Monitoring of chimerism following allogeneic haematopoietic stem cell transplantation (HSCT): technical recommendations for the use of short tandem repeat (STR) based techniques, on behalf of the United Kingdom National External Quality Assessment Service for Leucocyte Immunophenotyping Chimerism Working Group

Performance Characteristics of Next-Generation Sequencing-Based Engraftment Monitoring and Microchimerism Detection in Allogeneic Hematopoietic Cell Transplantation: A Practical Approach for Clinical Assay Validation

Chimerism analysis by next-generation sequencing (NGS) is an emerging method for engraftment monitoring after allogeneic hematopoietic cell transplantation. A high-sensitivity method is required for the detection of microchimerism (<1% chimerism), which may have clinical utility in early relapse detection, allograft monitoring in organ transplantation, and other allogeneic cellular therapies (such as microtransplantations). As more clinical laboratories adopt this method, a thorough assessment of performance is needed. This study evaluated one such NGS-based assay that uses both single-nucleotide polymorphisms and insertions/deletions as genetic markers. An assessment of accuracy, linearity, sensitivity, and reproducibility was performed. Analytical sensitivity was 0.2% donor for single donor and 0.5% donors for double donors. The assay showed a high degree of reproducibility over a full range of chimerism. Comparison to short-tandem-repeat (STR) PCR showed high concordance; yet <5% chimerism was consistently detected by NGS, but not by STR-PCR. Comparison to real-time quantitative PCR showed high concordance, but with lower correlation in the midrange (40% to 60% chimerism). Overall, the assay showed consistent performance with high sensitivity and accuracy compared with STR-PCR and real-time quantitative PCR across a full range of chimerism in the setting of single-donor and multidonor transplantations. In addition, criteria for quality metrics were established for sequencing performance and data analysis and considerations made for clinical laboratory validation of NGS-based chimerism assay and analysis software.

The impact of donor-specific antibodies' presence on the outcome post-allogeneic hematopoietic stem cell transplantation: a survey from a single center

Introduction

Donor-specific antibodies (DSAs) correspond to anti-HLA antibodies of the recipient that are specifically directed to a mismatched antigen of the donor. In the setting of solid organ transplantation DSAs are associated with rejection. Their role is still debated in allogeneic cell transplantation. International guidelines recommend testing patients for DSA before transplant, and if possible, choosing a donor with negative screening.

Methods

We collected clinical data of 236 recipients of alloSCT, performed at our institution from March 2019 to October 2023, to evaluate their impact on engraftment. Serum from all patients was tested for DSA.

Results

186 patients (79%) achieved sustained myeloid engraftment within day 30 post alloSCT. Thirty-two out 236 (13%) patients engrafted after day 30 post alloSCT. The median times to neutrophil engraftment and platelet engraftment were respectively 21 days (range 11-121 days) and 19 days (range 10-203 days). Fourteen out 236 patients (6%) experienced PrGF. .Twenty-nine patients (12 %) were DSA-positive. Among 29 patients with DSA positivity, 17 had a haploidentical donor and 12 had a UD donor. DSA positivity directly correlates respectively with neutrophil and platelets engraftment failure at 30 days after alloSCT (p=0.01 and p= 0.0004). Univariate Cox analysis showed that factors, including DSAs positivity, disease type, disease status, donor type, conditioning regimen, patient's age, and CD34+ were correlated with neutrophil and platelet engraftment failure at 30 days after alloSCT. Younger patients with DSA negativity, with acute leukemia, in complete response at the time of transplant, who received a higher dose of CD34+ cells from a sibling donor after a myeloablative conditioning regimen, have a reduced risk of neutrophil and platelet engraftment failure at day +30 post alloSCT.Multivariate analysis confirmed the impact of the presence of DSA only for platelet engraftment, confirming the role of type and status disease, donor type, recipient age, and CD34+ cells infused on engraftment. DSA presence has no impact on TRM, DFS, and OS.

Discussion

PrGF has a multifactorial pathogenesis, where DSA is not the only player, but its impact could vary depending on the transplant platform. Thus patient screening may be helpful to choose the best donor and transplant strategy.

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.

Can novel methods replace the gold standard chimerism method after allogeneic hematopoietic stem cell transplantation?

After hematopoietic stem cell transplantation, chimerism assay is a useful approach to monitor the success of the transplant and to select the appropriate treatment strategy, such as donor leukocyte infusion or immunosuppressive drug dosage. Short tandem repeat PCR is the method that has been accepted as the gold standard for chimerism. However, it has not yet been sufficient to detect mixed chimerism in patients with minimal residual disease. Simultaneously, recent years have been marked by developing sensitive, high-throughput, and accurate molecular genetic assays. These novel methods have subsequently been adapted for the analysis of post-transplant chimerism. In this review, we discuss the technical features of both novel and conventional gold standard chimerism assays. We also discuss their advantages and disadvantages.

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

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

Graft-versus-host disease after autologous stem cell transplantation in a recipient who underwent allogeneic stem cell transplantation 20 years earlier

A literature review does not provide information about the safety of autologous hematopoietic stem cell transplantation (HSCT) in a recipient who has previously received allogeneic HSCT. We treated a 69-year-old woman with diffuse large B cell lymphoma. The patient received autologous stem cell transplantation (ASCT) in the second complete remission of malignant lymphoma. The patient had undergone allogeneic hematopoietic SCT (allo-HSCT) for chronic myeloid leukemia 20 years ago. Chronic myeloid leukemia had been in complete remission for the previous 20 years. Thus, the patient received autologous and allogenic HSCT 20 years apart. ASCT involves the patient receiving "self" hematopoietic cells from an allogeneic donor. In other words, this is immunologically the second allo-HSCT. The allo-HSCT 20 years ago was undergone by a related healthy brother, a human leukocyte antigen (HLA) 8/8 full matched donor. The conditioning regimen was reduced-intensity consisting of fludarabine and busulfan. The patient did not experience acute or chronic graft-versus-host disease (GVHD) after allo-HSCT. The second transplantation, ASCT was performed to the MEAM conditioning regimen. Engraftment was uneventful, and complete donor chimerism had been achieved even after ASCT. She suffered from an acute gastric mucosal lesion 52 days after ASCT. Pathological finding of gastric mucosa was nonspecific acute gastritis with significant neutrophil infiltration. Sex chromosome analysis of gastric mucosa demonstrated that mucosal cells had XX signals, whereas infiltrating neutrophils had XY signals. We speculated the patient onset of an acute gastric GVHD in this recipient after the second transplantation. This case remarked infiltration of neutrophils triggered GVHD reaction by resetting allogeneic immune reaction after the second transplantation. We describe a rare occurrence of GVHD reaction in a recipient of ASCT following allo-HSCT.

Genetic Findings of Potential Donor Origin following Hematopoietic Cell Transplantation: Recommendations on Donor Disclosure and Genetic Testing from the World Marrow Donor Association

Following hematopoietic cell transplantation (HCT), recipients are subjected to extensive genetic testing to monitor the efficacy of the transplantation and identify relapsing malignant disease. This testing is increasingly including the use of large gene panels, which may lead to incidental identification of genetic and molecular information of potential donor origin. Deciphering whether variants are of donor origin, and if so, whether there are clinical implications for the donor can prove challenging. In response to queries from donor registries and transplant centers regarding best practices in managing donors when genetic mutations of potential donor origin are identified, the Medical Working Group of the World Marrow Donor Association established an expert group to review available evidence and develop a framework to aid decision making. These guidelines aim to provide recommendations on predonation consenting, postdonation testing of recipients, and informing and managing donors when findings of potential donor origin are identified in recipients post-transplantation. It is recognized that registries will have different access to resources and financing structures, and thus whenever possible, we have made suggestions on how recommendations can be adapted.

