Potent costimulation of human CD8 T cells by anti-4-1BB and anti-CD28 on synthetic artificial antigen presenting cells

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.

Upstream open reading frames regulate translation of cancer-associated transcripts and encode HLA-presented immunogenic tumor antigens

BACKGROUND

Upstream open reading frames (uORFs) represent translational control elements within eukaryotic transcript leader sequences. Recent data showed that uORFs can encode for biologically active proteins and human leukocyte antigen (HLA)-presented peptides in malignant and benign cells suggesting their potential role in cancer cell development and survival. However, the role of uORFs in translational regulation of cancer-associated transcripts as well as in cancer immune surveillance is still incompletely understood.

METHODS

We examined the translational regulatory effect of 29 uORFs in 13 cancer-associated genes by dual-luciferase assays. Cellular expression and localization of uORF-encoded peptides (uPeptides) were investigated by immunoblotting and immunofluorescence-based microscopy. Furthermore, we utilized mass spectrometry-based immunopeptidome analyses in an extensive dataset of primary malignant and benign tissue samples for the identification of naturally presented uORF-derived HLA-presented peptides screening for more than 2000 uORFs.

RESULTS

We provide experimental evidence for similarly effective translational regulation of cancer-associated transcripts through uORFs initiated by either canonical AUG codons or by alternative translation initiation sites (aTISs). We further demonstrate frequent cellular expression and reveal occasional specific cellular localization of uORF-derived peptides, suggesting uPeptide-specific biological implications. Immunopeptidome analyses delineated a set of 125 naturally presented uORF-derived HLA-presented peptides. Comparative immunopeptidome profiling of malignant and benign tissue-derived immunopeptidomes identified several tumor-associated uORF-derived HLA ligands capable to induce multifunctional T cell responses.

CONCLUSION

Our data provide direct evidence for the frequent expression of uPeptides in benign and malignant human tissues, suggesting a potentially widespread function of uPeptides in cancer biology. These findings may inspire novel approaches in direct molecular as well as immunotherapeutic targeting of cancer-associated uORFs and uPeptides.

Combining a CAR and a chimeric costimulatory receptor enhances T cell sensitivity to low antigen density and promotes persistence

Despite the high remission rates achieved using T cells bearing a chimeric antigen receptor (CAR) against hematogical malignancies, there is still a considerable proportion of patients who eventually experience tumor relapse. Clinical studies have established that mechanisms of treatment failure include the down-regulation of target antigen expression and the limited persistence of effective CAR T cells. We hypothesized that dual targeting mediated by a CAR and a chimeric costimulatory receptor (CCR) could simultaneously enhance T cell cytotoxicity and improve durability. Concomitant high-affinity engagement of a CD38-binding CCR enhanced the cytotoxicity of BCMA-CAR and CD19-CAR T cells by increasing their functional binding avidity. In comparison to second-generation BCMA-CAR or CD19-CAR T cells, double-targeted CAR + CD38-CCR T cells exhibited increased sensitivity to recognize and lyse tumor variants of multiple myeloma and acute lymphoblastic leukemia with low antigen density in vitro. In addition, complimentary costimulation by 4-1BB and CD28 endodomains provided by the CAR and CCR combination conferred increased cytokine secretion and expansion and improved persistence in vivo. The cumulatively improved properties of CAR + CCR T cells enabled the in vivo eradication of antigen-low tumor clones, which were otherwise resistant to treatment with conventional CAR T cells. Therefore, multiplexing targeting and costimulation through the combination of a CAR and a CCR is a powerful strategy to improve the clinical outcomes of CAR T cells by enhancing cytotoxic efficacy and persistence, thus preventing relapses of tumor clones with low target antigen density.

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.

Influence of antigen density and immunosuppressive factors on tumor-targeted costimulation with antibody-fusion proteins and bispecific antibody-mediated T cell response

Target expression heterogeneity and the presence of an immunosuppressive microenvironment can hamper severely the efficiency of immunotherapeutic approaches. We have analyzed the potential to encounter and overcome such conditions by a combinatory two-target approach involving a bispecific antibody retargeting T cells to tumor cells and tumor-directed antibody-fusion proteins with costimulatory members of the B7 and TNF superfamily. Targeting the tumor-associated antigens EpCAM and EGFR with the bispecific antibody and costimulatory fusion proteins, respectively, we analyzed the impact of target expression and the influence of the immunosuppressive factors IDO, IL-10, TGF-β, PD-1 and CTLA-4 on the targeting-mediated stimulation of T cells. Here, suboptimal activity of the bispecific antibody at diverse EpCAM expression levels could be effectively enhanced by targeting-mediated costimulation by B7.1, 4-1BBL and OX40L in a broad range of EGFR expression levels. Furthermore, the benefit of combined costimulation by B7.1/4-1BBL and 4-1BBL/OX40L was demonstrated. In addition, the expression of immunosuppressive factors was shown in all co-culture settings, where blocking of prominent factors led to synergistic effects with combined costimulation. Thus, targeting-mediated costimulation showed general promise for a broad application covering diverse target expression levels, with the option for further selective enhancement by the identification and blockade of main immunosuppressive factors of the particular tumor environment.

