Characterization of 7A5: A Human CD137 (4-1BB) Receptor Binding Monoclonal Antibody with Differential Agonist Properties That Promotes Antitumor Immunity.

The CD137 receptor plays a key role in mediating immune response by promoting T cell proliferation, survival, and memory. Effective agonism of CD137 has the potential to reinvigorate potent antitumor immunity either alone or in combination with other immune-checkpoint therapies. In this study, we describe the discovery and characterization of a unique CD137 agonist, 7A5, a fully human IgG1 Fc effector-null monoclonal antibody. The biological properties of 7A5 were investigated through in vitro and in vivo studies. 7A5 binds CD137, and the binding epitope overlaps with the CD137L binding site based on structure. 7A5 engages CD137 receptor and activates NF-κB cell signaling independent of cross-linking or Fc effector function. In addition, T cell activation measured by cytokine IFNγ production is induced by 7A5 in peripheral blood mononuclear cell costimulation assay. Human tumor xenograft mouse models reconstituted with human immune cells were used to determine antitumor activity in vivo. Monotherapy with 7A5 inhibits tumor growth, and this activity is enhanced in combination with a PD-L1 antagonist antibody. Furthermore, the intratumoral immune gene expression signature in response to 7A5 is highly suggestive of enhanced T cell infiltration and activation. Taken together, these results demonstrate 7A5 is a differentiated CD137 agonist antibody with biological properties that warrant its further development as a cancer immunotherapy. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/4/988/F1.large.jpg.

Bispecific Targeting of PD-1 and PD-L1 Enhances T-cell Activation and Antitumor Immunity.

The programmed cell death protein 1 receptor (PD-1) and programmed death ligand 1 (PD-L1) coinhibitory pathway suppresses T-cell-mediated immunity. We hypothesized that cotargeting of PD-1 and PD-L1 with a bispecific antibody molecule could provide an alternative therapeutic approach, with enhanced antitumor activity, compared with monospecific PD-1 and PD-L1 antibodies. Here, we describe LY3434172, a bispecific IgG1 mAb with ablated Fc immune effector function that targets both human PD-1 and PD-L1. LY3434172 fully inhibited the major inhibitory receptor-ligand interactions in the PD-1 pathway. LY3434172 enhanced functional activation of T cells in vitro compared with the parent anti-PD-1 and anti-PD-L1 antibody combination or respective monotherapies. In mouse tumor models reconstituted with human immune cells, LY3434172 therapy induced dramatic and potent antitumor activity compared with each parent antibody or their combination. Collectively, these results demonstrated the enhanced immunomodulatory (immune blockade) properties of LY3434172, which improved antitumor immune response in preclinical studies, thus supporting its evaluation as a novel bispecific cancer immunotherapy.

Discovery and preclinical characterization of the antagonist anti-PD-L1 monoclonal antibody LY3300054.

BACKGROUND: Modulation of the PD-1/PD-L1 axis through antagonist antibodies that block either receptor or ligand has been shown to reinvigorate the function of tumor-specific T cells and unleash potent anti-tumor immunity, leading to durable objective responses in a subset of patients across multiple tumor types. RESULTS: Here we describe the discovery and preclinical characterization of LY3300054, a fully human IgG1λ monoclonal antibody that binds to human PD-L1 with high affinity and inhibits interactions of PD-L1 with its two cognate receptors PD-1 and CD80. The functional activity of LY3300054 on primary human T cells is evaluated using a series of in vitro T cell functional assays and in vivo models using human-immune reconstituted mice. LY3300054 is shown to induce primary T cell activation in vitro, increase T cell activation in combination with anti-CTLA4 antibody, and to potently enhance anti-tumor alloreactivity in several xenograft mouse tumor models with reconstituted human immune cells. High-content molecular analysis of tumor and peripheral tissues from animals treated with LY3300054 reveals distinct adaptive immune activation signatures, and also previously not described modulation of innate immune pathways. CONCLUSIONS: LY3300054 is currently being evaluated in phase I clinical trials for oncology indications.

Correction to: Discovery and preclinical characterization of the antagonist anti-PD-L1 monoclonal antibody LY3300054.

Unfortunately, after publication of this article [1], it was noticed that corrections to the legends of Figs. 1 and 2 were not correctly incorporated. The correct legends can be seen below.

Spiny mice (Acomys cahirinus) do not respond to thymus-independent type 2 antigens.

