The ABCs of artificial antigen presentation

Artificial Methods for T Cell Activation: Critical Tools in T Cell Biology and T Cell Immunotherapy

Antigen-specific immunity conferred by T lymphocytes is a result of complex molecular interactions at the immunological synapse. A variety of biomimetic approaches have been devised to artificially induce T cell activation either to study the T cell biology or to expand and prime the therapeutic T cell populations. Here we first briefly review the molecular and cellular, structural and phenotypical bases that are involved in T cell activation. The artificial methods for T cell activation are then discussed in two grand categories, the soluble (3D) and the surface-anchored (2D) platforms with their design parameters. With the growing number of successful adoptive T cell therapies, the spurring demands for effective and safe T cell expansion as well as precise control over resulting T cell functions and phenotypes warrant the extensions of engineering parameters in the development of novel methodologies for T cell activation.

Surface-Engineering of Red Blood Cells as Artificial Antigen Presenting Cells Promising for Cancer Immunotherapy

The development of artificial antigen presenting cells (aAPCs) to mimic the functions of APCs such as dendritic cells (DCs) to stimulate T cells and induce antitumor immune responses has attracted substantial interests in cancer immunotherapy. In this work, a unique red blood cell (RBC)-based aAPC system is designed by engineering antigen peptide-loaded major histocompatibility complex-I and CD28 activation antibody on RBC surface, which are further tethered with interleukin-2 (IL2) as a proliferation and differentiation signal. Such RBC-based aAPC-IL2 (R-aAPC-IL2) can not only provide a flexible cell surface with appropriate biophysical parameters, but also mimic the cytokine paracrine delivery. Similar to the functions of matured DCs, the R-aAPC-IL2 cells can facilitate the proliferation of antigen-specific CD8+ T cells and increase the secretion of inflammatory cytokines. As a proof-of-concept, we treated splenocytes from C57 mice with R-aAPC-IL2 and discovered those splenocytes induced significant cancer-cell-specific lysis, implying that the R-aAPC-IL2 were able to re-educate T cells and induce adoptive immune response. This work thus presents a novel RBC-based aAPC system which can mimic the functions of antigen presenting DCs to activate T cells, promising for applications in adoptive T cell transfer or even in direct activation of circulating T cells for cancer immunotherapy.

Unbiased Identification of T-Cell Receptors Targeting Immunodominant Peptide-MHC Complexes for T-Cell Receptor Immunotherapy

T-cell receptor (TCR) immunotherapy uses T cells engineered with new TCRs to enable detection and killing of cancer cells. Efficacy of TCR immunotherapy depends on targeting antigenic peptides that are efficiently presented by the best-suited major histocompatibility complex (MHC) molecules of cancer cells. However, efficient strategies are lacking to easily identify TCRs recognizing immunodominant peptide-MHC (pMHC) combinations utilizing any of the six possible MHC class I alleles of a cancer cell. We generated an MHC cell library and developed a platform approach to detect, isolate, and re-express TCRs specific for immunodominant pMHCs. The platform approach was applied to identify a human papillomavirus (HPV16) oncogene E5-specific TCR, recognizing a novel, naturally processed pMHC (HLA-B*15:01) and a cytomegalovirus-specific TCR targeting an immunodominant pMHC (HLA-B*07:02). The platform provides a useful tool to isolate in an unbiased manner TCRs specific for novel and immunodominant pMHC targets for use in TCR immunotherapy.

Paracrine release of IL-2 and anti-CTLA-4 enhances the ability of artificial polymer antigen-presenting cells to expand antigen-specific T cells and inhibit tumor growth in a mouse model

Accumulating evidence indicates that bead-based artificial antigen-presenting cells (aAPCs) are a powerful tool to induce antigen-specific T cell responses in vitro and in vivo. To date, most conventional aAPCs have been generated by coupling an antigen signal (signal 1) and one or two costimulatory signals, such as anti-CD28 with anti-LFA1 or anti-4-1BB (signal 2), onto the surfaces of cell-sized or nanoscale magnetic beads or polyester latex beads. The development of a biodegradable scaffold and the combined use of multiple costimulatory signals as well as third signals for putative clinical applications is the next step in the development of this technology. Here, a novel biodegradable aAPC platform for active immunotherapy was developed by co-encapsulating IL-2 and anti-CTLA-4 inside cell-sized polylactic-co-glycolic acid microparticles (PLGA-MPs) while co-coupling an H-2Kb/TRP2-Ig dimer and anti-CD28 onto the surface. Cytokines (activating signal) and antibodies (anti-inhibition signal) were efficiently co-encapsulated in PLGA-MP-based aAPCs and co-released without interfering with each other. The targeted, sustained co-release of IL-2 and anti-CTLA-4 achieved markedly enhanced, synergistic effects in activating and expanding tumor antigen-specific T cells both in vitro and in vivo, as well as in inhibiting tumor growth in a mouse melanoma model, as compared with conventional two-signal aAPCs and IL-2 or anti-CTLA-4 single-released aAPCs. These data revealed the feasibility and importance of the paracrine release of multiple costimulatory molecules and cytokines from biodegradable aAPCs and thus provide a proof of principle for the future use of polymeric aAPCs for active immunotherapy of tumors and infectious diseases.

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.

