Inhibitory Fc Research Articles

Abstract PO-26: Prognostic significance of Fc gamma receptor IIB expression in the response of previously untreated diffuse large B-cell lymphomas to anti-CD20 monoclonal antibodies: Differing impact of rituximab and obinutuzumab

Abstract Background: The anti-CD20 monoclonal antibody (mAb), obinutuzumab (G), has shown improved outcomes versus rituximab (R) in indolent lymphomas; however, no improvement was seen in diffuse large B-cell lymphoma (DLBCL), and the molecular basis is unclear. The inhibitory Fc gamma receptor IIB (Fc γRIIB), expressed on lymphoma cells, can impair the effects of direct targeting mAbs, such as R, by binding and internalizing them, reducing opsonization and limiting FcγR-mediated killing. We hypothesized that FcγRIIB expression on cellular effectors and/or the lymphoma confers treatment resistance in some patients (pts) and evaluated if outcomes differ for therapies involving a non-internalized mAb (G). Methods: We evaluated correlates between FCGR2B mRNA and/or FcγRIIB protein expression and pt outcomes in two discovery cohorts of de novo DLBCL treated with R-CHOP (Arthur et al. 2018, n=372; Schmitz et al. 2018, n=234), and the phase III GOYA trial (NCT01287741; n=552), which compared R-CHOP with G-CHOP in pts with previously untreated DLBCL. FCGR2B mRNA expression was assessed by RNA-Seq, and protein expression was assessed in evaluable cohorts by immunohistochemistry, using tissue microarrays with macrophages identified by CD68. FCGR2B expression was also measured by a NanoString assay (Arthur cohort). Cox regression analyzed the impact of FcγRIIB/FCGR2B expression on progression-free survival (PFS), with univariate and multivariate models adjusted for International Prognostic Index (IPI), cell of origin (COO), and BCL2 protein expression. Results: In the discovery cohorts, a higher FCGR2B expression was significantly associated with shorter PFS (Arthur: HR 1.09 [95% CI: 1.01–1.19], P=0.036; Schmitz: HR 1.13 [95% CI: 1.02–1.26], P=0.0243). Expression by NanoString strongly correlated with RNA-Seq, confirming the association with shorter PFS (HR 1.13 [95% CI: 1.04–1.23], P=0.0048). In GOYA, a significant association between PFS and FCGR2B was observed in the R arm (HR 1.26 [95% CI: 1.00–1.58], P=0.0455), with no prognostic effect observed for G (HR 0.91 [95% CI: 0.69–1.20], P=0.5). Pts with high FCGR2B expression appeared to benefit more from G than R (HR 0.67 [95% CI: 0.44–1.02], P=0.0622), in contrast to pts with low FCGR2B expression (HR 1.58 [95% CI: 1.00–2.50], P=0.0503). In both Arthur and GOYA cohorts, FCGR2B expression by RNA-Seq was associated with FcγRIIB on the tumor, which correlated with a shorter PFS for R (HR 2.17 [95% CI: 1.04–4.50], P=0.03), but not G (HR 1.37 [95% CI: 0.66–2.87], P=0.4). This prognostic effect on PFS was independent of established prognostic biomarkers, IPI, COO and BCL2. Conclusion: High FcγRIIB/FCGR2B expression in pts with DLBCL has prognostic value in those treated with R and may confer differential responsiveness to R or G. Citation Format: Laura K. Hilton, Malgorzata Nowicka, Margaret Ashton-Key, Chantal E. Hargreaves, Chern Lee, Russell Foxall, Matthew J. Carter, Stephen A. Beers, Kathleen N. Potter, Christopher R. Bolen, Christian Klein, Andrea Knapp, Farheen Mir, Matthew Rose-Zerilli, Cathy Burton, Wolfram Klapper, David W. Scott, Laurie H. Sehn, Umberto Vitolo, Maurizio Martelli, Marek Trneny, Graham W. Slack, Pedro Farinha, Jonathan C. Strefford, Mikkel Z. Oestergaard, Ryan D. Morin, Mark S. Cragg. Prognostic significance of Fc gamma receptor IIB expression in the response of previously untreated diffuse large B-cell lymphomas to anti-CD20 monoclonal antibodies: Differing impact of rituximab and obinutuzumab [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-26.

Memory T cell-mediated rejection is mitigated by FcγRIIB expression on CD8+ T cells.

