Relapse of acute myeloid leukemia after allogeneic hematopoietic cell transplantation: clinical features and outcomes

Current status of conditioning regimens in haploidentical hematopoietic cell transplantation

The development of effective prophylaxis strategies against graft-versus-host disease (GVHD) has contributed to the widespread use of haploidentical related hematopoietic cell transplantation (Haplo-HCT). Currently, GVHD prophylaxis containing posttransplant cyclophosphamide (PTCY) is considered the standard of care in Haplo-HCT, and recent studies have shown comparable results for PTCY-based Haplo-HCT and HCT from other donor sources. The conditioning regimen plays an important role in eradicating tumor cells to prevent disease relapse and suppressing the recipient's immune system to facilitate engraftment. PTCY-based Haplo-HCT was initially developed using a nonmyeloablative conditioning regimen consisting of fludarabine, cyclophosphamide and low-dose total body irradiation, but high relapse rates reinforced the need to intensify the conditioning regimen. In this respect, various myeloablative and reduced-intensity conditioning regimens have been investigated. However, the optimal conditioning regimens for PTCY-based Haplo-HCT have not yet been established, and this issue needs to be addressed based on data from patients undergoing the procedure. In this article, we review the existing literature on conditioning regimens for PTCY-based Haplo-HCT and discuss future perspectives.

Efficacy and safety of cladribine in combination with busulfan and cyclophosphamide as an intensive conditioning regimen preceding allogeneic hematopoietic stem cell transplantation in relapsed or refractory acute myeloid leukemia

BACKGROUND

Cladribine, an analogue of deoxyadenosine, is used for therapy of hematological malignancies. Cladribine-containing regimen has been recommended as a rescue therapy for relapsed or refractory (R/R) acute myeloid leukemia (AML). Its combination with busulfan plus cyclophosphamide (BuCy), as an intensive conditioning regimen prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT), requires more clinical evidence. This study aimed to explore the efficacy and safety of cladribine plus BuCy administered as an intensive conditioning regimen before allo-HSCT in R/R AML patients.

METHODS

Twenty-three R/R AML patients, who underwent cladribine plus BuCy intensive conditioning regimen before allo-HSCT, were retrospectively analyzed. The median (range) follow-up duration time of observation was 0.73 (0.08-2.69) years.

RESULTS

The median (range) returned levels of mononuclear cells were 11.5 (6.1-18.5) x 108/kg and CD34+ cells were 5.5 (3.5-9.3) x 106/kg. The median (range) time of platelet reconstitution was 13.0 (9.0-21.0) days and neutrophil reconstitution was 14.0 (11.0-26.0) days. The incidence of conditioning regimen related toxicity (CRRT) affected 69.6% of patients; all CRRT-affected patients had grade I-II symptoms, including gastrointestinal tract (39.1%), oral cavity (26.1%), liver (8.7%), and kidney (4.3%) CRRTs. The incidence of acute graft-versus-host disease (GVDH) included 30.4% among all patients with 4.3% of grade III-IV acute GVHD, and 34.8% of chronic GVHD. During the follow-up period, 4 (17.4%) patients relapsed, and 6 (26.1%) patients died (cause of death: disease relapse, n = 3; infection, n = 2; GVHD, n = 1). The 1-year and 2-year accumulating event-free survival rates were 66.3% and 53.1%, respectively. The 1-year accumulating overall survival rate was 74.7% and 2-year survival rate was 64.0%.

CONCLUSION

Cladribine plus BuCy intensive conditioning regimen before allo-HSCT exhibits favorable treatment efficacy with acceptable toxicity in R/R AML patients.