A novel flow-cytometric based method to assess post-HSCT donor chimerism exploiting RNA hybridization

Analysis of donor-recipient chimerism after hematopoietic stem cell transplantation (HSCT) is of pivotal importance for patient's clinical management, especially in the context of mixed chimerism. Patients are routinely monitored for chimerism in sorted subsets of peripheral blood cells. However, measurement of chimerism in sorted immune cell subsets is technically challenging and time consuming. We here propose a novel, flow cytometry-based approach to detect donor cell chimerism in sex-mismatched HSCT. We exploit RNA PrimeFlow™ system, based on RNA hybridization, to detect mRNA from a lysine demethylase encoded by Y chromosome, KDM5D. This approach allows to distinguish male and female derived cells with around 1% sensitivity. The procedure can be coupled with multiparametric immunophenotyping to assess chimerism in specific immune cell subsets without the need for prior FACS-sorting. We apply this method to a cohort of HSCT patients (n = 10) and we show that it is consistent with standard PCR-based method. We also show that different T lymphocyte subsets display variable degrees of donor chimerism, especially in CD8+ T cell compartment where we observe an enrichment for recipient chimerism in central memory T cells. This method can be exploited to advance current knowledge on immune reconstitution focusing on specific subsets avoiding prior FACS-sorting.

Seventy-five years of service: an overview of the College of American Pathologists' proficiency testing program in histocompatibility and identity testing

The Histocompatibility and Identity Testing Committee offers an overview of the College of American Pathologists' (CAP) Proficiency Testing (PT) program, commemorating its significant 75th anniversary in 2024. The CAP PT program has undergone significant growth and evolution over the years, ultimately achieving Centers for Medicare and Medicaid Services approval. In 1979, CAP's partnership with the American Association for Clinical Histocompatibility Testing marked a pivotal moment, leading to the creation of the first proficiency testing survey in 1980. This laid the foundation for various PT programs managed by the CAP Histocompatibility and Identity Testing Committee, including HLA antibody testing, HLA molecular typing, engraftment monitoring, parentage/relationship testing, HLA disease associations and drug risk, and HLA-B27 typing. Each program's distinctive considerations, grading methodologies, and future prospects are detailed here, highlighting the continual evolution of histocompatibility and identity testing PT to support emerging technologies and evolving laboratory practices in the field.

One fits all: a highly sensitive combined ddPCR/pyrosequencing system for the quantification of microchimerism after hematopoietic and solid organ transplantation

OBJECTIVES

A combined digital droplet PCR (ddPCR)/pyrosequencing assay system was developed that demonstrated advantages applicable to multiple qualitative and quantitative molecular genetic diagnostic applications. Data for characterizing this combined approach for hematologic stem cell transplantation (HSCT) and allele quantification from graft-derived cell-free (cf) DNA in solid organ transplantation (SOT) is presented.

METHODS

ddPCR and pyrosequencing assays targeting 32 SNPs/markers were established. ddPCR results from 72 gDNAs of 55 patients after allogeneic HSCT and 107 plasma-cfDNAs of 25 liver transplant recipients were compared with established methods/markers, i.e. short-tandem-repeat PCR and ALT, respectively.

RESULTS

The ddPCR results were in good agreement with the established marker. The limit of detection was 0.02 % minor allele fraction. The relationship between ddPCR and STR-PCR was linear with R2=0.98 allowing to transfer previously established clinical STR-PCR cut-offs to ddPCR; 50-fold higher sensitivity and a variation coefficient of <2 % enable the use of low DNA concentrations (e.g. pre-sorted cells). ddPCR detected liver allograft injury at least as sensitive as ALT suggesting that ddPCR is a reliable method to monitor the transplant integrity, especially when other biomarkers are lacking (e.g. kidney).

CONCLUSIONS

Combining pyrosequencing for genotyping and ddPCR for minor allele quantification enhances sensitivity and precision for the patient after HSCT and SOT. The assay is designed for maximum flexibility. It is expected to be suitable for other applications (sample tracking, prenatal diagnostics, etc.).

Donor/recipient origin of lung cancer after lung transplantation by DNA short tandem repeat analysis

Background

Lung cancer is more common in posttransplant recipients than in the general population. The objective of this study was to examine the chimerism donor/recipient cell origin of graft cancer in recipients of lung transplant.

Methods

A retrospective chart review was conducted at Foch Hospital for all lung transplantations from 1989 to 2020. Short tandem repeat PCR (STR-PCR) analysis, the gold standard technique for chimerism quantification, was used to determine the donor/recipient cell origin of lung cancers in transplant patients.

Results

Fourteen (1.4%) of the 1,026 patients were found to have graft lung cancer after lung transplantation, and one developed two different lung tumors in the same lobe. Among the 15 lung tumors, 10 (67%) presented with adenocarcinoma, four (27%) with squamous cell carcinoma and one with small cell lung cancer. STR analysis showed that the origin of the cancer was the donor in 10 patients (71%), the recipient in three patients (21%), and was undetermined in one patient. Median time to diagnosis was 62 months.

Conclusion

The prevalence of lung cancer in lung transplant recipients is very low. However, the results of our study showed heterogeneity of genetic alterations, with 21% being of recipient origin. Our results highlight the importance of donor selection and medical supervision after lung transplantation.

Transfusion-Associated Graft-Versus-Host Disease in Adults

Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare but fatal complication of blood transfusion that usually develops two to 30 days following a blood transfusion giving rise to graft versus host disease (GVHD) clinical features that are consisting of fever, skin rash, jaundice, diarrhea, and pancytopenia. The disease is fulminant in most patients with a mortality rate of >90% of cases. The main aim of this review is to enhance awareness among medical practitioners about this fatal disease. Data were extracted manually from the main medical databases (Medline, Scopus, and Google Scholar) after the revision of selected articles and assessed for their contribution to the knowledge of TA-GVHD. TA-GVHD occurs when the viable donor T-cells in the blood or blood products attack the recipient's tissues which his/her immune system is incapable to destroy due to several reasons. The recipient's tissues that are usually involved in TA-GVHD include the liver, intestine, skin, lungs, and bone marrow. Any blood component either whole blood, packed red blood cells (RBCs), platelets, or fresh non-frozen plasma that contains viable T lymphocytes can cause TA-GVHD. Host immunodeficiency, transfusion of fresh blood, and partial human leukocyte antigen (HLA) matching between the donors and the recipients represent the major risk factors of TA-GVHD. Partial HLA matching includes immunocompetent recipients who receive blood from a first-degree relative also, seen in genetically homogenous populations because of high rates of consanguineous marriage. The diagnosis of TA-GVHD is mainly suspected based on clinical manifestations. However, a histopathological study of either skin or rectal biopsy is diagnostic. The treatment of TA-GVHD is generally not effective, unless the patient received emergency stem cell transplantation, while prevention via irradiation of blood or blood products represents the standard of care for this disease. In conclusion, medical practitioners should have a high index of suspicion for this disease. Moreover, future clinical trials targeting and comparing the outcomes of the different therapeutic options for TA-GVHD are required.

