Exciting progress in the field of cancer immunotherapy has renewed the urgency of the need for basic studies of immunoregulation in both adaptive cell lineages and innate cell lineages. Here we found a central role for major histocompatibility complex (MHC) class I in controlling the phagocytic function of macrophages. Our results demonstrated that expression of the common MHC class I component β2-microglobulin (β2M) by cancer cells directly protected them from phagocytosis. We further showed that this protection was mediated by the inhibitory receptor LILRB1, whose expression was upregulated on the surface of macrophages, including tumor-associated macrophages. Disruption of either MHC class I or LILRB1 potentiated phagocytosis of tumor cells both in vitro and in vivo, which defines the MHC class I–LILRB1 signaling axis as an important regulator of the effector function of innate immune cells, a potential biomarker for therapeutic response to agents directed against the signal-regulatory protein CD47 and a potential target of anti-cancer immunotherapy.

Natural Killer (NK) cells play an important role in the early immune response to cancer. The NKp44 activating receptor is the only Natural Cytotoxicity Receptor that is expressed exclusively by primate NK cells; yet, its cellular ligands remain largely unknown. Proliferating Cell Nuclear Antigen (PCNA) is overexpressed in cancer cells. We show that the NKp44 receptor recognizes PCNA. Their interaction inhibits NK cell function through the NKp44-Immunoreceptor Tyrosine-based Inhibitory Motif (ITIM). The physical interaction of NKp44 and PCNA is enabled by recruitment of target cell PCNA to the NK immunological synapse. We demonstrate that PCNA promotes cancer survival by immune evasion through inhibition of NKp44-mediated NK cell attack.

Natural Killer (NK) cells recognize and destroy tumors and virus-infected cells in an antibody-independent manner. The regulation of NK cells is mediated by activating and inhibiting receptors on the NK cell surface. One important family of activating receptors is the natural cytotoxicity receptors (NCRs) which include NKp30, NKp44 and NKp46. The NCRs initiate tumor targeting by recognition of heparan sulfate on cancer cells. This study aims to elucidate heparan sulfate structural motifs that are important for NCR binding. Microarray and surface plasmon resonance experiments with a small library of heparan sulfate/heparin oligosaccharides helped to clarify the binding preferences of the three NCRs. We demonstrate that the NCRs interact with highly charged HS/heparin structures, but differ in preferred modification patterns and chain lengths. The affinity of NKp30 and NKp44 for synthetic HS/heparin is approximately one order of magnitude higher than the affinity of NKp46. We further show the relevance of synthetic HS/heparin for the binding of NCRs to tumor cells and for NCR-mediated activation of natural killer cells. In conclusion, NCRs recognize different microdomains on heparan sulfate with different affinities.

Dengue virus (DV) and West Nile virus (WNV) have become a global concern due to their widespread distribution and their ability to cause a variety of human diseases. Antiviral immune defenses involve NK cells. In the present study, we investigated the interaction between NK cells and these two flaviviruses. We show that the NK-activating receptor NKp44 is involved in virally mediated NK activation through direct interaction with the flavivirus envelope protein. Recombinant NKp44 directly binds to purified DV and WNV envelope proteins and specifically to domain III of WNV envelope protein; it also binds to WNV virus-like particles. These WNV-virus-like particles and WNV-domain III of WNV envelope protein directly bind NK cells expressing high levels of NKp44. Functionally, interaction of NK cells with infective and inactivated WNV results in NKp44-mediated NK degranulation. Finally, WNV infection of cells results in increased binding of rNKp44 that is specifically inhibited by anti-WNV serum. WNV-infected target cells induce IFN-γ secretion and augmented lysis by NKp44-expressing primary NK cells that are blocked by anti-NKp44 Abs. Our findings show that triggering of NK cells by flavivirus is mediated by interaction of NKp44 with the flavivirus envelope protein.

Summary Hematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are hematopoietic stem cells (HSCs), which are multipotent, self-renewing and generate the entire repertoire of blood and immune cells throughout an animal’s life 1 . While there are comprehensive studies on vertebrate HSC self-renewal, differentiation, physiological regulation and niche occupation, relatively little is known about their evolutionary origin and their niches. Here we study the hematopoietic system of Botryllus schlosseri , a colonial tunicate that has vasculature, circulating blood cells, and interesting stem cell biology and immunity characteristics 2 – 8 . Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other 3 , 4 , 7 . Using flow-cytometry, whole-transcriptome sequencing of defined cell populations and diverse functional assays, we identified HSCs, progenitors, immune-effector cells, and an HSC niche, and demonstrated that self-recognition inhibits allospecific cytotoxic reactions. Our study reveals that HSC and myeloid lineage immune cells emerged in a common ancestor of tunicates and vertebrates, and these results also suggest that hematopoietic bone marrow and the B. schlosseri endostyle niche evolved from a common origin.

