Mixed hematopoietic chimerism after allogeneic bone marrow transplantation: the impact of quantitative PCR analysis for prediction of relapse and graft rejection in children

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.

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.

CD19+ lineage chimerism, an early biomarker after anti-CD19 CAR-T cell therapy in patients previously receiving a hematopoietic stem cell transplantation

Treatment targeting CD19 by a chimeric antigen receptor expressed on T cells (anti-CD19 CAR-T) has led to a breakthrough in the management and treatment of relapsed and refractory B- cell acute lymphoblastic leukemia (B-ALL). After infusion, the efficacy of anti-CD19 CAR-T is monitored by bone marrow negative minimal residual disease and the absence of peripheral CD19⁺ B lymphocytes (B-cell aplasia). In patients who have received an allogenic Hematopoietic Stem Cell Transplantation (HSCT) prior to treatment with anti-CD19 CAR-T, monitoring lineage-specific chimerism could be helpful. We found that on 4 patients who received anti-CD19 CAR-T cells after HSCT and achieved early complete response, CD19⁺ lineage mixed chimerism but not CD3⁺ lineage mixed chimerism monitored by molecular techniques anticipated earlier than B-cell aplasia determined by flow cytometry, lack of effectiveness of anti-CD19 CAR-T and leukemia relapse. Donor lymphocyte infusions (DLIs) did not prevent relapse but recovered CD3⁺ full donor chimerism. We suggest that continuous lineage chimerism analysis should be done routinely in patients who receive anti-CD19 CAR-T cells after HSCT and achieve complete remission because it can support early treatment intervention. However, the role of DLI in this setting is unclear, so further prospective studies should be developed.

The incidence, clinical outcome, and protective factors of mixed chimerism following hematopoietic stem cell transplantation for severe aplastic anemia

OBJECTIVES

The aim of our study was to determine possible predictors and clinical course of mixed chimerism (MC) in aplastic anemia after transplantation.

METHODS

A total of 207 transplants were obtained from haploidentical donors (HID) using busulfan (Bu), cyclophosphamide (Cy), and anti-thymocyte globulin (ATG) regimens, and 69 transplants from matched related donors (MRD) and 29 transplants from unrelated donors (URD) using Cy/ATG regimens were obtained.

RESULTS

Incidences of MC were 1.93 ± 0.01%, 20.29 ± 0.01%, and 35.71 ± 0.01% in HID, MRD, and URD transplantation (p < .001). In multivariate analysis, incidence of MC was significantly higher in patients without adding Bu in conditioning (p < .001) and receiving a lower number of CD3 + cells in graft (p = .042). MC was associated with significantly lower II-IV aGvHD (3.70% vs. 27.7%, p = .007), but higher secondary graft rejection rates (14.8% vs. 0.4%, p < .001) and poorer overall survival (72.7 ± 8.9% vs. 89.6 ± 2.0%, p = .011) than those of donor chimerism cohort.

CONCLUSIONS

Mixed chimerism was an unsettling status even in non-malignancy. Haploidentical transplantation with more intense regimen by adding Bu to Cy and ATG was associated with reduced MC following HSCT for SAA. An intensified regimen should be explored in matched related or unrelated donors.

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.

Different aspects of stem cell procedures in children with poor responding AML: when is HSCT the best answer?

Acute myeloid leukemia in children is a heterogeneous disease with different morphological and cytogenetic features. New diagnostic tools and treatments, improved supportive care and the use of genomic tissue typing in selecting donors for hematopoietic stem cell transplantation (HSCT) adds to increased survival rates. Candidates to HSCT in first complete remission are patients with cytogenetic or molecular unfavorable prognostic markers, or blasts >15% after first induction. The use of minimal residual disease can also identify children benefiting from HSCT in first complete remission and the patients post HSCT with signs of relapse. The outcome and cure rate of acute myeloid leukemia, still remains poor and new diagnostic tools and treatments strategies need to be evaluated. In this management perspective, future management of novel minimal residual disease tools are discussed, conditioning therapies, as well as different transplantation procedures including haplo-transplantation and haplo-identical natural killer cell transplantation, but also altered graft-versus-host-disease treatments.

Monitoring of hematopoietic chimerism by real-time quantitative PCR of micro insertions/deletions in samples with low DNA quantities

BACKGROUND

Sensitive and accurate methods to detect hematopoietic chimerism after hematopoietic stem cell transplantation (HSCT) are essential to evaluate engraftment and to monitor response to therapeutic procedures such as donor lymphocyte infusion. Continuous long-term follow up, however, requires large amounts of pre-HSCT samples limiting the application of many widely used techniques for sensitive chimerism monitoring.

METHODS

DNAs from 42 normal healthy donors and 16 HSCT donor/recipient pairs were employed to validate the use of allele-specific insertion/deletion (indel) quantitative real-time polymerase chain reaction (qPCR) to quantify chimerism in samples with low amounts of DNA. Consequently, indel-qPCR analyses of samples from 16 HSCT patients were compared to short-tandem repeat (STR) specific PCR analyses.

RESULTS

Typing with reduced amounts of input DNA (15 vs. 60 ng) allowed for the reliable distinction of positive (mean threshold cycle (ct) 28.05) and negative (ct >36) signals. The high informativity of primer/probe sets, with 12 out of 19 markers exceeding 20% informativity, was confirmed in our cohort (n = 74). Importantly, a fourfold reduction of input DNA compared to published protocols did not alter PCR efficiencies and allowed for a more sensitive detection of chimerism in 7 of 16 HSCT patients compared to results obtained by STR-PCR.

CONCLUSIONS

Our data suggest that indel-qPCR is a more sensitive technique for the detection of hematopoietic chimerism compared to STR-PCR and works efficiently for samples with low amounts of DNA.

Peripheral blood cells chimerism after unrelated cord blood transplantation in children: kinetics, predictive factors and impact on post-transplant outcome

This study aimed to describe kinetics of complete donor chimerism occurrence (cDC, >99·9% donor) after unrelated cord blood transplantation (UCBT), to identify its predictive factors and its impact on post-transplant outcome. Ninety-four children who received single UCBT after a myeloablative conditioning regimen had blood chimerism evaluation at predefined post-transplant dates, using a real-time polymerase chain reaction method with 0·1% sensitivity. Cumulative incidence of cDC at 1 year post-transplantation was 61·8%. Three predictive factors were identified in multivariate analysis: history of malignant disease (P = 0·03), older age (above 2·16 years, the first quartile of age, P = 0·0055) and higher level of cord/recipient human leucocyte antigen mismatch (4/6 vs. 5-6/6, P < 0·001) increased the probability of post-transplant cDC. Although graft cell dose had a strong impact on haematological recovery, it did not apparently influence cDC occurrence. Early cDC (i.e. more than 99·9% donor chimerism on days 15-30 post-transplant) appeared useful to predict engraftment (P = 0·003) as well as acute and chronic graft-versus-host disease (GvHD). Severe acute or chronic GvHD never occurred in patients with DC ≤99·9%, suggesting than even minimal residual host haematopoiesis is associated with a very low risk of GvHD after UCBT.

