Clinical responses with T lymphocytes targeting malignancy-associated κ light chains

Accelerating chimeric antigen receptor therapy in chronic lymphocytic leukemia: The development and challenges of chimeric antigen receptor T-cell therapy for chronic lymphocytic leukemia

Studies of chimeric antigen receptor (CAR) T-cell therapy in chronic lymphocytic leukemia (CLL) have demonstrated the potential to produce deep remissions-and possibly cures-in some patients with heavily pretreated, high-risk, relapsed, and refractory disease. Unfortunately, most clinical trials of CAR T cells in CLL report complete responses only in the minority of patients, although recent studies have begun to elucidate the factors most predictive of response. These studies have suggested strategies for optimizing CAR T-cell fitness as well as the pre-existing host immune response, approaches that will likely lead to improvements in the efficacy of CAR T cells in CLL. Treating patients earlier in the course of their disease or using combination therapies with CAR T cells may further enhance efficacy. In this review, we summarize the existing literature on CAR T cell therapy in CLL, discuss mechanisms of response and resistance, and describe challenges facing the field.

Facing the future: challenges and opportunities in adoptive T cell therapy in cancer

INTRODUCTION

In recent years, immunotherapy for the treatment of solid cancer has emerged as a promising therapeutic alternative. Adoptive cell therapy (ACT), especially T cell-based, has been found to cause tumor regression and even cure in a percentage of treated patients. Checkpoint inhibitors further underscore the potential of the T cell compartment in the treatment of cancer. Not all patients respond to these treatments; however, many challenges remain.

AREAS COVERED

This review covers the challenges and progress in tumor antigen target identification and selection, and cell product manufacturing for T cell ACT. Tumor immune escape mechanisms and strategies to overcome those in the context of T cell ACT are also discussed.

EXPERT OPINION

The immunotherapy toolbox is rapidly expanding and improving, and the future promises further breakthroughs in the T cell ACT field. The heterogeneity of the tumor microenvironment and the multiplicity of tumor immune escape mechanisms pose formidable challenges to successful T cell immunotherapy in solid tumors, however. Individualized approaches and strategies combining treatments targeting different immunotherapeutic aspects will be needed in order to expand the applicability and improve the response rates in future.

CRISPR/Cas9-based genome editing in the era of CAR T cell immunotherapy

The advent of engineered T cells as a form of immunotherapy marks the beginning of a new era in medicine, providing a transformative way to combat complex diseases such as cancer. Following FDA approval of CAR T cells directed against the CD19 protein for the treatment of acute lymphoblastic leukemia and diffuse large B cell lymphoma, CAR T cells are poised to enter mainstream oncology. Despite this success, a number of patients are unable to receive this therapy due to inadequate T cell numbers or rapid disease progression. Furthermore, lack of response to CAR T cell treatment is due in some cases to intrinsic autologous T cell defects and/or the inability of these cells to function optimally in a strongly immunosuppressive tumor microenvironment. We describe recent efforts to overcome these limitations using CRISPR/Cas9 technology, with the goal of enhancing potency and increasing the availability of CAR-based therapies. We further discuss issues related to the efficiency/scalability of CRISPR/Cas9-mediated genome editing in CAR T cells and safety considerations. By combining the tools of synthetic biology such as CARs and CRISPR/Cas9, we have an unprecedented opportunity to optimally program T cells and improve adoptive immunotherapy for most, if not all future patients.

CAR T Cell Toxicity: Current Management and Future Directions

By late 2018, 2 chimeric antigen receptor T (CAR T) cell products have been approved by US and European regulatory authorities. Tisagenlecleucel (Kymriah, Novartis) is indicated in the treatment of patients up to 25 years of age with B-cell acute lymphoblastic leukemia (ALL) that is refractory or in second or later relapse, or adult patients with large B-cell lymphoma relapsed or refractory (r/r) after 2 or more lines of systemic therapy, including diffuse large B-cell lymphoma (DLBCL) not otherwise specified, high grade B-cell lymphoma and DLBCL arising from follicular lymphoma. Axicabtagene ciloleucel (Yescarta, Kite) is indicated for the treatment of adult patients with large B-cell lymphoma relapsed or refractory after 2 or more lines of systemic therapy, including DLBCL not otherwise specified, primary mediastinal large B-cell lymphoma, high grade B-cell lymphoma, and DLBCL arising from follicular lymphoma (ZUMA-1 trial). This review will offer a practical guide for the recognition and management of the most important toxicities related to the use of the current commercial CAR T cells, and also highlight strategies to diminish these side effects in the future.

Safety and efficacy of targeting CD138 with a chimeric antigen receptor for the treatment of multiple myeloma

After unprecedented successes in B-cell malignancies, chimeric antigen receptor T cells have recently been investigated for the treatment of multiple myeloma. Chimeric antigen receptor targeting T cells B-cell maturation antigen (BCMA) on malignant plasma cells have led to impressive clinical responses in recent trials. However, BCMA-negative relapses have been observed, supporting the need for complementary treatment strategies. Here, we explored the feasibility of targeting CD138 (syndecan-1), a surface marker expressed on both normal and malignant plasma cells. We showed that T cells from both healthy donors and from multiple myeloma patients, when transduced with a CD138-specific chimeric antigen receptor, can eliminate tumor cell lines and primary myeloma cells both in vitro and in vivo. CD138 is also expressed by putative myeloma stem cells identified by Hoechst staining, and these cells can be eliminated by CD138-specific chimeric antigen receptor T cells. Preclinical analyses did not identify any on target off tumor cytotoxicity against normal epithelial or endothelial cells, further supporting the rationale for the use of adoptively transferred CD138-specific chimeric antigen receptor T cells for the treatment of patients with relapsed/refractory multiple myeloma.

Cancer Immunotherapy with T Cells Carrying Bispecific Receptors That Mimic Antibodies

Tumors are inherently heterogeneous in antigen expression, and escape from immune surveillance due to antigen loss remains one of the limitations of targeted immunotherapy. Despite the clinical use of adoptive therapy with chimeric antigen receptor (CAR)-redirected T cells in lymphoblastic leukemia, treatment failure due to epitope loss occurs. Targeting multiple tumor-associated antigens (TAAs) may thus improve the outcome of CAR-T cell therapies. CARs developed to simultaneously target multiple targets are limited by the large size of each single-chain variable fragment and compromised protein folding when several single chains are linearly assembled. Here, we describe single-domain antibody mimics that function within CAR parameters but form a very compact structure. We show that antibody mimics targeting EGFR and HER2 of the ErbB receptor tyrosine kinase family can be assembled into receptor molecules, which we call antibody mimic receptors (amR). These amR can redirect T cells to recognize two different epitopes of the same antigen or two different TAAs in vitro and in vivo.

