Modular Immune Organoids with Integrin Ligand Specificity Differentially Regulate Ex Vivo B Cell Activation

Biomaterial engineering strategies for B cell immunity modulations

B cell immunity has a penetrating effect on human health and diseases. Therapeutics aiming to modulate B cell immunity have achieved remarkable success in combating infections, autoimmunity, and malignancies. However, current treatments still face significant limitations in generating effective long-lasting therapeutic B cell responses for many conditions. As the understanding of B cell biology has deepened in recent years, clearer regulation networks for B cell differentiation and antibody production have emerged, presenting opportunities to overcome current difficulties and realize the full therapeutic potential of B cell immunity. Biomaterial platforms have been developed to leverage these emerging concepts to augment therapeutic humoral immunity by facilitating immunogenic reagent trafficking, regulating T cell responses, and modulating the immune microenvironment. Moreover, biomaterial engineering tools have also advanced our understanding of B cell biology, further expediting the development of novel therapeutics. In this review, we will introduce the general concept of B cell immunobiology and highlight key biomaterial engineering strategies in the areas including B cell targeted antigen delivery, sustained B cell antigen delivery, antigen engineering, T cell help optimization, and B cell suppression. We will also discuss our perspective on future biomaterial engineering opportunities to leverage humoral immunity for therapeutics.

New tools for immunologists: models of lymph node function from cells to tissues

The lymph node is a highly structured organ that mediates the body's adaptive immune response to antigens and other foreign particles. Central to its function is the distinct spatial assortment of lymphocytes and stromal cells, as well as chemokines that drive the signaling cascades which underpin immune responses. Investigations of lymph node biology were historically explored in vivo in animal models, using technologies that were breakthroughs in their time such as immunofluorescence with monoclonal antibodies, genetic reporters, in vivo two-photon imaging, and, more recently spatial biology techniques. However, new approaches are needed to enable tests of cell behavior and spatiotemporal dynamics under well controlled experimental perturbation, particularly for human immunity. This review presents a suite of technologies, comprising in vitro, ex vivo and in silico models, developed to study the lymph node or its components. We discuss the use of these tools to model cell behaviors in increasing order of complexity, from cell motility, to cell-cell interactions, to organ-level functions such as vaccination. Next, we identify current challenges regarding cell sourcing and culture, real time measurements of lymph node behavior in vivo and tool development for analysis and control of engineered cultures. Finally, we propose new research directions and offer our perspective on the future of this rapidly growing field. We anticipate that this review will be especially beneficial to immunologists looking to expand their toolkit for probing lymph node structure and function.

Profiling Germinal Center-like B Cell Responses to Conjugate Vaccines Using Synthetic Immune Organoids

Glycoengineered bacteria have emerged as a cost-effective platform for rapid and controllable biosynthesis of designer conjugate vaccines. However, little is known about the engagement of such conjugates with naïve B cells to induce the formation of germinal centers (GC), a subanatomical microenvironment that converts naïve B cells into antibody-secreting plasma cells. Using a three-dimensional biomaterials-based B-cell follicular organoid system, we demonstrate that conjugates triggered robust expression of hallmark GC markers, B cell receptor clustering, intracellular signaling, and somatic hypermutation. These responses depended on the relative immunogenicity of the conjugate and correlated with the humoral response in vivo. The occurrence of these mechanisms was exploited for the discovery of high-affinity antibodies against components of the conjugate on a time scale that was significantly shorter than for typical animal immunization-based workflows. Collectively, these findings highlight the potential of synthetic organoids for rapidly predicting conjugate vaccine efficacy as well as expediting antigen-specific antibody discovery.