Analysis of hematopoietic stem cell transplant engraftment: use of loss or gain of microsatellite alleles to identify residual hematopoietic malignancy

Polymorphic short tandem repeat (STR), or microsatellite, loci have been widely used to analyze chimerism status after allogeneic hematopoietic stem cell transplantation. The presence of a patient's DNA, as identified by STR analysis, may indicate residual or recurrent malignant disease or may represent normal hematopoiesis of patient origin. The ratio of patient-derived to donor-derived alleles is used to calculate the relative amount of patient cells (both benign and malignant) to donor cells. STRs on chromosomes known to be gained or lost in a patient's tumor are generally ignored because it is difficult to perform meaningful calculations of mixed chimerism. However, in this study, we present evidence that STR loci on gained or lost chromosomes are useful in distinguishing the benign or malignant nature of chimeric DNA. In the peripheral blood or bone marrow of 4 hematopoietic stem cell transplantation patients with leukemia or lymphoma, we identified tumor DNA on the basis of STR loci showing copy number alteration. We propose that a targeted evaluation of STR loci showing altered copy number in posttransplant chimerism analysis can provide evidence of residual cancer cells.

Increasing hematopoietic microchimerism is a reliable indicator of incipient AML relapse

INTRODUCTION

The reoccurrence or increase in autologous hematopoiesis after allogeneic transplantation has been linked to incipient leukemia relapse. However, the importance of such an emergency regarding microchimerism (i.e. mixed chimerism below 1% of autologous cells) still remains controversial, as fluctuating microchimerism can be observed for a very long time after transplantation.

METHODS

Using real-time PCR (RQ-PCR), we compare peripheral blood samples obtained from patients with acute myeloid leukemia (AML) before hematological relapse and those taken during complete remission (i.e. either complete cytogenetic remission or complete molecular remission where applicable). By comparison of these two groups, we describe microchimerism dynamics clearly connected with imminent AML relapse. Additionally, we compare applicability of RQ-PCR and conventional PCR with fragment analysis.

RESULTS

Mere reappearance of autologous hematopoiesis within patients with complete donor chimerism is alarming, and another sample with further increase confirms ongoing relapse. In case of patients with continuous microchimerism, another two consecutive samples with increasing trend are required. RQ-PCR predicted a significantly higher number of hematological relapses (87%vs. 39%) with a median anticipation period of 33 days, 26 days earlier than conventional PCR (P= 0.0002). Moreover, the outcome of microchimerism dynamics was in complete agreement with monitoring of minimal residual disease when analyzed from the same cell compartment.

CONCLUSION

Within this paper, we emphasize the importance of microchimerism monitoring as a reliable indicator of incipient AML relapse, especially in patients where no other specific molecular marker is available.

Application of allele-specific quantitative PCR using genomic DNA to monitor minimal residual disease based on mutant gene levels following allogeneic hematopoietic stem cell transplantation in patients with hematological malignancies: comparison of mutant levels with autologous DNA percentage by short tandem repeat-PCR

BACKGROUND

Quantitative evaluation of minimal residual disease (MRD) following hematopoietic stem cell transplantation (HSCT) is indispensable for patients with hematological malignancies. In addition to established MRD markers such as immunoglobulin and T-cell receptor gene rearrangements, fusion genes, or aberrantly expressed genes, single nucleotide mutations are considered one of the MRD markers that reflect the malignant cell clone.

METHODS

We compared the quantity of mutant genes by allele-specific quantitative polymerase chain reaction (AS-qPCR) for single nucleotide mutations (TP53 410T>A and PTPN11 1508G>A) with the percentage of autologous DNA by short tandem repeat (STR)-PCR.

RESULTS

Following HSCT, the quantity of mutant genes detected by AS-qPCR correlated with the percentage of autologous DNA assessed by the STR-PCR. Moreover, mutant DNAs were detected at a quantifiable level before relapse, whereas the percentage of autologous DNA was less than 5%, that is, complete chimerism.

CONCLUSIONS

The AS-qPCR approach for single nucleotide mutations was accurate and highly sensitive for monitoring pre-transplantation as well as post-transplantation MRD. AS-qPCR for single nucleotide mutation is suitable for monitoring MRD in patients who lack previously established MRD markers.

PCR for monitoring of minimal residual disease in hematologic malignancy

Monitoring minimal residual disease (MRD) is useful to evaluate therapeutic response and risk of relapse in patients with hematologic malignancy. Currently available quantitative MRD assays are fluorescence in situ hybridization of chromosomal aberrations; multiparameter flow cytometry of leukemia-associated immunophenotypes; and quantitative polymerase chain reaction (qPCR) analysis of fusion genes, immunoglobulin/T-cell receptor gene rearrangements, genetic alterations, or over-expressed genes. Among the PCR-based markers, genetic alterations are found in acute myelogenous leukemia patients with cytogenetically normal karyotype and can be considered as applicable targets for monitoring of MRD. Screening, confirmation and quantification procedures are important to develop the patient- or tumor-specific MRD assays using the PCR-based markers. Wild-type blocking PCR or coamplification at lower denaturing temperature-PCR is suited for screening of low-abundant genetic alterations, and allele-specific qPCR using primers including mismatched base and locked nucleic acids can quantify not only insertion and duplication of several nucleotides but also single nucleotide mutation in the presence of an excess amount of wild-type nucleotides. In addition to the well-established MRD markers, such as immunoglobulin/T-cell receptor gene rearrangements and fusion genes, utilizing potential MRD markers such as genetic alterations may expand the spectrum of patients in whom MRD can be monitored.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation

Relapse is a major cause of treatment failure after allogeneic hematopoietic stem cell transplantation (alloHSCT). Treatment options for relapse have been inadequate, and the majority of patients ultimately die of their disease. There is no standard approach to treating relapse after alloHSCT. Withdrawal of immune suppression and donor lymphocyte infusions are commonly used for all diseases; although these interventions are remarkably effective for relapsed chronic myelogenous leukemia, they have limited efficacy in other hematologic malignancies. Conventional and novel chemotherapy, monoclonal antibody therapy, targeted therapies, and second transplants have been utilized in a variety of relapsed diseases, but reports on these therapies are generally anecdotal and retrospective. As such, there is an immediate need for well-designed, disease-specific trials for treatment of relapse after alloHSCT. This report summarizes current treatment options under investigation for relapse after alloHSCT in a disease-specific manner. In addition, recommendations are provided for specific areas of research necessary in the treatment of relapse after alloHSCT.