Chimeric Antigen Receptors for T-Cell Malignancies

Development of chimeric antigen receptor (CAR)-modified T cells for the treatment of T-lineage leukemia and lymphoma has encountered several unique challenges. The most widely expressed tumor antigen targets for malignant T cells are often also expressed on non-malignant T cells. Transducing T cells with CARs targeted to these shared antigens can therefore promote over-activation or fratricide of CAR T cells, reducing their therapeutic potency. If fratricide is resolved, clinical CAR T cell activity may eliminate normal T-cell subsets and cause temporary immunosuppression. In this review, we summarize the preclinical development of CAR-based therapies for T-cell malignancies and discuss strategies to minimize toxicities associated with on-target fratricide and off-tumor activity.

Cellular immunotherapy as a therapeutic approach in multiple myeloma

INTRODUCTION

Immunotherapy seeks to restore and augment the unique ability of the immune system to recognize and kill malignant cells. This strategy has previously been incorporated into standard of care in myeloma with the use of immunomodulatory drugs and allogeneic transplant. The following review will discuss the rationale for immunotherapy to reverse critical aspects of the immunosuppressive milieu in myeloma and avenues where cellular therapies are now revolutionizing myeloma treatment. Areas covered: A particular focus is outcomes of clinical trials in myeloma published in PubMed database or abstract form using vaccines or adoptive cell transfer: marrow infiltrating lymphocytes, T-cell receptor and chimeric antigen receptor T cells. Expert commentary: Immunotherapy has extraordinary potential in myeloma. Combinations of cellular therapies with immunomodulatory molecules or checkpoint inhibitors are likely to be synergistic and now underway. Future directions include neoantigen or nanoparticle vaccines and further modifications of engineered T cells such as use of dual-antigens, suicide genes or allogeneic cells.

Immunotherapeutic Approaches for Multiple Myeloma: Where Are We Now?

PURPOSE OF REVIEW

The treatment landscape for multiple myeloma has evolved rapidly with the availability of multiple new drugs; however, although patient survival has improved, the disease remains incurable. Multiple myeloma is characterized by the unregulated growth of malignant plasma cells accompanied by immune dysfunction as well as disrupted immune surveillance mechanisms. Here, we analyze clinical modalities, with a focus on monoclonal antibodies and adoptive cellular therapy that enhance patients' immune systems and overcome these defects.

RECENT FINDINGS

Early clinical trials with PD-1 inhibitors were promising, but randomized phase III trials with immunomodulatory drugs showed increased toxicities. Monoclonal antibodies targeting surface antigens led to substantial clinical efficiency in relapsed myeloma. Chimeric antigen receptor (CAR) T cell therapy for multiple myeloma represents a significant advance, as exciting and dramatic responses in early clinical trials have been seen. Immunotherapeutic approaches are promising and can augment or replace the current standard of care, with the potential to offer extended survival for myeloma patients.

Immunotherapy in myeloma: how far have we come?

The treatment of multiple myeloma (MM) has evolved substantially over the past decades, leading to a significantly improved outcome of MM patients. The introduction of high-dose therapy, especially, and autologous stem cell transplantation, as well as the development of new drugs, such as immunomodulatory drugs (IMiDs) and proteasome inhibitors have contributed to the improvement in survival. However, eventually most MM patients relapse, which indicates that there is a need for new agents and novel treatment strategies. Importantly, the long-term survival in a subset of MM patients after allogeneic stem cell transplantation illustrates the potential of immunotherapy in MM, but allogeneic stem cell transplantation is also associated with a high rate of treatment-related mortality. Recently, a better insight into several immune-evasion mechanisms, which contribute to tumor progression, has resulted in the development of active and well-tolerated novel forms of immunotherapy. These immunotherapeutic agents can be used as monotherapy, or, even more successfully, in combination with other established anti-MM agents to further improve depth and duration of response by preventing the outgrowth of resistant clones. This review will discuss the mechanisms used by MM cells to evade the immune system, and also provide an overview of currently approved immunotherapeutic drugs, such as IMiDs (e.g. lenalidomide and pomalidomide) and monoclonal antibodies that target cell surface antigens present on the MM cell (e.g. elotuzumab and daratumumab), as well as novel immunotherapies (e.g. chimeric antigen receptor T-cells, bispecific antibodies and checkpoint inhibitors) currently in clinical development in MM.

Eradication of Neuroblastoma by T Cells Redirected with an Optimized GD2-Specific Chimeric Antigen Receptor and Interleukin-15

PURPOSE

A delay in encountering the cognate antigen while in the circulation, and the suboptimal costimulation received at the tumor site are key reasons for the limited activity of chimeric antigen receptor-redirected T cells (CAR-T) in solid tumors. We have explored the benefits of incorporating the IL15 cytokine within the CAR cassette to provide both a survival signal before antigen encounter, and an additional cytokine signaling at the tumor site using a neuroblastoma tumor model.

EXPERIMENTAL DESIGN

We optimized the construct for the CAR specific for the NB-antigen GD2 without (GD2.CAR) or with IL15 (GD2.CAR.15). We then compared the expansion, phenotype, and antitumor activity of T cells transduced with these constructs against an array of neuroblastoma cell lines in vitro and in vivo using a xenogeneic metastatic model of neuroblastoma.

RESULTS

We observed that optimized GD2.CAR.15-Ts have reduced expression of the PD-1 receptor, are enriched in stem cell-like cells, and have superior antitumor activity upon repetitive tumor exposures in vitro and in vivo as compared with GD2.CAR-Ts. Tumor rechallenge experiments in vivo further highlighted the role of IL15 in promoting enhanced CAR-T antitumor activity and survival, both in the peripheral blood and tissues. Finally, the inclusion of the inducible caspase-9 gene (iC9) safety switch warranted effective on demand elimination of the engineered GD2.CAR.15-Ts.