WT1-guided pre-emptive therapy after allogeneic hematopoietic stem cell transplantation in patients with acute myeloid leukemia

Measurable residual disease (MRD)-guided pre-emptive therapies are now widely used to prevent post-transplant hematological relapse in patients with acute myeloid leukemia (AML). This single-center retrospective study aimed to clarify the significance of pre-emptive treatment based on Wilms' tumor gene-1 mRNA (WT1) monitoring for MRD in patients with AML who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). Patients with AML who received chemotherapy for hematological relapse or WT1 increase after allo-HSCT were eligible for inclusion. From January 2017 to June 2022, 30 patients with a median age of 57 (16-70) years were included and stratified into two groups: 10 with WT1 increase and 20 with hematological relapse. The median times from HCT to WT1 increase or hematological relapse were 309 days (range: 48-985) or 242 days (range: 67-1116), respectively. Less intensive chemotherapy using azacitidine or cytarabine was selected for all patients with WT1 increase and 12 (60%) with hematological relapse. The 1-year overall survival and event-free survival rates for WT1 increase and hematological relapse were 70% vs. 44% (P = 0.024) and 70% vs. 29% (P = 0.029), respectively. These real-world data suggest that WT1-guided pre-emptive therapy may be superior to therapy after hematological relapse in patients with AML who have undergone allo-HSCT.

Continuously improving outcome over time after second allogeneic stem cell transplantation in relapsed acute myeloid leukemia: an EBMT registry analysis of 1540 patients

Second allogeneic stem cell transplantation (alloSCT2) is among the most effective treatments for acute myeloid leukemia (AML) relapse after first alloSCT (alloSCT1). Long-term EBMT registry data were used to provide large scale, up-to-date outcome results and to identify factors for improved outcome. Among 1540 recipients of alloSCT2, increasing age, better disease control and performance status before alloSCT2, more use of alternative donors and higher conditioning intensity represented important trends over time. Between the first (2000-2004) and last (2015-2019) period, two-year overall and leukemia-free survival (OS/LFS) increased considerably (OS: 22.5-35%, LFS: 14.5-24.5%). Cumulative relapse incidence (RI) decreased from 64% to 50.7%, whereas graft-versus-host disease and non-relapse mortality (NRM) remained unchanged. In multivariable analysis, later period of alloSCT2 was associated with improved OS/LFS (HR = 0.47/0.53) and reduced RI (HR = 0.44). Beyond, remission duration, disease stage and patient performance score were factors for OS, LFS, RI, and NRM. Myeloablative conditioning for alloSCT2 decreased RI without increasing NRM, leading to improved OS/LFS. Haploidentical or unrelated donors and older age were associated with higher NRM and inferior OS. In summary, outcome after alloSCT2 has continuously improved over the last two decades despite increasing patient age. The identified factors provide clues for the optimized implementation of alloSCT2.

Donor Lymphocyte Infusion in the Treatment of Post-Transplant Relapse of Acute Myeloid Leukemias and Myelodysplastic Syndromes Significantly Improves Overall Survival: A French-Italian Experience of 134 Patients

BACKGROUND

Disease relapse after allogeneic stem cell transplantation (allo-SCT) is the main challenge for curing acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). We investigated the overall survival (OS) after allo-SCT relapse according to different therapeutic approaches.

METHODS

We analyzed 134 patients who relapsed after allo-SCT performed between 2015 and 2021 at Saint-Antoine University Hospital, Paris and Spedali Civili di Brescia, Brescia. Of these, 103 (77%) were treated, comprising 69/103 (67%) who received therapy in overt relapse and 34/103 (33%) who were treated in a pre-emptive manner when molecular/cytogenetics recurrence or mixed chimerism occurred. The treatment was donor lymphocyte infusion (DLI)-based for 40/103 (39%) patients.

RESULTS

The 1-, 2-, and 5-year OS of patients treated with DLI (n = 40) was 67%, 34%, and 34%, respectively, for those treated preventively (n = 20) and 43%, 20%, and 20%, respectively, for those treated in overt relapse (n = 20) (p < 0.01). The 1-, 2-, and 5-year OS of patients treated without DLI (n = 63) was 54%, 40%, and 26%, respectively, for those treated preventively (n = 14) and 17%, 5%, and 0%, respectively, for those treated in overt relapse (n = 49) (p < 0.01).

