4a epitope appear most potent as they inhibit the differentiation of T cell precursors into mature cytotoxic T lymphocytes (CTL) and target cell lysis by established CTL lines and clones. To elucidate the mechanism through which these peptides mediate their inhibitory effect on T lymphocytes, peptide binding proteins were isolated from T cell lysates. We show that the inhibitory Bw4a peptide binds two members of the heat-shock protein (HSP) 70 family, constitutively expressed HSC70 and heat-inducible HSP70. Peptide binding to HSC/HSP70 is sequence specific and follows the rules defined by the HSC70 binding motif. Most intriguing, however, is the strict correlation of peptide binding to HSC/HSP70 and the functional effects such that only inhibitory peptides bind to HSC70 and HSP70 whereas noninhibitory peptides do not bind. This correlation suggests that small molecular weight HLA-derived peptides may modulate T cell responses by directly interacting with HSPs. In contrast to numerous reports of HSP70 expression at the surface of antigen-presenting cells and some tumor cells, we find no evidence that HSC/HSP70 are expressed at the surface of the affected T cells. Therefore, we believe that the peptides' immunodulatory effects are not mediated through a signaling event initiated by interaction of peptide with surface HSP, but favor a model similar to the action of other immunomodulatory compounds, FK506 and cyclosporin A, with a role for HSC/HSP70 similar to that for immunophilins, FKBPs and CyP40.
Chemotaxis of human T lymphoblastoma cells of the Tsup-1 line, which migrate similarly to blood T cells, through a layer of basement membrane-like Matrigel on a polycarbonate micropore filter was evoked by vasoactive intestinal peptide (VIP; concentration for a maximal response, 10(-7)M), IL-2 (10(-9)M), and the chemokines RANTES (10(-10)M) and macrophage inflammatory protein-1 alpha (10(-10)M). Chemotactic concentrations of each factor increased Tsup-1 cell secretion of matrix metalloproteinase-9 (MMP-9), with significant responses by 4 h for VIP, IL-2, and IL-4, but only after 24 h for macrophage inflammatory protein-1 alpha and RANTES, as quantified by Western blots and zymography. 3H-Labeled type IV human collagen incorporated in the Matrigel layer was degraded by migrating Tsup-1 cells, as assessed by release of radioactive fragments of the collagen. The in situ degradation of type IV collagen in Matrigel by migrating Tsup-1 cells was enhanced most significantly by VIP, IL-2, and IL-4 after 4 h at concentrations that increased the secretion of MMP-9 optimally, but only after 24 h by macrophage inflammatory protein-1 alpha and RANTES. The specific MMP inhibitor GM6001 suppressed Tsup-1 cell MMP activity evoked by all stimuli, as determined by zymography and in situ degradation of 3H-Labeled type IV human collagen. The chemotactic migration of Tsup-1 cells through Matrigel, but not through a filter alone, in response to optimal concentrations of VIP, IL-2, and IL-4, but not the chemokines, was inhibited by GM6001, with a concentration dependence similar to that for suppression of MMP activity. Thus elicitation of T cell chemotactic migration through a model basement membrane by stimuli that increase MMP activity early in the response depends on degradation of matrix proteins by MMP, whereas stimuli that recruit MMP late may rely on early activation of other proteases.
RANTES is a member of a large family of cytokines, called chemokines, which are thought to play a regulatory role in inflammatory processes. We have made recombinant human RANTES protein which was used to generate a panel of anti-RANTES monoclonal antibodies. Following characterization, select anti-RANTES monoclonal antibodies were used for immunohistologic staining of a large panel of normal, diseased and fetal tissue sections. Diseased tissues included eleven lymphomas and eight renal tumors. Most tissues were also tested in parallel for RANTES mRNA by in situ hybridization using RANTES mRNA specific oligomeric probes. As expected, most normal adult tissues contain few, if any, RANTES positive cells. In contrast, RANTES expression dramatically increases in inflammatory sites. In addition, megakaryocytes, some tumours, and select fetal tissues express high levels of RANTES message and protein. These results indicate a wider expression of RANTES than previously appreciated and suggest multiple physiologic roles for this soluble factor.
Human cytolytic T lymphocytes specific for autologous Burkitt's lymphoma express the gamma, delta T cell receptor and recognize immunoglobulin idiotype in an MHC-unrestricted manner. Antibodies against a member of the heat shock protein 70 family inhibit this specific cytotoxicity, implicating these molecules in tumor recognition and antigen presentation. Such data is relevant to the design of novel immunotherapies for cancer and provides new insights into target recognition by gamma, delta T cells.
RANTES is a chemoattractant cytokine (chemokine) whose gene is expressed immediately after stimulation of several cell types but upregulated late (3 to 5 days) after activation in normal T lymphocytes. Here we describe two cis-acting elements in the human RANTES promoter that act in T lymphocytes. One site interacts with NFIL6, which is activated within the first 24 h after T-cell activation. The second site binds an apparently novel complex that is upregulated later, between days 3 and 5. These data provide an explanation for the immediate-early expression of RANTES in some cell types and identify apparently novel factors contributing to late RANTES transcription in T cells. The results reveal a developmental switch occurring during normal T-cell maturation coincident with the onset of terminal differentiation and the binding of late-acting factors to sequences of the RANTES promoter.
