Antigen-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide antigens linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-SP) has been demonstrated to be a highly efficient method for inducing peripheral, antigen-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. Here, we show that apoptotic Ag-SP accumulate in the splenic marginal zone where their uptake by F4/80+ macrophages induces production of IL-10 which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 which is essential for Ag-SP tolerance induction. Ag-SP infusion also induces Tregs which are dispensable for tolerance induction, but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. We show for the first time that tolerance results from the synergistic effects of two distinct mechanisms – PD-L1-dependent T cell-intrinsic unresponsiveness and the activation of Tregs. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting MS.

MYC is a major cancer driver but is documented to be a difficult therapeutic target itself. Here, we report on the biological activity, the structural basis, and therapeutic effects of the family of multitargeted compounds that simultaneously disrupt functions of two critical MYC-mediating factors through inhibiting the acetyllysine binding of BRD4 and the kinase activity of PI3K. We show that the dual-action inhibitor impairs PI3K/BRD4 signaling in vitro and in vivo and affords maximal MYC down-regulation. The concomitant inhibition of PI3K and BRD4 blocks MYC expression and activation, promotes MYC degradation, and markedly inhibits cancer cell growth and metastasis. Collectively, our findings suggest that the dualactivity inhibitor represents a highly promising lead compound for the development of novel anticancer therapeutics.T he MYC gene is frequently altered in human cancer. It encodes a transcription factor that binds to and regulates nearly 10-15% of genes in the human genome (1-3). The MYC targets mediate fundamental biological processes necessary for cell survival and general well-being, ranging from gene-expression and cell-cycle programs to cell proliferation and response to DNA damage, thereby establishing MYC as a global transcriptional regulator. MYC is overexpressed or amplified in many human cancers, which results in genome instability and deregulation of an array of signaling pathways responsible for malignant transformation. MYC expression level as well as synthesis, stability, and posttranslational modifications (PTMs) of the MYC protein are tightly regulated via several pathways, including PI3K-AKTmTOR and RAS-MAPK (4). Particularly, PI3K activation blocks MYC degradation through inhibiting GSK3β-dependent MYC phosphorylation at threonine 58, elevating MYC levels and inducing MYC-dependent oncogenic programs (4, 5).MYC gene expression has recently been linked to the activity of the BET (bromodomains and extraterminal domain) family of transcriptional coactivators (6-9). The BET protein BRD4 is found enriched at MYC and other oncogenes superenhancer and promoter regions, and transcriptional silencing of MYC coincides with the release of BET proteins from its locus, indicating that BET proteins can regulate MYC expression (10, 11). BRD4 itself is linked to multiple human malignancies: It forms chromosomal translocations in squamous carcinoma and NUT midline carcinoma, plays a role in progression of acute myeloid leukemia, and is up-regulated in breast cancer (7,(12)(13)(14). BRD4 contains a pair of bromodomains (BDs) that belong to the family of evolutionarily conserved structural modules that recognize acetyllysine PTMs in histones and nonhistone proteins (15, 16). Interestingly, BD1 and BD2 of BRD4 have distinct acetyllysine binding functions (17). BD1 binds to diacetylated histones, including histone H4 diacetylated at lysine 5 and lysine 8 (H4K5acK8ac), and this interaction helps to recruit or stabilize BRD4-containing transcription complexes at target gene promoters and enhancers. The se...

The ability of different forms of myelin peptides to induce tolerance for the treatment of preestablished murine experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, was evaluated. i.v. administration of myelin peptidepulsed, ethylene carbodiimide-fixed syngeneic splenocytes, but not soluble myelin peptide monomers or oligomers, proved exceedingly effective at treating preestablished EAE, resulting in amelioration of disease progression. In addition to the lack of therapeutic efficacy of soluble peptide and peptide oligomer, administering them i.v. after the onset of clinical symptoms in many but not all peptide-induced EAE models led to a rapid-onset anaphylactic reaction characterized by respiratory distress, erythema, decreased body temperature, unresponsiveness, and, often, death. By using anti-IgE antibody treatments and mice with targeted mutations of the Fc␥RIII ␣-chain or the common ␥-chain of Fc RI and Fc␥RI͞III, we demonstrate that IgE crosslinking of Fc RI appears to be necessary and sufficient for myelin peptide-induced anaphylaxis. The implications of these findings to myelin peptide͞ protein tolerance strategies for the treatment of multiple sclerosis are discussed.myelin ͉ tolerance M ultiple sclerosis (MS) is a CNS-demyelinating disease characterized by the perivascular infiltration of inflammatory mononuclear cells (1). Although the etiology of MS is unknown, evidence from human patients (2-4) and an animal model of MS, experimental autoimmune encephalomyelitis (EAE) (5-7), supports a major pathogenic role for autoreactive myelin-specific CD4 ϩ T cells, which are a logical target for clinical therapies. Two protocols that have shown promise in inducing antigen-specific immune tolerance for the prevention and͞or treatment of EAE are the i.v. injection of soluble protein, peptide, or peptide oligomers (8-10) and the i.v. injection of myelin proteins or peptides chemically coupled to syngeneic splenocytes [antigen-coupled splenocytes (Ag-SP)] (11). We performed a side-by-side comparison of these two tolerance protocols in preventing EAE induction and ameliorating ongoing EAE. We found that i.v. injection of soluble peptide monomer was not particularly effective when administered at any time point tested, and a soluble peptide oligomer was only fully effective when administered after immunization (day ϩ7) but before the onset of clinical symptoms of EAE. In contrast, i.v. administration of Ag-SP proved effective at preventing the onset of clinical symptoms and treating preestablished disease. In addition, an unexpected result of the administration of soluble peptide and peptide oligomer after the onset of clinical symptoms in many, but not all, peptide-induced EAE models was a rapid-onset anaphylactic reaction characterized by respiratory distress, erythema, decreased body temperature, unresponsiveness, and often death. This result is especially alarming given the proposed use of peptide-based tolerance therapies for the treatment of autoimmune diseases.Anaphylaxis i...

The probability that epitope spreading occurs in multiple sclerosis (MS) and the fact that patients have been shown to respond to multiple myelin epitopes concurrently makes the use of peptidespecific tolerance therapies targeting single epitopes problematic. To attempt to overcome this limitation, we have employed cocktails of peptides in the ECDI coupled-APC tolerance system in mice to determine if T cell responses to multiple autoepitopes can be targeted simultaneously. Preventative tolerance induced with splenocytes coupled with a peptide cocktail of four distinct encephalitogenic epitopes ) inhibited initiation of active EAE induced with each individual peptide and by a mixture of the four peptides by preventing activation of autoreactive Th1 cells and subsequent infiltration of inflammatory cells into the CNS. Most relevant to treatment of clinical MS, therapeutic tolerance initiated by splenocytes coupled with the peptide cocktail administered at the peak of acute disease prevented clinical relapses due to epitope spreading and ameliorated a diverse disease induced with a mixture of the four peptides. Interestingly, therapeutic tolerance appeared to be mediated by a mechanism distinct from preventative tolerance, i.e. by significantly increasing the levels of production of the antiinflammatory cytokines TGF-β and/or IL-10 in both the periphery and the CNS.