Chimeric antigen receptor T-cell therapy for marrow and extramedullary relapse of infant acute lymphoblastic leukemia

Overcoming the challenges of primary resistance and relapse after CAR-T cell therapy

INTRODUCTION

While CAR T-cell therapy has led to remarkable responses in relapsed B-cell hematologic malignancies, only 50% of patients ultimately have a complete, sustained response. Understanding the mechanisms of resistance and relapse after CAR T-cell therapy is crucial to future development and improving outcomes.

AREAS COVERED

We review reasons for both primary resistance and relapse after CAR T-cell therapies. Reasons for primary failure include CAR T-cell manufacturing problems, suboptimal fitness of autologous T-cells themselves, and intrinsic features of the underlying cancer and tumor microenvironment. Relapse after initial response to CAR T-cell therapy may be antigen-positive, due to CAR T-cell exhaustion or limited persistence, or antigen-negative, due to antigen-modulation on the target cells. Finally, we discuss ongoing efforts to overcome resistance to CAR T-cell therapy with enhanced CAR constructs, manufacturing methods, alternate cell types, combinatorial strategies, and optimization of both pre-infusion conditioning regimens and post-infusion consolidative strategies.

EXPERT OPINION

There is a continued need for novel approaches to CAR T-cell therapy for both hematologic and solid malignancies to obtain sustained remissions. Opportunities for improvement include development of new targets, optimally combining existing CAR T-cell therapies, and defining the role for adjunctive immune modulators and stem cell transplant in enhancing long-term survival.

Leukapheresis and Tisagenlecleucel Manufacturing Outcomes in Patients Age <3 Years with Relapsed/Refractory Acute Lymphoblastic Leukemia

Tisagenlecleucel is approved for the treatment of relapsed/refractory (r/r) B cell acute lymphoblastic leukemia (B-ALL) in patients up to age 25 years based on the results of a pivotal trial (ELIANA) in pediatric and young adult patients. However, that trial did not include patients age <3 years because of the challenges posed by leukapheresis of very young and low-weight patients. Data on leukapheresis material and manufacturing outcomes among patients age <3 years have been collected since the time of global regulatory approval. Here we report leukapheresis characteristics and manufacturing outcomes for tisagenlecleucel produced for patients age <3 years in US and non-US commercial settings. Qualified patients with r/r B-ALL were age <3 years at the time of request for commercial tisagenlecleucel, with manufacturing data starting after August 30, 2017 (date of first US Food and Drug Administration approval). Leukapheresis and manufacturing outcomes data were stratified by age and weight. CD3+ cell count and CD3+/total nucleated cell (TNC) percentages were obtained from the leukapheresis material; leukocyte subpopulations were obtained via quality control vials. Of the 146 tisagenlecleucel quality control batches analyzed for CD3+ cell count and CD3+/TNC%, 86 batches (84 patients) were from US sites and 60 batches were from non-US sites. The median patient age and weight were 1.2 years and 10.4 kg at US sites and 1.5 years and 10.5 kg at non-US sites. Globally, 137 of 146 batches (94%) were manufactured within specifications across 16 countries. Among tisagenlecleucel batches manufactured in the United States between 2017 and 2021, there was a trend toward increasing CD3+ counts, CD3+/TNC%, and manufactured dose of chimeric antigen receptor (CAR) T cells; there was no difference in median days of collection by patient age or weight. Globally, a trend toward 1 or more potential additional collection days was observed for patients weighing ≤10 kg. Leukapheresis and tisagenlecleucel manufacturing in pediatric patients with r/r B-ALL age <3 years, including infants (<1 year), and low weight are feasible. As global experience with leukapheresis and patient identification for CAR-T cell therapy increased over time, a corresponding improvement in tisagenlecleucel manufacturing success has been observed. Clinical outcome data for these patients are currently being explored.

The Evolution of Chimeric Antigen Receptor T-Cell Therapy in Children, Adolescents and Young Adults with Acute Lymphoblastic Leukemia

Chimeric antigen receptor T-cell (CAR T) therapy is a revolutionary treatment for pediatric, adolescent and young adult patients (AYA) with relapsed/refractory B-cell acute lymphoblastic leukemia. While the landscape of immunotherapy continues to rapidly evolve, widespread use of CAR T therapy is limited and many questions remain regarding the durability of CAR T therapy, methods to avoid CAR T therapy resistance and the role of consolidative stem cell transplant. Modified strategies to develop effective and persistent CAR T cells at lower costs and decreased toxicities are warranted. In this review we present current indications, limitations and future directions of CAR T therapy for ALL in the pediatric and AYA population.

Leukapheresis guidance and best practices for optimal chimeric antigen receptor T-cell manufacturing

Chimeric antigen receptor (CAR) T-cell therapy is an individualized immunotherapy that genetically reprograms a patient's T cells to target and eliminate cancer cells. Tisagenlecleucel is a US Food and Drug Administration-approved CD19-directed CAR T-cell therapy for patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia and r/r diffuse large B-cell lymphoma. Manufacturing CAR T cells is an intricate process that begins with leukapheresis to obtain T cells from the patient's peripheral blood. An optimal leukapheresis product is essential to the success of CAR T-cell therapy; therefore, understanding factors that may affect the quality or T-cell content is imperative. CAR T-cell therapy requires detailed organization throughout the entire multistep process, including appropriate training of a multidisciplinary team in leukapheresis collection, cell processing, timing and coordination with manufacturing and administration to achieve suitable patient care. Consideration of logistical parameters, including leukapheresis timing, location and patient availability, when clinically evaluating the patient and the trajectory of their disease progression must be reflected in the overall collection strategy. Challenges of obtaining optimal leukapheresis product for CAR T-cell manufacturing include vascular access for smaller patients, achieving sufficient T-cell yield, eliminating contaminating cell types in the leukapheresis product, determining appropriate washout periods for medication and managing adverse events at collection. In this review, the authors provide recommendations on navigating CAR T-cell therapy and leukapheresis based on experience and data from tisagenlecleucel manufacturing in clinical trials and the real-world setting.

