BAFF-R, a newly identified TNF receptor that specifically interacts with BAFF

B cell homeostasis has been shown to critically depend on BAFF, the B cell activation factor from the tumor necrosis factor (TNF) family. Although BAFF is already known to bind two receptors, BCMA and TACI, we have identified a third receptor for BAFF that we have termed BAFF-R. BAFF-R binding appears to be highly specific for BAFF, suggesting a unique role for this ligand-receptor interaction. Consistent with this, the BAFF-R locus is disrupted in A/WySnJ mice, which display a B cell phenotype qualitatively similar to that of the BAFF-deficient mice. Thus, BAFF-R appears to be the principal receptor for BAFF-mediated mature B cell survival.

BAFF binds to the tumor necrosis factor receptor-like molecule B cell maturation antigen and is important for maintaining the peripheral B cell population

The tumor necrosis factor (TNF) family member B cell activating factor (BAFF) binds B cells and enhances B cell receptor-triggered proliferation. We find that B cell maturation antigen (BCMA), a predicted member of the TNF receptor family expressed primarily in mature B cells, is a receptor for BAFF. Although BCMA was previously localized to the Golgi apparatus, BCMA was found to be expressed on the surface of transfected cells and tonsillar B cells. A soluble form of BCMA, which inhibited the binding of BAFF to a B cell line, induced a dramatic decrease in the number of peripheral B cells when administered in vivo. Moreover, culturing splenic cells in the presence of BAFF increased survival of a percentage of the B cells. These results are consistent with a role for BAFF in maintaining homeostasis of the B cell population.

Antibody blockade of the Cripto CFC domain suppresses tumor cell growth in vivo

Cripto, a cell surface-associated protein belonging to the EGF-CFC family of growth factor-like molecules, is overexpressed in many human solid tumors, including 70-80% of breast and colon tumors, yet how it promotes cell transformation is unclear. During embryogenesis, Cripto complexes with Alk4 via its unique cysteine-rich CFC domain to facilitate signaling by the TGF-beta ligand Nodal. We report, for the first time to our knowledge, that Cripto can directly bind to another TGF-beta ligand, Activin B, and that Cripto overexpression blocks Activin B growth inhibition of breast cancer cells. This result suggests a novel mechanism for antagonizing Activin signaling that could promote tumorigenesis by deregulating growth homeostasis. We show that an anti-CFC domain antibody, A8.G3.5, both disrupts Cripto-Nodal signaling and reverses Cripto blockade of Activin B-induced growth suppression by blocking Cripto's association with either Alk4 or Activin B. In two xenograft models, testicular and colon cancer, A8.G3.5 inhibited tumor cell growth by up to 70%. Both Nodal and Activin B expression was found in the xenograft tumor, suggesting that either ligand could be promoting tumorigenesis. These data validate that functional blockade of Cripto inhibits tumor growth and highlight antibodies that block Cripto signaling mediated through its CFC domain as an important class of antibodies for further therapeutic development.

Signaling through the lymphotoxin beta receptor induces the death of some adenocarcinoma tumor lines

Surface lymphotoxin (LT) is a heteromeric complex of LT-alpha and LT-beta chains that binds to the LT-beta receptor (LT-beta-R), a member of the tumor necrosis factor (TNF) family of receptors. The biological function of this receptor-ligand system is poorly characterized. Since signaling through other members of this receptor family can induce cell death, e.g., the TNF and Fas receptors, it is important to determine if similar signaling events can be communicated via the LT-beta-R. A soluble form of the surface complex was produced by coexpression of LT-alpha and a converted form of LT-beta wherein the normally type II LT-beta membrane protein was changed to a type I secreted form. Recombinant LT-alpha 1/beta 2 was cytotoxic to the human adenocarcinoma cell lines HT-29, WiDr, MDA-MB-468, and HT-3 when added with the synergizing agent interferon (IFN) gamma. When immobilized on a plastic surface, anti-LT-beta-R monoclonal antibodies (mAbs) induced the death of these cells, demonstrating direct signaling via the LT-beta-R. Anti-LT-beta-R mAbs were also identified that inhibited ligand-induced cell death, whereas others were found to potentiate the activity of the ligand when added in solution. The human WiDr adenocarcinoma line forms solid tumors in immunocompromised mice, and treatment with an anti-LT-beta-R antibody combined with human IFN-gamma arrested tumor growth. The delineation of a biological signaling event mediated by the LT-beta-R opens a window for further studies on its immunological role, and furthermore, activation of the LT-beta-R may have an application in tumor therapy.

