Affinity of human IgG subclasses to mouse Fc gamma receptors

Functional Attributes of Antibodies, Effector Cells, and Target Cells Affecting NK Cell-Mediated Antibody-Dependent Cellular Cytotoxicity

Ab-dependent cellular cytotoxicity (ADCC) is one of the most important effector mechanisms of tumor-targeting Abs in current immunotherapies. In ADCC and other Ab-dependent activation of myeloid effector cells, close cell-cell contact (between effector and target cell) and formation of immunological synapses are required. However, we still lack basic knowledge on the principal factors influencing ADCC potential by therapeutic Abs. In this study we investigated the combined roles of five factors affecting human NK cell-mediated ADCC, namely: 1) Ag density, 2) target cell membrane composition, 3) IgG FcγR polymorphism, 4) FcγR-blocking cytophilic Abs, and 5) Ab fucosylation. We demonstrate that the magnitude of NK cell-mediated ADCC responses is predominantly influenced by Ag density and Ab fucosylation. Afucosylation consistently induced efficient ADCC, even at very low Ag density, where fucosylated target Abs did not elicit ADCC. On the side of the effector cell, the FcγRIIIa-Val/Phe158 polymorphism influenced ADCC potency, with NK cells expressing the Val158 variant showing more potent ADCC. In addition, we identified the sialic acid content of the target cell membrane as an important inhibitory factor for ADCC. Furthermore, we found that the presence and glycosylation status of aspecific endogenous Abs bound to NK cell FcγRIIIa (cytophilic Abs) determine the blocking effect on ADCC. These five parameters affect the potency of Abs in vitro and should be further tested as predictors of in vivo capacity.

Synergistic cancer immunotherapy combines MVA-CD40L induced innate and adaptive immunity with tumor targeting antibodies

Virus-based vaccines and appropriate costimulation potently enhance antigen-specific T cell immunity against cancer. Here we report the use of recombinant modified vaccinia virus Ankara (rMVA) encoding costimulatory CD40L against solid tumors. Therapeutic treatment with rMVA-CD40L-expressing tumor-associated antigens results in the control of established tumors. The expansion of tumor-specific cytotoxic CD8⁺ T cells is essential for the therapeutic antitumor effects. Strikingly, rMVA-CD40L also induces strong natural killer (NK) cell activation and expansion. Moreover, the combination of rMVA-CD40L and tumor-targeting antibodies results in increased therapeutic antitumor efficacy relying on the presence of Fc receptor and NK cells. We describe a translationally relevant therapeutic synergy between systemic viral vaccination and CD40L costimulation. We show strengthened antitumor immune responses when both rMVA-CD40L-induced innate and adaptive immune mechanisms are exploited by combination with tumor-targeting antibodies. This immunotherapeutic approach could translate into clinical cancer therapies where tumor-targeting antibodies are employed.

CD40 agonists have been investigated as a strategy to awaken the immune system against cancers. Here, the authors use a virus encoding CD40L and tumour-associated antigens to enhance innate and adaptive immunity that together with tumour targeting antibodies controls the growth of tumours in mice.

Development of a Pertactin-Coated Beads Approach for Screening of Functional Monoclonal Antibodies

Vaccine manufacturers have recently focused on the development of in vitro potency assays to promote 3R's strategy to replace animal testing. To be able to develop an in vitro potency assay, the immunological characteristics of the monoclonal antibodies used in the assay should be well understood as these antibodies likely reflect the biological activity of a vaccine product. The PRN antigen is one of the immunogenic antigens included in many commercialized acellular pertussis vaccines. Development of an in vitro potency assay for PRN is challenging as the biological properties of PRN are not well understood. In addition, binding of Bordetella pertussis to human cells occurs through multiple bacterial molecules, which makes it very challenging to assess if antibodies contribute to prevention of bacterial adhesion. To overcome these challenges, the functionality of several in-house anti-PRN mAbs has been investigated through a novel approach using PRN-coated beads. We were able to consistently quantify the inhibition of PRN-mediated adhesion for each anti-PRN mAb. Application of the protein-coated beads model has not only enabled screening of functional anti-PRN mAbs but can also be expanded for screening of antibodies against other bacterial or viral antigens.