CONCLUSIONS

Our results guide new therapeutic options for GD2.CAR-Ts in patients with neuroblastoma, and CAR-T development for a broad range of solid tumors.

Glycan-directed CAR-T cells

Cancer immunotherapy is rapidly advancing in the treatment of a variety of hematopoietic cancers, including pediatric acute lymphoblastic leukemia and diffuse large B cell lymphoma, with chimeric antigen receptor (CAR)-T cells. CARs are genetically encoded artificial T cell receptors that combine the antigen specificity of an antibody with the machinery of T cell activation. However, implementation of CAR technology in the treatment of solid tumors has been progressing much slower. Solid tumors are characterized by a number of challenges that need to be overcome, including cellular heterogeneity, immunosuppressive tumor microenvironment (TME), and, in particular, few known cancer-specific targets. Post-translational modifications that differentially occur in malignant cells generate valid cell surface, cancer-specific targets for CAR-T cells. We previously demonstrated that CAR-T cells targeting an aberrant O-glycosylation of MUC1, a common cancer marker associated with changes in cell adhesion, tumor growth and poor prognosis, could control malignant growth in mouse models. Here, we discuss the field of glycan-directed CAR-T cells and review the different classes of antibodies specific for glycan-targeting, including the generation of high affinity O-glycopeptide antibodies. Finally, we discuss historic and recently investigated glycan targets for CAR-T cells and provide our perspective on how targeting the tumor glycoproteome and/or glycome will improve CAR-T immunotherapy.

Cell-based immunotherapy approaches for multiple myeloma

Despite the arrival of novel therapies, multiple myeloma (MM) remains incurable and new treatment options are needed. Chimeric antigen receptor (CAR) T cells are genetically modified T cells that express a CAR directed against specific tumour antigens. CAR T cells are able to kill target tumour cells and may result in long-lasting immune responses in vivo. The rapid development of CAR technologies has led to clinical trials in haematological cancers including MM, and CAR T cells might evolve into a standard treatment in the next few years. Only small patient cohorts with relapsed or refractory disease have so far been investigated, but promising preliminary results with high response rates have been  obtained in phase I clinical trials with B cell maturation antigen (BCMA), CD19, CD38 and κ-light-chain CAR T cells. Additional preclinical studies on CD38 and SLAMF7-CAR T cells in MM treatment yielded preclinical results that merit further investigation. Beyond the T cell approach, recent studies have focussed on CAR natural killer (NK) cells in order to increase the reactivity of these effector cells. Finally, to investigate the targeting of intracellular antigens, cellular therapies based on engineered T cell receptors (TCRs) are in development. In this review, we discuss results from preclinical and early-phase clinical trials testing the feasibility and safety of CAR T cell administration in MM, as well as early studies into approaches that utilise CAR NK cell and genetically modified TCRs.

CAR T Cell Therapy of Non-hematopoietic Malignancies: Detours on the Road to Clinical Success

Chimeric antigen receptor (CAR)-engineered T cells represent a breakthrough in personalized medicine. In this strategy, a patient's own T lymphocytes are genetically reprogrammed to encode a synthetic receptor that binds a tumor antigen, allowing T cells to recognize and kill antigen-expressing cancer cells. As a result of complete and durable responses in individuals who are refractory to standard of care therapy, CAR T cells directed against the CD19 protein have been granted United States Food and Drug Administration (FDA) approval as a therapy for treatment of pediatric and young adult acute lymphoblastic leukemia and diffuse large B cell lymphoma. Human trials of CAR T cells targeting CD19 or B cell maturation antigen in multiple myeloma have also reported early successes. However, a clear and consistently reproducible demonstration of the clinical efficacy of CAR T cells in the setting of solid tumors has not been reported to date. Here, we review the history and status of CAR T cell therapy for solid tumors, potential T cell-intrinsic determinants of response and resistance as well as extrinsic obstacles to the success of this approach for much more prevalent non-hematopoietic malignancies. In addition, we summarize recent strategies and innovations that aim to augment the potency of CAR T cells in the face of multiple immunosuppressive barriers operative within the solid tumor microenvironment. Advances in the field of CAR T cell biology over the coming years in the areas of safety, reliability and efficacy against non-hematopoietic cancers will ultimately determine how transformative adoptive T cell therapy will be in the broader battle against cancer.

Chimeric antigen receptor-modified T cell therapy in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), a common type of B cell chronic lymphoproliferative disorder in adults, has witnessed enormous development in its treatment in recent years. New drugs such as ibrutinib, idelalisib, and venetoclax have achieved great success in treating relapsed and refractory (R/R) CLL. In addition, with the development of immunotherapy, chimeric antigen receptor-engineered T cells (CAR-T) therapy, a novel adoptive immune treatment, has also become more and more important in treating R/R CLL. It combines the advantages of T cells and B cells via ex vivo gene transfer technology and is able to bind targets recognized by specific antibodies without antigen presentation, thus breaking the restriction of major histocompatibility complex. So far, there have been lots of studies exploring the application of CAR-T therapy in CLL. In this review, we describe the structure of chimeric antigen receptor, the preclinical, and clinical results of CAR-T therapy against CLL, along with its adverse events and advances in efficacy.

Practical Considerations for Antibodies in Myeloma

The development of the monoclonal antibodies daratumumab and elotuzumab has expanded treatment options for multiple myeloma and led to great improvement in patient outcomes. These agents have favorable safety profiles and synergize effectively with established agents used in the management of myeloma, namely immunomodulatory drugs and proteasome inhibitors. This article reviews the rationale for use of monoclonal antibodies in myeloma, current approved indications for daratumumab and elotuzumab, the manner in which these agents are used in the overall management of myeloma, and specific challenges associated with their use in the clinic. It also highlights other, emerging drug combinations that incorporate daratumumab or elotuzumab and profiles new therapeutic antibodies currently under development.

Therapy for relapsed multiple myeloma

Despite significant progress in our understanding and the development of novel therapies, most patients with multiple myeloma will experience relapse of their disease. Therapy of relapsed myeloma has improved due to the availability of novel agents that are highly active against the disease. However, the selection of therapy can be challenging due to the emergence of toxicities, comorbidities and frailty. In the following we discuss our approach to the treatment of the patient with relapsed myeloma.

