The CD70/CD27 pathway plays a significant role in the control of immunity and tolerance, and previous studies demonstrated that targeting murine CD27 (mCD27) with agonist mAbs can mediate antitumor efficacy. We sought to exploit the potential of this pathway for immunotherapy by developing 1F5, a fully human IgG1 mAb to human CD27 (hCD27) with agonist activity. We developed transgenic mice expressing hCD27 under control of its native promoter for in vivo testing of the Ab. The expression and regulation of hCD27 in hCD27-transgenic (hCD27-Tg) mice were consistent with the understood biology of CD27 in humans. In vitro, 1F5 effectively induced proliferation and cytokine production from hCD27-Tg–derived T cells when combined with TCR stimulation. Administration of 1F5 to hCD27-Tg mice enhanced Ag-specific CD8+ T cell responses to protein vaccination comparably to an agonist anti-mCD27 mAb. In syngeneic mouse tumor models, 1F5 showed potent antitumor efficacy and induction of protective immunity, which was dependent on CD4+ and CD8+ T cells. The requirement of FcR engagement for the agonistic and antitumor activities of 1F5 was demonstrated using an aglycosylated version of the 1F5 mAb. These data with regard to the targeting of hCD27 are consistent with previous reports on targeting mCD27 and provide a rationale for the clinical development of the 1F5 mAb, for which studies in advanced cancer patients have been initiated under the name CDX-1127.

Phosphorylation of the NR1 subunit of NMDA receptors (NMDARs) at serine (S) 897 is markedly reduced in schizophrenia patients. However, the role of NR1 S897 phosphorylation in normal synaptic function and adaptive behaviors are unknown. To address these questions, we generated mice in which the NR1 S897 is replaced with alanine (A). This knock-in mutation causes severe impairment in NMDAR synaptic incorporation and NMDAR-mediated synaptic transmission. Furthermore, the phosphomutant animals have reduced AMPA receptor (AMPAR)-mediated synaptic transmission, decreased AMPAR GluR1 subunit in the synapse, and impaired long-term potentiation. Finally, the mutant mice exhibit behavioral deficits in social interaction and sensorimotor gating. Our results suggest that an impairment in NR1 phosphorylation leads to glutamatergic hypofunction that can contribute to behavioral deficits associated with psychiatric disorders.

2861 CD27, a lymphoid cell-specific TNFR superfamily member, is constitutively expressed on the majority of T cells, some NK cells and memory B cells. Through interaction with its ligand CD70, CD27 transduces a co-stimulatory signal promoting T cell and NK cell activation and cytotoxicity. In addition, CD27 is also expressed on many lymphoid-originated hematological neoplastic cells, such as chronic lymphocytic leukemia, mantle cell lymphoma, and Waldenstrom macroglobulinemia, thus being a potential direct target for antibody therapy. To generate potential antibodies for clinical development, we immunized human Ig transgenic mice and developed a panel of CD27 specific human mAbs. Clone 1F5 was identified as a lead based on its high affinity to both human and monkey CD27, enhanced co-stimulation of T cells, and ADCC of CD27-expressing lymphoblastic cell lines. Using SCID mice challenged with CD27-expressing human lymphoid cell lines, we demonstrated that 1F5 mediates conventional antibody effector function. Compared to human IgG1 isotype control (huIgG1), 1F5 at doses ranging 33 μg – 500 μg (x 6) significantly delayed the growth of Burkitt's lymphoma Raji even when administration was initiated 1 week after tumor inoculation. Similar anti-tumor activity was observed against other CD27-expressing tumor lines including, Daudi and T-originated acute lymphoblastic leukemia CCRF-CEM. In order to investigate 1F5 in vivo agonistic activities and T cell-mediated tumor eradication, a human CD27 transgenic mouse model (hCD27-Tg) was generated and backcrossed onto C57BL/6 and BALB/c backgrounds. The expression profile and regulation of the human CD27 transgene driven by its own promoter were similar to that observed with endogenous mouse CD27. In addition to enhancing T cell responses when combined with vaccination, 1F5 treatment was highly effective against syngeneic mouse tumors including lymphoma BCL1 (BALB/c) and thymoma EL4-derived E.G7 (C57BL/6). For the BCL1 model, various dose levels of 1F5 mAb were delivered to mice intraperitoneally on days 3, 5, 7, 9 and 11 after i.v. administration of 107 BCL1 cells to huCD27 Tg and control animals. Controls including hCD27-Tg mice treated with saline or isotype control, or WT mice treated with 1F5 all performed consistently, leading to 50% survival approximately 23 days after tumor challenge. Treatment of mice with mAb, 1F5 substantially improved the 50% survival in a dose dependent fashion to >70 days post tumor challenge at the higher dose levels. Based on the promising efficacy data with anti-CD27 mAb 1F5 in immunocompromised and immunocompetent lymphoma models, a clinical grade product, referred to as CDX-1127 was manufactured and tested for safety. To assess the potential for 1F5 to mediate lymphocyte activation, we investigated its ability to induce proliferation and cytokine release from human PBMC or purified T cell cultures. Consistent with the known biology of CD27 we demonstrated the 1F5 mAb does not lead to direct activation of lymphocytes in the absence of additional signals. However, combining 1F5 with suboptimal levels of T cell receptor stimulation using anti-CD3 mAb (OKT3) was shown to enhance proliferation of human T cells. Two studies were performed using cynomolgus macaques. There were no CDX-1127 related mortalities or changes noted in the clinical condition, food appetence, body weights and body temperature, ophthalmic, electrocardiographic and clinical pathology assessments, organ weights and bone marrow assessments. In addition, there were no major differences in the percentage of lymphocyte populations between control and CDX-1127 treated animals at the end of the study demonstrating that the antibody did not significantly deplete normal CD27-expresssing cells. Based on the pre-clinical studies we are planning a Phase 1 clinical trial of CDX-1127 in patients with hematological malignancies and selected solid tumors. The trial is designed with separate arms to independently assess the safety and activity of CDX-1127 in hematologic malignancies, in which the antibody may act through multiple mechanisms, and in solid tumors where it would be fully dependent on indirect immune mechanisms. Disclosures: He: Celldex Therapeutics, Inc.: Employment. Thomas:Celldex Therapeutics, Inc.: Employment. Weidlick:Celldex Therapeutics, Inc.: Employment. Vitale:Celldex Therapeutics, Inc.: Employment. O'Neill:Celldex Therapeutics, Inc.: Employment. Prostak:Celldex Therapeutics, Inc.: Employment. Sundarapandiyan:Celldex Therapeutics, Inc.: Employment. Marsh:Celldex Therapeutics, Inc.: Employment. Yellin:Celldex Therapeutics, Inc.: Employment. Davis:Celldex Therapeutics, Inc.: Employment. Keler:Celldex Therapeutics, Inc.: Employment.