Neutralizing antibodies against Mayaro virus require Fc effector functions for protective activity

Despite causing outbreaks of fever and arthritis in multiple countries, no countermeasures exist against Mayaro virus (MAYV), an emerging mosquito-transmitted alphavirus. We generated 18 neutralizing mAbs against MAYV, 11 of which had "elite" activity that inhibited infection with EC50 values of <10 ng/ml. Antibodies with the greatest inhibitory capacity in cell culture mapped to epitopes near the fusion peptide of E1 and in domain B of the E2 glycoproteins. Unexpectedly, many of the elite neutralizing mAbs failed to prevent MAYV infection and disease in vivo. Instead, the most protective mAbs bound viral antigen on the cell surface with high avidity and promoted specific Fc effector functions, including phagocytosis by neutrophils and monocytes. In subclass switching studies, murine IgG2a and humanized IgG1 mAb variants controlled infection better than murine IgG1 and humanized IgG1-N297Q variants. An optimally protective antibody response to MAYV and possibly other alphaviruses may require tandem virus neutralization by the Fab moiety and effector functions of the Fc region.

Mouse IgG2a Antibodies Specific for the Commensal Streptococcus mitis Show Stronger Cross-Reactivity with Streptococcus pneumoniae than IgG1 Antibodies

Here we show that mouse IgG2a and IgG1 antibodies specific for the commensal Streptococcus mitis cross-react with pathogen Streptococcus pneumoniae serotypes 2 and 4, although the cross-reactivity conferred by IgG2a is stronger than that by IgG1 antibodies. These findings may be important for understanding the S. mitis-induced IgG isotype responses and have consequences for the development of an effective pneumococcal vaccine.

Single-Cell Intravital Microscopy of Trastuzumab Quantifies Heterogeneous in vivo Kinetics

Cell-to-cell heterogeneity can substantially impact drug response, especially for monoclonal antibody (mAb) therapies that may exhibit variability in both delivery (pharmacokinetics) and action (pharmacodynamics) within solid tumors. However, it has traditionally been difficult to examine the kinetics of mAb delivery at a single-cell level and in a manner that enables controlled dissection of target-dependent and -independent behaviors. To address this issue, here we developed an in vivo confocal (intravital) microscopy approach to study single-cell mAb pharmacology in a mosaic xenograft comprising a mixture of cancer cells with variable expression of the receptor HER2. As a proof-of-principle, we applied this model to trastuzumab therapy, a HER2-targeted mAb widely used for treating breast and gastric cancer patients. Trastuzumab accumulated to a higher degree in HER2-over expressing tumor cells compared to HER2-low tumor cells (~5:1 ratio at 24 h after administration) but importantly, the majority actually accumulated in tumor-associated phagocytes. For example, 24 h after IV administration over 50% of tumoral trastuzumab was found in phagocytes whereas at 48 h it was >80%. Altogether, these results reveal the dynamics of how phagocytes influence mAb behavior in vivo, and demonstrate an application of intravital microscopy for quantitative single-cell measurement of mAb distribution and retention in tumors with heterogeneous target expression. © 2019 International Society for Advancement of Cytometry.

Functional diversification of hybridoma-produced antibodies by CRISPR/HDR genomic engineering

Hybridoma technology is instrumental for the development of novel antibody therapeutics and diagnostics. Recent preclinical and clinical studies highlight the importance of antibody isotype for therapeutic efficacy. However, since the sequence encoding the constant domains is fixed, tuning antibody function in hybridomas has been restricted. Here, we demonstrate a versatile CRISPR/HDR platform to rapidly engineer the constant immunoglobulin domains to obtain recombinant hybridomas, which secrete antibodies in the preferred format, species, and isotype. Using this platform, we obtained recombinant hybridomas secreting Fab' fragments, isotype-switched chimeric antibodies, and Fc-silent mutants. These antibody products are stable, retain their antigen specificity, and display their intrinsic Fc-effector functions in vitro and in vivo. Furthermore, we can site-specifically attach cargo to these antibody products via chemoenzymatic modification. We believe that this versatile platform facilitates antibody engineering for the entire scientific community, empowering preclinical antibody research.

Targeting B-cell malignancies with the beta-emitting anti-CD37 radioimmunoconjugate 177Lu-NNV003

Purpose

The aim of this study was to explore the β-emitting lutetium-177 labelled anti-CD37 antibody NNV003 (¹⁷⁷Lu-NNV003, Humalutin®) for the treatment of non-Hodgkin’s lymphoma in in vitro studies and in animal models.

Methods

Cytotoxicity of ¹⁷⁷Lu-NNV003 was measured in REC-1 (mantle cell lymphoma) and DOHH-2 (diffuse large B cell lymphoma) cell lines. Biodistribution was studied in mice bearing subcutaneous DOHH-2 or MEC-2 (chronic lymphocytic leukaemia) xenografts. The therapeutic effect of a single injection of ¹⁷⁷Lu-NNV003 was measured in mice intravenously or subcutaneously injected with REC-1 cells. Haematological and histopathological assessments were used to evaluate the toxic effect of ¹⁷⁷Lu-NNV003. The immunotherapeutic effect of NNV003 was assessed by measuring binding to Fcγ receptors, activation of ADCC and ADCP. NNV003’s immunogenicity potential was assessed using in silico immunogenicity prediction tools.