Anti-Multiple Myeloma Activity of Nanobody-Based Anti-CD38 Chimeric Antigen Receptor T Cells

Chimeric antigen receptor T cells (CAR-Ts) are a promising strategy for the treatment of many cancers, including multiple myeloma (MM), a hematological malignancy characterized by the high expression of CD38. To broaden the applications of using CD38 as a therapeutic target for the disease, we developed a new nanobody against CD38 and constructed a CD38-CAR that was composed of this nanobody as the targeting domain, and 4-1BB and CD3ζ as the costimulatory and activating domains, in a lentiviral vector. CD3⁺ T cells from healthy individuals were transduced with the CD38-CAR at an efficiency higher than 60%, as determined by CD38-CAR expression using flow cytometry. The CD38-CAR-Ts proliferated efficiently and produced more inflammatory cytokines, such as IL-2, IFN-γ, and TNF-α, when activated. The CD38-CAR-Ts effectively lysed CD38⁺ MM cell lines, including LP-1, RPMI 8226, OPM2, and MOLP8, and primary MM cells from multiple myeloma patients. The specificity was demonstrated by the fact that CD38-CAR-Ts showed little cytotoxicity on LP-1 cells with CD38 knocked out or on K562 cells, which do not express CD38. CD38-CAR-Ts appeared to have a very slight cytotoxicity against CD38⁺ fractions of T cells, B cells, and natural killer cells. In addition, the lysis of CD34⁺ hematopoietic progenitor cells did not completely inhibit the development of colony-forming units. In vivo, CD38-CAR-Ts inhibited tumor growth in NOD/SCID mice that were subcutaneously inoculated with RPMI 8226 cells. These results demonstrate that the CD38-CAR-Ts constructed with the anti-CD38 nanobody are a promising approach for the treatment of multiple myeloma.

4-1BB enhancement of CAR T function requires NF-κB and TRAFs

Chimeric antigen receptors (CARs) have an antigen-binding domain fused to transmembrane, costimulatory, and CD3ζ domains. Two CARs with regulatory approval include a CD28 or 4-1BB costimulatory domain. While both CARs achieve similar clinical outcomes, biologic differences have become apparent but not completely understood. Therefore, in this study we aimed to identify mechanistic differences between 4-1BB and CD28 costimulation that contribute to the biologic differences between the 2 CARs and could be exploited to enhance CAR T cell function. Using CD19-targeted CAR T cells with 4-1BB we determined that enhancement of T cell function is driven by NF-κB. Comparison to CAR T cells with CD28 also revealed that 4-1BB is associated with more antiapoptotic proteins and dependence on persistence for B cell killing. While TNF receptor-associated factor 2 (TRAF2) has been presupposed to be required for 4-1BB costimulation in CAR T cells, we determined that TRAF1 and TRAF3 are also critical. We observed that TRAFs impacted CAR T viability and proliferation, as well as cytotoxicity and/or cytokines, in part by regulating NF-κB. Our study demonstrates how 4-1BB costimulation in CAR T cells impacts antitumor eradication and clinical outcomes and has implications for enhanced CAR design.

Chimeric antigen receptor modified T-cells for cancer treatment

T cells engineered with the chimeric antigen receptor (CAR) are rapidly emerging as an important immunotherapy for hematologic malignancies. The anti-cluster of differentiation (CD)19 CAR-T cell therapy has been remarkably successful against refractory/relapsed acute lymphoblastic leukemia (ALL), and a complete remission rate as high as 90% was observed, in both children and adults. Although the achievement of clinical efficacy using CAR-T cell therapy for solid tumors has encountered several obstacles that were associated with the multiple mechanisms contributing to an immunosuppressive microenvironment, investigators are exploring more optimized approaches to improve the efficiency of CAR-T in solid tumors. In addition, cytokine release syndrome (CRS) and neurotoxicity following CAR-T cell therapy can be severe or even fatal; therefore, the management of these toxicities is significant. Herein, we briefly review the structure of CAR-T and some novel CAR designs, the clinical application of CAR-T cell therapies, as well as the assessment and management of toxicities.

Synthetic immunology: T-cell engineering and adoptive immunotherapy

During the past decades, the rapidly-evolving cancer is hard to be thoroughly eliminated even though the radiotherapy and chemotherapy do exhibit efficacy in some degree. However, a breakthrough appeared when the adoptive cancer therapy [1] was developed, especially T cells armed with chimeric antigen receptors (CARs) showed great potential in tumor clinical trials recently. CAR-T cells successfully elevated the efficiency and specificity of cytotoxicity. In this review, we will talk about the design of CAR and CAR-included combinatory therapeutic applications in the principles of systems and synthetic immunology.

T Cells Genetically Modified to Express an Anti-B-Cell Maturation Antigen Chimeric Antigen Receptor Cause Remissions of Poor-Prognosis Relapsed Multiple Myeloma

Purpose Therapies with novel mechanisms of action are needed for multiple myeloma (MM). T cells can be genetically modified to express chimeric antigen receptors (CARs), which are artificial proteins that target T cells to antigens. B-cell maturation antigen (BCMA) is expressed by normal and malignant plasma cells but not normal essential cells. We conducted the first-in-humans clinical trial, to our knowledge, of T cells expressing a CAR targeting BCMA (CAR-BCMA). Patients and Methods Sixteen patients received 9 × 106 CAR-BCMA T cells/kg at the highest dose level of the trial; we are reporting results of these 16 patients. The patients had a median of 9.5 prior lines of MM therapy. Sixty-three percent of patients had MM refractory to the last treatment regimen before protocol enrollment. T cells were transduced with a γ-retroviral vector encoding CAR-BCMA. Patients received CAR-BCMA T cells after a conditioning chemotherapy regimen of cyclophosphamide and fludarabine. Results The overall response rate was 81%, with 63% very good partial response or complete response. Median event-free survival was 31 weeks. Responses included eradication of extensive bone marrow myeloma and resolution of soft-tissue plasmacytomas. All 11 patients who obtained an anti-MM response of partial response or better and had MM evaluable for minimal residual disease obtained bone marrow minimal residual disease-negative status. High peak blood CAR+ cell levels were associated with anti-MM responses. Cytokine-release syndrome toxicities were severe in some cases but were reversible. Blood CAR-BCMA T cells were predominantly highly differentiated CD8+ T cells 6 to 9 days after infusion. BCMA antigen loss from MM was observed. Conclusion CAR-BCMA T cells had substantial activity against heavily treated relapsed/refractory MM. Our results should encourage additional development of CAR T-cell therapies for MM.