CONCLUSIONS

Relapse treatment with a pre-emptive strategy was associated with improved outcomes, particularly when DLI was employed.

Allogeneic stem cell transplant recipients surviving at least 2 years without relapse: outcome and risk factors

Outcomes of 2-year survivours undergoing allo-haematopoietic stem cell transplantation at Oslo University Hospital were retrospectively assessed with the objectives of identification of risk factors for late death as possible means for precautionary measures and interventions to improve long-term survival. 421 patients with haematological malignancy, transplanted between 2005 and 2019, alive and free of disease after 2 years were included with data reported from The OUS-HSCT registry. Median follow-up was 6.2 years (2.016.1), and 232 patients (55%) were observed for minimum 5 years. The probability of being alive 5 and 10 years after HSCT was 86% and 76%. Primary risk factors for late death included initial diagnosis of age ≥ 60 years, chronic lymphocytic leukaemia (CLL), previous blood stream- or invasive fungal infection (BSI, IFI), and chronic graft-versus-host disease (cGVHD). Transplant-related mortality (TRM) and relapse at 5 years were 9.0% and 7.7%, respectively. Two factors were associated with the latter: cytomegalovirus (CMV) seronegative donor and CLL. Compared with the age- and gender-matched Norwegian general population, life expectancy was lower for each disease, except for CML. The prospect for the long-term survival is good for 2-year survivors of the allogeneic hematopoietic stem cell transplantation. However, life expectancy remains inferior to the age- and gender-matched general population. Optimising prophylaxis and treatment for chronic GVHD, BSI and IFI are needed along with the improved adherence to guidelines for early detection of secondary malignancies. Measures to improve immune reconstitution, possibly the microbiota, and the use of CMV seropositive donors regardless of recipient sero-status may be warranted and should be addressed in further studies.

Microenvironment in acute myeloid leukemia: focus on senescence mechanisms, therapeutic interactions, and future directions

Acute myeloid leukemia (AML) is a disease with a dismal prognosis, mainly affecting the elderly. In recent years, new drugs have improved life expectancy and quality of life, and a better understanding of the genetic-molecular nature of the disease has shed light on previously unknown aspects of leukemogenesis. In parallel, increasing attention has been attracted to the complex interactions between cells and soluble factors in the bone marrow (BM) environment, collectively known as the microenvironment. In this review, we discuss the central role of the microenvironment in physiologic and pathologic hematopoiesis and the mechanisms of senescence, considered a fundamental protective mechanism against the proliferation of damaged and pretumoral cells. The microenvironment also represents a fertile ground for the development of myeloid malignancies, and the leukemic niche significantly interacts with drugs commonly used in AML treatment. Finally, we focus on the role of the microenvironment in the engraftment and complications of allogeneic hematopoietic stem cell transplantation, the only curative option in a conspicuous proportion of patients.

Donor lymphocyte infusion for prophylaxis and treatment of relapse in pediatric hematologic malignancies after allogeneic hematopoietic stem cell transplant

BACKGROUND

Donor lymphocyte infusion (DLI) is effective for managing patients with hematologic malignancies after allogeneic hematopoietic stem cell transplant (HSCT). However, few studies have explored its optimal use in pediatric populations. Herein, we report our single-center experiences of DLI and factors for predicting its outcomes.

METHODS

This retrospective study included pediatric patients who had received DLI (between June 1998 and December 2022) after allogeneic HSCT. Data regarding patient characteristics, preemptive DLI disease status, and DLI characteristics were collected. The primary outcomes were overall survival (OS), event-free survival (EFS), and graft-vs-host-disease (GVHD) development.