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

Relapse has become the major cause of treatment failure after allogeneic stem cell transplantation. Outcome of patients with clinical relapse after transplantation generally remains poor, but intervention prior to florid relapse improves outcome for certain hematologic malignancies. To detect early relapse or minimal residual disease, sensitive methods such as molecular genetics, tumor-specific molecular primers, fluorescein in situ hybridization, and multiparameter flow cytometry (MFC) are commonly used after allogeneic stem cell transplantation to monitor patients, but not all of them are included in the commonly employed disease-specific response criteria. The highest sensitivity and specificity can be achieved by molecular monitoring of tumor- or patient-specific markers measured by polymerase chain reaction-based techniques, but not all diseases have such targets for monitoring. Similar high sensitivity can be achieved by determination of donor chimerism, but its specificity regarding detection of relapse is low and differs substantially among diseases. Here, we summarize the current knowledge about the utilization of such sensitive monitoring techniques based on tumor-specific markers and donor cell chimerism and how these methods might augment the standard definitions of posttransplant remission, persistence, progression, relapse, and the prediction of relapse. Critically important is the need for standardization of the different residual disease techniques and to assess the clinical relevance of minimal residual disease and chimerism surveillance in individual diseases, which in turn, must be followed by studies to assess the potential impact of specific interventional strategies.

Impact of hematopoietic chimerism at day +14 on engraftment after unrelated donor umbilical cord blood transplantation for hematologic malignancies

BACKGROUND

Cord blood transplant is a feasible treatment alternative for adult patients with hematologic malignancies lacking a suitable HLA-matched donor. However, the kinetics of myeloid recovery is slow, and primary graft failure cannot be detected easily early after transplantation. We investigated the impact of hematopoietic chimerism status from unselected marrow cells 14 days after transplantation on predicting engraftment after a cord blood transplant.

DESIGN AND METHODS

Seventy-one adult patients with hematologic malignancies undergoing single-unit unrelated donor cord blood transplantation after a myeloablative conditioning regimen were included in the study. All patients received conditioning regimens based on busulfan, thiotepa and antithymocyte globulin. Chimerism status was assessed analyzing short tandem repeat polymorphisms.

RESULTS

The cumulative incidence of myeloid engraftment at 1 month was significantly lower in patients with mixed chimerism than in those with complete donor chimerism (55% vs. 94%; p<0.0001). For patients achieving myeloid recovery, the median time of engraftment was 16 days when donor chimerism at day + 14 was higher than 90%, compared with 24 days when donor chimerism was below this level (p<0.001). A donor chimerism level of 65% was found to be the best cut-off point for predicting primary graft failure, with a sensitivity of 97% and a specificity of 80%. The incidence of primary graft failure was 67% for patients with less than 65% donor chimerism at day +14 as compared to only 2% for those with more than 65% donor chimerism (p<0.001). Patients with mixed chimerism also had a lower cumulative incidence of platelet engraftment than those with complete chimerism (62% vs. 89%; p=0.01).

CONCLUSIONS

Donor-recipient chimerism status at day +14 predicts engraftment after a single-unit cord blood transplant in adults.

Allogeneic transplantation for pediatric acute lymphoblastic leukemia: the emerging role of peritransplantation minimal residual disease/chimerism monitoring and novel chemotherapeutic, molecular, and immune approaches aimed at preventing relapse

Although improved donor sources and supportive care have decreased transplantation-related mortality over the past decade, relapse remains the principal cause of failure after allogeneic transplantation for high-risk pediatric acute lymphoblastic leukemia (ALL). Emerging tools of minimal residual disease (MRD) and chimerism monitoring before and after transplantation have defined those children at highest risk for relapse and provide the opportunity for intervention to prevent relapse. Specific methods aimed at decreasing relapse include the use of intensive treatment before transplantation to increase the percentage of patients undergoing the procedure with negative MRD, optimal transplantation preparative regimens, and posttransplantation interventions with targeted or immunologic therapy. Early data demonstrate decreased relapse with the use of sirolimus for all types of ALL and imatinib for ALL with the Philadelphia chromosome (Ph(+) ALL) after transplantation. Patients with increasing chimerism or MRD have been shown to benefit from early withdrawal of immune suppression or donor lymphocyte infusion. Finally, various targeted immunologic therapies, including monoclonal antibodies, killer cell immunoglobulin-like receptor mismatching, natural killer cell therapy, and targeted T cell therapies, are emerging that also could have an affect on relapse and improve survival after transplantation for pediatric ALL.

Engraftment kinetics and hematopoietic chimerism after reduced-intensity conditioning with fludarabine and treosulfan before allogeneic stem cell transplantation

Reduced-intensity conditioning with fludarabine and treosulfan before allogeneic stem cell transplantation (SCT) was introduced several years ago. Although its feasibility has recently been proven, only limited data are available on myelotoxicity, engraftment kinetics, and the significance of hematopoietic chimerism using this novel conditioning regimen. To clarify these open questions, we analyzed 27 patients with various hematological diseases, who received allogeneic SCT preceded by fludarabine/treosulfan conditioning. Further assessment endpoints included graft-vs-host disease (GvHD), mortality, and overall survival (OS). Allogeneic SCT was followed by neutropenia (absolute neutrophil count < or = 0.5 x 10(9)/l) and thrombocytopenia (platelets < or = 20 x 10(9)/l) in all patients. All patients showed stable neutrophil engraftment, and all except one had stable platelet engraftment. Grades II-IV acute GvHD was found in 48% of patients, whereas 52% developed chronic GvHD. The treatment-related mortality on day +100, 1 year after SCT, and at the last follow-up was 11, 26, and 33%, respectively. We found complete chimerism rates of 46, 57, and 72% on days +28, +56, and at the last follow-up or before death, respectively. The underlying malignancy tended to relapse more frequently in patients with mixed chimerism than in those with complete chimerism on day +28 as well as on day +56 (not significant). Additionally, no significant association was found between hematopoietic chimerism and donor type, GvHD, or OS, respectively. We conclude that reduced-intensity conditioning with fludarabine and treosulfan before allogeneic SCT is myeloablative, provides stable engraftment, and leads to complete chimerism in the majority of patients.

Correlation of minimal residual disease by assessing Wilms tumor gene expression and engraftment by variable number of tandem repeats in children with leukemia posthematopoietic stem cell transplantation

An important measure to ensure successful follow-up in patients with allogeneic stem cell transplant is to evaluate for engraftment. Recent studies have shown that detecting minimal residual disease is important in order to predict early clinical relapse. We followed 88 leukemic patients with pre- and posttransplant Wilms tumor gene (WT1) levels to predict relapse and variable number of tandem repeats (VNTR) for engraftment. We have found that high pretransplant WT1 levels correlated significantly with relapse in all patient groups, but more significantly in the acute nonlymphoblastic leukemia (ANLL) patients. Posttransplant WT1 level correlated with VNTR status such that low WT1 is associated invariably with VNTR of 100% donor origin, while high WT1 is associated with VNTR of 20%. The association is significant in all patients, specifically in ANLL patients. In this preliminary study, we demonstrate that patients harboring detectable levels of WT1 prior to stem cell transplant have a higher chance of relapse, and posttransplant WT1 and VNTR status appeared to be dependent parameters predicting relapse when present in the posttransplant period. By combining 2 highly sensitive molecular techniques, we have found that this combined technique provided us with a promising alternative for overcoming the limitations imposed by each separate procedure. More studies are necessary before we can come to any significant conclusions.