Tailoring Biomaterials for Cancer Immunotherapy: Emerging Trends and Future Outlook

Cancer immunotherapy, as a paradigm shift in cancer treatment, has recently received tremendous attention. The active cancer vaccination, immune checkpoint blockage (ICB) and chimeric antigen receptor (CAR) for T-cell-based adoptive cell transfer are among these developments that have achieved a significant increase in patient survival in clinical trials. Despite these advancements, emerging research at the interdisciplinary interface of cancer biology, immunology, bioengineering, and materials science is important to further enhance the therapeutic benefits and reduce side effects. Here, an overview of the latest studies on engineering biomaterials for the enhancement of anticancer immunity is given, including the perspectives of delivery of immunomodulatory therapeutics, engineering immune cells, and constructing immune-modulating scaffolds. The opportunities and challenges in this field are also discussed.

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.

Use of Engineered Exosomes Expressing HLA and Costimulatory Molecules to Generate Antigen-specific CD8+ T Cells for Adoptive Cell Therapy

Dendritic cell-derived exosomes (DEX) comprise an efficient stimulator of T cells. However, the production of sufficient DEX remains a barrier to their broad applicability in immunotherapeutic approaches. In previous studies, genetically engineered K562 have been used to generate artificial antigen presenting cells (AAPC). Here, we isolated exosomes from K562 cells (referred to as CoEX-A2s) engineered to express human leukocyte antigen (HLA)-A2 and costimulatory molecules such as CD80, CD83, and 41BBL. CoEX-A2s were capable of stimulating antigen-specific CD8 T cells both directly and indirectly via CoEX-A2 cross-dressed cells. Notably, CoEX-A2s also generated similar levels of HCMV pp65-specific and MART1-specific CD8 T cells as DEX in vitro. The results suggest that these novel exosomes may provide a crucial reagent for generating antigen-specific CD8 T cells for adoptive cell therapies against viral infection and tumors.

Interrogating Cellular Functions with Designer Janus Particles

Janus particles have two distinct surfaces or compartments. This enables novel applications that are impossible with homogeneous particles, ranging from the engineering of active colloidal metastructures to creating multimodal therapeutic materials. Recent years have witnessed a rapid development of novel Janus structures and exploration of their applications, particularly in the biomedical arena. It, therefore, becomes crucial to understand how Janus particles with surface or structural anisotropy might interact with biological systems and how such interactions may be exploited to manipulate biological responses. This perspective highlights recent studies that have employed Janus particles as novel toolsets to manipulate, measure, and understand cellular functions. Janus particles have been shown to have biological interactions different from uniform particles. Their surface anisotropy has been used to control the cell entry of synthetic particles, to spatially organize stimuli for the activation of immune cells, and to enable direct visualization and measurement of rotational dynamics of particles in living systems. The work included in this perspective showcases the significance of understanding the biological interactions of Janus particles and the tremendous potential of harnessing such interactions to advance the development of Janus structure-based biomaterials.

Future directions in chimeric antigen receptor T cell therapy

PURPOSE OF REVIEW

The impact of immunotherapy has grown exponentially in the past 5 years. Principle illustrations are encouraging results with engineered T cells expressing a chimeric antigen receptor (CAR). This experimental therapy is developing simultaneously in pediatric and adult clinical trials, making this field particularly relevant and exciting for pediatric oncologists.

RECENT FINDINGS

CAR-modified T cells targeting CD19 have produced dramatic antitumor responses in patients with relapsed/refractory B cell acute lymphoblastic leukemia. Clinical trials from several institutions, in both children and adults, using distinct CAR T cell products have demonstrated similar high complete remission rates of 61-93%, with durable remissions observed. Although the development of CARs for other malignancies has lagged behind, research into novel approaches to overcome inherent challenges is promising.

SUMMARY

Clinical trials of CAR-modified T cells have produced unprecedented results and are anticipated to have a broader impact as this approach expands into other indications, including other cancers and frontline therapy. The potential for long-term disease control, if fully realized, will have a transformative impact on the field.

Construction of a new anti-CD19 chimeric antigen receptor and the anti-leukemia function study of the transduced T cells

Chimeric antigen receptor (CAR) transduced T cells have been used to efficiently kill the target tumor cells depending on the single chain variable fragment (scFv) against the specific tumor associated antigen. Here we show the high specific cytotoxicity of the CAR-T cells with very low effector to target cell (E:T) ratio owing to the CD19-scFv, which was constructed in our laboratory and proved to be highly effective in our previous study. Four plasmids containing three generation of CAR were constructed by cloning the CD19-CAR fragment into the lentiviral vector pCDH. CD3 positive T cells were successfully transduced and the CAR protein expression was confirmed by flow cytometry and Western blot. When cocultured with CD19 positive leukemia cell line Nalm-6 cells, CAR-T cells showed specific cytotoxicity: the percentage of target cells decreased to 0 in 24 hours; IL-2, IFN-γ and TNF-α produced in cocultured supernatants increased obviously; and the cytotoxicity reached more than 80%, still remarkable even when the E:T ratio was as low as 1:4. Dynamic change of cell interaction between CAR-T and leukemia cells was visually tracked by using living cells workstation for the first time. A NOD/SCID B-ALL murine model was established using Nalm-6 cells inoculation with a morbidity rate of 100%, and the survival time was prolonged statistically with CAR-T cell treatment. These data demonstrate that the CAR-T cells we prepared could be a promising treatment strategy for CD19 positive tumor diseases.

