NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: report from the Committee on Disease-Specific Methods and Strategies for Monitoring Relapse following Allogeneic Stem Cell Transplantation. Part I: Methods, acute leukemias, and myelodysplastic syndromes

Donor lymphocyte infusion after allogeneic haematopoietic cell transplantation for haematological malignancies: basic considerations and best practice recommendations from the EBMT

Since the early description of three patients with relapsed leukaemia after allogeneic haematopoietic cell transplantation (HCT) who obtained complete remission after donor lymphocyte infusions (DLIs), the added value of this procedure to induce or maintain graft-versus-leukaemia immunity has been undisputed. For more than 30 years, DLIs have become common practice as prophylactic, pre-emptive, or therapeutic immunotherapy. However, as with many aspects of allogeneic HCT, centres have developed their own routines and practices, and many questions related to the optimal applications and toxicity, or to the immunobiology of DLI induced tumour-immunity, remain. As a part of the Practice Harmonization and Guidelines Committee and the Cellular Therapy and Immunobiology Working Party of the European Society for Blood and Marrow Transplantation effort, a panel of experts with clinical and translational knowledge in transplantation immunology and cellular therapy met during a 2-day workshop in September, 2023, in Lille, France, and developed a set of consensus-based recommendations for the application of unmanipulated DLI after allogeneic HCT for haematological malignancies. Given the absence of prospective data in the majority of publications, these recommendations are mostly based on retrospective studies and expert consensus.

Engraftment and Measurable Residual Disease Monitoring after Hematopoietic Stem Cell Transplantation: Comparison of Two Chimerism Test Strategies, Next-Generation Sequencing versus a Combination of Short-Tandem Repeats and Quantitative PCR

Chimerism testing supports the study of engraftment and measurable residual disease (MRD) in patients after allogeneic hematopoietic stem cell transplant. In chimerism MRD, relapse can be predicted by increasing mixed chimerism (IMC), recipient increase ≥0.1% in peripheral blood, and proliferating recipient cells as a surrogate of tumor activity. Conventionally, the combination of short-tandem repeat (STR) and quantitative PCR (qPCR) was needed to ensure assay sensitivity and accuracy in all chimerism status. We evaluated the use of next-generation sequencing (NGS) as an alternate technique. The median numbers of informative markers in unrelated/related cases were 124/82 (NGS; from 202 single-nucleotide polymorphism), 5/3 (qPCR), and 17/10 (STR). Assay sensitivity was 0.22% (NGS), 0.1% (qPCR), and 1% (STR). NGS batch (4 to 48 samples) required 19.60 to 24.80 hours and 1.52 to 2.42 hours of hands-on time (comparable to STR/qPCR). NGS assay cost/sample was $91 to $151, similar to qPCR ($99) but higher than STR ($27). Using 56 serial DNAs from six post-transplant patients monitored by the qPCR/STR, the correlation with NGS was strong for percentage recipient (y = 1.102x + 0.010; R2 = 0.968) and percentage recipient change (y = 0.892x + 0.041; R2 = 0.945). NGS identified all 17 IMC events detected by qPCR (100% sensitivity). The NGS chimerism provides sufficient sensitivity, accuracy, and economical/logistical feasibility in supporting engraftment and MRD monitoring.

Analysis of Subset Chimerism for MRD-Detection and Pre-Emptive Treatment in AML

Allogeneic hematopoietic stem cell transplantation (alloHCT) represents the only potentially curative treatment in high-risk AML patients, but up to 40% of patients suffer from relapse after alloHCT. Treatment of overt relapse poses a major therapeutic challenge and long-term disease control is achieved only in a minority of patients. In order to avoid post-allograft relapse, maintenance as well as pre-emptive therapy strategies based on MRD-detection have been used. A prerequisite for the implementation of pre-emptive therapy is the accurate identification of patients at risk for imminent relapse. Detection of measurable residual disease (MRD) represents an effective tool for early relapse prediction in the post-transplant setting. However, using established MRD methods such as multicolor flow cytometry or quantitative PCR, sensitive MRD monitoring is only applicable in about half of the patients with AML and advanced MDS undergoing alloHCT. Donor chimerism analysis, in particular when performed on enriched leukemic stem and progenitor cells, e.g. CD34+ cells, is a sensitive method and has emerged as an alternative option in the post alloHCT setting. In this review, we will focus on the current strategies for lineage specific chimerism analysis, results of pre-emptive treatment using this technology as well as future developments in this field.

Role of Minimal Residual Disease Testing in Acute Myeloid Leukemia

Minimal or measurable residual disease (MRD) after therapy is the most important independent prognostic factor in acute myeloid leukemia. MRD measured by multiparametric flow cytometry and real-time quantitative polymerase chain reaction has been integrated into risk stratification and used to guide future treatment strategies. Recent technological advances have allowed the application of the novel molecular method, high-throughput sequencing, in MRD detection in clinical practice to improve sensitivity and specificity. Randomized studies are needed to address outstanding issues, including the optimal methods and timing of MRD testing and interlaboratory standardization to facilitate comparisons, to further improve MRD-directed interventions.

