CD34(+) lineage specific donor cell chimerism for the diagnosis and treatment of impending relapse of AML or myelodysplastic syndrome after allo-SCT

CD34 Chimerism Directed Donor Lymphocyte Infusion With or Without Azacitidine Results in Reduced Relapse and Superior Overall Survival When Full Donor Chimerism is Achieved in Allogeneic Stem Cell Transplant Recipients With Acute Myeloid Leukaemia/Myelodysplastic Syndrome

BACKGROUND

Regular monitoring of CD34 donor chimerism (DC) is a highly sensitive method of predicting relapse in allogeneic stem cell transplant (alloHSCT) recipients with AML/MDS. A fall of CD34 DC below 80% is an indicator of ensuing relapse. There are limited studies assessing the efficacy of donor lymphocyte infusion (DLI) triggered by mixed CD34 DC (MDC), in addressing falling chimerism.

PATIENTS AND METHODS

We performed a retrospective analysis of consecutive alloHSCT patients between 2012 to 2023 who received DLI (with or without azacitidine) for CD34 MDC without morphologic relapse at the time of infusion.

RESULTS

Of the 21 patients with follow up CD34 DC available, 14 (66.7%) achieved CD34 full donor chimerism (FDC) following DLI with or without azacitidine (dli-FDC), while 7 (33.3%) did not (dli-MDC). The 2-year cumulative incidence of relapse (CIR) was significantly lower in dli-FDC compared to dli-MDC (21.4% vs. 85.7%, P < 0.001), correlating with superior overall survival (OS; median years not reached vs. 0.67 years [95% CI, 0.58-ND], P < .001). Rates of grade II-IV acute GVHD post-DLI were 14.9%, and moderate-severe cGVHD was 42.8% in the dli-FDC group. The 5-year nonrelapse mortality (NRM) of the dli-FDC group was 7.1% following DLI.

CONCLUSION

Our study shows the restoration of CD34 FDC post-DLI is associated with reduced relapse and improved overall survival, with low NRM.

Prospects and Potential for Chimerism Analysis after Allogeneic Hematopoietic Stem Cell Transplantation

Chimerism analysis after allogeneic hematopoietic stem cell transplantation serves to confirm engraftment, indicate relapse of hematologic malignancy, and attribute graft failure to either immune rejection or poor graft function. Short tandem repeat PCR (STR-PCR) is the prevailing method, followed by quantitative real-time PCR (qPCR), with detection limits of 1-5% and 0.1%, respectively. Chimerism assays using digital PCR or next-generation sequencing, both of which are more sensitive than STR-PCR, are increasingly used. Stable mixed chimerism is usually not associated with poor outcomes in non-malignant diseases, but recipient chimerism may foretell relapse of hematologic malignancies, so higher detection sensitivity may be beneficial in such cases. Thus, the need for and the type of intervention, e.g., immunosuppression regimen, donor lymphocyte infusion, and/or salvage second transplantation, should be guided by donor chimerism in the context of the feature and/or residual malignant cells of the disease to be treated.

Assessment of chimerism by next generation sequencing: A comparison to STR/qPCR methods

Chimerism analysis is used to evaluate patients after allogeneic hematopoietic stem cell transplant (allo-HSCT) for engraftment and minimal measurable residual disease (MRD) monitoring. A combination of short-tandem repeat (STR) and quantitative polymerase chain reaction (qPCR) was required to achieve both sensitivity and accuracy in the patients with various chimerism statuses. In this study, an insertion/deletion-based multiplex chimerism assay by next generation sequencing (NGS) was evaluated using 5 simulated unrelated donor-recipient combinations from 10 volunteers. Median number of informative markers detected was 8 (range = 5 - 11). The limit of quantitation (LoQ) was determined to be 0.1 % recipient. Assay sample number/batch was 10-20 and total assay time was 19-31 h (manual labor = 2.1 h). Additionally, 50 peripheral blood samples from 5 allo-HSCT recipients (related: N = 4; unrelated: N = 1) were tested by NGS and STR/qPCR. Median number of informative markers detected was 7 (range = 4 - 12). Results from both assays demonstrated a strong correlation (Y = 0.9875X + 0.333; R2 = 0.9852), no significant assay bias (difference mean - 0.08), and 100 % concordant detection of percent recipient increase ≥ 0.1 % (indicator of increased relapse risk). NGS-based chimerism assay can support all allo-HSCT for engraftment and MRD monitoring and simplify clinical laboratory workflow compared to STR/qPCR.

