HLA tetramer-based artificial antigen-presenting cells for stimulation of CD4+ T cells

Emerging approaches for T cell-stimulating platform development

T cells are key mediators of the adaptive immune response, playing both direct and supporting roles in the destruction of foreign pathogenic threats as well as pathologically transformed host cells. The natural process through which T cells are activated requires coordinated molecular interactions between antigen-presenting cells and T cells. Promising advances in biomaterial design have catalyzed the development of artificial platforms that mimic the natural process of T cell stimulation, both to bolster the performance of cell therapies by activating T cells ex vivo prior to adoptive cell transfer and to directly activate T cells in vivo as off-the-shelf treatments. This review focuses on innovative strategies in T cell-stimulating platform design for applications in cancer therapy. We specifically highlight progress in bead-based artificial antigen-presenting cell engineering, hydrogel-based scaffolds, DNA-based systems, alternative polymeric strategies, and soluble activation approaches. Collectively, these advances are expanding the repertoire of tools for targeted immune activation.

Artificial antigen-presenting cells: the booster for the obtaining of functional adoptive cells

Adoptive cell therapy (ACT) achieves substantial efficacy in the treatment of hematological malignancies and solid tumours, while enormous endeavors have been made to reduce relapse and extend the remission duration after ACT. For the genetically engineered T cells, their functionality and long-term anti-tumour potential depend on the specificity of the T cell receptor (TCR) or chimeric antigen receptor (CAR). In addition, the therapeutic benefit is directly to sufficient activation and proliferation of engineered T cells. Artificial antigen-presenting cells (aAPCs), as powerful boosters for ACT, have been applied to provide sustained stimulation of the cognate antigen and facilitate the expansion of sufficient T cells for infusion. In this review, we summarize the aAPCs used to generate effector cells for ACT and underline the mechanism by which aAPCs enhance the functionality of the effector cells. The manuscript includes investigations ranging from basic research to clinical trials, which we hope will highlight the importance of aAPCs and provide guidance for novel strategies to improve the effectiveness of ACT.

Particle-Based Artificial Antigen-Presenting Cell Systems for T Cell Activation in Adoptive T Cell Therapy

T cell-based adoptive cell therapy (ACT) has emerged as a promising treatment for various diseases, particularly cancers. Unlike other immunotherapy modalities, ACT involves directly transferring engineered T cells into patients to eradicate diseased cells; hence, it necessitates methods for effectively activating and expanding T cells in vitro. Artificial antigen-presenting cells (aAPCs) have been widely developed based on biomaterials, particularly micro- and nanoparticles, and functionalized with T cell stimulatory antibodies to closely mimic the natural T cell-APC interactions. Due to their vast clinical utility, aAPCs have been employed as an off-the-shelf technology for T cell activation in FDA-approved ACTs, and the development of aAPCs is constantly advancing with the emergence of aAPCs with more sophisticated designs and additional functionalities. Here, we review the recent advancements in particle-based aAPCs for T cell activation in ACTs. Following a brief introduction, we first describe the manufacturing processes of ACT products. Next, the design and synthetic strategies for micro- and nanoparticle-based aAPCs are discussed separately to emphasize their features, advantages, and limitations. Then, the impact of design parameters of aAPCs, such as size, shape, ligand density/mobility, and stiffness, on their functionality and biomedical performance is explored to provide deeper insights into the design concepts and principles for more efficient and safer aAPCs. The review concludes by discussing current challenges and proposing future perspectives for the development of more advanced aAPCs.

Cell-Sized Lipid Vesicles as Artificial Antigen-Presenting Cells for Antigen-Specific T Cell Activation

In this study, efficient T cell activation is demonstrated using cell-sized artificial antigen-presenting cells (aAPCs) with protein-conjugated bilayer lipid membranes that mimic biological cell membranes. The highly uniform aAPCs are generated by a facile method based on standard droplet microfluidic devices. These aAPCs are able to activate the T cells in peripheral blood mononuclear cells, showing a 28-fold increase in interferon gamma (IFNγ) secretion, a 233-fold increase in antigen-specific CD8 T cells expansion, and a 16-fold increase of CD4 T cell expansion. The aAPCs do not require repetitive boosting or additional stimulants and can function at a relatively low aAPC-to-T cell ratio (1:17). The research presents strong evidence that the surface fluidity and size of the aAPCs are critical to the effective formation of immune synapses essential for T cell activation. The findings demonstrate that the microfluidic-generated aAPCs can be instrumental in investigating the physiological conditions and mechanisms for T cell activation. Finally, this method demonstrates the feasibility of customizable aAPCs for a cost-effective off-the-shelf approach to immunotherapy.

Shape matters: Biodegradable anisotropic nanoparticle artificial antigen presenting cells for cancer immunotherapy

Artificial antigen presenting cells are biomimetic particles that recapitulate the signals presented by natural antigen presenting cells in order to stimulate T cells in an antigen-specific manner using an acellular platform. We have engineered an enhanced nanoscale biodegradable artificial antigen presenting cell by modulating particle shape to achieve a nanoparticle geometry that allows for increased radius of curvature and surface area for T cell contact. The non-spherical nanoparticle artificial antigen presenting cells developed here have reduced nonspecific uptake and improved circulation time compared both to spherical nanoparticles and to traditional microparticle technologies. Additionally, the anisotropic nanoparticle artificial antigen presenting cells efficiently engage with and activate T cells, ultimately leading to a marked anti-tumor effect in a mouse melanoma model that their spherical counterparts were unable to achieve. STATEMENT OF SIGNIFICANCE: Artificial antigen presenting cells (aAPC) can activate antigen-specific CD8+ T cells but have largely been limited to microparticle-based platforms and ex vivo T cell expansion. Although more amenable to in vivo use, nanoscale aAPC have traditionally been ineffective due to limited surface area available for T cell interaction. In this work, we engineered non-spherical biodegradable nanoscale aAPC to investigate the role of particle geometry and develop a translatable platform for T cell activation. The non-spherical aAPC developed here have increased surface area and a flatter surface for T cell engagement and, therefore, can more effectively stimulate antigen-specific T cells, resulting in anti-tumor efficacy in a mouse melanoma model.

