The Neutrophil:The Underdog That Packs a Punch in the Fight against Cancer

The advent of immunotherapy has had a major impact on the outcome and overall survival in many types of cancer. Current immunotherapeutic strategies typically aim to (re)activate anticancer T cell immunity, although the targeting of macrophage-mediated anticancer innate immunity has also emerged in recent years. Neutrophils, although comprising approximate to 60% of all white blood cells in the circulation, are still largely overlooked in this respect. Nevertheless, neutrophils have evident anticancer activity and can induce phagocytosis, trogocytosis, as well as the direct cytotoxic elimination of cancer cells. Furthermore, therapeutic tumor-targeting monoclonal antibodies trigger anticancer immune responses through all innate Fc-receptor expressing cells, including neutrophils. Indeed, the depletion of neutrophils strongly reduced the efficacy of monoclonal antibody treatment and increased tumor progression in various preclinical studies. In addition, the infusion of neutrophils in murine cancer models reduced tumor progression. However, evidence on the anticancer effects of neutrophils is fragmentary and mostly obtained in in vitro assays or murine models with reports on anticancer neutrophil activity in humans lagging behind. In this review, we aim to give an overview of the available knowledge of anticancer activity by neutrophils. Furthermore, we will describe strategies being explored for the therapeutic activation of anticancer neutrophil activity

Inhibition of Autophagy Does Not Re-Sensitize Acute Myeloid Leukemia Cells Resistant to Cytarabine

Elevated activation of the autophagy pathway is currently thought to be one of the survival mechanisms allowing therapy-resistant cancer cells to escape elimination, including for cytarabine (AraC)-resistant acute myeloid leukemia (AML) patients. Consequently, the use of autophagy inhibitors such as chloroquine (CQ) is being explored for the re-sensitization of AraC-resistant cells. In our study, no difference in the activity of the autophagy pathway was detected when comparing AraC-Res AML cell lines to parental AraC-sensitive AML cell lines. Furthermore, treatment with autophagy inhibitors CQ, 3-Methyladenine (3-MA), and bafilomycin A1 (BafA1) did not re-sensitize AraC-Res AML cell lines to AraC treatment. However, in parental AraC-sensitive AML cells, treatment with AraC did activate autophagy and, correspondingly, combination of AraC with autophagy inhibitors strongly reduced cell viability. Notably, the combination of these drugs also yielded the highest level of cell death in a panel of patient-derived AML samples even though not being additive. Furthermore, there was no difference in the cytotoxic effect of autophagy inhibition during AraC treatment in matched de novo and relapse samples with differential sensitivity to AraC. Thus, inhibition of autophagy may improve AraC efficacy in AML patients, but does not seem warranted for the treatment of AML patients that have relapsed with AraC-resistant disease

EGFR-selective activation of CD27 co-stimulatory signaling by a bispecific antibody enhances anti-tumor activity of T cells

A higher density of tumor infiltrating lymphocytes (TILs) in the tumor microenvironment, particularly cytotoxic CD8 + T cells, is associated with improved clinical outcome in various cancers. However, local inhibitory factors can suppress T cell activity and hinder anti-tumor immunity. Notably, TILs from various cancer types express the co-stimulatory Tumor Necrosis Factor receptor CD27, making it a potential target for co-stimulation and re-activation of tumor-infiltrated and tumor-reactive T cells. Anti-cancer therapeutics based on exploiting CD27-mediated T cell co-stimulation have proven safe, but clinical responses remain limited. This is likely because current monoclonal antibodies fail to effectively activate CD27 signaling, as this receptor requires higher-order receptor cross-linking. Here, we report on a bispecific antibody, CD27xEGFR, that targets both CD27 and the tumor antigen, epidermal growth factor receptor (EGFR). By targeting EGFR, which is commonly expressed on carcinomas, CD27xEGFR induced cancer cell-localized crosslinking and activation of CD27. The design of CD27xEGFR includes an Fc-silent domain, which is designed to minimize potential toxicity by reducing Fc gamma receptor-mediated binding and activation of immune cells. CD27xEGFR bound to both of its targets simultaneously and triggered EGFR-restricted co-stimulation of T cells as measured by T cell proliferation, T cell activation markers, cytotoxicity and IFN-γ release. Further, CD27xEGFR augmented T cell cytotoxicity in a panel of artificial antigen-presenting carcinoma cell line models, leading to Effector-to-Target ratio-dependent elimination of cancer cells. Taken together, we present the in vitro characterization of a novel bispecific antibody that re-activates T cell immunity in EGFR-expressing cancers through targeted co-stimulation of CD27. </p