Analysis of the immune system of spiny mice (Acomys cahirinus) has been limited. Originally grouped with Mus, Acomys has recently been placed closer to Meriones (gerbils). This study compared immunity in Acomys, Mus, and Meriones. Lymphocytes from all rodents examined proliferated in response to mitogen and superantigen stimulation. Only Mus T cells responded to anti-CD3 stimulation. Acomys, like Meriones, and Mus that express xid, did not respond to thymus-independent type 2 antigens. Flow cytometric analyses revealed that T cell-specific MAbs did not bind Acomys or Meriones lymphocytes. The B cell-specific anti-CD45R (B220) MAb detected all rodent B cells and revealed the absence of a CD45R(lo) subset in the peritoneal cavity of Acomys and Meriones. Bone marrow from Acomys and Meriones failed to reconstitute B cell function in SCID mice. Thus, in terms of immunity, Acomys appears to be more similar to Meriones than Mus.

Nonlymphoid peritoneal cells suppress the T cell response to Mls.

Comparative analyses of the ability of lymphoid tissue to present the minor lymphocyte stimulatory (Mls) superantigen Mls-1a in vitro revealed that all tissues containing mature B cells, except peritoneal cavity (PerC) cells, induced Mls-1a-specific T cell activation. Irradiation and mitomycin C treatment, addition of IL-2 and IL-12, and neutralization of IL-10 and TGF-beta did not restore Mls-1a antigen presentation by PerC cells. Co-culture studies revealed that PerC cells actively suppress the T cell response to Mls-1a. PerC cells from severe-combined immune-defective (SCID) mice also suppressed this response indicating that nonlymphoid cells mediate this effect. These results suggest that in addition to antigen processing and presentation, resident peritoneal cavity cells may temper lymphocyte activation.

Removal of a C-terminal serine residue proximal to the inter-chain disulfide bond of a human IgG1 lambda light chain mediates enhanced antibody stability and antibody dependent cell-mediated cytotoxicity.

Optimization of biophysical properties is a critical success factor for the developability of monoclonal antibodies with potential therapeutic applications. The inter-domain disulfide bond between light chain (Lc) and heavy chain (Hc) in human IgG1 lends structural support for antibody scaffold stability, optimal antigen binding, and normal Fc function. Recently, human IgG1λ has been suggested to exhibit significantly greater susceptibility to reduction of the inter Lc-Hc disulfide bond relative to the same disulfide bond in human IgG1κ. To understand the molecular basis for this observed difference in stability, the sequence and structure of human IgG1λ and human IgG1κ were compared. Based on this Lc comparison, three single mutations were made in the λ Lc proximal to the cysteine residue, which forms a disulfide bond with the Hc. We determined that deletion of S214 (dS) improved resistance of the association between Lc and Hc to thermal stress. In addition, deletion of this terminal serine from the Lc of IgG1λ provided further benefit, including an increase in stability at elevated pH, increased yield from transient transfection, and improved in vitro antibody dependent cell-mediated cytotoxicity (ADCC). These observations support the conclusion that the presence of the terminal serine of the λ Lc creates a weaker inter-chain disulfide bond between the Lc and Hc, leading to slightly reduced stability and a potential compromise in IgG1λ function. Our data from a human IgG1λ provide a basis for further investigation of the effects of deleting terminal serine from λLc on the stability and function of other human IgG1λ antibodies.

Pleiotropic stromal effects of vascular endothelial growth factor receptor 2 antibody therapy in renal cell carcinoma models.

The benefits of inhibiting vascular endothelial growth factor (VEGF) signaling in cancer patients are predominantly attributed to effects on tumor endothelial cells. Targeting non-endothelial stromal cells to further impact tumor cell growth and survival is being pursued through the inhibition of additional growth factor pathways important for the survival and/or proliferation of these cells. However, recent data suggest that VEGF receptor (VEGFR)-specific inhibitors may target lymphatic vessels and pericytes in addition to blood vessels. Here, in fact, we demonstrate that DC101 (40 mg/kg, thrice a week), an antibody specific to murine VEGFR2, significantly reduces all three of these stromal components in subcutaneous (SKRC-29) and orthotopic (786-O-LP) models of renal cell carcinoma (RCC) established in nu/nu athymic mice. Sunitinib (40 mg/kg, once daily), a receptor tyrosine kinase inhibitor of VEGFR2 and other growth factor receptors, also caused significant loss of tumor blood vessels in RCC models but had weaker effects than DC101 on pericytes and lymphatic vessels. In combination, sunitinib did not significantly add to the effects of DC101 on tumor blood vessels, lymphatic vessels, or pericytes. Nevertheless, sunitinib increased the effect of DC101 on tumor burden in the SKRC-29 model, perhaps related to its broader specificity. Our data have important implications for combination therapy design, supporting the conclusion that targeting VEGFR2 alone in RCC has the potential to have pleiotropic effects on tumor stroma.