Chimerism Testing by Next Generation Sequencing for Detection of Engraftment and Early Disease Relapse in Allogeneic Hematopoietic Cell Transplantation and an Overview of NGS Chimerism Studies

Chimerism monitoring after allogenic Hematopoietic Cell Transplantation (allo-HCT) is critical to determine how well donor cells have engrafted and to detect relapse for early therapeutic intervention. The aim of this study was to establish and detect mixed chimerism and minimal residual disease using Next Generation Sequencing (NGS) testing for the evaluation of engraftment and the detection of early relapse after allo-HCT. Our secondary aim was to compare the data with the existing laboratory method based on Short Tandem Repeat (STR) analysis. One hundred and seventy-four DNA specimens from 46 individuals were assessed using a commercially available kit for NGS, AlloSeq HCT NGS (CareDx), and the STR-PCR assay. The sensitivity, precision, and quantitative accuracy of the assay were determined using artificially created chimeric constructs. The accuracy and linearity of the assays were evaluated in 46 post-transplant HCT samples consisting of 28 levels of mixed chimerism, which ranged from 0.3-99.7%. There was a 100% correlation between NGS and STR-PCR chimerism methods. In addition, 100% accuracy was attained for the two external proficiency testing surveys (ASHI EMO). The limit of detection or sensitivity of the NGS assay in artificially made chimerism mixtures was 0.3%. We conducted a review of all NGS chimerism studies published online, including ours, and concluded that NGS-based chimerism analysis using the AlloSeq HCT assay is a sensitive and accurate method for donor-recipient chimerism quantification and minimal residual disease relapse detection in patients after allo-HCT compared to STR-PCR assay.

Bias reduction improves accuracy and informativity of high-throughput sequencing chimerism assays

BACKGROUND AND AIMS

Chimerism monitoring by means of high-throughput sequencing of biallelic polymorphisms has shown promising advantages for patient follow-up after hematopoietic stem cell transplantation. Yet, the presence of method bias precludes achievement of an assay's theoretically attainable informativity rate, as method bias necessitates the exclusion of some markers. This method bias arises because of preferential observation of one allele over the other, and for some allelic constellations because of stochasticity.

RESULTS

This paper suggests how preferential allelic observation may lead to method bias, and when and why such bias necessitates the exclusion of markers. It is shown that also markers that remain informative suffer a reduction in trueness and precision due to method bias. A bias reduction approach in the data analysis phase is introduced and shown to improve trueness and precision under all circumstances, meriting its universal adoption. This bias reduction furthermore allows to achieve an assay's theoretically achievable informativity rate, though at the cost of reduced sensitivity. Several strategies to consider in the assay design phase that may lower biases are proposed.

CONCLUSION

Improved design and data analysis of chimerism assays increase the accuracy, applicability, and cost-effectiveness of high-throughput sequencing chimerism assays.

Cost-Effective Next Generation Sequencing-Based STR Typing with Improved Analysis of Minor, Degraded and Inhibitor-Containing DNA Samples

Forensic DNA profiles are established by multiplex PCR amplification of a set of highly variable short tandem repeat (STR) loci followed by capillary electrophoresis (CE) as a means to assign alleles to PCR products of differential length. Recently, CE analysis of STR amplicons has been supplemented by high-throughput next generation sequencing (NGS) techniques that are able to detect isoalleles bearing sequence polymorphisms and allow for an improved analysis of degraded DNA. Several such assays have been commercialised and validated for forensic applications. However, these systems are cost-effective only when applied to high numbers of samples. We report here an alternative, cost-efficient shallow-sequence output NGS assay called maSTR assay that, in conjunction with a dedicated bioinformatics pipeline called SNiPSTR, can be implemented with standard NGS instrumentation. In a back-to-back comparison with a CE-based, commercial forensic STR kit, we find that for samples with low DNA content, with mixed DNA from different individuals, or containing PCR inhibitors, the maSTR assay performs equally well, and with degraded DNA is superior to CE-based analysis. Thus, the maSTR assay is a simple, robust and cost-efficient NGS-based STR typing method applicable for human identification in forensic and biomedical contexts.

Hematopoietic stem cell transplantation for inborn errors of immunity: 30-year single-center experience

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents an effective treatment for a variety of inborn errors of immunity (IEI). We report the experience of children affected by IEI who received allo-HSCT over a period of 32 years at IRCCS Istituto Giannina Gaslini, Genoa, Italy. HSCTs were performed in 67 children with IEI. Kaplan-Meier estimates of overall survival (OS) rate at 5 years in the whole group of patients was 83.4% after a median follow-up of 4 years. Median age at transplant was 2.5 years. Eight allo-HSCTs were complicated by either primary or secondary graft failure (GF), the overall incidence of this complication being 10.9%. Incidence of grade 3-4 acute GvHD (aGvHD) was 18.7%, significantly lower in the haploidentical transplant cohort (p = 0.005). Year of transplant (≤2006 vs. >2006) was the main factor influencing the outcome. In fact, a significant improvement in 5-year OS was demonstrated (92.5% >2006 vs. 65% ≤2006, p = 0.049). Frequency of severe aGvHD was significantly reduced in recent years (≤2006 61.5%, vs. >2006 20%, p = 0.027). A significant progress has been the introduction of the TCR αβ/CD19-depleted haploidentical platform, which was associated with the absence of severe aGvHD. However, it was associated with 23.5% incidence of GF. All but one patient experiencing GF in the this specific cohort were successfully retransplanted. In summary, allo-HSCT is confirmed to be an effective treatment for children with IEI, even in the absence of an HLA-matched donor.

Busulfan, fludarabine, and melphalan are effective conditioning for pediatric and young adult patients with myeloid malignancies underdoing matched sibling or alternative donor transplantation

BACKGROUND

Allogeneic hematopoietic cell transplantation (allo-HCT) remains a curative option for patients with high-risk myeloid malignancies.

PROCEDURE

We present our 10-year experience (October 2012 to October 2021) of consecutive allo-HCT in patients with myeloid malignancies treated on the pediatric HCT service and conditioned with myeloablative targeted dose-busulfan (BU), fludarabine (FLU), and melphalan (MEL). Twenty-three children, adolescents, and young adult patients (CAYA) (median age 15.4 years) with acute myeloid leukemia (AML, n = 17), myelodysplastic syndrome (MDS, n = 4), or chronic myeloid leukemia (CML, n = 2) underwent allo-HCT post-BU-FLU-MEL. Four patients had treatment-related AML/MDS. Donor/stem cell source was matched sibling donor (MSD) PBSC (n = 7), matched unrelated donor (MUD) PBSC (n = 2), umbilical cord blood (UCB) (n = 3), or haploidentical-BMT (n = 11). Risk stratification was low (n = 2), intermediate (n = 15), high (n = 3), and very high risk (n = 1). The two patients with CML had failed tyrosine kinase inhibitor therapies.

RESULTS

With a median follow-up of 41.6 months, the relapse rate is only 4.5% with an overall survival (OS) 100%, progression-free survival (PFS) 95.5%, and graft-versus-host-free-relapse-free survival (GRFS) 67.8%. The donor source and the acute graft-versus-host disease (GvHD) prophylaxis regimen significantly impacted grade II-IV aGvHD 66.7% versus 19.2% (p = .039) and chronic graft-versus-host-disease (cGvHD) 66.7% versus 0% (p = .002) in the patients receiving MSD or MUD PBSC compared to haplo-BMT, respectively, resulting in improved GRFS in haplo-BMT, 83.3% compared to 40% matched donor peripheral blood stem cell transplant (PBSCT) (p = .025).