Systemic RNAi-mediated Gene Silencing in Nonhuman Primate and Rodent Myeloid Cells

Leukocytes are central regulators of inflammation and the target cells of therapies for key diseases, including autoimmune, cardiovascular, and malignant disorders. Efficient in vivo delivery of small interfering RNA (siRNA) to immune cells could thus enable novel treatment strategies with broad applicability. In this report, we develop systemic delivery methods of siRNA encapsulated in lipid nanoparticles (LNP) for durable and potent in vivo RNA interference (RNAi)-mediated silencing in myeloid cells. This work provides the first demonstration of siRNA-mediated silencing in myeloid cell types of nonhuman primates (NHPs) and establishes the feasibility of targeting multiple gene targets in rodent myeloid cells. The therapeutic potential of these formulations was demonstrated using siRNA targeting tumor necrosis factor-α (TNFα) which induced substantial attenuation of disease progression comparable to a potent antibody treatment in a mouse model of rheumatoid arthritis (RA). In summary, we demonstrate a broadly applicable and therapeutically relevant platform for silencing disease genes in immune cells.

Multivalent nanobodies targeting death receptor 5 elicit superior tumor cell killing through efficient caspase induction

Multiple therapeutic agonists of death receptor 5 (DR5) have been developed and are under clinical evaluation. Although these agonists demonstrate significant anti-tumor activity in preclinical models, the clinical efficacy in human cancer patients has been notably disappointing. One possible explanation might be that the current classes of therapeutic molecules are not sufficiently potent to elicit significant response in patients, particularly for dimeric antibody agonists that require secondary cross-linking via Fcγ receptors expressed on immune cells to achieve optimal clustering of DR5. To overcome this limitation, a novel multivalent Nanobody approach was taken with the goal of generating a significantly more potent DR5 agonist. In the present study, we show that trivalent DR5 targeting Nanobodies mimic the activity of natural ligand, and furthermore, increasing the valency of domains to tetramer and pentamer markedly increased potency of cell killing on tumor cells, with pentamers being more potent than tetramers in vitro. Increased potency was attributed to faster kinetics of death-inducing signaling complex assembly and caspase-8 and caspase-3 activation. In vivo, multivalent Nanobody molecules elicited superior anti-tumor activity compared to a conventional DR5 agonist antibody, including the ability to induce tumor regression in an insensitive patient-derived primary pancreatic tumor model. Furthermore, complete responses to Nanobody treatment were obtained in up to 50% of patient-derived primary pancreatic and colon tumor models, suggesting that multivalent DR5 Nanobodies may represent a significant new therapeutic modality for targeting death receptor signaling.

Comparison of soluble decoy IgG fusion proteins of BAFF-R and BCMA as antagonists for BAFF

BAFF is considered a therapeutic target because dysregulated production of BAFF can induce systemic lupus erythematosus-like phenotype in mice, and elevated levels of BAFF are associated with disease severity in systemic lupus erythematosus and rheumatoid arthritis patients. Fc fusion decoy receptors, BCMA-Fc and BAFF-R-Fc, are therapeutic candidates for blocking BAFF. While studying their interactions with BAFF, we found that BAFF-R-Fc is more effective than BCMA-Fc for blocking BAFF binding to its receptors. We also found that a trimeric BAFF can bind more than one BAFF-R-Fc but only one BCMA-Fc. Moreover, we show that, in contrast to monovalent BAFF-R-Fc, monovalent BCMA does not form stable complexes with BAFF. Differences in their interaction with BAFF predict BAFF-R-Fc would be a better inhibitor. Indeed, we show BAFF-R-Fc is 10-fold more efficacious than BCMA-Fc for blocking BAFF-induced B cell proliferation in vitro and for blocking BAFF-mediated survival of mouse splenic B lymphocytes in vivo.

Systematic mutational mapping of sites on human interferon-beta-1a that are important for receptor binding and functional activity