Rapid Expansion of Highly Functional Antigen-Specific T Cells from Patients with Melanoma by Nanoscale Artificial Antigen-Presenting Cells

PURPOSE

Generation of antigen-specific T cells from patients with cancer employs large numbers of peripheral blood cells and/or tumor-infiltrating cells to generate antigen-presenting and effector cells commonly requiring multiple rounds of restimulation ex vivo. We used a novel paramagnetic, nanoparticle-based artificial antigen-presenting cell (nano-aAPC) that combines anti-CD28 costimulatory and human MHC class I molecules that are loaded with antigenic peptides to rapidly expand tumor antigen-specific T cells from patients with melanoma.

EXPERIMENTAL DESIGN

Nano-aAPC-expressing HLA-A*0201 molecules and costimulatory anti-CD28 antibody and HLA-A*0201 molecules loaded with MART-1 or gp100 class I-restricted peptides were used to stimulate CD8 T cells purified from the peripheral blood of treatment-naïve or PD-1 antibody-treated patients with stage IV melanoma. Expanded cells were restimulated with fresh peptide-pulsed nano-aAPC at day 7. Phenotype analysis and functional assays including cytokine release, cytolysis, and measurement of avidity were conducted.

RESULTS

MART-1-specific CD8 T cells rapidly expanded up to 1,000-fold by day 14 after exposure to peptide-pulsed nano-aAPC. Expanded T cells had a predominantly stem cell memory CD45RA⁺/CD62L⁺/CD95⁺ phenotype; expressed ICOS, PD-1, Tim3, and LAG3; and lacked CD28. Cells from patients with melanoma were polyfunctional; highly avid; expressed IL2, IFNγ, and TNFα; and exhibited cytolytic activity against tumor cell lines. They expanded 2- to 3-fold after exposure to PD-1 antibody in vivo, and expressed a highly diverse T-cell receptor V beta repertoire.

CONCLUSIONS

Peptide-pulsed nano-aAPC rapidly expanded polyfunctional antigen-specific CD8 T cells with high avidity, potent lytic function, and a stem cell memory phenotype from patients with melanoma.

Opportunities and Challenges for Antibodies against Intracellular Antigens

Therapeutic antibodies are one most significant advances in immunotherapy, the development of antibodies against disease-associated MHC-peptide complexes led to the introduction of TCR-like antibodies. TCR-like antibodies combine the recognition of intracellular proteins with the therapeutic potency and versatility of monoclonal antibodies (mAb), offering an unparalleled opportunity to expand the repertoire of therapeutic antibodies available to treat diseases like cancer. This review details the current state of TCR-like antibodies and describes their production, mechanisms as well as their applications. In addition, it presents an insight on the challenges that they must overcome in order to become commercially and clinically validated.

Combined CD28 and 4-1BB Costimulation Potentiates Affinity-tuned Chimeric Antigen Receptor-engineered T Cells

PURPOSE

Targeting nonspecific, tumor-associated antigens (TAA) with chimeric antigen receptors (CAR) requires specific attention to restrict possible detrimental on-target/off-tumor effects. A reduced affinity may direct CAR-engineered T (CAR-T) cells to tumor cells expressing high TAA levels while sparing low expressing normal tissues. However, decreasing the affinity of the CAR-target binding may compromise the overall antitumor effects. Here, we demonstrate the prime importance of the type of intracellular signaling on the function of low-affinity CAR-T cells.

EXPERIMENTAL DESIGN

We used a series of single-chain variable fragments (scFv) with five different affinities targeting the same epitope of the multiple myeloma-associated CD38 antigen. The scFvs were incorporated in three different CAR costimulation designs and we evaluated the antitumor functionality and off-tumor toxicity of the generated CAR-T cells in vitro and in vivo.

RESULTS

We show that the inferior cytotoxicity and cytokine secretion mediated by CD38 CARs of very low-affinity (K _d < 1.9 × 10^-6 mol/L) bearing a 4-1BB intracellular domain can be significantly improved when a CD28 costimulatory domain is used. Additional 4-1BB signaling mediated by the coexpression of 4-1BBL provided the CD28-based CD38 CAR-T cells with superior proliferative capacity, preservation of a central memory phenotype, and significantly improved in vivo antitumor function, while preserving their ability to discriminate target antigen density.

CONCLUSIONS

A combinatorial costimulatory design allows the use of very low-affinity binding domains (K _d < 1 μmol/L) for the construction of safe but also optimally effective CAR-T cells. Thus, very-low-affinity scFvs empowered by selected costimulatory elements can enhance the clinical potential of TAA-targeting CARs.