Stable mixed chimerism after hematopoietic stem cell transplantation in Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disease characterized by thrombocytopenia, eczema, impaired cellular and humoral immunity, and increased susceptibility to malignancy and autoimmunity. The only curative treatment for WAS is hematopoietic stem cell transplantation, especially in the presence of a matched sibling donor or matched unrelated donor. Here, we report the case of a 2.5-yr-old boy with WAS that resulted in mixed chimerism after having received bone marrow from his phenotypically identical grandfather. Although the patient has persistent thrombocytopenia (platelet counts 50-80 x 10(9)/L), he is currently alive and doing well at 36 months post-transplant and is free of any bleeding episodes.

Long-term outcome after haploidentical stem cell transplantation in children

We present an update of our results with transplantation of highly purified stem cells from one to three loci mismatched parental donors. Sixty-three pediatric patients with acute lymphoblastic leukemias (n = 32), acute myeloid, chronic myeloid and myelomonocytic leukemias (n = 13), myelodysplastic syndromes (n = 4), lymphomas (n = 4), and various nonmalignant diseases (n = 10) underwent transplantation. Mobilized peripheral-blood stem cells were selected with either anti-CD34- or anti-CD133-coated microbeads. Patients received a median of 19.5 x 10(6) purified cells and <25,000 CD3+ T lymphocytes per kilogram, with no regular posttransplant pharmacological immunosuppression. Engraftment occurred in 98% of patients (primary sustained engraftment, 83%; engraftment after reconditioning/stem cell boosts, 15%). Moreover, all survivors but one had a stable three-lineage engraftment with a median follow up of 4.1 years (range 0.6-8 years). Primary acute graft-versus-host disease (GvHD) grade II was seen in only 7% of patients. No severe primary acute GvHD grades III-IV occurred. Thirteen percent of the patients developed transient chronic GvHD. Probability of disease-free survival (DFS) at 3 years was 60% for patients with nonmalignant diseases and 48% for patients with acute lymphatic leukemia (ALL)/non-Hodgkin lymphoma (NHL) in complete remission (CR)1-3. None of the ALL/NHL patients with active disease survived. Children with acute and chronic myeloid leukemias had a poorer outcome (3-year DFS = 18%), whereas two of four patients with myelodysplastic syndrome (MDS) are alive. Relapse probability of the whole group was not significantly increased when compared to a historical control group. The incidence of lethal viral infections was 18% between 1995 and 2002 and has since been reduced to 8% by the introduction of new therapeutic strategies. In summary, the use of stem cells from haploidentical parental donors should be strongly considered in all children who need transplantation but lack an identical donor.

Is there a role for minimal residual disease levels in the treatment of ALL patients who receive allogeneic stem cells?

Relapse is the major complication after allogeneic stem cell transplantation (SCT) for acute lymphoblastic leukemia (ALL) in children. Since it has been possible to measure minimal residual disease (MRD) by real-time quantitative polymerase chain reaction, this parameter is used more frequently in the treatment of ALL. In this article, the role of MRD and chimerism in the treatment and monitoring of pediatric transplantation recipients is described. Pre-SCT MRD levels can predict the risk of relapse and can thus be used to adjust treatment. Post-SCT MRD levels and changes in chimerism can predict relapses as well, although not many treatment options are available today, except relying on a graft-versus-leukemia effect mediated by graft-versus-host disease. Finding new treatments will be the challenge for the near future.

Children with myelodysplastic syndrome (MDS) and increasing mixed chimaerism after allogeneic stem cell transplantation have a poor outcome which can be improved by pre-emptive immunotherapy

We recently reported that virtually all children with acute leukaemia and myelodysplastic syndrome (MDS) who develop the phenotype of increasing mixed chimaerism (MC) after allogeneic stem cell transplantation (allo-SCT) will relapse. We therefore performed a prospective, multi-centre study focused on children with MDS (n = 65; advanced MDS = 44, refractory cytopenia = 21) after allo-SCT in order to determine to what extent relapse can be prevented by pre-emptive immunotherapy on the basis of increasing MC. Analyses of chimaerism in 44 patients with advanced MDS revealed 31 cases with complete chimaerism (CC)/low-level MC/transient MC, 11 cases with increasing MC and two cases with decreasing MC. The same analyses in 21 MDS patients with refractory cytopenia revealed 17 cases with CC/low-level MC, one case with increasing MC and three cases with decreasing MC. Pre-emptive immunotherapy performed on each patient that showed increasing MC improved event-free survival from 0%, as seen in prior studies, to 50%. We therefore conclude that pre-emptive immunotherapy is an effective treatment option to prevent impending relapse in children with MDS after allo-SCT.

Impact of chimaerism analysis and kinetics on allogeneic haematopoietic stem cell transplantation outcome after conventional and reduced-intensity conditioning regimens

This retrospective study aimed to analyse the impact on overall survival (OS) and event-free survival (EFS) of chimaerism status and kinetics following allogeneic conventional and reduced-intensity conditioning haematopoietic stem cell transplantation, and to compare this with the impact of other well-known factors. We investigated the chimaerism status of 187 patients [84 females, 103 males; median age 39.5 years (range, 17-62 years)]. After transplantation, 121 patients (65%) presented full donor chimaerism (FDC) and 63 (34%) mixed chimaerism (MC). For MC, we divided the population into patients who presented regressive mixed chimaerism (RMC) (21 patients: 11%), stable mixed chimaerism (SMC) (20 patients: 11%) and progressive mixed chimaerism (PMC) (22 patients: 12%). At last follow-up, 71 patients were alive and 116 had died (48% from disease progression and 52% from transplant-related causes). With a mean follow-up of 39.4 and 34.8 months, the 5-year probabilities of OS and EFS for the total group were, respectively, 55% and 43%: 69.5% and 61% for FDC, 35.4% and 25% for RMC, 42.6% and 28.6% for SMC, and 21% and 10.4% for PMC (P < 0.0001 and P < 0.0001). Multivariate analysis only showed a significant impact of chimaerism status on OS, as well as acute and chronic graft-versus-host disease on EFS, with a trend for conditioning regimen.

Fanconi anemia: contribution of molecular analyses to the identification of bone marrow graft donors and the study of chimerism in grafted patients

We report on the effectiveness of molecular studies regarding Fanconi anemia (FA) for a better selection of bone marrow graft donors and for post-transplant follow up. Ten unrelated FA patients and their families were analyzed by microsatellite markers. In 9 cases, the cytogenetic investigation of potential human leukocyte antigen (HLA)-identical related donors was normal, and the molecular analyses confirmed that they were also either normal or heterozygous carriers. For 1 patient, cytogenetic analysis of an HLA-identical sibling donor yielded ambiguous results with a relatively high number of chromosomal breakages using cross-linking agents. However, genotyping of this potential donor demonstrated his heterozygous state. Nine patients have received allogeneic bone marrow transplantation from HLA-matched related donors. Microsatellite analysis showed complete chimerism (CC) in all cases. The median follow up was 54 months (range 8-144 months). One patient out of 9 with CC rejected her graft without prior detection of a transitional mixed chimerism. Among these patients, 1 died 25 months after the transplantation of a chronic graft-versus-host-disease (GVHD). We conclude that, when the cytogenetic studies are not conclusive, molecular analyses are crucial to distinguish heterozygous carriers from asymptomatic FA Tunisian patients. Molecular analyses also allowed the evaluation of hematopoietic chimerism after allogeneic bone marrow transplantation and might be of value to identify patients with a high risk for graft rejection.