Low-Dose Decitabine Monotherapy Reverses Mixed Chimerism in Adult Patients After Allogeneic Hematopoietic Stem Cell Transplantation With Myeloablative Conditioning Regimen: A Pilot Phase II Study

T cell mixed chimerism (MC) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) with myeloablative conditioning for hematological malignancies may indicate engraftment failure or disease relapse. Immune modulation, such as donor lymphocyte infusion (DLI) or the rapid tapering-off or stopping of immunosuppressive treatment, can reverse MC to full donor chimerism (FDC). However, the development or aggravation of graft-versus-host disease (GvHD) and the related mortality remain major concerns with immune modulation. In this prospective, single-arm study (NCT03663751), we tested the efficacy and safety of low-dose decitabine (LD-DAC, 5 mg/m² daily for 5 days and repeated every 6–8 weeks) without immune modulation in the treatment of patients with MC to prevent MC-associated relapse and/or graft failure. A total of 14 patients were enrolled. All the patients received myeloablative conditioning regimens, and MC was documented from day +30 to day +180 after allo-HSCT with a donor chimerism level ranging from 59 to 97% without detectable measurable residual disease (MRD). Eleven patients (78.6%) responded favorably to treatment, showing increased levels of donor chimerism (≥95%), while nine achieved FDC. All of these patients maintained their responses for a median of 11 months (3–22). The three patients who failed to respond favorably eventually either relapsed or experienced graft failure. All three were alive and in remission at the last follow-up after the second allo-HSCT. LD-DAC monotherapy was well tolerated and exerted limited hematological and nonhematological toxicities. New-onset GvHD symptoms were observed only in two patients. Overall, the estimated 2-year overall survival (OS) and event-free survival (EFS) after allo-HSCT were 90.9 ± 8.7% and 67.0 ± 13.7%, respectively. In conclusion, LD-DAC alone could reverse MC in most patients after allo-HSCT with myeloablative conditioning, while those who achieved FDC enjoyed long-term EFS without major complications. Further prospective studies with larger sample sizes are warranted to confirm the benefits of LD-DAC.

H60: A Unique Murine Hematopoietic Cell-Restricted Minor Histocompatibility Antigen for Graft-versus-Leukemia Effect

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important treatment for many types of hematological malignancies. Matching of donor and recipient for the major histocompatibility complex (MHC) improves the HSCT reconstitution, but donor-derived T cells reactive to non-MHC encoded minor histocompatibility antigens (MiHAs) can induce graft-versus-host disease (GVHD) while also being needed for graft-versus-leukemia (GVL) effects. MiHAs are allelically variant self-peptides presented conventionally on MHC molecules, but are alloantigenic in transplantation settings. Immunodominant MiHAs are most strongly associated with GVHD and GVL. There is need for mouse paradigms to understand these contradictory effects. H60 is a highly immunodominant mouse MiHA with hematopoietic cell-restricted expression. Immunodominance of H60 is tightly associated with its allelic nature (presence vs. absence of the transcripts), and the qualitative (TCR diversity) and quantitative (frequency) traits of the reactive T cells. The identity as a hematopoietic cell-restricted antigen (HRA) of H60 assists the appearance of the immunodominace in allo-HSCT circumstances, and generation of GVL effects without induction of serious GVHD after adoptive T cell transfer. Also it allows the low avidity T cells to escape thymic negative selection and exert GVL effect in the periphery, which is a previously unevaluated finding related to HRAs. In this review, we describe the molecular features and immunobiology in detail through which H60 selectively exerts its potent GVL effect. We further describe how lessons learned can be extrapolated to human allo-HCST.

Personalized Chimerism Test that Uses Selection of Short Tandem Repeat or Quantitative PCR Depending on Patient's Chimerism Status

Chimerism testing is used to monitor engraftment and risk of relapse after allogeneic hematopoietic stem cell transplantation for hematologic malignancies. Although short tandem repeat (STR) method is widely used among clinical laboratories, quantitative PCR (qPCR) provides better sensitivity (0.1%) than STR (1% to 5%) but is less accurate than STR for patients in mixed chimerism. qPCR chimerism allows evaluation of residual recipient cells as a surrogate of measurable residual disease. To achieve higher sensitivity and accuracy, we applied qPCR or STR based on patient chimerism status (recipient alleles <5% or ≥5%, respectively). Of the 230 patients tested by STR in a 1-year period, excluding 10 deceased patients, 30 qPCR markers were genotyped and 167 patients converted to qPCR chimerism (76%), including eight patients undergoing multiple-donor transplantation. STR was continued on 53 patients (24%) for the following reasons: mixed chimerism (n = 23), lack of donor or pretransplantation DNA (n = 22), and insufficient qPCR informative markers [8 of 60 patients with related donors (13.3%)]. qPCR detected residual recipient chimerism in 85.5% of patients with complete chimerism by STR (<5% recipient). Selecting STR or qPCR testing based on each patient's chimerism status facilitates sensitive and accurate chimerism testing in clinical settings. In addition, we discuss clinical relevance of chimerism testing for measurable residual disease detection in various hematologic malignancies.

The consensus on the monitoring, treatment, and prevention of leukemia relapse after allogeneic hematopoietic stem cell transplantation in China

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important curative therapy for patients with leukemia. However, relapse remains the leading cause of death after transplantation. In recent years, substantial progress has been made by Chinese physicians in the field of establishment of novel transplant modality, patient selection, minimal residual disease (MRD) monitoring, and immunological therapies, such as modified donor lymphocyte infusion (DLI) and chimeric antigen receptor T (CART) cells, as well as MRD-directed intervention for relapse. Most of these unique systems are distinct from those in the Western world. In this consensus, we reviewed the efficacy of post-HSCT relapse management practice from available Chinese studies on behalf of the HSCT workgroup of the Chinese Society of Hematology, Chinese Medical Association, and compared these studies withthe consensus or guidelines outside China. We summarized the consensus on routine practices of post-HSCT relapse management in China and focused on the recommendations of MRD monitoring, risk stratification directed strategies, and modified DLI system. This consensus will likely contribute to the standardization of post-HSCT relapse management in China and become an inspiration for further international cooperation to refine global practices.