The HLA ligandome landscape of chronic myeloid leukemia delineates novel T-cell epitopes for immunotherapy

Antileukemia immunity plays an important role in disease control and maintenance of tyrosine kinase inhibitor (TKI)-free remission in chronic myeloid leukemia (CML). Thus, antigen-specific immunotherapy holds promise for strengthening immune control in CML but requires the identification of CML-associated targets. In this study, we used a mass spectrometry–based approach to identify naturally presented HLA class I– and class II–restricted peptides in primary CML samples. Comparative HLA ligandome profiling using a comprehensive dataset of different hematological benign specimens and samples from CML patients in deep molecular remission delineated a panel of novel frequently presented CML-exclusive peptides. These nonmutated target antigens are of particular relevance because our extensive data-mining approach suggests the absence of naturally presented BCR-ABL– and ABL-BCR–derived HLA-restricted peptides and the lack of frequent tumor-exclusive presentation of known cancer/testis and leukemia-associated antigens. Functional characterization revealed spontaneous T-cell responses against the newly identified CML-associated peptides in CML patient samples and their ability to induce multifunctional and cytotoxic antigen-specific T cells de novo in samples from healthy volunteers and CML patients. Thus, these antigens are prime candidates for T-cell–based immunotherapeutic approaches that may prolong TKI-free survival and even mediate cure of CML patients.

Enrich and Expand Rare Antigen-specific T Cells with Magnetic Nanoparticles

We have developed a tool to both enrich and expand antigen-specific T cells. This can be helpful in cases such as to A) detect the existence of antigen-specific T cells, B) probe the dynamics of antigen-specific responses, C) understand how antigen-specific responses affect disease state such as autoimmunity, D) demystify heterogeneous responses for antigen-specific T cells, or E) utilize antigen-specific cells for therapy. The tool is based on a magnetic particle that we conjugate antigen-specific and T cell co-stimulatory signals, and that we term as artificial antigen presenting cells (aAPCs). Consequently, since the technology is simple to produce, it can easily be adopted by other laboratories; thus, our purpose here is to describe in detail the fabrication and subsequent use of the aAPCs. We explain how to attach antigen-specific and co-stimulatory signals to the aAPCs, how to utilize them to enrich for antigen-specific T cells, and how to expand antigen-specific T cells. Furthermore, we will highlight engineering design considerations based on experimental and biological information of our experience with characterizing antigen-specific T cells.

Artificial antigen-presenting cells are superior to dendritic cells at inducing antigen-specific cytotoxic T lymphocytes

Adoptive immunotherapy is a promising cancer treatment that entails infusion of immune cells manipulated to have antitumor specificity, in vitro. Antigen-specific cytotoxic T lymphocytes are the main executors of transformed cells during cancer immunotherapy. To induce antigen-specific cytotoxic T lymphocytes, we developed artificial antigen-presenting cells (aAPCs) by engineering K562 cells with electroporation to direct the stable expression of HLA-A∗0201, CD80, and 4-1BBL. Our findings demonstrate that after three stimulation cycles, the aAPCs promoted the induction of antigen-specific cytotoxic T lymphocytes with a less differentiated "young" phenotype, which enhanced immune responses with superior cytotoxicity. This novel, easy, and cost-effective approach to inducing antigen-specific cytotoxic T lymphocytes provides the possibility of improved cancer therapies.

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.

Engineering Platforms for T Cell Modulation

T cells are crucial contributors to mounting an effective immune response and increasingly the focus of therapeutic interventions in cancer, infectious disease, and autoimmunity. Translation of current T cell immunotherapies has been hindered by off-target toxicities, limited efficacy, biological variability, and high costs. As T cell therapeutics continue to develop, the application of engineering concepts to control their delivery and presentation will be critical for their success. Here, we outline the engineer's toolbox and contextualize it with the biology of T cells. We focus on the design principles of T cell modulation platforms regarding size, shape, material, and ligand choice. Furthermore, we review how application of these design principles has already impacted T cell immunotherapies and our understanding of T cell biology. Recent, salient examples from protein engineering, synthetic particles, cellular and genetic engineering, and scaffolds and surfaces are provided to reinforce the importance of design considerations. Our aim is to provide a guide for immunologists, engineers, clinicians, and the pharmaceutical sector for the design of T cell-targeting platforms.

The natural HLA ligandome of glioblastoma stem-like cells: antigen discovery for T cell-based immunotherapy

Glioblastoma is the most frequent malignant primary brain tumor. In a hierarchical tumor model, glioblastoma stem-like cells (GSC) play a major role in tumor initiation and maintenance as well as in therapy resistance and recurrence. Thus, targeting this cellular subset may be key to effective immunotherapy. Here, we present a mass spectrometry-based analysis of HLA-presented peptidomes of GSC and glioblastoma patient specimens. Based on the analysis of patient samples (n = 9) and GSC (n = 3), we performed comparative HLA peptidome profiling against a dataset of normal human tissues. Using this immunopeptidome-centric approach we could clearly delineate a subset of naturally presented, GSC-associated HLA ligands, which might serve as highly specific targets for T cell-based immunotherapy. In total, we identified 17 antigens represented by 41 different HLA ligands showing natural and exclusive presentation both on GSC and patient samples. Importantly, in vitro immunogenicity and antigen-specific target cell killing assays suggest these peptides to be epitopes of functional CD8+ T cell responses, thus rendering them prime candidates for antigen-specific immunotherapy of glioblastoma.