Donor-reactive memory T cells generated via heterologous immunity represent a potent barrier to long-term graft survival following transplantation because of their increased precursor frequency, rapid effector function, altered trafficking patterns, and reduced reliance on costimulation signals for activation. Thus, the identification of pathways that control memory T cell survival and secondary recall potential may provide new opportunities for therapeutic intervention. Here, we discovered that donor-specific effector/memory CD8+ T cell populations generated via exposure to acute vs latent vs chronic infections contain differential frequencies of CD8+ T cells expressing the inhibitory Fc receptor FcγRIIB. Results indicated that frequencies of FcγRIIB-expressing CD8+ donor-reactive memory T cells inversely correlated with allograft rejection. Furthermore, adoptive T cell transfer of Fcgr2b-/- CD8+ T cells resulted in an accumulation of donor-specific CD8+ memory T cells and enhanced recall responses, indicating that FcγRIIB functions intrinsically to limit T cell CD8+ survival in vivo. Lastly, we show that deletion of FcγRIIB on donor-specific CD8+ memory T cells precipitated costimulation blockade-resistant rejection. These data therefore identify a novel cell-intrinsic inhibitory pathway that functions to limit the risk of memory T cell-mediated rejection following transplantation and suggest that therapeutic manipulation of this pathway could improve outcomes in sensitized patients.

Recombinant Factor VIII Fc Inhibits B Cell Activation via Engagement of the FcγRIIB Receptor.

The development of neutralizing antibodies (inhibitors) against factor VIII (FVIII) is a major complication of hemophilia A treatment. The sole clinical therapy to restore FVIII tolerance in patients with inhibitors remains immune tolerance induction (ITI) which is expensive, difficult to administer and not always successful. Although not fully understood, the mechanism of ITI is thought to rely on inhibition of FVIII-specific B cells (1). Its efficacy might therefore be improved through more aggressive B cell suppression. FcγRIIB is an inhibitory Fc receptor that down-regulates B cell signaling when cross-linked with the B cell receptor (BCR). We sought to investigate if recombinant FVIII Fc (rFVIIIFc), an Fc fusion molecule composed of FVIII and the Fc region of immunoglobulin G1 (IgG1) (2), is able to inhibit B cell activation more readily than FVIII. rFVIIIFc was able to bind FVIII-exposed and naïve B cells from hemophilia A mice as well as a FVIII-specific murine B cell hybridoma line (413 cells). An anti-FcγRIIB antibody and FVIII inhibited binding, suggesting that rFVIIIFc is able to interact with both FcγRIIB and the BCR. Furthermore, incubation of B cells from FVIII-exposed mice and 413 cells with rFVIIIFc resulted in increased phosphorylation of SH-2 containing inositol 5-phosphatase (SHIP) when compared to FVIII. B cells from FVIII-exposed hemophilia A mice also exhibited decreased extracellular signal-regulated kinase (ERK) phosphorylation when exposed to rFVIIIFc. These differences were absent in B cells from naïve, non-FVIII exposed hemophilic mice suggesting an antigen-dependent effect. Finally, rFVIIIFc was able to inhibit B cell calcium flux induced by anti-Ig F(ab)2. Our results therefore indicate that rFVIIIFc is able to crosslink FcγRIIB and the BCR of FVIII-specific B cells, causing inhibitory signaling in these cells.

Fcγ Receptor IIB Controls Skin Inflammation in an Active Model of Epidermolysis Bullosa Acquisita.

