Role of chimeric antigen receptor T-cell therapy: bridge to transplantation or stand-alone therapy in pediatric acute lymphoblastic leukemia

Long-term follow-up of CD19-CAR T-cell therapy in children and young adults with B-ALL

The tremendous successes of CD19-directed CAR T cells in children and young adults with B-cell acute lymphoblastic leukemia (B-ALL) has led to the more widespread use of this important treatment modality. With an ability to induce remission and potentially lead to long-term survival in patients with multiply relapsed/chemotherapy refractory disease, more children are now receiving this therapy with the hope of inducing a long-term durable remission (with or without consolidative hematopoietic cell transplantation). While overcoming the acute toxicities was critical to its broad implementation, the emerging utilization requires close evaluation of subacute and delayed toxicities alongside a consideration of late effects and issues related to survivorship following CAR T cells. In this underexplored area of toxicity monitoring, this article reviews the current state of the art in relationship to delayed toxicities while highlighting areas of future research in the study of late effects in children and young adults receiving CAR T cells.

Leveraging health care technology to improve health outcomes and reduce outcome disparities in AYA leukemia

Significant improvements have occurred for adolescent and young adult (AYA) B-cell acute lymphoblastic leukemia (B-ALL) patients following the widespread adoption of "pediatric-inspired" treatment regimens for AYA patients cared for in adult oncology settings. However, for AYA patients, aged 15 to 39, an outcomes gap remains in B-ALL, necessitating the incorporation of novel therapies into up-front treatment regimens. As a result, clinical trial enrollment remains the current standard of care for AYA B-ALL across disease subtypes when available and accessible. Currently, several up-front trials are looking to incorporate the use of inotuzumab, blinatumomab, and chimeric antigen receptor T-cell therapy into existing chemotherapy backbones for AYA patients, as well as tyrosine kinase inhibitors for both Philadelphia-positive (Ph+) and Ph-like B-ALL. In addition to ongoing attempts to improve up-front treatments by incorporating immunotherapy and targeted approaches, the increased use of next generation sequencing for measurable residual disease evaluation has led to superior risk-stratification and a decreased need to pursue consolidative hematopoietic stem cell transplantation during the first complete remission for many patients.

INSPIRED Symposium Part 2: Prevention and Management of Relapse Following Chimeric Antigen Receptor T Cell Therapy for B Cell Acute Lymphoblastic Leukemia

Although CD19-directed chimeric antigen receptor (CAR) T cell therapy (CAR-T) for relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) has been transformative in inducing and sustaining remission, relapse rates remain unacceptably high, with approximately 50% of children and young adults experiencing relapse within the first year postinfusion. Emerging strategies to extend the durability of remission involve the use of prognostic biomarkers to identify those at high risk of relapse or incorporate strategies aimed to enhancing functional CAR T cell persistence. Nonetheless, with antigen loss/down-regulation or evolution to lineage switch as major mechanisms of relapse, optimizing single antigen targeting alone is insufficient. Here, with a focus on relapse prevention strategies, including postinfusion surveillance and treatment approaches being explored to optimize post-CAR-T management (eg, combinatorial antigen targeting strategies, preemptive hematopoietic cell transplantation), we review the current state of the art in the prevention and management of post CAR-T relapse. We highlight the advancements in the field and identify gaps in the literature to guide future research in optimizing the prevention and management of post-CAR-T relapse in children and young adults with B-ALL.

Long-term outcomes following CAR T cell therapy: what we know so far

Chimeric antigen receptors (CAR) are engineered fusion proteins designed to target T cells to antigens expressed on cancer cells. CAR T cells are now an established treatment for patients with relapsed and/or refractory B cell lymphomas, B cell acute lymphoblastic leukaemia and multiple myeloma. At the time of this writing, over a decade of follow-up data are available from the initial patients who received CD19-targeted CAR T cells for B cell malignancies. Data on the outcomes of patients who received B cell maturation antigen (BCMA)-targeted CAR T cells for multiple myeloma are more limited owing to the more recent development of these constructs. In this Review, we summarize long-term follow-up data on efficacy and toxicities from patients treated with CAR T cells targeting CD19 or BCMA. Overall, the data demonstrate that CD19-targeted CAR T cells can induce prolonged remissions in patients with B cell malignancies, often with minimal long-term toxicities, and are probably curative for a subset of patients. By contrast, remissions induced by BCMA-targeted CAR T cells are typically more short-lived but also generally have only limited long-term toxicities. We discuss factors associated with long-term remissions, including the depth of initial response, malignancy characteristics predictive of response, peak circulating CAR levels and the role of lymphodepleting chemotherapy. We also discuss ongoing investigational strategies designed to improve the length of remission following CAR T cell therapy.