Escape from thymic deletion and anti-leukemic effects of T cells specific for hematopoietic cell-restricted antigen

Whether hematopoietic cell-restricted distribution of antigens affects the degree of thymic negative selection has not been investigated in detail. Here, we show that T cells specific for hematopoietic cell-restricted antigens (HRA) are not completely deleted in the thymus, using the mouse minor histocompatibility antigen H60, the expression of which is restricted to hematopoietic cells. As a result, low avidity T cells escape from thymic deletion. This incomplete thymic deletion occurs to the T cells developing de novo in the thymus of H60-positive recipients in H60-mismatched bone marrow transplantation (BMT). H60-specific thymic deletion escapee CD8⁺ T cells exhibit effector differentiation potentials in the periphery and contribute to graft-versus-leukemia effects in the recipients of H60-mismatched BMT, regressing H60⁺ hematological tumors. These results provide information essential for understanding thymic negative selection and developing a strategy to treat hematological tumors.

Usefulness of Post-Transplant Hematopoietic Chimera Monitoring by Use of the Quantitative Fluorescence Polymerase Chain Reaction Method

BACKGROUND

In the light of an increasing number of hematopoietic stem cell transplantations and more frequent use of reduced-intensity conditioning as preparative regimens for hematopoietic stem cell transplantation, post-transplant cell chimera monitoring is considered a necessity.

METHODS

The quantitative fluorescence polymerase chain reaction method, along with the commercial AmpFSTR SGMPlus kit, was applied in research on hematopoietic chimeras.

RESULTS

The total of 102 patients who had undergone allogenic transplantations were investigated. Chimerism monitoring was commenced on the seventh day after transplantation and lasted up to 12 years in some cases, according to the instituted schedule.

CONCLUSIONS

The kit has been shown to be fully sufficient for determining genetic profiles of recipients and donors and selecting informative markers. The method has been proven effective and satisfactory for assessing quantitative chimeras.

Tolerability and Clinical Activity of Post-Transplantation Azacitidine in Patients Allografted for Acute Myeloid Leukemia Treated on the RICAZA Trial

Disease relapse is the major causes of treatment failure after allogeneic stem cell transplantation (SCT) in patients with acute myeloid leukemia (AML). As well as demonstrating significant clinical activity in AML, azacitidine (AZA) upregulates putative tumor antigens, inducing a CD8(+) T cell response with the potential to augment a graft-versus-leukemia effect. We, therefore, studied the feasibility and clinical sequelae of the administration of AZA during the first year after transplantation in 51 patients with AML undergoing allogeneic SCT. Fourteen patients did not commence AZA either because of transplantation complications or withdrawal of consent. Thirty-seven patients commenced AZA at a median of 54 days (range, 40 to 194 days) after transplantation, which was well tolerated in the majority of patients. Thirty-one patients completed 3 or more cycles of AZA. Sixteen patients relapsed at a median time of 8 months after transplantation. No patient developed extensive chronic graft-versus-host disease. The induction of a post-transplantation CD8(+) T cell response to 1 or more tumor-specific peptides was studied in 28 patients. Induction of a CD8(+) T cell response was associated with a reduced risk of disease relapse (hazard ratio [HR], .30; 95% confidence interval [CI], .10 to .85; P = .02) and improved relapse-free survival (HR, .29; 95% CI, .10 to .83; P = .02) taking into account death as a competing risk. In conclusion, AZA is well tolerated after transplantation and appears to have the capacity to reduce the relapse risk in patients who demonstrate a CD8(+) T cell response to tumor antigens. These observations require confirmation in a prospective clinical trial.

A multigene array for measurable residual disease detection in AML patients undergoing SCT

AML is a diagnosis encompassing a diverse group of myeloid malignancies. Heterogeneous genetic etiology, together with the potential for oligoclonality within the individual patient, have made the identification of a single high-sensitivity marker of disease burden challenging. We developed a multiple gene measurable residual disease (MG-MRD) RQ-PCR array for the high-sensitivity detection of AML, retrospectively tested on 74 patients who underwent allo-SCT at the NHLBI in the period 1994-2012. MG-MRD testing on peripheral blood samples prior to transplantation demonstrated excellent concordance with traditional BM-based evaluation and improved risk stratification for post-transplant relapse and OS outcomes. Pre-SCT assessment by MG-MRD predicted all clinical relapses occurring in the first 100 days after allo-SCT compared with 57% sensitivity using WT1 RQ-PCR alone. Nine patients who were negative for WT1 prior to transplantation were correctly reclassified into a high-risk MG-MRD-positive group, associated with 100% post-transplant mortality. This study provides proof of principle that a multiple gene approach may be superior to the use of WT1 expression alone for AML residual disease detection.

Possible role of minor h antigens in the persistence of donor chimerism after stem cell transplantation; relevance for sustained leukemia remission

Persistent complete donor chimerism is an important clinical indicator for remissions of hematological malignancies after HLA-matched allogeneic stem cell transplantation (SCT). However, the mechanisms mediating the persistence of complete donor chimerism are poorly understood. The frequent coincidence of complete donor chimerism with graft-versus-leukemia effects and graft-versus-host disease suggests that immune responses against minor histocompatibility antigens (mHags) are playing an important role in suppressing the host hematopoiesis after allogeneic SCT. Here, we investigated a possible relationship between donor immune responses against the hematopoiesis-restricted mHag HA-1 and the long-term kinetics of host hematopoietic chimerism in a cohort of 10 patients after allogeneic HLA-matched, HA-1 mismatched SCT. Functional HA-1 specific CTLs (HA-1 CTLs) were detectable in 6/10 patients lysing host-type hematopoietic cells in vitro. Presence of HA-1 CTLs in the peripheral blood coincided with low host hematopoiesis levels quantified by highly sensitive mHag specific PCR. Additionally, co-incubation of host type CD34⁺ cells with HA-1 CTLs isolated after allogeneic SCT prevented progenitor and cobblestone area forming cell growth in vitro and human hematopoietic engraftment in immunodeficient mice. Conversely, absence or loss of HA-1 CTLs mostly coincided with high host hematopoiesis levels and/or relapse. In summary, in this first study, presence of HA-1 CTLs paralleled low host hematopoiesis levels. This coincidence might be supported by the capacity of HA-1 CTLs isolated after allogeneic SCT to specifically eliminate host type hematopoietic stem/progenitor cells. Additional studies involving multiple mismatched mHags in more patients are required to confirm this novel characteristic of mHag CTLs as factor for the persistence of complete donor chimerism and leukemia remission after allogeneic SCT.