A systematic mutational analysis of human interferon-beta-1a (IFN-beta) was performed to identify regions on the surface of the molecule that are important for receptor binding and for functional activity. The crystal structure of IFN-beta-1a was used to design a panel of 15 mutant proteins, in each of which a contiguous group of 2-8 surface residues was mutated, in most instances to alanine. The mutants were analyzed for activity in vitro in antiviral and in antiproliferation assays, and for their ability to bind to the type I IFN (ifnar1/ifnar2) receptor on Daudi cells and to a soluble ifnar2 fusion protein (ifnar2-Fc). Abolition of binding to ifnar2-Fc for mutants A2, AB1, AB2, and E established that the ifnar2 binding site on IFN-beta comprises parts of the A helix, the AB loop, and the E helix. Mutations in these areas, which together define a contiguous patch of the IFN-beta surface, also resulted in reduced affinity for binding to the receptor on cells and in reductions in activity of 5-50-fold in functional assays. A second receptor interaction site, concluded to be the ifnar1 binding site, was identified on the opposite face of the molecule. Mutations in this region, which encompasses parts of the B, C, and D helices and the DE loop, resulted in disparate effects on receptor binding and on functional activity. Analysis of antiproliferation activity as a function of the level of receptor occupancy allowed mutational effects on receptor activation to be distinguished from effects on receptor binding. The results suggest that the binding energy from interaction of IFN-beta with ifnar2 serves mainly to stabilize the bound IFN/receptor complex, whereas the binding energy generated by interaction of certain regions of IFN-beta with ifnar1 is not fully expressed in the observed affinity of binding but instead serves to selectively stabilize activated states of the receptor.

Epitope-dependent effect of anti-murine TIM-1 monoclonal antibodies on T cell activity and lung immune responses

The TAPR locus containing the TIM gene family is implicated in the development of atopic inflammation in mouse, and TIM-1 allelic variation has been associated with the incidence of atopy in human patient populations. In this study, we show that manipulation of the TIM-1 pathway influences airway inflammation and pathology. Anti-TIM-1 mAbs recognizing distinct epitopes differentially modulated OVA-induced lung inflammation in the mouse. The epitopes recognized by these Abs were mapped, revealing that mAbs to both the IgV and stalk domains of TIM-1 have therapeutic activity. Unexpectedly, mAbs recognizing unique epitopes spanning exon 4 of the mucin/stalk domains exacerbated immune responses. Using Ag recall response studies, we demonstrate that the TIM-1 pathway acts primarily by modulating the production of T(H)2 cytokines. Furthermore, ex vivo cellular experiments indicate that TIM-1 activity controls CD4(+) T cell activity. These studies validate the genetic hypothesis that the TIM-1 locus is linked to the development of atopic disease and suggest novel therapeutic strategies for targeting asthma and other atopic disorders.

Characterization of antihuman IFNAR-1 monoclonal antibodies: epitope localization and functional analysis

The type I interferon receptor (IFNAR) is composed of two subunits, IFNAR-1 and IFNAR-2, encoding transmembrane polypeptides. IFNAR-2 has a dominant role in ligand binding, but IFNAR-1 contributes to binding affinity and to differential ligand recognition. A panel of five monoclonal antibodies (mAb) to human IFNAR-1 (HuIFNAR-1) was produced and characterized. The reactivity of each mAb toward HuIFNAR-1 on native and transfected cells and in Western blot and ELISA formats was determined. In functional assays, one mAb, EA12, blocked IFN-a2 binding to human cells and interfered with Stat activation and antiviral activity. Epitopes for the mAb were localized to subdomains of the HuIFNAR-1 extracellular domain by differential reactivity of the mAb to a series of human/bovine IFNAR-1 chimeras. The antibody EA12 seems to require native HuIFNAR-1 for reactivity and does not map to a single subdomain, perhaps recognizing an epitope containing noncontiguous sequences in at least two subdomains. In contrast, the epitopes of the non-neutralizing mAb FB2, AA3, and GB8 mapped, respectively, to the first, second, and third subdomains of HuIFNAR-1. The mAb DB2 primarily maps to the fourth subdomain, although its reactivity may be affected by other determinants.

Divalent cations stabilize the alpha 1 beta 1 integrin I domain

Recent structural and functional analyses of alpha integrin subunit I domains implicate a region in cation and ligand binding referred to as the metal ion-dependent adhesion site (MIDAS). Although the molecular interactions between Mn2+ and Mg2+ and the MIDAS region have been defined by crystallographic analyses, the role of cation in I domain function is not well understood. Recombinant alpha 1 beta 1 integrin I domain (alpha1-I domain) binds collagen in a cation-dependent manner. We have generated and characterized a panel of antibodies directed against the alpha1-I domain, and selected one (AJH10) that blocks alpha 1 beta 1 integrin function for further study. The epitope of AJH10 was localized within the loop between the alpha 3 and alpha 4 helices which contributes one of the metal coordination sites of the MIDAS structure. Kinetic analyses of antibody binding to the I domain demonstrate that divalent cation is required to stabilize the epitope. Denaturation experiments demonstrate that cation has a dramatic effect on the stabilization of the I domain structure. Mn2+ shifts the point at which the I domain denatures from 3.4 to 6.3 M urea in the presence of the denaturant, and from 49.5 to 58.6 degrees C following thermal denaturation. The structural stability provided to the alpha1-I domain by divalent cations may contribute to augmented ligand binding that occurs in the presence of these cations.