Epidermolysis bullosa acquisita (EBA) is an autoimmune skin blistering disease characterized by IgG autoantibodies (aAb) against type VII collagen (COL7). The mechanisms controlling the formation of such aAbs and their effector functions in the skin tissue are incompletely understood. Here, we assessed whether the inhibitory IgG Fc receptor, FcγRIIB, controls the development of autoimmune skin blistering disease in an active model of EBA. For this purpose, we immunized congenic EBA-susceptible B6.SJL-H2s (B6.s) and B6.s-Fcgr2b−/− mice with the immunodominant vWFA2 region of COL7. B6.s-Fcgr2b−/− mice developed a strong clinical phenotype with 15 ± 3.3% of affected body surface area at week 4. In contrast, the body surface area in B6.s mice was affected to a maximum of 5% at week 6 with almost no disease signs at week 4. Surprisingly, we already found strong but similar COL7-specific serum IgG1 and IgG2b aAb production at week 2. Further, aAb and C3b deposition in the skin of B6.s and B6.s-Fcgr2b−/− mice increased between weeks 2 and 6 after vWFA2 immunization. Importantly, neutrophil skin infiltration and activation was much stronger in B6s-Fcgr2b−/− than in B6.s mice and already present at week 2. Also, the early aAb response in B6.s-Fcgr2b−/− mice was more diverse than in wt B6.s mice. Reactive oxygen species (ROS) release from infiltrating neutrophils play a crucial role as mediator of skin inflammation in EBA. In line, sera from B6.s and B6.s-Fcgr2b−/− mice induced strong ROS release from bone marrow-neutrophils in vitro. In contrast to the antibody-transfer-induced EBA model, individual targeting of FcγRIII or FcγRIV decreased ROS release to 50%. Combined FcγR blocking abrogated ROS release from BM neutrophils. Also, ROS release induced by COL7-specific serum IgG aAbs was significantly higher using BM neutrophils from B6.s-Fcgr2b−/− than from B6.s mice. Together, our findings identified FcγRIIB as a suppressor of skin inflammation in the active EBA model through inhibition of early epitope spreading, protection from strong early neutrophil infiltration to and activation of neutrophils in the skin and suppression of FcγRIII activation by IgG1 aAbs which drive strong ROS release from neutrophils leading to tissue destruction at the dermal-epidermal junction.

Keeping T-he Killers at Bay via FcγRIIb

Understanding how cytotoxic Tcells are regulated is key for enhancing or suppressing their activity in tumor or transplantation settings. A study by Morris etal. (2020) in this issue of Immunity shows that crosslinking of inhibitory Fc receptor FcγRIIb by the suppressive cytokine Fgl2 limits cytotoxic CD8+ Tcell responses by inducing Tcell apoptosis.

Signaling through the Inhibitory Fc Receptor FcγRIIB Induces CD8+ T Cell Apoptosis to Limit T Cell Immunity

Effector CD8+ Tcells are important mediators of adaptive immunity, and receptor-ligand interactions that regulate their survival may have therapeutic potential. Here, we identified a subset of effector CD8+ Tcells that expressed the inhibitory fragment crystallizable (Fc) receptor FcγRIIB following activation and multiple rounds of division. CD8+ Tcell-intrinsic genetic deletion of Fcgr2b increased CD8+ effector Tcell accumulation, resulting in accelerated graft rejection and decreased tumor volume in mouse models. Immunoglobulin G (IgG) antibody was not required for FcγRIIB-mediated control of CD8+ Tcell immunity, and instead, the immunosuppressive cytokine fibrinogen-like 2 (Fgl2) was a functional ligand for FcγRIIB on CD8+ Tcells. Fgl2 induced caspase-3/7-mediated apoptosis in Fcgr2b+, but not Fcgr2b-/-, CD8+ Tcells. Increased expression of FcγRIIB correlated with freedom from rejection following withdrawal from immunosuppression in a clinical trial of kidney transplant recipients. Together, these findings demonstrate a cell-intrinsic coinhibitory function of FcγRIIB in regulating CD8+ Tcell immunity.

Abstract C028: Discovery and characterization of next generation monoclonal antibodies targeting the inhibitory Fc gamma receptor CD32b for the treatment of B and plasma cell malignancies

Abstract CD32b (FcγR2b), the sole inhibitory Fcγ receptor, negatively regulates immune function and is expressed throughout B cell development and on their malignant counterparts with the highest expression found on multiple myeloma. Additionally, CD32b expression on tumor cells is known to sequester IgG Fc thereby providing a mechanism of resistance to therapeutic monoclonal antibodies (mAb) with Fc dependent activity. Taken together, CD32b represents an attractive tumor antigen for targeting with a mAb. To this end, two anti-CD32b mAbs, NVS32b1 and NVS32b2, were developed. The complementarity-determining regions (CDRs) of these antibodies bind the CD32b Fc binding domain with high specificity and affinity while the Fc region is afucosylated enabling enhanced activation of FcγR on immune effector cells. This specificity and optimized potency is highlighted in whole blood assays where NVS32b2 depletes CD32b positive B cells but spares immune subsets with low CD32b expression or expression of the homologous CD32a. The antibodies mediate potent killing of opsonized cells via antibody dependent cell-mediated cytotoxicity, antibody dependent cellular phagocytosis, and complement dependent cytotoxicity. Additionally, NVS32b mAbs’ CDR block the CD32b Fc binding domain, thereby minimizing CD32b mediated resistance to therapeutic mAbs with Fc dependent activity including rituximab, obinutuzumab, and daratumumab. In vivo, NVS32b mAbs demonstrate robust antitumor activity against CD32b positive xenografts and immunomodulatory activity including recruitment of intratumoral macrophages. The NVS32b mAbs’ activity against malignant B and plasma cells featuring a range of CD32b expression demonstrates their therapeutic potential, as a single agent or in combination with therapeutics including mAbs with Fc dependent activity. Citation Format: Haihui Lu, Dongshu Chen, Sunyoung Jang, Babette Wolf, Stefan Ewert, Meghan Flaherty, Fangmin Xu, Sinan Isim, Yeonjiu Shim, Christina Dornelas, Nicole Balke, Xavier Charles Leber, Meike Scharenberg, Johanna Koelln, Eugene Choi, Rebecca Ward, Jennifer Johnson, Thomas Calzascia, Isabelle Isnardi, Juliet Williams, Heather Huet, Emma Lees, Matthew J Meyer. Discovery and characterization of next generation monoclonal antibodies targeting the inhibitory Fc gamma receptor CD32b for the treatment of B and plasma cell malignancies [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C028. doi:10.1158/1535-7163.TARG-19-C028