Separating T Cell Targeting Components onto Magnetically Clustered Nanoparticles Boosts Activation

T cell activation requires the coordination of a variety of signaling molecules including T cell receptor-specific signals and costimulatory signals. Altering the composition and distribution of costimulatory molecules during stimulation greatly affects T cell functionality for applications such as adoptive cell therapy (ACT), but the large diversity in these molecules complicates these studies. Here, we develop and validate a reductionist T cell activation platform that enables streamlined customization of stimulatory conditions. This platform is useful for the optimization of ACT protocols as well as the more general study of immune T cell activation. Rather than decorating particles with both signal 1 antigen and signal 2 costimulus, we use distinct, monospecific, paramagnetic nanoparticles, which are then clustered on the cell surface by a magnetic field. This allows for rapid synthesis and characterization of a small number of single-signal nanoparticles which can be systematically combined to explore and optimize T cell activation. By increasing cognate T cell enrichment and incorporating additional costimulatory molecules using this platform, we find significantly higher frequencies and numbers of cognate T cells stimulated from an endogenous population. The magnetic field-induced association of separate particles thus provides a tool for optimizing T cell activation for adoptive immunotherapy and other immunological studies.

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.

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.

Identification of Immunogenic Epitopes by MS/MS

The interrogation of cell surface-presented immunogenic epitopes is of great importance to differentiate diseased cells in consequence to malignant transformation or viral infections. On the basis of this knowledge, next-generation immunotherapies against cancers, autoimmunity, or infectious diseases can be developed. The identification of altered peptide repertoires of transformed cells renders mass spectrometry-based analysis indispensable. This is evident considering the low correlation of gene or protein expression alterations, respectively, with changes in the peptide repertoire rendering those analyses less informative. Nevertheless, immunogenicity of peptides appearing to be exclusively found on diseased cells has to be finally proven in T cell-based assays. This review highlights the capabilities and limitations of mass spectrometry in the identification of entire immunopeptidomes, as well as individual potential immunogenic epitopes with a strong focus on cancer. Furthermore, an overview of state-of-the-art immunogenicity screens is presented.

Surface engineering for lymphocyte programming

The once nascent field of immunoengineering has recently blossomed to include approaches to deliver and present biomolecules to program diverse populations of lymphocytes to fight disease. Building upon improved understanding of the molecular and physical mechanics of lymphocyte activation, varied strategies for engineering surfaces to activate and deactivate T-Cells, B-Cells and natural killer cells are in preclinical and clinical development. Surfaces have been engineered at the molecular level in terms of the presence of specific biological factors, their arrangement on a surface, and their diffusivity to elicit specific lymphocyte fates. In addition, the physical and mechanical characteristics of the surface including shape, anisotropy, and rigidity of particles for lymphocyte activation have been fine-tuned. Utilizing these strategies, acellular systems have been engineered for the expansion of T-Cells and natural killer cells to clinically relevant levels for cancer therapies as well as engineered to program B-Cells to better combat infectious diseases.

Artificial antigen-presenting cells expressing AFP(158-166) peptide and interleukin-15 activate AFP-specific cytotoxic T lymphocytes

Professional antigen-presenting cells (APCs) are potent generators of tumor antigen-specific cytotoxic T lymphocytes (CTLs) for adoptive immunotherapy; however, generation of APCs is cumbersome, expensive, and subject to the tumor microenvironment. Artificial APCs (aAPCs) have been developed as a cost-effective alternative to APCs. We developed a cellular aAPC that efficiently generated alpha-fetoprotein (AFP)-specific CTLs. We genetically modified the human B cell lymphoma cell line BJAB with a lentiviral vector to establish an aAPC called BA15. The expression of AFP_158-166-HLA-A*02:01 complex, CD80, CD86, and interleukin (IL)-15 in BA15 cells was assessed. The efficiency of BA15 at generating AFP-specific CTLs and the specific cytotoxicity of CTLs against AFP+ cells were also determined. BA15 cells expressed high levels of AFP_158-166 peptide, HLA-A2, CD80, CD86, and IL-15. BA15 cells also exhibited higher efficiency in generating AFP-specific CTLs than did dendritic cells. These CTLs had greater cytotoxicity against AFP+ hepatocellular carcinoma cells than did CTLs obtained from dendritic cells in vitro and in vivo. Our novel aAPC system could provide a robust platform for the generation of functional AFP-specific CTLs for adoptive immunotherapy of hepatocellular carcinoma.