Chimeric antigen receptor-modified T cells: CD19 and the road beyond

The ability to harness a patient's immune system to target malignant cells is now transforming the treatment of many cancers, including hematologic malignancies. The adoptive transfer of T cells selected for tumor reactivity or engineered with natural or synthetic receptors has emerged as an effective modality, even for patients with tumors that are refractory to conventional therapies. The most notable example of adoptive cell therapy is with T cells engineered to express synthetic chimeric antigen receptors (CARs) that reprogram their specificity to target CD19. CAR T cells have shown remarkable antitumor activity in patients with refractory B-cell malignancies. Ongoing research is focused on understanding the mechanisms of incomplete tumor elimination, reducing toxicities, preventing antigen escape, and identifying suitable targets and strategies based on established and emerging principles of synthetic biology for extending this approach to other hematologic malignancies. This review will discuss the current status, challenges, and potential future applications of CAR T-cell therapy in hematologic malignancies.

Programming CAR-T cells to kill cancer

T cells engineered to express chimeric antigen receptors (CARs) that are specific for tumour antigens have led to high complete response rates in patients with haematologic malignancies. Despite this early success, major challenges to the broad application of CAR-T cells as cancer therapies remain, including treatment-associated toxicities and cancer relapse with antigen-negative tumours. Targeting solid tumours with CAR-T cells poses additional obstacles because of the paucity of tumour-specific antigens and the immunosuppressive effects of the tumour microenvironment. To overcome these challenges, T cells can be programmed with genetic modules that increase their therapeutic potency and specificity. In this Review Article, we survey major advances in the engineering of next-generation CAR-T therapies for haematologic cancers and solid cancers, with particular emphasis on strategies for the control of CAR specificity and activity and on approaches for improving CAR-T-cell persistence and overcoming immunosuppression. We also lay out a roadmap for the development of off-the-shelf CAR-T cells.

Clinical development of CAR T cells-challenges and opportunities in translating innovative treatment concepts

Chimeric antigen receptor (CAR) T cell therapy, together with checkpoint inhibition, has been celebrated as a breakthrough technology due to the substantial benefit observed in clinical trials with patients suffering from relapsed or refractory B‐cell malignancies. In this review, we provide a comprehensive overview of the clinical trials performed so far worldwide and analyze parameters such as targeted antigen and indication, CAR molecular design, CAR T cell manufacturing, anti‐tumor activities, and related toxicities. More than 200 CAR T cell clinical trials have been initiated so far, most of which aim to treat lymphoma or leukemia patients using CD19‐specific CARs. An increasing number of studies address solid tumors as well. Notably, not all clinical trials conducted so far have shown promising results. Indeed, in a few patients CAR T cell therapy resulted in severe adverse events with fatal outcome. Of note, less than 10% of the ongoing CAR T cell clinical trials are performed in Europe. Taking lead from our analysis, we discuss the problems and general hurdles preventing efficient clinical development of CAR T cells as well as opportunities, with a special focus on the European stage.

Antigenic targets of CAR T Cell Therapy. A retrospective view on clinical trials

Chimeric antigen receptor (CAR) T cell therapy is anticipated to be increasingly implemented in the context of cancer treatment after two current FDA approval of anti-CD19 CAR-T cells (Kymriah™ & Yescarta™). The success of CD19 is mainly attributable to the proper selection of the antigen, CD19, as the target of the disease, highlighting the importance of target selection for other CAR therapies. Therefore, here we performed a global analysis of targets that are the prime focus for various CAR T cell therapies in human clinical trials.

CAR T Cells and Other Cellular Therapies for Multiple Myeloma: 2018 Update

Cellular therapies are a rapidly evolving approach to myeloma treatment, which bring a unique mechanism of action with the potential to overcome drug resistance and induce long-term remissions. Two primary approaches are being studied: non-gene-modified strategies, which rely on the endogenous anti-myeloma T-cell repertoire, and gene-modified strategies, which introduce a new T-cell receptor (TCR) or a chimeric antigen receptor (CAR) to confer novel antigen specificity. CAR T cells show the greatest activity to date. Multiple antigen targets, including B-cell maturation antigen (BCMA), CD19, CD38, CD138, and SLAMF7, are being explored for myeloma, and BCMA has emerged as the most promising. Preliminary data from four phase I studies of BCMA CAR T cells, each using a different CAR construct, that involved 90 evaluable patients with relapsed/refractory disease have been reported. These data show response rates of 60% to 100%, including minimal residual disease (MRD)-negative complete remissions, at effective doses (> 10⁸ CAR-positive cells) after lymphodepleting conditioning. Response durability has been more variable, likely related to differences in CAR T-cell products, lymphodepleting regimens, patient selection criteria, and/or underlying biology/prognostic factors. In the two most recent studies, however, most patients remained progression free with median follow-up time of 6 to 10 months; some ongoing remissions lasted more than 1 year. Toxicities are similar to those from CD19 CAR T cells and include cytokine release syndrome and neurotoxicity that is reversible but can be severe. Multiple BCMA CAR T-cell studies are ongoing. Future directions include combinations with immunomodulatory drugs, checkpoint inhibitors, or other CAR T cells, as well as use of gene-edited cellular products to enhance the safety and efficacy of this approach.

Advances on chimeric antigen receptor-modified T-cell therapy for oncotherapy

Tumor treatment is still complicated in the field of medicine. Tumor immunotherapy has been the most interesting research field in cancer therapy. Application of chimeric antigen receptor T (CAR-T) cell therapy has recently achieved excellent clinical outcome in patients, especially those with CD19-positive hematologic malignancies. This phenomenon has induced intense interest to develop CAR-T cell therapy for cancer, especially for solid tumors. However, the performance of CAR-T cell treatment in solid tumor is not as satisfactory as that in hematologic disease. Clinical studies on some neoplasms, such as glioblastoma, ovarian cancer, and cholangiocarcinoma, have achieved desirable outcome. This review describes the history and evolution of CAR-T, generalizes the structure and preparation of CAR-T, and summarizes the latest advances on CAR-T cell therapy in different tumor types. The last section presents the current challenges and prospects of CAR-T application to provide guidance for subsequent research.