Elucidation of the structure of MHC molecules has provided profound new insights into their function in antigen presentation. In addition, structural studies have implicated certain regions of MHC molecules in specific functions. Although much of MHC biology has concentrated on the extensive polymorphism among these molecules, there is also evolutionary pressure to maintain the relatively monomorphic portions of these molecules. Drs. Krensky and Clayberger have found that synthetic peptides corresponding to linear sequences of HLA molecules have immunomodulatory effects both in vitro and in vivo. In this paper, they review the structure of HLA molecules and their studies of HLA derived peptides as novel immunotherapeutics. Members of the heat shock protein 70 family are implicated in the HLA derived peptide immunosuppressive pathway.
In summary, synthetic peptides corresponding to linear sequences of HLA class I molecules can inhibit T-cell responses in vitro and in vivo. These peptides induce immunologic tolerance by binding to hsp-70 family members, causing an increase in intracellular calcium, and down-regulating the nuclear factor of activated T cells, NF-AT. We suggest that heat shock proteins may function as novel immunophilins (Fig 2). Like cyclophilins and FK 506 binding proteins, heat shock proteins are ubiquitous, are involved in protein folding and trafficking, and bind exogenous drugs. Cyclosporine and FK 506 exert immunosuppressive effects by binding immunophilins, which as a result interrupt the phosphatase activity of calcineurin. Although the precise pathways involved in the synthetic HLA peptide effects are not as well worked out, it seems likely that peptide binding to heat shock protein is disrupting normal events in T-cell activation, giving rise to an apparently permanent state of anergy.
Organ transplantation is now the treatment of choice for end stage organ failure. The ultimate goal in transplantation remains the development of strategies to induce specific tolerance to the allograft. The major histocompatibility complex (MHC) antigens are the principal targets of the immune response to allografts and T cell recognition of allo-MHC is the initial event which initiates allograft rejection. The availability of sequences of MHC genes in mice, rats and humans has made it possible to prepare synthetic peptides for the study of the role of MHC peptides in allorecognition and tolerance induction. New evidence confirms that there are at least two distinct, but not necessarily mutually exclusive, pathways of allorecognition. In the so-called "direct" pathway T cells recognize intact allo-MHC molecules on the surface of donor cells. These MHC molecules contain an array of endogenous peptides bound in their antigen presentation groove. In the "indirect" pathway, T cells recognize specific processed alloantigen presented as peptides in the context of self MHC by antigen-presenting cells (APCs). In addition, there is ample evidence that synthetic MHC peptides can immunomodulate the alloimmune response both in vitro and vivo, and that potent allo-tolerance can be induced with synthetic MHC peptides. Two types of effects mediated by synthetic MHC peptides have been demonstrated: (1) suppression of the alloimmune response by relatively non-polymorphic peptides and (2) antigen-specific unresponsiveness induced by polymorphic peptides. The mechanisms mediating the immunomodulatory effects of synthetic effects of synthetic class I and class II MHC peptides and the potential for clinical applications are reviewed.
Synthetic peptides corresponding to linear sequences of HLA class I molecules have profound immunomodulatory effects in vitro and in vivo. Recent clinical trials confirm their potential as the therapeutics for transplantation and for a variety of immune-mediated diseases. These peptides also inhibit NK responses in vivo in humans. The importance of the carboxy end of the alpha 1 alpha helix in negative signaling to both T cells and NK cells focuses attention on new targets for immunotherapy.
BACKGROUND: The pathogenesis of transplantation-associated accelerated atherosclerosis is poorly understood, but it is likely to be an alloimmune response involving infiltration of the vessel wall by T lymphocytes and monocytes leading to smooth muscle cell proliferation and extracellular matrix deposition. RANTES is a chemokine that selectively chemoattracts T lymphocytes, NK cells, monocytes, and eosinophils. The expression of RANTES in accelerated atherosclerosis was investigated by in situ hybridization and immunohistochemistry. METHODS: Coronary arteries from six patients undergoing accelerated atherosclerosis were obtained at the time of retransplantation. Normal coronary arteries from two patients with idiopathic dilated cardiomyopathy were used as controls. Messenger RNA for RANTES was localized with digoxigenin-labeled complementary DNA probes. RANTES protein was detected by use of a monoclonal antibody and a three-step horseradish peroxidase method. RESULTS: RANTES mRNA and protein were detected in the lymphocytes, macrophages, myofibroblasts, and endothelial cells of arteries undergoing accelerated atherosclerosis but not in normal coronary arteries. CONCLUSIONS: In view of its in vitro biologic activity and in vivo expression pattern, RANTES may be a pivotal mediator of the cellular infiltrate seen in graft atherosclerosis. This information may help in the design of novel diagnostic and therapeutic approaches to this increasingly important disease process.
Although gamma delta T cells have been postulated to act as a surveillance mechanism that eliminates transformed or otherwise damaged cells, little is known about tumor recognition by gamma delta T cells, including the Ags that are recognized and the molecules that present them. Previously, we described human gamma delta CTL that recognize the autologous B cell lymphoma. Here we report that these gamma delta CTL lyse heterologous cells transfected with the tumor Ig lambda chain gene. Furthermore, the lambda chain is recognized as processed peptide in an Id-specific manner. T cell recognition does not involve classical MHC molecules, but it could be blocked by Abs directed against the heat shock protein grp75. These findings show a specific gamma delta T cell response to a highly polymorphic Ag such as tumor Id and implicate heat shock protein as a molecule required for recognition.