Impact of the revised International Prognostic Scoring System, cytogenetics and monosomal karyotype on outcome after allogeneic stem cell transplantation for myelodysplastic syndromes and secondary acute myeloid leukemia evolving from myelodysplastic syndromes: a retrospective multicenter study of the European Society of Blood and Marrow Transplantation

The aim of this study was to determine the impact of the revised 5-group International Prognostic Scoring System cytogenetic classification on outcome after allogeneic stem cell transplantation in patients with myelodysplastic syndromes or secondary acute myeloid leukemia who were reported to the European Society for Blood and Marrow Transplantation database. A total of 903 patients had sufficient cytogenetic information available at stem cell transplantation to be classified according to the 5-group classification. Poor and very poor risk according to this classification was an independent predictor of shorter relapse-free survival (hazard ratio 1.40 and 2.14), overall survival (hazard ratio 1.38 and 2.14), and significantly higher cumulative incidence of relapse (hazard ratio 1.64 and 2.76), compared to patients with very good, good or intermediate risk. When comparing the predictive performance of a series of Cox models both for relapse-free survival and for overall survival, a model with simplified 5-group cytogenetics (merging very good, good and intermediate cytogenetics) performed best. Furthermore, monosomal karyotype is an additional negative predictor for outcome within patients of the poor, but not the very poor risk group of the 5-group classification. The revised International Prognostic Scoring System cytogenetic classification allows patients with myelodysplastic syndromes to be separated into three groups with clearly different outcomes after stem cell transplantation. Poor and very poor risk cytogenetics were strong predictors of poor patient outcome. The new cytogenetic classification added value to prediction of patient outcome compared to prediction models using only traditional risk factors or the 3-group International Prognostic Scoring System cytogenetic classification.

Real-time assessment of relapse risk based on the WT1 marker in acute leukemia and myelodysplastic syndrome patients after hematopoietic cell transplantation

Relapse is the major cause of treatment failure after allogeneic hematopoietic cell transplantation (alloHCT) for acute leukemia and myelodysplastic syndrome (MDS). Wilms' tumor Ag (WT1) is overexpressed in the majority of acute leukemia and MDS patients and has been proposed as a universal diagnostic marker for detection of impending relapse. Comprehensive studies have shown that WT1 transcript levels have predictive value in acute leukemia patients in CR after chemotherapy. However, the focus of this study is the period after alloHCT for predicting relapse onset. We analyzed the accumulation of WT1 mRNA transcripts in PB of 82 leukemia and MDS patients and defined specific molecular ratios for relapse prediction. The extensively validated WT1/c-ABL ratio was used to normalize increases in WT1 transcript levels. The observed lead time of crossing or exceeding set WT1 levels is presented along with linear interpolation to estimate the calculated day the WT1 thresholds were crossed. The WT1/c-ABL transcript ratio of 50 or above yielded 100% specificity and 75% sensitivity reliably predicting future relapse with an observed average of 29.4 days (s.d.=19.8) and a calculated average of 63 days (s.d.=29.3) lead time before morphologic confirmation. A lower ratio of 20 or above gave lower specificity, but higher sensitivity (84.8% and 87.5%, respectively) identified more patients who relapsed, at earlier times, providing an earlier warning with actual average lead time of 49.1 days (s.d.=30.8) and calculated average of 78 days (s.d.=28.8). WT1 transcript levels serve as a diagnostic relapse test with greater sensitivity than the morphologic approach used in the clinic as a readout.

Adoptive immunotherapy with genetically modified lymphocytes in allogeneic stem cell transplantation

Hematopoietic stem cell transplantation from a healthy donor (allo-HSCT) represents the most potent form of cellular adoptive immunotherapy to treat malignancies. In allo-HSCT, donor T cells are double edge-swords: highly potent against residual tumor cells, but potentially highly toxic, and responsible for graft versus host disease (GVHD), a major clinical complication of transplantation. Gene transfer technologies coupled with current knowledge on cancer immunology have generated a wide range of approaches aimed at fostering the immunological response to cancer cells, while avoiding or controlling GVHD. In this review, we discuss cell and gene therapy approaches currently tested in preclinical models and in clinical trials.

Comparison of chimerism and minimal residual disease monitoring for relapse prediction after allogeneic stem cell transplantation for adult acute lymphoblastic leukemia

Little data are available on the relative merits of chimerism and minimal residual disease (MRD) monitoring for relapse prediction after allogeneic hematopoietic stem cell transplantation (HCT). We performed a retrospective analysis of serial chimerism assessments in 101 adult HCT recipients with acute lymphoblastic leukemia (ALL) and of serial MRD assessments in a subgroup of 22 patients. All patients had received myeloablative conditioning. The cumulative incidence of relapse was significantly higher in the patients with increasing mixed chimerism (in-MC) compared with those with complete chimerism, low-level MC, and decreasing MC, but the sensitivity of in-MC detection with regard to relapse prediction was only modest. In contrast, MRD assessment was highly sensitive and specific. Patients with MRD positivity after HCT had the highest incidence of relapse among all prognostic groups analyzed. The median time from MRD positivity to relapse was longer than the median time from detection of in-MC, but in some cases in-MC preceded MRD positivity. We conclude that MRD assessment is a powerful prognostic tool that should be included in the routine post-transplantation monitoring of patients with ALL, but chimerism analysis may provide additional information in some cases. Integration of these tools and clinical judgment should allow optimal decision making with regard to post-transplantation therapeutic interventions.