Ultrasensitive chimerism enhances measurable residual disease testing after allogeneic hematopoietic cell transplantation

Increasing mixed chimerism (reemerging recipient cells) after allogeneic hematopoietic cell transplant (allo-HCT) can indicate relapse, the leading factor determining mortality in blood malignancies. Most clinical chimerism tests have limited sensitivity and are primarily designed to monitor engraftment. We developed a panel of quantitative polymerase chain reaction assays using TaqMan chemistry capable of quantifying chimerism in the order of 1 in a million. At such analytic sensitivity, we hypothesized that it could inform on relapse risk. As a proof-of-concept, we applied our panel to a retrospective cohort of patients with acute leukemia who underwent allo-HCT with known outcomes. Recipient cells in bone marrow aspirates (BMAs) remained detectable in 97.8% of tested samples. Absolute recipient chimerism proportions and rates at which these proportions increased in BMAs in the first 540 days after allo-HCT were associated with relapse. Detectable measurable residual disease (MRD) via flow cytometry in BMAs after allo-HCT showed limited correlation with relapse. This correlation noticeably strengthened when combined with increased recipient chimerism in BMAs, demonstrating the ability of our ultrasensitive chimerism assay to augment MRD data. Our technology reveals an underappreciated usefulness of clinical chimerism. Used side by side with MRD assays, it promises to improve identification of patients with the highest risk of disease reoccurrence for a chance of early intervention.

Peripheral Blood CD34 Donor Chimerism has Greater Clinical Utility Than CD3 for Detecting Relapse after Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia or Myelodysplastic Syndrome

Monitoring of donor chimerism (DC) may detect early relapse following allogeneic hematopoietic stem cell transplantation (allo-SCT) for acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Most centers use unfractionated peripheral blood or T cells to monitor DC, although CD34⁺ DC may be more predictive. The limited adoption of CD34⁺ DC may be due to the lack of detailed, comparative studies. To address this knowledge gap, we compared peripheral blood CD34⁺ and CD3⁺ DC in 134 patients who underwent allo-SCT for AML or MDS. In July 2011, the Alfred Hospital Bone Marrow Transplantation Service adopted routine monitoring of DC in the lineage-specific CD34⁺ and CD3⁺ cell subsets from peripheral blood at 1, 2, 3, 4, 6, 9, and 12 months post-transplantation for AML or MDS. Immunologic interventions, including rapid withdrawal of immunosuppression, azacytidine, and donor lymphocyte infusion, were prespecified for CD34⁺ DC ≤80%. Overall, CD34⁺ DC ≤80% detected 32 of 40 relapses (positive predictive value [PPV], 68%; negative predictive value [NPV], 91%), compared with 13 of 40 relapses for CD3⁺ DC ≤80% (PPV, 52%; NPV, 75%). Receiver operating characteristic analysis showed the superiority of CD34⁺ DC, with the greatest value at day 120 post-transplantation. CD3⁺ DC provided additional value in only 3 cases, preceding CD34⁺ DC ≤80% by 1 month. We further show that the CD34⁺ DC sample can be used to detect NPM1^mut, with the combination of CD34⁺ DC ≤80% and NPM1^mut identifying the highest risk of relapse. Among the 24 patients in morphologic remission at the time of CD34⁺ DC ≤80%, 13 (54%) responded to immunologic interventions (rapid withdrawal of immunosuppression, azacitidine, or donor lymphocyte infusion) with recovery of CD34⁺ DC >80%, and 11 of these patients remained in complete remission for a median of 34 months (range, 28 to 97 months). In contrast, the other 9 patients did not respond to the clinical intervention and relapsed within a median of 59 days after detecting CD34⁺ DC ≤80%. The CD34⁺ DC was significantly higher in responders than in nonresponders (median, 72% versus 56%; P = .015, Mann-Whitney U test). Overall, monitoring of CD34⁺ DC was considered clinically useful (with early diagnosis of relapse enabling preemptive therapy or predicting low risk of relapse) in 107 of 125 evaluable patients (86%). Our findings show that peripheral blood CD34⁺ DC is feasible and superior to CD3⁺ DC for predicting relapse. It also provides a source of DNA for measurable residual disease testing, which may further stratify the risk of relapse. If validated by an independent cohort, our results suggest that CD34⁺ should be used in preference to CD3⁺ DC for detecting early relapse and guiding immunologic interventions following allo-SCT for AML or MDS.

Allogeneic stem cell transplantation for patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a heterogenous group of clonal hematopoietic stem cell neoplasms primarily affecting older persons, associated with dysplastic changes of bone marrow cells, peripheral cytopenias, and various risk of leukemic transformation. Although treatment with several drugs has shown improved disease control, allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative treatment for MDS. The number of patients receiving a transplant, as well as survival, have increased past years because of the use of reduce-intensity conditioning regimens (RIC) as well as the use of haploidentical donors for transplantation. With treatment-related mortality as main limitation, pre-transplant evaluation is essential to assess risks for this older group of patients. In a recent randomized study, allo-HSCT with RIC for patients >50 years old with higher-risk MDS demonstrated superiority in survival compared with hypomethylating agents. Genetic mutations have been shown to significantly impact treatment outcomes including after transplant. Recently, a transplant-specific risk score (which includes age, donor type, performance status, cytogenetic category, recipient's cytomegalovirus status, percentage of blasts, and platelet count) has shown superiority in transplantation outcome prediction, compared with previous scoring systems. Survival remains low for most patients with TP53 mutations and novel treatment strategies are needed, such as administration of natural killer cells post-transplant, as there is no clear evidence that maintenance therapy after transplantation can improve outcomes.

