A Good Manufacturing Practice procedure to engineer donor virus-specific T cells into potent anti-leukemic effector cells

Stipulations of cell and gene therapy and the ties to biomanufacturing

Cell and gene therapy (CGT) products are emerging and innovative biopharmaceuticals that hold promise for treating diseases that are otherwise beyond the scope of conventional medicines. The evolution of CGT from a research idea to a promising therapeutic product is due to the complementary advancements across various scientific disciplines. First, the innovations and advancements in gene editing and delivery technology have provided fundamental tools to manipulate genes and cells for therapeutic pursuits. Second, advancements in applied and translational research, including how clinical trials are designed, performed, evaluated, and analyzed, have transformed the technology into a potential therapeutic product. Third, advancements in scaling up the production of CGT products have been critical in delivering the product for preclinical studies, clinical trials, and approved treatments. In parallel, regulatory requirements have continuously evolved, with lessons learned from translational studies and biomanufacturing. These combined efforts have transformed CGT products from a promising concept into a reality with the potential to treat a wide range of diseases. However, continued R&D and regulatory oversight are crucial to further improve the safety, efficacy, and accessibility of CGT products.

Finding potential targets in cell-based immunotherapy for handling the challenges of acute myeloid leukemia

Acute myeloid leukemia (AML) is a hostile hematological malignancy under great danger of relapse and poor long-term survival rates, despite recent therapeutic advancements. To deal with this unfulfilled clinical necessity, innovative cell-based immunotherapies have surfaced as promising approaches to improve anti-tumor immunity and enhance patient outcomes. In this comprehensive review, we provide a detailed examination of the latest developments in cell-based immunotherapies for AML, including chimeric antigen receptor (CAR) T-cell therapy, T-cell receptor (TCR)-engineered T-cell therapy, and natural killer (NK) cell-based therapies. We critically evaluate the unique mechanisms of action, current challenges, and evolving strategies to improve the efficacy and safety of these modalities. The review emphasizes how promising these cutting-edge immune-based strategies are in overcoming the inherent complexities and heterogeneity of AML. We discuss the identification of optimal target antigens, the importance of mitigating on-target/off-tumor toxicity, and the need to enhance the persistence and functionality of engineered immune effector cells. All things considered, this review offers a thorough overview of the rapidly evolving field of cell-based immunotherapy for AML, underscoring the significant progress made and the ongoing efforts to translate these innovative approaches into more effective and durable treatments for this devastating disease.

Production of donor-derived cytotoxic T lymphocytes with potent anti-leukemia activity for adoptive immunotherapy in high-risk pediatric patients given haploidentical hematopoietic stem cell transplantation

BACKGROUND AIMS

Somatic cell therapy based on the infusion of donor-derived cytotoxic T lymphocytes (CTL) able to recognize patients' leukemia blasts (LB) is a promising approach to control leukemia relapse after allogeneic HSCT. The success of this approach strongly depends on the ex vivo generation of high-quality donor-derived anti-leukemia CTL in compliance with Good Manufacturing Practices (GMP). We previously described a procedure for generating large numbers of donor-derived anti-leukemia CTL through stimulation of CD8-enriched lymphocytes with dendritic cells (DCs) pulsed with apoptotic LB in the presence of interleukin (IL)-12, IL-7 and IL-15. Here we report that the use of IFN-DC and the addition of IFNα2b during the priming phase significantly improve the generation of an efficient anti-leukemia T cells response in vitro.

METHODS

Using this approach, 20 high-risk pediatric patients given haploidentical HSCT for high-risk acute leukemia were enrolled and 51 batches of advanced therapy medical products (ATMP), anti-leukemia CTL, were produced.

RESULTS

Quality controls demonstrated that all batches were sterile, free of mycoplasma and conformed to acceptable endotoxin levels. Genotype analysis confirmed the molecular identity of the ATMP based on the starting biological material used for their production. The majority of ATMP were CD3+/CD8+ cells, with a memory/terminal activated phenotype, including T-central memory populations. ATMP were viable after thawing, and most ATMP batches displayed efficient capacity to lyse patients' LB and to secrete interferon-γ and tumor necrosis factor-α.

CONCLUSIONS

These results demonstrated that our protocol is highly reproducible and allows the generation of large numbers of immunologically safe and functional anti-leukemia CTL with a high level of standardization.

Trial Watch: Adoptive TCR-Engineered T-Cell Immunotherapy for Acute Myeloid Leukemia

Simple Summary

Acute myeloid leukemia (AML) is a type of blood cancer with an extremely grim prognosis. This is due to the fact that the majority of patients will relapse after frontline treatment. Overall survival of relapsed AML is very low, and treatment options are few. T lymphocytes harnessed with antitumor T-cell receptors (TCRs) can produce objective clinical responses in certain cancers, such as melanoma, but have not entered the main road for AML. In this review, we describe the current status of the field of TCR-T-cell therapies for AML.

Abstract

Despite the advent of novel therapies, acute myeloid leukemia (AML) remains associated with a grim prognosis. This is exemplified by 5-year overall survival rates not exceeding 30%. Even with frontline high-intensity chemotherapy regimens and allogeneic hematopoietic stem cell transplantation, the majority of patients with AML will relapse. For these patients, treatment options are few, and novel therapies are urgently needed. Adoptive T-cell therapies represent an attractive therapeutic avenue due to the intrinsic ability of T lymphocytes to recognize tumor cells with high specificity and efficiency. In particular, T-cell therapies focused on introducing T-cell receptors (TCRs) against tumor antigens have achieved objective clinical responses in solid tumors such as synovial sarcoma and melanoma. However, contrary to chimeric antigen receptor (CAR)-T cells with groundbreaking results in B-cell malignancies, the use of TCR-T cells for hematological malignancies is still in its infancy. In this review, we provide an overview of the status and clinical advances in adoptive TCR-T-cell therapy for the treatment of AML.