HLA class I-restricted MYD88 L265P-derived peptides as specific targets for lymphoma immunotherapy

Genome sequencing has uncovered an array of recurring somatic mutations in different non-Hodgkin lymphoma (NHL) subtypes. If affecting protein-coding regions, such mutations may yield mutation-derived peptides that may be presented by HLA class I proteins and recognized by cytotoxic T cells. A recurring somatic and oncogenic driver mutation of the Toll-like receptor adaptor protein MYD88, Leu265Pro (L265P) was identified in up to 90% of different NHL subtype patients. We therefore screened the potential of MYD88L265P-derived peptides to elicit cytotoxic T cell responses as tumor-specific neoantigens. Based on in silico predictions, we identified potential MYD88L265P-containing HLA ligands for several HLA class I restrictions. A set of HLA class I MYD88L265P-derived ligands elicited specific cytotoxic T cell responses for HLA-B*07 and -B*15. These data highlight the potential of MYD88L265P mutation-specific peptide-based immunotherapy as a novel personalized treatment approach for patients with MYD88L265P+ NHLs that may complement pharmacological approaches targeting oncogenic MyD88 L265P signaling.

Induction of anti-tumor CD8 T cell responses by experimental ECP-induced human dendritic antigen presenting cells

Extracorporeal photochemotherapy (ECP), or photopheresis, is distinguished by the specificity of the clinically potent immunologic reactions it initiates or regulates. The selectivity of ECP-induced immunoprotection for the malignant clone in cutaneous T cell lymphoma (CTCL), and for the pathogenic clones in allograft rejection and graft-versus-host disease (GVHD), has suggested a central mechanistic role for dendritic antigen presenting cells (DC). Discovery of ECP's induction of monocyte-derived DC, via monocyte signaling by ECP-plate activated platelets, and the absolute dependency of experimental ECP on such induced DC, supports that premise. Herein, we show that ECP-induced DC are capable of stimulating CD8 T cell responses to tumor antigens with which they are loaded. They internalize an antigen-specific melanoma-associated protein then present it onto a class I major histocompatibility, which then stimulates expansion of anti-tumor CD8 T cell populations. We conclude that ECP-induced DC prominently contribute to its initiation of anti-tumor immunity and raise the possibility that the therapy may be applicable to the immunotherapeutic management of a broader spectrum of cancers.

A combined approach of human leukocyte antigen ligandomics and immunogenicity analysis to improve peptide-based cancer immunotherapy

The breakthrough development of immune checkpoint inhibitors as clinically effective novel therapies demonstrates the potential of cancer immunotherapy. The identification of suitable targets for specific immunotherapy, however, remains a challenging task. Most peptides previously used for vaccination in clinical trials were able to elicit strong immunological responses but failed with regard to clinical benefit. This might, at least partly, be caused by an inadequate peptide selection, usually derived from established tumor-associated antigens which are not necessarily presented as human leukocyte antigen (HLA) ligands. Recently, HLA ligandome analysis revealed cancer-associated peptides, which have been used in clinical trials showing encouraging impact on survival. To improve peptide-based cancer immunotherapy, our group established a combined approach of HLA ligandomics and immunogenicity analysis for the identification of vaccine peptides. This approach is based on the identification of naturally presented HLA ligands on tumor samples, the selection of tumor-associated/tumor-specific HLA ligands and their subsequent testing for immunogenicity in vitro. In this review, we want to present our pipeline for the identification of vaccine peptides, focusing on ovarian cancer, and want to discuss differences to other approaches. Furthermore, we want to give a short outlook of a potential multi-peptide vaccination trial using the novel identified peptides.

The antigenic landscape of multiple myeloma: mass spectrometry (re)defines targets for T-cell-based immunotherapy

Direct analysis of HLA-presented antigens by mass spectrometry provides a comprehensive view on the antigenic landscape of different tissues/malignancies and enables the identification of novel, pathophysiologically relevant T-cell epitopes. Here, we present a systematic and comparative study of the HLA class I and II presented, nonmutant antigenome of multiple myeloma (MM). Quantification of HLA surface expression revealed elevated HLA molecule counts on malignant plasma cells compared with normal B cells, excluding relevant HLA downregulation in MM. Analyzing the presentation of established myeloma-associated T-cell antigens on the HLA ligandome level, we found a substantial proportion of antigens to be only infrequently presented on primary myelomas or to display suboptimal degrees of myeloma specificity. However, unsupervised analysis of our extensive HLA ligand data set delineated a panel of 58 highly specific myeloma-associated antigens (including multiple myeloma SET domain containing protein) which are characterized by frequent and exclusive presentation on myeloma samples. Functional characterization of these target antigens revealed peptide-specific, preexisting CD8(+) T-cell responses exclusively in myeloma patients, which is indicative of pathophysiological relevance. Furthermore, in vitro priming experiments revealed that peptide-specific T-cell responses can be induced in response-naive myeloma patients. Together, our results serve to guide antigen selection for T-cell-based immunotherapy of MM.