Access to Chimeric Antigen Receptor T Cell Clinical Trials in Underrepresented Populations: A Multicenter Cohort Study of Pediatric and Young Adult Acute Lymphobastic Leukemia Patients

Chimeric antigen receptor T cell (CAR-T) therapy is a promising approach to improve survival for children and adults with relapsed/refractory (r/r) B cell acute lymphoblastic leukemia (B-ALL), but these clinical trials might not be equally accessible to patients of low socioeconomic status (SES) or to patients from racial or ethnic minority groups. We sought to describe the sociodemographic characteristics of pediatric and adolescent and young adult (AYA) patients enrolled in CAR-T clinical trials and to compare these characteristics to those of other patients with r/r B-ALL. We conducted a multicenter retrospective cohort study at 5 pediatric consortium sites to compare the sociodemographic characteristics of patients treated and enrolled in CAR-T trials at their home institution, other patients with r/r B-ALL treated at these sites, and patients referred from an external hospital for CAR-T trials. The patients were age 0 to 27 years with r/r B-ALL treated at 1 of the consortium sites between 2012 and 2018. Clinical and demographic data were collected from the electronic health record. We calculated distance from home to treating institution and assigned SES scores based on census tract. Among the 337 patients treated for r/r B-ALL, 112 were referred from an external hospital to a consortium site and enrolled in a CAR-T trial and 225 were treated primarily at a consortium site, with 34% enrolled in a CAR-T trial. Patients treated primarily at a consortium site had similar characteristics regardless of trial enrollment. Lower proportions of Hispanic patients (37% versus 56%; P = .03), patients whose preferred language was Spanish (8% versus 22%; P = .006), and publicly insured patients (38% versus 65%; P = .001) were referred from an external hospital than were treated primarily at a consortium site and enrolled in a CAR-T trial. Patients who are Hispanic, Spanish-speaking, or publicly insured are underrepresented in referrals from external hospitals to CAR-T centers. External provider implicit bias also may influence referral of these patients. Establishing partnerships between CAR-T centers and external hospital sites may improve provider familiarity, patient referral, and patient access to CAR-T clinical trials.

The Choice of Either Conventional Chemotherapy or Inotuzumab Ozogamicin as Bridging Regimen Does Not Appear To Impact Clinical Response to CD19-Directed CAR-T Therapy in Pediatric B-ALL

Bridging therapy (BT) given during the period between T-cell collection and initiation of lymphodepleting chemotherapy is indicated for most children with B-cell acute lymphoblastic leukemia (B-ALL) undergoing treatment with tisagenlecleucel (tisa-cel), a CD19-directed chimeric antigen receptor T-cell (CAR-T) therapy. Both conventional chemotherapy agents and B-cell directed antibody-based therapies such as antibody-drug conjugates and bispecific T-cell engagers have been used as systemic forms of BT. The purpose of this retrospective study was to evaluate if there are detectable differences in clinical outcomes based on the type of BT given (conventional chemotherapy or inotuzumab). A retrospective analysis was performed on all patients treated with tisa-cel at Cincinnati Children's Hospital Medical Center for B-ALL with bone marrow disease (with or without extramedullary disease). Patients who did not receive systemic BT were excluded. Only 1 patient received blinatumomab as BT and was therefore not included in this analysis to focus the analysis on the use of inotuzumab. Pre-infusion characteristics and post-infusion outcomes were collected. Fisher's exact test was used for categorical variables, and t-test or Mann-Whitney test was used for continuous parametric and non-parametric variables respectively. Mantel-Cox was used for survival analyses. Thirty-two patients received BT before CD19 CAR-T for medullary leukemia; 24 received conventional chemotherapy, and 8 received inotuzumab ozogamicin (InO). Cohorts were evenly matched regarding CAR-T indication, recipient age, and median CAR-T cell dose. There were no significant differences between the groups for attaining a minimal residual disease (MRD)-negative complete response after CAR-T, the percentage of patients who maintained prolonged B-cell aplasia, or the median duration of B-cell aplasia. Thirty-seven percent of patients in the conventional chemotherapy group and 43% in the antibody-based therapy group relapsed, with a median time to relapse in both groups of 5 months. No differences in event-free survival, the cumulative incidence of relapse, or overall survival were seen between the two groups. Initial response to tisa-cel, relapse rate, and survival were similar between patients who received BT with conventional chemotherapy or InO therapy. Because low disease burden at the time of infusion is a positive prognostic factor, choice of bridging regimen should focus on therapy that is anticipated to effectively lower disease burden and minimize treatment-related toxicity. Given the limitations associated with the single center retrospective analysis, a larger, multicenter study is needed to further explore these findings.

Clinical trials for chimeric antigen receptor T-cell therapy: lessons learned and future directions

PURPOSE OF REVIEW

The purpose of this review is to summarize the status and utilization of chimeric antigen receptor T-cell (CAR-T) therapy based on the most recent clinical trials in patients with leukemia and lymphoma. Additionally, this review will highlight limitations in current strategies, discuss efforts in toxicity mitigation, and outline future directions for investigation.

RECENT FINDINGS

CD19 targeted CAR-T-cell therapy (CD19-CAR) is highly effective in patients with relapsed/refractory (r/r) B-cell hematologic malignancies. However, multiple challenges have arisen, particularly life-threatening adverse events, such as cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome. Despite these challenges, recent CD19-CAR trials, including two randomized studies, have demonstrated both impressive initial results along with durable responses. Combined with results emerging from 'real-world' experience, the efficacy of CAR-T-cells is high, propelling CAR-T-cells studies targeting alternate B-cell antigens [e.g. CD20, CD22 and CD269 (BCMA)] and other targets for hematologic malignancies, along with solid and CNS tumors.

SUMMARY

Given the benefit for CD19-CAR, determining the appropriate place in utilization for both an individual patient's treatment course and more broadly in the generalized treatment paradigm is critically needed. We discuss the most recent trials exploring this topic and future directions in the field.