Hematopoietic chimerism after allogeneic stem cell transplantation: a comparison of quantitative analysis by automated DNA sizing and fluorescent in situ hybridization

Background

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is performed mainly in patients with high-risk or advanced hematologic malignancies and congenital or acquired aplastic anemias. In the context of the significant risk of graft failure after allo-HSCT from alternative donors and the risk of relapse in recipients transplanted for malignancy, the precise monitoring of posttransplant hematopoietic chimerism is of utmost interest. Useful molecular methods for chimerism quantification after allogeneic transplantation, aimed at distinguishing precisely between donor's and recipient's cells, are PCR-based analyses of polymorphic DNA markers. Such analyses can be performed regardless of donor's and recipient's sex. Additionally, in patients after sex-mismatched allo-HSCT, fluorescent in situ hybridization (FISH) can be applied.

Methods

We compared different techniques for analysis of posttransplant chimerism, namely FISH and PCR-based molecular methods with automated detection of fluorescent products in an ALFExpress DNA Sequencer (Pharmacia) or ABI 310 Genetic Analyzer (PE). We used Spearman correlation test.

Results

We have found high correlation between results obtained from the PCR/ALF Express and PCR/ABI 310 Genetic Analyzer. Lower, but still positive correlations were found between results of FISH technique and results obtained using automated DNA sizing technology.

Conclusions

All the methods applied enable a rapid and accurate detection of post-HSCT chimerism.

How and when should we monitor chimerism after allogeneic stem cell transplantation?

SUMMARY

Chimerism analysis has become an important tool for the peri-transplant surveillance of engraftment. It offers the possibility to realize impending graft rejection and can serve as an indicator for the recurrence of the underlying malignant or nonmalignant disease. Most recently, these investigations have become the basis for treatment intervention, for example, to avoid graft rejection, to maintain engraftment and to treat imminent relapse by pre-emptive immunotherapy. This invited review focuses on the clinical implications of characterization of hematopoietic chimerism in stem cell transplantation.

Diagnostic chimerism analysis after allogeneic stem cell transplantation: new methods and markers

Analysis of chimerism after allogeneic hematopoietic cell transplantation is important for assessing engraftment and the early detection of graft failure. In addition, the monitoring of minimal residual disease and early detection of imminent relapse has also become an important issue. Novel transplant procedures, for example dose-reduced conditioning protocols, rely on chimerism analysis to guide intervention, i.e. the reduction of immunosuppression or infusion of donor lymphocytes. During the last 30 years, several methods for the analysis of chimerism after hematopoietic cell transplantation have been published. Currently, fluorescent in situ hybridization (XY-FISH) analysis of sex chromosomes after transplantation from a sex-mismatched donor or analysis of polymorphic DNA sequences, i.e. short tandem repeats (STR) or variable number of tandem repeats (VNTR), are the most widely used procedures used in the assessment of chimerism. Two major diagnostic fields can be defined for chimerism analysis: the period of engraftment and the detection of minimal residual disease. Although STR-PCR and FISH analysis are very useful in the diagnosis of engraftment and graft failure, they are only of limited use in the monitoring of minimal residual disease, largely because of its limited level of sensitivity (1-5% for the minor population). Several novel procedures to improve this level of detection have been reported in recent years. One focus has been the use of real-time PCR techniques based on analysis of the Y-chromosome or, more recently, single nucleotide polymorphism (SNPs). These procedures combine quantitative analysis with high sensitivity (10(-4) to 10(-6)), and hold great potential for the future. In addition, the combination of cell sorting based on leukemia-specific immunophenotype and STR-PCR has been successfully used for minimal residual disease detection. First clinical data using these procedures indicate that intervention (e.g. the reduction of immunosuppression or donor lymphocyte infusion) may be effective in the minimal residual disease situation, even in high risk diseases like acute myeloid leukemia and acute lymphoblastic leukemia. The optimal timing of these diagnostic interventions is a critical issue and has to be further optimized. Whether this will ultimately improve the survival of patients with leukemia after transplantation has to be shown in prospective studies.

Mixed hematopoietic chimerism at day 90 following allogenic myeloablative stem cell transplantation is a predictor of relapse and survival

We retrospectively analyzed the prognostic significance of mixed chimerism and associated clinical parameters in 80 patients following unmanipulated allogenic stem cell transplantation. Chimerism studies were performed on marrow aspirates using fluorescent in situ hybridization and variable number tandem repeats techniques at day +30, day +90 and +12 months. The median overall survival (OS) was 24 months (range, 1-56 months). Mixed chimerism was found in 23, 28 and 14% of patients at day +30 (1 month), +90 (3 months), and +12 months, respectively. Day +30 chimerism studies failed to provide any prognostic information. Day +90 mixed chimeras (MC) had significantly higher relapse rates compared to day +90 complete chimeras (CC) at 6 months (P=0.03) and 18 months when compared to MC (P=0.03) following transplant. The median OS in day +90 MC and day+90 CC were, respectively (95% CI, 2-35 months), compared to 47 months (95% CI, 20-74 months) (P=0.02). In conclusion, chimerism studies on day +30 could be reserved for patients who fail to demonstrate engraftment. Day +90 MC had higher relapse rates and lower OS, and therefore may be considered for novel therapies and future studies.

Strategies and clinical implications of chimerism diagnostics after allogeneic hematopoietic stem cell transplantation

Analysis of donor chimerism has become a routine method for the documentation of engraftment after allogeneic hematopoietic stem cell transplantation (HSCT). In recent years several groups have also focused on the application of this technique for the detection of relapsing disease after allogeneic HSCT. This review addresses technical issues (sensitivity, specificity) and discusses the advantages and limitations of methods currently used for chimerism analysis and their usefulness for the detection of MRD. In addition, the potential impact of novel procedures, e.g. subset chimerism or real-time PCR-based procedures, is discussed.

Increasing mixed chimerism is an important prognostic factor for unfavorable outcome in children with acute lymphoblastic leukemia after allogeneic stem-cell transplantation: possible role for pre-emptive immunotherapy?

PURPOSE

We recently reported that children with acute leukemias who show increasing mixed chimerism (MC) after allogeneic stem-cell transplantation have a significantly enhanced risk of relapse. Here we present the results of a prospective multicenter study to investigate (1) whether relapse of acute lymphoblastic leukemia (ALL) can be determined in advance by serial analysis of chimerism, and (2) if outcome can be influenced by withdrawal of immunosuppression and/or by low-dose donor lymphocyte infusion when increasing MC is detected.