T-Cell Dysfunction as a Limitation of Adoptive Immunotherapy: Current Concepts and Mitigation Strategies

Simple Summary

T cells are immune cells that can be used to target infections or cancers. Adoptive T-cell immunotherapy leverages these properties and/or confers new features to T cells through ex vivo manipulations prior to their use in patients. However, as a “living drug,” the function of these cells can be hampered by several built-in physiological constraints and external factors that limit their efficacy. Manipulating T cells ex vivo can impart dysfunctional features to T cells through repeated stimulations and expansion, but it also offers many opportunities to improve the therapeutic potential of these cells, including emerging interventions to prevent or reverse T-cell dysfunction developing ex vivo or after transfer in patients. This review outlines the various forms of T-cell dysfunction, emphasizes how it affects various types of T-cell immunotherapy approaches, and describes current and anticipated strategies to limit T-cell dysfunction.

Abstract

Over the last decades, cellular immunotherapy has revealed its curative potential. However, inherent physiological characteristics of immune cells can limit the potency of this approach. Best defined in T cells, dysfunction associated with terminal differentiation, exhaustion, senescence, and activation-induced cell death, undermine adoptive cell therapies. In this review, we concentrate on how the multiple mechanisms that articulate the various forms of immune dysfunction impact cellular therapies primarily involving conventional T cells, but also other lymphoid subtypes. The repercussions of immune cell dysfunction across the full life cycle of cell therapy, from the source material, during manufacturing, and after adoptive transfer, are discussed, with an emphasis on strategies used during ex vivo manipulations to limit T-cell dysfunction. Applicable to cellular products prepared from native and unmodified immune cells, as well as genetically engineered therapeutics, the understanding and potential modulation of dysfunctional features are key to the development of improved cellular immunotherapies.

Off-the-Shelf Allogeneic T Cell Therapies for Cancer: Opportunities and Challenges Using Naturally Occurring "Universal" Donor T Cells

Chimeric antigen receptor (CAR) engineered T cell therapies individually prepared for each patient with autologous T cells have recently changed clinical practice in the management of B cell malignancies. Even though CARs used to redirect polyclonal T cells to the tumor are not HLA restricted, CAR T cells are also characterized by their endogenous T cell receptor (TCR) repertoire. Tumor-antigen targeted TCR-based T cell therapies in clinical trials are thus far using “conventional” αβ-TCRs that recognize antigens presented as peptides in the context of the major histocompatibility complex. Thus, both CAR- and TCR-based adoptive T cell therapies (ACTs) are dictated by compatibility of the highly polymorphic HLA molecules between donors and recipients in order to avoid graft-versus-host disease and rejection. The development of third-party healthy donor derived well-characterized off-the-shelf cell therapy products that are readily available and broadly applicable is an intensive area of research. While genome engineering provides the tools to generate “universal” donor cells that can be redirected to cancers, we will focus our attention on third-party off-the-shelf strategies with T cells that are characterized by unique natural features and do not require genome editing for safe administration. Specifically, we will discuss the use of virus-specific T cells, lipid-restricted (CD1) T cells, MR1-restricted T cells, and γδ-TCR T cells. CD1- and MR1-restricted T cells are not HLA-restricted and have the potential to serve as a unique source of universal TCR sequences to be broadly applicable in TCR-based ACT as their targets are presented by the monomorphic CD1 or MR1 molecules on a wide variety of tumor types. For each cell type, we will summarize the stage of preclinical and clinical development and discuss opportunities and challenges to deliver off-the-shelf targeted cellular therapies against cancer.

Transgenic CD8αβ co-receptor rescues endogenous TCR function in TCR-transgenic virus-specific T cells

BACKGROUND

Genetically engineered virus-specific T cells (VSTs) are a platform for adoptive cell therapy after allogeneic hematopoietic stem cell transplantation. However, redirection to a tumor-associated antigen by the introduction of a transgenic T-cell receptor (TCR) reduces anti-viral activity, thereby impeding the possibility of preventing or treating two distinct complications-malignant relapse and viral infection-with a single cell therapy product. Availability of CD8αβ co-receptor molecules can significantly impact class I restricted T-cell activation, and thus, we interrogated whether transgenic CD8αβ improves anti-viral activity mediated by native VSTs with or without a co-expressed transgenic TCR (TCR8).

METHODS

Our existing clinical VST manufacturing platform was adapted and validated to engineer TCR+ or TCR8+ VSTs targeting cytomegalovirus and Epstein-Barr virus. Simultaneous anti-viral and anti-tumor function of engineered VSTs was assessed in vitro and in vivo. We used pentamer staining, interferon (IFN)-γ enzyme-linked immunospot (ELISpot), intracellular cytokine staining (ICS), cytotoxicity assays, co-cultures, and cytokine secretion assays for the in vitro characterization. The in vivo anti-tumor function was assessed in a leukemia xenograft mouse model.

RESULTS

Both transgenic CD8αβ alone and TCR8 had significant impact on the anti-viral function of engineered VSTs, and TCR8+ VSTs had comparable anti-viral activity as non-engineered VSTs as determined by IFN-γ ELISpot, ICS and cytotoxicity assays. TCR8-engineered VSTs had improved anti-tumor function and greater effector cytokine production in vitro, as well as enhanced anti-tumor function against leukemia xenografts in mice.