Results

¹⁷⁷Lu-NNV003 showed an activity dependent antiproliferative effect in all cell lines. Maximum tumour uptake in vivo was 45% of injected activity/g in MEC-2 tumours and 15% injected activity/g in DOHH-2 tumours. In mice injected intravenously with REC-1 cells, ¹⁷⁷Lu-NNV003 (50–100 MBq/kg) improved survival compared to control groups (p < 0.02). In mice with subcutaneous REC-1 xenografts, 500 MBq/kg ¹⁷⁷Lu-NNV003 extended survival compared to the control treatments (p < 0.005). Transient haematological toxicity was observed in all mice treated with radioactivity. NNV003 induced ADCC and ADCP and was predicted to have a lower immunogenicity potential than its murine counterpart.

Conclusion

¹⁷⁷Lu-NNV003 had a significant anti-tumour effect and a favourable toxicity profile. These results warrant further clinical testing in patients with CD37-expressing B cell malignancies.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04417-1) contains supplementary material, which is available to authorized users.

Differentiation between control subjects and patients with chronic spontaneous urticaria based on the ability of anti-IgE autoantibodies (AAbs) to induce FcεRI crosslinking, as compared to anti-FcεRIα AAbs

BACKGROUND

The reported prevalences of IgG autoantibodies (AAbs) to FcεRIα and IgE in sera from patients with chronic spontaneous urticaria (CSU) have varied, and these AAbs are also often observed in healthy control subjects. Regarding the histamine release activity of purified IgG from patients with CSU, the number of examined patients has been small. Thus, we sought to determine the prevalence and FcεRI crosslinking ability of these AAbs in a large number of patients with CSU and non-atopic control (NC) subjects.

METHODS

We compared the concentrations of anti-IgE and anti-FcεRIα AAbs and the abilities of these AAbs to cause FcεRI aggregation in patients with CSU (n = 134) and NC subjects (n = 55) using ELISA and an in vitro elicitation test, respectively.

RESULTS

The concentration of anti-IgE AAbs was significantly different between the NC subjects and the CSU patients (P < 0.0001, cutoff value: 0.558 μg/mL), whereas the concentration of anti-FcεRIα AAbs was not. A significant difference in the duration of illness was noted between patients with lower and those with higher concentrations of anti-IgE AAbs relative to the cutoff value. The abilities of anti-IgE AAbs, but not anti-FcεRIα AAbs, to induce FcεRI crosslinking were significantly higher in CSU patients than in NC subjects (P = 0.0106).

CONCLUSIONS

In the Japanese population of CSU patients studied, the ability of the anti-IgE AAbs to induce FcεRI crosslinking differed significantly between NC subjects and CSU patients, suggesting the involvement of anti-IgE AAbs in the pathogenesis of CSU in the Japanese population.

Reduced FcRn-mediated transcytosis of IgG2 due to a missing Glycine in its lower hinge

Neonatal Fc-receptor (FcRn), the major histocompatibility complex (MHC) class I-like Fc-receptor, transports immunoglobuline G (IgG) across cell layers, extending IgG half-life in circulation and providing newborns with humoral immunity. IgG1 and IgG2 have similar half-lives, yet IgG2 displays lower foetal than maternal concentration at term, despite all known FcRn binding residues being preserved between IgG1 and IgG2. We investigated FcRn mediated transcytosis of V_H-matched IgG1 and IgG2 and mutated variants thereof lacking Fc-gamma receptor (FcγR) binding in human cells expressing FcRn. We observed that FcγR binding was not required for transport and that FcRn transported less IgG2 than IgG1. Transport of IgG1 with a shortened lower hinge (ΔGly236, absent in germline IgG2), was reduced to levels equivalent to IgG2. Conversely, transport of IgG2 + Gly236 was increased to IgG1 levels. Gly236 is not a contact residue between IgG and FcRn, suggesting that its absence leads to an altered conformation of IgG, possibly due to a less flexible Fab, positioned closer to the Fc portion. This may sterically hinder FcRn binding and transport. We conclude that the lack of Gly236 is sufficient to explain the reduced FcRn-mediated IgG2 transcytosis and accounts for the low maternal/fetal IgG2 ratio at term.