CONCLUSIONS

Our results demonstrate that BU-FLU-MEL is efficacious conditioning for disease control in young patients with myeloid malignancies undergoing MSD or alternative donor allo-HCT, but in the setting of PBSC grafts with cyclosporine A-methotrexate (CSA-MTX) GvHD prophylaxis, it results in an unacceptably high incidence of GvHD.

New methods for the quantification of mixed chimerism in transplantation

Background

Quantification of chimerism showing the proportion of the donor in a recipient is essential for the follow-up of hematopoietic stem cell transplantation but can also be useful to document an immune tolerance situation after solid organ transplantation. Historically, chimerism has been quantified from genomic DNA, but with technological advances, chimerism from donor-derived cell-free DNA seems particularly relevant in solid organ transplantation.

Methods

The reference method was until recently the short tandem repeat technique, but new innovative techniques as digital PCR (dPCR) and NGS, have revolutionized the quantification of chimerism, such as the so-called microchimerism analysis. After a short review of chimerism methods, a comparison of chimerism quantification data for two new digital PCR systems (QIAcuity™ dPCR (Qiagen^®) and QuantStudio Absolute Q (ThermoFisher^®) and two NGS-based chimerism quantification methods (AlloSeq HCT™ (CareDx^®) and NGStrack™ (GenDX^®)) was performed.

Results

These new methods were correlated and concordant to routinely methods (r²=0.9978 and r²=0.9974 for dPCR methods, r²=0.9978 and r²=0.9988 for NGS methods), and had similar high performance (sensitivity, reproductibility, linearity).

Conclusion

Finally, the choice of the innovative method of chimerism within the laboratory does not depend on the analytical performances because they are similar but mainly on the amount of activity and the access to instruments and computer services.

Evaluation of a quantitative PCR-based method for chimerism analysis of Japanese donor/recipient pairs

Chimerism analysis is a surrogate indicator of graft rejection or relapse after allogeneic hematopoietic stem cell transplantation (HSCT). Although short tandem repeat PCR (STR-PCR) is the usual method, limited sensitivity and technical variability are matters of concern. Quantitative PCR-based methods to detect single nucleotide polymorphisms (SNP-qPCR) are more sensitive, but their informativity and quantitative accuracy are highly variable. For accurate and sensitive chimerism analysis, a set of KMR kits (GenDx, Utrecht, Netherlands), based on detection of insertions/deletions (indels) by qPCR, have been developed. Here, we investigated informativity and validated the accuracy of KMR kits in Japanese donor/recipient pairs and virtual samples of DNA mixtures representative of Japanese genetic diversity. We found that at least one recipient-specific marker among 39 KMR-kit markers was informative in all of 65 Japanese donor/recipient pairs. Moreover, the percentage of recipient chimerism estimated by KMRtrack correlated well with ratios of mixed DNA in virtual samples and with the percentage of chimerism in HSCT recipients estimated by STR-PCR/in-house SNP-qPCR. Moreover, KMRtrack showed better sensitivity with high specificity when compared to STR-PCR to detect recipient chimerism. Chimerism analysis with KMR kits can be a standardized, sensitive, and highly informative method to evaluate the graft status of HSCT recipients.

Comparisons of unmanipulated haploidentical donor, unrelated cord blood donor and matched unrelated donor hematopoietic stem cell transplantation in pediatric acquired severe aplastic anemia: a single center study

We retrospectively analyzed the outcomes of 240 pediatric SAA patients who underwent unmanipulated alternative HSCT between September 2012 and November 2020 at our center. The incidence of GF (PGF + SGF) was higher in the UCBD cohort compared to the MUD and HID cohorts [(13.5% ± 6.5%) vs (0%), and (1.6% ± 5.3%), respectively, p = .0001]. The incidence of platelet engraftment within 180 days post-HSCT was lower in the UCBD cohort (82.4% ± 2.3%) compared to the HID group (96.2% ± 1.3%) and the MUD group (97.4% ± 0.5%) (p = .020). the median duration time for platelet engraftment in the UCBD cohort was 29 days, longer than in HID cohort 14 days and the MUD cohort 13 days (p = .005). UCBD cohort had a lower 3-year failure-free survival (FFS) (70.5% ± 8.4%) compared to the HID cohort (81.1% ± 4.3%) and the MUD cohort (92.5% ± 3.1%) (p = .030) and lower 3-year GVHD/relapse free survival (GRFS) (63.3% ± 9.5.4%) compared to the HID cohort (75.5% ± 6.8%) and MUD cohort (87.9% ± 4.5%) (p = .002). UCBD-HSCT had inferior FFS and GRFS compared to an HSCT with an HID or MUD in pediatric patients with acquired SAA. A UCBD-HSCT had a higher GF and lower incidence of platelet engraftment and longer platelet engraftment time.

A Primer on Chimerism Analysis: A Straightforward, Thorough Review

Short tandem repeat (STR) analysis to assess chimerism is a critical aspect of routine care particularly in patients facing stem cell transplants but is also relevant in other clinical scenarios. STR analysis provides a means to assess donor and recipient cellular origins in a patient, and, as such, can inform engraftment, rejection, and relapse status in stem cell transplant recipients. In this review of STR testing, the most commonly used method to assess chimerism, its background, procedural details, and clinical utility are discussed.

Toxic epidermal necrolysis-like acute graft-versus-host disease in pediatric bone marrow transplant patients: Case series and review of the literature

BACKGROUND/OBJECTIVES

Complications of hematopoietic stem cell transplant (HSCT) include acute graft-versus-host disease (aGVHD). Severe cutaneous aGVHD can present with generalized erythroderma, desquamation, and bullae which can mimic toxic epidermal necrolysis (TEN). TEN occurs in response to a culprit medication. Transplant patients are often on many medications, making it difficult to distinguish between the two conditions. Given that TEN-like aGVHD is rare, we describe a case series of pediatric patients and review the literature.

METHODS

This is a multi-institutional case series of children who developed TEN-like aGVHD following bone marrow transplantation. Demographic, clinical, and treatment information was collected.

RESULTS

Ten patients were identified. Median age at transplantation was 8.5 years (range 0.12-17 years). Median time from transplant to first skin symptoms was 35 days (range 6-110 days) and to first TEN-like symptoms was 40 days (range 16-116 days). 7/10 had other organ GVHD involvement. All patients were on concurrent medications at time of first skin symptoms including immunosuppression for GVHD prophylaxis, infection prophylaxis or treatment, and pain medication. Treatments for TEN-like aGVHD included immunosuppression.

CONCLUSIONS

We observe that patients with > or equal to 50% BSA involvement of their skin with TEN-like aGVHD, extracutaneous GVHD, and lack of reepithelization tend to have poor outcomes. Given the rarity of this condition, multidisciplinary care of these patients is important for accurate and timely diagnosis and treatment.