Combinatorial treatment rescues tumour-microenvironment-mediated attenuation of MALT1 inhibitors in B-cell lymphomas

Activated B-cell-like diffuse large B-cell lymphomas (ABC-DLBCLs) are characterized by constitutive activation of nuclear factor κB driven by the B-cell receptor (BCR) and Toll-like receptor (TLR) pathways. However, BCR-pathway-targeted therapies have limited impact on DLBCLs. Here we used >1,100 DLBCL patient samples to determine immune and extracellular matrix cues in the lymphoid tumour microenvironment (Ly-TME) and built representative synthetic-hydrogel-based B-cell-lymphoma organoids accordingly. We demonstrate that Ly-TME cellular and biophysical factors amplify the BCR-MYD88-TLR9 multiprotein supercomplex and induce cooperative signalling pathways in ABC-DLBCL cells, which reduce the efficacy of compounds targeting the BCR pathway members Bruton tyrosine kinase and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1). Combinatorial inhibition of multiple aberrant signalling pathways induced higher antitumour efficacy in lymphoid organoids and implanted ABC-DLBCL patient tumours in vivo. Our studies define the complex crosstalk between malignant ABC-DLBCL cells and Ly-TME, and provide rational combinatorial therapies that rescue Ly-TME-mediated attenuation of treatment response to MALT1 inhibitors.

Pre-clinical models to define correlates of protection for SARS-CoV-2

A defined immune profile that predicts protection against a pathogen-of-interest, is referred to as a correlate of protection (CoP). A validated SARS-CoV-2 CoP has yet to be defined, however considerable insights have been provided by pre-clinical vaccine and animal rechallenge studies which have fewer associated limitations than equivalent studies in human vaccinees or convalescents, respectively. This literature review focuses on the advantages of the use of animal models for the definition of CoPs, with particular attention on their application in the search for SARS-CoV-2 CoPs. We address the conditions and interventions required for the identification and validation of a CoP, which are often only made possible with the use of appropriate in vivo models.

Engineering early memory B-cell-like phenotype in hydrogel-based immune organoids

Memory B cells originate in response to antigenic stimulation in B-cell follicles of secondary lymphoid organs where naive B cells undergo maturation within a subanatomical microenvironment, the germinal centers. The understanding of memory B-cell immunology and its regulation is based primarily on sophisticated experiments that involve mouse models. To date, limited evidence exists on whether memory B cells can be successfully engineered ex vivo, specifically using biomaterials-based platforms that support the growth and differentiation of B cells. Here, we report the characterization of a recently reported maleimide-functionalized poly(ethylene glycol) (PEG) hydrogels as immune organoids towards the development of early memory B-cell phenotype and germinal center-like B cells. We demonstrate that the use of interleukin 9 (IL9), IL21, and bacterial antigen presentation as outer membrane-bound fragments drives the conversion of naive, primary murine B cells to early memory phenotype in ex vivo immune organoids. These findings describe the induction of early memory B-cell-like phenotype in immune organoids and highlight the potential of synthetic organoids as a platform for the future development of antigen-specific bona fide memory B cells for the study of the immune system and generation of therapeutic antibodies.

Integrative lymph node-mimicking models created with biomaterials and computational tools to study the immune system

The lymph node (LN) is a vital organ of the lymphatic and immune system that enables timely detection, response, and clearance of harmful substances from the body. Each LN comprises of distinct substructures, which host a plethora of immune cell types working in tandem to coordinate complex innate and adaptive immune responses. An improved understanding of LN biology could facilitate treatment in LN-associated pathologies and immunotherapeutic interventions, yet at present, animal models, which often have poor physiological relevance, are the most popular experimental platforms. Emerging biomaterial engineering offers powerful alternatives, with the potential to circumvent limitations of animal models, for in-depth characterization and engineering of the lymphatic and adaptive immune system. In addition, mathematical and computational approaches, particularly in the current age of big data research, are reliable tools to verify and complement biomaterial works. In this review, we first discuss the importance of lymph node in immunity protection followed by recent advances using biomaterials to create in vitro/vivo LN-mimicking models to recreate the lymphoid tissue microstructure and microenvironment, as well as to describe the related immuno-functionality for biological investigation. We also explore the great potential of mathematical and computational models to serve as in silico supports. Furthermore, we suggest how both in vitro/vivo and in silico approaches can be integrated to strengthen basic patho-biological research, translational drug screening and clinical personalized therapies. We hope that this review will promote synergistic collaborations to accelerate progress of LN-mimicking systems to enhance understanding of immuno-complexity.