Biomimetic dendritic polymeric microspheres induce enhanced T cell activation and expansion for adoptive tumor immunotherapy

A variety of bioactive materials are currently developed to expand T cells ex vivo for adoptive T cell immunotherapy, also known as called artificial antigen-presenting cells (aAPCs). However, almost all the reported designs exhibit relatively smooth surface modified with T cell activating biomolecules, and therefore cannot well mimic the dendritic morphological characteristics of dendritic cells (DCs), the most important type of natural antigen-presenting cells (APCs) with high specific surface areas. Here, we propose a hydrophilic monomer-mediated surface morphology control strategy to synthesize biocompatible dendritic poly(N-isopropylacrylamide) (PNIPAM) microspheres for constructing aAPCs with surface morphology mimicking natural APCs (e.g., DCs). Interestingly, when maintaining the same ligands density, dendritic polymeric microspheres-based aAPCs (DPM beads) can more efficiently expand CD8⁺ T cells than that with smooth surfaces. Moreover, adoptive transfer of antigen-specific CD8⁺ T cells expanded by the DPM beads show significant antitumor effect of B16-OVA tumor bearing mice. Therefore, we provide a new concept for constructing biomimetic aAPCs with enhanced T cell expansion ability.

Large Scale Ex Vivo Expansion of γδ T cells Using Artificial Antigen-presenting Cells

Higher γδ T cell counts in patients with malignancies are associated with better survival. However, γδ T cells are rare in the blood and functionally impaired in patients with malignancies. Promising results are reported on the treatment of various malignancies with in vivo expansion of autologous γδ T cells using zoledronic acid (zol) and interleukin-2 (IL-2). Here we demonstrated that zol and IL-2, in combination with a novel genetically engineered K-562 CD3scFv/CD137L/CD28scFv/IL15RA quadruplet artificial antigen-presenting cell (aAPC), efficiently expand allogeneic donor-derived γδ T cells using a Good Manufacturing Practice (GMP) compliant protocol sufficient to achieve cell doses for future clinical use. We achieved a 633-fold expansion of γδ T cells after day 10 of coculture with aAPC, which exhibited central (47%) and effector (43%) memory phenotypes. In addition, >90% of the expanded γδ T cells expressed NKG2D, although they have low cell surface expression of PD1 and LAG3 inhibitory checkpoint receptors. In vitro real-time cytotoxicity analysis showed that expanded γδ T cells were effective in killing target cells. Our results demonstrate that large-scale ex vivo expansion of donor-derived γδ T cells in a GMP-like setting can be achieved with the use of quadruplet aAPC and zol/IL-2 for clinical application.

Highly tailorable gellan gum nanoparticles as a platform for the development of T cell activator systems

Background

T cell priming has been shown to be a powerful immunotherapeutic approach for cancer treatment in terms of efficacy and relatively weak side effects. Systems that optimize the stimulation of T cells to improve therapeutic efficacy are therefore in constant demand. A way to achieve this is through artificial antigen presenting cells that are complexes between vehicles and key molecules that target relevant T cell subpopulations, eliciting antigen-specific T cell priming. In such T cell activator systems, the vehicles chosen to deliver and present the key molecules to the targeted cell populations are of extreme importance. In this work, a new platform for the creation of T cell activator systems based on highly tailorable nanoparticles made from the natural polymer gellan gum (GG) was developed and validated.

Methods

GG nanoparticles were produced by a water in oil emulsion procedure, and characterized by dynamic light scattering, high resolution scanning electronic microscopy and water uptake. Their biocompatibility with cultured cells was assessed by a metabolic activity assay. Surface functionalization was performed with anti-CD3/CD28 antibodies via EDC/NHS or NeutrAvidin/Biotin linkage. Functionalized particles were tested for their capacity to stimulate CD4⁺ T cells and trigger T cell cytotoxic responses.

Results

Nanoparticles were approximately 150 nm in size, with a stable structure and no detectable cytotoxicity. Water uptake originated a weight gain of up to 3200%. The functional antibodies did efficiently bind to the nanoparticles, as confirmed by SDS-PAGE, which then targeted the desired CD4⁺ populations, as confirmed by confocal microscopy. The developed system presented a more sustained T cell activation over time when compared to commercial alternatives. Concurrently, the expression of higher levels of key cytotoxic pathway molecules granzyme B/perforin was induced, suggesting a greater cytotoxic potential for future application in adoptive cancer therapy.

Conclusions

Our results show that GG nanoparticles were successfully used as a highly tailorable T cell activator system platform capable of T cell expansion and re-education.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00297-z.

Recent advances in biomaterial-boosted adoptive cell therapy

Adoptive immunotherapies based on the transfer of functional immune cells hold great promise in treating a wide range of malignant diseases, especially cancers, autoimmune diseases, and infectious diseases. However, manufacturing issues and biological barriers lead to the insufficient population of target-selective effector cells at diseased sites after adoptive transfer, hindering effective clinical translation. The convergence of immunology, cellular biology, and materials science lays a foundation for developing biomaterial-based engineering platforms to overcome these challenges. Biomaterials can be rationally designed to improve ex vivo immune cell expansion, expedite functional engineering, facilitate protective delivery of immune cells in situ, and navigate the infused cells in vivo. Herein, this review presents a comprehensive summary of the latest progress in biomaterial-based strategies to enhance the efficacy of adoptive cell therapy, focusing on function-specific biomaterial design, and also discusses the challenges and prospects of this field.

Nanoparticles Engineered as Artificial Antigen-Presenting Cells Induce Human CD4+ and CD8+ Tregs That Are Functional in Humanized Mice

Artificial antigen-presenting cells (aAPCs) are synthetic versions of naturally occurring antigen-presenting cells (APCs) that, similar to natural APCs, promote efficient T effector cell responses in vitro. This report describes a method to produce acellular tolerogenic aAPCs made of biodegradable poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) and encapsulating IL-2 and TGF-β for a paracrine release to T cells. We document that these aAPCs can induce both human CD4+ and CD8+ T cells to become FoxP3+ T regulatory cells (Tregs). The aAPC NP-expanded human Tregs are functional in vitro and can modulate systemic autoimmunity in vivo in humanized NSG mice. These findings establish a proof-of-concept to use PLGA NPs as aAPCs for the induction of human Tregs in vitro and in vivo, highlighting the immunotherapeutic potential of this targeted approach to repair IL-2 and/or TGF-β defects documented in certain autoimmune diseases such as systemic lupus erythematosus.

Engineering Nano-Therapeutics to Boost Adoptive Cell Therapy for Cancer Treatment

Although adoptive transfer of therapeutic cells to cancer patients is demonstrated with great success and fortunately approved for the treatment of leukemia and B-cell lymphoma, potential issues, including the unclear mechanism, complicated procedures, unfavorable therapeutic efficacy for solid tumors, and side effects, still hinder its extensive applications. The explosion of nanotechnology recently has led to advanced development of novel strategies to address these challenges, facilitating the design of nano-therapeutics to improve adoptive cell therapy (ACT) for cancer treatment. In this review, the emerging nano-enabled approaches, that design multiscale artificial antigen-presenting cells for cell proliferation and stimulation in vitro, promote the transducing efficiency of tumor-targeting domains, engineer therapeutic cells for in vivo imaging, tumor infiltration, and in vivo functional sustainability, as well as generate tumoricidal T cells in vivo, are summarized. Meanwhile, the current challenges and future perspectives of the nanostrategy-based ACT for cancer treatment are also discussed in the end.

