Clinical and Biological Correlates of Neurotoxicity Associated with CAR T-cell Therapy in Patients with B-cell Acute Lymphoblastic Leukemia

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.

Elusive Neurotoxicity in T Cell-Boosting Anticancer Therapies

Several T cell-boosting anticancer therapies (including anti-CD19 CAR-T cells and bi-specific T cell engagers, BiTEs) have been approved by the FDA for specific clinical indications. Their potency has been demonstrated in various clinical trials, but some life-threatening complications such as neurotoxicity remain poorly understood. Thus, by conducting multifaceted investigations, a better understanding of T cell immunotherapy-associated neurotoxicity to bridge the gap between basic research and clinical practice is urgently needed.

CAR-T immunotherapy: how will it change treatment for acute lymphoblastic leukemia and beyond?

Introduction

The recent approval of CD19 chimeric antigen receptor (CAR) T cells for refractory or second relapse of B cell acute lymphoblastic leukemia (B-ALL) has led to a paradigm shift. Besides being an alternative to chemotherapy and antibody-based approaches, CAR-T cells have become the first successful example of "personalized medicine."

Areas covered

In clinical trials, tisagenlecleucel demonstrated higher response rates than prior therapies, and led to durable remissions lasting up to years for some children. Toxicities like cytokine release syndrome and neurotoxicity, while potentially reversible, have limited usage of CAR-T cells at certified centers with expertise in cellular therapy. Strategies to deal with B-ALL relapse after CAR-T remain an open area of research.

Expert opinion

Going forward, improvements will likely be seen in managing the side effects of CAR-T therapy as well as usage of CAR-T cells upfront as a replacement for chemotherapy or allogeneic bone marrow transplant for B-ALL. Further advances will need to reduce the biomanufacturing time needed to generate CAR-T cells as well as develop biomarkers that predict CAR-T persistence and/or toxicities.

Chimeric antigen receptor T-cell therapy for B-cell non-Hodgkin lymphoma: opportunities and challenges

B-cell non-Hodgkin lymphoma (NHL) is the most frequent hematologic malignancy. Despite the refinement of chemoimmunotherapy, a substantial number of patients experience chemorefractory disease. Anti-CD19 chimeric antigen receptor (CAR) T-cell therapy is considered the most promising and effective therapy to overcome chemorefractory B-cell NHL. Based on the promising results obtained from pivotal trials, the US Food and Drug Administration and European Medicines Agency approved anti-CD19 CAR T-cell therapy for relapsed/refractory diffuse large B-cell lymphoma. Nonetheless, there remain several controversial issues and problems awaiting solutions, including optimal management of toxicities, overcoming relapsed/refractory disease after CAR T-cell therapy, and improving CAR-T manufacturing platform. Definite unmet medical needs among patients with chemorefractory B-cell NHL still exist. CAR T-cell therapy might be a game changer that can defeat chemorefractory B-cell NHL, and further clinical development is warranted. In this review, we summarize the recent clinical developments, clinical implications, and perspectives of CAR T-cell therapy, focusing on B-cell NHL.

B-cell depleting immunotherapies: therapeutic opportunities and toxicities

INTRODUCTION

The last few years have witnessed what can certainly be defined as a 'period of renaissance' for immunotherapy in the field of hematological malignancies. In particular, antibody-mediated and cell-mediated immunotherapy have significantly changed the treatment approach of patients with B-cell lymphoproliferative disorders. These therapies, initially employed in patients with refractory/relapsed disease, are now integrated in the treatment of newly diagnosed patients. Together with the therapeutic success, we have also learnt that these innovative therapies can induce relevant, sometimes life-threatening or even fatal, side effects. Areas covered: In this review article, we analyzed the applicative therapeutic scenario and the peculiar toxicities associated with approaches of immunotherapy, paying particular attention to the new emerging side effects, substantially unknown before the introduction of these therapies. Expert commentary: Both monoclonal antibodies and cell therapy with lymphocytes genetically modified to be redirected against leukemia targets through the transduction with chimeric antigen receptors (CARs) have obtained unprecedented success in rescuing patients with resistant B-cell malignancies. Complications, such as neurotoxicity, cytokine release syndrome or persistent B-cell lymphopenia, must always be taken into consideration and diagnosed in a timely manner in patients with B-cell neoplasms to guarantee optimal management, thus avoiding they blunting the efficacy of immunotherapy.