PLAN B for immunotherapy: Promoting and leveraging anti-tumor B cell immunity

Current immuno-oncology primarily focuses on adaptive cellular immunity mediated by T lymphocytes. The other important lymphocytes, B cells, are largely ignored in cancer immunotherapy. B cells are generally considered to be responsible for humoral immune response to viral and bacterial infections. The role of B cells in cancer immunity has long been under debate. Recently, increasing evidence from both preclinical and clinical research has shown that B cells can also induce potent anti-cancer immunity, via humoral and cellular immune responses. Yet it is unclear how to efficiently integrate B cell immunity in cancer immunotherapy. In the current perspective, anti-tumor immunity of B cells is discussed regarding antibody production, antigen presentation, cytokine release and contribution to intratumoral tertiary lymphoid structures. Afterwards, immunosuppressive regulatory phenotypes of B cells are summarized. Furthermore, strategies to activate and modulate B cells using nanomedicines and biomaterials are discussed. This article provides a unique perspective on "PLAN B" (promoting and leveraging anti-tumor B cell immunity) using nanomedicines and biomaterials for cancer immunotherapy. This is envisaged to form a new research direction with the potential to reach the next breakthrough in immunotherapy.

In Vitro Miniaturized Tuberculosis Spheroid Model

Tuberculosis (TB) is a public health concern that impacts 10 million people around the world. Current in vitro models are low throughput and/or lack caseation, which impairs drug effectiveness in humans. Here, we report the generation of THP-1 human monocyte/macrophage spheroids housing mycobacteria (TB spheroids). These TB spheroids have a central core of dead cells co-localized with mycobacteria and are hypoxic. TB spheroids exhibit higher levels of pro-inflammatory factor TNFα and growth factors G-CSF and VEGF when compared to non-infected control. TB spheroids show high levels of lipid deposition, characterized by MALDI mass spectrometry imaging. TB spheroids infected with strains of differential virulence, Mycobacterium tuberculosis (Mtb) HN878 and CDC1551 vary in response to Isoniazid and Rifampicin. Finally, we adapt the spheroid model to form peripheral blood mononuclear cells (PBMCs) and lung fibroblasts (NHLF) 3D co-cultures. These results pave the way for the development of new strategies for disease modeling and therapeutic discovery.

Lymph Nodes-On-Chip: Promising Immune Platforms for Pharmacological and Toxicological Applications

Organs-on-chip are gaining increasing attention as promising platforms for drug screening and testing applications. However, lymph nodes-on-chip options remain limited although the lymph node is one of the main determinants of the immunotoxicity of newly developed pharmacological drugs. In this review, we describe existing biomimetic lymph nodes-on-chip, their design, and their physiological relevance to pharmacology and shed the light on future directions associated with lymph node-on-chip design and implementation in drug discovery and development.

Organoid Polymer Functionality and Mode of Klebsiella Pneumoniae Membrane Antigen Presentation Regulates Ex Vivo Germinal Center Epigenetics in Young and Aged B Cells

Antibiotic-resistant bacteria are a major global health threat that continues to rise due to a lack of effective vaccines. Of concern are Klebsiella pneumoniae that fail to induce in vivo germinal center B cell responses, which facilitate antibody production to fight infection. Immunotherapies using antibodies targeting antibiotic-resistant bacteria are emerging as promising alternatives, however, they cannot be efficiently derived ex vivo, necessitating the need for immune technologies to develop therapeutics. Here, PEG-based immune organoids were developed to elucidate the effects of polymer end-point chemistry, integrin ligands, and mode of K. pneumoniae antigen presentation on germinal center-like B cell phenotype and epigenetics, to better define the lymph node microenvironment factors regulating ex vivo germinal center dynamics. Notably, PEG vinyl sulfone or acrylate failed to sustain primary immune cells, but functionalization with maleimide (PEG-4MAL) led to B cell expansion and germinal center-like induction. RNA sequencing analysis of lymph node stromal and germinal center B cells showed niche associated heterogeneity of integrin-related genes. Incorporation of niche-mimicking peptides revealed that collagen-1 promoted germinal center-like dynamics and epigenetics. PEG-4MAL organoids elucidated the impact of K. pneumoniae outer membrane-embedded protein antigen versus soluble antigen presentation on germinal centers and preserved the response across young and aged mice.