Biomaterials to enhance antigen-specific T cell expansion for cancer immunotherapy

T cells are often referred to as the 'guided missiles' of our immune system because of their capacity to traffic to and accumulate at sites of infection or disease, destroy infected or mutated cells with high specificity and sensitivity, initiate systemic immune responses, sterilize infections, and produce long-lasting memory. As a result, they are a common target for a range of cancer immunotherapies. However, the myriad of challenges of expanding large numbers of T cells specific to each patient's unique tumor antigens has led researchers to develop alternative, more scalable approaches. Biomaterial platforms for expansion of antigen-specific T cells offer a path forward towards broadscale translation of personalized immunotherapies by providing "off-the-shelf", yet modular approaches to customize the phenotype, function, and specificity of T cell responses. In this review, we discuss design considerations and progress made in the development of ex vivo and in vivo technologies for activating antigen-specific T cells, including artificial antigen presenting cells, T cell stimulating scaffolds, biomaterials-based vaccines, and artificial lymphoid organs. Ultimate translation of these platforms as a part of cancer immunotherapy regimens hinges on an in-depth understanding of T cell biology and cell-material interactions.

Generation of Antitumor T Cells For Adoptive Cell Therapy With Artificial Antigen Presenting Cells

Adoptive cell therapy with ex vivo expanded tumor infiltrating lymphocytes or gene engineering T cells expressing chimeric antigen receptors (CAR) is a promising treatment for cancer patients. This production utilizes T-cell activation and transduction with activation beads and RetroNectin, respectively. However, the high cost of production is an obstacle for the broad clinical application of novel immunotherapeutic cell products. To facilitate production we refined our approach by using artificial antigen presenting cells (aAPCs) with receptors that ligate CD3, CD28, and the CD137 ligand (CD137L or 41BBL), as well as express the heparin binding domain (HBD), which binds virus for gene-transfer. We have used these aAPC for ex vivo gene engineering and expansion of tumor infiltrating lymphocytes and CAR T cells. We found that aAPCs can support efficacious T-cell expansion and transduction. Moreover, aAPCs expanded T cells exhibit higher production of IFN-γ and lower traits of T-cell exhaustion compared with bead expanded T cells. Our results suggest that aAPC provide a more physiological stimulus for T-cell activation than beads that persistently ligate T cells. The use of a renewable cell line to replace 2 critical reagents (beads and retronectin) for CAR T-cell production can significantly reduce the cost of production and make these therapies more accessible to patients.

Materials for Immunotherapy

Breakthroughs in materials engineering have accelerated the progress of immunotherapy in preclinical studies. The interplay of chemistry and materials has resulted in improved loading, targeting, and release of immunomodulatory agents. An overview of the materials that are used to enable or improve the success of immunotherapies in preclinical studies is presented, from immunosuppressive to proinflammatory strategies, with particular emphasis on technologies poised for clinical translation. The materials are organized based on their characteristic length scale, whereby the enabling feature of each technology is organized by the structure of that material. For example, the mechanisms by which i) nanoscale materials can improve targeting and infiltration of immunomodulatory payloads into tissues and cells, ii) microscale materials can facilitate cell-mediated transport and serve as artificial antigen-presenting cells, and iii) macroscale materials can form the basis of artificial microenvironments to promote cell infiltration and reprogramming are discussed. As a step toward establishing a set of design rules for future immunotherapies, materials that intrinsically activate or suppress the immune system are reviewed. Finally, a brief outlook on the trajectory of these systems and how they may be improved to address unsolved challenges in cancer, infectious diseases, and autoimmunity is presented.

Nanoparticles for Immune Stimulation Against Infection, Cancer, and Autoimmunity

Vaccination using nanocarrier-based delivery systems has recently emerged as a promising approach for meeting the continued challenge posed by infectious diseases and cancer. A diverse portfolio of nanocarriers of various sizes, compositions, and physical parameters have now been developed, and this diversity provides an opportunity for the rational design of vaccines that can mediate targeted delivery of various antigens and adjuvants or immune regulatory agents in ways unachievable with classical vaccination approaches. This flexibility allows control over the characteristics of vaccine-elicited immune responses such that they can be tailored to be effective in circumstances where classical vaccines have failed. Furthermore, the utility of nanocarrier-based immune modulation extends to the treatment of autoimmune disease where precisely targeted inhibition of immune responses is desirable. Clearly, the selection of appropriate nanocarriers, antigens, adjuvants, and other components underpins the efficacy of these nanoimmune interventions. Herein, we provide an overview of currently available nanocarriers of various types and their physical and pharmacological properties with the goal of providing a resource for researchers exploring nanomaterial-based approaches for immune modulation and identify some information gaps and unexplored questions to help guide future investigation.

Fabrication of Anisotropic Polymeric Artificial Antigen Presenting Cells for CD8+ T Cell Activation

Artificial antigen presenting cells (aAPC) are a promising platform for immune modulation due to their potent ability to stimulate T cells. Acellular substrates offer key advantages over cell-based aAPC, including precise control of signal presentation parameters and physical properties of the aAPC surface to modulate its interactions with T cells. aAPC constructed from anisotropic particles, particularly ellipsoidal particles, have been shown to be more effective than their spherical counterparts at stimulating T cells due to increased binding and larger surface area available for T cell contact, as well as reduced nonspecific uptake and enhanced pharmacokinetic properties. Despite increased interest in anisotropic particles, even widely accepted methods of generating anisotropic particles such as thin-film stretching can be challenging to implement and use reproducibly. To this end, we describe a protocol for the rapid, standardized fabrication of biodegradable anisotropic particle-based aAPC with tunable size, shape, and signal presentation for T cell expansion ex vivo or in vivo, along with methods to characterize their size, morphology, and surface protein content, and to assess their functionality. This approach to fabricating anisotropic aAPC is scalable and reproducible, making it ideal for generating aAPC for "off-the-shelf" immunotherapies.