Cellular therapy in combination with cytokines improves survival in a xenograft mouse model of ovarian cancer

Studies have shown enhanced survival of ovarian cancer patients in which the tumors are infiltrated with tumor infiltrating lymphocytes and natural killer cells showing the importance of immune surveillance and recognition in ovarian cancer. Therefore, in this study, we tested cellular immunotherapy and varying combinations of cytokines (IL-2 and/or pegylated-IFNα-2b) in a xenograft mouse model of ovarian cancer. SKOV3-AF2 ovarian cancer cells were injected intra-peritoneally (IP) into athymic nude mice. On day 7 post-tumor cell injection, mice were injected IP with peripheral blood mononuclear cells (PBMC; 5 × 10(6) PBMC) and cytokine combinations [IL-2 ± pegylated-IFNα-2b (IFN)]. Cytokine injections were continued weekly for IFN (12,000 U/injection) and thrice weekly for IL-2 (4000 U/injection). Mice were euthanized when they became moribund due to tumor burden at which time tumor and ascitic fluid were measured and collected. Treatment efficacy was measured by improved survival at 8 weeks and overall survival by Kaplan-Meier analysis. We observed that the mice tolerated all treatment combinations without significant weight loss or other apparent illness. Mice receiving PBMC plus IL-2 showed improved median survival (7.3 weeks) compared to mice with no treatment (4.2 weeks), IL-2 (3.5 weeks), PBMC (4.0 weeks), or PBMC plus IL-2 and IFN (4.3 weeks), although PBMC plus IL-2 was not statistically different than PBMC plus IFN (5.5 weeks, p > 0.05). We demonstrate that cytokine-stimulated cellular immune therapy with PBMC and IL-2 was well tolerated and resulted in survival advantage compared to untreated controls and other cytokine combinations in the nude-mouse model.

Enhancement of the antigen-specific cytotoxic T lymphocyte-inducing ability in the PMDC11 leukemic plasmacytoid dendritic cell line via lentiviral vector-mediated transduction of the caTLR4 gene

The aim of the present study was to enhance the efficiency of leukemia immunotherapy by increasing the antigen-specific cytotoxic T lymphocyte-inducing ability of leukemia cells. The leukemic plasmacytoid dendritic cell line PMDC05 containing the HLA-A02/24 antigen, which was previously established in our laboratory (Laboratory of Hematology and Oncology, Graduate School of Health Sciences, Niigata University, Niigata, Japan), was used in the present study. It exhibited higher expression levels of CD80 following transduction with lentiviruses encoding the CD80 gene. This CD80-expressing PMDC05 was named PMDC11. In order to establish a more potent antigen-presenting cell for cellular immunotherapy of tumors or severe infections, PMDC11 cells were transduced with a constitutively active (ca) toll-like receptor 4 (TLR4) gene using the Tet-On system (caTLR4-PMDC11). CD8⁺ T cells from healthy donors with HLA-A02 were co-cultured with mutant WT1 peptide-pulsed PMDC11, lipopolysaccharide (LPS)-stimulated PMDC11 or caTLR4-PMDC11 cells. Interleukin (IL)-2 (50 IU/ml) and IL-7 (10 ng/ml) were added on day three of culture. Priming with mutant WT1 peptide-pulsed PMDC11, LPS-stimulated PMDC11 or caTLR4-PMDC11 cells was conducted once per week and two thirds of the IL-2/IL-7 containing medium was replenished every 3–4 days. Immediately prior to the priming with these various PMDC11 cells, the cultured cells were analyzed for the secretion of interferon (IFN)-γ in addition to the percentage and number of CD8⁺/WT1 tetramer⁺ T cells using flow cytometry. caTLR4-PMDC11 cells were observed to possess greater antigen-presenting abilities compared with those of PMDC11 or LPS-stimulated PMDC11 cells in a mixed leukocyte culture. CD8 T cells positive for the WT1 tetramer were generated following 3–4 weeks of culture and CD8⁺/WT1 tetramer⁺ T cells were markedly increased in caTLR4-PMDC11-primed CD8⁺ T cell culture compared with PMDC11 or LPS-stimulated PMDC11-primed CD8⁺ T cell culture. These CD8⁺ T cells co-cultured with caTLR4-PMDC11 cells were demonstrated to secrete IFN-γ and to be cytotoxic to WT1-expressing target cells. These data suggested that the antigen-specific cytotoxic T lymphocyte (CTL)-inducing ability of PMDC11 was potentiated via transduction of the caTLR4 gene. The present study also suggested that caTLR4-PMDC11 cells may be applied as potent antigen-presenting cells for generating antigen-specific CTLs in adoptive cellular immunotherapy against tumors and severe viral infections.

