Transplant in AML with measurable residual disease: proceed or defer?

Engineering the best transplant outcome for high-risk acute myeloid leukemia: the donor, the graft and beyond

Allogeneic hemopoietic cell transplantation remains the goal of therapy for high-risk acute myeloid leukemia (AML). However, treatment failure in the form of leukemia relapse or severe graft-versus-host disease remains a critical area of unmet need. Recently, significant progress has been made in the cell therapy-based interventions both before and after transplant. In this review, the Stem Cell Engineering Committee of the International Society for Cell and Gene Therapy summarizes the literature regarding the identification of high risk in AML, treatment approaches before transplant, optimal transplant platforms and measures that may be taken after transplant to ideally prevent, or, if need be, treat AML relapse. Although some strategies remain in the early phases of clinical investigation, they are built on progress in pre-clinical research and cellular engineering techniques that are already improving outcomes for children and adults with high-risk malignancies.

Prognostic impact of number of induction courses to attain complete remission in patients with acute myeloid leukemia transplanted with either a matched sibling or human leucocyte antigen 10/10 or 9/10 unrelated donor: An Acute Leukemia Working Party European Society for Blood and Marrow Transplantation study

INTRODUCTION

For the majority of patients with acute myeloid leukemia (AML) an allogeneic stem cell transplant (SCT) in first complete remission (CR) is preferred. However, whether the number of courses required to achieve CR has a prognostic impact is unclear. It is unknown which factors remain important in patients requiring more than one course of induction to attain remission.

METHODS

This Acute Leukaemia Working Party study from the European Society for Blood and Marrow Transplantation identified adults who received an allograft in first CR from either a fully matched sibling or 10/10 or 9/10 human leucocyte antigen (HLA)-matched unrelated donor (HLA-A, HLA-B, HLA-C, HLA-DR, or HLA-DQ). Univariate and multivariate analyses were undertaken to identify the prognostic impact of one or two courses of induction to attain CR.

RESULTS

A total of 4995 patients were included with 3839 (77%) patients attaining a CR following one course of induction chemotherapy (IND1), and 1116 patients requiring two courses (IND2) to attain CR. IND2 as compared to IND1 was a poor prognostic factor in a univariate analysis and remained so in a multivariate Cox model, resulting in an increased hazard ratio of relapse (1.38; 95% confidence interval [CI], 1.16-1.64; p = .0003) and of death (1.27; 95% CI, 1.09-1.47; p = .002). Adverse prognostic factors in a multivariate analysis of the outcomes of patients requiring IND2 included age, FLT3-ITD, adverse cytogenetics, and performance status. Pretransplant measurable residual disease retained a prognostic impact regardless of IND1 or IND2.

CONCLUSION

Initial response to chemotherapy as determined by number of courses to attain CR, retained prognostic relevance even following SCT in CR.

Novel immunotherapies in the treatment of AML: is there hope?

The success of allogeneic stem cell transplantation has demonstrated the potential for immunotherapy to treat acute myeloid leukemia (AML). Although alternative T-cell-based immunotherapies have shown efficacy, they also pose the risk of on-target off-leukemia hematotoxicity. So far, adoptive autologous or allogeneic chimeric antigen receptor (CAR) T/natural killer cell therapy is almost exclusively employed as a bridge-to-transplant strategy in the context of clinical trials. For now, clinical trials predominantly target lineage-restricted antigens, but emerging approaches focus on leukemia-associated/specific intracellular target antigens, including dual and split targeting strategies. Adapter CAR T cells and T-cell-recruiting bispecific antibodies offer transient exposure with enhanced safety and multitargeting potential against antigen-escape variants. However, these have yet to demonstrate sustained responses and should be used earlier to treat low leukemia burden, preferably if measurable residual disease is present. To address immune dysregulation and enhance T-cell fitness, novel CAR T and bispecific designs, along with combinatorial strategies, might prove essential. Furthermore, genetic associations with inflammatory bone marrow signatures suggest the need for tailored platforms in defined AML subtypes. The eagerly anticipated results of trials investigating magrolimab, an anti-CD47 antibody targeting the "do not eat me" signal in p53-mutated AML, should shed further light on the potential of these evolving immunotherapeutic approaches.

Measurable residual disease in patients undergoing allogeneic transplant for acute myeloid leukemia

The most common indication for allogeneic hematopoietic cell transplant (alloHCT) is maintenance of remission after initial treatment for patients with acute myeloid leukemia (AML). Loss of remission, relapse, remains however the most frequent cause of alloHCT failure. There is strong evidence that detectable persistent disease burden ("measurable residual disease", MRD) in patients with AML in remission prior to alloHCT is associated with increased risk of post-transplant relapse. MRD status as a summative assessment of response to pre-transplant therapy may allow superior patient-personalized risk stratification compared with models solely incorporating pre-treatment variables. An optimal methodology for AML MRD detection has not yet been established, but molecular methods such as DNA-sequencing may have additional prognostic utility compared to current approaches. There is growing evidence that intervention on AML MRD positivity may improve post-transplant outcomes. New initiatives will generate actionable data on the clinical utility of AML MRD testing for patients undergoing alloHCT.

Targeting Measurable Residual Disease (MRD) in Acute Myeloid Leukemia (AML): Moving beyond Prognostication

Measurable residual disease (MRD) assessment in acute myeloid leukemia (AML) has an established role in disease prognostication, particularly in guiding decisions for hematopoietic cell transplantation in first remission. Serial MRD assessment is now routinely recommended in the evaluation of treatment response and monitoring in AML by the European LeukemiaNet. The key question remains, however, if MRD in AML is clinically actionable or "does MRD merely portend fate"? With a series of new drug approvals since 2017, we now have more targeted and less toxic therapeutic options for the potential application of MRD-directed therapy. Recent approval of NPM1 MRD as a regulatory endpoint is also foreseen to drastically transform the clinical trial landscape such as biomarker-driven adaptive design. In this article, we will review (1) the emerging molecular MRD markers (such as non-DTA mutations, IDH1/2, and FLT3-ITD); (2) the impact of novel therapeutics on MRD endpoints; and (3) how MRD might be used as a predictive biomarker to guide therapy in AML beyond its prognostic role, which is the focus of two large collaborative trials: AMLM26 INTERCEPT (ACTRN12621000439842) and MyeloMATCH (NCT05564390).