Developing a Multidisciplinary Approach for Engineering Stem Cell Organoids

Recent advances in stem cell biology, synthetic biology, bioengineering, and biotechnology have included significant work leading to the development of stem cell-derived organoids. The growing popularity of organoid research and use of organoids is widely due to the fact that these three-dimensional cellular structures better model human physiology compared to traditional in vitro and in vivo methods by recapitulating many biologically relevant parameters. Organoids show great promise for a wide range of applications, such as for use in disease modeling, drug discovery, and regenerative medicine. However, many challenges associated with reproducibility and scale up still remain. Identification of the conditions which generate a robust environment that predictably promotes cellular self-assembly and organization leading to organoid formation is critical and requires a multidisciplinary approach. To accomplish this we need to identify a cellular source, engineer a matrix to stimulate cell-cell and cell-matrix interactions, and provide the biochemical and biophysical cues which mimic that of the in vivo environment. Discussion of the components needed for organoid development and formation is reviewed herein, as well as specific organoid examples and the promise of this research for the future.

Engineered materials for organoid systems

Organoids are 3D cell culture systems that mimic some of the structural and functional characteristics of an organ. Organoid cultures provide the opportunity to study organ-level biology in models that mimic human physiology more closely than 2D cell culture systems or non-primate animal models. Many organoid cultures rely on decellularized extracellular matrices as scaffolds, which are often poorly chemically defined and allow only limited tunability and reproducibility. By contrast, the biochemical and biophysical properties of engineered matrices can be tuned and optimized to support the development and maturation of organoid cultures. In this Review, we highlight how key cell-matrix interactions guiding stem-cell decisions can inform the design of biomaterials for the reproducible generation and control of organoid cultures. We survey natural, synthetic and protein-engineered hydrogels for their applicability to different organoid systems and discuss biochemical and mechanical material properties relevant for organoid formation. Finally, dynamic and cell-responsive material systems are investigated for their future use in organoid research.

Injectable mechanical pillows for attenuation of load-induced post-traumatic osteoarthritis

Osteoarthritis (OA) of the knee joint is a degenerative disease initiated by mechanical stress that affects millions of individuals. The disease manifests as joint damage and synovial inflammation. Post-traumatic osteoarthritis (PTOA) is a specific form of OA caused by mechanical trauma to the joint. The progression of PTOA is prevented by immediate post-injury therapeutic intervention. Intra-articular injection of anti-inflammatory therapeutics (e.g. corticosteroids) is a common treatment option for OA before end-stage surgical intervention. However, the efficacy of intra-articular injection is limited due to poor drug retention time in the joint space and the variable efficacy of corticosteroids. Here, we endeavored to characterize a four-arm maleimide-functionalized polyethylene glycol (PEG-4MAL) hydrogel system as a 'mechanical pillow' to cushion the load-bearing joint, withstand repetitive loading and improve the efficacy of intra-articular injections of nanoparticles containing dexamethasone, an anti-inflammatory agent. PEG-4MAL hydrogels maintained their mechanical properties after physiologically relevant cyclic compression and released therapeutic payload in an on-demand manner under in vitro inflammatory conditions. Importantly, the on-demand hydrogels did not release nanoparticles under repetitive mechanical loading as experienced by daily walking. Although dexamethasone had minimal protective effects on OA-like pathology in our studies, the PEG-4MAL hydrogel functioned as a mechanical pillow to protect the knee joint from cartilage degradation and inhibit osteophyte formation in an in vivo load-induced OA mouse model.