The mythological chimera and new era of relapse prediction post-transplant

Allogeneic hemopoietic stem cell transplantation is the treatment of choice for high-risk or relapsed acute leukemia. However, unfortunately, relapse post-transplant continues to be the most common cause of treatment failure with 20-80% of patients relapsing based on disease risk and status at transplant. Advances in molecular profiling of different hematological malignancies have enabled us to monitor low level disease before and after transplant and develop a more personalized approach to the management of these disease including early detection post-transplant. While, in general, detectable disease by morphology remains the gold standard to diagnosing relapse, multiple approaches have allowed detection of cancer cells earlier, using peripheral blood-based methods with sensitivities as high as 1:10⁶, together called minimal/measurable residual disease (MRD) detection. However, a in significant number of patients with acute leukemia where no such molecular markers exist it remains challenging to detect early relapse. In such patients who receive transplantation, chimerism monitoring remains the only option. An increase in mixed chimerism in post allogeneic HCT patients has been correlated with relapse in multiple studies. However, chimerism monitoring, while commonly accepted as a tool for assessing engraftment, has not been routinely used for relapse detection, at least in part because of the lack of standardized, high sensitivity, reliable methods for chimerism detection. In this paper, we review the various methods employed for MRD and chimerism detection post-transplant and discuss future trends in MRD and chimerism monitoring from the viewpoint of the practicing transplant physician.

Incomplete chimerism following myeloablative and anti-thymocyte globulin-conditioned hematopoietic cell transplantation is a risk factor for relapse and chronic graft-versus-host disease

BACKGROUND AIMS

The value of routine chimerism determination after myeloablative hematopoietic cell transplantation (HCT) is unclear, particularly in the setting of anti-thymocyte globulin (ATG)-based graft-versus-host disease (GVHD) prophylaxis.

METHODS

Blood samples were collected at 3 months post-HCT from 558 patients who received myeloablative conditioning and ATG-based GVHD prophylaxis. Chimerism was assessed using multiplex polymerase chain reaction of short tandem repeats in sorted T cells (CD3+) and leukemia lineage cells (CD13+CD33+ for myeloid malignancies and CD19+ for B-lymphoid malignancies). ATG exposure was determined using a flow cytometry-based assay. The primary outcomes of interest were relapse and chronic GVHD (cGVHD).

RESULTS

Incomplete (<95%) T-cell chimerism and leukemia lineage chimerism were present in 17% and 4% of patients, respectively. Patients with incomplete T-cell chimerism had a significantly greater incidence of relapse (36% versus 22%, subhazard ratio [SHR] = 2.03, P = 0.001) and lower incidence of cGVHD (8% versus 25%, SHR = 0.29, P < 0.001) compared with patients with complete chimerism. In multivariate modeling, patients with high post-transplant ATG area under the curve and any cytomegalovirus (CMV) serostatus other than donor/recipient seropositivity (non-D+R+) had an increased likelihood of incomplete T-cell chimerism. Patients with incomplete leukemia lineage chimerism had a significantly greater incidence of relapse (50% versus 23%, SHR = 2.70, P = 0.011) and, surprisingly, a greater incidence of cGVHD (45% versus 20%, SHR = 2.64, P = 0.003).

CONCLUSIONS

High post-transplant ATG exposure and non-D+R+ CMV serostatus predispose patients to incomplete T-cell chimerism, which is associated with an increased risk of relapse. The increased risk of cGVHD with incomplete B-cell/myeloid chimerism is a novel finding that suggests an important role for recipient antigen-presenting cells in cGVHD pathogenesis.

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.

Chimerism analysis for clinicians: a review of the literature and worldwide practices

This review highlights literature pertinent to chimerism analysis in the context of hematopoietic cell transplantation (HCT). We also conducted a survey of testing practices of program members of CIBMTR worldwide. Questions included testing methods, time points, specimen type, cell lineage tested and testing indications. Recent literature suggests that detection of low level mixed chimerism has a clinical utility in predicting relapse. There is also increasing recognition of HLA loss relapse to potentially guide rescue decisions in cases of relapse. These developments coincide with wider access to high sensitivity next generation sequencing (NGS) in clinical laboratories. Our survey revealed a heterogeneity in practices as well as in findings and conclusions of published studies. Although the most commonly used method is STR, studies support more sensitive methods such as NGS, especially for predicting relapse. There is no conclusive evidence to support testing chimerism in BM over PB, particularly when using a high sensitivity testing method. Periodic monitoring of chimerism especially in diagnoses with a high risk of relapse is advantageous. Lineage specific chimerism is more sensitive than whole blood in predicting impending relapse. Further studies that critically assess how to utilize chimerism testing results will inform evidence based clinical management decisions.