Chimeric Antigen Receptor T Cell Therapy Targeting CD19-Positive Leukemia and Lymphoma in the Context of Stem Cell Transplantation

Novel therapies with chimeric antigen receptor (CAR)-transduced T cells (TCs) sparked new hope for patients with relapsed or refractory CD19-positive leukemia or lymphoma even after stem cell therapies. This review focuses on CARs recognizing the B cell antigen CD19. Both retroviral and lentiviral vectors are used, encoding various anti-CD19 CAR constructs comprising costimulatory molecules such as CD28, CD137/4-1BB, and OX40 either alone (second-generation CARs) or in combination (third-generation CARs). Current, up-to-date published studies on anti-CD19 CAR therapy for acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), and non-Hodgkin lymphoma (NHL) with observed side effects are discussed and an outlook on 58 ongoing trials is given. Clinical responses were achieved in up to 81% of ALL, 50% of CLL, and 40% of NHL patients. Factors with potential influence on the clinical outcome might be the design of the vector, the preconditioning regimen, and the number and quality of transfused CAR TCs. The applicability of clinical CAR TC therapy might include relapse after allogeneic stem cell transplantation (alloSCT), and ineligibility for or "bridging" until alloSCT. In summary, CAR therapy represents a highly promising treatment option even in heavily pretreated patients.

Clinical manufacturing of CAR T cells: foundation of a promising therapy

The treatment of cancer patients with autologous T cells expressing a chimeric antigen receptor (CAR) is one of the most promising adoptive cellular therapy approaches. Reproducible manufacturing of high-quality, clinical-grade CAR-T cell products is a prerequisite for the wide application of this technology. Product quality needs to be built-in within every step of the manufacturing process. We summarize herein the requirements and logistics to be considered, as well as the state of the art manufacturing platforms available. CAR-T cell therapy may be on the verge of becoming standard of care for a few clinical indications. Yet, many challenges pertaining to manufacturing standardization and product characterization remain to be overcome in order to achieve broad usage and eventual commercialization of this therapeutic modality.

Artificial antigen-presenting cells expressing HLA class II molecules as an effective tool for amplifying human specific memory CD4(+) T cells

Owing to their multiple immune functions, CD4(+) T cells are of major interest for immunotherapy in chronic viral infections and cancer, as well as for severe autoimmune diseases and transplantation. Therefore, standardized methods allowing rapid generation of a large number of CD4(+) T cells for adoptive immunotherapy are still awaited. We constructed stable artificial antigen-presenting cells (AAPCs) derived from mouse fibroblasts. They were genetically modified to express human leukocyte antigen (HLA)-DR molecules and the human accessory molecules B7.1, Intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-3 (LFA-3). AAPCs expressing HLA-DR1, HLA-DR15 or HLA-DR51 molecules and loaded with peptides derived from influenza hemagglutinin (HA), myelin basic protein (MBP) or factor VIII, respectively, activated specific CD4(+) T-cell clones more effectively than Epstein-Barr virus (EBV)-transformed B cells. We also showed that AAPCs were able to take up and process whole Ag proteins, and present epitopes to specific T cells. In primary cultures, AAPCs loaded with HA peptide allowed generation of specific Th1 lymphocytes from healthy donors as demonstrated by tetramer and intracellular cytokine staining. Although AAPCs were less effective than autologous peripheral blood mononuclear cells (PBMCs) to stimulate CD4(+) T cells in primary culture, AAPCs were more potent to reactivate and expand memory Th1 cells in a strictly Ag-dependent manner. As the availability of autologous APCs is limited, the AAPC system represents a stable and reliable tool to achieve clinically relevant numbers of CD4(+) T cells for adoptive immunotherapy. For fundamental research in immunology, AAPCs are also useful to decipher mechanisms involved in the development of human CD4 T-cell responses.

B Cells Loaded with Synthetic Particulate Antigens: A Versatile Platform To Generate Antigen-Specific Helper T Cells for Cell Therapy

Adoptive cell therapy represents a promising approach for several chronic diseases. This study describes an innovative strategy for biofunctionalization of nanoparticles, allowing the generation of synthetic particulate antigens (SPAg). SPAg activate polyclonal B cells and vectorize noncognate proteins into their endosomes, generating highly efficient stimulators for ex vivo expansion of antigen-specific CD4+ T cells. This method also allows harnessing the ability of B cells to polarize CD4+ T cells into effectors or regulators.

CAR T-cells merge into the fast lane of cancer care

Chimeric antigen receptors (CARs) can be introduced into T-cells redirecting them to target specific tumor antigens. CAR-modified T cells targeting CD19 have shown remarkable activity against CD19+ malignancies including B cell acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), and non-Hodgkin lymphomas (NHL). Complete remission rates as high as 90% have been observed for patients with relapsed and refractory ALL and greater than 50% response rates have been seen in heavily pre-treated CLL and NHL. Excitingly, some remissions have been durable without any additional therapy, a finding which correlates with in-vivo T-cell persistence and B-cell aplasia. The major treatment related toxicities include B-cell aplasia, neurologic toxicities, and a potentially severe cytokine release syndrome. This review summarizes outcomes for patients treated with CD19-CAR T-cells while exploring the field's challenges and future directions.