PATIENTS AND METHODS

Serial and quantitative analysis of chimerism was performed using a fluorescent-based short-tandem-repeat-polymerase chain reaction in 163 children with ALL.

RESULTS

One hundred one patients revealed complete chimerism (CC) or low-level MC (CC/low-level MC); increasing MC was found in 46 patients; and decreasing MC, in 16 patients. Relapse was significantly more frequent in patients with increasing MC (26 of 46) than in patients with CC/low-level MC (eight of 101) or in patients with decreasing MC (0 of 16; P <.0001). The probability of 3-year event-free survival (EFS) was 54% for all patients, 66% for patients with CC/low-level MC (n = 101), 66% for patients with decreasing MC (n = 16), and 23% for patients with increasing MC (n = 46; P <.0001). Of the 46 patients with increasing MC, 31 received immunotherapy. This group had a significantly higher 3-year EFS estimate (37%) than the 15 patients who did not receive immunotherapy (0%; P <.001).

CONCLUSION

Serial analysis of chimerism reliably identifies patients at highest risk to relapse. The 3-year EFS of patients with increasing MC without immunotherapy was 0%, by which overt relapse could be prevented in a considerable group of patients.

Significance of chimerism in hematopoietic stem cell transplantation: new variations on an old theme

The main goal of post-transplantation monitoring in hematopoietic stem cell transplantation (HSCT) is to predict negative events, such as disease relapse, graft rejection and graft-versus-host disease, in order to intervene with appropriate therapy. In this context, chimerism analysis is an important method in monitoring post HSCT outcome. Mixed chimerism (MC) is mainly evaluated to define engraftment and relapse. Detection of MC is a prerequisite in both myeloablative and nonmyeloablative HSCT, in order to assess the graft status and decide later therapeutic strategies such as donor lymphocyte infusion. In this review, we discuss various techniques including erythrocyte phenotyping, cytogenetic analysis, fluorescent in situ hybridization, restriction fragment length polymorphism, STR/VNTR analysis and real-time quantitative PCR, along with the various methods used to detect minimal residual disease (MRD) in different diseases such as chronic myeloid leukemia, acute myelomonocytic leukemia or acute lymphoblastic leukemia. The review mainly highlights the optimal methodological approach, which needs to be informative, sensitive and quantitatively accurate for MC detection. Future of post HSCT graft monitoring lies in the selection of the most accurate and sensitive technique to determine both MC and MRD. Such an approach would be helpful in not only determining relapse or rejection, but also in ascertaining various responses to different treatment modalities.

Increasing mixed chimerism defines a high-risk group of childhood acute myelogenous leukemia patients after allogeneic stem cell transplantation where pre-emptive immunotherapy may be effective

Children with leukemias and increasing mixed chimerism (increasing MC) after allogeneic stem cell transplantation have the highest risk to relapse. Early immunological intervention was found to be effective in these cases. To substantiate this on a defined group of pediatric acute myelogenous leukemia (AML) patients, we performed serial analysis of post transplant chimerism and pre-emptive immunotherapy in patients with increasing MC. In total, 81 children were monitored, 62 patients revealed complete chimerism (CC), low-level MC or decreasing MC. Increasing MC was detected in 19 cases. Despite early immunological intervention relapse was still significantly more frequent in patients with increasing MC (9/19) than in patients with CC, low-level or decreasing MC (8/62, P<0.005). The probability of 3-year event-free survival (EFS) was 52% for all patients (n=81), 59% for patients with CC, low-level MC, 60% for patients with decreasing MC (n=62), and 28% for patients with increasing MC (n=19, P<0.005). Patients with increasing MC who received early immunological intervention showed a significantly enhanced probability for event-free survival (pEFS 36%, n=15) compared to patients with increasing MC without intervention (pEFS 0%, n=4, P<0.05). These results prove that pediatric AML patients with increasing MC are at highest risk for relapse and that early immunological intervention can prevent relapse in these patients.

Prompt initiation of immunotherapy in children with an increasing number of autologous cells after allogeneic HCT can induce complete donor-type chimerism: a report of 14 children

Immunotherapy consisting of withdrawal of immunosuppression and/or donor lymphocyte infusions was initiated in 14 children (10 acute lymphoblastic leukemia, three acute myeloblastic leukemia and one myelodysplastic syndrome) with an increasing amount of autologous DNA (increasing mixed chimerism, inMC) detected after allogeneic hematopoietic cell transplantation (HCT). Two children were in relapse when inMC was detected, 12 remained in CR. Children with overt relapse at the time of cessation of cyclosporine A (CsA) received "debulking" chemotherapy. One of them developed acute grade III graft-versus-host disease, converted to complete donor chimerism (CC) and achieved remission. Another patient did not respond and died due to disease progression. Among 12 children treated in remission, 11 responded with conversion to CC, seven after CsA withdrawal and four after DLI. One patient did not respond, rejected the graft and died due to pulmonary aspergillosis. In one patient, the response was transient, inMC reappeared and frank relapse occurred. One patient developed isolated CNS relapse despite conversion to CC, but achieved CR after conventional treatment. One child died in CC due to infection. No graft-versus-host disease (GvHD)-related death occurred. A total of 10 patients are alive in remission with median follow-up of 338 days. Our results support the hypothesis that chimerism-guided immunotherapy after alloHCT may prevent progression to hematological relapse.

Rapid induction of complete donor chimerism by the use of a reduced-intensity conditioning regimen composed of fludarabine and melphalan in allogeneic stem cell transplantation for metastatic solid tumors

We evaluated the feasibility and efficacy of a reduced-intensity conditioning (RIC) regimen of fludarabine and melphalan to achieve rapid complete donor chimerism after allogeneic stem cell transplantation (SCT) in patients with metastatic solid tumors. Between January 1999 and January 2003, 8 patients with metastatic breast cancer (BC) and 15 with metastatic renal cell carcinoma (RCC) underwent allogeneic SCT after an RIC regimen of 5 days of fludarabine and 2 days of melphalan. Filgrastim-mobilized stem cells from HLA-identical related or unrelated donors were infused. Prophylaxis for graft-versus-host disease (GVHD) consisted of tacrolimus and methotrexate. All 22 evaluable patients had 100% donor chimerism at day 30 and at all measurement times thereafter. One patient died 19 days after SCT. Nine patients (39%) had grades II to IV acute GVHD and 10 patients (43%) had chronic GVHD. Five patients (22%) died of nonrelapse treatment-related complications. Treatment-related disease response was seen in 10 patients (45%), with 3 complete responses, 2 partial responses, and 5 minor responses. Fludarabine-melphalan is a feasible and effective RIC regimen for allogeneic SCT in metastatic BC and RCC. It induces rapid complete donor chimerism without the need for donor lymphocyte infusion. Tumor regression associated with GVHD is consistent with graft-versus-tumor effect.