RETRACTED: The impact of second-donor lymphocyte infusion on secondary graft failure after allogeneic hematopoietic stem cell transplantation through activation of Foxp3 and regulatory T cells

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). The Editor of Cytotherapy has retracted this article. The article duplicates significant parts of a paper that had already appeared in Transplantation and Cellular Therapy, Volume 28, Issue 3, 2022, Pages 152.e1-152.e7, https://doi.org/10.1016/j.jtct.2021.12.017 In accordance with Committee on Publication Ethics (COPE) and Elsevier's policies, the authors have been contacted. After considering the author's response, the decision has been made to retract the paper. Redundant publications overweigh the relative importance of published findings and distort the academic record of the authors. One of the conditions of submission of a paper for publication is therefore that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

The clinical application of SNP-based next-generation sequencing (SNP-NGS) for evaluation of chimerism and microchimerism after HLA-mismatched stem cell microtransplantation

Genetic diagnostic methods for evaluation of chimerism after HSCT, such as STR-PCR and XY-FISH, have limited sensitivity. When donor chimerism is in the micro range (< 1%), deviations in the accuracy of assessment are the most significant disadvantage of these common methods. We developed a highly sensitive method that applies SNPs based on NGS in order to explore the value of donor cell microchimerism in microtransplantation (MST). This improved SNP-NGS approach has higher sensitivity (0.01–0.05%) and only requires a small amount of DNA (8–200 ng). We retrospectively analyzed the clinical data of 48 patients with AML who received HLA-mismatched stem cell MST at our center to assess the impact of microchimerism on clinical prognosis. Patients whose duration of microchimerism was > 10.5 months (median) had a relapse rate of 26.1%, and had better 5-year LFS and OS (73.4% and 82.6%). In contrast, patients whose duration of microchimerism was < 10.5 months had a higher relapse rate (69.6%), and their 5-year LFS and OS were 30.4% and 43.5%. In conclusion, duration of donor chimerism is highly valuable for assessment of survival and prognosis in patients with AML who have received HLA-mismatched stem cell MST, especially the intermediate-risk group.

Mixed T cell CHIMERISM in bone marrow at day+30 after allogeneic stem cell transplantation: Correlation with acute GVHD grades III-IV and no impact on relapse and overall survival

OBJECTIVES

Early chimerism analysis is important to assess engraftment in allogeneic hematopoietic stem cell transplantations.

METHODS

We retrospectively investigated the impact of T-cell chimerism at day 30 in bone marrow on acute graft-versus-host disease (aGVHD), relapse, and overall survival in 142 adult allo-transplanted patients.

RESULTS

The majority of patients (89%) received myeloablative conditioning and 90% have undergone T-cell replete donor graft. At day 30, 103 patients showed T-complete chimerism with prevalence in haploidentical transplants, whereas 39 cases had CD3+ mixed chimerism, including 30 patients transplanted with HLA identical donors, and 21 with T-cell donors<90%. T-cell chimerism at day 30 was weakly inversely related to aGVHD grades II-IV (p = .078) with no cases of grades III-IV aGVHD in patients with CD3+ <95%. Mixed T-cell chimerism did not impact on relapse (p = .448) and five of the seven patients who relapsed had T-cell chimerism ≤90%. Older age and active disease at transplant had a statistically significant negative effect on overall survival (p = .01 and p = .0001, respectively), whereas mixed CD3+ chimerism did not.

CONCLUSIONS

T lymphocyte chimerism analysis at day +30 in bone marrow could identify allo-transplanted patients at major risk of aGVHD grades III-IV (CD3+ donors >95%) mainly post-myeloablative conditioning regimen.

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

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

High levels of donor-derived cell-free DNA in a case of graft-versus-host-disease following liver transplantation

The diagnosis of graft-versus-host-disease (GVHD) after solid organ transplantation is made difficult by its variable clinical presentation and lack of sensitive and specific biomarkers to evaluate the immune state of transplant recipients. Emerging noninvasive diagnostic techniques like the quantification of donor-derived cell-free DNA (dd-cfDNA) for surveillance may improve the current standard-of-care. Herein, we report the use of this methodology in a patient with GVHD and corresponding levels of dd-cfDNA without any evidence of graft injury. Correlation of dd-cfDNA levels with the clinical course and its novel application here could lead to improvements in the rapid diagnosis of GVHD and in monitoring of response to treatment.

Lineage-specific early complete donor chimerism and risk of relapse after allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia

Recipient–donor chimerism is routinely analyzed after allogeneic hematopoietic stem cell transplantation (HSCT) to monitor engraftment and graft rejection. For malignancies, chimerism can also be used to screen for disease relapse post-HSCT but methodology and interpretation of results are not standardized and likely depend on underlying diagnosis. We have implemented highly sensitive and accurate methodologies for chimerism analysis for the purpose of improving relapse prediction. Here, we report an exploratory retrospective analysis of clinical routine chimerism results from all 154 HSCTs for acute myeloid leukemia (AML) performed at our center during the years 2015–2020 with the aim of suggesting a clinically useful threshold at which risk of relapse is high. Relapse was not reliably predicted based on single elevated chimerism values obtained before time of overt relapse. However, early complete donor chimerism, here defined as recipient DNA < 0.2% in CD33⁺ cells in any blood or bone marrow sample taken during the first 60 days after HSCT, correlated inversely with relapse during the observation time (log-rank test P = 0.033). We propose that achievement of complete chimerism determined early after HSCT using sensitive methods can be used for risk-stratification of AML patients.

Total Body Irradiation-Based Conditioning Regimen Improved the Survival of Adult Patients With T-Cell Lymphoblastic Lymphoma After Allogeneic Peripheral Blood Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is one of the consolidation modalities for adult patients with T-cell lymphoblastic lymphoma (T-LBL). However, the optimal conditioning regimen needs to be explored. In the present study, 40 patients with T-LBL undergoing allo-HSCT were retrospectively analyzed, including 23/40 (57.5%) with total body irradiation (TBI)–based conditioning regimen and 17/40 (42.5%) with busulfan (BU)-based regimen. TBI–based regimen significantly increased the cumulative incidence (CI) of grade II to IV acute graft-versus-host disease (aGvHD) as compared with BU-based regimen (13.0% vs 0%, P = 0.000). The relapse risk was significantly lowered in TBI-based group with a 2-year CI of relapse (CIR) of 9.1% as compared with that of 49.6% in BU-based group (P = 0.008). The 1-year and 2-year non-relapse mortalities (NRMs) for all patients were 5.0% and 10.3%, respectively. The 1-year and 2-year NRMs were 8.9% and 16.0% in TBI-based group, and 0.00% and 0.00% in BU-based group (P = 0.140). The 2-year probabilities of overall survival (OS) and relapse-free survival (RFS) were 83.0% [95% confidence interval, 63.4%–100%] and 74.0% (95% confidence interval, 54.4%–93.6%) in TBI-based group, which were higher than that of 35.0% (95% confidence interval, 0.0%–72.2%) and 50.0% (95% confidence interval, 24.5%–75.4%) in BU-based group, respectively (P = 0.020 for OS and P = 0.081 for RFS). In multivariate analysis, TBI-based regimen significantly reduced the risk of relapse [subdistribution hazard ratio (SHR) = 0.030, 95% CI, 0.002–0.040, P = 0.000] and improved the OS [hazard ratio (HR) 0.121, 95% CI, 0.021–0.683, P = 0.017] as an independent prognostic factor. These results suggested that TBI-based regimen might be an optimal choice for adult patients with T-LBL undergoing allo-HSCT.