The use of chimeric antigen receptor T cells in patients with non-Hodgkin lymphoma

Resistance to conventional lines of therapy develops in approximately 20% of all patients with lymphoma. These patients have a dismal prognosis, with an expected median survival of 6.3 months. In recent years, T-cell immunotherapy has demonstrated a remarkable capacity to induce complete and durable clinical responses in patients with chemotherapy-refractory lymphoma. A major contributor to the success of immunotherapy has been the advent of genetic engineering technologies that introduce a chimeric antigen receptor (CAR) into T cells to focus their killing activity on tumor cells. The adoptive transfer of autologous CAR T-cell products specific for the pan-B-cell antigen CD19 have now received approval from the US Food and Drug Administration (FDA) for the treatment of relapsed or chemotherapy-resistant B-cell non-Hodgkin lymphoma. This review is designed to showcase the clinical efficacy and unique toxicities of individually developed CAR T-cell products for the treatment of lymphomas and their evolution from the laboratory bench to commercialization.

CAR T cell therapy for B-cell lymphomas

B-cell non-Hodgkin's lymphoma (NHLs)is a very heterogonous malignancy with diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) as the most common subtypes. Standard treatment with anti-CD20 based chemoimmunotherapy is usually very effective for disease control. However a significant proportion of patients with high-risk features (double hit lymphoma, transformed lymphomas or early relapses) will become refractory to standard therapies and will have limited alternatives for cure. Adoptive therapy with chimeric antigen receptor (CAR) T-cells is a new paradigm for effective treatment of poor prognosis lymphomas. Here we review the biology of poor risk DLBCL and FL, the rationale for CAR T-cell therapy in malignant lymphoma and the efficacy/toxicity profile of CD19 directed CAR T cell therapy for DLBCL and FL from early single center studies to multicenter/global clinical trial with different CAR T cell constructs.

CAR T Cells in Trials: Recent Achievements and Challenges that Remain in the Production of Modified T Cells for Clinical Applications

The adoptive transfer of chimeric antigen receptor (CAR)-modified T cells is attracting growing interest for the treatment of malignant diseases. Early trials with anti-CD19 CAR T cells have achieved spectacular remissions in B-cell leukemia and lymphoma, so far refractory, very recently resulting in the Food and Drug Administration approval of CD19 CAR T cells for therapy. With further applications and increasing numbers of patients, the reproducible manufacture of high-quality clinical-grade CAR T cells is becoming an ever greater challenge. New processing techniques, quality-control mechanisms, and logistic developments are required to meet both medical needs and regulatory restrictions. This paper summarizes the state-of-the-art in manufacturing CAR T cells and the current challenges that need to be overcome to implement this type of cell therapy in the treatment of a variety of malignant diseases and in a greater number of patients.

CARs and other T cell therapies for MM: The clinical experience

Harnessing the endogenous immune system to eliminate malignant cells has long been an intriguing approach. After considerable success in the treatment of B-cell acute lymphoblastic leukemia, chimeric antigen receptor (CAR)-modified T cells have entered early clinical evaluation in the field of multiple myeloma (MM). The choice of suitable non-CD19 target antigens is challenging and a variety of myeloma-associated surface molecules have been under preclinical investigation. Most recent clinical protocols have focused on targeting B-cell maturation antigen (BCMA), and early results are promising. The trials differ in receptor constructs, patient selection, dosing strategies and conditioning chemotherapy and will thus pave the way to eventually define the optimal parameters. Other sources for autologous T-cell therapy of MM include affinity-enhanced T-cell receptor-modified cells and marrow infiltrating lymphocytes. In summary, adoptive T-cell transfer for the treatment of MM is still in its infancy, but if early response rates indicate durability, will be a paradigm changing therapeutic modality for the treatment of MM.

An APRIL-based chimeric antigen receptor for dual targeting of BCMA and TACI in multiple myeloma

B-cell maturation antigen (BCMA) is a promising therapeutic target for multiple myeloma (MM), but expression is variable, and early reports of BCMA targeting chimeric antigen receptors (CARs) suggest antigen downregulation at relapse. Dual-antigen targeting increases targetable tumor antigens and reduces the risk of antigen-negative disease escape. "A proliferation-inducing ligand" (APRIL) is a natural high-affinity ligand for BCMA and transmembrane activator and calcium-modulator and cyclophilin ligand (TACI). We quantified surface tumor expression of BCMA and TACI on primary MM cells (n = 50). All cases tested expressed BCMA, and 39 (78%) of them also expressed TACI. We engineered a third-generation APRIL-based CAR (ACAR), which killed targets expressing either BCMA or TACI (P < .01 and P < .05, respectively, cf. control, effector-to-target [E:T] ratio 16:1). We confirmed cytolysis at antigen levels similar to those on primary MM, at low E:T ratios (56.2% ± 3.9% killing of MM.1s at 48 h, E:T ratio 1:32; P < .01) and of primary MM cells (72.9% ± 12.2% killing at 3 days, E:T ratio 1:1; P < .05, n = 5). Demonstrating tumor control in the absence of BCMA, we maintained cytolysis of primary tumor expressing both BCMA and TACI in the presence of a BCMA-targeting antibody. Furthermore, using an intramedullary myeloma model, ACAR T cells caused regression of an established tumor within 2 days. Finally, in an in vivo model of tumor escape, there was complete ACAR-mediated tumor clearance of BCMA+TACI- and BCMA-TACI+ cells, and a single-chain variable fragment CAR targeting BCMA alone resulted in outgrowth of a BCMA-negative tumor. These results support the clinical potential of this approach.

Engineering chimeric antigen receptor-T cells for cancer treatment

Intratumor heterogeneity of tumor clones and an immunosuppressive microenvironment in cancer ecosystems contribute to inherent difficulties for tumor treatment. Recently, chimeric antigen receptor (CAR) T-cell therapy has been successfully applied in the treatment of B-cell malignancies, underscoring its great potential in antitumor therapy. However, functional challenges of CAR-T cell therapy, especially in solid tumors, remain. Here, we describe cancer-immunity phenotypes from a clonal-stromal-immune perspective and elucidate mechanisms of T-cell exhaustion that contribute to tumor immune evasion. Then we assess the functional challenges of CAR-T cell therapy, including cell trafficking and infiltration, targeted-recognition and killing of tumor cells, T-cell proliferation and persistence, immunosuppressive microenvironment and self-control regulation. Finally, we delineate tumor precision informatics and advancements in engineered CAR-T cells to counteract inherent challenges of the CAR-T cell therapy, either alone or in combination with traditional therapeutics, and highlight the therapeutic potential of this approach in future tumor precision treatment.