The possible role of cross-reactive dengue virus antibodies in Zika virus pathogenesis

Zika virus (ZIKV) has been known for decades to circulate in Africa and Asia. However, major complications of a ZIKV infection have recently become apparent for reasons that are still not fully elucidated. One of the hypotheses for the seemingly increased pathogenicity of ZIKV is that cross-reactive dengue antibodies can enhance a ZIKV infection through the principle of antibody-dependent enhancement (ADE). Recently, ADE in ZIKV infection has been studied, but conclusive evidence for the clinical importance of this principle in a ZIKV infection is lacking. Conversely, the widespread circulation of ZIKV in dengue virus (DENV)-endemic regions raises new questions about the potential contribution of ZIKV antibodies to DENV ADE. In this review, we summarize the results of the evidence to date and elaborate on other possible detrimental effects of cross-reactive flavivirus antibodies, both for ZIKV infection and the risk of ZIKV-related congenital anomalies, DENV infection, and dengue hemorrhagic fever.

Programming Isotype-Specific Plasma Cell Function

Helper T cell induced plasma cells (PCs) that secrete class-switched neutralizing antibody are paramount to effective immunity. Following class-switch recombination (CSR), antigen-activated B cells differentiate into extrafollicular PCs or mature in germinal centers (GCs) to produce high-affinity memory B cells and follicular PCs. Many studies focus on the core transcriptional programs that drive central PC functions of longevity and antibody secretion. However, it is becoming clear that these central programs are further subdivided across antibody isotype with separable transcriptional trajectories. Divergent functions emerge at CSR, persist through PC terminal differentiation and further assort memory PC function following antigen recall. Here, we emphasize recent work that assorts divergent isotype-specific PC function across four major modules of immune protection.

Idelalisib for optimized CD19-specific chimeric antigen receptor T cells in chronic lymphocytic leukemia patients

Despite encouraging results with chimeric antigen receptor T (CART) cells, outcome can still be improved by optimization of the CART cell generation process. The proportion of less-differentiated T cells within the transfused product is linked to enhanced in vivo CART cell expansion and long-term persistence. The clinically approved PI3Kδ inhibitor idelalisib is well established in the treatment of B cell malignancies. Besides B cell receptor pathway inhibition, idelalisib can modulate T cell differentiation and function. Here, detailed longitudinal analysis of idelalisib-induced effects on T cell phenotype and function was performed during CART cell production. A third generation CD19.CAR.CD28.CD137zeta CAR vector system was used. CART cells were generated from peripheral blood mononuclear cells of healthy donors (HDs) and chronic lymphocytic leukemia (CLL) patients. Idelalisib-based CART cell generation resulted in an enrichment of less-differentiated naïve-like T cells (CD45RA+CCR7+), decreased expression of the exhaustion markers PD-1 and Tim-3, as well as upregulation of the lymph node homing marker CD62L. Idelalisib increased transduction efficiency, but did not impair viability and cell expansion. Strikingly, CD4:CD8 ratios that were altered in CART cells from CLL patients were approximated to ratios in HDs by idelalisib. Furthermore, in vivo efficacy of idelalisib-treated CART cells was validated in a xenograft mouse model. Intracellular TNF-α and IFN-γ production decreased in presence of idelalisib. This effect was reversible after resting CART cells without idelalisib. In summary, PI3Kδ inhibition with idelalisib can improve CART cell products, particularly when derived from CLL patients. Further studies with idelalisib-based CART cell generation protocols are warranted.

Multiple Variables at the Leukocyte Cell Surface Impact Fc γ Receptor-Dependent Mechanisms

Fc γ receptors (FcγR) expressed on the surface of human leukocytes bind clusters of immunoglobulin G (IgG) to induce a variety of responses. Many therapeutic antibodies and vaccine-elicited antibodies prevent or treat infectious diseases, cancers and autoimmune disorders by binding FcγRs, thus there is a need to fully define the variables that impact antibody-induced mechanisms to properly evaluate candidate therapies and design new intervention strategies. A multitude of factors influence the IgG-FcγR interaction; one well-described factor is the differential affinity of the six distinct FcγRs for the four human IgG subclasses. However, there are several other recently described factors that may prove more relevant for disease treatment. This review covers recent reports of several aspects found at the leukocyte membrane or outside the cell that contribute to the cell-based response to antibody-coated targets. One major focus is recent reports covering post-translational modification of the FcγRs, including asparagine-linked glycosylation. This review also covers the organization of FcγRs at the cell surface, and properties of the immune complex. Recent technical advances provide high-resolution measurements of these often-overlooked variables in leukocyte function and immune system activation.