CD19 Chimeric Antigen Receptor Therapy for Refractory Aggressive B-Cell Lymphoma

PURPOSE

Anti-CD19–directed chimeric antigen receptor (CAR) T-cell therapy has had a resounding effect on the treatment of chemotherapy-insensitive aggressive B-cell non-Hodgkin lymphoma (B-NHL). There are now two US Food and Drug Administration (FDA)–approved products available for treating these patients, and a third product is expected to be approved in the coming months. The question remains: Is there a preferred or best product for my patient? However, answering that question is more complicated than simply balancing the reported efficacy and toxicity results.

DESIGN

This review outlines potential confounding factors involving the three products and their pivotal clinical trials and highlights additional considerations of manufacturing reliability and overall cost that must be considered when weighing one product against another. It will also review the directions in which the field is moving and strategies being examined to improve efficacy as well as toxicity.

CONCLUSION

Because a randomized three-arm clinical trial is unlikely, a product may have to be chosen on the basis of results from treatment centers that have experience with all three products. But by the time those results are available, they are likely to be outdated because, given the rapid evolution of the field, the next product will probably have been identified.

Mechanisms and Management of Chimeric Antigen Receptor T-Cell Therapy-Related Toxicities

Chimeric antigen receptor T-cell (CAR-T) therapy has proven to be a very effective cancer immunotherapy. Axicabtagene ciloleucel and tisagenlecleucel are the first-in-class anti-CD19 CAR-T currently available for relapsed/refractory adult large B-cell lymphoma. Tisagenlecleucel is also available for pediatric and young adult (up to age 25 years) patients with relapsed/refractory B-acute lymphoblastic leukemia. Cytokine release syndrome (CRS) and CAR-T-associated encephalopathy syndrome (neurotoxicity) are the most common adverse effects associated with CAR-T therapy. They can lead to significant morbidity and preclude widespread use of this treatment modality. Treatment-related deaths from severe CRS and cerebral edema have been reported. There is a significant heterogeneity in the side-effect profile of different CAR-T products under investigation and there is a need to develop standardized guidelines for toxicity grading and management. Here, we summarize the current literature on pathogenesis, clinical presentation, and management of CRS and neurotoxicity. The different grading systems of CRS and management protocols used in different trials have made it difficult to compare the outcomes of different CAR-T therapies. Several prevention strategies such as predictive biomarkers of CRS and neurotoxicity and modified CAR-T with 'built-in' safety mechanisms are being studied, with the potential to greatly expand the safety and applicability of CAR-T treatment across various malignancies.

Approval of First CAR-Ts: Have we Solved all Hurdles for ATMPs?

T cells are known as the most potent killer cells of the immune system, designed by nature to prevent unwanted challenges. The first class of therapeutic products harnessing the power of T cells for target-specific treatment of oncological diseases was bispecific antibodies. The first T-cell engaging bispecific antibodies that obtained approval were catumaxomab and blinatumomab^1,2. Eight years later, the first chimeric antigen receptor (CAR)-T cells received regulatory approval³. CAR-T cells are the cellular interpretation of T-cell engaging therapies and have shown remarkable clinical results. CAR-T cells belong to the regulatory group of advanced therapy medicinal products (ATMPs). Due to the cell-/gene-based complex nature, ATMPs are far more challenging to develop than other, more defined, medicinal products. Despite very encouraging clinical results, there have been many set-backs in the development of ATMPs during the past 20 years. Therefore, the approval of the first two CAR-Ts KYMRIAH and YESCARTA is highly encouraging for the field. In this article we review the current landscape of CAR-Ts as a special class of ATMPs. This comprises the pathway to approval including the use of dedicated regulatory tools and challenges that were faced during the procedure. Furthermore, we highlight important future trends in the field.