Nanoscale artificial antigen presenting cells for cancer immunotherapy

Exciting developments in cancer nanomedicine include the engineering of nanocarriers to deliver drugs locally to tumors, increasing efficacy and reducing off-target toxicity associated with chemotherapies. Despite nanocarrier advances, metastatic cancer remains challenging to treat due to barriers that prevent nanoparticles from gaining access to remote, dispersed, and poorly vascularized metastatic tumors. Instead of relying on nanoparticles to directly destroy every tumor cell, immunotherapeutic approaches target immune cells to train them to recognize and destroy tumor cells, which, due to the amplification and specificity of an adaptive immune response, may be a more effective approach to treating metastatic cancer. One novel technology for cancer immunotherapy is the artificial antigen presenting cell (aAPC), a micro- or nanoparticle-based system that mimics an antigen presenting cell by presenting important signal proteins to T cells to activate them against cancer. Signal 1 molecules target the T cell receptor and facilitate antigen recognition by T cells, signal 2 molecules provide costimulation essential for T cell activation, and signal 3 consists of secreted cues that further stimulate T cells. Classic microscale aAPCs present signal 1 and 2 molecules on their surface, and biodegradable polymeric aAPCs offer the additional capability of releasing signal 3 cytokines and costimulatory molecules that modulate the T cell response. Although particles of approximately 5-10 μm in diameter may be considered the optimal size of an aAPC for ex vivo cellular expansion, nanoscale aAPCs have demonstrated superior in vivo pharmacokinetic properties and are more suitable for systemic injection. As sufficient surface contact between T cells and aAPCs is essential for activation, nano-aAPCs with microscale contact surface areas have been created through engineering approaches such as shape manipulation and nanoparticle clustering. These design strategies have demonstrated greatly enhanced efficacy of nano-aAPCs, endowing nano-aAPCs with the potential to be among the next generation of cancer nanomedicines.

A miRNA181a/NFAT5 axis links impaired T cell tolerance induction with autoimmune type 1 diabetes

Molecular checkpoints that trigger the onset of islet autoimmunity or progression to human type 1 diabetes (T1D) are incompletely understood. Using T cells from children at an early stage of islet autoimmunity without clinical T1D, we find that a microRNA181a (miRNA181a)-mediated increase in signal strength of stimulation and costimulation links nuclear factor of activated T cells 5 (NFAT5) with impaired tolerance induction and autoimmune activation. We show that enhancing miRNA181a activity increases NFAT5 expression while inhibiting FOXP3+ regulatory T cell (Treg) induction in vitro. Accordingly, Treg induction is improved using T cells from NFAT5 knockout (NFAT5ko) animals, whereas altering miRNA181a activity does not affect Treg induction in NFAT5ko T cells. Moreover, high costimulatory signals result in phosphoinositide 3-kinase (PI3K)-mediated NFAT5, which interferes with FoxP3+ Treg induction. Blocking miRNA181a or NFAT5 increases Treg induction in murine and humanized models and reduces murine islet autoimmunity in vivo. These findings suggest targeting miRNA181a and/or NFAT5 signaling for the development of innovative personalized medicines to limit islet autoimmunity.

Bioengineering of Artificial Antigen Presenting Cells and Lymphoid Organs

The immune system protects the body against a wide range of infectious diseases and cancer by leveraging the efficiency of immune cells and lymphoid organs. Over the past decade, immune cell/organ therapies based on the manipulation, infusion, and implantation of autologous or allogeneic immune cells/organs into patients have been widely tested and have made great progress in clinical applications. Despite these advances, therapy with natural immune cells or lymphoid organs is relatively expensive and time-consuming. Alternatively, biomimetic materials and strategies have been applied to develop artificial immune cells and lymphoid organs, which have attracted considerable attentions. In this review, we survey the latest studies on engineering biomimetic materials for immunotherapy, focusing on the perspectives of bioengineering artificial antigen presenting cells and lymphoid organs. The opportunities and challenges of this field are also discussed.

Type 1 diabetes vaccine candidates promote human Foxp3(+)Treg induction in humanized mice

Immune tolerance is executed partly by Foxp3⁺regulatory T (Treg) cells, which suppress autoreactive T cells. In autoimmune type 1 diabetes (T1D) impaired tolerance promotes destruction of insulin-producing β-cells. The development of autoantigen-specific vaccination strategies for Foxp3⁺Treg-induction and prevention of islet autoimmunity in patients is still in its infancy. Here, using human haematopoietic stem cell-engrafted NSG-HLA-DQ8 transgenic mice, we provide direct evidence for human autoantigen-specific Foxp3⁺Treg-induction in vivo. We identify HLA-DQ8-restricted insulin-specific CD4⁺T cells and demonstrate efficient human insulin-specific Foxp3⁺Treg-induction upon subimmunogenic vaccination with strong agonistic insulin mimetopes in vivo. Induced human Tregs are stable, show increased expression of Treg signature genes such as Foxp3, CTLA4, IL-2Rα and TIGIT and can efficiently suppress effector T cells. Such Foxp3⁺Treg-induction does not trigger any effector T cells. These T1D vaccine candidates could therefore represent an expedient improvement in the challenge to induce human Foxp3⁺Tregs and to develop novel precision medicines for prevention of islet autoimmunity in children at risk of T1D.

Type 1 diabetes is associated with the loss of self-tolerance to the insulin-producing β-cells in the pancreas. Here the authors show that vaccination with insulin mimetopes can induce human insulin-specific regulatory T cells to mediate tolerance in a humanized mouse model.

Biodegradable nanoellipsoidal artificial antigen presenting cells for antigen specific T-cell activation

Non-spherical nanodimensional artificial antigen presenting cells (naAPCs) offer the potential to systemically induce an effective antigen-specific immune response. In this report it is shown biodegradable ellipsoidal naAPCs mimic the T-Cell/APC interaction better than equivalent spherical naAPCs. In addition, it is demonstrated ellipsoidal naAPCs offer reduced non-specific cellular uptake and a superior pharmacokinetic profile compared to spherical naAPCs.

Linking form to function: Biophysical aspects of artificial antigen presenting cell design

Artificial antigen presenting cells (aAPCs) are engineered platforms for T cell activation and expansion, synthesized by coupling T cell activating proteins to the surface of cell lines or biocompatible particles. They can serve both as model systems to study the basic aspects of T cell signaling and translationally as novel approaches for either active or adoptive immunotherapy. Historically, these reductionist systems have not been designed to mimic the temporally and spatially complex interactions observed during endogenous T cell-APC contact, which include receptor organization at both micro- and nanoscales and dynamic changes in cell and membrane morphologies. Here, we review how particle size and shape, as well as heterogenous distribution of T cell activating proteins on the particle surface, are critical aspects of aAPC design. In doing so, we demonstrate how insights derived from endogenous T cell activation can be applied to optimize aAPC, and in turn how aAPC platforms can be used to better understand endogenous T cell stimulation. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.