Mapping of IFN-beta epitopes important for receptor binding and biologic activation: comparison of results achieved using antibody-based methods and alanine substitution mutagenesis

The epitopes important for receptor binding and activation of human interferon-beta1a (IFN-beta1a) were mapped with monoclonal antibodies (mAb), grouped on the basis of their specificity and ability to neutralize biologic activity, and alanine scanning mutagenesis (ASM). The binding properties of nine mAb were defined, using ASM-IFN-beta mutants having alanine substituted at targeted, surface-exposed residues. The results were correlated with the mAb neutralizing potency. Of six mAb that bound either at or adjacent to the IFNAR-2 receptor chain binding site defined by the ASM epitopes, only three had measurable neutralizing activity. Two of these inhibited IFN-beta/IFNAR-2 complex formation, suggesting that steric hindrance of receptor binding constitutes their mechanism of neutralization. However, two mAb that bound to sites remote from the IFNAR-2 binding site on IFN-beta also inhibited IFN-beta/IFNAR-2 complex formation and demonstrated potent neutralizing activity. Thus, neutralizing mAb may employ mechanisms other than steric blockade to inhibit directly the binding of receptor by cytokine, limiting their usefulness as tools to define precise receptor-ligand interaction sites.

Human type I interferon receptor, IFNAR, is a heavily glycosylated 120-130 kD membrane protein

Type I interferons (IFNs) bind and signal through cell surface receptors that share at least one common component. One candidate for such a component is the interferon-alpha receptor (IFNAR). Genetic studies have shown that the IFNAR gene product is required for response to many type I interferons. However, these studies also suggest that the IFNAR protein interacts with an additional receptor component(s) to form functionally complete type I IFN receptors. Although these genetic studies have contributed significantly to understanding the type I IFN receptors. Although these genetic studies have contributed significantly to understanding the type I IFN receptors, little biochemical characterization of IFNAR and its function has been reported. To facilitate biochemical studies of the IFNAR gene product, a monoclonal antibody, GB8, recognizing the extracellular domain of IFNAR was prepared. The epitope for GB8 maps to the second extracellular domain of IFNAR between amino acids 278 and 293. GB8 identifies IFNAR in western blots of cell membranes as a broad band with molecular mass ranging from 100 to 150 kD in membranes from CHO cells overexpressing the human IFNAR gene to 136-150 kD in Daudi cell membranes. Such variations in the mean value and the range of molecular mass between IFNAR in different cell lines suggest differences in glycosylation. The majority of glycosylation is N-linked, although there may also be a small amount O-linked oligosaccharide. Deglycosylation of IFNAR in Daudi cell membranes results in a 70 kD IFNAR species, indicating that nearly half of the apparent molecular mass of Daudi cell IFNAR is contributed by carbohydrate moieties.

Determining the affinity and stoichiometry of interactions between unmodified proteins in solution using Biacore

We describe a general Biacore method for measuring equilibrium binding affinities and stoichiometries for interactions between unmodified proteins and their unmodified ligands free in solution. Mixtures of protein and ligand are preequilibrated at different ratios in solution and then analyzed by Biacore using a sensor chip surface that detects only unbound analyte. Performing the Biacore analysis under mass transport limited conditions allows the concentration of unbound analyte to be determined from the initial velocity of binding. Plots of initial velocity versus the concentration of the varied binding partner are fitted to a quadratic binding equation to give the affinity and stoichiometry of binding. We demonstrate the method using soluble Her2 extracellular domain binding to monovalent, bivalent, and trivalent forms of an anti-Her2 antibody. The affinity we measured agrees with that obtained from conventional Biacore kinetic analysis, and the stoichiometries for the resulting 1:1, 1:2, and 1:3 complexes were confirmed by gel filtration with in-line light scattering. The method is applicable over an affinity range of approximately 100 pM to 1 μM and is particularly useful when there is concern that covalently modifying one or the other binding partner might affect its binding properties or where multivalency might otherwise complicate a quantitative analysis of binding.