Monitoring of hematopoietic chimerism after sex-mismatched allogeneic stem cell transplantation (alloSCT) by dual-color FISH analysis of X and Y chromosomes

Hematopoietic chimerism was monitored in 18 patients with various diseases after gender-mismatched allogeneic stem cell transplantation (alloSCT). To detect host and donor cells, FISH analysis of sex chromosomes was applied. X and Y chromosomes were detected simultaneously in interphase nuclei by two-color probes. Chimerism was examined sequentially in post-transplant peripheral blood and bone marrow as well as in purified T cells. Patients with complete donor or decreasing host chimerism have not rejected or relapsed but experienced a high incidence of acute graft versus host disease (aGvHD). The clinical value of stable mixed chimerism detection remains uncertain. However, it appears to be associated with a lower risk of aGvHD. Three patients with an increase in host cells rejected their grafts. The immunotherapy was introduced to four other patients with increasing host chimerism. All of them responded, however, one relapsed in CNS despite the conversion to complete donor chimerism in both bone marrow and peripheral blood. We concluded that two-color FISH analysis of sex chromosomes was a valuable tool for chimerism monitoring and provided significant clinical data.

Platelet chimerism by polymerase chain reaction (PCR) utilizing variable number of tandem repeats (VNTR) in allogeneic stem cell transplant in children: a new novel approach to full chimerism analysis

Evaluation of chimerism following allogeneic transplantation has been performed traditionally focusing on two cellular compartments, namely lymphoid and myeloid. However, none has been described so far to evaluate platelet chimerism. In order to achieve full chimerism in all three cellular compartments, we prospectively obtained 138 samples of peripheral blood in 55 patients at different post transplant periods following allogeneic hematopoietic transplantation. Evaluation of chimerism was performed utilizing tests of variable number of tandem repeat (VNTR) and sex determination by quantitative polymerase chain reaction (PCR). Tests for platelet chimerism using platelet-rich plasma were simultaneously analyzed with samples for T-cell lymphoid and myeloid compartments. Complete donor chimerism was noted in 49 of 55 patients (89%), while the remaining six have split chimerism ranging from 34 to 98%. There is significant difference (P=0.0004) between the percentages of donor DNA in all three cellular compartments comparing the means+/-s.e.m. (myeloid 95.60+/-0.9, T-cell lymphocytes 87.6+/-1.9, and the platelets 90.8+/-1.5); however, comparison between the medians is not statistically significant. This study represents an additional step towards achieving full chimerism and the observation may help reduce the number of unnecessary platelet transfusions once chimerism is noted in that cellular compartment.

Lineage-specific chimaerism after stem cell transplantation in children following reduced intensity conditioning: potential predictive value of NK cell chimaerism for late graft rejection

Chimaerism of FACS-sorted leucocyte subsets (CD14+, CD15+, CD3-/56+, CD3+/4+, CD3+/8+, CD19+) was monitored prospectively between days +14 and +100 in 39 children undergoing allogeneic stem cell transplantation with reduced intensity-conditioning regimens. Cell subsets exceeding 1% of nucleated cells were subject to cell sorting. Chimaerism was analysed by dual-colour FISH and/or by short tandem repeat-polymerase chain reaction. The chimaerism pattern on day +28 was evaluated with regard to its correlation with graft rejection. Of 39 patients, nine patients had donor chimaerism (DC) in all subsets. Mixed/recipient chimaerism (MC/RC) was detectable within T cells in 62%, within NK cells in 39% and within monocytes and granulocytes in 38% of the patients. The correlation of secondary graft rejection with the chimaerism pattern on day +28 revealed the strongest association between RC in NK-cells (P<0.0001), followed by T cells (P=0.001), and granulocytes and monocytes (P=0.034). Notably, patients with RC in T cells rejected their graft only if MC or RC was also present in the NK-cell subset. By contrast, none of the children with DC in NK cells experienced a graft rejection. These observations suggest that, in the presence of recipient T-cell chimaerism, the chimaerism status in NK-cells on day +28 might be able to identify patients at high risk for late graft rejection.

Monthly prospective analysis of hematopoietic chimerism after allogeneic hematopoietic cell transplantation

SUMMARY

Hematopoietic chimerism (HpC) was assayed monthly using a sensitive, polymerase chain reaction (PCR) -based method in consecutive patients. Between January 1998 and April 2002, 181 patients underwent non-T cell depleted allogeneic hematopoietic cell transplantation (HCT). A total of 163 patients were evaluable for HpC at 1 month (11 early deaths; no informative band for HpC analysis/no genomic DNA in seven). In all, 53 of 163 patients (33%, median recipient DNA of 15% (range 5-95)), 39 of 151 patients (26%), and 27 of 142 patients (19%) showed mixed chimerism (MC) at 1, 2, and 3 months after HCT, respectively. Conditioning regimen (busulfan-fludarabine-ATG vs BuCy, relative risk 3.99 (95% CI 1.16-10.92)), neutrophil engraftment (>/=day 17 vs </=day 16, relative risk 2.49 (95% CI 1.14-5.41)), and acute graft-versus-host disease within 30 days (none vs yes, relative risk 4.78 (95% CI 1.50-15.17)) were independent variables that showed significant correlation with having >/=5% recipient DNA at 1 month. Five patients experienced secondary graft failure. All five patients showed MC at 1 month with median recipient DNA of 40%. None of the 109 patients with complete chimerism experienced graft failure (P=0.002). Our study showed that MC shown on monthly analysis of HpC after allogeneic HCT is a significant predictor of secondary graft failure. Bone Marrow Transplantation (2003) 32, 423-431. doi:10.1038/sj.bmt.1704147

Transfusion-related problems following major ABO-incompatible bone marrow transplantation

A case of acute myelocytic leukemia has been reported in which the patient's surviving original B lymphocytes after pretransplant-conditioning chemotherapy probably reproduced hemagglutinins that reacted with red blood cells (RBCs) derived from engrafted donor marrow for a prolonged period of time. Although the direct antiglobulin test was negative and hemagglutinins were not detectable in the patient's sera but only in the eluate, the antibodies reappeared in the sera. Therefore, it is important to confirm that the eluate does not contain antibodies that would react with donor-derived RBCs when the type of red cell used for transfusion is switched from the patient's type to the donor's type in a major ABO-mismatched bone marrow transplantation (BMT). Testing of ABO subgroups using lectins is also recommended to avoid a delayed hemolytic transfusion reaction following BMT.