CONCLUSION

Incorporation of transgenic CD8αβ into vectors for TCR-targetable antigens preserves anti-viral activity of TCR transgenic VSTs while simultaneously supporting tumor-directed activity mediated by a transgenic TCR. Our approach may provide clinical benefit in preventing and treating viral infections and malignant relapse post-transplant.

HA-1H T-Cell Receptor Gene Transfer to Redirect Virus-Specific T Cells for Treatment of Hematological Malignancies After Allogeneic Stem Cell Transplantation: A Phase 1 Clinical Study

Graft-vs.-leukemia (GVL) reactivity after HLA-matched allogeneic stem cell transplantation (alloSCT) is mainly mediated by donor T cells recognizing minor histocompatibility antigens (MiHA). If MiHA are targeted that are exclusively expressed on hematopoietic cells of recipient origin, selective GVL reactivity without severe graft-vs.-host-disease (GVHD) may occur. In this phase I study we explored HA-1H TCR gene transfer into T cells harvested from the HA-1H negative stem-cell donor to treat HA-1H positive HLA-A^*02:01 positive patients with high-risk leukemia after alloSCT. HA-1H is a hematopoiesis-restricted MiHA presented in HLA-A^*02:01. Since we previously demonstrated that donor-derived virus-specific T-cell infusions did not result in GVHD, we used donor-derived EBV and/or CMV-specific T-cells to be redirected by HA-1H TCR. EBV and/or CMV-specific T-cells were purified, retrovirally transduced with HA-1H TCR, and expanded. Validation experiments illustrated dual recognition of viral antigens and HA-1H by HA-1H TCR-engineered virus-specific T-cells. Release criteria included products containing more than 60% antigen-specific T-cells. Patients with high risk leukemia following T-cell depleted alloSCT in complete or partial remission were eligible. HA-1H TCR T-cells were infused 8 and 14 weeks after alloSCT without additional pre-conditioning chemotherapy. For 4/9 included patients no appropriate products could be made. Their donors were all CMV-negative, thereby restricting the production process to EBV-specific T-cells. For 5 patients a total of 10 products could be made meeting the release criteria containing 3–280 × 10⁶ virus and/or HA-1H TCR T-cells. No infusion-related toxicity, delayed toxicity or GVHD occurred. One patient with relapsed AML at time of infusions died due to rapidly progressing disease. Four patients were in remission at time of infusion. Two patients died of infections during follow-up, not likely related to the infusion. Two patients are alive and well without GVHD. In 2 patients persistence of HA-1H TCR T-cells could be illustrated correlating with viral reactivation, but no overt in-vivo expansion of infused T-cells was observed. In conclusion, HA-1H TCR-redirected virus-specific T-cells could be made and safely infused in 5 patients with high-risk AML, but overall feasibility and efficacy was too low to warrant further clinical development using this strategy. New strategies will be explored using patient-derived donor T-cells isolated after transplantation transduced with HA-1H-specific TCR to be infused following immune conditioning.

Next-generation CAR T cells to overcome current drawbacks

As a rapidly emerging treatment in the oncology field, adoptive transfer of autologous, genetically modified chimeric antigen receptor (CAR) T cells has shown striking efficacy and is curative in certain relapsed/refractory patients with hematologic malignancy. This treatment modality of using a "living drug" offers many tantalizing and novel therapeutic strategies for cancer patients whose remaining treatment options may have otherwise been limited. Despite the early success of CAR T cells in hematologic malignancies, many barriers remain for widespread adoption. General barriers include cellular manufacturing limitations, baseline quality of the T cells, adverse events post-infusion such as cytokine release syndrome (CRS) and neurotoxicity, and host rejection of non-human CARs. Additionally, each hematologic disease presents unique mechanisms of relapse which have to be addressed in future clinical trials if we are to augment the efficacy of CAR T treatment. In this review, we will describe current barriers to hindering efficacy of CAR T-cell treatment for hematologic malignancies in a disease-specific manner and review recent innovations aimed at enhancing the potency and applicability of CAR T cells, with the overall goal of building a framework to begin incorporating this form of therapy into the standard medical management of blood cancers.

T cell optimization for graft-versus-leukemia responses

Protection from relapse after allogeneic hematopoietic cell transplantation (HCT) is partly due to donor T cell-mediated graft-versus-leukemia (GVL) immune responses. Relapse remains common in HCT recipients, but strategies to augment GVL could significantly improve outcomes after HCT. Donor T cells with αβ T cell receptors (TCRs) mediate GVL through recognition of minor histocompatibility antigens and alloantigens in HLA-matched and -mismatched HCT, respectively. αβ T cells specific for other leukemia-associated antigens, including nonpolymorphic antigens and neoantigens, may also deliver an antileukemic effect. γδ T cells may contribute to GVL, although their biology and specificity are less well understood. Vaccination or adoptive transfer of donor-derived T cells with natural or transgenic receptors are strategies with potential to selectively enhance αβ and γδ T cell GVL effects.

Improving CAR T cell therapy by optimizing critical quality attributes

Whether as a cure or bridge to transplant, chimeric antigen receptor (CAR)-T cell therapies have shown dramatic outcomes for the treatment of hematologic malignancies, and particularly relapsed/refractory B cell leukemia and lymphoma. However, these therapies are not effective for all patients, and are not without toxicities. The challenge now is to optimize these products and their manufacture. The manufacturing process is complex and subject to numerous variabilities at each step. These variabilities can affect the critical quality attributes of the final product, and this can ultimately impact clinical outcomes. This review will focus on optimizing the manufacturing variables that can impact the safety, purity, potency, consistency and durability of CAR-T cells.