Follicular Dendritic Cells Modulate Germinal Center B Cell Diversity through FcγRIIB

SUMMARYFollicular dendritic cells (FDCs), a rare and enigmatic stromal cell type in the B cell follicles of secondary lymphoid organs, store and present antigen to B cells. While essential for germinal center (GC) responses, their exact role during GC B cell selection remains unknown. FDCs upregulate the inhibitory IgG Fc receptor FcγRIIB during GC formation. We show that the stromal deficiency of FcγRIIB does not affect GC B cell frequencies compared to wild-type mice. However, in the absence of FcγRIIB on FDCs, GCs show aberrant B cell selection during autoreactive and selective foreign antigen responses. These GCs are more diverse as measured by the AidCreERT2 -confetti system and show the persistence of IgM+ clones with decreased numbers of IgH mutations. Our results show that FDCs can modulate GC B cell diversity by the upregulation of FcγRIIB. Permissive clonal selection and subsequent increased GC diversity may affect epitope spreading during autoimmunity and foreign responses.

Contribution of Fcγ receptor IIB to creating a suppressive tumor microenvironment in a mouse model.

Various immune cells are recruited in the tumor microenvironment. It is well established that cellular immune responses, such as cytotoxic or suppressive activities, play an important role in regulating tumor growth and metastasis. However, the contribution of humoral immune responses against tumors is poorly understood. Fc receptors constitute critical elements for the up- or downregulation of immune responses through immune complexes. Here, we examined the potential role of the inhibitory Fc receptor, Fcγ receptor IIB (FcγRIIB), in tumor immunity using a mouse model. Our findings indicated that tumor-specific antibodies are induced in tumor-bearing mice and control tumor immunity. FcγRIIB deletion significantly improved both cellular and humoral immunity against tumors and delayed tumor growth. These findings indicated that spontaneous antibodies against tumors create a suppressive tumor microenvironment through FcγRIIB signaling, thus suggesting an attractive therapeutic target for cancer immunotherapy.

The Complex Association of FcγRIIb With Autoimmune Susceptibility.

FcγRIIb is the only inhibitory Fc receptor and controls many aspects of immune and inflammatory responses. The observation 19 years ago that FcγRIIb−/− mice generated by gene targeting in 129 derived ES cells developed severe lupus like disease when backcrossed more than 7 generations into C57BL/6 background initiated extensive research on the functional understanding of this strong autoimmune phenotype. The genomic region in the distal part of Chr1 both in human and mice in which the FcγR gene cluster is located shows a high level of complexity in relation to the susceptibility to SLE. Specific haplotypes of closely linked genes including the FcγRIIb and Slamf genes are associated with increased susceptibility to SLE both in mice and human. Using forward and reverse genetic approaches including in human GWAS and in mice congenic strains, KO mice (germline and cell type specific, on different genetic background), knockin mice, overexpressing transgenic mice combined with immunological models such as adoptive transfer of B cells from Ig transgenic mice the involved genes and the causal mutations and their associated functional alterations were analyzed. In this review the results of this 19 years extensive research are discussed with a focus on (genetically modified) mouse models.