Translational aspects in targeting the stromal tumour microenvironment: from bench to bedside

Solid tumours comprise, not only malignant cells but also a variety of stromal cells and extracellular matrix proteins. These components interact via an array of signalling pathways to create an adaptable network that may act to promote or suppress cancer progression. To date, the majority of anti-tumour chemotherapeutic agents have principally sought to target the cancer cell. Consequently, resistance develops because of clonal evolution, as a result of selection pressure during tumour expansion. The concept of activating or inhibiting other cell types within the tumour microenvironment is relatively novel and has the advantage of targeting cells which are genetically stable and less likely to develop resistance. This review outlines key players in the stromal tumour microenvironment and discusses potential targeting strategies that may offer therapeutic benefit.

CD19-Targeted CAR T Cells: A New Tool in the Fight against B Cell Malignancies

Adoptive cell immunotherapy is a novel tool in the fight against cancer. Serving both effector and memory functions for the immune system, T cells make an obvious candidate for adoptive cell immunotherapy. By modifying native T cells with a chimeric antigen receptor (CAR), these cells can theoretically be targeted against any extracellular antigen. To date, the best-studied and clinically validated CAR T cells recognize CD19, a cell surface molecule on B cells and B cell malignancies. These CD19-directed T cells have shown clinical utility in chronic lymphocytic leukemia, acute lymphoblastic leukemia (ALL), and non-Hodgkin's lymphomas, with some patients achieving long-term disease remissions after treatment. This review will briefly summarize the current data supporting the use of adoptively transferred CAR T cells for the treatment of CD19-positive malignancies. Given these exciting results, the Food and Drug Administration has granted a 'breakthrough' designation for several variations of CD19-directed CAR T cells for treatment of adult and pediatric relapsed/refractory ALL.

CD19-targeted chimeric antigen receptor T-cell therapy for acute lymphoblastic leukemia

Relapsed and refractory acute lymphoblastic leukemia (ALL) remains difficult to treat, with minimal improvement in outcomes seen in more than 2 decades despite advances in upfront therapy and improved survival for de novo ALL. Adoptive transfer of T cells engineered to express a chimeric antigen receptor (CAR) has emerged as a powerful targeted immunotherapy, showing striking responses in highly refractory populations. Complete remission (CR) rates as high as 90% have been reported in children and adults with relapsed and refractory ALL treated with CAR-modified T cells targeting the B-cell-specific antigen CD19. Distinct CAR designs across several studies have produced similar promising CR rates, an encouraging finding. Even more encouraging are durable remissions observed in some patients without additional therapy. Duration of remission and CAR-modified T-cell persistence require further study and more mature follow-up, but emerging data suggest these factors may distinguish CAR designs. Supraphysiologic T-cell proliferation, a hallmark of this therapy, contributes to both efficacy and the most notable toxicity, cytokine release syndrome (CRS), posing a unique challenge for toxicity management. This review will discuss the current landscape of CD19 CAR clinical trials, CRS pathophysiology and management, and remaining challenges.

The journey from discoveries in fundamental immunology to cancer immunotherapy

Recent advances in cancer immunotherapy have directly built on 50 years of fundamental and technological advances that made checkpoint blockade and T cell engineering possible. In this review, we intend to show that research, not specifically designed to bring relief or cure to any particular disease, can, when creatively exploited, lead to spectacular results in the management of cancer. The discovery of thymus immune function, T cells, and immune surveillance bore the seeds for today's targeted immune interventions and chimeric antigen receptors.

Direct Toll-Like Receptor 8 signaling increases the functional avidity of human CD8+ T lymphocytes generated for adoptive T cell therapy strategies

Adoptive transfer of in vitro activated and expanded antigen-specific cytotoxic T lymphocytes (CTLs) is a promising therapeutic strategy for infectious diseases and cancers. Obtaining in vitro a sufficient amount of highly specific cytotoxic cells and capable of retaining cytotoxic activity in vivo remains problematic. We studied the role of Toll-Like Receptor-8 (TLR8) engagement on peripheral CTLs activated with melanoma antigen MART-1-expressing artificial antigen-presenting cells (AAPCs). After a 3-week co-culture, 3–27% of specific CTLs were consistently obtained. CTLs expressed TLR8 in the intracellular compartment and at the cell surface. Specific CTLs activated with a TLR8 agonist (CL075) 24 h before the end of the culture displayed neither any change in their production levels of molecules involved in cytotoxicity (IFN-γ, Granzyme B, and TNF-α) nor major significant change in their cell surface phenotype. However, these TLR8-stimulated lymphocytes displayed increased cytotoxic activity against specific peptide-pulsed target cells related to an increase in specific anti-melanoma CTL functional avidity. TLR8 engagement on CTLs could, therefore, be useful in different immunotherapy strategies.

An in silico analysis of nanoparticle/cell diffusive transfer: application to nano-artificial antigen-presenting cell:T-cell interaction

Polymeric nanoparticles (nano-paAPCs) modified with T-cell antigens and encapsulating immunostimulatory or immunoinhibitory factors may act as artificial antigen-presenting cells to circulating immune cells, improving the selective delivery of encapsulated drug or cytokine to antigen-specific T-cells. Paracrine delivery of encapsulated agents from these nanoparticles to adjacent cells facilitate sustained delivery lowering the overall administered dose, thus enhancing the overall drug efficacy while reducing toxicity of pleiotropic factors. Little is known mathematically regarding the local concentration of released agent that accumulates around a nanoparticle that is near or embeds in a cell. These concentration fields are calculated here in an attempt to understand paracrine efficacy of these nano-paAPC systems. The significant factor accumulation that can occur if the particles were to embed in the cell membrane may explain observed experimental data regarding enhanced T-cell activation and nanoparticle-mediated improvement in the drug delivery process to non-internalizing cellular targets.