RESULTS

The study cohort comprised 17 patients with acute leukemia, 3 with chronic leukemia, and 3 with lymphoma. Prophylactic, preemptive, and therapeutic DLI were used in seven, seven, and nine patients, respectively. Patients' median age and DLI dose were 9 years and 4.6 × 10 7 CD3 + cells/kg, respectively. The 5-year OS, EFS, and nonrelapse mortality were 43.5%, 38.3%, and 13.3%, respectively. Approximately 39% of the patients developed grade III or IV acute GVHD, whereas moderate/severe chronic GVHD (cGVHD) occurred in 30% of the evaluable patients. Patients' disease status before HSCT ( p = 0.009) and DLI ( p = 0.018) were the key factors influencing EFS. The implementation of a dose escalation schedule was associated with a marginal reduction in the risk of moderate/severe cGVHD ( p = 0.051). A DLI dose of ≥5 × 10 7 CD3 + cells/kg was significantly associated with a high moderate to severe cGVHD risk ( p = 0.002) and reduced OS ( p = 0.089).

CONCLUSION

Patients' disease status before HSCT and DLI may help predict EFS. The use of DLI as a prophylactic and preemptive modality leads to a favorable 5-year EFS. To safely deliver DLI in children, clinicians must maintain vigilant monitoring and prepare patients in advance when escalating the dose to ≥5 × 10 7 CD3 + cells/kg.

A novel risk model for predicting early relapse in acute myeloid leukemia patients undergoing allogeneic hematopoietic stem-cell transplantation

Relapse remains the leading cause of death in acute myeloid leukemia (AML) patients following allogeneic hematopoietic stem-cell transplantation (allo-HSCT), limiting the efficacy of allo-HSCT. Thus, the ability to identify high-risk patients in a manner that permits early intervention has the potential to improve survival outcomes. We retrospectively enrolled 414 younger patients (aged 14-60 years) with AML who received allo-HSCT between January 2014 and May 2020. From June 2020 to June 2021, 110 consecutive patients were included prospectively in the validation cohort. The primary outcome was early relapse (relapse within 1 year). The cumulative incidence of early relapse after allo-HSCT was 11.8%. The overall survival rate for patients who relapsed within 1-year was 4.1% at 3 years after relapse. After multivariable adjustment, statistically significant associations between primary resistance, pre-transplantation measurable residual disease, DNMT3A mutation, or white blood cell count at diagnosis and early relapse were observed. An early relapse prediction model was developed based on these factors and the model performed well. Patients deemed to have a high risk or a low risk of early relapse had early relapse rates of 26.2% and 6.8%, respectively (P < 0.001). The prediction model could be used to help identify patients at risk for early relapse and to guide personalized relapse prevention.

Overcoming relapse: prophylactic or pre-emptive use of azacitidine or FLT3 inhibitors after allogeneic transplantation for AML or MDS

Relapse remains the most critical obstacle in treatment by allogeneic hematopoietic stem cell transplantation (HSCT). Non-relapse mortality has improved annually, but relapse mortality remains high. Post-transplant maintenance treatment, such as hypomethylating agents and FMS-like tyrosine kinase 3 (FLT3) inhibitors, has been investigated for decades as a means of preventing disease relapse after HSCT. Other factors besides the relapse tendency of the primary disease that can affect the transition of estimated disease burden in patients undergoing HSCT are disease status at HSCT (non-remission, remission with minimal/measurable residual disease (MRD), and remission without MRD) and conditioning regimen intensity. Optimal selection of patients at high risk for relapse who can tolerate a long duration of therapy is pivotal for successful post-transplant maintenance therapy. In this review, we provide an overview of current progress in research on post-transplant maintenance treatment using azacitidine or FLT3 inhibitors for preventing disease relapse after HSCT for AML or MDS, and discuss the future outlook in this area.

Post-transplant cyclophosphamide and early mixed donor Chimerism in myeloid malignancies; a single-center experience

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative option for high-risk myeloid malignancies. Post-transplant cyclophosphamide (PT-Cy) has proven to be effective for graft versus host disease (GVHD) prophylaxis. Given that graft-versus-tumor (GVT) effect plays a major role in reducing the risk of disease relapse, the application of PT-Cy must balance the risk of relapse. Mixed chimerism (MC) refers to a state of concurrent presence of recipient and donor cells post allo-HSCT which may precede relapse disease.