Abstract 1538: Margetuximab mediates greater Fc-dependent anti-tumor activities than trastuzumab or pertuzumab in vitro

Abstract Margetuximab (M) is an investigational Fc-engineered anti-HER2 monoclonal antibody (mAb) with potential for greater immune-mediated anti-tumor activity than trastuzumab (T). M and T bind the same subdomain IV epitope, but M binds with higher affinity to activating Fc receptor, CD16A (FcγRIIIA), and lower affinity to inhibitory Fc receptor, CD32B (FcγRIIB). Pertuzumab (P) binds to a subdomain II epitope and has the same wild type Fc domain as T. We compared in vitro properties of M, T and P and combinations of M+P and T+P to evaluate Fc domain contributions to anti-HER2 mAb mediated activities. By surface plasmon resonance, M, T and P bound to the HER2 extracellular domain with similar high affinity. Binding affinities of M and T were unchanged if P was pre-bound, indicating lack of interaction. M, T and P exhibited comparable binding to HER2-expressing cell lines. Anti-proliferative activities of M and T toward HER23+ cells (N87, SKBR3 or BT474) in the absence or presence of ligands (EGF or HRG1β) were similar, whereas P exhibited weaker activity. In the absence of ligands, M+P or T+P were comparably as active as M or T alone. In presence of ligands, M+P and T+P were generally more active than M or T alone. Antibody-dependent cell-mediated cytotoxicity (ADCC) was evaluated with N87 and SKBR3 target cells (HER23+, expressing a reporter gene to measure viability) and NK effector cells from donors with differing CD16A158 genotypes. M was 7- to 84-fold more potent than T, as well as 69- to 744-fold more potent than P. Greater differences generally were seen with effector NK cells bearing the more common CD16A158 FF and VF genotypes than with the less common, high affinity CD16A158 VV genotype. While addition of P enhanced mean potency of T by 2- to 3-fold, no such effect was seen with M; however, M or M+P was 7- to 25-fold more potent than T+P. Results with JIMT-1 cells (HER22+) were similar, albeit with lower differential than with HER23+ target cells. NK cells were monitored by flow cytometry following incubation of peripheral blood mononuclear cells with HER2+ target cells and mAbs. M induced greater expression of markers of activation (CD137), cytolytic capability (granzyme B, perforin) and proliferation (Ki67) than T. An anti-HER2 mAb with an inactivated Fc domain was ineffective, indicating that induced changes in NK cells were Fc-dependent. In conclusion, M and T bind HER2 with similar affinity and exhibit comparable anti-proliferative activity that is enhanced by addition of P if ligands (EGF or HRG1β) are present. Relative to T, M mediates superior ADCC with effector cells of all CD16A genotypes and promotes greater NK cell activation and expansion. The M+P combination maintains superior ADCC compared to the T+P combination. Citation Format: Liqin Liu, Yinhua Yang, Robert Burns, Jonathan Li, Haiquan Li, Sergey Gorlatov, Paul Moore, Jeffrey Nordstrom. Margetuximab mediates greater Fc-dependent anti-tumor activities than trastuzumab or pertuzumab in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1538.

A single infection with a malaria parasite protects mice from lethal autoimmune glomerulonephritis

Abstract The progression of autoimmune diseases such as Systemic Lupus Erythematous (SLE) can be altered by environmental factors, including parasitic infections. Epidemiological studies have shown a relative absence of SLE in West Africa (areas of endemic malaria), even though SLE is highly prevalent in populations of African descent living outside of Africa. We hypothesize that malaria infections might reduce the incidence of lupus. In the present work, we assess the effect of the non-lethal Plasmodium yoelii 17XNL in a well-characterized animal model of SLE (FcγRIIB−/−). Mice deficient in the inhibitory Fc receptor for IgG (FcγRIIB) develop spontaneous disease driven by the production of anti-nuclear autoantibodies, a broad immune activation, splenomegaly, anemia and lethal glomerulonephritis with a pathology similar to human SLE. We infected FcγRIIB−/− mice at 2 months of age with P. yoelii and followed the progression of autoimmune disease for 5 months. Infection with P. yoelii increased the titer of a broad range of autoantibodies, with concomitant immune-complex deposition and complement fixation in the kidney. While lupus-prone mice succumbed from renal disease detected by protein in urine, malaria-infected lupus-prone mice did not develop proteinuria or lethal disease. Infection with the parasite did not alter tolerance mechanisms leading to lupus but instead prevented end-point tissue pathology. P. yoelii infection seems to inhibit pathogenic leukocyte infiltration without affecting the autoimmune inflammation of glomeruli. These results indicate a possible route for lupus protection that specifically targets renal function, which remains a cause of the substantial morbidity and mortality in SLE patients.