The Impact of FcγRI Binding on Immuno-PET

Antibodies are promising vectors for PET imaging. However, the high uptake of radioimmunoconjugates in nontarget tissues such as the liver and spleen hampers their performance as radiotracers. This off-target uptake can lead to suboptimal tumor-to-background activity concentration ratios, decreasing the contrast of images and reducing their diagnostic utility. A possible cause of this uptake is the sequestration of radioimmunoconjugates by immune cells bearing Fc-γ-receptors (FcγR) that bind to the Fc regions of antibodies. Methods: Since the heavy chain glycans influence the affinity of FcγR for the Fc domain, we set out to investigate whether radioimmunoconjugates with truncated glycans would exhibit altered binding to FcγRI and, in turn, improved in vivo performance. Using the HER2-targeting antibody trastuzumab, we synthesized a series of desferrioxamine-bearing immunoconjugates with differing glycosylation states and interrogated their FcγRI binding via surface plasmon resonance, enzyme-linked immunosorbent assay, and flow cytometry. Furthermore, we labeled these immunoconjugates with ⁸⁹Zr and explored their biodistribution in athymic nude, NSG, and humanized NSG mice bearing human epidermal growth factor receptor 2-expressing human breast cancer xenografts. Results: We observed a strong correlation between the impaired in vitro FcγRI binding of deglycosylated immunoconjugates and significant decreases in the in vivo off-target uptake of the corresponding ⁸⁹Zr-labeled radioimmunoconjugates (i.e., liver activity concentrations are reduced by ∼3.5-fold in humanized NSG mice). These reductions in off-target uptake were accompanied by concomitant increases in the tumoral activity concentrations of the glycoengineered radioimmunoconjugates, ultimately yielding improved tumor-to-healthy organ contrast and higher quality PET images. Conclusion: Our findings suggest that the deglycosylation of antibodies represents a facile strategy for improving the quality of immuno-PET in animal models as well as in certain patient populations.

The Binding of Human IgG to Minipig FcγRs - Implications for Preclinical Assessment of Therapeutic Antibodies

Purpose

The Göttingen minipig is a relevant non-rodent species for regulatory toxicological studies. Yet, its use with therapeutic antibodies has been limited by the unknown binding properties of human immunoglobulins (huIgG) to porcine Fc gamma receptors (poFcγR) influencing safety and efficacy readouts. Therefore, knowing IgG-FcγR interactions in the animal model is a prerequisite for the use of minipigs in preclinical safety and efficacy studies with therapeutic antibodies.

Methods

Here, we describe the cloning and expression of poFcγRs and their interactions with free and complexed human therapeutic IgG1 by surface plasmon resonance and flow cytometry.

Results

We show here that poFcγRIa, poFcγRIIa, and poFcγRIIb bind huIgG1 antibodies with comparable affinities as corresponding huFcγRs. Importantly, poFcγRs bind huIgG immune complexes with high avidity, thus probably allowing human-like effector functions. However, poFcγRIIIa binds poIgG1a but not to huIgG1.

Conclusions

The lack of binding of poFcγRIIIa to huIgG1 might cause underestimation of FcγRIIIa-mediated efficacy or toxicity as mediated by porcine natural killer cells. Therefore, the suitability of minipigs in preclinical studies with human therapeutic antibodies has to be assessed case by case. Our results facilitate the use of Göttingen minipigs for assessment of human therapeutic antibodies in preclinical studies.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2574-y) contains supplementary material, which is available to authorized users.

Tumor Tissue Explant Culture of Patient-Derived Xenograft as Potential Prioritization Tool for Targeted Therapy

Despite of remarkable progress made in the head and neck cancer (HNC) therapy, the survival rate of this metastatic disease remain low. Tailoring the appropriate therapy to patients is a major challenge and highlights the unmet need to have a good preclinical model that will predict clinical response. Hence, we developed an accurate and time efficient drug screening method of tumor ex vivo analysis (TEVA) system, which can predict patient-specific drug responses. In this study, we generated six patient derived xenografts (PDXs) which were utilized for TEVA. Briefly, PDXs were cut into 2 × 2 × 2 mm3 explants and treated with clinically relevant drugs for 24 h. Tumor cell proliferation and death were evaluated by immunohistochemistry and TEVA score was calculated. Ex vivo and in vivo drug efficacy studies were performed on four PDXs and three drugs side-by-side to explore correlation between TEVA and PDX treatment in vivo. Efficacy of drug combinations was also ventured. Optimization of the culture timings dictated 24 h to be the time frame to detect drug responses and drug penetrates 2 × 2 × 2 mm3 explants as signaling pathways were significantly altered. Tumor responses to drugs in TEVA, significantly corresponds with the drug efficacy in mice. Overall, this low cost, robust, relatively simple and efficient 3D tissue-based method, employing material from one PDX, can bypass the necessity of drug validation in immune-incompetent PDX-bearing mice. Our data provides a potential rationale for utilizing TEVA to predict tumor response to targeted and chemo therapies when multiple targets are proposed.