OBJECTIVE

We investigated the impact of PT-Cy on early MC (EMC) and disease relapse in patients with a myeloid malignancy post allo-HSCT.

STUDY DESIGN

This retrospective single-center study included patients that underwent allo-HSCT between 2015 and 2021. Patient and disease characteristics were collected from the electronic health records. EMC was defined as <95% donor cells at day 90-120 post allo-HSCT.

RESULTS

A total of 144 patient that received an allo-HSCT were included in the study. One hundred and eight (75%) patients received PT-Cy as part of the GVHD prophylaxis regimen. The majority underwent allo-HSCT for acute myeloid leukemia (62%) or myelodysplastic syndrome (31%). Sixty-five percent received allo-HSCT from a matched unrelated donor transplant and 65% received a myeloablative conditioning regimen. A lower rate of chronic GVHD (p = 0.03) and a higher rate of EMC (p = 0.04) were observed in patients that received PT-Cy. PT-Cy was not associated with overall survival (OS) and relapse-free survival (RFS). Multivariable analysis identified measurable residual disease status (p = 0.003), hematopoietic cell transplantation-specific comorbidity index (p = 0.012) and chronic GVHD (p = 0.006) as independent prognostic variables for OS. AML-adverse risk (p = 0.004) and EMC (p = 0.018) were independently prognostic for RFS. While EMC overall was not significantly associated with higher risk of relapse, EMC was associated with shorter RFS within adverse-risk AML patients.

CONCLUSION

Our study shows that PT-Cy was associated with an increased risk of EMC. The predictive value of EMC for relapse remains unclear and may depend on the underlying disease, which should be validated in a larger cohort.

Venetoclax plus hypomethylating agents versus intensive chemotherapy for hematological relapse of myeloid malignancies after allo-HSCT

Introduction

Since allogeneic stem cell transplantation (allo-HSCT) is considered one of the curative treatments for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), hematological relapse following allo-HSCT remained a crucial concern for patients' survival.

Methods

We retrospectively compared patients who received venetoclax plus hypomethylating agents (VEN+HMA, n=23) or intensive chemotherapy (IC, n=42) for hematological relapse of myeloid malignancies after allo-HSCT. HMA selection included decitabine (n=2) and azacitidine (n=21), and combined donor lymphocyte infusion was administered to 21 and 42 patients in VEN+HMA and IC groups, respectively.

Results

Median age of all patients was 39 (16-64) years old. Overall response rates, including complete response (CR), CR with incomplete recovery of normal neutrophil or platelet counts (CRi) and partial response (PR), were not significantly different between VEN+HMA and IC groups (60.1% versus 64.3%, P=0.785). CR/CRi rate was 52.2% in VEN+HMA and 59.5% in IC group (P=0.567). The rate of relapse after response was 66.7% in VEN+HMA group and 40.7% in IC group (P=0.176). Median overall survival was 209.0 (95%CI 130.9-287.1) days for VEN+HMA group versus 211.0 (95%CI 28.7-393.3) days for IC group (P=0.491). The incidence of lung infection (17.4% versus 50.0%, P=0.010), thrombocytopenia (73.9% versus 95.2%, P=0.035) and acute graft-versus-host disease (aGvHD) (50.0% versus 13.0%, P=0.003) was significantly higher in IC group.

Discussion

In conclusion, VEN+HMA is not inferior to IC regimen in terms of improving response and survival, and is associated with a lower incidence of adverse events and aGvHD. However, further research is required to enhance long-term survival.