FROM THE CLINICAL EDITOR

In this interesting article, the authors utilized nanosized polymeric artificial presenting cells (nano-paAPC) that released cytokine to study the effects after interaction with T cells. It was found that nano-paAPC were able to embed into cell membrane, with subsequent enhanced T-cell activation. The findings provide further understanding of immune cell interaction and are considered to be important for designing nanoparticles engineered to deliver cytokines or immumodulatory factors to specific immune cells.

Chimeric antigen receptor T-cell therapy for ALL

Relapsed and refractory leukemias pose substantial challenges in both children and adults, with very little progress being made in more than a decade. Targeted immunotherapy using chimeric antigen receptor (CAR)-modified T cells has emerged as a potent therapy with an innovative mechanism. Dramatic clinical responses with complete remission rates as high as 90% have been reported using CAR-modified T cells directed against the B-cell-specific antigen CD19 in patients with relapsed/refractory acute lymphoblastic leukemia. Supraphysiologic T-cell proliferation, a hallmark of this therapy, contributes to both efficacy and the most notable toxicity, cytokine release syndrome, posing a unique challenge for toxicity management. Further studies are necessary to identify additional targets, standardize approaches to cytokine release syndrome management, and determine the durability of remissions.

Janus particles as artificial antigen-presenting cells for T cell activation

Here we show that the multifunctionality of Janus particles can be exploited for in vitro T cell activation. We engineer bifunctional Janus particles on which the spatial distribution of two ligands, anti-CD3 and fibronectin, mimics the "bull's eye" protein pattern formed in the membrane junction between a T cell and an antigen-presenting cell. Different levels of T cell activation can be achieved by simply switching the spatial distribution of the two ligands on the surfaces of the "bull's eye" particles. We find that the ligand pattern also affects clustering of intracellular proteins. This study demonstrates that anisotropic particles, such as Janus particles, can be developed as artificial antigen-presenting cells for modulating T cell activation.

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.

A carbon nanotube-polymer composite for T-cell therapy

Clinical translation of cell therapies requires strategies that can manufacture cells efficiently and economically. One promising way to reproducibly expand T cells for cancer therapy is by attaching the stimuli for T cells onto artificial substrates with high surface area. Here, we show that a carbon nanotube-polymer composite can act as an artificial antigen-presenting cell to efficiently expand the number of T cells isolated from mice. We attach antigens onto bundled carbon nanotubes and combined this complex with polymer nanoparticles containing magnetite and the T-cell growth factor interleukin-2 (IL-2). The number of T cells obtained was comparable to clinical standards using a thousand-fold less soluble IL-2. T cells obtained from this expansion were able to delay tumour growth in a murine model for melanoma. Our results show that this composite is a useful platform for generating large numbers of cytotoxic T cells for cancer immunotherapy.

Human cell-based artificial antigen-presenting cells for cancer immunotherapy

Adoptive T-cell therapy, where anti-tumor T cells are first prepared in vitro, is attractive since it facilitates the delivery of essential signals to selected subsets of anti-tumor T cells without unfavorable immunoregulatory issues that exist in tumor-bearing hosts. Recent clinical trials have demonstrated that anti-tumor adoptive T-cell therapy, i.e. infusion of tumor-specific T cells, can induce clinically relevant and sustained responses in patients with advanced cancer. The goal of adoptive cell therapy is to establish anti-tumor immunologic memory, which can result in life-long rejection of tumor cells in patients. To achieve this goal, during the process of in vitro expansion, T-cell grafts used in adoptive T-cell therapy must be appropriately educated and equipped with the capacity to accomplish multiple, essential tasks. Adoptively transferred T cells must be endowed, prior to infusion, with the ability to efficiently engraft, expand, persist, and traffic to tumor in vivo. As a strategy to consistently generate T-cell grafts with these capabilities, artificial antigen-presenting cells have been developed to deliver the proper signals necessary to T cells to enable optimal adoptive cell therapy.

Artificial antigen-presenting cells expressing CD80, CD70, and 4-1BB ligand efficiently expand functional T cells specific to tumor-associated antigens

Professional antigen-presenting cells (APCs), notably dendritic cells (DCs), are the most potent for expanding antigen-specific T cells ex vivo. However, the labor-intensive and expensive procedure for customized preparation of autologous APCs has hampered their broad clinical application. Artificial APC (aAPC) systems, which can be readily prepared from off-the-shelf components, have been proposed as a promising alternative to custom-made professional APCs. Here, in order to develop a novel aAPC system, we established K562 erythroleukemia cells expressing different combinations of co-stimulatory molecule ligands, CD80, CD70, and/or 4-1BB ligand (4-1BBL). When nucleofected with in vitro-generated mRNA encoding a tumor-associated antigen, MART-1, the K562 cells expressing all of CD80, CD70, and 4-1BBL were the most efficient for expansion of functional T cells specific to an HLA-A2-restricted immunodominant epitope, MART-126-35. In addition, only the K562 cells expressing all three of these co-stimulatory molecule ligands could clearly expand T cells specific to other less immunogenic antigen epitopes, gp100154-162 and Cyp1B1239-247, through transfection with in vitro generated gp100 and Cyp1B1 mRNA, respectively. These results indicated that non-redundant and synergistic effects of co-stimulation via CD28/CD80, CD27/CD70, and 4-1BB/4-1BBL might be critical for eliciting efficient expansion of T cells; co-stimulation via the 4-1BB/4-1BBL interaction might expand antigen-specific T cells by preventing apoptotic cell death triggered by specific antigens in the presence of the CD28/CD80 and CD27/CD70 signaling. Taken together, our findings suggested that this K562-based aAPC system expressing CD80, CD70, and 4-1BBL would be useful for efficiently stimulating functional antigen-specific T cells ex vivo, in particular when detailed information on the epitope specificities is unavailable.