Nanoparticle-based immunotherapy for cancer

The design of nanovaccines capable of triggering effective antitumor immunity requires an understanding of how the immune system senses and responds to threats, including pathogens and tumors. Equally important is an understanding of the mechanisms employed by tumor cells to evade immunity and an appreciation of the deleterious effects that antitumor immune responses can have on tumor growth, such as by skewing tumor cell composition toward immunologically silent tumor cell variants. The immune system and tumors engage in a tug-of-war driven by competition where promoting antitumor immunity or tumor cell death alone may be therapeutically insufficient. Nanotechnology affords a unique opportunity to develop therapeutic compounds than can simultaneously tackle both aspects, favoring tumor eradication. Here, we review the current status of nanoparticle-based immunotherapeutic strategies for the treatment of cancer, ranging from antigen/adjuvant delivery vehicles (to professional antigen-presenting cell types of the immune system) to direct tumor antigen-specific T-lymphocyte-targeting compounds and their combinations thereof.

Towards efficient cancer immunotherapy: advances in developing artificial antigen-presenting cells

Active anti-cancer immune responses depend on efficient presentation of tumor antigens and co-stimulatory signals by antigen-presenting cells (APCs). Therapy with autologous natural APCs is costly and time-consuming and results in variable outcomes in clinical trials. Therefore, development of artificial APCs (aAPCs) has attracted significant interest as an alternative. We discuss the characteristics of various types of acellular aAPCs, and their clinical potential in cancer immunotherapy. The size, shape, and ligand mobility of aAPCs and their presentation of different immunological signals can all have significant effects on cytotoxic T cell activation. Novel optimized aAPCs, combining carefully tuned properties, may lead to efficient immunomodulation and improved clinical responses in cancer immunotherapy.

Analysis, Isolation, and Activation of Antigen-Specific CD4(+) and CD8(+) T Cells by Soluble MHC-Peptide Complexes

T cells constitute the core of adaptive cellular immunity and protect higher organisms against pathogen infections and cancer. Monitoring of disease progression as well as prophylactic or therapeutic vaccines and immunotherapies call for conclusive detection, analysis, and sorting of antigen-specific T cells. This is possible by means of soluble recombinant ligands for T cells, i.e., MHC class I-peptide (pMHC I) complexes for CD8(+) T cells and MHC class II-peptide (pMHC II) complexes for CD4(+) T cells and flow cytometry. Here we review major developments in the development of pMHC staining reagents and their diverse applications and discuss perspectives of their use for basic and clinical investigations.

Nanoengineering approaches to the design of artificial antigen-presenting cells

Artificial antigen-presenting cells (aAPCs) have shown great initial promise for ex vivo activation of cytotoxic T cells. The development of aAPCs has focused mainly on the choice of proteins to use for surface presentation to T cells when conjugated to various spherical, microscale particles. We review here biomimetic nanoengineering approaches that have been applied to the development of aAPCs that move beyond initial concepts about aAPC development. This article also discusses key technologies that may be enabling for the development of nano- and micro-scale aAPCs with nanoscale features, and suggests several future directions for the field.

Biomimetic delivery with micro- and nanoparticles

The nascent field of biomimetic delivery with micro- and nanoparticles (MNP) has advanced considerably in recent years. Drawing inspiration from the ways that cells communicate in the body, several different modes of "delivery" (i.e., temporospatial presentation of biological signals) have been investigated in a number of therapeutic contexts. In particular, this review focuses on (1) controlled release formulations that deliver natural soluble factors with physiologically relevant temporal context, (2) presentation of surface-bound ligands to cells, with spatial organization of ligands ranging from isotropic to dynamically anisotropic, and (3) physical properties of particles, including size, shape and mechanical stiffness, which mimic those of natural cells. Importantly, the context provided by multimodal, or multifactor delivery represents a key element of most biomimetic MNP systems, a concept illustrated by an analogy to human interpersonal communication. Regulatory implications of increasingly sophisticated and "cell-like" biomimetic MNP systems are also discussed.

MHC class II tetramers

MHC class II tetramers have emerged as an important tool for characterization of the specificity and phenotype of CD4 T cell immune responses, useful in a large variety of disease and vaccine studies. Issues of specific T cell frequency, biodistribution, and avidity, coupled with the large genetic diversity of potential class II restriction elements, require targeted experimental design. Translational opportunities for immune disease monitoring are driving the rapid development of HLA class II tetramer use in clinical applications, together with innovations in tetramer production and epitope discovery.

Controlled major histocompatibility complex-T cell receptor signaling allows efficient generation of functional, antigen-specific CD8+ T cells from embryonic stem cells and thymic progenitors

Generation of early T cells by coculturing stem cells on notch-ligand-expressing OP9 stromal cells (OP9-DL1) has been widely reported. However, further differentiation of these cells into mature, antigen-specific, functional T cells, without retroviral transduction of T cell receptors (TcRs), is yet to be achieved. In the thymic niche this differentiation is controlled by the interaction of developing TcRs with major histocompatibility (MHC) molecules on stromal cells. We hypothesized that by providing exogenous antigen-specific MHC/TcR signals, stem and progenitor cells could be engineered into functional, effector T cells specific for the same antigen. Here we demonstrate that both thymus-derived immature T cells (double positive [DP]: CD4+CD8+) and mouse embryonic stem cells can be efficiently differentiated into antigen-specific CD8+ T cells using either MHC tetramers or peptide-loaded stromal cells. DP cells, following MHC/TcR signaling, retained elevated recombination activating gene-1 levels, suggesting continuing TcR gene rearrangement. Both DP and embryonic stem-cell-derived CD8+ T cells showed significant cytotoxic T lymphocytes activity against antigen-loaded target cells, indicating that these cells are functional. Such directed differentiation strategy could provide an efficient method for generating functional, antigen-specific T cells from stem cells for potential use in adoptive T cell therapy.

Adoptive therapy using antigen-specific T-cell clones

T-cell therapy involves the ex vivo isolation and expansion of antigen-specific T cells for adoptive transfer. The use of T-cell clones represents one embodiment of this approach and provides a uniform population of effector cells, so that parameters contributing to an effective response can be rigorously evaluated. T cells of defined specificity, phenotype, and function are isolated and expanded; when infused into patients, these intrinsic factors can be considered in light of extrinsic factors such as the type of conditioning regimen, cytokine support, and immunomodulatory reagents. In this chapter, 2 topics related to the use of antigen-specific T-cell clones are discussed: first, advances enabling the isolation and expansion of antigen-specific T-cell clones for human trials of adoptive therapy, and second, a contextual framework of advantages and limitations in which the use of adoptively transferred T-cell clones can be judiciously applied as a means to dissect the requirements for effective therapy.