Feasibility of treating post-transplantation minimal residual disease in children with acute leukemia

Outcomes are poor for patients with hematologic malignancies who experience overt relapse after allogeneic hematopoietic stem cell transplantation (HCT). Data on outcomes of post-transplantation minimal residual disease (MRD) are limited. In this single-institution, retrospective cohort analysis of children with acute leukemia and myelodysplastic syndrome, we document the pattern of relapse with a primary focus on outcomes of post-transplantation MRD. Forty of 93 patients (43%) who underwent a first allogeneic HCT and had systematic pretransplantation and post-transplantation MRD evaluations at +30, +60, +90, +180 days and +1 and +2 years post-transplantation experienced relapse. The median time to relapse was 4.8 months post-transplantation, with a median survival of 4 months post-relapse. Despite frequent, systematic, routine post-HCT disease restaging evaluation, 31 patients (78%) presented with overt disease at the time of relapse. Seven patients with acute leukemia who had post-transplantation MRD presented at a median of 1 month post-transplantation. Owing to rapid disease progression or treatment-related mortality, there was no improvement in survival in those patients whose leukemia was detected in a state of MRD post-transplantation. Our results suggest that early intervention strategies targeting post-transplantation MRD for relapse prevention in acute leukemia may not be feasible.

Relapse assessment following allogeneic SCT in patients with MDS and AML

Options to pre-emptively treat impending relapse of myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML) after allogeneic haematopoietic stem cell transplantation (allo-SCT) continuously increase. In recent years, the spectrum of diagnostic methods and parameters to perform post-transplant monitoring in patients with AML and MDS has grown. Cytomorphology, histomorphology, and chimaerism analysis are the mainstay in any panel of post-transplant monitoring. This may be individually combined with multiparameter flow cytometry (MFC) for the detection of residual cells with a leukaemia phenotype and quantitative real-time polymerase chain reaction (RQ-PCR) to assess gene expression, e.g., of WT1 or the residual mutation load (e.g., in case of an NPM1 mutation). Data evaluating the aforementioned methods alone or in combination are discussed in this review with particular emphasis on data pointing towards their suitability to steer pre-emptive post-transplant interventions such as immunotherapy, chemotherapy or therapy with demethylating agents.

New approaches to manipulate minimal residual disease after allogeneic stem cell transplantation

Minimal residual disease (MRD) is a complex topic that has been studied extensively in hematologic malignancies given its clinical implications related to prognosis. However, methods to monitor and treat MRD, especially after stem cell transplantation, are not well defined and vary in different disease processes. Alternative transplant strategies, such as reduced-intensity conditioning, have altered the way we assess and address MRD after transplantation. Development of new diagnostic tools have allowed for higher sensitivity and specificity of testing. Both targeted chemotherapeutic agents and immunotherapies have been developed to treat MRD in hopes of improving patient outcomes. This article aims to address ways to define and manipulate MRD specifically after stem cell transplantation.

Postallogeneic monitoring with molecular markers detected by pretransplant next-generation or Sanger sequencing predicts clinical relapse in patients with myelodysplastic/myeloproliferative neoplasms

Relapse is the major cause of treatment failure after allogeneic stem-cell transplantation (AHSCT) for patients with myelodysplastic syndrome/myeloproliferative syndrome neoplasms (MDS/MPN). We evaluated the impact of molecular mutations on outcome and the value of molecular monitoring post-transplantation. We screened 45 patients with chronic myelomonocytic leukemia (n = 39 patients, including seven with transformed-acute myeloid leukemia), MDS/MPN unclassifiable (n = 5), and atypical BCR-ABL1-negative CML (n = 1) for mutations in ASXL1, CBL, NRAS, and TET2 genes by molecular genetics including a sensitive next-generation sequencing (NGS) technique. In 36 patients, sufficient DNA was available for molecular analyses. In particular, TET2 and CBL mutations were screened applying amplicon deep sequencing. In 89% of cases, at least one mutation could be detected: ASXL1: n = 18 (50%); CBL: n = 7 (19%); TET2: n = 15 (42%); and NRAS: n = 11 (32%). Survival after AHSCT at 5 yr was 46% (95% CI 28-64%) and was not influenced by any mutation. After a median of 6 months after AHSCT in 33% of the patients, one of the molecular markers was still detectable, resulting in a higher incidence of relapse than in patients with undetectable mutations (50% vs. 15%, P = 0.04). In conclusion, pretransplant molecular mutation analysis can help to detect biomarkers in patients with MPN/MDS, which may be subsequently used as minimal residual disease markers after AHSCT.

Proceedings from the National Cancer Institute's Second International Workshop on the Biology, Prevention, and Treatment of Relapse after Hematopoietic Stem Cell Transplantation: introduction

Despite advances in hematopoietic stem cell transplantation (HSCT) for the treatment of hematologic malignancies, relapse remains the leading cause of death after transplant. Biologic and clinical investigations are needed to combat this primary cause of death after transplantation. The National Cancer Institute held international workshops in 2009 and 2012 to help address this problem. Three major initiatives for coordinated research were proposed: 1) To establish multicenter networks for basic, translational, epidemiologic and clinical research; 2) To establish a network of biorepositories for the collection of samples before and after HSCT to aid in laboratory and clinical studies; and 3) To refine, implement and study proposed definitions for disease-specific response and relapse and for monitoring of minimal residual disease. The workshop in 2012 also featured nine presentations, summaries of which follow in three manuscripts.