Relapsed acute lymphoblastic leukaemia after allogeneic stem cell transplantation: a therapeutic dilemma challenging the armamentarium of immunotherapies currently available (case reports)

While survival rates in paediatric acute lymphoblastic leukaemia (ALL) nowadays exceed 90%, systemic ALL relapse, especially after haemopoietic stem cell transplantation (HSCT), is associated with a poor outcome. As there is currently no standardized treatment for this situation, individualized treatment is often pursued. Exemplified by two clinical scenarios, the aim of this article is to highlight the challenge for treating physicians to find a customized treatment strategy integrating the role of conventional chemotherapy, immunotherapeutic approaches and second allogeneic HSCT. Case 1 describes a 2-year-old girl with an early isolated bone marrow relapse of an infant KMT2A-rearranged B-cell precursor ALL after allogeneic HSCT. After bridging chemotherapy and lymphodepleting chemotherapy, chimeric antigen receptor (CAR) T-cells (tisagenlecleucel) were administered for remission induction, followed by a second HSCT from the 9/10 human leukocyte antigen (HLA)-matched mother. Case 2 describes a 16-year-old girl with a late, isolated bone marrow relapse of B-cell precursor ALL after allogeneic HSCT who experienced severe treatment toxicities including stage IV renal insufficiency. After dose-reduced bridging chemotherapy, CAR T-cells (tisagenlecleucel) were administered for remission induction despite a CD19^- clone without prior lymphodepletion due to enhanced persisting toxicity. This was followed by a second allogeneic HSCT from the haploidentical mother. While patient 2 relapsed around Day + 180 after the second HSCT, patient 1 is still in complete remission >360 days after the second HSCT. Both cases demonstrate the challenges associated with systemic ALL relapse after first allogeneic HSCT, including chemotherapy-resistant disease and persisting organ damage inflicted by previous therapy. Immunotherapeutic approaches, such as CAR T-cells, can induce remission and enable a second allogeneic HSCT. However, optimal therapy for systemic ALL relapse after first HSCT remains to be defined.

Real-World Use of Tisagenlecleucel in Infant Acute Lymphoblastic Leukemia

Infants with B-cell acute lymphoblastic leukemia (B-ALL) have poor outcomes due to chemotherapy resistance leading to high relapse rates. Tisagenlecleucel, a CD19-directed chimeric antigen receptor T-cell (CART) therapy, is FDA approved for relapsed or refractory (R/R) B-ALL in patients ≤25 years; however, the safety and efficacy of this therapy in young patients is largely unknown since children <3 years of age were excluded from licensing studies. We retrospectively evaluated data from the Pediatric Real-World CAR Consortium to examine outcomes of patients with infant B-ALL who received tisagenlecleucel between 2017 and 2020 (n=14). Sixty-four percent of patients (n=9) achieved minimal residual disease (MRD)-negative remission post-CART and 50% of patients remain in remission at last follow-up. All patients with high disease burden at time of CART infusion (>M1 marrow) were refractory to this therapy (n=5). Overall, tisagenlecleucel was tolerable in this population, with only 3 patients experiencing > grade 3 cytokine release syndrome. No neurotoxicity was reported. This is the largest report of tisagenlecleucel use in infant B-ALL and shows that this therapy is safe and can be effective in this population. Incorporating this novel immunotherapy into the treatment of infant B-ALL offers a promising therapy for a highly aggressive leukemia.

Characterization of Extramedullary Disease in B-ALL and Response to CAR T-cell Therapy

A substantial fraction of patients with relapsed/refractory B-ALL will have non-CNS EMD.

CAR T cells may have limited efficacy in multifocal non-CNS EMD, and serial imaging is needed to identify and monitor EMD.

Chimeric antigen receptor (CAR) T cells effectively eradicate medullary B-cell acute lymphoblastic leukemia (B-ALL) and can traffic to and clear central nervous system (CNS) involvement. CAR T-cell activity in non-CNS extramedullary disease (EMD) has not been well characterized. We systematically evaluated CAR T-cell kinetics, associated toxicities, and efficacy in B-ALL non-CNS EMD. We conducted a retrospective review of B-ALL patients with non-CNS EMD who were screened for/enrolled on one of three CAR trials (CD19, CD22, and CD19/22) at our institution. Non-CNS EMD was identified according to histology or radiographic imaging at extramedullary sites excluding the cerebrospinal fluid and CNS parenchyma. Of ∼180 patients with relapsed/refractory B-ALL screened across multiple early-phase trials over an 8-year period, 38 (21.1%) presented with isolated non-CNS EMD (n = 5) or combined medullary/non-CNS EMD (n = 33) on 18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) imaging. A subset receiving CAR T cells (18 infusions) obtained FDG PET/CT scans preinfusion and postinfusion to monitor response. At best response, 72.2% (13 of 18) of patients showed a medullary minimal residual disease–negative complete remission and complete (n = 7) or partial (n = 6) non-CNS EMD response. Non-CNS EMD responses to CAR T cells were delayed (n = 3), and residual non-CNS EMD was substantial; rarely, discrepant outcomes (marrow response without EMD response) were observed (n = 2). Unique CAR-associated toxicities at non-CNS EMD sites were seen in select patients. CAR T cells are active in B-ALL non-CNS EMD. Still, non-CNS EMD response to CAR T cells may be delayed and suboptimal, particularly with multifocal disease. Serial FDG PET/CT scans are necessary for identifying and monitoring non-CNS EMD.