An immunologically relevant rodent model demonstrates safety of therapy using a tumour-specific IgE

BACKGROUND

Designing biologically informative models for assessing the safety of novel agents, especially for cancer immunotherapy, carries substantial challenges. The choice of an in vivo system for studies on IgE antibodies represents a major impediment to their clinical translation, especially with respect to class-specific immunological functions and safety. Fcε receptor expression and structure are different in humans and mice, so that the murine system is not informative when studying human IgE biology. By contrast, FcεRI expression and cellular distribution in rats mirror that of humans.

METHODS

We are developing MOv18 IgE, a human chimeric antibody recognizing the tumour-associated antigen folate receptor alpha. We created an immunologically congruent surrogate rat model likely to recapitulate human IgE-FcεR interactions and engineered a surrogate rat IgE equivalent to MOv18. Employing this model, we examined in vivo safety and efficacy of antitumour IgE antibodies.

RESULTS

In immunocompetent rats, rodent IgE restricted growth of syngeneic tumours in the absence of clinical, histopathological or metabolic signs associated with obvious toxicity. No physiological or immunological evidence of a "cytokine storm" or allergic response was seen, even at 50 mg/kg weekly doses. IgE treatment was associated with elevated serum concentrations of TNFα, a mediator previously linked with IgE-mediated antitumour and antiparasitic functions, alongside evidence of substantially elevated tumoural immune cell infiltration and immunological pathway activation in tumour-bearing lungs.

CONCLUSION

Our findings indicate safety of MOv18 IgE, in conjunction with efficacy and immune activation, supporting the translation of this therapeutic approach to the clinical arena.

In Vivo Delivery of Synthetic Human DNA-Encoded Monoclonal Antibodies Protect against Ebolavirus Infection in a Mouse Model

Synthetically engineered DNA-encoded monoclonal antibodies (DMAbs) are an in vivo platform for evaluation and delivery of human mAb to control against infectious disease. Here, we engineer DMAbs encoding potent anti-Zaire ebolavirus (EBOV) glycoprotein (GP) mAbs isolated from Ebola virus disease survivors. We demonstrate the development of a human IgG1 DMAb platform for in vivo EBOV-GP mAb delivery and evaluation in a mouse model. Using this approach, we show that DMAb-11 and DMAb-34 exhibit functional and molecular profiles comparable to recombinant mAb, have a wide window of expression, and provide rapid protection against lethal mouse-adapted EBOV challenge. The DMAb platform represents a simple, rapid, and reproducible approach for evaluating the activity of mAb during clinical development. DMAbs have the potential to be a mAb delivery system, which may be advantageous for protection against highly pathogenic infectious diseases, like EBOV, in resource-limited and other challenging settings.

Development of a simple new flow cytometric antibody-dependent cellular cytotoxicity (ADCC) assay with excellent sensitivity

Antibody-based therapeutic strategies have become recognized as useful clinical options in several types of cancer, often with the expectation that such therapies will trigger target cell elimination via antibody-dependent cellar cytotoxicity (ADCC) by natural killer cells. The successful development of therapeutic monoclonal antibodies (mAbs) requires an assay system that permits a critical evaluation of their physicochemical and biological characteristics. At present a number of ADCC assay systems have been reported, however, there is still room for improvement in terms of usability, operability and sensitivity. Here we report a novel flow cytometric ADCC assay that uses a human natural killer cell line stably transfected with mouse FcγRIII, and Fc receptor common-γ chain (FcRγ) and a reporter gene as effector cells. This assay relies on discriminating effector and target cells by their differential immunofluorescence, which allows for clear-cut gating and accurate calculation of the number of surviving cells in a target population. This assay is easy and quick to perform and provides reliable data even for low frequency target cells in assay samples and with low concentrations of mAbs. Furthermore, our approach allows us to identify synergistic ADCC activity of mAbs with different epitope specificities on the same target antigen.

Modulation of Antibody Responses to the V1V2 and V3 Regions of HIV-1 Envelope by Immune Complex Vaccines