Dendritic cells pulsed with leukemia cell-derived exosomes more efficiently induce antileukemic immunities

Dendritic cells (DCs) and tumor cell-derived exosomes have been used to develop antitumor vaccines. However, the biological properties and antileukemic effects of leukemia cell-derived exosomes (LEXs) are not well described. In this study, the biological properties and induction of antileukemic immunity of LEXs were investigated using transmission electron microscopy, western blot analysis, cytotoxicity assays, and animal studies. Similar to other tumor cells, leukemia cells release exosomes. Exosomes derived from K562 leukemia cells (LEX_K562) are membrane-bound vesicles with diameters of approximately 50–100 μm and harbor adhesion molecules (e.g., intercellular adhesion molecule-1) and immunologically associated molecules (e.g., heat shock protein 70). In cytotoxicity assays and animal studies, LEXs-pulsed DCs induced an antileukemic cytotoxic T-lymphocyte immune response and antileukemic immunity more effectively than did LEXs and non-pulsed DCs (P<0.05). Therefore, LEXs may harbor antigens and immunological molecules associated with leukemia cells. As such, LEX-based vaccines may be a promising strategy for prolonging disease-free survival in patients with leukemia after chemotherapy or hematopoietic stem cell transplantation.

Antibody-modified T cells: CARs take the front seat for hematologic malignancies

T cells redirected to specific antigen targets with engineered chimeric antigen receptors (CARs) are emerging as powerful therapies in hematologic malignancies. Various CAR designs, manufacturing processes, and study populations, among other variables, have been tested and reported in over 10 clinical trials. Here, we review and compare the results of the reported clinical trials and discuss the progress and key emerging factors that may play a role in effecting tumor responses. We also discuss the outlook for CAR T-cell therapies, including managing toxicities and expanding the availability of personalized cell therapy as a promising approach to all hematologic malignancies. Many questions remain in the field of CAR T cells directed to hematologic malignancies, but the encouraging response rates pave a wide road for future investigation.

[Immunotherapy for colorectal cancer]

Recent studies have underlined the close link between immune response and prognosis of patients with colorectal cancer (CRC). Immune response understanding combined with biotechnology progress of the last years has allowed development of immunotherapy strategies in CRC. Immunotherapy strategies are divided in "active" or "passive" strategies (patients immune system stimulation or not) and considering the activation of antigen specific immune response or not. These immunotherapy strategies are well tolerated and induced cellular and humoral response correlated with clinical response. Many monoclonal antibodies targeting signalisation pathways or angiogenic growth factors have demonstrated their efficacy in CRC. Multiple vaccine strategies, using different tumour associated antigens, have demonstrated a biological efficacy but with poor clinical results. Results are more promising in adjuvant setting but need to be confirmed by randomized trials. Adoptive immunotherapy with transfer of tumour associated antigen specific T cell is probably the most promising strategy. Actually, except monoclonal antibodies, immunotherapy is not used in clinical practice in CRC due to the lack of results and absence of standardisation.

Fine tuning and efficient T cell activation with stimulatory aCD3 nanoarrays

Anti-CD3 (aCD3) nanoarrays fabricated by self-assembled nanopatterning combined with site-directed protein immobilization techniques represent a novel T cell stimulatory platform that allows tight control over ligand orientation and surface density. Here, we show that activation of primary human CD4+ T cells, defined by CD69 upregulation, IL-2 production and cell proliferation, correlates with aCD3 density on nanoarrays. Immobilization of aCD3 through nanopatterning had two effects: cell activation was significantly higher on these surfaces than on aCD3-coated plastics and allowed unprecedented fine-tuning of T cell response.

A light-driven anti-cancer dual-therapeutic cassette enhances solid tumour regression

The majority of anticancer therapeutics have failed to control the target cancers. Thus, new rational design concepts are critical. In most of the biological reactions, a cascade pathway is used to activate appropriate responses. In the cascade pathway, a small signal derived from neighboring environments can be amplified and it further triggers overwhelming and specialized responses. It can be applied to achieve powerful therapeutic effects for novel drug design strategies. Inspired by this concept, we design a preferential dual anti-cancer therapeutic cassette composed of (i) DNA/RNA nanostructures as both anticancer containers and target ligands and (ii) a gold nanocrystal as localized heat inducers. We demonstrate that this multi-modular platform is superior to conventional cancer medications in that it had higher drug loading efficiency, tunable drug release, and intrinsic serum stability characteristics. Both doxorubicin chemotherapy and thermal ablation exert a powerful synergistic killing effect that resulted in prostate cancer regression both in vitro and in vivo. We speculate that our novel anti-cancer drug system can be adapted to effectively destroy many different types of solid cancers.