Multiscale engineering of immune cells and lymphoid organs

Immunoengineering applies quantitative and materials-based approaches for the investigation of the immune system and for the development of therapeutic solutions for various diseases, such as infection, cancer, inflammatory diseases and age-related malfunctions. The design of immunomodulatory and cell therapies requires the precise understanding of immune cell formation and activation in primary, secondary and ectopic tertiary immune organs. However, the study of the immune system has long been limited to in vivo approaches, which often do not allow multidimensional control of intracellular and extracellular processes, and to 2D in vitro models, which lack physiological relevance. 3D models built with synthetic and natural materials enable the structural and functional recreation of immune tissues. These models are being explored for the investigation of immune function and dysfunction at the cell, tissue and organ levels. In this Review, we discuss 2D and 3D approaches for the engineering of primary, secondary and tertiary immune structures at multiple scales. We highlight important insights gained using these models and examine multiscale engineering strategies for the design and development of immunotherapies. Finally, dynamic 4D materials are investigated for their potential to provide stimuli-dependent and context-dependent scaffolds for the generation of immune organ models.

Ex vivo synthetic immune tissues with T cell signals for differentiating antigen-specific, high affinity germinal center B cells

Most antigen discovery and vaccine development aimed at driving functional B cell responses rely on mouse immunizations studies. To date, there is no 3D ex vivo immune tissues, which are capable of driving antigen-specific B cell responses to rapidly determine the humoral immunogenicity of antigens, understand the role of extracellular matrix in humoral immunity, and generate high affinity antibody responses. This can be attributed to the complexity of B cell differentiation and affinity maturation process in the germinal center (GC) reaction, which makes these highly specialized cells susceptible to rapid apoptosis ex vivo. We have previously reported immune tissues that show ex vivo GC-like response, however in a non-antigen specific manner. Here, we report a maleimide (MAL)-functionalized polyethylene glycol (PEG)-based designer immune tissues that modulate B cell differentiation and enriches antigen-specific GC B cells in the presence of T-cell like signals. With the 3D synthetic immune tissue platform, we assessed various hydrogel design parameters to control ex vivo GC reaction. Using an Ezh2fl/fl Cγ1-cre transgenic mouse model, we demonstrated ex vivo IgG1 antibody class switching. Using immune tissues developed from a B1-8hi mutant mouse that represents a recombined antibody variable region derived from a 4-hydroxy-3-nitrophenylacetyl (NP) hapten binding antibody (B1-8), we demonstrate antigen specificity and selective enrichment of antigen-specific B cells with high affinity at both cell surface and secreted levels in integrin ligand-dependent manner. The ex vivo antigen-specific platform technology offers use in scientific understanding of immunobiology, matrix immunology, and in biotechnology applications, ranging from the antigen testing, vaccine development, and generation of antibodies against diseases.

Organ-on-a-Chip for Cancer and Immune Organs Modeling

Bridging the gap between findings in preclinical 2D cell culture models and in vivo tissue cultures has been challenging; the simple microenvironment of 2D monolayer culture systems may not capture the cellular response to drugs accurately. Three-dimensional organotypic models have gained increasing interest due to their ability to recreate precise cellular organizations. These models facilitate investigation of the interactions between different sub-tissue level components through providing physiologically relevant microenvironments for cells in vitro. The incorporation of human-sourced tissues into these models further enables personalized prediction of drug responses. Integration of microfluidic units into the 3D models can be used to control their local environment, dynamic simulation of cell behaviors, and real-time readout of drug testing data. Cancer and immune system related diseases are severe burdens to our health care system and have created an urgent need for high-throughput, and effective drug development plans. This review focuses on recent progress in the development of "cancer-on-a-chip" and "immune organs-on-a-chip" systems designed to study disease progression and predict drug-induced responses. Future challenges and opportunities are also discussed.