Minor Histocompatibility Antigen-Specific T Cells

Minor Histocompatibility (H) antigens are major histocompatibility complex (MHC)/Human Leukocyte Antigen (HLA)-bound peptides that differ between allogeneic hematopoietic stem cell transplantation (HCT) recipients and their donors as a result of genetic polymorphisms. Some minor H antigens can be used as therapeutic T cell targets to augment the graft-vs.-leukemia (GVL) effect in order to prevent or manage leukemia relapse after HCT. Graft engineering and post-HCT immunotherapies are being developed to optimize delivery of T cells specific for selected minor H antigens. These strategies have the potential to reduce relapse risk and thereby permit implementation of HCT approaches that are associated with less toxicity and fewer late effects, which is particularly important in the growing and developing pediatric patient. Most minor H antigens are expressed ubiquitously, including on epithelial tissues, and can be recognized by donor T cells following HCT, leading to graft-vs.-host disease (GVHD) as well as GVL. However, those minor H antigens that are expressed predominantly on hematopoietic cells can be targeted for selective GVL. Once full donor hematopoietic chimerism is achieved after HCT, hematopoietic-restricted minor H antigens are present only on residual recipient malignant hematopoietic cells, and these minor H antigens serve as tumor-specific antigens for donor T cells. Minor H antigen-specific T cells that are delivered as part of the donor hematopoietic stem cell graft at the time of HCT contribute to relapse prevention. However, in some cases the minor H antigen-specific T cells delivered with the graft may be quantitatively insufficient or become functionally impaired over time, leading to leukemia relapse. Following HCT, adoptive T cell immunotherapy can be used to treat or prevent relapse by delivering large numbers of donor T cells targeting hematopoietic-restricted minor H antigens. In this review, we discuss minor H antigens as T cell targets for augmenting the GVL effect in engineered HCT grafts and for post-HCT immunotherapy. We will highlight the importance of these developments for pediatric HCT.

TEG001 Insert Integrity from Vector Producer Cells until Medicinal Product

Despite extensive usage of gene therapy medicinal products (GTMPs) in clinical studies and recent approval of chimeric antigen receptor (CAR) T cell therapy, little information has been made available on the precise molecular characterization and possible variations in terms of insert integrity and vector copy numbers of different GTMPs during the complete production chain. Within this context, we characterize αβT cells engineered to express a defined γδT cell engineered to express a defined γδT receptor (TEG) currently used in a first-in-human clinical study (NTR6541). Utilizing targeted locus amplification in combination with next generation sequencing for the vector producer clone and TEG001 products, we report on five single-nucleotide variants and nine intact vector copies integrated in the producer clone. The vector copy number in TEG001 cells was on average a factor 0.72 (SD 0.11) below that of the producer cell clone. All nucleotide variants were transferred to TEG001 without having an effect on cellular proliferation during extensive in vitro culture. Based on an environmental risk assessment of the five nucleotide variants present in the non-coding viral region of the TEG001 insert, there was no altered environmental impact of TEG001 cells. We conclude that TEG001 cells do not have an increased risk for malignant transformation in vivo.

Framework engineering to produce dominant T cell receptors with enhanced antigen-specific function

TCR-gene-transfer is an efficient strategy to produce therapeutic T cells of defined antigen specificity. However, there are substantial variations in the cell surface expression levels of human TCRs, which can impair the function of engineered T cells. Here we demonstrate that substitutions of 3 amino acid residues in the framework of the TCR variable domains consistently increase the expression of human TCRs on the surface of engineered T cells.The modified TCRs mediate enhanced T cell proliferation, cytokine production and cytotoxicity, while reducing the peptide concentration required for triggering effector function up to 3000-fold. Adoptive transfer experiments in mice show that modified TCRs control tumor growth more efficiently than wild-type TCRs. Our data indicate that simple variable domain modifications at a distance from the antigen-binding loops lead to increased TCR expression and improved effector function. This finding provides a generic platform to optimize the efficacy of TCR gene therapy in humans.

CD4 Donor Lymphocyte Infusion Can Cause Conversion of Chimerism Without GVHD by Inducing Immune Responses Targeting Minor Histocompatibility Antigens in HLA Class II

Under non-inflammatory conditions HLA class II is predominantly expressed on hematopoietic cells. Therefore, donor CD4 T-cells after allogeneic stem cell transplantation (alloSCT) may mediate graft-vs.-leukemia reactivity without graft-vs.-host disease (GVHD). We analyzed immune responses in four patients converting from mixed to full donor chimerism without developing GVHD upon purified CD4 donor lymphocyte infusion (DLI) from their HLA-identical sibling donor after T-cell depleted alloSCT. In vivo activated T-cells were clonally isolated after CD4 DLI. Of the alloreactive T-cell clones, 96% were CD4 positive, illustrating the dominant role of CD4 T-cells in the immune responses. We identified 9 minor histocompatibility antigens (MiHA) as targets for alloreactivity, of which 8 were novel HLA class II restricted MiHA. In all patients, MiHA specific CD4 T-cells were found that were capable to lyse hematopoietic cells and to recognize normal and malignant cells. No GVHD was induced in these patients. Skin fibroblasts forced to express HLA class II, were recognized by only two MiHA specific CD4 T-cell clones. Of the 7 clones that failed to recognize fibroblasts, two targeted MiHA were encoded by genes not expressed in fibroblasts, presentation of one MiHA was dependent on HLA-DO, which is absent in fibroblasts, and T-cells recognizing the remaining 4 MiHA had an avidity that was apparently too low to recognize fibroblasts, despite clear recognition of hematopoietic cells. In conclusion, purified CD4 DLI from HLA-identical sibling donors can induce conversion from mixed to full donor chimerism with graft-vs.-malignancy reactivity, but without GVHD, by targeting HLA class II restricted MiHA.