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.

HLA ligandome analysis identifies the underlying specificities of spontaneous antileukemia immune responses in chronic lymphocytic leukemia (CLL)

The breakthrough development of clinically effective immune checkpoint inhibitors illustrates the potential of T-cell-based immunotherapy to effectively treat malignancies. A remaining challenge is to increase and guide the specificities of anticancer immune responses, e.g., by therapeutic vaccination or by adoptive T-cell transfer. By analyzing the landscape of naturally presented HLA class I and II ligands of primary chronic lymphocytic leukemia (CLL), we delineated a novel category of tumor-associated T-cell antigens based on their exclusive and frequent representation in the HLA ligandome of leukemic cells. These antigens were validated across different stages and mutational subtypes of CLL and found to be robustly represented in HLA ligandomes of patients undergoing standard chemo-/immunotherapy. We demonstrate specific immune recognition of these antigens exclusively in CLL patients, with the frequencies of representation in CLL ligandomes correlating with the frequencies of immune recognition by patient T cells. Moreover, retrospective survival analysis revealed survival benefits for patients displaying immune responses to these antigens. These results directly imply these nonmutant self-peptides as pathophysiologically relevant tumor antigens and encourages their implementation for cancer immunotherapy.

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.

Antigen-specific activation and cytokine-facilitated expansion of naive, human CD8+ T cells

Antigen-specific priming of human, naive T cells has been difficult to assess. Owing to the low initial frequency in the naive cell pool of specific T cell precursors, such an analysis has been obscured by the requirements for repeated stimulations and prolonged culture time. In this protocol, we describe how to evaluate antigen-specific priming of CD8(+) cells 10 d after a single specific stimulation. The assay provides reference conditions, which result in the expansion of a substantial population of antigen-specific T cells from the naive repertoire. Various conditions and modifications during the priming process (e.g., testing new cytokines, co-stimulators and so on) can now be directly compared with the reference conditions. Factors relevant to achieving effective priming include the dendritic cell preparation, the T cell preparation, the cell ratio at the time of priming, the serum source used for the experiment and the timing of addition and concentration of the cytokines used for expansion. This protocol is relevant for human immunology, vaccine biology and drug development.

Latex bead-based artificial antigen-presenting cells induce tumor-specific CTL responses in the native T-cell repertoires and inhibit tumor growth

Cell-free artificial antigen-presenting cells (aAPCs) were generated by coupling H-2K(b)/TRP2 tetramers together with anti-CD28 and anti-4-1BB antibodies onto cell-sized latex beads and injected intravenously and subcutaneously into naïve mice and antigen-primed mice (B6, H-2K(b)). Vigorous tumor antigen-specific CTL responses in the native T-cell repertoire in each mouse model were elicited as evaluated by measuring surface CD69 and CD25, intracellular IFN-γ, tetramer staining and cytolysis of melanoma cells. Furthermore, the aAPCs efficiently inhibited subcutaneous tumor growth and markedly delayed tumor progression in tumor-bearing mice. These data suggest that bead-based aAPCs represent a potential strategy for the active immunotherapy of cancers or persistent infections.

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.

Cytotoxic T-lymphocyte immunotherapy for ovarian cancer: a pilot study

The objective was to evaluate the toxicity and feasibility of intraperitoneal infusion of tumor-specific cytotoxic T lymphocytes (CTL) as therapy for recurrent ovarian cancer, and to determine if repetitive cycles of CTL generation and infusion measurably increases the host's ovarian cancer immune response. In this study, 7 subjects with recurrent ovarian cancer confined to the peritoneal cavity underwent up to 4 cycles, each cycle beginning with a leukapheresis for collection of precursor lymphocytes, which were stimulated in vitro with mucin 1, a tumor-specific antigen found commonly in ovarian cancer cells. The resulting new CTL for each cycle were reintroduced into the host by intraperitoneal infusion. Immunologic parameters (killer cells, cytokine production, memory T lymphocytes, and natural killer cells) were studied. Toxicity, CA-125, and survival data were also evaluated. The tumor marker CA-125 was nonstatistically significantly reduced after the first month of immunotherapy. However, after that it rose. Killer cells, cytokine production, and memory T lymphocytes increased after the first cycle of stimulation, but plateaued or reduced thereafter. The percent of natural killer cells inversely correlated with other immune parameters. Median survival was 11.5 months. One subject is free of disease since December, 2000. Multiple cycles, beyond 1 cycle, of T-cell stimulation followed by adoptive T-cell infusion, may not enhance the in vivo immune response.