Targeting the Antibody Checkpoints to Enhance Cancer Immunotherapy-Focus on FcγRIIB.

Immunotherapy with therapeutic antibodies has increased survival for patients with hematologic and solid cancers. Still, a significant fraction of patients fails to respond to therapy or acquire resistance. Understanding and overcoming mechanisms of resistance to antibody drugs, and in particular those common to antibody drugs as a class, is therefore highly warranted and holds promise to improve response rates, duration of response and potentially overall survival. Activating and inhibitory Fc gamma receptors (FcγR) are known to coordinately regulate therapeutic activity of tumor direct-targeting antibodies. Similar, but also divergent, roles for FcγRs in controlling efficacy of immune modulatory antibodies e.g., checkpoint inhibitors have been indicated from mouse studies, and were recently implicated in contributing to efficacy in the human clinical setting. Here we discuss evidence and mechanisms by which Fc gamma receptors–the “antibody checkpoints”–regulate antibody-induced antitumor immunity. We further discuss how targeted blockade of the sole known inhibitory antibody checkpoint FcγRIIB may help overcome resistance and boost activity of clinically validated and emerging antibodies in cancer immunotherapy.

IgE Antibodies: From Structure to Function and Clinical Translation.

Immunoglobulin E (IgE) antibodies are well known for their role in mediating allergic reactions, and their powerful effector functions activated through binding to Fc receptors FcεRI and FcεRII/CD23. Structural studies of IgE-Fc alone, and when bound to these receptors, surprisingly revealed not only an acutely bent Fc conformation, but also subtle allosteric communication between the two distant receptor-binding sites. The ability of IgE-Fc to undergo more extreme conformational changes emerged from structures of complexes with anti-IgE antibodies, including omalizumab, in clinical use for allergic disease; flexibility is clearly critical for IgE function, but may also be exploited by allosteric interference to inhibit IgE activity for therapeutic benefit. In contrast, the power of IgE may be harnessed to target cancer. Efforts to improve the effector functions of therapeutic antibodies for cancer have almost exclusively focussed on IgG1 and IgG4 subclasses, but IgE offers an extremely high affinity for FcεRI receptors on immune effector cells known to infiltrate solid tumours. Furthermore, while tumour-resident inhibitory Fc receptors can modulate the effector functions of IgG antibodies, no inhibitory IgE Fc receptors are known to exist. The development of tumour antigen-specific IgE antibodies may therefore provide an improved immune functional profile and enhanced anti-cancer efficacy. We describe proof-of-concept studies of IgE immunotherapies against solid tumours, including a range of in vitro and in vivo evaluations of efficacy and mechanisms of action, as well as ex vivo and in vivo safety studies. The first anti-cancer IgE antibody, MOv18, the clinical translation of which we discuss herein, has now reached clinical testing, offering great potential to direct this novel therapeutic modality against many other tumour-specific antigens. This review highlights how our understanding of IgE structure and function underpins these exciting clinical developments.

The genomic organization and expression pattern of the low-affinity Fc gamma receptors (Fc\u03b3R) in the G\xf6ttingen minipig

Safety and efficacy of therapeutic antibodies are often dependent on their interaction with Fc receptors for IgG (FcγRs). The Göttingen minipig represents a valuable species for biomedical research but its use in preclinical studies with therapeutic antibodies is hampered by the lack of knowledge about the porcine FcγRs. Genome analysis and sequencing now enabled the localization of the previously described FcγRIIIa in the orthologous location to human FCGR3A. In addition, we identified nearby the gene coding for the hitherto undescribed putative porcine FcγRIIa. The 1′241 bp long FCGR2A cDNA translates to a 274aa transmembrane protein containing an extracellular region with high similarity to human and cattle FcγRIIa. Like in cattle, the intracellular part does not contain an immunoreceptor tyrosine-based activation motif (ITAM) as in human FcγRIIa. Flow cytometry of the whole blood and single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) of Göttingen minipigs revealed the expression profile of all porcine FcγRs which is compared to human and mouse. The new FcγRIIa is mainly expressed on platelets making the minipig a good model to study IgG-mediated platelet activation and aggregation. In contrast to humans, minipig blood monocytes were found to express inhibitory FcγRIIb that could lead to the underestimation of FcγR-mediated effects of monocytes observed in minipig studies with therapeutic antibodies.

OMIP-051 - 28-color flow cytometry panel to characterize B cells and myeloid cells.