SUMMARY Colonial tunicates are the only chordate that possess two distinct developmental pathways to produce an adult body: either sexually through embryogenesis or asexually through a stem cell-mediated renewal termed blastogenesis. Using the colonial tunicate Botryllus schlosseri , we combine transcriptomics and microscopy to build an atlas of the molecular and morphological signatures at each developmental stage for both pathways. The general molecular profiles of these processes are largely distinct. However, the relative timing of organogenesis and ordering of tissue-specific gene expression are conserved. By comparing the developmental pathways of B. schlosseri with other chordates, we identify hundreds of putative transcription factors with conserved temporal expression. Our findings demonstrate that convergent morphology need not imply convergent molecular mechanisms but that it showcases the importance that tissue-specific stem cells and transcription factors play in producing the same mature body through different pathways.

KIR2DL4 (CD158d) is a distinct member of the killer cell Ig-like receptor (KIR) family in human NK cells that can induce cytokine production and cytolytic activity in resting NK cells. Soluble HLA-G, normally expressed only by fetal-derived trophoblast cells, was reported to be a ligand for KIR2DL4; however, KIR2DL4 expression is not restricted to the placenta and can be found in CD56high subset of peripheral blood NK cells. We demonstrated that KIR2DL4 can interact with alternative ligand(s), expressed by cells of epithelial or fibroblast origin. A genome-wide high-throughput siRNA screen revealed that KIR2DL4 recognition of cells surface ligand(s) is directly regulated by heparan sulfate (HS) glucosamine 3-O-sulfotransferase 3B1 (HS3ST3B1). KIR2DL4 was found to directly interact with HS/heparin, and the D0-domain of KIR2DL4 was essential for this interaction. Accordingly, exogenous HS/heparin can regulate cytokine production by KIR2DL4-expressing NK cells and HEK293T cells (HEK293T-2DL4) and induces differential localization of KIR2DL4 to rab5+ and rab7+ endosomes, thus leading to down-regulation of cytokine production and degradation of the receptor. Furthermore, we showed that intimate interaction of syndecan-4 (SDC4) HS Proteo-Glycan (HSPG) and KIR2DL4 directly affects receptor endocytosis and membrane trafficking.

Trastuzumab, a targeted anti-human epidermal-growth-factor receptor-2 (HER2) monoclonal antibody, represents a mainstay in the treatment of HER2-positive (HER2+) breast cancer. Although trastuzumab treatment is highly efficacious for early-stage HER2+ breast cancer, the majority of advanced-stage HER2+ breast cancer patients who initially respond to trastuzumab acquire resistance to treatment and relapse, despite persistence of HER2 gene amplification/overexpression. Here, we sought to leverage HER2 overexpression to engage antibody-dependent cellular phagocytosis (ADCP) through a combination of trastuzumab and anti-CD47 macrophage checkpoint immunotherapy. We have previously shown that blockade of CD47, a surface protein expressed by many malignancies (including HER2+ breast cancer), is an effective anticancer therapy. CD47 functions as a “don’t eat me” signal through its interaction with signal regulatory protein-α (SIRPα) on macrophages to inhibit phagocytosis. Hu5F9-G4 (magrolimab), a humanized monoclonal antibody against CD47, blocks CD47’s “don’t eat me” signal, thereby facilitating macrophage-mediated phagocytosis. Preclinical studies have shown that combining Hu5F9-G4 with tumor-targeting antibodies, such as rituximab, further enhances Hu5F9-G4’s anticancer effects via ADCP. Clinical trials have additionally demonstrated that Hu5F9-G4, in combination with rituximab, produced objective responses in patients whose diffuse large B cell lymphomas had developed resistance to rituximab and chemotherapy. These studies led us to hypothesize that combining Hu5F9-G4 with trastuzumab would produce an anticancer effect in antibody-dependent cellular cytotoxicity (ADCC)-tolerant HER2+ breast cancer. This combination significantly suppressed the growth of ADCC-tolerant HER2+ breast cancers via Fc-dependent ADCP. Our study demonstrates that combining trastuzumab and Hu5F9-G4 represents a potential new treatment option for HER2+ breast cancer patients, even for patients whose tumors have progressed after trastuzumab.