The adaptive immune system confers protection by generating a diverse repertoire of antibody receptors that are rapidly expanded and contracted in response to specific targets. Next-generation DNA sequencing now provides the opportunity to survey this complex and vast repertoire. In the present work, we describe a set of tools for the analysis of antibody repertoires and their application to elucidating the dynamics of the response to viral vaccination in human volunteers. By analyzing data from 38 separate blood samples across 2 y, we found that the use of the germ-line library of V and J segments is conserved between individuals over time. Surprisingly, there appeared to be no correlation between the use level of a particular VJ combination and degree of expansion. We found the antibody RNA repertoire in each volunteer to be highly dynamic, with each individual displaying qualitatively different response dynamics. By using combinatorial phage display, we screened selected VH genes paired with their corresponding VL library for affinity against the vaccine antigens. Altogether, this work presents an additional set of tools for profiling the human antibody repertoire and demonstrates characterization of the fast repertoire dynamics through time in multiple individuals responding to an immune challenge.next-generation sequencing | influenza | immunology T he immune system is able to rapidly sense and respond to a vast array of invading organisms. Its arsenal contains systems that are immediately effective against commonly seen patterns (innate immunity) and systems that are capable of responding to novel invaders (adaptive immunity). Given the acute nature and diversity of infections, the immune system must be capable of rapid recognition of a pathogen, amplification of the response, and subsequent contraction of the response after the resolution of the infection. Adaptive immune responses rely on the continuous selection and amplification of specific clones from an enormous library of immune receptors (antibodies and T cell receptors). Specifically, stimulation of B-cell immunity results in the synthesis of antibodies that are secreted into the blood stream or into the mucosa as well as the programming of B memory cells that play a crucial role in the generation of rapid protective responses upon reinfection.Currently, many immunology studies depend on characterizing lymphocyte subsets (e.g., assaying cell-surface receptors) and the ability to correlate them to encoded genetic information (1). Recent advances in next-generation sequencing (NGS) (2) have enabled any DNA-encodable assay to produce massive amounts of data. Indeed, NGS has enabled unprecedented views into the immune repertoire, as its immune receptor diversity is genetically encoded within a complex collection of lymphocytes (3-8).The present study set out to dissect the rapid dynamics of the complete human peripheral antibody response against a controlled immune challenge (vaccination), without the a priori notion of cell state markers or functions...

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Glycans anchored to residue N297 of the antibody IgG Fc domain are critical in mediating binding toward FcγRs to direct both adaptive and innate immune responses. However, using a full length bacterial IgG display system, we have isolated aglycosylated Fc domains with mutations that confer up to a 160-fold increase in the affinity toward the low affinity FcγRIIa-R131 allele as well as high selectivity against binding to the remarkably homologous human inhibitory receptor, FcγRIIb. The mutant Fc domain (AglycoT-Fc1004) contained a total of 5 amino acid substitutions that conferred an activating to inhibitory ratio of 25 (A/I ratio; FcyRIIa-R131:FcγRIIb). Incorporation of this engineered Fc into trastuzumab, an anti-Her2 antibody, resulted in a 75% increase in tumor cell phagocytosis by macrophages compared to that of the parental glycosylated trastuzumab with both medium and low Her2-expressing cancer cells. A mathematical model has been developed to help explain how receptor affinity and the A/I ratio relate to improved antibody dependent cell-mediated phagocytosis. Our model provides guidelines for the future engineering of Fc domains with enhanced effector function.

All clinically approved antibodies are of the IgG isotype and mediate the clearance of target cells via binding to Fcγ receptors and complement (C1q). Even though IgA can elicit powerful cytotoxic action via FcαRI receptor binding, IgA antibodies have not been amenable to therapeutic development. Here, we report the engineering of a "cross-isotype" antibody, IgGA, which combines the effector functions of both IgG and IgA. IgGA binds to FcαRI with an affinity comparable to that of IgA, and to the activating Fcγ receptors, FcγRI and FcγRIIa, with high affinity, and displays increased binding to C1q compared to IgG. Unlike trastuzumab-IgG, trastuzumab-IgGA potently activates both neutrophils and macrophages to kill Her2(+) cancer cells. Furthermore, IgGA mediates greater complement-dependent cytotoxicity than IgG1 or IgA antibodies. The multitude of IgGA effector functions could be important for therapeutic purposes and highlights the concept of engineering antibodies that combine effector functions from multiple antibody isotypes.

• Fc-engineered mAb promotes NK cell ADCC via better activation, serial killing, and kinetic boosting at higher target cell densities.• Enhanced target killing also increased frequency of NK cell apoptosis, but this effect is donor-dependent.The efficacy of most therapeutic monoclonal antibodies (mAbs) targeting tumor antigens results primarily from their ability to elicit potent cytotoxicity through effectormediated functions. We have engineered the fragment crystallizable (Fc) region of the immunoglobulin G (IgG) mAb, HuM195, targeting the leukemic antigen CD33, by introducing the triple mutation Ser293Asp/Ala330Leu/Ile332Glu (DLE), and developed Time-lapse Imaging Microscopy in Nanowell Grids to analyze antibody-dependent cellmediated cytotoxicity kinetics of thousands of individual natural killer (NK) cells and mAb-coated target cells. We demonstrate that the DLE-HuM195 antibody increases both the quality and the quantity of NK cell-mediated antibody-dependent cytotoxicity by endowing more NK cells to participate in cytotoxicity via accrued CD16-mediated signaling and by increasing serial killing of target cells. NK cells encountering targets coated with DLE-HuM195 induce rapid target cell apoptosis by promoting simultaneous conjugates to multiple target cells and induce apoptosis in twice the number of target cells within the same period as the wild-type mAb. Enhanced target killing was also associated with increased frequency of NK cells undergoing apoptosis, but this effect was donor-dependent. Antibody-based therapies targeting tumor antigens will benefit from a better understanding of cell-mediated tumor elimination, and our work opens further opportunities for the therapeutic targeting of CD33 in the treatment of acute myeloid leukemia. (Blood. 2014;124(22):3241-3249) Introduction Therapeutic monoclonal antibodies (mAbs) elicit functional responses through many different mechanisms, including antibody-dependent cell-mediated cytotoxicity (ADCC), complement dependent cytotoxicity, antibody-dependent cell-mediated phagocytosis (ADCP), and direct induction of apoptosis in tumor cells.1 By using the principles of glycoengineering and mutagenesis, Fc variants have been isolated that show either increased affinity for the activating receptors or altered selectivity for the activating/inhibitory receptors. [2][3][4] Preliminary clinical data with such antibodies Fc-engineered to improve the ADCC/ADCP potential and targeting CD19, CD20, Her2, or CD40 have shown reasonable promise in improving the therapeutic potential of mAb.5-8 Natural killer (NK) cells occupy a pivotal role in immunity: not only can they exert direct cytotoxicity toward infected or tumor cells but they also participate in shaping the adaptive response. 9,10 In the context of mAb treatment, NK cells are unique in that they express only the low-affinity activating FcgR CD16 (FcgRIIIa), and no inhibitory antibody receptors, underscoring a significant role in ADCC.11-13 Several studies using mouse tumor models have established a link between ...