A gene-networked gel matrix-supported lipid bilayer as a synthetic nucleus system

A spheroidal transgene-networked gel matrix was designed as a synthetic nucleus system. It was spheroidically manufactured using both advanced lithography and DNA nanotechnology. Stable Aqueorea coerulescens green fluorescent protein (AcGFP)-encoding gene cross-networks have been optimized in various parameters: the number of gene-networked gel (G-net-gel) spheroids, the concentration of a AcGFP plasmid in the scaffold, and the molar ratio between the X-DNA building blocks and the gene. It was then assessed that 800 units of the gene networked gel matrix at a 4000:1 molar ratio of X-DNA blocks and AcGFP gene components accomplished 20-fold enhanced in vitro protein expression efficiency for 36 h. Furthermore, once with lipid capping, it reproduced the natural nucleus system, demonstrating the 2-fold increased levels of messenger RNAs (mRNAs) relative to solution phase vectors.

Analysis of TCR activation kinetics in primary human T cells upon focal or soluble stimulation

Signaling through the TCR is crucial for the generation of different cellular responses including proliferation, differentiation, and apoptosis. A growing body of evidence indicates that differences in the magnitude and the duration of the signal are critical determinants in eliciting cellular responses. Here, we have analyzed signaling dynamics induced upon TCR ligation in primary human T cells. We used CD3 antibodies either cross-linked in solution (sAbs) or immobilized on microbeads (iAbs), two widely employed methods to stimulate T cells in vitro. We show that classical sAbs stimulation induces a transient and abortive response, whereas iAbs induce sustained TCR-mediated signaling, resulting in productive T-cell responses previously observed only in antigen-specific murine systems. In summary, our analysis documents TCR signaling kinetics and suggests that iAbs are better suited for studying TCR-mediated signaling as they mimic antigen specific systems.

A stepwise protocol to coat aAPC beads prevents out-competition of anti-CD3 mAb and consequent experimental artefacts

Artificial antigen-presenting cells (aAPC) are widely used for both clinical and basic research applications, as cell-based or bead-based scaffolds, combining immune synapse components of interest. Adequate and controlled preparation of aAPCs is crucial for subsequent immunoassays. We reveal that certain proteins such as activatory anti-CD3 antibody can be out-competed by other proteins (e.g. inhibitory receptor ligands such as PDL1:Fc) during the coating of aAPC beads, under the usually performed coating procedures. This may be misleading, as we found that decreased CD8 T cell activity was not due to inhibitory receptor triggering but rather because of unexpectedly low anti-CD3 antibody density on the beads upon co-incubation with inhibitory receptor ligands. We propose an optimized protocol, and emphasize the need to quality-control the coating of proteins on aAPC beads prior to their use in immunoassays.

A novel system of artificial antigen-presenting cells efficiently stimulates Flu peptide-specific cytotoxic T cells in vitro

Therapeutic numbers of antigen-specific cytotoxic T lymphocytes (CTLs) are key effectors in successful adoptive immunotherapy. However, efficient and reproducible methods to meet the qualification remain poor. To address this issue, we designed the artificial antigen-presenting cell (aAPC) system based on poly(lactic-co-glycolic acid) (PLGA). A modified emulsion method was used for the preparation of PLGA particles encapsulating interleukin-2 (IL-2). Biotinylated molecular ligands for recognition and co-stimulation of T cells were attached to the particle surface through the binding of avidin-biotin. These formed the aAPC system. The function of aAPCs in the proliferation of specific CTLs against human Flu antigen was detected by enzyme-linked immunospot assay (ELISPOT) and MTT staining methods. Finally, we successfully prepared this suitable aAPC system. The results show that IL-2 is released from aAPCs in a sustained manner over 30 days. This dramatically improves the stimulatory capacity of this system as compared to the effect of exogenous addition of cytokine. In addition, our aAPCs promote the proliferation of Flu antigen-specific CTLs more effectively than the autologous cellular APCs. Here, this aAPC platform is proved to be suitable for expansion of human antigen-specific T cells.

Membrane-bound HSP70-engineered myeloma cell-derived exosomes stimulate more efficient CD8(+) CTL- and NK-mediated antitumour immunity than exosomes released from heat-shocked tumour cells expressing cytoplasmic HSP70

Exosomes (EXO) derived from tumour cells have been used to stimulate antitumour immune responses, but only resulting in prophylatic immunity. Tumour-derived heat shock protein 70 (HSP70) molecules are molecular chaperones with a broad repertoire of tumour antigen peptides capable of stimulating dendritic cell (DC) maturation and T-cell immune responses. To enhance EXO-based antitumour immunity, we generated an engineered myeloma cell line J558_HSP expressing endogenous P1A tumour antigen and transgenic form of membrane-bound HSP70 and heat-shocked J558_HS expressing cytoplasmic HSP70, and purified EXO_HSP and EXO_HS from J558_HSP and J558_HS tumour cell culture supernatants by ultracentrifugation. We found that EXO_HSP were able to more efficiently stimulate maturation of DCs with up-regulation of Ia^b, CD40, CD80 and inflammatory cytokines than EXO_HS after overnight incubation of immature bone-marrow-derived DCs (5 × 10⁶ cells) with EXO (100 μg), respectively. We also i.v. immunized BALB/c mice with EXO (30 μg/mouse) and assessed P1A-specific T-cell responses after immunization. We demonstrate that EXO_HSP are able to stimulate type 1 CD4⁺ helper T (Th1) cell responses, and more efficient P1A-specific CD8⁺ cytotoxic T lymphocyte (CTL) responses and antitumour immunity than EXO_HS. In addition, we further elucidate that EXO_HSP-stimulated antitumour immunity is mediated by both P1A-specific CD8⁺ CTL and non-P1A-specific natural killer (NK) responses. Therefore, membrane-bound HSP70-expressing tumour cell-released EXO may represent a more effective EXO-based vaccine in induction of antitumour immunity.