Successful combination treatment with azacitidine and venetoclax as a bridging therapy for third allogenic stem cell transplantation in a patient with 11q23/MLL-rearranged complex karyotype acute myeloid leukemia

Translocation t(6;11) occurs in approximately 5% of patients with acute myeloid leukemia (AML) corresponding to 11q23/mixed lineage leukemia (MLL) rearrangement. The AF6 gene on chromosome 6q27 is the fusion partner of the MLL gene on 11q23 in t(6;11), which results in a poor prognosis. The case of a patient with 11q23/MLL-rearranged AML who successfully underwent a third allogeneic stem cell transplantation after treatment with azacitidine (AZA) and venetoclax (VEN) is presented in this article. This report suggests that a combination of AZA and VEN is an effective therapeutic approach for relapsed and refractory MLL-rearranged AML.

The prevention of disease relapse after allogeneic hematopoietic cell transplantation in acute myeloid leukemia

Disease relapse represents by far the most frequent cause of hematopoietic cell transplantation (HCT) failure. Patients with acute leukemia suffering relapse after HCT have limited conventional treatment options with little possibility of cure and represent, de facto, suitable candidates for the evaluation of novel cellular and biological-based therapies. Donor lymphocyte infusions (DLI) has been one of the first cellular therapies adopted to treat post HCT relapse of acute leukemia patients and still now, it is widely adopted in preemptive and prophylactic settings, with renewed interest for manipulated cellular products such as NK-DLI. The acquisition of novel biological insights into pathobiology of leukemia relapse are translating into the clinic, with novel combinations of target therapies and novel agents, helping delineate new therapeutical landscapes. Hypomethylating agents alone or in combination with novel drugs demonstrated their efficacy in pre-clinical models and controlled trials. FLT3 inhibitors represent an essential therapeutical instrument incorporated in post-transplant maintenance strategies. The Holy grail of allogeneic transplantation lies in the separation of graft-vs.-host disease from graft vs. tumor effects and after more than five decades, is still the most ambitious goal to reach and many ways to accomplish are on their way.

Azacitidine and donor lymphocyte infusion for patients with relapsed acute myeloid leukemia and myelodysplastic syndromes after allogeneic hematopoietic stem cell transplantation: A meta-analysis

Background

For patients with relapsed acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) after allogeneic hematopoietic stem cell transplantation (allo-HSCT), azacitidine with donor lymphocyte infusion (DLI) is a feasible option to perform a preemptive or salvage treatment. However, its efficacy lacked comprehensive analysis, and this study aimed to fill this gap.

Methods

We searched potential studies in PUBMED, EMBASE, and the Cochrane Central Register of Controlled Trials. Thirteen studies involving 811 patients were analyzed. The inverse variance method was used to calculate the pooled proportion and 95% confidence interval (CI). Subgroup analysis was performed to explore the source of heterogeneity.

Results

The rate of pooled complete remission + partial remission (CR + PR), CR, and 2-year overall survival (OS) were 30% (95% CI: 22%-39%), 21% (95% CI: 16%-28%), and 31% (95% CI: 27%-35%), respectively. The pooled acute graft-versus-host disease (GvHD) and chronic GvHD rates were 15% (95% CI: 9%-23%) and 14% (95% CI: 8%-23%), respectively. Adverse cytogenetics and a higher percentage of bone marrow (BM) blasts at relapse were correlated with worse CR + PR and CR (interaction p < 0.05). Higher 2-year OS was found in patients with lower BM blasts at relapse or a longer time from allo-HSCT to relapse (interaction p < 0.05). Furthermore, the preemptive treatment for molecular relapse/minimal residual disease positivity resulted in much better outcomes than that for hematological relapse, both in terms of CR and 2-year OS (interaction p < 0.001).

Conclusion

The regimen of azacitidine and DLI could safely improve the outcomes of relapsed AML/MDS after allo-HSCT, especially in those with signs of early relapse. The administration of targeted medicines in azacitidine-based therapies may further improve the outcomes of relapsed AML/MDS.