Serial quantification of lymphoid and myeloid mixed chimerism using multiplex PCR amplification of short tandem repeat-markers predicts graft rejection and relapse, respectively, after allogeneic transplantation of CD34+ selected cells from peripheral blood

We used multiplex amplification of nine microsatellite sequences (PCR-STR) to analyse chimerism in pure populations of T cells and neutrophils from peripheral blood from 40 patients submitted to an allogeneic transplant, 22 having received a T-cell depleted (TCD) peripheral blood graft by means of CD34(+) selection (allo-PBT/CD34(+)), and 18, an unmodified graft (allo-SCT; 13 allogeneic bone marrow transplants and five allo-PBT). T-cell mixed chimerism (TcMC) was observed in 16 of the 22 (72.3%) patients receiving an allo-PBT/CD34(+), but in only one of the 18 (5.5%) patients receiving an allo-SCT (P=0.0001). TcMC was transient (n=6), stable (n=7), and associated with poor haematopoietic engraftment (n=4). All patients with TcMC who developed graft failure had more than 30% of host T cells. Myeloid MC (MyMC) was observed in four (19%) allo-PBT/CD34(+) patients and in three (17%) allo-SCT patients (P=NS). Five out of seven (71%) patients with MyMC relapsed, all of them diagnosed with myeloid malignancies, as compared with two of the 20 (10%) patients with complete donor chimerism (P&<0.0001). In conclusion, TcMC appears in a significant number of allo-PBT/CD34(+) patients and may be associated with poor engraftment when the percentage of host T cells is >30%; likewise, MyMC appears in a small percentage of recipients of both allo-PBT/CD34(+) and allo-SCT patients, and is associated with leukaemia relapse in myeloid malignancies.

Megakaryocyte chimerism after allogeneic stem cell transplantation in children

The aim of this study was to investigate the extent and the clinical implications of mixed chimerism in megakaryocytes after stem cell transplantation (SCT). Polymerase chain reaction analyzing allele length polymorphisms was used to determine the origin of immunomagnetically isolated megakaryocytes and leukocyte subpopulations after SCT in 13 children. Eleven were unselected consecutive cases while two were included due to known leukocyte mixed chimerism. Recipient DNA was detected in the megakaryocytes in six out of the 11 cases at levels between 1 and 100%. Coinciding mixed chimerism in the leukocyte populations was detected in two of the 11 cases. Of the two selected cases with known leukocyte mixed chimerism, two boys with aplastic anemia and Wiskott-Aldrich syndrome had 1-5 and 70% recipient megakaryocytes, respectively. Although the four relapses or deaths, within the 13 months of observation, were restricted to patients with multilineage or isolated megakaryocyte (n = 1) mixed chimerism, it was not possible to link any other apparent clinical problems, except a prolonged thrombocytopenia in one case, to the mixed chimerism in this limited study group.

Distinct contributions of CD4(+) and CD8(+) naive and memory T-cell subsets to overall T-cell-receptor repertoire complexity following transplantation of T-cell-depleted CD34-selected hematopoietic progenitor cells from unrelated donors

Normalization of restricted T-cell-receptor (TCR) repertoire is critical following T-cell-depleted (TCD) stem cell transplantation. We present a prospective study analyzing respective contributions of naive and memory T-cell subsets within the CD4(+) and CD8(+) compartments to the evolution of overall TCR-repertoire complexity following transplantation of CD34-selected peripheral blood progenitor cells from unrelated donors. During the first year after transplantation, sorted CD4/45RA, CD4/45R0, CD8/45RA, and CD8/45R0 subsets were analyzed at 3-month intervals for TCR-repertoire complexity by CDR3 size spectratyping. Skew in TCR-repertoire was observed only in early memory-type T cells. CD4(+) and CD8(+) subsets differed in clonal distribution of CDR3 sizes, with rapid Gaussian normalization of bands in CD4/45R0(+) T cells. Naive T cells displayed normal repertoire complexity and contributed significantly to skew correction. Our data provide direct evidence for an important role of de novo maturation of naive T cells in normalization of an initially restricted TCR-repertoire following transplantation of CD34-selected, TCD-depleted peripheral blood progenitors from unrelated donors.

Second hematopoietic stem cell transplantation for the treatment of graft failure, graft rejection or relapse after allogeneic transplantation

Failure to engraft after hematopoietic stem cell transplantation (graft dysfunction) or to sustain engraftment (graft rejection) is a formidable complication due to many possible factors. These include inadequate stem cell numbers, infections, graft-versus-host disease and immunological mediated processes. Fortunately, this complication is uncommon and can be overcome by additional hematopoietic stem cell infusions. Multiple treatment alternatives have been explored including hematopoietic growth factors, additional infusions of stem cells alone, with augmented immunosuppression or with additional cytotoxic therapy. Various sources of the additional stem cells are feasible including the original donor, using another donor, using stem cells collected from the marrow or after cytokine mobilization from the peripheral blood. This report will overview this complication and review the various studies that have attempted to define both cause and therapy. However, a lack of well-designed prospective studies has made definitive recommendations difficult although basic principles have been established.

Long-term follow-up of persisting mixed chimerism after partially T cell-depleted allogeneic stem cell transplantation

Using red cell phenotyping (RCP) and/or cytogenetics (CYT) we identified 19 patients with persisting mixed chimerism (MC) among 231 patients transplanted with partially T cell-depleted stem cell grafts from HLA-identical siblings. Persisting MC is defined as MC for more than 2 years in patients without any evidence of relapse. Median leukemia-free survival in these patients was 150 (range, 50-218) months. Diagnoses were ALL (n= 10); AML (n = 2); CML (n = 2); NHL (n = 2); MDS (n= 1); MM (n = 1) and SAA (n = 1). Purpose of this study was the long-term follow-up of MC and definition of patterns of chimerism in the various subsets of PBMCs and granulocytes. Using a PCR-STR technique CD3(+)/CD4(+) (T4 lymphocytes), CD3(+)/CD8(+) (T8 lymphocytes), CD45(+)/CD19(+) (B lymphocytes), CD45(+)/CD14(+) (monocytes), CD45(+)/CD15(+) (granulocytes) and CD3(-)/CD56(+) (NK-cells) were analyzed. The majority of patients with persisting MC were conditioned with a less intensive conditioning regimen and had little GVHD. Sequential monitoring of the chimerism resulted in a group of patients (n = 7) with very slow transient mixed chimerism that resulted in complete DC after median 7 years. Another nine patients had a relatively high percentage of persisting autologous cells for a median of 12 years and in three patients we observed a stable low percentage of autologous cells. Only two out of 19 patients (AML-CR1, CML-CP1) relapsed during follow-up. Both patients had a relatively high percentage of autologous cells. Chimerism in granulocytes and PBMC subsets was analyzed at a median of 8 years after SCT in nine patients. In five patients mixed chimerism simultaneously detected by RCP and CYT was associated with MC in all subsets. Within each individual patient the percentages of donor and recipient cells were very different between the different subsets. Two CML-CP1 patients were mixed chimera in only two subsets and in one patient these subsets represented pending relapse. In another two patients mixed chimerism with a very low number of autologous red cells was not found in the PBMCs because of the different sensitivity level of the RCP and the PCR-STR technique. We conclude that in patients with persisting mixed chimerism after partially T cell-depleted SCT a remarkable number of patients had lymphoid malignancies, the majority of the patients were conditioned with less intensive conditioning regimens and the mixed chimerism was not correlated with relapse. Chimerism in granulocytes and PBMC subsets did show great intra-individual differences in the subsets and these data correlated well with RCP and CYT data with the exception of the NK cells.