Standardizing CAR-T therapy: Getting it scaled up

CAR-T therapy, grafting the specificity of a monoclonal antibody onto a T cell to target certain cancer cells, has been recognized as a promising therapeutic approach for cancer control as evidenced by the two CAR-T products proved by FDA in 2017. However, the unique heterogeneity of CAR-T therapy has restricted its production in a limited number of institutions and made it a boutique oncotherapy. By reviewing outstanding issues surrounding the commercial scale production of CAR-T therapy, we conclude that achieving mass production of CAR-T therapy without sacrificing its personalized nature is a worldwild challenge for making CAR-T a key element in the next generation of precision medicine, which can be achieved by standardizing 7 prominent factors that collectively determine the scale of CAR-T manufacturing.

Prevention and treatment of relapse after stem cell transplantation by cellular therapies

Despite recent advances in reducing therapy-related mortality after allogeneic stem cell transplantation (alloSCT) relapse remains the major cause of treatment failure and little progress has been achieved in the last decades. At the 3rd International Workshop on Biology, Prevention, and Treatment of Relapse held in Hamburg/Germany in November 2016 international experts presented and discussed recent developments in the field. Here, the potential of cellular therapies including unspecific and specific T cells, genetically modified T cells, CAR-T cells, NK-cells, and second allografting in prevention and treatment of relapse after alloSCT are summarized.

Industrializing Autologous Adoptive Immunotherapies: Manufacturing Advances and Challenges

Cell therapy has proven to be a burgeoning field of investigation, evidenced by hundreds of clinical trials being conducted worldwide across a variety of cell types and indications. Many cell therapies have been shown to be efficacious in humans, such as modified T-cells and natural killer (NK) cells. Adoptive immunotherapy has shown the most promise in recent years, with particular emphasis on autologous cell sources. Chimeric Antigen Receptor (CAR)-based T-cell therapy targeting CD19-expressing B-cell leukemias has shown remarkable efficacy and reproducibility in numerous clinical trials. Recent marketing approval of Novartis' Kymriah™ (tisagenlecleucel) and Gilead/Kite's Yescarta™ (axicabtagene ciloleucel) by the FDA further underscores both the promise and legwork to be done if manufacturing processes are to become widely accessible. Further work is needed to standardize, automate, close, and scale production to bring down costs and democratize these and other cell therapies. Given the multiple processing steps involved, commercial-scale manufacturing of these therapies necessitates tighter control over process parameters. This focused review highlights some of the most recent advances used in the manufacturing of therapeutic immune cells, with a focus on T-cells. We summarize key unit operations and pain points around current manufacturing solutions. We also review emerging technologies, approaches and reagents used in cell isolation, activation, transduction, expansion, in-process analytics, harvest, cryopreservation and thaw, and conclude with a forward-look at future directions in the manufacture of adoptive immunotherapies.

Generation of CD20-specific TCRs for TCR gene therapy of CD20low B-cell malignancies insusceptible to CD20-targeting antibodies

Immunotherapy of B-cell leukemia and lymphoma with CD20-targeting monoclonal antibodies (mAbs) has demonstrated clinical efficacy. However, the emergence of unresponsive disease due to low or absent cell surface CD20 urges the need to develop additional strategies. In contrast to mAbs, T-cells via their T-cell receptor (TCR) can recognize not only extracellular but also intracellular antigens in the context of HLA molecules. We hypothesized that T-cells equipped with high affinity CD20-targeting TCRs would be able to recognize B-cell malignancies even in the absence of extracellular CD20. We isolated CD8⁺ T-cell clones binding to peptide-MHC-tetramers composed of HLA-A*02:01 and CD20-derived peptide SLFLGILSV (CD20_SLF) from HLA-A*02:01^neg healthy individuals to overcome tolerance towards self-antigens such as CD20. High avidity T-cell clones were identified that readily recognized and lysed primary HLA-A2^pos B-cell leukemia and lymphoma in the absence of reactivity against CD20-negative but HLA-A2^pos healthy hematopoietic and nonhematopoietic cells. The T-cell clone with highest avidity efficiently lysed malignant cell-lines that had insufficient extracellular CD20 to be targeted by CD20 mAbs. Transfer of this TCR installed potent CD20-specificity onto recipient T-cells and led to lysis of CD20^low malignant cell-lines. Moreover, our approach facilitates the generation of an off-the-shelf TCR library with broad applicability by targeting various HLA alleles. Using the same methodology, we isolated a T-cell clone that efficiently lysed primary HLA-B*07:02^pos B-cell malignancies by targeting another CD20-derived peptide. TCR gene transfer of high affinity CD20-specific TCRs can be a valuable addition to current treatment options for patients suffering from CD20^low B-cell malignancies.

Specific Adoptive Cellular Immunotherapy in Allogeneic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents a treatment option for a diversity of advanced hematopoietic malignancies providing hope for long-term responses especially due to immunogenic effects associated with the treatment modality. Despite respectable progress in the field, relapses and/or opportunistic infections are major reasons for the high treatment-related mortality. However, a number of novel immunotherapeutic approaches using defined cell populations have been developed to directly target residual malignant cells as well as defined infectious diseases. We here provide an overview of current adoptive cellular immunotherapies in the context of allo-HSCT and close with an outlook on new directions within the field.

PRAME as a Potential Target for Immunotherapy in Metastatic Uveal Melanoma

Importance

Uveal melanoma (UM) is an intraocular primary malignant neoplasm that often gives rise to metastatic disease for which there are no effective therapies. A substantial proportion of UMs express the cancer-testis antigen PRAME (preferentially expressed antigen in melanoma), which can potentially be targeted by adoptive T-cell therapy.