Long-Term Mixed Chimerism After Ex Vivo/In Vivo T Cell-Depleted Allogeneic Hematopoietic Cell Transplantation in Patients With Myeloid Neoplasms

In patients who have undergone allogeneic hematopoietic cell transplantation (HCT), myeloid mixed donor chimerism (MC) is a risk factor for disease relapse. In contrast, several studies found favorable outcome in patients with lymphoid MC. Thus far, most studies evaluating MC focused on a short-term follow-up period. Here, we report the first case series of long-term survivors with MC. We screened 1,346 patients having undergone HCT for myeloid neoplasms at our center from 1996 to 2016; 443 patients with data on total peripheral blood mononuclear cells (PBMC)/CD4⁺/CD34⁺ short tandem repeat (STR) donor chimerism (DC) and follow-up ≥24 months post-HCT were included. We identified 10 patients with long-term MC (PBMC DC <95% at ≥12 months post-HCT). Median follow-up was 11 years. All patients had received combined ex vivo/in vivo T cell-depleted (TCD) peripheral blood stem cells; none experienced ≥grade 2 acute graft-versus-host disease (GVHD). The mean total PBMC, CD4⁺, and CD34⁺ DC of all patients were 95.88%, 85.84%, and 90.15%, respectively. Reduced-intensity conditioning (RIC) was associated with a trend to lower mean total DC. Of note, two patients who experienced relapse had lower CD34⁺ DC but higher CD4⁺ DC as compared with patients in continuous remission. Bone marrow evaluation revealed increased CD4⁺/FOXP3⁺ cells in patients with MC, which might indicate expansion of regulatory T cells (T_regs). Our results support known predictive factors associated with MC such as RIC and TCD, promote the value of CD34⁺ MC as a potential predictor of relapse, highlight the potential association of CD4⁺ MC with reduced risk of GVHD, and indicate a possible role of T_regs in the maintenance of immune tolerance post-HCT.

Myelodysplastic syndromes: Biological and therapeutic consequences of the evolving molecular aberrations landscape

Myelodysplastic syndromes (MDS) are clonal hematopoietic disorders with heterogeneous presentation, ranging from indolent disease courses to aggressive diseases similar to acute myeloid leukemia (AML). Approximately 90% of MDS patients harbor recurrent mutations , which – with the exception of mutated SF3B1 –have not (yet) been included into the diagnostic criteria or risk stratification for MDS. Accumulating evidence suggests their utility for diagnostic workup, treatment indication and prognosis. Subsequently, in patients with unexplained cytopenia or dysplasia identification of these mutations may lead to earlier diagnosis. The acquisition and expansion of additional driver mutations usually antecedes further disease progression to higher risk MDS or secondary AML and thus, can be clinically helpful to detect individuals that may benefit from aggressive treatment approaches. Here, we review our current understanding of somatic gene mutations, gene expression patterns and flow cytometry regarding their relevance for disease evolution from pre-neoplastic states to MDS and potentially AML.

Effective Immunosurveillance After Allogeneic Hematopoietic Stem Cell Transplantation in Acute Myeloid Leukemia

The number of patients receiving allogeneic hematopoietic stem cell transplantation (alloHCT) has increased constantly over the last years due to advances in transplant technology development, supportive care, transplant safety, and donor availability. Currently, acute myeloid leukemia (AML) is the most frequent indication for alloHCT. However, disease relapse remains the main cause of therapy failure. Therefore, concepts of maintaining and, if necessary, reinforcing a strong graft-versus-leukemia (GvL) effect is crucial for the prognosis and long-term survival of the patients. Over the last decades, it has become evident that effective immunosurveillance after alloHCT is an entangled complex of donor-specific characteristics, leukemia-associated geno- and phenotypes, and acquired resistance mechanisms. Furthermore, adoption of effector cells such as natural killer (NK) cells, alloreactive and regulatory T-cells with their accompanying receptor repertoire, and cell–cell interactions driven by messenger molecules within the stem cell and the bone marrow niche have important impact. In this review of pre- and posttransplant elements and mechanisms of immunosurveillance, we highlight the most important mechanisms after alloHCT.

A practical guide to chimerism analysis: Review of the literature and testing practices worldwide

BACKGROUND AND PURPOSE

Currently there are no widely accepted guidelines for chimerism analysis testing in hematopoietic cell transplantation (HCT) patients. The objective of this review is to provide a practical guide to address key aspects of performing and utilizing chimerism testing results. In developing this guide, we conducted a survey of testing practices among laboratories that are accredited for performing engraftment monitoring/chimerism analysis by either the American Society for Histocompatibility & Immunogenetics (ASHI) and/or the European Federation of Immunogenetics (EFI). We interpreted the survey results in the light of pertinent literature as well as the experience in the laboratories of the authors.

RECENT DEVELOPMENTS

In recent years there has been significant advances in high throughput molecular methods such as next generation sequencing (NGS) as well as growing access to these technologies in histocompatibility and immunogenetics laboratories. These methods have the potential to improve the performance of chimerism testing in terms of sensitivity, availability of informative genetic markers that distinguish donors from recipients as well as cost.