Relapse after allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia: an overview of prevention and treatment

Despite therapeutic progress in acute myeloid leukemia (AML), relapse post-allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a major challenge. Here, we aim to provide an overview of prevention and treatment of relapse in this population, including cell-based and pharmacologic options. Post-transplant maintenance therapy is used in patients who have undetectable measurable residual disease (MRD), while pre-emptive treatment is administered upon detection of MRD. Prompt transfusion of prophylactic donor lymphocyte infusion (DLI) was found to be effective in preventing relapse and overcoming the negative impact of detectable MRD. In addition, patients with persistent targetable mutations can benefit from targeted post-transplant pharmacological interventions. IDH inhibitors have shown promising results in relapsed/refractory AML. Hypomethylating agents, such as decitabine and azacitidine, have been studied in the post-allo-HSCT setting, both as pre-emptive and prophylactic. Venetoclax has been shown effective in combination with hypomethylating agents or low-dose cytarabine in patients with newly diagnosed AML, especially those unfit for intensive chemotherapy. FLT3 inhibitors, the topic of another section in this review series, have significantly improved survival in FLT-3-ITD mutant AML. The role of other cell-based therapies, including CAR-T cells, in AML is currently being investigated.

The significance of mixed chimaerism and cell lineage chimaerism monitoring in paediatric patients post haematopoietic stem cell transplant

Haematopoietic stem cell transplants (HSCTs) are carried out across the world to treat haematological and immunological diseases which would otherwise prove fatal. Certain diseases are predominantly encountered in paediatric patients, such severe primary immunodeficiencies (PID) and diseases of inborn errors of metabolism (IEM). Chimaerism testing for these disorders has different considerations compared to adult diseases. This review focuses on the importance of cell-lineage-specific chimaerism testing and examines the appropriate cell populations to be assessed in individual paediatric patient groups. By analysing disease-associated subpopulations, abnormalities are identified significantly earlier than in whole samples and targeted clinical decisions can be made. Chimaerism methods have evolved over time and lead to an ever-increasing level of sensitivity and biomarker arrays to distinguish between recipient and donor cells. Short tandem repeat (STR) is still the gold standard for routine chimaerism assessment, and hypersensitive methods such as quantitative and digital polymerase chain reaction (PCR) are leading the forefront of microchimaerism testing. The rise of molecular methods operating with minute DNA amounts has been hugely beneficial to chimaerism testing of paediatric samples. As HSCTs are becoming increasingly personalised and risk-adjusted towards a child's individual needs, chimaerism testing needs to adapt alongside these medical advances ensuring the best possible care.

Different recovery patterns of CMV-specific and WT1-specific T cells in patients with acute myeloid leukemia undergoing allogeneic hematopoietic cell transplantation: Impact of CMV infection and leukemia relapse

In allogeneic hematopoietic cell transplantation (allo-HSCT), both virus-specific T cells and leukemia-specific T cells need to be reconstituted to protect patients from virus infections and primary disease relapse. Cytomegalovirus (CMV) infection remains an important cause of morbidity and mortality after allo-HSCT. Emerging data indicate that CMV reactivation is associated with reduced risk of leukemia relapse in patients with acute myeloid leukemia (AML) undergoing allo-HSCT. In a cohort of 24 WT1+ AML patients during the first year following HSCT, CMV specific CD8+ T cells (CMV-CTL) reconstituted much faster than WT1-specific CD8+ T cell (WT1-CTL) after allo-SCT. Moreover, CMV-CTL expressed lower levels of exhaustion markers and were more functional as identified by production of IFN-γ/TNF-α and expression of Eomes/T-bet. Interestingly, our patients with CMV reactivation presented higher frequency of CMV-CTL, lower levels of Eomes+T-bet- and higher levels of Eomes+T-bet+ expression in response to WT1 and CMV pp65 antigen during the first year after transplantation as compared to patients without CMV reactivation. Kinetics of CMV-CTL and WT1-CTL after transplantation might be associated with measurable residual disease and later leukemia relapse. Our results support that CMV reactivation, aside from the CMV-CTL reconstitution, could influence WT1-CTL reconstitution after allo-HSCT, thus potentially contributing to the remission/relapse of AML.