Killer artificial antigen-presenting cells: the synthetic embodiment of a 'guided missile'

At present, the treatment of T-cell-dependent autoimmune diseases relies exclusively on strategies leading to nonspecific suppression of the immune systems causing a substantial reduced ability to control concomitant infections or malignancies. Furthermore, long-term treatment with most drugs is accompanied by several serious adverse effects and does not consequently result in cure of the primary immunological malfunction. By contrast, antigen-specific immunotherapy offers the potential to achieve the highest therapeutic efficiency in accordance with minimal adverse effects. Therefore, several studies have been performed utilizing antigen-presenting cells specifically engineered to deplete allo- or antigen-specific T cells ('guided missiles'). Many of these strategies take advantage of the Fas/Fas ligand signaling pathway to efficiently induce antigen-presenting cell-mediated apoptosis in targeted T cells. In this article, we discuss the advantages and shortcomings of a novel non-cell-based 'killer artificial antigen-presenting cell' strategy, developed to overcome obstacles related to current cell-based approaches for the treatment of T-cell-mediated autoimmunity.

Antigen presentation on artificial acellular substrates: modular systems for flexible, adaptable immunotherapy

BACKGROUND

Recent findings on T cells and dendritic cells have elucidated principles that can be used for a bottom-up approach to engineering artificial antigen presentation on synthetic substrates.

OBJECTIVE/METHODS

To compare the latest artificial antigen-presenting cell (aAPC) technology, focussing on acellular systems because they offer advantages such as easy tunability and rapid point-of-care application compared with cellular systems. We review acellular aAPC performance and discuss their promise for clinical applications.

RESULTS/CONCLUSION

Acellular aAPCs are a powerful alternative to natural-cell-based therapies, offering flexibility and modularity for incorporation oSf a variety of stimuli, hence increasing precision. Current technologies should adapt physiologically important signals within safe materials to more closely approximate their cellular counterparts. These constructs could be administered parenterally as APC replacements for active vaccines or used ex vivo for adoptive immunotherapy.

Soluble HLA/peptide monomers cross-linked with co-stimulatory antibodies onto a streptavidin core molecule efficiently stimulate antigen-specific T cell responses

Soluble MHC-peptide complexes, commonly referred to as tetramers, have been shown to induce strong cross-linking of TCR and CD8, resulting in a vigorous activation followed by a rapid non-apoptotic CD8(+) T cell death. This has limited tetramer use for antigen-specific T cells isolation and cloning, as sorted tetramer positive cells were shown to possess compromised functional integrity. Here we show that the cross-linking of a secondary co-stimulatory signal into oligomeric MHC:peptide complexes prevents such cell death, and in contrast strongly stimulates antigen-specific T cell responses. Such soluble antigen-presenting complexes (sAPCs) containing MHC:peptide complexes linked to either anti-CD27 or anti-CD28 antibodies were capable of priming and expanding HLA-A*0201 restricted CMV specific T cells and also of generating functional HLA-A*0301 restricted BCR/ABL-specific T cell responses. These sAPCs constitute an encouraging alternative method for generating antigen-specific T cells that could be applied to a variety of antigens.

Permanent silencing of NKG2A expression for cell-based therapeutics

Natural killer (NK) and T-cell cytotoxicity is significantly reduced by signaling via CD94/NKG2A receptors. High levels of NKG2A on NK cells have been shown to compromise the graft-versus-leukemia effect in hematopoietic stem cell transplantation. We therefore evaluated the functional relevance of NKG2A silencing for the cytotoxic potential of genetically engineered NK and T cells. Lentiviral vectors containing short hairpin RNA (shRNA) sequences targeting NKG2A transcripts were used to transduce NKG2A(+) primary NK and T cells. NKG2A expression levels were measured by flow cytometry and real-time PCR. The effect of NKG2A silencing on the cytolytic potential of NK and T cells was evaluated in cytotoxicity assays using K562 and B lymphoblastoid cells as targets. Granzyme B mRNA transcript levels were detected by real-time PCR. The transduction of inducible RNAi cassettes containing the sequences for shRNAs targeting NKG2A reduced protein expression in NK and T cells by up to 95%. The cytotoxicity assays demonstrated that NKG2A silencing effectively enhanced NK and CD8+ T-cell lysis by up to 40% and 15%, respectively. However, lysis of K562 cells which lack human leukocyte antigen-E, the ligand of NKG2A, was associated with an upregulation of the natural cytotoxicity receptor NKp30 in NKG2A-silenced NK cells. Our data suggest that RNAi-mediated silencing of NKG2A in effector cells could improve the efficacy of cell-based immunotherapies but also show that indirect effects of NKG2A knockdown exist that have to be considered when designing therapeutic protocols with genetically engineered NK or T cells.

Adoptive transfer of pTRP2-specific CTLs expanding by bead-based artificial antigen-presenting cells mediates anti-melanoma response

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, the lack of efficient methods for their in vitro priming and expansion has become a bottleneck to the development of vaccines and adoptive transfer strategies. Synthetic artificial antigen-presenting cells (aAPCs) are now emerging as an attractive tool for eliciting and expanding CTL responses. This study reported a novel approach for targeting malignant melanoma with pTRP2-specific cytotoxic T lymphocytes (CTLs) expanded from the C57BL/6 splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive Transfer of CTLs specific for malignant melanoma expanding by the aAPCs can mediate effective anti-melanoma response. These results suggested the bead-based aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could provide a useful tool for the reproducible expansion of specific CTLs for adoptive immunotherapy.

Synthetic CD4+ T cell-targeted antigen-presenting cells elicit protective antitumor responses

CD4(+) helper T cells are critical for protective immune responses and yet suboptimally primed in response to tumors. Cell-based vaccination strategies are under evaluation in clinical trials but limited by the need to derive antigen-presenting cells (APC) from patients or compatible healthy donors. To overcome these limitations, we developed CD4(+) T cell-targeted synthetic microbead-based artificial APC (aAPC) and used them to activate CD4(+) T lymphocytes specific for a tumor-associated model antigen (Ag) directly from the naive repertoire. In vitro, aAPC specifically primed Ag-specific CD4(+) T cells that were activated to express high levels of CD44, produced mainly interleukin 2, and could differentiate into Th1-like or Th2-like cells in combination with polarizing cytokines. I.v. administration of aAPC led to Ag-specific CD4(+) T-cell activation and proliferation in secondary lymphoid organs, conferred partial protection against subcutaneous tumors, and prevented the establishment of lung metastasis. Taken together, our data support the use of cell-free, synthetic aAPC as a specific and versatile alternative to expand peptide-specific CD4(+) T cells in adoptive and active immunotherapy.