Outcome and prognostic factors for patients who relapse after allogeneic hematopoietic stem cell transplantation

Disease relapse remains a major obstacle to the success of allogeneic hematopoietic stem cell transplantation (HSCT), yet little is known about the relevant prognostic factors after relapse. We studied 1080 patients transplanted between 2004 and 2008, among whom 351 relapsed. The 3-year postrelapse overall survival (prOS) rate was 19%. Risk factors for mortality after relapse included shorter time to relapse, higher disease risk index at HSCT, myeloablative conditioning, high pretransplantation comorbidity index, and graft-versus-host disease (GVHD) occurring before relapse. Important prognostic factors did not vary by disease type. Based on this, we could stratify patients into 3 groups, with 3-year prOS rates of 36%, 14%, and 3% (P < .0001). This score was validated in an historical cohort of 276 patients. Postrelapse donor lymphocyte infusion or repeat HSCT was associated with improved prOS, as was the development of GVHD after relapse. These differences remained significant in models that accounted for other prognostic factors and in landmark analyses of patients who survived at least 2 months from relapse. The results of this study may aid with prognostication and management of patients who relapse after HSCT and motivate the design of clinical trials aimed at relapse prevention or treatment in higher-risk patients.

Impact of donor source on hematopoietic cell transplantation outcomes for patients with myelodysplastic syndromes (MDS)

Allogeneic hematopoietic cell transplantation (HCT) from human leukocyte antigen (HLA) matched related donor (MRD) and matched unrelated donors (MUD) produces similar survival for patients with acute myelogenous leukemia. Whether these results can be extended to patients with myelodysplastic syndromes (MDS) is unknown. Therefore, analysis of post-HCT outcomes for MDS was performed. Outcomes of 701 adult MDS patients who underwent HCT between 2002 and 2006 were analyzed (MRD [n = 176], 8 of 8 HLA-A, -B, -C, -DRB1 allele matched MUD [n = 413], 7 of 8 MUD [ n = 112]). Median age was 53 years (range, 22-78 years). In multivariate analyses, MRD HCT recipients had similar disease free survival (DFS) and survival rates compared with 8 of 8 MUD HCT recipients (relative risk [RR] 1.13 [95% confidence interval (CI) 0.91-1.42] and 1.24 [95% CI 0.98-1.56], respectively), and both MRD and 8 of 8 MUD had superior DFS (RR 1.47 [95% CI 1.10-1.96] and 1.29 [95% CI 1.00-1.66], respectively) and survival (RR 1.62 [95% CI 1.21-2.17] and 1.30 [95% CI 1.01-1.68], respectively) compared with 7 of 8 MUD HCT recipients. In patients with MDS, MRD remains the best stem cell source followed by 8 of 8 MUD. Transplantation from 7 of 8 MUD is associated with significantly poorer outcomes.

Proceedings from the National Cancer Institute's Second International Workshop on the Biology, Prevention, and Treatment of Relapse After Hematopoietic Stem Cell Transplantation: part III. Prevention and treatment of relapse after allogeneic transplantation

In the Second Annual National Cancer Institute's Workshop on the Biology, Prevention, and Treatment of Relapse after Hematopoietic Stem Cell Transplantation, the Scientific/Educational Session on the Prevention and Treatment of Relapse after Allogeneic Transplantation highlighted progress in developing new therapeutic approaches since the first relapse workshop. Recent insights that might provide a basis for the development of novel, practical clinical trials were emphasized, including utilization of newer agents, optimization of donor lymphocyte infusion (DLI), and investigation of novel cellular therapies. Dr. de Lima discussed pre-emptive and maintenance strategies to prevent relapse after transplantation, for example, recent promising results suggestive of enhanced graft-versus-tumor activity with hypomethylating agents. Dr. Schmid provided an overview of adjunctive strategies to improve cell therapy for relapse, including cytoreduction before DLI, combination of targeted agents with DLI, and considerations in use of second transplantations. Dr. Porter addressed strategies to enhance T cell function, including ex vivo activated T cells and T cell engineering, and immunomodulatory approaches to enhance T cell function in vivo, including exogenous cytokines and modulation of costimulatory pathways.

Risk-adapted donor lymphocyte infusion based on chimerism and donor source in pediatric leukemia

Donor lymphocyte infusion (DLI) is commonly used to treat leukemia relapse following stem cell transplantation. In florid relapse, however, the efficacy of DLI is limited with substantial risk of severe graft-versus-host disease (GvHD). Here, we develop a novel risk-adapted strategy characterized by pre-emptive DLI initiated at the time of mixed chimerism, a small starting dose based on donor source, dose-escalation guided by real-time chimerism monitoring and withholding of DLI immediately in patients achieving full donor chimerism. A total of 178 DLIs were given to 38 patients with mixed chimerism; thereafter, 33 patients (86.8%) had donor chimerism successfully increased, including 30 (78.9%) who had chimerism fully converted back to 100% donor. Cumulative incidence of relapse was significantly lower (P=0.00004) and overall survival higher (P=0.0003) in patients with chimerism fully corrected as compared with those of patients whose chimerism remained mixed. Only 13.2% of the patients developed acute grade III-IV GvHD with no associated mortality. In conclusion, the risk-adapted DLI strategy is useful in minimizing the risk of childhood leukemia relapse, GvHD and death.