[Management of cytokine release syndrome in adult and pediatric patients undergoing CAR-T cell therapy for hematological malignancies: Recommendation of the French Society of Bone Marrow and cellular Therapy (SFGM-TC)]

The cytokine release syndrome (CRS) is the most common complication after adoptive immunotherapies such as chimeric antigen receptor T cells (CAR-T). The incidence varies from 30 to 100% depending on the CAR-T construct, cell doses and the underlying disease. Severe cases may involve 10 to 30% of patients. The triggering event is the activation of the CAR-T, after meeting with their target. The T cell activation leads to the release of effector cytokines, such as IFNγ, TNFα and IL2, that are responsible for the activating of monocyte/macrophage system, resulting in the production of pro-inflammatory cytokines, (including IL6, IFN-γ, IL10, MCP1) and associated with a significant elevation of CRP and ferritin. The CRS usually appears between 1 and 14days after the infusion of the cells and can last from 1 to 10days. Rare fatal cases have been reported in the literature. The first symptom is often a fever, sometimes very high, which must alert and reinforce the surveillance. In moderate forms, one can find fatigue, headache, rash, arthralgia and myalgia. T cell-related encephalopathy (CRES) syndrome may occur concomitantly. In case of aggravation, a vasoplegic shock associating capillary leakage and respiratory distress can occur. Close clinical monitoring is essential right from the injection to quickly detect the first symptoms. The treatment of severe forms, in addition to symptomatic management involves monoclonal antibodies targeting the IL6 or IL6 receptor, and sometimes steroids. Close cooperation with intensive care units is essential since 20 to 50% of patients require intensive care unit transfer.

Harmonizing Immune Effector Toxicity Reporting

In this issue of BBMT, a multicenter group of investigators convened by the American Society of Blood and Marrow Transplantation outlines new consensus definitions and grading systems for the most common toxicities associated with immune effector cell therapies, including cytokine release syndrome and the newly named immune cell-associated neurotoxicity syndrome.

ASTCT Consensus Grading for Cytokine Release Syndrome and Neurologic Toxicity Associated with Immune Effector Cells

Chimeric antigen receptor (CAR) T cell therapy is rapidly emerging as one of the most promising therapies for hematologic malignancies. Two CAR T products were recently approved in the United States and Europe for the treatment ofpatients up to age 25years with relapsed or refractory B cell acute lymphoblastic leukemia and/or adults with large B cell lymphoma. Many more CAR T products, as well as other immunotherapies, including various immune cell- and bi-specific antibody-based approaches that function by activation of immune effector cells, are in clinical development for both hematologic and solid tumor malignancies. These therapies are associated with unique toxicities of cytokine release syndrome (CRS) and neurologic toxicity. The assessment and grading of these toxicities vary considerably across clinical trials and across institutions, making it difficult to compare the safety of different products and hindering the ability to develop optimal strategies for management of these toxicities. Moreover, some aspects of these grading systems can be challenging to implement across centers. Therefore, in an effort to harmonize the definitions and grading systems for CRS and neurotoxicity, experts from all aspects of the field met on June 20 and 21, 2018, at a meeting supported by the American Society for Transplantation and Cellular Therapy (ASTCT; formerly American Society for Blood and Marrow Transplantation, ASBMT) in Arlington, VA. Here we report the consensus recommendations of that group and propose new definitions and grading for CRS and neurotoxicity that are objective, easy to apply, and ultimately more accurately categorize the severity of these toxicities. The goal is to provide a uniform consensus grading system for CRS and neurotoxicity associated with immune effector cell therapies, for use across clinical trials and in the postapproval clinical setting.

Cancer Stem Cells and Immunosuppressive Microenvironment in Glioma

Glioma is one of the most common malignant tumors of the central nervous system and is characterized by extensive infiltrative growth, neovascularization, and resistance to various combined therapies. In addition to heterogenous populations of tumor cells, the glioma stem cells (GSCs) and other nontumor cells present in the glioma microenvironment serve as critical regulators of tumor progression and recurrence. In this review, we discuss the role of several resident or peripheral factors with distinct tumor-promoting features and their dynamic interactions in the development of glioma. Localized antitumor factors could be silenced or even converted to suppressive phenotypes, due to stemness-related cell reprogramming and immunosuppressive mediators in glioma-derived microenvironment. Furthermore, we summarize the latest knowledge on GSCs and key microenvironment components, and discuss the emerging immunotherapeutic strategies to cure this disease.

Neurotoxicity Associated with CD19-Targeted CAR-T Cell Therapies

Neurotoxicity is an important and common complication of chimeric antigen receptor-T cell therapies. Acute neurologic signs and/or symptoms occur in a significant proportion of patients treated with CD19-directed chimeric antigen receptor-T cells for B-cell malignancies. Clinical manifestations include headache, confusion, delirium, language disturbance, seizures and rarely, acute cerebral edema. Neurotoxicity is associated with cytokine release syndrome, which occurs in the setting of in-vivo chimeric antigen receptor-T cell activation and proliferation. The mechanisms that lead to neurotoxicity remain unknown, but data from patients and animal models suggest there is compromise of the blood-brain barrier, associated with high levels of cytokines in the blood and cerebrospinal fluid, as well as endothelial activation. Corticosteroids, interleukin-6-targeted therapies, and supportive care are frequently used to manage patients with neurotoxicity, but high-quality evidence of their efficacy is lacking.