Stoichiometry of LTβR Binding to LIGHT

LTbetaR is a member of the TNF receptor family of proteins. It binds to two different cell surface ligands, LIGHT, a homotypic trimer, and LTalpha1beta2, a heterotypic trimer. We have measured the affinities of the dimeric IgG fusion protein, LTbetaRIgG, and monomeric LTbetaR protein binding to both LIGHT and LTalpha1beta2 using surface plasmon resonance and found values of <0.1 and 38 nM for LIGHT and <0.1 and 48 nM for LTalpha1beta2, respectively. We also determined the stoichiometries of binding for both forms of the receptor LTbetaRIgG and LTbetaR binding to LIGHT. The data obtained from several biophysical methods are consistent with receptor polypeptide to trimeric ligand ratios of 2:1. The determined masses of the complexes using SEC-LS corresponded to a single LTbetaRIgG bound to a LIGHT trimer, or two LTbetaR bound per LIGHT. Sedimentation velocity of varied ratios of LTbetaR to a fixed concentration of LIGHT were analyzed by SEDANAL and were successfully fit with a model with two tight binding sites on LIGHT and one poor affinity site. Isothermal calorimetric titration of LIGHT with either LTbetaR or LTbetaRIgG also demonstrated stoichiometries of 1:2 and 1:1, respectively. The binding of LTbetaR to LIGHT was endothermic and, hence, entropy-driven. TNFR p55 (extracellular domain) complexed with the trimeric ligand, TNFbeta, exhibits a 3:1 receptor/ligand stoichiometry. This complex has been used as the prototypical model setting the receptor-ligand complexation paradigm for the entire TNF family. The LTbetaR/LIGHT binding stoichiometry of 2:1 demonstrated here does not fit the paradigm. This has numerous implications for cell biology including signaling requiring only dimerization of LTbetaR rather than trimerization as expected from the structural paradigm.

Enzyme immunoassay using native envelope glycoprotein (gp160) for detection of human immunodeficiency virus type 1 antibodies

An enzyme immunoassay using the purified native gp160 for the detection of human immunodeficiency virus type 1 (HIV-1) antibody was developed. This assay was determined to be highly specific, since (i) 157 serum samples that were confirmed negative by Western blot (immunoblot) (WB) were negative, (ii) 41 serum samples from populations with medical conditions that might cause nonspecific assay reactivity were all negative, and (iii) all 15 serum samples that showed false-positive reactions in one or more commercial HIV-1 screening tests were negative. The assay gave 100% specificity with a randomly selected and unlinked panel of 1,000 serum samples from healthy blood donors. The sensitivity of the assay was assessed by testing 238 samples confirmed as HIV-1 antibody positive by a standardized WB assay. All 238 serum samples (100%) were reactive in the native gp160 assay. In a dilution panel of 14 weakly WB-positive serum samples, 7 samples reacted two-to fivefold more strongly in the gp160 assay than in a virus lysate-based assay; the remaining 7 samples gave comparable reactivities in the two tests. The reactivities of 13 of these 14 serum samples in the gp160 assay were higher than in a commercial enzyme immunoassay that uses a recombinant envelope protein as the antigen. The native gp160 assay was more sensitive to identify seroconversion. In a well-characterized panel of sequential blood samples from a seroconverter, the new assay detected antibodies at least one sample ahead of the other commercial assays tested.

PSGL-1 Blockade Induces Classical Activation of Human Tumor-associated Macrophages

The immune suppressive microenvironment is a major culprit for difficult-to-treat solid cancers. Particularly, inhibitory tumor-associated macrophages (TAM) define the resistant nature of the tumor milieu. To define tumor-enabling mechanisms of TAMs, we analyzed molecular clinical datasets correlating cell surface receptors with the TAM infiltrate. Though P-selectin glycoprotein ligand-1 (PSGL-1) is found on other immune cells and functions as an adhesion molecule, PSGL-1 is highly expressed on TAMs across multiple tumor types. siRNA-mediated knockdown and antibody-mediated inhibition revealed a role for PSGL-1 in maintaining an immune suppressed macrophage state. PSGL-1 knockdown or inhibition enhanced proinflammatory mediator release across assays and donors in vitro. In several syngeneic mouse models, PSGL-1 blockade alone and in combination with PD-1 blockade reduced tumor growth. Using a humanized tumor model, we observed the proinflammatory TAM switch following treatment with an anti-PSGL-1 antibody. In ex vivo patient-derived tumor cultures, a PSGL-1 blocking antibody increased expression of macrophage-derived proinflammatory cytokines, as well as IFNγ, indicative of T-cell activation. Our data demonstrate that PSGL-1 blockade reprograms TAMs, offering a new therapeutic avenue to patients not responding to T-cell immunotherapies, as well as patients with tumors devoid of T cells.