T-cell Immunotherapies and the Role of Nonclinical Assessment: The Balance between Efficacy and Pathology

Gene-engineered T-cell therapies have the potential to revolutionize the treatment of cancer. These therapies have shown exceptional clinical efficacy specifically in the field of B-cell malignancies and the first products (Kymriah™ and Yescarta™) have recently been approved in the United States for specific indications. The power of these treatments is also linked with a distinct set of toxicities both predicted and unpredicted, including off-tumor activity, cytokine release syndromes, and neurotoxicity, occasionally with fatal consequences. As these therapies begin to reach more patients, it is critical to develop the nonclinical tools to adequately determine the mechanisms driving these toxicities, to assess the safety risks of candidate products, and to develop strategies for safety management.

Immunopathogenesis and immunotherapy of multiple myeloma

Despite the advent of novel therapies and improvements in survival, multiple myeloma (MM) remains an incurable disease. Thus, new treatment strategies including immunotherapies are needed for MM patients with stable disease after induction chemotherapy as well as for disease control in patients with advanced disease. However, profound immune dysregulation not only of B cells, but also of other immune cells such as natural killer cells, T cells, and dendritic cells and increase in the number of immunosuppressive cells, i.e., regulatory T and B cells and myeloid-derived suppressor cells, have been demonstrated in advanced MM patients, which may be involved in disease progression. Because of immune dysfunction, immunotherapies have not shown clinical efficacy in MM patients. It is therefore crucial to resolve immunosuppressive mechanisms and improve immune responses, especially in advanced MM patients. Recently, excellent clinical efficacy of new immunotherapeutic strategies such as immunomodulatory drug-intensified monoclonal antibody treatment, immune checkpoint inhibitors, and chimeric antigen receptor T-cell therapy targeting B cell maturation antigen has been reported in advanced-stage MM patients. Those new treatments or their combination will improve prognosis and possibly point toward a cure for myeloma.

Prediction of novel target genes and pathways involved in bevacizumab-resistant colorectal cancer

Bevacizumab combined with cytotoxic chemotherapy is the backbone of metastatic colorectal cancer (mCRC) therapy; however, its treatment efficacy is hampered by therapeutic resistance. Therefore, understanding the mechanisms underlying bevacizumab resistance is crucial to increasing the therapeutic efficacy of bevacizumab. The Gene Expression Omnibus (GEO) database (dataset, GSE86525) was used to identify the key genes and pathways involved in bevacizumab-resistant mCRC. The GEO2R web tool was used to identify differentially expressed genes (DEGs). Functional and pathway enrichment analyses of the DEGs were performed using the Database for Annotation, Visualization, and Integrated Discovery(DAVID). Protein–protein interaction (PPI) networks were established using the Search Tool for the Retrieval of Interacting Genes/Proteins database(STRING) and visualized using Cytoscape software. A total of 124 DEGs were obtained, 57 of which upregulated and 67 were downregulated. PPI network analysis showed that seven upregulated genes and nine downregulated genes exhibited high PPI degrees. In the functional enrichment, the DEGs were mainly enriched in negative regulation of phosphate metabolic process and positive regulation of cell cycle process gene ontologies (GOs); the enriched pathways were the phosphoinositide 3-kinase-serine/threonine kinase signaling pathway, bladder cancer, and microRNAs in cancer. Cyclin-dependent kinase inhibitor 1A(CDKN1A), toll-like receptor 4 (TLR4), CD19 molecule (CD19), breast cancer 1, early onset (BRCA1), platelet-derived growth factor subunit A (PDGFA), and matrix metallopeptidase 1 (MMP1) were the DEGs involved in the pathways and the PPIs. The clinical validation of the DEGs in mCRC (TNM clinical stages 3 and 4) revealed that high PDGFA expression levels were associated with poor overall survival, whereas high BRCA1 and MMP1 expression levels were associated with favorable progress free survival(PFS). The identified genes and pathways can be potential targets and predictors of therapeutic resistance and prognosis in bevacizumab-treated patients with mCRC.

Cancer immunotherapy beyond immune checkpoint inhibitors

Malignant cells have the capacity to rapidly grow exponentially and spread in part by suppressing, evading, and exploiting the host immune system. Immunotherapy is a form of oncologic treatment directed towards enhancing the host immune system against cancer. In recent years, manipulation of immune checkpoints or pathways has emerged as an important and effective form of immunotherapy. Agents that target cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), programmed cell death receptor-1 (PD-1), and programmed cell death ligand-1 (PD-L1) are the most widely studied and recognized. Immunotherapy, however, extends beyond immune checkpoint therapy by using new molecules such as chimeric monoclonal antibodies and antibody drug conjugates that target malignant cells and promote their destruction. Genetically modified T cells expressing chimeric antigen receptors are able to recognize specific antigens on cancer cells and subsequently activate the immune system. Native or genetically modified viruses with oncolytic activity are of great interest as, besides destroying malignant cells, they can increase anti-tumor activity in response to the release of new antigens and danger signals as a result of infection and tumor cell lysis. Vaccines are also being explored, either in the form of autologous or allogenic tumor peptide antigens, genetically modified dendritic cells that express tumor peptides, or even in the use of RNA, DNA, bacteria, or virus as vectors of specific tumor markers. Most of these agents are yet under development, but they promise to be important options to boost the host immune system to control and eliminate malignancy. In this review, we have provided detailed discussion of different forms of immunotherapy agents other than checkpoint-modifying drugs. The specific focus of this manuscript is to include first-in-human phase I and phase I/II clinical trials intended to allow the identification of those drugs that most likely will continue to develop and possibly join the immunotherapeutic arsenal in a near future.

Advances in immunotherapy in multiple myeloma

PURPOSE OF REVIEW

Here, we explore the significant progress made in the treatment of multiple myeloma, focusing on immunotherapy and the promise it has offered to patients suffering from advanced disease.