Augmented lymphocyte expansion from solid tumors with engineered cells for costimulatory enhancement

Treatment of patients with adoptive T-cell therapy requires expansion of unique tumor-infiltrating lymphocyte (TIL) cultures from single-cell suspensions processed from melanoma biopsies. Strategies which increase the expansion and reliability of TIL generation from tumor digests are necessary to improve access to TIL therapy. Previous studies have evaluated artificial antigen presenting cells for their antigen-specific and costimulatory properties. We investigated engineered cells for costimulatory enhancement (ECCE) consisting of K562 cells that express 4-1BBL in the absence of artificial antigen stimulation. ECCE accelerated TIL expansion and significantly improved TIL numbers (P=0.001) from single-cell melanoma suspensions. TIL generated with ECCE contain significantly more CD8CD62L and CD8CD27 T cells then comparable interleukin-2-expanded TIL and maintained antitumor reactivity. Moreover, ECCE improved TIL expansion from nonmelanoma-cell suspensions similar to that seen with melanoma tumors. These data demonstrate that the addition of ECCE to TIL production will enable the treatment of patients that are ineligible using current methods.

In vitro stimulation and expansion of human tumour-reactive CD8+ cytotoxic T lymphocytes by anti-CD3/CD28/CD137 magnetic beads

Adoptive immunotherapy with tumour-reactive CD8(+) cytotoxic T lymphocytes (CTLs) requires efficient in vitro approaches allowing the expansion of CTLs to large numbers prior infusion. Here, we investigated the antigen-independent activation and the expansion of human T cells in peripheral blood mononuclear cells (PBMCs) and in tumour-reactive CTLs using Dynabeads coated with monoclonal antibodies to CD3 and to the costimulatory molecules CD28 and CD137 (4-1BB). T cells in PBMCs showed an increased expansion rate of 15- to 17-fold during a 2-week culture period using antibody-conjugated beads with interleukin-2 (IL-2) added versus IL-2 alone. No significant difference between CD3/CD28 beads and CD3/CD28/CD137 beads was observed (P = 0.4). In contrast, expansion of tumour-reactive CD8(+) CTLs over 2 weeks was more efficient using CD3/CD28/CD137 beads (14.4-fold ± 1.2) compared with CD3/CD28 beads (10.6-fold ± 0.7) (P = 0.03) and matched well to the control arm using weekly stimulation with tumour cells. Although all modes of in vitro stimulation decreased the expression of central memory markers CD62L and CCR7 on CTLs, bead-activated cultures expressed consistently higher levels than tumour-stimulated cultures. CTLs analysed after bead-induced expansion versus weekly tumour stimulation showed equal IFN-γ production in ELISPOT assay. Furthermore, cytotoxicity assays demonstrated an either unchanged or slightly reduced capability of tumour cell lysis for antigen-independent stimulated CTLs versus those that maintained on weekly tumour stimulation, regardless of which type of beads was used. Our data suggest that the conjugation of anti-CD137 antibodies to conventional CD3/CD28 beads results in a minor but significant increase in the expansion capacity for tumour-reactive CD8(+) CTLs.

Genetic engineering of T cells for adoptive immunotherapy

To be effective for the treatment of cancer and infectious diseases, T cell adoptive immunotherapy requires large numbers of cells with abundant proliferative reserves and intact effector functions. We are achieving these goals using a gene therapy strategy wherein the desired characteristics are introduced into a starting cell population, primarily by high efficiency lentiviral vector-mediated transduction. Modified cells are then expanded using ex vivo expansion protocols designed to minimally alter the desired cellular phenotype. In this article, we focus on strategies to (1) dissect the signals controlling T cell proliferation; (2) render CD4 T cells resistant to HIV-1 infection; and (3) redirect CD8 T cell antigen specificity.

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.

A cryptic vascular endothelial growth factor T-cell epitope: identification and characterization by mass spectrometry and T-cell assays

Vascular endothelial growth factor (VEGF) is involved in various physiologic processes, such as angiogenesis or wound healing, but is also crucial in pathologic events, such as tumor growth. Thus, clinical anti-VEGF treatments have been developed that could already show beneficial effects for cancer patients. In this article, we describe the first VEGF-derived CD8(+) T-cell epitope. The natural HLA ligand SRFGGAVVR was identified by differential mass spectrometry in two primary renal cell carcinomas (RCC) and was significantly overpresented on both tumor tissues. SRFGGAVVR is derived from a cryptic translated region of VEGF presumably by initiation of translation at the nonclassic start codon CUG(499). SRFGGAVVR-specific T cells were generated in vitro using peptide-loaded dendritic cells or artificial antigen-presenting cells. SRFGGAVVR-specific CD8(+) T cells, identified by HLA tetramer analysis after in vitro stimulation, were fully functional T effector cells, which were able to secrete IFN-gamma on stimulation and killed tumor cells in vitro. Additionally, we have quantitatively analyzed VEGF mRNA and protein levels in RCC tumor and normal tissue samples by gene chip analysis, quantitative reverse transcription-PCR, in situ hybridization, and bead-based immunoassay. In the future, T cells directed against VEGF as a tumor-associated antigen may represent a possible way of combining peptide-based anti-VEGF immunotherapy with already existent anti-VEGF cancer therapies.