SUMMARY

The results of the survey revealed a great deal of heterogeneity in chimerism testing practices among participating laboratories. The most consistent response indicated monitoring of engraftment within the first 30 days. These responses are reflective of published literature. Additional clinical indications included early detection of impending relapse as well as identification of cases of HLA-loss relapse.

Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia: Who, When, and How?

Although the majority of patients with acute myeloid leukemia (AML) treated with intensive chemotherapy achieve a complete remission (CR), many are destined to relapse if treated with intensive chemotherapy alone. Allogeneic stem cell transplant (allo-SCT) represents a pivotally important treatment strategy in fit adults with AML because of its augmented anti-leukemic activity consequent upon dose intensification and the genesis of a potent graft-versus-leukemia effect. Increased donor availability coupled with the advent of reduced intensity conditioning (RIC) regimens has dramatically increased transplant access and consequently allo-SCT is now a key component of the treatment algorithm in both patients with AML in first CR (CR1) and advanced disease. Although transplant related mortality has fallen steadily over recent decades there has been no real progress in reducing the risk of disease relapse which remains the major cause of transplant failure and represents a major area of unmet need. A number of therapeutic approaches with the potential to reduce disease relapse, including advances in induction chemotherapy, the development of novel conditioning regimens and the emergence of the concept of post-transplant maintenance, are currently under development. Furthermore, the use of genetics and measurable residual disease technology in disease assessment has improved the identification of patients who are likely to benefit from an allo-SCT which now represents an increasingly personalized therapy. Future progress in optimizing transplant outcome will be dependent on the successful delivery by the international transplant community of randomized prospective clinical trials which permit examination of current and future transplant therapies with the same degree of rigor as is routinely adopted for non-transplant therapies.

Development and performance of a next generation sequencing (NGS) assay for monitoring of mixed chimerism

The aim of this study was to evaluate the performance of a novel NGS-based assay to monitor mixed chimerism (MC) and compare its technical capacity to established techniques for chimerism analysis. Artificial and clinical samples with increasing amounts of patient DNA were compared using real-time PCR detection of indels and SNP, fragment analysis of short-tandem repeats (STR) and NGS analysis of indels. Real-time PCR displayed excellent sensitivity (>0,01%) but poor accuracy (>20 CV% at MC > 20%), while fragment analysis exhibited good accuracy (<5 CV% at MC > 20%) with limited sensitivity (>2,5%). In contrast, NGS chimerism demonstrated a sensitivity (>0,1%) equal to real-time PCR and an accuracy equal or better than STR analysis throughout an extensive range of mixed chimerism (0,1 - 100%). To evaluate performance of the separate techniques for chimerism determination, 75 retrospective patient monitoring samples (3-7 weeks post-HSCT) with low (<5%), intermediate (5-20%) or high mixed chimerism (>20%) were analyzed. The between run precision for the NGS assay varied from 0,72% (>20% MC) to 7,38% (MC < 5%). In conclusion, NGS displayed a combination of high sensitivity with good accuracy in both artificial and clinical chimerism samples.

Genetics of progression from MDS to secondary leukemia

Our understanding of the genetics of acute myeloid leukemia (AML) development from myelodysplastic syndrome (MDS) has advanced significantly as a result of next-generation sequencing technology. Although differences in cell biology and maturation exist between MDS and AML secondary to MDS, these 2 diseases are genetically related. MDS and secondary AML cells harbor mutations in many of the same genes and functional categories, including chromatin modification, DNA methylation, RNA splicing, cohesin complex, transcription factors, cell signaling, and DNA damage, confirming that they are a disease continuum. Differences in the frequency of mutated genes in MDS and secondary AML indicate that the order of mutation acquisition is not random during progression. In almost every case, disease progression is associated with clonal evolution, typically defined by the expansion or emergence of a subclone with a unique set of mutations. Monitoring tumor burden and clonal evolution using sequencing provides advantages over using the blast count, which underestimates tumor burden, and could allow for early detection of disease progression prior to clinical deterioration. In this review, we outline advances in the study of MDS to secondary AML progression, with a focus on the genetics of progression, and discuss the advantages of incorporating molecular genetic data in the diagnosis, classification, and monitoring of MDS to secondary AML progression. Because sequencing is becoming routine in the clinic, ongoing research is needed to define the optimal assay to use in different clinical situations and how the data can be used to improve outcomes for patients with MDS and secondary AML.