Effect of donor lymphocyte infusion from two types of donors on Mixed Chimerism with Secondary Graft Failure after allogeneic haematopoietic stem cell transplantation

Mixed chimerism (MC) and secondary graft failure (SGF) with recipient-or donor-type chimerism is a major obstacle in allogeneic hematopoietic stem cell transpl- antation (HSCT). Donor lymphocyte infusion(DLI) can eradicate minimal residual disease or be used to rescue a hematologic relapse, being able to induce durable remissions after HSCT.This study aimed to analyse the efficacy and immune mecha- nism of DLI from the original and alternative donor for patients of mixed donor chimerism with SGF . The alternative donor refers to the candidate relative donor who did not initially provide stem cells include HLA-matched sibling donor(MSD) or HLA- haploidentical donor (HID). We conducted a retrospective study of 246 patients with a median age of 37 (9-58) years who were regularly detected MC, complete donor chimera (CC) and regulatory T cells (Treg). The median diagnosis time of SGF was 69 (39-141) days after transplantation . Sixteen patients of SGF received DLI from the alternative donor, including 3 patients who chose DLI from the original donor with no initial response and 13 patients who directly chose DLI from the alternative donor. Sixteen patients with SGF exsisted mixed chimerism synchronously and the rate calculated overall chimerism of MC was 63% (range, 42%-85%) after transplantation. The proportion of Treg decreased significantly in SGF patients from a median of (2.66% ±0.80%) to (0.93%±0.57%) at a time point after transplantation (p=0.02).The DLI of the alternative donor in 14 patients achieved complete response and MC gradually convert to CC state, simultaneously there was significant increase in the Treg fraction [SGF vs CR: (0.93% ± 0.57%) vs (3.61%±0.82%), p=0.01)].For the clinical nonres- ponders from two types of donor there was no significant change in MC and Treg cells. The OS and DFS at 2 years after DLI were 69.7%±3.19 % and 61.3%±4.80%, respectively. DLI from the alternative donor may be an effective treatment for MC with SGF and the mechanism is closely related to the activation of Treg cells level.

Unmanipulated haploidentical donor and matched unrelated donor hematopoietic stem cell transplantation in patients with paroxysmal nocturnal hemoglobinuria: a single-center study

We analyzed the outcomes of 32 patients with paroxysmal nocturnal hemoglobinuria (PNH) who underwent either a haploidentical donor (HID) or a matched unrelated donor (MUD) hematopoietic stem cell transplantation (HSCT). Seventeen patients received an HSCT from an HID and 15 patients received an HSCT from an MUD. The median follow-up time of the surviving patients was 36 months (range: 12-96 months). No significant differences were observed in the 3-year overall survival (OS) between the HID and MUD cohorts (74.1%±11.4% vs. 93.3%±6.4%, respectively, p=.222) or in the 3-year failure-free survival (68.8%±11.8% vs. 86.7%±8.8%, respectively, p=.307). Treatment-related mortality occurred in five patients. A univariate analysis of risk factors revealed platelet engraftment failure negatively impacted OS and FFS. We conclude that HID and MUD-HSCT are feasible and can be effective options for those PNH patients with concomitant bone marrow failure, recurrent life-threatening thrombosis, and uncontrollable hemolysis.

Use of chimerism analysis after allogeneic stem cell transplantation: Belgian guidelines and review of the current literature

Background: Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment option in both adult and pediatric patients with malignant and non-malignant hematological diseases.  Chimerism analysis, which determines the donor or recipient origin of hematopoietic cells in HSCT recipients, is an essential aspect of post-HSCT follow-up.Objectives: To review the current literature and develop Belgian consensus guidelines for the use of chimerism analysis in the standard of care after allogeneic HSCT.Methods: Non-systematic review of the literature in consultancy with the members of the BHS transplantation committee.Results: Clinical application with regards to prediction of graft failure or relapse as well as cell source are reviewed. A consensus guideline on the use of chimerism analysis after HSCT is presented.Conclusion: Monitoring of the dynamics or kinetics of a patient's chimerism status by serial analysis at fixed time points, as well as on suspicion of relapse or graft failure, is needed to monitor engraftment levels, as well as disease control and possible relapse.

Intensive monitoring of minimal residual disease and chimerism after allogeneic hematopoietic stem cell transplantation for acute leukemia in children

Posttransplant leukemia detection before overt relapse is key to the success of immunotherapeutic interventions, as they are more efficient when leukemia burden is low. However, optimal schedule and monitoring methods are not well defined. We report the intensive bone marrow monitoring of minimal residual disease (MRD) using flow cytometry (FC) and nested reverse transcription polymerase chain reaction (RT-PCR) whenever a fusion transcript allowed it and chimerism by PCR at 11 timepoints in the first 2 years after transplant. Seventy-one transplants were performed in 59 consecutive children, for acute myeloid (n = 38), lymphoid (n = 31), or mixed-phenotype (n = 2) leukemia. MRD was monitored in 62 cases using FC (n = 58) and/or RT-PCR (n = 35). Sixty-seven percent of leukemia recurrences were detected before overt relapse, with a detection rate of 89% by RT-PCR and 40% by FC alone. Increased mixed chimerism was never the first evidence of recurrence. Two patients monitored by RT-PCR relapsed without previous MRD detection, one after missed scheduled evaluation and the other 4.7 years post transplant. Among the 22 cases with MRD detection without overt relapse, 19 received therapeutic interventions. Eight (42%) never relapsed. In conclusion, intensive marrow monitoring by RT-PCR effectively allows for early detection of posttransplant leukemia recurrence.

Comparison of Three CD3-Specific Separation Methods Leading to Labeled and Label-Free T Cells

T cells are an essential part of the immune system. They determine the specificity of the immune response to foreign substances and, thus, help to protect the body from infections and cancer. Recently, T cells have gained much attention as promising tools in adoptive T cell transfer for cancer treatment. However, it is crucial not only for medical purposes but also for research to obtain T cells in large quantities, of high purity and functionality. To fulfill these criteria, efficient and robust isolation methods are needed. We used three different isolation methods to separate CD3-specific T cells from leukocyte concentrates (buffy coats) and Ficoll purified PBMCs. To catch the target cells, the Traceless Affinity Cell Selection (TACS^®) method, based on immune affinity chromatography, uses CD-specific low affinity Fab-fragments; while the classical Magnetic Activated Cell Sorting (MACS^®) method relies on magnetic beads coated with specific high affinity monoclonal antibodies. The REAlease^® system also works with magnetic beads but, in contrast to MACS^®, low-affinity antibody fragments are used. The target cells separated by TACS^® and REAlease^® are “label-free”, while cells isolated by MACS^® still carry the cell specific label. The time required to isolate T cells from buffy coat by TACS^® and MACS^® amounted to 90 min and 50 min, respectively, while it took 150 min to isolate T cells from PBMCs by TACS^® and 110 min by REAlease^®. All methods used are well suited to obtain T cells in large quantities of high viability (>92%) and purity (>98%). Only the median CD4:CD8 ratio of approximately 6.8 after REAlease^® separation differed greatly from the physiological conditions. MACS^® separation was found to induce proliferation and cytokine secretion. However, independent of the isolation methods used, stimulation of T cells by anti CD3/CD28 resulted in similar rates of proliferation and cytokine production, verifying the functional activity of the isolated cells.

CAR-T after Stem Cell Transplantation in B-Cell Lymphoproliferative Disorders: Are They Really Autologous or Allogenic Cell Therapies?

Allogenic hematopoietic stem cell transplantation (allo-HSCT) is one of the standard treatments for B-cell lymphoproliferative disorders; however, deep relapses are common after an allo-HSCT, and it is associated with poor prognosis. A successful approach to overcome these relapses is to exploit the body's own immune system with chimeric antigen receptor (CAR) T-cells. These two approaches are potentially combinatorial for treating R/R B-cell lymphoproliferative disorders. Several clinical trials have described different scenarios in which allo-HSCT and CAR-T are successively combined. Further, for all transplanted patients, assessment of chimerism is important to evaluate the engraftment success. Nonetheless, for those patients who previously received an allo-HSCT there is no monitorization of chimerism before manufacturing CAR T-cells. In this review, we focus on allo-HSCT and CAR-T treatments and the different sources of T-cells for manufacturing CAR T-cells.