Objective

To determine whether there may be a rationale for PRAME-directed T-cell therapy for metastatic UM.

Design, Setting, and Participants

An experimental study using a retrospective cohort of 64 patients with UM (median follow-up, 62 months) was conducted from January 8, 2015, to November 20, 2016, at the Leiden University Medical Center. Clinical, histopathologic, and genetic parameters were compared between 64 PRAME-positive and PRAME-negative UMs. HLA class I restricted, PRAME-specific T cells were stimulated with UM cell lines to measure their antigen-specific reactivity against these cell lines, which were analyzed for PRAME expression by real-time quantitative polymerase chain reaction. Uveal melanoma metastases from 16 unrelated patients were assessed for PRAME expression by messenger RNA fluorescence in situ hybridization and for HLA class I expression by immunofluorescence staining.

Main Outcomes and Measures

Interferon γ production for antigen-specific reactivity and detection of PRAME and HLA class I expression in primary and metastatic UM.

Results

Of the 64 patients in the study (31 women and 33 men; mean [SD] age at the time of enucleation, 60.6 [15.6] years), PRAME expression was negative in 35 primary UMs and positive in 29 primary UMs. Positive PRAME expression was associated with a high largest basal diameter (15.0 vs 12.0 mm; P = .005), ciliary body involvement (59% vs 26%; P = .008), and amplification of chromosome 8q (66% vs 23%; P = .002). PRAME-specific T cells reacted against 4 of 7 UM cell lines, demonstrating that T-cell reactivity correlated with PRAME expression. Metastatic UM samples were positive for PRAME messenger RNA in 11 of 16 patients and for HLA class I in 10 of 16 patients, with 8 of 16 patients demonstrating coexpression of both PRAME and HLA class I.

Conclusions and Relevance

PRAME is expressed in many primary and metastatic UMs, and about half of the metastatic UMs coexpress PRAME and HLA class I. The finding that PRAME-specific T cells in this study reacted against PRAME-positive UM cell lines suggests a potential role for PRAME-directed immunotherapy for selected patients with metastatic UM.

Generation of populations of antigen-specific cytotoxic T cells using DCs transfected with DNA construct encoding HER2/neu tumor antigen epitopes

BACKGROUND

Recent fundamental and clinical studies have confirmed the effectiveness of utilizing the potential of the immune system to remove tumor cells disseminated in a patient's body. Cytotoxic T lymphocytes (CTLs) are considered the main effectors in cell-mediated antitumor immunity. Approaches based on antigen presentation to CTLs by dendritic cells (DCs) are currently being intensively studied, because DCs are more efficient in tumor antigen presentation to T cells through their initiation of strong specific antitumor immune responses than other types of antigen-presenting cells. Today, it has become possible to isolate CTLs specific for certain antigenic determinants from heterogeneous populations of mononuclear cells. This enables direct and specific cell-mediated immune responses against cells carrying certain antigens. The aim of the present study was to develop an optimized protocol for generating CTL populations specific for epitopes of tumor-associated antigen HER2/neu, and to assess their cytotoxic effects against the HER2/neu-expressing MCF-7 tumor cell line.

METHODS

The developed protocol included sequential stages of obtaining mature DCs from PBMCs from HLA A*02-positive healthy donors, magnet-assisted transfection of mature DCs with the pMax plasmid encoding immunogenic peptides HER2 p369-377 (E75 peptide) and HER2 p689-697 (E88 peptide), coculture of antigen-activated DCs with autologous lymphocytes, magnetic-activated sorting of CTLs specific to HER2 epitopes, and stimulation of isolated CTLs with cytokines (IL-2, IL-7, and IL-15).

RESULTS

The resulting CTL populations were characterized by high contents of CD8⁺ cells (71.5% in cultures of E88-specific T cells and 90.2% in cultures of E75-specific T cells) and displayed strong cytotoxic effects against the MCF-7 cell line (percentages of damaged tumor cells in samples under investigation were 60.2 and 65.7% for E88- and E75-specific T cells, respectively; level of spontaneous death of target cells was 17.9%).

CONCLUSIONS

The developed protocol improves the efficiency of obtaining HER2/neu-specific CTLs and can be further used to obtain cell-based vaccines for eradicating targeted tumor cells to prevent tumor recurrence after the major tumor burden has been eliminated and preventing metastasis in patients with HER2-overexpressing tumors.

Cells as advanced therapeutics: State-of-the-art, challenges, and opportunities in large scale biomanufacturing of high-quality cells for adoptive immunotherapies

Therapeutic cells hold tremendous promise in treating currently incurable, chronic diseases since they perform multiple, integrated, complex functions in vivo compared to traditional small-molecule drugs or biologics. However, they also pose significant challenges as therapeutic products because (a) their complex mechanisms of actions are difficult to understand and (b) low-cost bioprocesses for large-scale, reproducible manufacturing of cells have yet to be developed. Immunotherapies using T cells and dendritic cells (DCs) have already shown great promise in treating several types of cancers, and human mesenchymal stromal cells (hMSCs) are now extensively being evaluated in clinical trials as immune-modulatory cells. Despite these exciting developments, the full potential of cell-based therapeutics cannot be realized unless new engineering technologies enable cost-effective, consistent manufacturing of high-quality therapeutic cells at large-scale. Here we review cell-based immunotherapy concepts focused on the state-of-the-art in manufacturing processes including cell sourcing, isolation, expansion, modification, quality control (QC), and culture media requirements. We also offer insights into how current technologies could be significantly improved and augmented by new technologies, and how disciplines must converge to meet the long-term needs for large-scale production of cell-based immunotherapies.