CD27 is a member of TNFR superfamily. It constitutively expresses on the majority of T cell and a subset of NK cells, playing key roles in T cell activation and survival and in NK cell proliferation and cytotoxicity upon interaction with ligand CD70. Some antibodies to mouse CD27 have been reported that display agonistic and anti-tumor activities while other mAbs had less anti-tumor activity and were depleting. We hypothesized that differences in these antibodies may be due to Fc receptor engagement, as has recently been shown for the adjuvant and anti-tumor activities of agonistic mouse CD40 mAbs, which is also member of TNFR superfamily. We have developed and previously described a human anti-human CD27 antibody (1F5) and a human CD27 transgenic mouse model (hCD27-Tg) to explore the therapeutic potential of targeting CD27. In this study, we examined the effect of modifying the constant regions of the 1F5 mAb on its ability to enhance antigen specific T cell responses. With the original 1F5 hIgG1 as template, a panel of 1F5 variants was made including 1F5 mIgG1, 1F5 mIgG2a, 1F5 mIgG1D265A and 1F5 hIgG1N297S using molecular cloning techniques. All of the variants retained equal binding to hCD27 as shown by ELISA and flow cytometry studies. In addition, Biacore analysis confirmed the expected pattern of binding to human and mouse FcαRs. Co-injection of 1F5 or its variants with ovalbumin enhanced antigen-specific CD8 T cell response to different extents, as detected by SIINFEKL-specific IFNα-ELISPOT and ICS. The 1F5 mIgG1 induced the highest number of IFNα-producing CD8+ cells, whereas 1F5 mIgG2a was very weak at enhancing the CD8 T cell response. The hIgG1 version of 1F5 was intermediate in activity. Introduction of the D265A mutation that disrupts FcαRs binding into the mIgG1 eliminated the co-stimulatory function of 1F5. Similarly, the 1F5 hIgG1N297S also showed reduced activity compared to the original 1F5 hIgG1. The isotype-specific effects on our anti-hCD27 mAb are surprisingly consistent with the findings described for the agonistic anti-mCD40 mAbs, and imply that engagement of the inhibitory Fcα receptors (FcαRIIb) is driving the co-stimulatory activity in this model. Interestingly, the 1F5 hIgG1 triggered a significant T cell response, despite the lack of FcαRIIb binding by Biacore analysis. The effect of these variants on anti-tumor activity in hCD27 transgenic mice is currently being investigated. The 1F5 hIgG1 mAb (CDX-1127) is currently undergoing clinical evaluation in a phase 1 trial of patients with advanced cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3519. doi:1538-7445.AM2012-3519

The most recent Ebola outbreak in West Africa resulted in over 28,000 suspected cases of infection and over 11,000 deaths. As no specific immune correlate has been associated with protection against Ebola to date, the development of a vaccine that generates robust humoral and cellular immune responses may be the best approach to achieve full protection. INO-4201 is a plasmid-based prophylactic vaccine targeting Zaire Ebola glycoprotein (GP), designed to prevent Ebola infection. INO-4201 encodes a consensus antigen that encompasses genetic variability from previous outbreak strains to broaden immune coverage for divergent Ebola virus variants. Intradermal (ID) administration of a 2 or 3-dose regimen of INO-4201 followed by in vivo electroporation with the CELLECTRA® device was well tolerated in 140 healthy volunteers with no related Grade 3 or Grade 4 SAEs reported. INO-4201 induced robust Ebola GP-specific antibody and T cell responses in the healthy volunteers. The majority of patients seroconverted, as gauged by binding ELISA after only 2 doses of INO-4201. EBOV GP specific T cell response were assessed by Interferon gamma (IFNγ) ELISpot revealing a mean peak response magnitude of 295 SFU per 106 PBMCs. Intracellular cytokine staining indicated that immunization with INO-4201 drove statistically significant increases in the production of IFNγ or Tumor Necrosis Factor alpha in both the CD8+ T cell compartment (p=0.001) and CD4+ T cell compartment (p=0.004). ID administration of INO-4201 using the CELLECTRA® device was well tolerated and immunogenic as assessed by both humoral and cellular EBOV GP-specific immunoassays supporting INO-4201 as a strong candidate for further clinical development of a prophylactic Ebola vaccine.