OMIP-051 - 28-color flow cytometry panel to characterize B cells and myeloid cells.

FCGR2B B2.4 Haplotype Predicts Increased Risk of Red Blood Cell Alloimmunization in Sickle Cell Disease Patients

Introduction: Red blood cell (RBC) alloimmunization is an important transfusion complication which is very prevalent among patients with sickle cell disease (SCD). Only part of patients is able to develop alloantibodies following antigen-mismatched transfusions, named the ‘immune responders’, who should be prospectively transfused with antigen-matched RBC units, comprising the most immunogenic erythrocyte antigens. Auto-immune diseases are a known risk factor for RBC alloimmunization, suggesting that auto-immunity and post-transfusion alloantibody development happen through similar physiopathological pathways. In this context, polymorphisms in FCGR2B gene have already been associated with several auto-immune disorders and, hypothetically, could be associated with RBC alloimmunization and help to identify the ‘immune responders’ in transfusion practice.Methods: In this case-control study, we enrolled 277 transfused SCD patients with retrospective data on alloimmunization status and transfusion exposure from two Brazilian centers. DNA samples (collected from March, 2017 to June, 2018) were extracted from whole blood samples using commercial kits (PureLink™ Genomic DNA®, Invitrogen, CA), and used for PCR amplification of promoter region of FCGR2B gene containing both -386G/C and -120T/A single nucleotide polymorphisms (SNPs) using gene-specific primer. SNPs of the FCGR2B were genotyped by direct Sanger sequencing (ABI3730XL, Applied Biosystems, CA). Cases had a positive history of alloimmunization with a clinically significant alloantibody and a minimum transfusion exposure of 1 RBC unit. Controls had a negative history of alloimmunization and having received ≥ 2 RBC units. Patients with autoimmune diseases or poor quality of DNA were excluded. Unadjusted and adjusted analyses were conducted by using Logistic Regression models to determine the association of covariates with binary outcome. Since the assumption of linearity in the logit was not supported, continuous covariates were categorized based on optimum cut-off point derived from ROC analysis. All statistical analyses were performed using SAS University Edition. A p-value of <0.05 was considered to be statistically significant.Results: A total of 237 patients met the eligibility criteria, 121 cases (alloimmunized) and 117 controls (non-alloimmunized). Majority of patients were female in cases (61%) and male in controls (86%), with mean age of 27.9 years (SD 15.3). Table 1 list the characteristics between the groups. RBC alloimmunization was associated with female sex (p<0.001), lifetime number of RBC units transfused (p=0.002) and FCGR2B 120T/A SNP (p=0.031). No statistically differences in the allele frequency of c.386C were observed between groups (p=0.602). FCGR2B -386G/C and -120T/A SNPs were in intense linkage disequilibrium. Three haplotypes of promoter region were identified as 2B.1 (-386G-120T), 2B.2 (-386C-120T) and 2B.4 (-386C-120A) with statistical significance (p=0.045). Logistic regression model was performed to assess the effects of age, gender, lifetime number of RBC units transfused and FCGR2B 2B.4 haplotype on the likelihood of RBC alloimmunization in patients with SCD. The analysis identified that female sex (OR 10.03, CI95% 5.16-19.49; p<0.001) and FCGR2B 2B.4 haplotype (OR 4.55, CI95% 1.11-18.65; p=0.035) predict increased risk of RBC alloimmunization in SCD patients as show in Table 2.Conclusions: SCD patients with the FCGR2B 2B.4 haplotype had over a 4-fold higher risk for RBC alloimmunization in comparison with patients without this haplotype and probably may be helpful to identify the ‘immune responders’. The presence of FCGR2B 2B.4 haplotype have been associated with increased expression of this inhibitory Fc gamma receptor in immune system cells, that was strongly associated with capacity of immune tolerance, regulating the development of antibodies. Future studies are needed to understand more about the functional and immune mechanism behind alloimmunization in SCD patients and ultimately improve our current preventive strategies. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Immunoglobulin E blockade during food allergen ingestion enhances the induction of inhibitory immunoglobulin G antibodies