Monitoring minimal residual/relapsing disease after allogeneic haematopoietic stem cell transplantation in adult patients with acute lymphoblastic leukaemia

Relapse after allogeneic haematopoietic stem cell transplantation (SCT) is a major cause of death in patients with acute lymphoblastic leukaemia (ALL). Here, we retrospectively analysed the contributions of lineage-sorted donor cell chimerism (sDCC) and quantitative PCR (qPCR) targeting disease-specific genetic rearrangements to detect minimal residual/relapsing disease (MRD) and predict impending relapse in 94 adult ALL patients after SCT. With a median follow-up of surviving patients (n = 61) of 3.3 years, qPCR and/or sDCC measurements turned positive in 38 patients (40%). Of these, 22 patients relapsed and 16 remained in complete remission. At 3 years, qPCR and/or sDCC positive patients showed an increased incidence of relapse (50% vs. 4%, p < 0.0001), decreased relapse-free survival (RFS, 40% vs. 85%, p < 0.0001), and decreased overall survival (OS, 47% vs. 87%, p 0.004). Both, qPCR and sDCC pre-detected 11 of 21 relapses occurring within the first two years after SCT and, overall, complemented for each other method in four of the relapsing and four of the non-relapsing cases. Patients receiving pre-emptive MRD-driven interventions (n = 11) or not (n = 10) showed comparable median times until relapse, RFS, and OS. In our single centre cohort, qPCR and sDCC were similarly effective and complementary helpful to indicate haematological relapse of ALL after SCT.

Quantitative chimerism in CD3-negative mononuclear cells predicts prognosis in acute myeloid leukemia patients after hematopoietic stem cell transplantation

Relapse is a major complication of acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (SCT). The objective of our study was to evaluate chimerism monitoring on the CD3-negative mononuclear cells by RQ-PCR to predict relapse of patients allografted for AML and to compare its performance with WT1 quantification. A cohort of 100 patients undergoing allogenic SCT for AML was retrospectively analyzed in a single institution. Patients without complete chimerism, defined as less than 0.01% of recipient's DNA in CD3-negative cells, had a significantly higher risk of relapse and a lower overall survival (p < 0.001). An increase in the percentage of recipient DNA in CD3-negative cells was associated with an increased risk of relapse (p < 0.001) but not with overall survival. Comparable performances between monitoring of CD3-negative cell chimerism and WT1 expression to predict relapse was observed up to more than 90 days before hematological relapse, with sensitivity of 82% and 78%, respectively, and specificity of 100% for both approaches. Quantitative specific chimerism of the CD3-negative mononuclear fraction, enriched in blastic cells, is a new and powerful tool for monitoring measurable residual disease and could be used for AML patients without available molecular markers.

Earlier relapse detection after allogeneic haematopoietic stem cell transplantation by chimerism assays: Digital PCR versus quantitative real-time PCR of insertion/deletion polymorphisms

Background

The analysis of molecular haematopoietic chimerisms (HC) has become a well-established method to monitor the transplant evolution and to assess the risk of relapse after allogeneic stem cells transplantation (allo-STC). Different techniques and molecular markers are being used for chimerism surveillance after transplantation, including quantitative real-time PCR (qPCR) and the recently developed digital PCR (dPCR). This study aims to compare the sensitivity and accuracy of both methods to quantify HC and predict early relapse.

Methodology

HC was evaluated using custom PCR systems for the specific detection of the Y-chromosome, null alleles and insertion-deletion polymorphisms. A total of 281 samples from 28 adult patients who underwent an allo-SCT were studied. Increasing mixed chimerism was detected prior to relapse in 100% of patients (18 relapses).

Results

Compared with conventional qPCR amplification, dPCR predicted relapse with a median anticipation period of 63 days versus 45.5 days by qPCR. Overall, 56% of the relapses were predicted earlier with dPCR whereas 38% of the relapses where detected simultaneously using both techniques and only in 1 case, relapse was predicted earlier with qPCR.

Conclusions

In conclusion, chimerism determination by dPCR constitutes a suitable technique for the follow-up of patients with haematological pathologies after allo-STC, showing greater sensitivity to predict an early relapse.

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.

Mutation Clearance after Transplantation for Myelodysplastic Syndrome

BACKGROUND

Allogeneic hematopoietic stem-cell transplantation is the only curative treatment for patients with myelodysplastic syndrome (MDS). The molecular predictors of disease progression after transplantation are unclear.

METHODS

We sequenced bone marrow and skin samples from 90 adults with MDS who underwent allogeneic hematopoietic stem-cell transplantation after a myeloablative or reduced-intensity conditioning regimen. We detected mutations before transplantation using enhanced exome sequencing, and we evaluated mutation clearance by using error-corrected sequencing to genotype mutations in bone marrow samples obtained 30 days after transplantation. In this exploratory study, we evaluated the association of a mutation detected after transplantation with disease progression and survival.