SIGNIFICANCE

This work is a significant and actionable advance, as it offers a novel approach to treating patients with cancer who do not respond to T-cell checkpoint inhibitors, as well as to patients with tumors lacking T-cell infiltration. We expect that this mechanism will be applicable in multiple indications characterized by infiltration of TAMs.

Comparison of the Effect of Dexmedetomidine and Remifentanil on Pain Control After Spinal Surgery: A Double-Blind, Randomized Clinical Trial

Background

A variety of spinal surgery procedures are performed on patients with different cardiac, vascular, and respiratory comorbidities. Postoperative pain management is a major determinant of hemodynamic and respiratory status in these patients and promotes clinical results, prevents complications, saves health services, and improves the quality of life of patients.

Objectives

We compared the effects of dexmedetomidine and remifentanil on pain control after spinal surgery.

Methods

Sixty patients aged 18 - 65 years undergoing spinal surgery were randomized into the two groups of dexmedetomidine and remifentanil. The dexmedetomidine group (group D, n = 30) received dexmedetomidine infusion (0.6 mcg/kg/h), and the remifentanil group (group R, n = 30) received remifentanil infusion (0.1 mcg/kg/min) from induction of anesthesia until extubation. Propofol (1.5 mg/kg) and fentanyl (2mcg/kg) were used to initiate anesthesia, and propofol (100 - 150 mcg/kg/min) was infused to maintain anesthesia. Postoperative pain, hemodynamic parameters, and recovery characteristics were evaluated after surgery.

Results

The mean pain intensity in the dexmedetomidine group was significantly lower than in the remifentanil group (2.98 ± 1.29 vs. 3.80 ± 1.1; P < 0.001). Hemodynamic changes in the dexmedetomidine group (MAP: 92.60 ± 5.56, HR: 73.07 ± 7) were less, and their condition was significantly more stable than in the remifentanil group (MAP: 93.85 ± 4.78, HR: 79.15 ± 7.03; P < 0.05). The mean arterial oxygen saturation (O₂ sat) in the dexmedetomidine group was significantly higher and more stable than in the remifentanil group (98.87 ± 0.51 vs. 97.92 ± 0.46; P < 0.05). The incidence of nausea and vomiting was significantly lower in the dexmedetomidine group compared to the remifentanil group (P < 0.05). The administration of analgesics in the post-anesthetic care unit (PACU) was significantly higher in the remifentanil group than the dexmedetomidine group (P = 0.016).

Conclusions

Anesthetic maintenance with either dexmedetomidine or remifentanil infusion until extubation provided more smooth and hemodynamically stable conditions, without complications. However, dexmedetomidine provides better analgesia, causes a more stable hemodynamic state, and reduces postoperative nausea-vomiting, shivering, and the need for analgesics.

Unveiling the Role of Charge Transfer in Enhanced Electrochemical Nitrogen Fixation at Single-Atom Catalysts on BX Sheets (X = As, P, Sb)

To tune single-atom catalysts (SACs) for effective nitrogen reduction reaction (NRR), we investigate various transition metals implanted on boron-arsenide (BAs), boron-phosphide (BP), and boron-antimony (BSb) using density functional theory (DFT). Interestingly, W-BAs shows high catalytic activity and excellent selectivity with an insignificant barrier of only 0.05 eV along the distal pathway and a surmountable kinetic barrier of 0.34 eV. The W-BSb and Mo-BSb exhibit high performances with limiting potentials of -0.19 and -0.34 V. The Bader-charge descriptor reveals that the charge transfers from substrate to *NNH in the first protonation step and from *NH₃ to substrate in the last protonation step, circumventing a big hurdle in NRR by achieving negative free energy change of *NH₂ to *NH₃. Furthermore, machine learning (ML) descriptors are introduced to reduce computational cost. Our rational design meets the three critical prerequisites of chemisorbing N₂ molecules, stabilizing *NNH, and destabilizing *NH₂ adsorbates for high-efficiency NRR.