Towards the development of human immune-system-on-a-chip platforms

Organ-on-a-chip (OoCs) platforms could revolutionize drug discovery and might ultimately become essential tools for precision therapy. Although many single-organ and interconnected systems have been described, the immune system has been comparatively neglected, despite its pervasive role in the body and the trend towards newer therapeutic products (i.e., complex biologics, nanoparticles, immune checkpoint inhibitors, and engineered T cells) that often cause, or are based on, immune reactions. In this review, we recapitulate some distinctive features of the immune system before reviewing microfluidic devices that mimic lymphoid organs or other organs and/or tissues with an integrated immune system component.

Beyond Tissue Stiffness and Bioadhesivity: Advanced Biomaterials to Model Tumor Microenvironments and Drug Resistance

Resistance to chemotherapy and pathway-targeted therapies poses a major problem in cancer research. While the fields of tumor biology and experimental therapeutics have already benefited from ex vivo preclinical tissue models, these models have yet to address the reasons for malignant transformations and the emergence of chemoresistance. With the increasing number of ex vivo models poised to incorporate physiological biophysical properties, along with the advent of genomic sequencing information, there are now unprecedented opportunities to better understand tumorigenesis and to design therapeutic approaches to overcome resistance. Here we discuss that new preclinical ex vivo models should consider - in addition to common biophysical parameters such as matrix stiffness and bioadhesivity - a more comprehensive milieu of tissue signaling, nuclear mechanics, immune response, and the gut microbiome.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell-microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.

Creating artificial lymphoid tissues to study immunity and hematological malignancies

PURPOSE OF REVIEW

The specialized microenvironments of lymphoid tissue affect immune cell function and progression of disease. However, current animal models are low throughput and a large number of human diseases are difficult to model in animals. Animal models are less amenable to manipulation of tissue niche components, signalling pathways, epigenetics, and genome editing than ex vivo models. On the other hand, conventional 2D cultures lack the physiological relevance to study precise microenvironmental interactions. Thus, artificial tissues are being developed to study these interactions in the context of immune development, function, and disease.

RECENT FINDINGS

New bone marrow and lymph node models have been created to, respectively, study microenvironmental interactions in hematopoiesis and germinal center-like biology. These models have also been extended to understand the effect of these interactions on the progression and therapeutic response in leukemia, multiple myeloma, and lymphoma.

SUMMARY

3D in-vitro immune models have elucidated new cellular, biochemical, and biophysical interactions as potential regulatory mechanisms, therapeutic targets, or biomarkers that previously could not be studied in animal models and conventional 2D cultures. Incorporation of advanced biomaterials, microfluidics, genome editing, and single-cell analysis tools will enable further studies of function, driver mutations, and tumor heterogeneity. Continual refinement will help inform the development of antibody and cell-based immunotherapeutics and patient-specific treatment plans.

Cellular self-assembly and biomaterials-based organoid models of development and diseases

Organogenesis and morphogenesis have informed our understanding of physiology, pathophysiology, and avenues to create new curative and regenerative therapies. Thus far, this understanding has been hindered by the lack of a physiologically relevant yet accessible model that affords biological control. Recently, three-dimensional ex vivo cellular cultures created through cellular self-assembly under natural extracellular matrix cues or through biomaterial-based directed assembly have been shown to physically resemble and recapture some functionality of target organs. These "organoids" have garnered momentum for their applications in modeling human development and disease, drug screening, and future therapy design or even organ replacement. This review first discusses the self-organizing organoids as materials with emergent properties and their advantages and limitations. We subsequently describe biomaterials-based strategies used to afford more control of the organoid's microenvironment and ensuing cellular composition and organization. In this review, we also offer our perspective on how multifunctional biomaterials with precise spatial and temporal control could ultimately bridge the gap between in vitro organoid platforms and their in vivo counterparts.

STATEMENT OF SIGNIFICANCE

Several notable reviews have highlighted PSC-derived organoids and 3D aggregates, including embryoid bodies, from a development and cellular assembly perspective. The focus of this review is to highlight the materials-based approaches that cells, including PSCs and others, adopt for self-assembly and the controlled development of complex tissues, such as that of the brain, gut, and immune system.