RESULTS

Sequencing identified at least one validated somatic mutation before transplantation in 86 of 90 patients (96%); 32 of these patients (37%) had at least one mutation with a maximum variant allele frequency of at least 0.5% (equivalent to 1 heterozygous mutant cell in 100 cells) 30 days after transplantation. Patients with disease progression had mutations with a higher maximum variant allele frequency at 30 days than those who did not (median maximum variant allele frequency, 0.9% vs. 0%; P<0.001). The presence of at least one mutation with a variant allele frequency of at least 0.5% at day 30 was associated with a higher risk of progression (53.1% vs. 13.0%; conditioning regimen-adjusted hazard ratio, 3.86; 95% confidence interval [CI], 1.96 to 7.62; P<0.001) and a lower 1-year rate of progression-free survival than the absence of such a mutation (31.3% vs. 59.3%; conditioning regimen-adjusted hazard ratio for progression or death, 2.22; 95% CI, 1.32 to 3.73; P=0.005). The rate of progression-free survival was lower among patients who had received a reduced-intensity conditioning regimen and had at least one persistent mutation with a variant allele frequency of at least 0.5% at day 30 than among patients with other combinations of conditioning regimen and mutation status (P≤0.001). Multivariate analysis confirmed that patients who had a mutation with a variant allele frequency of at least 0.5% detected at day 30 had a higher risk of progression (hazard ratio, 4.48; 95% CI, 2.21 to 9.08; P<0.001) and a lower 1-year rate of progression-free survival than those who did not (hazard ratio for progression or death, 2.39; 95% CI, 1.40 to 4.09; P=0.002).

CONCLUSIONS

The risk of disease progression was higher among patients with MDS in whom persistent disease-associated mutations were detected in the bone marrow 30 days after transplantation than among those in whom these mutations were not detected. (Funded by the Leukemia and Lymphoma Society and others.).

Early tapering of immunosuppressive agents after HLA-matched donor transplantation can improve the survival of patients with advanced acute myeloid leukemia

Disease recurrence is the most important obstacle to achieve long-term survival for patients with advanced acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). In order to reduce the relapse risk and improve the survival, the strategy of early tapering of immunosuppressive agents was prospectively evaluated. Thirty-one patients with advanced AML received early tapering of immunosuppressive drugs, while 32 patients with AML in complete remission (CR) were given the routine tapering of immunosuppressive agents after HLA-matched donor transplantation. All advanced AML patients achieved CR after allo-HSCT. At 24 months after transplantation, relapse incidences were 22% in advanced group and 16% in CR group (P = 0.553); disease-free survival (DFS) and overall survival (OS) were 57.7 and 57.8% in advanced group, while in CR group were 66.6% (P = 0.388) and 66.2% (P = 0.423); immunosuppressive agent-free DFS (IDFS) were similar between two groups (P = 0.407). Acute graft-versus-host disease (aGvHD) incidences were similar between two groups (P = 0.311). Chronic GvHD (cGvHD) incidence was much higher in advanced group than in CR group (70.4 vs 38.7%, P = 0.02), but severe cGvHD had no difference. In multivariate analysis, cGvHD was an independent prognostic factor for lower risk of relapse and better DFS and OS; early tapering of immunosuppressive agents was an independent prognostic factor for cGvHD. The study suggested that advanced AML patients could be directly treated with allo-HSCT and its survival could be improved through the strategy of early tapering of immunosuppressive agents without significant adverse effects ( Clinicaltrials.org NCT03150134).

Targeting interleukin-2 to the bone marrow stroma for therapy of acute myeloid leukemia relapsing after allogeneic hematopoietic stem cell transplantation

The antibody-based delivery of IL2 to extracellular targets expressed in the easily accessible tumor-associated vasculature has shown potent antileukemic activity in xenograft and immunocompetent murine models of acute myelogenous leukemia (AML), especially in combination with cytarabine. Here, we report our experience with 4 patients with relapsed AML after allogeneic hematopoietic stem cell transplantation (allo-HSCT), who were treated with the immunocytokine F16-IL2, in combination with low-dose cytarabine. One patient with disseminated extramedullary AML lesions achieved a complete metabolic response identified by PET/CT, which lasted 3 months. Two of 3 patients with bone marrow relapse achieved a blast reduction with transient molecular negativity. One of the 2 patients enjoyed a short complete remission before AML relapse occurred 2 months after the first infusion of F16-IL2. In line with a site-directed delivery of the cytokine, F16-IL2 led to an extensive infiltration of immune effector cells in the bone marrow. Grade 2 fevers were the only nonhematologic side effects in 2 patients. Grade 3 cytokine-release syndrome developed in the other 2 patients but was manageable in both cases with glucocorticoids. The concept of specifically targeting IL2 to the leukemia-associated stroma deserves further evaluation in clinical trials, especially in patients who relapse after allo-HSCT.