Immunoglobulin E (IgE)-mediated food allergy is a growing problem with no curative therapy. 1 Renz H. Allen K.J. Sicherer S.H. et al. Food allergy. Nat Rev Dis Primers. 2018; 4: 17098 Crossref PubMed Scopus (179) Google Scholar Oral immunotherapy (OIT) has shown promise, but its utility is limited by reactions during treatment and a lack of sustained protection after therapy. Immunoglobulin E antibodies trigger hypersensitivity reactions to foods. Their effects, mediated by the high-affinity Immunoglobulin E receptor (FcεRI) on mast cells and basophils, can be countered by IgG antibodies of shared specificity signaling via the inhibitory Fc receptor, FcγRIIb. 2 Malbec O. Daeron M. The mast cell IgG receptors and their roles in tissue inflammation. Immunol Rev. 2007; 217: 206-221 Crossref PubMed Scopus (116) Google Scholar Oral immunotherapy induces only modest reductions in specific IgE antibodies but stimulates dramatic increases in inhibitory IgG. 3 Burton O.T. Logsdon S.L. Zhou J.S. et al. Oral immunotherapy induces IgG antibodies that act through FcgammaRIIb to suppress IgE-mediated hypersensitivity. J Allergy Clin Immunol. 2014; 134: 1310-1317 Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar , 4 Santos A.F. James L.K. Bahnson H.T. et al. IgG inhibits peanut-induced basophil and mast cell activation in peanut-tolerant children sensitized to peanut major allergens. J Allergy Clin Immunol. 2015; 135: 1249-1256 Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar

Epistatic Interactions Between Mutations of Deoxyribonuclease 1-Like 3 and the Inhibitory Fc Gamma Receptor IIB Result in Very Early and Massive Autoantibodies Against Double-Stranded DNA.

Autoantibodies against double-stranded DNA (anti-dsDNA) are a hallmark of systemic lupus erythematosus (SLE). It is well documented that anti-dsDNA reactive B lymphocytes are normally controlled by immune self-tolerance mechanisms operating at several levels. The evolution of high levels of IgG anti-dsDNA in SLE is dependent on somatic hypermutation and clonal selection, presumably in germinal centers from non-autoreactive B cells. Twin studies as well as genetic studies in mice indicate a very strong genetic contribution for the development of anti-dsDNA as well as SLE. Only few single gene defects with a monogenic Mendelian inheritance have been described so far that are directly responsible for the development of anti-dsDNA and SLE. Recently, among other mutations, rare null-alleles for the deoxyribonuclease 1 like 3 (DNASE1L3) and the Fc gamma receptor IIB (FCGR2B) have been described in SLE patients and genetic mouse models. Here, we demonstrate that double Dnase1l3- and FcgR2b-deficient mice in the C57BL/6 background exhibit a very early and massive IgG anti-dsDNA production. Already at 10 weeks of age, autoantibody production in double-deficient mice exceeds autoantibody levels of diseased 9-month-old NZB/W mice, a long established multigenic SLE mouse model. In single gene-deficient mice, autoantibody levels were moderately elevated at early age of the mice. Premature autoantibody production was accompanied by a spontaneous hyperactivation of germinal centers, early expansions of T follicular helper cells, and elevated plasmablasts in the spleen. Anti-dsDNA hybridomas generated from double-deficient mice show significantly elevated numbers of arginines in the CDR3 regions of the heavy-chain as well as clonal expansions and diversification of B cell clones with moderate numbers of somatic mutations. Our findings show a strong epistatic interaction of two SLE-alleles which prevent early and high-level anti-dsDNA autoantibody production. Both genes apparently synergize to keep in check excessive germinal center reactions evolving into IgG anti-dsDNA antibody producing B cells.

Abstract 4731: Contribution of FcγRIIB to creating the suppressive tumor microenvironment

Abstract Various immune cells are recruited in tumor microenvironment. It is well established that cellular immune responses, such as cytotoxic or suppressive activities play an important role in regulating tumor growth and metastasis. However, contribution of humoral immune responses against tumor is incompletely understood. The Fc receptors constitute critical elements for activating or down-regulating immune responses through immunoglobulin immune complex. Here, we examined the potential role of inhibitory Fc receptor, Fc gamma RIIb in tumor immunity using mice model. Current findings indicate that tumor-specific antibodies are induced and control tumor immunity. Deletion of Fc gamma RIIb receptor significantly improves both cellular and humoral anti-tumor immunity, delays tumor growth. These findings indicate that spontaneous antibody against tumor create the suppressive tumor microenvironment through Fc gamma RIIb signaling, and suggests attractive therapeutic target for cancer immunotherapy. Citation Format: Yuki Kasahara, Hidekazu Shirota, Chikashi Ishioka. Contribution of FcγRIIB to creating the suppressive tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4731.