Minimal residual disease in acute myeloid leukaemia

Technological advances in the laboratory have led to substantial improvements in clinical decision making through the introduction of pretreatment prognostic risk stratification factors in acute myeloid leukaemia (AML). Unfortunately, similar progress has not been made in treatment response criteria, with the definition of 'complete remission' in AML largely unchanged for over half a century. Several clinical trials have demonstrated that high-sensitivity measurements of residual disease burden during or after treatment can be performed, that results are predictive for clinical outcome and can be used to improve outcomes by guiding additional therapeutic intervention to patients in clinical complete remission, but at increased relapse risk. We review these recent trials, the characteristics and challenges of the modalities currently used to detect minimal residual disease (MRD), and outline opportunities to both refine detection and improve clinical use of MRD measurements. MRD measurement is already the standard of care in other myeloid malignancies, such as chronic myelogenous leukaemia and acute promyelocytic leukaemia (APL). It is our belief that response criteria for non-APL AML should be updated to include assessment for molecular complete remission and recommendations for post-consolidation surveillance should include regular monitoring for molecular relapse as standard of care.

Minimal residual disease after allogeneic stem cell transplant: a comparison among multiparametric flow cytometry, Wilms tumor 1 expression and chimerism status (Complete chimerism versus Low Level Mixed Chimerism) in acute leukemia

Relapse represents the main cause of treatment failure after allogeneic stem cell transplant (allo-SCT). The detection of minimal residual disease (MRD) by multiparametric flow cytometry (MFC), chimerism, cytogenetics and molecular analysis may be critical to prevent relapse. Therefore, we assessed the overall agreement among chimerism (low level mixed chimerism [LL-MC] vs. complete chimerism [CC]), MFC and Wilms tumor 1 (WT1) mRNA to detect MRD and investigated the impact of MRD obtained from the three methods on patient outcome. Sixty-seven fresh bone marrow (BM) samples from 24 patients (17 acute myeloid leukemia [AML], seven acute lymphoblastic leukemia [ALL]) in complete remission (CR) after allo-SCT were investigated at different time points. A moderate agreement was found among the three techniques investigated. A higher concordance between positive results from MFC (75.0% vs. 32.7%, p = 0.010) and WT1 (58.3% vs. 29.1%, p = 0.090) was detected among LL-MC rather than CC samples. Relapse-free survival (RFS) and overall survival (OS) were found to be higher in MRD negative patients than in MRD positive patients analyzed with MFC and WT1. Our results discourage the use of low autologous signals as the only marker of MRD, and suggest the usefulness of MFC and WT1 real-time quantitative polymerase chain reaction (RQ-PCR) in stratifying patients with respect to risk of relapse.

Cellular therapy following allogeneic stem-cell transplantation

Allogeneic hematopoietic stem-cell transplantation (HSCT) is the most effective approach for many patients with hematologic malignancies. Unfortunately, relapse remains the most common cause of death after allogeneic HSCT, and the prognosis of relapsed disease is poor for most patients. Induction of a graft-versus-leukemia (GVL), or graft-versus-tumor, effect through the use of donor leukocyte infusion (DLI), or donor lymphocyte infusion, has been remarkably successful for relapsed chronic myelogenous leukemia. Unfortunately, response to DLI in other hematologic malignancies is much less common and depends on many factors including histology, pace and extent of relapse, and time from HSCT to relapse. Furthermore, graft-versus-host disease (GVHD) is common after DLI and often limits successful immunotherapy. Ultimately, manipulations to minimize GVHD while preserving or enhancing GVL are necessary to improve outcomes for relapse after allogeneic HSCT.

Genomic loss of mismatched human leukocyte antigen and leukemia immune escape from haploidentical graft-versus-leukemia

Recent developments in cell processing and immunosuppressive strategies has allowed the safe infusion of high numbers of donor T cells in the context of clinical haploidentical hematopoietic stem cell transplantation (HSCT). Haploidentical T cells display an intrinsic ability to recognize and eliminate residual patient leukemic cells, largely due to alloreactivity against the patient-specific human leukocyte antigen (HLA) molecules encoded on the mismatched haplotype. However, recent evidence has shown that leukemia, like many other tumors displaying pronounced genomic instability, is frequently able to evade this potent graft-versus-leukemia effect by undergoing de novo genomic mutations, which result in the permanent loss of only those HLA molecules targeted by haploidentical donor T-cell alloreactivity. This review summarizes the recent clinical and experimental evidence regarding this phenomenon, and its therapeutic and clinical consequences.

ABO chimerism determined by real-time polymerase chain reaction analysis after ABO-incompatible haematopoietic stem cell transplantation

BACKGROUND

The dynamic alteration of ABO blood group in ABO-incompatible haematopoietic stem cell transplantation can be well defined by ABO chimerism analysis. In view of the intrinsic difference in ABO phenotypes or genotypes between donor and recipient in ABO incompatible transplantation, ABO allele-associated nucleotide polymorphic sites could theoretically be used as available informative markers for chimerism analysis.

MATERIALS AND METHODS

We chose nucleotide polymorphism sites (261, 467, 802, 803 and 1,061) of common ABO alleles to use as markers from 76 randomly chosen donors and assessed the limit of linear detection of a specifically designed real-time quantitative polymerase chain reaction using SYBR Green I dye with these sites for a chimerism assay.

RESULTS

We successfully established the real-time quantitative polymerase chain reaction for detecting 261, 467(mutated) and 803 sites and their limits of linear detection, which were at least 10(-3), 10(-2) and 10(-2), respectively. The limits of linear detection between heterozygous DNA and homozygous DNA with 261 or 803 sites were not significantly different.