Chimerism-based pre-emptive immunotherapy with fast withdrawal of immunosuppression and donor lymphocyte infusions after allogeneic stem cell transplantation for pediatric hematologic malignancies

The presence of increasing host chimerism or persistent mixed chimerism (MC) after hematopoietic stem cell transplantation for leukemia in children is a predictor of relapse. To reduce the risk of relapse, we prospectively studied post-transplantation chimerism-based immunotherapy (IT) using fast withdrawal of immunosuppression (FWI) and donor lymphocyte infusions (DLI) in children with early post-transplantation MC. Forty-three children with hematologic malignancies at 2 institutions were enrolled prospectively in this study from 2009 until 2012 and were followed for a mean of 42 (SD, 10) months. Twelve patients (28%) were assigned to the observation arm based on the presence of graft-versus-host disease (GVHD) or full donor chimerism (FDC), and 5 (12%) sustained early events and could not undergo intervention. Twenty-six (60%) patients with MC were assigned to IT with FWI, which started at a median of 49 days (range, 35 to 85 days) after transplantation. Fourteen patients proceeded to DLI after FWI. Toxicities of treatment included GVHD, which developed in 19% of patients undergoing intervention, with 1 of 26 (4%) dying from GVHD and 1 (4%) still requiring therapy for chronic GVHD 21 months after DLI. Patients with MC undergoing IT had similar 2-year event-free survival (EFS) (73%; 95% confidence interval (CI), 55% to 91%) compared with patients who achieved FDC spontaneously (83%; 95% CI, 62% to 100%); however, because 50% of all relapses in the IT occurred later than 2 years after transplantation, the EFS declined to 55% (95% CI, 34% to 76%) at 42 (SD, 11) months. There were no late relapses in the observation group. EFS in the entire cohort was 58% (95% CI, 42% to 73%) at 42 (SD, 11) months after transplantation. Evidence of disease before transplantation remained a significant predictor of relapse, whereas development of chronic GVHD was protective against relapse.

Treatment strategies in patients with AML or high-risk myelodysplastic syndrome relapsed after Allo-SCT

Non-relapse mortality after Allo-SCT has significantly decreased over the last years. Nevertheless, relapse remains a major cause for post SCT mortality in patients with AML and high-risk myelodysplastic syndrome (MDS). In this retrospective single-center analysis, we have analyzed the treatment outcomes of 108 patients with AML or MDS, who relapsed after Allo-SCT. Seventy of these patients (65%) were treated with salvage therapies containing chemotherapy alone, allogeneic cell-based treatment or the combination of both. Thirty-eight patients (35%) received palliative treatment. Median OS after diagnosis of relapse was 130 days. Compared with patients who received chemotherapy alone, response to salvage therapy was significantly improved in patients treated with a combination of chemo- and allogeneic cell-based therapy (CR rate 57% vs 13%, P=0.002). Among risk factors concerning pretreatment characteristics, disease status before first Allo-SCT, and details of transplantation, only the time interval from Allo-SCT to relapse was an independent predictor of response to salvage therapy and OS. These data confirmed that time to relapse after transplantation is an important prognostic factor. Up to now, only patients eligible for treatment regimens containing allogeneic cell-based interventions achieved relevant response rates.

Early donor chimerism levels predict relapse and survival after allogeneic stem cell transplantation with reduced-intensity conditioning

The success of hematopoietic stem cell transplantation (HSCT) with reduced-intensity conditioning (RIC) is limited by a high rate of disease relapse. Early risk assessment could potentially improve outcomes by identifying appropriate patients for preemptive strategies that may ameliorate this high risk. Using a series of landmark analyses, we investigated the predictive value of early (day-30) donor chimerism measurements on disease relapse, graft-versus-host disease, and survival in a cohort of 121 patients allografted with a uniform RIC regimen. Chimerism levels were analyzed as continuous variables. In multivariate analysis, day-30 whole blood chimerism levels were significantly associated with relapse (hazard ratio [HR] = .90, P < .001), relapse-free survival (HR = .89, P < .001), and overall survival (HR = .94, P = .01). Day-30 T cell chimerism levels were also significantly associated with relapse (HR = .97, P = .002), relapse-free survival (HR = .97, P < .001), and overall survival (HR = .99, P = .05). Multivariate models that included T cell chimerism provided a better prediction for these outcomes compared with whole blood chimerism. Day-30 chimerism levels were not associated with acute or chronic graft-versus-host disease. We found that high donor chimerism levels were significantly associated with a low lymphocyte count in the recipient before transplant, highlighting the impact of pretransplant lymphopenia on the kinetics of engraftment after RIC HSCT. In summary, low donor chimerism levels are associated with relapse and mortality and can potentially be used as an early predictive and prognostic marker. These findings can be used to design novel approaches to prevent relapse and to improve survival after RIC HSCT.

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.

Allogeneic transplantation in the UK: an aggregation of marginal gains?

A number of advances in clinical practice that are considered routine in modern allogeneic transplant programmes lack definitive supporting evidence, partly because they may offer modest incremental benefits that are difficult to demonstrate in a statistically robust manner given the relatively small cohorts of patients who undergo such procedures. Nevertheless, these marginal gains probably contribute therapeutically meaningful overall benefit, particularly when aggregated. We review the evidence for a number of these practices in terms of impact on transplant outcomes, with particular reference to the setting of T cell depletion as widely practiced in the United Kingdom, including high resolution tissue typing, surveillance for and therapy of infectious complications, chimerism-directed immune modulation and more sensitive monitoring for residual or progressive disease.