Prophylactic HIV vaccines must elicit antibodies (Abs) against the virus envelope glycoproteins (Env) to effectively prevent HIV infection. We investigated a vaccine platform that utilizes immune complexes made of Env proteins gp120 and monoclonal Abs (mAbs) against different gp120 epitopes. We previously observed alterations in V3 antigenicity upon formation of certain gp120/mAb complexes and demonstrated the ability of these complexes to modulate the elicitation of V3 Ab responses. However, the effects on the V1V2 domain, an important target for Abs that correlate with vaccine-induced protection against HIV, have not been studied, nor have immune complex vaccines made with non-B subtype Env. This study compared subtypes B (JRFL) and CRF_01.AE (A244) Env gp120 proteins in complex with selected gp120-specific mAbs. Allosteric and antigenic changes were detected on these immune complexes, indicating that gp120/mAb interaction induces alterations on the Env surface that may modify the Env immunogenic properties. To evaluate this idea, mice were immunized with gp120/mAb complexes or their uncomplexed gp120 counterparts. The overall serum IgG titers elicited against gp120 were comparable, but a marked skewing toward V1V2 or V3 was evident and dependent on the gp120 strain and the specificity of the mAb used to form the complexes. Compared with uncomplexed gp120_JRFL, gp120_JRFL complexed with CD4bs or V1V2 mAbs, but not with C2 or V3 mAbs, elicited V3 Abs of greater titers and breadth, and Abs more capable of neutralizing tier 1 virus. Epitope mapping revealed a shift to a more conserved site in the V3 crown. However, the complexes did not enhance V1V2 Ab response, and the elicited V1V2 Abs were not cross-reactive. This profile contrasts with Ab responses to gp120_A244/mAb complexes. Notably, gp120_A244/mAb complexes induced higher levels of V1V2 Abs with some cross-reactivity, while also stimulating weak or strain-specific V3 Abs. Sera from gp120_A244/mAb complex-immunized animals displayed no measurable virus neutralization but did mediate Ab-dependent cellular phagocytosis, albeit at levels similar to that induced by gp120_A244 alone. These data indicate the potential utility of immune complexes as vaccines to shape Ab responses toward or away from Env sites of interest.

Trastuzumab upregulates PD-L1 as a potential mechanism of trastuzumab resistance through engagement of immune effector cells and stimulation of IFNγ secretion

Here, we report that treatment of syngeneic mouse tumors transduced to overexpress human epidermal growth factor receptor-2 (HER2) with the anti-human HER2 antibody trastuzumab upregulated the level of programmed death-ligand 1 (PD-L1), an important negative regulator of T-cell response, in a transgenic mouse model immune-tolerant to human HER2. We further found that trastuzumab alone had no detectable effect on the level of PD-L1 expression in monocultures of HER2-overexpressing human breast cancer cells but upregulated PD-L1 in the same panel of HER2-overexpressing breast cancer cells when they were co-cultured with human peripheral blood mononuclear cells, and the upregulation of PD-L1 could be blocked by an IFNγ-neutralizing antibody. Inhibition of HER2 intrinsic signaling via HER2 expression knockdown or kinase inhibition had variable and cell-context-specific effects on downregulating the PD-L1 level. Analysis of The Cancer Genome Atlas database showed no direct correlation between HER2 and PD-L1 at the messenger RNA level. Trastuzumab-mediated upregulation of PD-L1 through engagement of immune effector cells may function as a potential mechanism of trastuzumab resistance. Our data justify further investigation of the value of adding anti-PD-1 or anti-PD-L1 therapy to trastuzumab-based treatment.

Fc-Mediated Anomalous Biodistribution of Therapeutic Antibodies in Immunodeficient Mouse Models

A critical benchmark in the development of antibody-based therapeutics is demonstration of efficacy in preclinical mouse models of human disease, many of which rely on immunodeficient mice. However, relatively little is known about how the biology of various immunodeficient strains impacts the in vivo fate of these drugs. Here we used immunoPET radiotracers prepared from humanized, chimeric, and murine mAbs against four therapeutic oncologic targets to interrogate their biodistribution in four different strains of immunodeficient mice bearing lung, prostate, and ovarian cancer xenografts. The immunodeficiency status of the mouse host as well as both the biological origin and glycosylation of the antibody contributed significantly to the anomalous biodistribution of therapeutic monoclonal antibodies in an Fc receptor-dependent manner. These findings may have important implications for the preclinical evaluation of Fc-containing therapeutics and highlight a clear need for biodistribution studies in the early stages of antibody drug development.Significance: Fc/FcγR-mediated immunobiology of the experimental host is a key determinant to preclinical in vivo tumor targeting and efficacy of therapeutic antibodies. Cancer Res; 78(7); 1820-32. ©2018 AACR.

Vaccination with a Recombinant H7 Hemagglutinin-Based Influenza Virus Vaccine Induces Broadly Reactive Antibodies in Humans

Zoonotic infections with high case fatality rates caused by avian H7N9 influenza viruses have been reported since early 2013 in China. Since then, the fifth wave of the H7N9 epidemic emerged in China, resulting in higher numbers of laboratory-confirmed cases than in previous years. Recently, H7N9 has started to antigenically drift and split into two new lineages, the Pearl River Delta and Yangtze River Delta clades, which do not match stockpiled H7 vaccines well. Humans are immunologically naive to these subtypes, and an H7N9 strain that acquires the capability of efficient human-to-human transmission poses a credible pandemic threat. Other characteristics of H7N9 are raising concerns as well, like its ability to bind to receptors in the human upper respiratory tract, the recent emergence of highly pathogenic variants, and the ability to quickly gain resistance to neuraminidase inhibitors. Therefore, developing and testing H7N9 vaccines constitutes a priority for pandemic preparedness.