Outcomes of third allogeneic hematopoietic stem cell transplantation in relapsed/refractory acute leukemia after a second transplantation

Relapsed acute leukemia after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is associated with poor prognosis. In a subset of patients, durable remissions can be achieved with a second allo-HSCT (allo-HSCT2). However, many patients experience relapse after allo-HSCT2 and they may be considered for a third allo-HSCT (allo-HSCT3). Nevertheless, the benefit of allo-HSCT3 remains unconfirmed. Thus, herein a retrospective analysis of 253 allo-HSCT3s in patients with relapsed/refractory acute leukemia was carried out. In total, 29 (11.5%) survived at a median follow-up of 794 days (range: 87-4 619). The 3-year leukemia-free survival and overall survival (OS) rates were 9.7% and 10.9%, respectively. Patients who maintained remission for ≥2 years after allo-HSCT2 had a significantly better 3-year OS (35.8%) than those who experienced early relapse (<1 year, 7.8%; 1-2 years, 14.0%; P = 0.004). Complete remission at allo-HSCT3, performance status score of 0-1 at allo-HSCT3, grade I acute graft-versus-host disease after allo-HSCT2, and relapse ≥2 years after allo-HSCT2 were associated with better survival in patients who received allo-HSCT3. The prognosis after allo-HSCT3 in patients with relapsed/refractory acute leukemia is generally unfavorable. However, given the lack of alternative treatment options, allo-HSCT3 may be considered in a group of patients.

Detecting and preventing post-hematopoietic cell transplant relapse in AML

PURPOSE OF REVIEW

Relapsed disease is the primary cause of mortality for acute myeloid leukemia (AML) patients after allogeneic hematopoietic cell transplantation (HCT). This review outlines the most recent advances in the detection and prevention of AML relapse following allogeneic HCT.

RECENT FINDINGS

Conventional methods for predicting post-HCT relapse rely on the molecular and cytogenetics features present at diagnosis. These methods are slow to reflect a growing understanding of the molecular heterogeneity of AML and impact of new therapies on post-HCT outcomes. The use of measurable residual disease (MRD) techniques, including multiparameter flow cytometry and molecular testing, may improve the prognostic ability of these models and should be incorporated into post-HCT surveillance whenever possible.In the post-HCT setting, FLT3 inhibitor maintenance data indicate that effective therapies can improve post-HCT outcomes. Maintenance data with DNA methyltransferase inhibitor monotherapy is less compelling and outcomes may improve with combinations. Early interventions directed at preemptive management of MRD may further improve post-HCT outcomes.

SUMMARY

Post-HCT AML relapse prevention has evolved to include more sensitive measures of disease detection and novel therapies that may improve outcomes of poor-risk AML patients. Additional work is needed to maintain this progress.

Donor derived leukemia in allogeneic transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) is a curative option for the treatment of eligible patients with hematological malignancies. This modality confers a risk for life-threatening complications, including the rare and underdiagnosed complication of donor-derived leukemia (DDL). DDL differs from relapse of the original malignancy in that DDL originates from the donor stem cells and is unrelated to the original diagnosis. Because DDL may be the same lineage as the original diagnosis, it is difficult to identify these cases and many remain unrecognized. There is no consensus of how to approach the treatment of patients with DDL, and their prognosis is poor considering that patients with DDL have already been treated for their original leukemia and have undergone alloHCT. DDL occurs following transplants using any donor stem cell source (bone marrow, peripheral blood and cord blood) and any donor type (matched/unmatched, related/unrelated and haploidentical). Both donor and recipient factors contribute to the development of DDL, and a better understanding of these factors is crucial to reduce the risk for the development of DDL. In this review, we provide an overview of DDL, including the incidence, diagnosis, etiology, prognosis, and treatment.