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.

Unexpected Short-Tandem-Repeat Patterns in Posttransplant Chimerism Testing: Investigation of 3 Cases with Help from Forensic Science

Chimerism testing by short tandem repeats (STRs) is used to monitor engraftment after allogeneic hematopoietic stem cell transplantation (HSCT). Generally, STR alleles are stable and transferred from parent to child or from donor to recipient. However, 3 cases did not follow this norm. Additional work-up with help from forensic literature solved these mysteries. In case 1, the patient received HSCT from his son. The son shared STR alleles in 22/23 loci except Penta E, which was explained by repeat expansion in the son. In case 2, the patient had been in remission for 14 years after HSCT for lymphoma and developed repeat expansion in CSF1PO in granulocytes. In case 3, a pre-HSCT patient demonstrated 3 alleles, with 2 peaks taller than the third, in the FGA locus (chromosome 4). A combination of a triallelic variant and leukemia-associated trisomy 4 explained the finding. STR number variants are rare and clinically inconsequential but can overlap malignancy-associated, clinically significant changes.

Performance Assessment of the Devyser High-Throughput Sequencing-Based Assay for Chimerism Monitoring in Patients after Allogeneic Hematopoietic Stem Cell Transplantation

Chimerism analysis is widely used to aid in the clinical management of patients after allogeneic hematopoietic stem cell transplantation. Many laboratories currently use assays based on polymerase chain reaction followed by capillary electrophoresis, with a limit of quantification of 1% to 5%. Assays with a lower limit of quantification could allow for earlier relapse detection, resulting in improved patient care. This study investigated the analytical, clinical, technical, and practical performance of the Devyser NGS chimerism assay, a commercial high-throughput sequencing-based assay for chimerism analysis. Performance of this assay was compared with that of the Promega PowerPlex 16 HS assay, a commercial capillary electrophoresis-based assay. A limit of quantification of 0.1% was achievable with the Devyser assay. The repeatability, reproducibility, trueness, and linearity of the Devyser assay were acceptable. The Devyser assay showed potential for earlier relapse detection compared with the Promega assay. Conclusive analysis was not possible for 3% of donor-recipient pairs with the Devyser assay due to an insufficient number of informative markers; this factor was not an issue for the Promega assay. Further improvements in assay design or data analysis may allow the assay's applicability to be extended to all donor-recipient pairs studied. Technical performance criteria for chimerism analysis by high-throughput sequencing were suggested and evaluated. Both assays were found to be practical for use in a clinical diagnostics laboratory.

Donor-Host Lineage-Specific Chimerism Monitoring and Analysis in Pediatric Patients Following Allogeneic Stem Cell Transplantation: Influence of Pretransplantation Variables and Correlation with Post-Transplantation Outcomes

The impact of donor-host chimerism in post-hematopoietic stem cell transplantation (HSCT) outcomes is poorly understood. We were interested in studying whether pre-HSCT variables influenced lineage-specific donor-host chimerism and how lineage-specific chimerism impacts post-HSCT outcomes. Our main objective was to study pre-HSCT variables as predictors of lineage-specific donor-host chimerism patterns and to better characterize the relationship between post-HSCT lineage-specific chimerism and adverse outcomes, including graft failure and disease relapse. We conducted a retrospective data analysis of all patients who underwent allogeneic HSCT at the Pediatric Transplantation and Cellular Therapy service at Memorial Sloan Kettering Cancer Center between January 2010 and June 2015 and had at least 2 measurements of split-lineage chimerism. The trend of lineage-specific donor-host chimerism post-HSCT and the impact of age, disease, graft type, and pretransplantation conditioning regimen on chimerism at 3 months and 12 months post-HSCT were studied. The Wilcoxon signed-rank test, Mann-Whitney-Wilcoxon test, and Cox proportional hazard models were used for statistical analyses. A total of 137 patients were included (median age, 11.3 years). Most patients had a hematologic malignancy (n = 95), and fewer had a nonmalignant disorder (n = 27) or primary immune deficiency (n = 15). Myeloablative conditioning regimens (n = 126) followed by T cell-depleted (TCD) peripheral blood stem cell or bone marrow grafts (n = 101) were most commonly used. Mixed chimerism (MC) of total peripheral blood leukocytes (PBLs) did not predict loss of donor chimerism in all lineages and when stable was not associated with graft failure or rejection in this analyses. Split chimerism with complete donor chimerism (CC) of myeloid, B, and natural killer cells, but not T cells, occurred early post-HSCT, but full donor T cell chimerism was achieved at 12 months post-HSCT by most patients. MC within the T cell lineage was the major contributor to PBL MC, with lower median donor T cell chimerism at 3 months than at 12 months (91%) post-HSCT (51% versus 91%; P < .0001). Predictors of MC at 3 and 12 months were (1) age <3 years (P = .01 for PBLs and P = .003 for myeloid lineage); (2) nonmalignant disorder (P = .007 for PBLs); and (3) the use of reduced-intensity conditioning regimens. TCD grafts produced lower donor T cell chimerism at 3 months post-HSCT compared with unmodified grafts (P < .0001), where T cell lineage CC was achieved early post-HSCT. The donor T cell chimerism was similar at 12 months in the 2 types of grafts. Umbilical cord blood grafts had CC in all lineages at all time points post-HSCT. Loss of donor B cell chimerism was associated with increased risk of relapse in hematologic malignancies (hazard ratio, 1.33; P = .05). Age, underlying disease, conditioning regimen, and graft manipulation can impact post-HSCT donor-host chimerism and be predictors for early MC. MC in total PBLs and T cells was not related to graft failure or disease relapse. Whole-blood PBL chimerism analysis is not sufficient to assess the significance of post-HSCT donor-host status; rather, lineage-specific chimerism, particularly for myeloid, T, and B cells, should be analyzed to guide interventions and inform outcomes.

Hematopoietic stem cell transplantation for inherited bone marrow failure syndromes: alternative donor and disease-specific conditioning regimen with unmanipulated grafts

Objective: The outcomes of alternative donor hematopoietic stem cell transplantation (HSCT) with unmanipulated grafts for Inherited bone marrow failure syndromes (IBMFS) are discouraging. Our study is to demonstrate that IBMFS with disease-specific characteristics requires a tailored conditioning regimens to enhance engraftment and reduce regimen related toxicities. Methods: We retrospectively analyzed 42 patients diagnosed with IBMFS and transplanted with an alternative donor graft at our center from November 2012 to August 2018. Twenty-seven patients had Fanconi anemia (FA), 7 had dyskeratosis congenita (DC), and 8 had severe congenital neutropenia (SCN). Patients received ex-vivo unmanipulated alternative donor grafts from a matched unrelated donor (MUD) (n = 22), haploidentical donor (HID) (n = 17) and unrelated cord blood donor (UCBD) (n = 3). FA and DC patient subgroups received reduce intensified conditioning (RIC), while SCN patients received a myeloablative conditioning (MAC) regimen. Results: The median follow-up time for the surviving patients was 38 months (range: 9-63 months). The failure-free survival (FFS) for entire cohort was 76.1%, and was 72.4%, 100% and 56.2% for patients with FA, DC and SCN, respectively. There were no primary graft failures. The cumulative incidence of aGVHD at day 100 was 48.1%. The cumulative incidence of cGVHD at 1 and 3 years was 35.0% and 69.3%, respectively. Conclusion: HSCT using alternative donors with unmanipulated grafts and disease-specific conditioning regimens for IBMFS patients shows promising survival.