Human influenza virus infections with avian subtype H7N9 viruses are a major public health concern and have encouraged the development of effective H7 prepandemic vaccines. In this study, baseline and postvaccination serum samples of individuals aged 18 years and older who received a recombinant H7 hemagglutinin vaccine with and without an oil-in-water emulsion (SE) adjuvant were analyzed using a panel of serological assays. While only a small proportion of individuals seroconverted to H7N9 as measured by the conventional hemagglutination inhibition assay, our data show strong induction of anti-H7 hemagglutinin antibodies as measured by an enzyme-linked immunosorbent assay (ELISA). In addition, cross-reactive antibodies against phylogenetically distant group 2 hemagglutinins were induced, presumably targeting the conserved stalk domain of the hemagglutinin. Further analysis confirmed an induction of stalk-specific antibodies, suggesting that epitopes outside the classical antigenic sites are targeted by this vaccine in the context of preexisting immunity to related H3 hemagglutinin. Antibodies induced by H7 vaccination also showed functional activity in antibody-dependent cell-mediated cytotoxicity reporter assays and microneutralization assays. Additionally, our data show that sera from hemagglutination inhibition seroconverters conferred protection in a passive serum transfer experiment against lethal H7N9 virus challenge in mice. Interestingly, sera from hemagglutination inhibition nonseroconverters also conferred partial protection in the lethal animal challenge model. In conclusion, while recombinant H7 vaccination fails to induce measurable levels of hemagglutination-inhibiting antibodies in most subjects, this vaccination regime induces homosubtypic and heterosubtypic cross-reactive binding antibodies that are functional and partly protective in a murine passive transfer challenge model.

IMPORTANCE Zoonotic infections with high case fatality rates caused by avian H7N9 influenza viruses have been reported since early 2013 in China. Since then, the fifth wave of the H7N9 epidemic emerged in China, resulting in higher numbers of laboratory-confirmed cases than in previous years. Recently, H7N9 has started to antigenically drift and split into two new lineages, the Pearl River Delta and Yangtze River Delta clades, which do not match stockpiled H7 vaccines well. Humans are immunologically naive to these subtypes, and an H7N9 strain that acquires the capability of efficient human-to-human transmission poses a credible pandemic threat. Other characteristics of H7N9 are raising concerns as well, like its ability to bind to receptors in the human upper respiratory tract, the recent emergence of highly pathogenic variants, and the ability to quickly gain resistance to neuraminidase inhibitors. Therefore, developing and testing H7N9 vaccines constitutes a priority for pandemic preparedness.

Decoding the Human Immunoglobulin G-Glycan Repertoire Reveals a Spectrum of Fc-Receptor- and Complement-Mediated-Effector Activities

Glycosylation of the immunoglobulin G (IgG)-Fc tail is required for binding to Fc-gamma receptors (FcγRs) and complement-component C1q. A variety of IgG1-glycoforms is detected in human sera. Several groups have found global or antigen-specific skewing of IgG glycosylation, for example in autoimmune diseases, viral infections, and alloimmune reactions. The IgG glycoprofiles seem to correlate with disease outcome. Additionally, IgG-glycan composition contributes significantly to Ig-based therapies, as for example IVIg in autoimmune diseases and therapeutic antibodies for cancer treatment. The effect of the different glycan modifications, especially of fucosylation, has been studied before. However, the contribution of the 20 individual IgG glycoforms, in which the combined effect of all 4 modifications, to the IgG function has never been investigated. Here, we combined six glyco-engineering methods to generate all 20 major human IgG1-glycoforms and screened their functional capacity for FcγR and complement activity. Bisection had no effect on FcγR or C1q-binding, and sialylation had no- or little effect on FcγR binding. We confirmed that hypo-fucosylation of IgG1 increased binding to FcγRIIIa and FcγRIIIb by ~17-fold, but in addition we showed that this effect could be further increased to ~40-fold for FcγRIIIa upon simultaneous hypo-fucosylation and hyper-galactosylation, resulting in enhanced NK cell-mediated antibody-dependent cellular cytotoxicity. Moreover, elevated galactosylation and sialylation significantly increased (independent of fucosylation) C1q-binding, downstream complement deposition, and cytotoxicity. In conclusion, fucosylation and galactosylation are primary mediators of functional changes in IgG for FcγR- and complement-mediated effector functions, respectively, with galactose having an auxiliary role for FcγRIII-mediated functions. This knowledge could be used not only for glycan profiling of clinically important (antigen-specific) IgG but also to optimize therapeutic antibody applications.