PSGL-1 is a novel macrophage checkpoint in immuno-oncology

e15090

Background: Macrophages are both antigen presenting and effector cells of the innate immune system and play an important role in tissue homeostasis as well as in activation and modulation of the adaptive immune response in disease. They display phenotypic heterogeneity in different tissue environments but can be broadly subdivided into pro-inflammatory M1 macrophages, which promote immune response, and anti-inflammatory M2 macrophages, which are associated with immune suppression. Under steady-state conditions, the populations of immune-stimulatory and immune-regulatory macrophages are balanced, but disruption of this balance can result in disease. In the tumor microenvironment, tumor-associated macrophages (TAMs) acquire an M2-like phenotype and maintain suppression of the immune system and promotion of tumor progression. Methods: For functional screening of anti-PSGL-1 antibodies, monocytes were isolated from peripheral blood mononuclear cells (PBMC) obtained from healthy donors and differentiated into M2 macrophages in the presence or absence of anti-PSGL-1 antibodies. On day 8 of the assay, phenotypic profile of cells was analyzed by flow cytometry and chemokines / cytokines were measured by Luminex. Mixed-lymphocyte reaction assay, SEB assay and an ex vivo tumor model were used to further assess antibody functionality in a multi-cellular assay format. For T cell assays, purified T cells from PBMC were stimulated in the presence or absence of anti-PSGL-1 antibodies and responses were characterized by flow cytometry and Luminex. Results: We have identified PSGL-1 as a novel macrophage checkpoint. Our work demonstrates that targeting PSGL-1 via an antagonistic antibody re-polarizes human primary M2 macrophages to a more M1-like state both phenotypically and functionally. We observe this M2-to-M1 switch to have an impact on immune cell communication in complex multi-cellular assays. Moreover, targeting of PSGL-1 in an ex vivo tumor system demonstrates that anti-PSGL-1 treatment can increase pro-inflammatory cytokine and chemokine production known to be associated with beneficial clinical response. These effects can be predominantly attributed to macrophage modulation, as antibody targeting PSGL-1 on purified T cells has a very small, if any, impact on their activation and effector function. Conclusions: Our results demonstrate that treatments inducing macrophage phenotypic switches can promote an immune response in a tumor setting across multiple tumor types and provide support for targeting the novel macrophage checkpoint PSGL-1 across multiple cancer indications.

Abstract P105: Targeting VSIG4, a novel macrophage checkpoint, repolarizes suppressive macrophages which induces an inflammatory response in primary cell in vitro assays and fresh human tumor cultures

VSIG4 (V-set immunoglobulin-domain-containing 4) is a B7 family related protein with known roles as a complement receptor involved in pathogen clearance, via interactions with C3 fragments, as well as a negative regulator of T cell activation by an undetermined mechanism. VSIG4 is expressed in tumor associated macrophages with exquisite specificity. In cancer, increased expression of VSIG4 has been associated with worse survival in multiple indications, including non-small cell lung cancer, multiple myeloma, ovarian cancer, stomach cancer and glioma, suggesting an important role in tumor immune evasion. Based upon computational analysis of transcript data across thousands of primary cancer and normal tissue samples, we hypothesized that VSIG4 has an important regulatory role in promoting M2-like immune suppressive macrophages in the tumor microenvironment, and that targeting VSIG4 via a monoclonal antibody could relieve VSIG4-mediated macrophage suppression by repolarizing tumor associated macrophages (TAMs) to an inflammatory phenotype capable of coordinating an anti-tumor immune response. Through a series of in vitro and ex vivo assays we demonstrate that anti-VSIG4 antibodies repolarize M2 macrophages and induce an immune response culminating in T cell activation. Anti-VSIG4 antibodies upregulate pro-inflammatory cytokines in M-CSF plus IL-10 driven monocyte-derived M2c macrophages, as well as in TAM-like macrophages in vitro derived from monocytes cultured in the presence of ascites fluid from ovarian cancer patients. To determine whether anti-VSIG4-induced macrophage repolarization can activate T cells, monocyte-derived M2c macrophages were co-cultured with autologous T cells in the presence of staphylococcal enterotoxin B (SEB) activation and anti-VSIG4 antibodies. Here, anti-VSIG4 antibodies upregulate both pro-inflammatory myeloid-derived cytokines (GM-CSF) and T cell-derived cytokines (IFNγ). To extend these observations to a relevant translational model, we treated fresh, patient-derived tumor samples with anti-VSIG4 antibodies and relevant controls ex vivo. Across numerous patient-derived samples, which included multiple tumor types, anti-VSIG4 treatment resulted in a significant upregulation of cytokines involved in TAM repolarization and T cell activation, and chemokines involved in immune cell recruitment, at levels greater than observed by treatment with anti-PD-1 or a clinical macrophage repolarizing agent (anti-ILT-4). Taken together, these data suggest that VSIG4 represents a promising new target capable of stimulating an anti-cancer response via multiple key immune mechanisms.

Citation Format: Steve Sazinsky, Ani Nguyen, Mohammad Zafari, Ryan Phennicie, Joe Wahle, Veronica Komoroski, Kathryn Rooney, Craig Mizzoni, Boris Klebanov, Jessica Ritter, Denise Manfra, Igor Feldman, Tatiana Novobrantseva. Targeting VSIG4, a novel macrophage checkpoint, repolarizes suppressive macrophages which induces an inflammatory response in primary cell in vitro assays and fresh human tumor cultures [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P105.

