Similarly, we hypothesized that MEDI6383 would protect conventional CD4 T cells from Treg-mediated suppression as has been reported for other OX40 agonists

Similarly, we hypothesized that MEDI6383 would protect conventional CD4 T cells from Treg-mediated suppression as has been reported for other OX40 agonists. and reduced tumor growth in the context of an alloreactive human T cell:tumor cell admix model in immunocompromised mice. Consistent with the role of OX40 costimulation in the growth of memory T cells, MEDI6383 administered to healthy non-human primates elicited peripheral blood CD4 and CD8 central and effector memory T cell proliferation as well as B cell proliferation. Together, these results suggest that OX40 agonism has the potential to enhance anti-tumor immunity in human malignancies. strong class=”kwd-title” Keywords: MEDI6383, OX40 ligand, OX40, immunotherapy, fusion protein Introduction The generation of an anti-tumor immune response as a therapeutic strategy in oncology has been studied for many years. Recently, immuno-oncology drugs have exhibited significant improvements over standard of care Tropanserin therapies in certain malignancies, exemplified by US Food and Drug Administration (FDA) approvals for anti-CTLA-4, anti-PD-1 and anti-PD-L1 monoclonal antibodies (mAb) (1). Despite this success, a significant number of malignancy patients do not respond to immunotherapies, respond incompletely, or discontinue therapy due to adverse events. Immunosuppressive mechanisms outside of the targeted pathway may prevent an effective anti-tumor immune response within the tumor microenvironment (TME) despite the presence or recruitment of anti-tumor T cells (2). Such factors include suppressive immune cells that include regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) capable of suppressing activated T cells. Therefore, additional therapies are needed that expand high affinity, tumor-specific Tropanserin T cells in regional draining lymph nodes or within the TME despite immunosuppression not currently resolved by immunologic checkpoint blockade. One strategy to promote an anti-tumor immune response that is different from checkpoint inhibition is usually to activate the TNF receptor superfamily (TNFRSF) of co-stimulatory T cell receptors. Agonist methods for these receptors currently undergoing clinical trials include antibodies and other technologies targeting CD137 (4-1BB; TNFRSF9), CD40 (TNFRSF5), CD27 (TNFRSF7), GITR (CD357; TNFRSF18), and OX40 (CD134; TNFRSF4) (3). OX40 is usually a TNFRSF member expressed on activated effector and memory, as well as regulatory, T cells. Development of Rabbit Polyclonal to RELT the mouse mAb 9B12, subsequently termed MEDI6469, was the first anti-human OX40 mAb in clinical development for advanced solid malignancies, and showed encouraging Tropanserin anti-tumor responses and a tolerable security profile (4). The mouse origin of the MEDI6469 antibody, however, limits its clinical utility to one cycle of treatment due to the emergence of human anti-mouse antibody (HAMA) responses. Subsequently, a humanized version of MEDI6469 termed MEDI0562 was created to avoid the immunogenicity seen with MEDI6469. This and other agonist anti-human OX40 mAbs have entered early phase clinical screening (5C7). OX40-specific mAbs, as bivalent OX40 binding moieties, have the potential to induce OX40 signaling when clustered, but have not been shown to be capable of trimerizing OX40 in the absence of clustering. In contrast, the naturally trimeric OX40 ligand (OX40L, CD252, TNFSF4) protein complex expressed by professional antigen-presenting cells (APCs) can trimerize OX40 directly. The engagement of OX40 by the OX40L, in concert with other co-stimulatory signals, promotes T cell activation, survival, expansion, and the formation of effector and central memory T cell pools. In contrast to OX40-specific mAbs, designed fusion proteins made up of the OX40L extracellular domain name (ECD) have been created to take advantage of the strong agonist properties of the ligand. Previously, a human OX40L ECD linked to a human IgG1 Fc domain name via a coiled-coil trimerization domain name from the yeast GCN4 protein had been expressed and characterized (8). It was found to naturally associate into a hexameric human OX40L fusion protein structure composed of two trimerized molecules covalently bound together through disulfide linkages found in the human IgG1 Fc domains. To build a hexameric human OX40L fusion protein suitable for clinical use, we designed a fully human OX40L fusion protein termed MEDI6383. This protein contains human OX40L ECDs fused to the trimerization domain name of the human TRAF2 protein and to human IgG domains to enable the formation of a covalently linked hexamer. Because the human IgG1 isotype can mediate match fixation and antibody-dependent cellular cytotoxicity (ADCC), we selected human IgG4 as the human IgG isotype to minimize the possibility of in vivo depletion of OX40-expressing effector T cells. Although human IgG4 was unlikely to mediate ADCC or match fixation, this isotype.