Recent advances in CAR T-cell toxicity: Mechanisms, manifestations and management

Chimeric antigen receptor (CAR) T-cell therapy is an effective new treatment for hematologic malignancies. Two CAR T-cell products are now approved for clinical use by the U.S. FDA: tisagenlecleucel for pediatric acute lymphoblastic leukemia (ALL) and adult diffuse large B-cell lymphoma subtypes (DLBCL), and axicabtagene ciloleucel for DLBCL. CAR T-cell therapies are being developed for multiple myeloma, and clear evidence of clinical activity has been generated. A barrier to widespread use of CAR T-cell therapy is toxicity, primarily cytokine release syndrome (CRS) and neurologic toxicity. Manifestations of CRS include fevers, hypotension, hypoxia, end organ dysfunction, cytopenias, coagulopathy, and hemophagocytic lymphohistiocytosis. Neurologic toxicities are diverse and include encephalopathy, cognitive defects, dysphasias, seizures, and cerebral edema. Our understanding of the pathophysiology of CRS and neurotoxicity is continually improving. Early and peak levels of certain cytokines, peak blood CAR T-cell levels, patient disease burden, conditioning chemotherapy, CAR T-cell dose, endothelial activation, and CAR design are all factors that may influence toxicity. Multiple grading systems for CAR T-cell toxicity are in use; a universal grading system is needed so that CAR T-cell products can be compared across studies. Guidelines for toxicity management vary among centers, but typically include supportive care, plus immunosuppression with tocilizumab or corticosteroids administered for severe toxicity. Gaining a better understanding of CAR T-cell toxicities and developing new therapies for these toxicities are active areas of laboratory research. Further clinical investigation of CAR T-cell toxicity is also needed. In this review, we present guidelines for management of CRS and CAR neurotoxicity.

Cytokine release syndrome and neurotoxicity after CD19 chimeric antigen receptor-modified (CAR-) T cell therapy

Chimeric antigen receptor-modified (CAR)-T cells have demonstrated impressive results in the treatment of haematological malignancies. However, cytokine release syndrome (CRS) and neurotoxicity are common toxicities which are potentially life-threatening in severe cases. Risk factors for CRS and neurotoxicity identified so far include disease burden, lymphodepletion intensity and CAR-T cell dose administered. Risk-adapted dosing, with lower CAR-T cell doses administered to B-cell acute lymphoblastic leukaemia patients with high marrow blast counts, has been successful at decreasing severe CRS rates in this population. Intervention with therapies, such as tocilizumab and corticosteroids, have been effective at ameliorating toxicity, enabling CAR-T cells to be administered safely to many patients without significantly compromising efficacy. Deeper understanding of the pathophysiology of underlying CRS and neurotoxicity will enable the development of novel approaches to reduce toxicity and improve outcomes.

Cytokine release syndrome: grading, modeling, and new therapy

Genetically modified T cells that express a chimeric antigen receptor (CAR) are opening a new frontier in cancer immunotherapy. CAR T cells currently are in clinical trials for many cancer types. Cytokine release syndrome (CRS) and neurotoxicities (CAR-related encephalopathy syndrome, CRES) are major adverse events limiting wide deployment of the CAR T cell treatment. Major efforts are ongoing to characterize the pathogenesis and etiology of CRS and CRES. Mouse models have been established to facilitate the study of pathogenesis of the major toxicities of CAR T cells. Myeloid cells including macrophages and monocytes, not the CAR T cells, were found to be the major cells mediating CRS and CRES by releasing IL-1 and IL-6 among other cytokines. Blocking IL-1 or depletion of monocytes abolished both CRS and CRES, whereas IL-6 blocker can ameliorate CRS but not CRES. Therefore, both IL-1 and IL-6 are major cytokines for CRS, though IL-1 is responsible for CRES. It was also demonstrated in the mouse models that blocking CRS does not interfere with the CAR T cell antitumor functions. We summarized new developments in the grading, modeling, and possible new therapeutic approaches for CRS and CRES in this review.