CD47, a multi-facetted target for cancer immunotherapy

CD47 is a ubiquitously expressed immunoregulatory protein best known for its so-called 'don't eat me' function that prevents phagocytic removal of healthy cells by the immune system. Many types of cancer present high levels of this don't eat me signal on their surface, thereby disrupting anti-cancer immune responses. Based on this observation, CD47 has become a prominent target in the field of cancer immunotherapy. Indeed, pre-clinical studies have shown therapeutic benefit of anti-CD47 antibodies in solid cancers and most notably B-cell malignancies. However, CD47 is also involved in various other important cellular processes, such as angiogenesis, cancer cell death and regulation of T-cell immunity, which can be modulated via interactions with thrombospondin-1. The therapeutic outcome of CD47-targeted immunotherapy therefore relies on the combined effects of all these processes. Here we will review the various physiological functions of CD47 and their implications in cancer biology. Further, we will review ongoing efforts and provide perspectives for exploiting CD47 as an immunotherapeutic target in cancer

Signal regulatory protein beta 2 is a novel positive regulator of innate anticancer immunity

In recent years, the therapeutic (re)activation of innate anticancer immunity has gained prominence, with therapeutic blocking of the interaction of Signal Regulatory Protein (SIRP)-α with its ligand CD47 yielding complete responses in refractory and relapsed B cell lymphoma patients. SIRP-α has as crucial inhibitory role on phagocytes, with e.g., its aberrant activation enabling the escape of cancer cells from immune surveillance. SIRP-α belongs to a family of paired receptors comprised of not only immune-inhibitory, but also putative immune-stimulatory receptors. Here, we report that an as yet uninvestigated SIRP family member, SIRP-beta 2 (SIRP-ß2), is strongly expressed under normal physiological conditions in macrophages and granulocytes at protein level. Endogenous expression of SIRP-ß2 on granulocytes correlated with trogocytosis of cancer cells. Further, ectopic expression of SIRP-ß2 stimulated macrophage adhesion, differentiation and cancer cell phagocytosis as well as potentiated macrophage-mediated activation of T cell Receptor-specific T cell activation. SIRP-ß2 recruited the immune activating adaptor protein DAP12 to positively regulate innate immunity, with the charged lysine 202 of SIRP-ß2 being responsible for interaction with DAP12. Mutation of lysine 202 to leucine lead to a complete loss of the increased adhesion and phagocytosis. In conclusion, SIRP-ß2 is a novel positive regulator of innate anticancer immunity and a potential costimulatory target for innate immunotherapy.</p

Signal regulatory protein beta 2 is a novel positive regulator of innate anticancer immunity

In recent years, the therapeutic (re)activation of innate anticancer immunity has gained prominence, with therapeutic blocking of the interaction of Signal Regulatory Protein (SIRP)-α with its ligand CD47 yielding complete responses in refractory and relapsed B cell lymphoma patients. SIRP-α has as crucial inhibitory role on phagocytes, with e.g., its aberrant activation enabling the escape of cancer cells from immune surveillance. SIRP-α belongs to a family of paired receptors comprised of not only immune-inhibitory, but also putative immune-stimulatory receptors. Here, we report that an as yet uninvestigated SIRP family member, SIRP-beta 2 (SIRP-ß2), is strongly expressed under normal physiological conditions in macrophages and granulocytes at protein level. Endogenous expression of SIRP-ß2 on granulocytes correlated with trogocytosis of cancer cells. Further, ectopic expression of SIRP-ß2 stimulated macrophage adhesion, differentiation and cancer cell phagocytosis as well as potentiated macrophage-mediated activation of T cell Receptor-specific T cell activation. SIRP-ß2 recruited the immune activating adaptor protein DAP12 to positively regulate innate immunity, with the charged lysine 202 of SIRP-ß2 being responsible for interaction with DAP12. Mutation of lysine 202 to leucine lead to a complete loss of the increased adhesion and phagocytosis. In conclusion, SIRP-ß2 is a novel positive regulator of innate anticancer immunity and a potential costimulatory target for innate immunotherapy.</p