DISCUSSION

ABO chimerism can be well analysed by real-time polymerase chain reaction with ABO gene-associated nucleotide polymorphic sites. This strategy could be very beneficial for the early and accurate judgement of the crucial point of transition in order to plan a safe transfusion strategy following ABO-incompatible transplantation.

Pretransplant MRD: the light is yellow, not red

In the study reported in this issue of Blood by Leung et al, detectable minimal residual disease (MRD) before hematopoietic stem cell transplantation (HSCT) was found to be prognostic for outcome, but did not prevent cure for children with acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML).

Monitoring of pediatric patients with malignant hematological diseases after allogeneic HSCT: Serbian experience

We describe the implementation of short tandem repeats-polymerase chain reaction (STR-PCR) chimerism analyses coupled with reverse transcription PCR detection of recurrent translocations characteristic for childhood leukemia in monitoring of patients after allogeneic hematopoietic stem cell transplantation in Serbia and the first clinical results thereof. Chimerism and minimal residual disease were regularly analyzed from blood and marrow samples of 26 pediatric patients taken after stem cell transplantation with a median follow-up of 17.6 months. Our results demonstrate that STR-based chimerism monitoring is sufficient in establishing the origin of engrafted cells after transplantation and in detecting graft rejection, but more specific and more sensitive method is necessary for identifying patients with threatening leukemia relapse.

Prognostic and therapeutic implications of minimal residual disease at the time of transplantation in acute leukemia

Relapse remains the major cause of treatment failure after hematopoietic cell transplantation (HCT) in acute leukemia, even in patients transplanted in morphologic CR. Various techniques now enable the sensitive quantification of 'minimal' amounts of residual disease (MRD) in patients with acute leukemia in remission. Numerous studies convincingly demonstrate that MRD at the time of transplantation is a powerful, independent predictor of subsequent relapse, with current detection levels of one leukemic cell in 10(5)-10(6) normal cells being prognostically relevant. This recognition provides the rationale to assign patients with detectable MRD (that is, 'MRD(+)' patients) to intensified therapies before, during, or after transplantation, although data supporting these strategies are still sparse. Limited evidence from observational studies suggests that outcomes with autologous HCT are so poor that MRD(+) patients should preferentially be assigned to allogeneic HCT, which can cure a subgroup of these patients, particularly if unmanipulated (T-cell replete) grafts and/or minimized immunosuppression are used to optimize the graft-vs-leukemia effect. Emerging data suggest that additional therapy with non-cross-resistant agents to decrease residual tumor burden before transplantation in MRD(+) patients might be beneficial. Further, other studies hint at immunotherapy (for example, rapid withdrawal of immunosuppression and/or donor lymphocyte infusions) as a means to prevent overt relapse if patients remain, or become, MRD(+) after HCT. Ultimately, controlled clinical studies are needed to define the value of MRD-directed therapies, and patients should be encouraged to enter such trials.

Diagnostic performance of whole-body MRI for the detection of persistent or relapsing disease in multiple myeloma after stem cell transplantation

OBJECTIVES

To compare the diagnostic performance of whole-body MRI (WBMRI) with haematological parameters for detecting persistent or relapsing disease in patients with multiple myeloma after stem cell transplantation.

METHODS

Sixty-six WBMRI acquisitions were performed in 33 patients with multiple myeloma at two time points after stem cell transplantation. Extent of disease and inter-test dynamics of intra- and extramedullary myeloma manifestations were compared (kappa statistics) with Uniform Response Criteria, comprising haematological parameters.

RESULTS

Using data from 66 sequential WBMRI acquisitions in 33 patients, 10 patients (30.3 %) were classified as having progressive disease and 23 (69.7 %) as being in remission. Eight (80 %) of the ten patients with progressive disease revealed intramedullary lesions, and two patients (20 %) had intra- and extramedullary lesions. WBMRI and laboratory tests were concordant in 26/33 (78.8 %) patients. We found an agreement of 51.2 %, 95 % confidence interval 19.8 %-82.6 %, between results from WBMRI and haematological parameters. WBMRI had a sensitivity of 63.6 %, specificity of 86.4 %, PPV of 70.0 %, NPV of 82.6 % and accuracy of 78.8 % for detection of remission.

CONCLUSIONS

WBMRI allows the detection and exact localisation of intra- and extramedullary myeloma manifestations after stem cell transplantation, but shows only moderate agreement with routinely performed laboratory tests for determination of remission.

Detectable minimal residual disease before hematopoietic cell transplantation is prognostic but does not preclude cure for children with very-high-risk leukemia

In patients with acute leukemia, detection of minimal residual disease (MRD) before allogeneic hematopoietic cell transplantation (HCT) correlates with risk of relapse. However, the level of MRD that is most likely to preclude cure by HCT is unclear, and the benefit of further chemotherapy to reduce MRD before HCT is unknown. In 122 children with very-high-risk acute lymphoblastic leukemia (ALL; n = 64) or acute myeloid leukemia (AML, n = 58), higher MRD levels at the time of HCT predicted a poorer survival after HCT (P = .0019); MRD was an independent prognostic factor in a multivariate analysis (P = .0035). However, the increase in risk of death associated with a similar increment of MRD was greater in ALL than in AML, suggesting that a pretransplantation reduction of leukemia burden would have a higher impact in ALL. At any given MRD level, survival rates were higher for patients treated in recent protocols: the 5-year overall survival for patients with ALL was 49% if MRD was detectable and 88% if it was not and the corresponding rates for patients with AML were 67% and 80%, respectively. Although MRD before HCT is a strong prognostic factor, its impact has diminished and should not be regarded as a contraindication for HCT.