Recent Developments in Cellular Immunotherapy for HSCT-Associated Complications

Allogeneic hematopoietic stem cell transplantation is associated with serious complications, and improvement of the overall clinical outcome of patients with hematological malignancies is necessary. During the last decades, posttransplant donor-derived adoptive cellular immunotherapeutic strategies have been progressively developed for the treatment of graft-versus-host disease (GvHD), infectious complications, and tumor relapses. To date, the common challenge of all these cell-based approaches is their implementation for clinical application. Establishing an appropriate manufacturing process, to guarantee safe and effective therapeutics with simultaneous consideration of economic requirements is one of the most critical hurdles. In this review, we will discuss the recent scientific findings, clinical experiences, and technological advances for cell processing toward the application of mesenchymal stromal cells as a therapy for treatment of severe GvHD, virus-specific T cells for targeting life-threating infections, and of chimeric antigen receptors-engineered T cells to treat relapsed leukemia.

Longitudinal analyses of leukemia-associated antigen-specific CD8+ T cells in patients after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment approach for patients with acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL). Graft versus leukemia (GVL) effects, which are exerted by donor T cells directed against leukemic-associated antigens (LAAs), are considered to play a crucial role in disease eradication. Although the expansion of cytotoxic T lymphocytes (CTLs) specific for cytomegalovirus (CMV) in response to an infection has been shown in multiple studies, data on CTLs mediating GVL effects are limited. To evaluate a potential increase or decrease of T lymphocytes specific for LAAs in the setting of allogeneic HSCT, we monitored leukemia-specific CD8⁺ T cells throughout the first year after HSCT in 18 patients using streptamer technology. A broad panel of promising LAAs was selected: Wilms tumor protein, proteinase 3, receptor for hyaluronan acid-mediated motility, apoptosis regulator Bcl-2, survivin, nucleophosmin, and fibromodulin. T cells specifically directed against AML- or CLL-associated antigens were found at very low frequencies in peripheral blood. Substantial frequencies of LAA-specific T cells could not be measured at any time point by flow cytometry. In contrast, abundant CMV-pp65-specific T cells were detected in CMV-seropositive patient-recipient pairs and an increase prompted by CMV infection could be demonstrated. In conclusion, T lymphocytes with specificities for the aforementioned LAAs can only be detected in minimal quantities in the early phase after allogeneic HSCT.

Allo-reactive T cells for the treatment of hematological malignancies

Several mechanisms can be responsible for control of hematological tumors by allo-reactive T cells. Following allogeneic stem cell transplantation (alloSCT) donor T cells recognizing genetic disparities presented on recipient cells and not on donor cells are main effectors of tumor control, but also of the detrimental graft versus host disease (GVHD). Since after transplantation normal hematopoiesis is of donor origin, any T cell response directed against polymorphic antigens expressed on hematopoietic recipient cells but not on donor cells will result in an anti-tumor response not affecting normal hematopoiesis. After fully HLA-matched alloSCT, T cells recognizing polymorphic peptides derived from proteins encoded by genes selectively expressed in hematopoietic lineages may result in anti-tumor responses without GVHD. Due to the high susceptibility of hematopoietic cells for T cell recognition, a low amplitude of the overall T cell response may also be in favor of the anti-tumor reactivity in hematological malignancies. A mismatch between donor and patient for specific HLA-alleles can also be exploited to induce a selective T cell response against patient (malignant) hematopoietic cells. If restricting HLA class II molecules are selectively expressed on hematopoietic cells under non-inflammatory circumstances, allo HLA class-II responses may control the tumor with limited risk of GVHD. Alternatively, T cells recognizing hematopoiesis-restricted antigens presented in the context of mismatched HLA alleles may be used to treat patients with hematological cancers. This review discusses various ways to manipulate the allo-immune response aiming to exploit the powerful ability of allo-reactive T-cells to control the malignancies without causing severe damage to non-hematopoietic tissues.

Assessment of the effector function of CMV-specific CTLs isolated using MHC-multimers from granulocyte-colony stimulating factor mobilized peripheral blood

BACKGROUND

Adoptive transfer of CMV-specific T cells has shown promising results in preventing pathological effects caused by opportunistic CMV infection in immunocompromised patients following allogeneic hematopoietic stem cell transplantation. The majority of studies have used steady-state leukapheresis for CMV-reactive product manufacture, a collection obtained prior to or months after G-CSF mobilization, but the procurement of this additional sample is often not available in the unrelated donor setting. If the cellular product for adoptive immunotherapy could be generated from the same G-CSF mobilized collection, the problems associated with the additional harvest could be overcome. Despite the tolerogenic effects associated with G-CSF mobilization, recent studies described that CMV-primed T cells generated from mobilized donors remain functional.

METHODS

MHC-multimers are potent tools that allow the rapid production of antigen-specific CTLs. Therefore, in the present study we have assessed the feasibility and efficacy of CMV-specific CTL manufacture from G-CSF mobilized apheresis using MHC-multimers.

RESULTS

CMV-specific CTLs can be efficiently isolated from G-CSF mobilized samples with Streptamers and are able to express activation markers and produce cytokines in response to antigenic stimulation. However, this anti-viral functionality is moderately reduced when compared to non-mobilized products.

CONCLUSIONS

The translation of Streptamer technology for the isolation of anti-viral CTLs from G-CSF mobilized PBMCs into clinical practice would widen the number of patients that could benefit from this therapeutic strategy, although our results need to be taken into consideration before the infusion of antigen-specific T cells obtained from G-CSF mobilized samples.