Single-atom catalysts supported on a hybrid structure of boron nitride/graphene for efficient nitrogen fixation via synergistic interfacial interactions

Hexagonal boron nitride (BN) shows significant chemical stability and promising thermal nitrogen reduction reaction (NRR) activity but suffers from low conductivity in electrolysis with a wide band gap. To overcome this problem, two-dimensional (2D) BN and graphene (G) are designed as a heterostructure, namely BN/G. According to density functional theory (DFT), the higher conductivity of G narrows the band gap of BN by inducing some electronic states near the Fermi energy level (Ef). Once transition metals (TMs) are anchored in the BN/G structure as single atom catalysts (SACs), the NRR activity improves as the inert BN basal layer activates with moderate *NH2 binding energy and further the band gap is reduced to zero. V (vanadium) and W (tungsten) SACs exhibit the best performance with limiting potentials of -0.22 and -0.41 V, respectively. This study helps in understanding the improvement of the NRR activity of BN, providing physical insights into the adsorbate-TM interaction.

Abstract P107: PSGL-1 blocking antibodies repolarize tumor associated macrophages, reduce suppressive myeloid populations and induce inflammation in the tumor microenvironment, leading to suppression of tumor growth

Suppressive myeloid populations in the tumor microenvironment are associated with worse survival of cancer patients and low effectiveness of T cell checkpoint inhibitors. Recently, several early clinical studies have produced positive data for therapies aimed at repolarizing suppressive myeloid populations in the tumor microenvironment. One new macrophage repolarizing target, PSGL-1, is expressed at high levels on immuno-suppressive TAMs and differentiated M2 macrophages. PSGL-1 has been shown to have an immune-modulatory activity, which includes its role in maintaining a suppressive functional macrophage state. To assess the ability of PSGL-1 antibodies to convert macrophages and the tumor microenvironment from an immuno-suppressive toward a pro-inflammatory state, we employed in vitro primary macrophage and multi-cellular assays, ex vivo patient-derived tumor cultures, and a humanized mouse PDX model. We have determined that our lead anti-PSGL-1 antibody repolarized M2-like macrophages to a more M1-like state both phenotypically and functionally as assessed in primary in vitro macrophage assays. Transcriptomics profiling of M2c macrophages showed that the anti-PSGL-1 antibody upregulated TNF-a/NF-kB and chemokine-mediated signaling, while downregulating oxidative phosphorylation, fatty acid metabolism and Myc signaling pathways, consistent with a broad M2-to-M1 shift of the macrophage state. Furthermore, these repolarized M1-like macrophages enhanced the inflammatory response in complex multi-cellular assays. The PSGL-1 antibody also showed efficacy in a humanized mouse PDX model of melanoma. The antibody suppressed tumor growth to a significantly greater degree compared to anti-PD-1. At the cellular and molecular levels, the anti-PSGL-1 treatment led to a more enhanced inflammatory microenvironment, including a reduced M2:M1 macrophage ratio, and an increase in systemic pro-inflammatory mediators. Compared to anti-PD-1 monotherapy, anti-PSGL-1 alone and in combination with anti-PD-1 increased the fraction of effector CD8+ T cells among the infiltrating T cells. Significant combination effects of anti-PSGL-1 plus anti-PD-1 were seen at the cellular and molecular levels within the tumor tissue, the spleen, and peripheral blood. Lastly, pre-clinical efficacy of our lead anti-PSGL-1 antibody was demonstrated using ex vivo cultures of fresh patient-derived tumors that preserve the cellular heterogeneity of the TME. Anti-PSGL-1 increased production of inflammatory cytokines and chemokines involved in immune activation of the TME and T cell recruitment. The data presented here provide biological and mechanistic support for clinical testing of antibodies targeting PSGL-1 for the treatment of cancer.

Citation Format: Ani Nguyen, Jessica Ritter, Mohammad Zafari, Denise Manfra, Veronica Komoroski, Brian O'Nuallain, Ryan Phennicie, Kevin Kauffman, Dominika Nowakowska, Joe Wahle, Steve Sazinsky, Michael Brehm, Igor Feldman, Tatiana Novobrantseva. PSGL-1 blocking antibodies repolarize tumor associated macrophages, reduce suppressive myeloid populations and induce inflammation in the tumor microenvironment, leading to suppression of tumor growth [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P107.