Preparing clinical grade Ag-specific T cells for adoptive immunotherapy trials

The production of clinical-grade T cells for adoptive immunotherapy has evolved from the ex vivo numerical expansion of tumor-infiltrating lymphocytes to sophisticated bioengineering processes often requiring cell selection, genetic modification and other extensive tissue culture manipulations, to produce desired cells with improved therapeutic potential. Advancements in understanding the biology of lymphocyte signaling, activation, homing and sustained in vivo proliferative potential have redefined the strategies used to produce T cells suitable for clinical investigation. When combined with new technical methods in cell processing and culturing, the therapeutic potential of T cells manufactured in academic centers has improved dramatically. Paralleling these technical achievements in cell manufacturing is the development of broadly applied regulatory standards that define the requirements for the clinical implementation of cell products with ever-increasing complexity. In concert with academic facilities operating in compliance with current good manufacturing practice, the prescribing physician can now infuse T cells with a highly selected or endowed phenotype that has been uniformly manufactured according to standard operating procedures and that meets federal guidelines for quality of investigational cell products. In this review we address salient issues related to the technical, immunologic, practical and regulatory aspects of manufacturing these advanced T-cell products for clinical use.

Expansion of human cytomegalovirus-specific T lymphocytes from unfractionated peripheral blood mononuclear cells with artificial antigen-presenting cells

BACKGROUND

The aim of this study was to find a simple and feasible method for ex vivo expansion of human cytomegalovirus (CMV)-specific cytotoxic T cells from unfractionated peripheral blood mononuclear cells (PBMNCs).

STUDY DESIGN AND METHODS

Unfractionated PBMNCs from three HLA-A*0201-CMV-seropositive donors were stimulated with CMVpp65(495-503) peptide-loaded HLA-A*0201-immunoglobulin fusion protein (HLA-A2-Ig) based artificial antigen-presenting cells (aAPCs) on Day 1. Once a week the CMV-specific T cells were harvested and restimulated with fresh aAPCs. T-cell cultures were maintained for 28 days and then analyzed.

RESULTS

With aAPCs and starting with 1x10(7) freshly isolated PBMNCs that were less than 0.1 percent CMV-specific, more than 1x10(7) T cells with a CMV-specific frequency greater than 93 percent in all donors tested were generated. Expanded CD8+ cytotoxic T lymphocytes were functionally active and showed antigen-specific secretion of interferon-gamma and cytotoxic activity. No alloreactivity against unpulsed HLA-A*0201-positive cells was detected.

CONCLUSION

Herein is reported the successful in vitro expansion of CMV-specific cytotoxic CD8+ T cells from unfractionated PBMNCs of healthy CMV-seropositive blood donors by the use of HLA-A2-Ig-based aAPCs. This study demonstrates that more than 1x10(7) CMV-specific T cells can be generated from approximately 1x10(7) unfractionated PBMNCs within 1 month under highly reproducible conditions.

HLA Tetramer Based Artificial Antigen-Presenting Cells Efficiently Stimulate CTLs Specific for Malignant Glioma

PURPOSE

The interleukin-13 receptor alpha 2 (IL-13R alpha 2) is a glioma-restricted cell-surface epitope not otherwise detected within the central nervous system. Here, we report a novel approach for targeting malignant glioma with IL-13R alpha 2-specific CTLs.

EXPERIMENTAL DESIGN

Artificial antigen-presenting cells (aAPC) were made by coating human leukocyte antigen (HLA)-A2/pIL-13R alpha 2(345-354) tetrameric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads, and used to stimulate IL-13R alpha 2-specific CTLs from the peripheral blood mononuclear cells of HLA-A2+ healthy donors. After multiple stimulations, the induced CTLs were analyzed for tetramer staining, IFN-gamma production, and CTL reactivity.

RESULTS

Tetramer staining assay showed that the induced CTLs specifically bound HLA-A2/pIL-13R alpha 2(345-354) tetramers. The CTLs specifically produced IFN-gamma in response to the HLA-A2/pIL-13R alpha 2(345-354)-aAPCs and exhibited specific lysis against T2 cells pulsed with the peptide pIL-13R alpha 2(345-354) and HLA-A2+ glioma cells expressing IL-13R alpha 2(345-354), whereas HLA-A2(-) glioma cell lines that express IL-13R alpha 2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-HLA class I monoclonal antibody.

CONCLUSION

The induced CTLs specific for IL-13R alpha 2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2+ patients with malignant glioma.

Induction of cytotoxic T-lymphocytes specific for malignant glioma by HLA dimer-based artificial antigen-presenting cells

AIM

The aim of this study was to investigate the novel approach for targeting malignant glioma.

METHODS

Interleukin-13 receptor alpha2 (IL-13Ralpha2)-specific cytotoxic T-cells (CTLs) were induced from the peripheral blood lymphocytes (PBLs) of human leukocyte antigen (HLA)-A2 positive healthy donors by multiple stimulations with artificial antigen-presenting cells (aAPCs) made by coating HLA-A2-Ig/pIL-13Ralpha2(345-354) dimeric complexes, anti-CD28 antibody, and CD83 molecules to cell-sized latex beads.

RESULTS

The induced CTLs exhibited a specific lysis against T2 cells pulsed with the peptide pIL-13Ralpha2(345-354) and HLA-A2(+) glioma cells expressing IL-13Ralpha2(345-354), while HLA-A2(-) glioma cell lines that express IL-13Ralpha2(345-354) could not be recognized by the CTLs. The peptide-specific activity was inhibited by the anti-HLA class I monoclonal antibody.

CONCLUSIONS

The induced CTLs specific for the IL-13Ralpha2(345-354) peptide could be a potential target of specific immunotherapy for HLA-A2(+) patients with malignant glioma.

