Elotuzumab, a recently approved antibody for the treatment of multiple myeloma, has been shown to stimulate Fcγ receptor (FcγR)-mediated antibody-dependent cellular cytotoxicity by natural killer (NK) cells toward myeloma cells. The modulatory effects of elotuzumab on other effector cells in the tumor microenvironment, however, has not been fully explored. Antibody-dependent cellular phagocytosis (ADCP) is a mechanism by which macrophages contribute to antitumor potency of monoclonal antibodies. Herein, we studied the NK cell independent effect of elotuzumab on tumor-associated macrophages using a xenograft tumor model deficient in NK and adaptive immune cells. We demonstrate significant antitumor efficacy of single-agent elotuzumab in immunocompromised xenograft models of multiple myeloma, which is in part mediated by Fc–FcγR interaction of elotuzumab with macrophages. Elotuzumab is shown in this study to induce phenotypic activation of macrophages in vivo and mediates ADCP of myeloma cells though a FcγR-dependent manner in vitro. Together, these findings propose a novel immune-mediated mechanism by which elotuzumab exerts anti-myeloma activity and helps to provide rationale for combination therapies that can enhance macrophage activity. Mol Cancer Ther; 17(7); 1454–63. ©2018 AACR.

Key Points: The combination of elotuzumab and an anti–PD-1 antibody leads to enhanced antitumor efficacy in mouse models. Enhanced antitumor activity is likely due to the promotion of tumor-infiltrating NK and T-cell activity.

Elotuzumab (Elo) is an IgG₁ monoclonal antibody targeting SLAMF7 (CS1, CRACC, and CD319), which is highly expressed on multiple myeloma (MM) cells, natural killer (NK) cells, and subsets of other leukocytes. By engaging with FcγRIIIA (CD16), Elo promotes potent NK cell–mediated antibody-dependent cellular cytotoxicity (ADCC) and macrophage-mediated antibody-dependent cellular phagocytosis (ADCP) toward SLAMF7⁺ MM tumor cells. Relapsed/refractory MM patients treated with the combination of Elo, lenalidomide, and dexamethasone have improved progression-free survival. We previously showed that Elo enhances NK cell activity via a costimulation mechanism, independent of CD16 binding. Here, we further studied the effect of Elo on cytotoxicity of CD16-negative NK-92 cells. Elo, but not other SLAMF7 antibodies, uniquely enhanced cytotoxicity mediated by CD16-negative NK-92 cells toward SLAMF7⁺ target cells. Furthermore, this CD16-independent enhancement of cytotoxicity required expression of SLAMF7 containing the full cytoplasmic domain in the NK cells, implicating costimulatory signaling. The CD16-independent costimulation by Elo was associated with increased expression of NKG2D, ICAM-1, and activated LFA-1 on NK cells, and enhanced cytotoxicity was partially reduced by NKG2D blocking antibodies. In addition, an Fc mutant form of Elo that cannot bind CD16 promoted cytotoxicity of SLAMF7⁺ target cells by NK cells from most healthy donors, especially if previously cultured in IL2. We conclude that in addition to promoting NK cell–mediated ADCC (CD16-dependent) responses, Elo promoted SLAMF7–SLAMF7 interactions in a CD16-independent manner to enhance NK cytotoxicity toward MM cells.

Viral infections are a natural part of our existence. They can affect us in many ways that are the result of the interaction between the viral pathogen and our immune system. Most times, the resulting immune response is beneficial for the host. The pathogen is cleared, thus protecting our vital organs with no other consequences. Conversely, the reaction of our immune system against the pathogen can cause organ damage (immunopathology) or lead to autoimmune disease. To date, there are several mechanisms for virus-induced autoimmune disease, including molecular mimicry and bystander activation, in support of the “fertile field” hypothesis (terms defined in our review). In contrast, viral infections have been associated with protection from autoimmunity through mechanisms that include Treg invigoration and immune deviation, in support of the “hygiene hypothesis”, also defined here. Infection with lymphocytic choriomeningitis virus (LCMV) is one of the prototypes showing that the interaction of our immune system with viruses can either accelerate or prevent autoimmunity. Studies using mouse models of LCMV have helped conceive and establish several concepts that we now know and use to explain how viruses can lead to autoimmune activation or induce tolerance. Some of the most important mechanisms established during the course of LCMV infection are described in this short review.

Background: The anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) monoclonal antibody, ipilimumab, has shown clinical benefit across multiple tumor types, both as monotherapy and in combination with nivolumab or chemotherapy. However, not all tumors respond, and peripheral effects can lead to immune-related adverse events. We characterized three novel anti–CTLA-4 antibodies: peptide-masked (PROBODY® conditionally activatable therapeutic [PB]), nonfucosylated (NF), and combined NF-PB (BMS-986288). Methods: We evaluated the preclinical characteristics, including the pharmacodynamics, tolerability, antitumor activity and efficacy, and peripheral immune responses, of these novel anti–CTLA-4 antibodies using in vitro systems, animal models, and human data. This includes data in preclinical mouse models of colorectal cancer as well as non-small cell lung cancer. Results: NF demonstrated greater T-cell priming and antitumor activity than both ipilimumab and the unmasked PB antibody in cell-based assays and mouse models. Whereas the intact PB antibody showed minimal CTLA-4 binding and peripheral immune activation, unmasking restored its functional activity to levels comparable with those of ipilimumab. Unmasked anti–CTLA-4 NF-PB retained the effectiveness of anti–CTLA-4 NF, and both molecules demonstrated more profound antitumor activity, increased effector memory T-cell response, and prolonged survival in mouse models compared with ipilimumab. Anti–CTLA-4 NF-PB demonstrated reduced peripheral immune responses than anti–CTLA-4 NF or ipilimumab in non-human primates and patients with solid tumors. Conclusion: Anti–CTLA-4 NF-PB has enhanced antitumor activity, efficacy, and reduced peripheral activity in preclinical models, and has the potential to provide therapeutic benefit in solid tumors.