Seatbelts in CAR therapy: How Safe Are CARS?

T-cells genetically redirected with a chimeric antigen receptor (CAR) to recognize tumor antigens and kill tumor cells have been infused in several phase 1 clinical trials with success. Due to safety concerns related to on-target/off-tumor effects or cytokine release syndrome, however, strategies to prevent or abate serious adverse events are required. Pharmacologic therapies; suicide genes; or novel strategies to limit the cytotoxic effect only to malignant cells are under active investigations. In this review, we summarize results and toxicities of investigations employing CAR redirected T-cells, with a focus on published strategies to grant safety of this promising cellular application.

Selection of adenovirus-specific and Epstein-Barr virus-specific T cells with major histocompatibility class I streptamers under Good Manufacturing Practice (GMP)-compliant conditions

BACKGROUND AIMS

Despite antiviral drug therapies, human adenovirus (HAdV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections still contribute substantially to transplant-related death of patients after hematopoietic stem cell transplantation. Earlier clinical studies demonstrated successful adoptive transfer of magnetically selected CMV-specific T cells via removable, and thus Good Manufacturing Practice-compliant, major histocompatibility class I streptamers. Thus, the primary focus of the present study was the selection of HAdV-streptamer+ T cells, although in three experiments, EBV-streptamer+ T cells were also selected.

METHODS

Cells from leukaphereses of healthy donors were prepared in large (1-6 × 10(9)) and small (25 × 10(6)) cell batches. Whereas the larger batch was directly labeled with streptamers to select HAdV- and/or EBV-specific T cells (large-scale), the smaller batch was used to generate in vitro virus-specific T-cell lines before streptamer labeling for streptamer selection (small-scale). Isolation of HAdV- and/or EBV-specific T cells was performed with the use of the CliniMACS device.

RESULTS

The purity of HAdV- and EBV-streptamer+ T cells among CD3+ cells, obtained from large-scale selection, was up to 6.7% and 44%, respectively. If HAdV- and EBV-streptamers were applied simultaneously, the purity of antigen-specific T cells reached up to 50.7%. A further increase in purity reaching up to 98% was achieved by small-scale selection of HAdV-specific T cells. All final products fulfilled the microbiological and chemical release criteria. Interferon-γ-response indicating functional activity was seen in 6 of 9 HAdV and 2 of 3 EBV large-scale selections and in 2 of 3 HAdV small-scale selections.

CONCLUSIONS

HAdV-streptamers were shown to be clinically feasible for few patients after the large-scale approach but for larger patient numbers if combined with EBV-streptamers or after the small-scale approach.

Towards a commercial process for the manufacture of genetically modified T cells for therapy

The recent successes of adoptive T-cell immunotherapy for the treatment of hematologic malignancies have highlighted the need for manufacturing processes that are robust and scalable for product commercialization. Here we review some of the more outstanding issues surrounding commercial scale manufacturing of personalized-adoptive T-cell medicinal products. These include closed system operations, improving process robustness and simplifying work flows, reducing labor intensity by implementing process automation, scalability and cost, as well as appropriate testing and tracking of products, all while maintaining strict adherence to Current Good Manufacturing Practices and regulatory guidelines. A decentralized manufacturing model is proposed, where in the future patients' cells could be processed at the point-of-care in the hospital.

Manufacture of tumor- and virus-specific T lymphocytes for adoptive cell therapies

Adoptive transfer of tumor-infiltrating lymphocytes (TILs) and genetically engineered T lymphocytes expressing chimeric antigen receptors (CARs) or conventional alpha/beta T-cell receptors (TCRs), collectively termed adoptive cell therapy (ACT), is an emerging novel strategy to treat cancer patients. Application of ACT has been constrained by the ability to isolate and expand functional tumor-reactive T cells. The transition of ACT from a promising experimental regimen to an established standard of care treatment relies largely on the establishment of safe, efficient, robust and cost-effective cell manufacturing protocols. The manufacture of cellular products under current good manufacturing practices (cGMPs) has a critical role in the process. Herein, we review current manufacturing methods for the large-scale production of clinical-grade TILs, virus-specific and genetically modified CAR or TCR transduced T cells in the context of phase I/II clinical trials as well as the regulatory pathway to get these complex personalized cellular products to the clinic.

Cell-based strategies to manage leukemia relapse: efficacy and feasibility of immunotherapy approaches

When treatment fails, the clinical outcome of acute leukemia patients is usually very poor, particularly when failure occurs after transplantation. A second allogeneic stem cell transplant could be envisaged as an effective and feasible salvage option in younger patients having a late relapse and an available donor. Unmanipulated or minimally manipulated donor T cells may also be effective in a minority of patients but the main limit remains the induction of severe graft-versus-host disease. This clinical complication has brought about a huge research effort that led to the development of leukemia-specific T-cell therapy aiming at the direct recognition of leukemia-specific rather than minor histocompatibility antigens. Despite a great scientific interest, the clinical feasibility of such an approach has proven to be quite problematic. To overcome this limitation, more research has moved toward the choice of targeting commonly expressed hematopoietic specific antigens by the genetic modification of unselected T cells. The best example of this is represented by the anti-CD19 chimeric antigen receptor (CD19.CAR) T cells. As a possible alternative to the genetic manipulation of unselected T cells, specific T-cell subpopulations with in vivo favorable homing and long-term survival properties have been genetically modified by CAR molecules. Finally, the use of naturally cytotoxic effector cells such as natural killer and cytokine-induced killer cells has been proposed in several clinical trials. The clinical development of these latter cells could also be further expanded by additional genetic modifications using the CAR technology.