Induction of tumor antigen-specific cytotoxic T cell responses in naïve mice by latex microspheres-based artificial antigen-presenting cell constructs

Latex microspheres-based artificial antigen-presenting cell constructs (aAPCs) are proved to be valuable tools to expand T cells ex vivo for adoptive cell therapy, but little is known about their potential for active immunization. In this report, HLA-A2/peptide tetramers were generated and co-coated with anti-mouse CD28 monoclonal antibody onto surface of cell-sized latex microspheres followed by immunization of naïve HLA-A2/K(b) transgenic mice. Five- to six-fold expansion of tumor antigen-specific CTLs was observed in the spleen after three rounds of immunization. The consequent splenocytes can efficiently recognize endogenously expressed tumor antigen on the surface of human target cells and cytolyze the tumor cells in an antigen-specific manner. This report provides initially the experimental evidence that latex microspheres-based aAPCs can effectively prime antigen-specific CTL proliferation and cytolysis in naïve mice. This may contribute to a better insight into the potential of microspheres-based aAPCs for active immunization.

Biomaterial-based notch signaling for the differentiation of hematopoietic stem cells into T cells

Thymocyte development takes place in a complex milieu of supportive cells and ECM that are responsible for the proliferation, adhesion, migration, and selection processes these cells undergo before reaching maturity. In recent years, the role of notch signaling in lymphocyte development, specifically T-cell development, has been extensively characterized. Although notch ligand mediated signals have been shown to be a necessary component of T-cell generation from stem cells, high-throughput, synthetic biomaterial-based systems for notch-directed stem-cell differentiation into lymphocytes are yet to be reported. Here, we present a microbead-based, artificial notch signaling system to study stem-cell differentiation into the T-cell lineage. Magnetic microbeads were functionalized with the notch ligand DLL4 using streptavidin-biotin binding and antibody-antigen coupling. Immunohistochemistry and flow cytometry analysis indicated approximately 65% conjugation efficiency. Efficient notch signaling through these functionalized microbeads was demonstrated through a myotube inhibition assay in C2C12 myoblasts. Thy1.2(+) early T cells were successfully generated from mouse bone marrow hematopoietic stem cells (BMHSCs) using DLL4 functionalized beads using both insert-based and mixed stromal cell (OP9) coculture conditions, indicating that stem cell-stromal cell physical contact is not necessary for DLL4 directed T-cell differentiation. Coculture studies with bead-to-cell ratios of 1:1 generated higher T-cell differentiation efficiencies, compared to bead-to-cell ratios of 5:1. These data demonstrate the promising potential of this biomaterial-based notch signaling system to generate T cells from stem cells and to elucidate the molecular interactions in T-cell development.

The human T cell response to melanoma antigens

The cornerstone of the concept of immunosurveillance in cancer should be the experimental demonstration of immune responses able to alter the course of in vivo spontaneous tumor progression. Elegant genetic manipulation of the mouse immune system has proved this tenet. In parallel, progress in understanding human T cell mediated immunity has allowed to document the existence in cancer patients of naturally acquired T cell responses to molecularly defined tumor antigens. Various attributes of cutaneous melanoma tumors, notably their adaptability to in vitro tissue culture conditions, have contributed to convert this tumor in the prototype for studies of human antitumor immune responses. As a consequence, the first human cytolytic T lymphocyte (CTL)-defined tumor antigen and numerous others have been identified using lymphocyte material from patients bearing this tumor, detailed analyses of specific T cell responses have been reported and a relatively large number of clinical trials of vaccination have been performed in the last 15 years. Thus, the "melanoma model" continues to provide valuable insights to guide the development of clinically effective cancer therapies based on the recruitment of the immune system. This chapter reviews recent knowledge on human CD8 and CD4 T cell responses to melanoma antigens.

Detection of low avidity desmoglein 3-reactive T cells in pemphigus vulgaris using HLA-DR beta 1*0402 tetramers

In the present study, we developed a HLA class II tetramer-based detection system utilizing DRB1*0402 tetramers loaded with recently identified immunodominant peptides of desmoglein 3 (Dsg3), the major autoantigen of pemphigus vulgaris (PV). Initial experiments demonstrated staining of a Dsg3-reactive T cell hybridoma which was derived from HLA-DR0402-transgenic mice with loaded PE-labeled DRbeta1*0402 tetramers. However, staining of autoreactive T cell clones (TCC) derived from PV patients resulted only in positive staining by addition of exogenous peptides to the staining reactions. There was a dose-dependent specific binding of TCC to the tetramers with the agonistic Dsg3 peptide which was not altered by exogenous unrelated Dsg3 peptide. Noteworthy, the TCC did not stain with HLA-DR4 tetramers complexed with unrelated Dsg3 peptides. The findings of this study suggest that HLA class II tetramers may provide a highly specific approach to monitor ex vivo the T cellular autoimmune response against Dsg3 in patients with PV.

Adoptive T-Cell Therapy of Cancer

Adoptive therapy involves the transfer of ex vivo expanded immune effector cells to patients as a means of augmenting the antitumor immune response. In general, this transfer is accomplished by harvesting cells from the peripheral blood, tumor sites, or draining lymph nodes and expanding effector cells in a specific or nonspecific fashion for adoptive transfer. This article describes the rationale for adoptive T-cell therapy, the developments that have led to the translational application of this strategy for the treatment of cancer, the challenges that have been addressed, and future approaches to the development of adoptive therapy as a treatment modality.

Induction of the Epstein-Barr virus latent membrane protein 2 antigen-specific cytotoxic T lymphocytes using human leukocyte antigen tetramer-based artificial antigen-presenting cells

Cytotoxic T lymphocytes (CTLs) specific for the Epstein-Barr virus (EBV) latent membrane protein 2 (LMP2) antigen are important reagents for the treatment of some EBV-associated malignancies, such as EBV-positive Hodgkin's disease and nasopharyngeal carcinoma. However, the therapeutic amount of CTLs is often hampered by the limited supply of antigen-presenting cells. To address this issue, an artificial antigen-presenting cell (aAPC) was made by coating a human leukocyte antigen (HLA)-pLMP2 tetrameric complex, anti-CD28 antibody and CD54 molecule to a cell-sized latex bead, which provided the dual signals required for T cell activation. By co-culture of the HLA-A2-LMP2 bearing aAPC and peripheral blood mononuclear cells from HLA-A2 positive healthy donors, LMP2 antigen-specific CTLs were induced and expanded in vitro. The specificity of the aAPC-induced CTLs was demonstrated by both HLA-A2-LMP2 tetramer staining and cytotoxicity against HLA-A2-LMP2 bearing T2 cell, the cytotoxicity was inhibited by the anti-HLA class I antibody (W6/32). These results showed that LMP2 antigen-specific CTLs could be induced and expanded in vitro by the HLA-A2-LMP2-bearing aAPC. Thus, aAPCs coated with an HLA-pLMP2 complex, anti-CD28 and CD54 might be promising tools for the enrichment of LMP2-specific CTLs for adoptive immunotherapy.