Human CD8 T cells generated in vitro from hematopoietic stem cells are functionally mature

BACKGROUND

T cell development occurs within the highly specialized thymus. Cytotoxic CD8 T cells are critical in adaptive immunity by targeting virally infected or tumor cells. In this study, we addressed whether functional CD8 T cells can be generated fully in vitro using human umbilical cord blood (UCB) hematopoietic stem cells (HSCs) in coculture with OP9-DL1 cells.

RESULTS

HSC/OP9-DL1 cocultures supported the differentiation of CD8 T cells, which were TCR/CD3(hi) CD27(hi) CD1a(neg) and thus phenotypically resembled mature functional CD8 single positive thymocytes. These in vitro-generated T cells also appeared to be conventional CD8 cells, as they expressed high levels of Eomes and low levels of Plzf, albeit not identical to ex vivo UCB CD8 T cells. Consistent with the phenotypic and molecular characterization, upon TCR-stimulation, in vitro-generated CD8 T cells proliferated, expressed activation markers (MHC-II, CD25, CD38), secreted IFN-γ and expressed Granzyme B, a cytotoxic T-cell effector molecule.

CONCLUSION

Taken together, the ability to direct human hematopoietic stem cell or T-progenitor cells towards a mature functional phenotype raises the possibility of establishing cell-based treatments for T-immunodeficiencies by rapidly restoring CD8 effector function, thereby mitigating the risks associated with opportunistic infections.

T-cell engineering for cancer immunotherapy

The adoptive transfer of tumor-reactive cells is a promising approach for the treatment of melanoma and some other cancers. To remedy the difficulties associated with the isolation and expansion of tumor-reactive T cells in most cancer patients, peripheral blood T cells can be retargeted to any chosen tumor antigen by the genetic transfer of an antigen-specific receptor. The transduced receptors may be human leukocyte antigen-restricted, heterodimeric T-cell antigen receptor (TCRs), or chimeric antigen receptors (CARs), which typically recognize native cell-surface antigens. Considerable progress has been made in recent years to address the challenges posed by the transfer of either receptor type. Vector and protein modifications enable the expression of TCR chains in human T cells at functional levels and with a reduced risk of mis-pairing with endogenous TCR chains. The combinatorial inclusion of activating and costimulatory domains in CARs has dramatically enhanced the signaling properties of the chimeric receptors described over a decade ago. Based on the effective T-cell transduction and expansion procedures now available to support clinical investigation, improved designer TCRs and second generation CARs targeting an array of antigens are being evaluated in a range of hematological malignancies and solid tumors.

Artificial antigen-presenting cells for use in adoptive immunotherapy

The observation that T cells can recognize and specifically eliminate cancer cells has spurred interest in the development of efficient methods to generate large numbers of T cells with specificity for tumor antigens that can be harnessed for use in cancer therapy. Recent studies have demonstrated that during encounter with tumor antigen, the signals delivered to T cells by professional antigen-presenting cells can affect T-cell programming and their subsequent therapeutic efficacy. This has stimulated efforts to develop artificial antigen-presenting cells that allow optimal control over the signals provided to T cells. In this review, we will discuss the advantages and disadvantages of cellular and acellular artificial antigen-presenting cell systems and their use in T-cell adoptive immunotherapy for cancer.

The application of exosomes as a nanoscale cancer vaccine

Cancer is a leading cause of death globally, and it is predicted and projected to continue rising as life expectancy increases. Although patient survival rates for some forms of cancers are high due to clinical advances in treatment protocols, the search for effective cancer vaccines remains the ultimate Rosetta Stone in oncology. Cervarix^®, Gardasil^®, and hepatitis B vaccines are currently employed in preventing certain forms of viral cancers. However, they are, strictly speaking, not ‘true’ cancer vaccines as they are prophylactic rather than therapeutic, are only effective against the oncogenic viruses, and do not kill the actual cancer cells. On April 2010, a new prostate cancer vaccine Provenge^® (sipuleucel-T) was approved by the US FDA, and it is the first approved therapeutic vaccine that utilizes antigen-presenting cell technology involving dendritic cells in cancer immunotherapy. Recent evidence suggests that the use of nanoscale particles like exosomes in immunotherapy could form a viable basis for the development of novel cancer vaccines, via antigen-presenting cell technology, to prime the immune system to recognize and kill cancer cells. Coupled with nanotechnology, engineered exosomes are emerging as new and novel avenues for cancer vaccine development. Here, we review the current knowledge pertaining to exosome technology in immunotherapy and also seek to address the challenges and future directions associated with it, in hopes of bringing this exciting application a step closer toward an effective clinical reality.