RECENT FINDINGS

Multiple myeloma, a B-cell malignancy, is characterized by unregulated plasma cell growth in the bone marrow as well as strong immunosuppression in the tumor microenvironment. mAbs targeting tumor antigens overcome this, increasing T-cell activation, multiple myeloma cell death, and depth of response. Similarly, adoptive T-cell therapy aims to engineer or isolate tumor-specific T cells for a targeted approach. Finally, peptide and dendritic cell/tumor fusion vaccines reeducate the immune system, expanding the immune response and generating long-term memory to prevent relapse of disease. Many of these approaches have been combined with existing therapies to enhance antitumor immunity.

SUMMARY

Immunotherapeutic approaches have remarkably changed the treatment paradigm for multiple myeloma, and encouraging patient responses have warranted further investigation into mAbs, adoptive T-cell therapy, vaccines, and combination therapy.

Chimeric antigen receptor T-cell therapies for multiple myeloma

Multiple myeloma (MM) is a nearly always incurable malignancy of plasma cells, so new approaches to treatment are needed. T-cell therapies are a promising approach for treating MM, with a mechanism of action different than those of standard MM treatments. Chimeric antigen receptors (CARs) are fusion proteins incorporating antigen-recognition domains and T-cell signaling domains. T cells genetically engineered to express CARs can specifically recognize antigens. Success of CAR-T cells (CAR-Ts) against leukemia and lymphoma has encouraged development of CAR-T therapies for MM. Target antigens for CARs must be expressed on malignant cells, but expression on normal cells must be absent or limited. B-cell maturation antigen is expressed by normal and malignant plasma cells. CAR-Ts targeting B-cell maturation antigen have demonstrated significant antimyeloma activity in early clinical trials. Toxicities in these trials, including cytokine release syndrome, have been similar to toxicities observed in CAR-T trials for leukemia. Targeting postulated CD19+ myeloma stem cells with anti-CD19 CAR-Ts is a novel approach to MM therapy. MM antigens including CD138, CD38, signaling lymphocyte-activating molecule 7, and κ light chain are under investigation as CAR targets. MM is genetically and phenotypically heterogeneous, so targeting of >1 antigen might often be required for effective treatment of MM with CAR-Ts. Integration of CAR-Ts with other myeloma therapies is an important area of future research. CAR-T therapies for MM are at an early stage of development but have great promise to improve MM treatment.

Hematologic Malignancies: Plasma Cell Disorders

Multiple myeloma (MM) is a plasma cell malignancy characterized by the growth of tumor cells in the bone marrow. Properties of the tumor microenvironment provide both potential tumor-promoting and tumor-restricting properties. Targeting underlying immune triggers for evolution of tumors as well as direct attack of malignant plasma cells is an emerging focus of therapy for MM. The monoclonal antibodies daratumumab and elotuzumab, which target the plasma cell surface proteins CD38 and SLAMF7/CS1, respectively, particularly when used in combination with immunomodulatory agents and proteasome inhibitors, have resulted in high response rates and improved survival for patients with relapsed and refractory MM. A number of other monoclonal antibodies are in various stages of clinical development, including those targeting MM cell surface antigens, the bone marrow microenvironment, and immune effector T cells such as antiprogrammed cell death protein 1 antibodies. Bispecific preparations seek to simultaneously target MM cells and activate endogenous T cells to enhance efficacy. Cellular immunotherapy seeks to overcome the limitations of the endogenous antimyeloma immune response through adoptive transfer of immune effector cells with MM specificity. Allogeneic donor lymphocyte infusion can be effective but can cause graft-versus-host disease. The most promising approach appears to be genetically modified cellular therapy, in which T cells are given novel antigen specificity through expression of transgenic T-cell receptors (TCRs) or chimeric antigen receptors (CARs). CAR T cells against several different targets are under investigation in MM. Infusion of CD19-targeted CAR T cells following salvage autologous stem cell transplantation (SCT) was safe and extended remission duration in a subset of patients with relapsed/refractory MM. CAR T cells targeting B-cell maturation antigen (BCMA) appear most promising, with dramatic remissions seen in patients with highly refractory disease in three ongoing trials. Responses are associated with degree of CAR T-cell expansion/persistence and often toxicity, including cytokine release syndrome (CRS) and neurotoxicity. Ongoing and future studies are exploring correlates of response, ways to mitigate toxicity, and "universal" CAR T cells.

Chimeric antigen receptor transduced T cells: Tuning up for the next generation

Chimeric antigen receptor (CAR) T cell therapy has recently achieved impressive clinical outcome in patients with CD19-positive hematologic malignancies. Extrapolation of CAR T cell treatment to solid tumors, however, has not yet yielded similar results. This might be due to intrinsic causes, e.g. insufficient CAR T cell activation or CAR toxicity as well as extrinsic factors displaying an unfavorable tumor environment for CAR T cells by raising physical and chemical barriers. In this review, we discuss the advantages as well as major obstacles of CAR T cell therapy, particularly in the context of solid tumors, and focus on efforts and novel strategies in CAR T cell development.

CD22-targeted CAR T cells induce remission in B-ALL that is naive or resistant to CD19-targeted CAR immunotherapy

Chimeric antigen receptor (CAR) T-cells targeting CD19 mediate potent effects in relapsed/refractory pre-B cell acute lymphoblastic leukemia (B-ALL) but antigen loss is a frequent cause of resistance to CD19-targeted immunotherapy. CD22 is also expressed on most B-ALL and usually retained following CD19 loss. We report results from a phase I trial testing a novel CD22-CAR in twenty-one children and adults, including 17 previously treated with CD19-directed immunotherapy. Dose dependent anti-leukemic activity was observed with complete remission in 73% (11/15) of patients receiving ≥ 1 × 10⁶ CD22-CART cells/kg, including 5/5 patients with CD19dim/neg B-ALL. Median remission duration was 6 months. Relapses were associated with diminished CD22 site density that likely permitted escape from killing by CD22-CART cells. These results are the first to eastablish the clinical activity of a CD22-CAR in pre-B cell ALL, including in leukemia resistant to anti-CD19 immunotherapy, demonstrating comparable potency to CD19-CART at biologically active doses in B-ALL. They also highlight the critical role played by antigen density in regulating CAR function. (Funded by NCI Intramural Research Program)