Eltrombopag for the treatment of poor graft function following allogeneic stem cell transplant: a retrospective multicenter study

This retrospective study assessed the effectiveness of eltrombopag (EPAG), a thrombopoietin receptor agonist, in the treatment of poor graft function (PGF) following an allogeneic haemopoietic stem cell transplantation (HSCT). Complete response was defined as normalization of blood counts, whereas partial response was defined as transfusion independence. A total of 48 patients with full donor chimerism after HSCT, received EPAG for a median of 120 days (range 10-591). Patients with uni- bi- or tri-lineage cytopenia started treatment at a median of 95 days (range 17-877) after HSCT. The overall response rate was 75%: 24 patients had a complete response and 12 had a partial response. Positive predictors of response were an HLA-matched donor, a CD34⁺ dose at transplant > 4 × 10⁶/kg, and starting EPAG treatment at least 90 days after HSCT. Patients with more than one positive predictor had a response rate of 92% for the overall patient cohort and 94% for patients with tri-lineage cytopenia. One-year survival was 89% for complete responders, 60% for partial responders and 20% for non-responders (p = 0.0004). EPAG improves peripheral blood counts in patients with poor graft function following HSCT. Response to EPAG can be predicted and has a significant impact on survival.

Chimerism Monitoring Techniques after Hematopoietic Stem Cell Transplantation: An Overview of the Last 15 Years of Innovations

Chimerism analysis is a well-established method for monitoring the state of hematopoietic stem cell transplantation (HSCT) over time by analyzing peripheral blood or bone marrow samples of the recipient in several malignant and non-malignant hematologic diseases. From a clinical point of view, a continuous monitoring is fundamental for an effective early therapeutic intervention. This paper provides a comparative overview of the main molecular biology techniques which can be used to study chimerism after bone marrow transplantation, focusing on their advantages and disadvantages. According to the examined literature, short tandem repeats (STR) analysis through simple PCR coupled with capillary electrophoresis (STR-PCR) is the most powerful method which guarantees a high power of differentiation between different individuals. However, other methods such as real-time quantitative PCR (qPCR), digital PCR (dPCR), and next-generation sequencing (NGS) technology were developed to overcome the technical limits of STR-PCR. In particular, these other techniques guarantee a higher sensitivity, which allows for the detection of chimerism at an earlier stage, hence expanding the window for therapeutic intervention. After a comparative evaluation of the various techniques, it seems clear that STR-PCR still remains the gold standard option for chimerism study, even if it is likely that both dPCR and NGS could supplement or even replace the common methods of STR analysis.

Chimerism Assay Using Single Nucleotide Polymorphisms Adjacent and in Linkage-Disequilibrium Enables Sensitive Disease Relapse Monitoring after Hematopoietic Stem-Cell Transplantation

BACKGROUND

Short tandem repeat (STR)-based chimerism analysis has been widely used for chimerism monitoring after hematopoietic stem-cell transplantation (HSCT), but technical artifacts can be problematic. We designed a chimerism assay using single nucleotide polymorphisms (SNPs) adjacent and in linkage-disequilibrium (CASAL), which doubly checked for SNP pairs, and thus could reduce background errors and increase analytical sensitivity.

METHODS

CASAL targeted 84 SNP pairs within 10 bp distance and in perfect linkage-disequilibrium. Using undiluted and serially diluted samples, baseline error rates, and linearity was calculated. Clinical performance of CASAL was evaluated in comparison with a conventional STR assay, using 191 posttransplant samples from 42 patients with HSCT.

RESULTS

CASAL had ∼10 times lower baseline error rates compared to that of ordinary next-generation sequencing. Limit of detection and quantification of CASAL were estimated to be 0.09 and 0.39%, respectively, with a linear range of 0.1-100%. CASAL correlated well with STR assay (r2 = 0.99) and the higher sensitivity enabled detection of low-level recipient chimerism and earlier prediction of relapse.

CONCLUSIONS

CASAL is a simple, analytically sensitive and accurate assay that can be used in clinical samples after HSCT with a higher performance compared to that of traditional assays. It should also be useful in other forensic and archeological testing.

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.

The Role of Bone Marrow Evaluation in Clinical Allergy and Immunology Practice: When and Why

Allergists and immunologists rely on other specialists for higher risk procedures such as biopsies of the lung or gastrointestinal tract. However, we perform and interpret a handful of procedures ourselves. Training programs have historically required competency for prescribing immunoglobulin infusions, patch testing, rhino laryngoscopy, lung function testing, and provocation testing for airway hyperreactivity even though other specialists often perform them. Bone marrow aspirations and biopsies are not included in fellowship training assessments despite a significant number of marrow evaluations being requested by allergists and immunologists. For example, nearly 1 marrow assessment per month has been requested over 2 years for patients in the Allergy Immunology Clinic at Walter Reed National Military Medical Center. Marrow assessments are often required for diagnosis, monitoring, and treatment-related toxicities. Interpretive and procedural competency would benefit the field given the range of diseases in clinical immunology practice that require marrow assessment. We have generated a comprehensive list of the major conditions that might require bone marrow assessments in any Allergy and Immunology practice. We then summarize the specific tests that must be ordered and show how to determine sample quality. Finally, some providers may desire procedural competency and for those individuals we discuss tips for the procedure.

Off-the-shelf EBV-specific T cell immunotherapy for rituximab-refractory EBV-associated lymphoma following transplantation

BACKGROUNDAdoptive transfer of donor-derived EBV-specific cytotoxic T-lymphocytes (EBV-CTLs) can eradicate EBV-associated lymphomas (EBV-PTLD) after transplantation of hematopoietic cell (HCT) or solid organ (SOT) but is unavailable for most patients.METHODSWe developed a third-party, allogeneic, off-the-shelf bank of 330 GMP-grade EBV-CTL lines from specifically consented healthy HCT donors. We treated 46 recipients of HCT (n = 33) or SOT (n = 13) with established EBV-PTLD, who had failed rituximab therapy, with third-party EBV-CTLs. Treatment cycles consisted of 3 weekly infusions of EBV-CTLs and 3 weeks of observation.RESULTSEBV-CTLs did not induce significant toxicities. One patient developed grade I skin graft-versus-host disease. Complete remission (CR) or sustained partial remission (PR) was achieved in 68% of HCT recipients and 54% of SOT recipients. For patients who achieved CR/PR or stable disease after cycle 1, one year overall survival was 88.9% and 81.8%, respectively. In addition, 3 of 5 recipients with POD after a first cycle who received EBV-CTLs from a different donor achieved CR or durable PR (60%) and survived longer than 1 year. Maximal responses were achieved after a median of 2 cycles.CONCLUSIONThird-party EBV-CTLs of defined HLA restriction provide safe, immediately accessible treatment for EBV-PTLD. Secondary treatment with EBV-CTLs restricted by a different HLA allele (switch therapy) can also induce remissions if initial EBV-CTLs are ineffective. These results suggest a promising potential therapy for patients with rituximab-refractory EBV-associated lymphoma after transplantation.TRIAL REGISTRATIONPhase II protocols (NCT01498484 and NCT00002663) were approved by the Institutional Review Board at Memorial Sloan Kettering Cancer Center, the FDA, and the National Marrow Donor Program.FUNDINGThis work was supported by NIH grants CA23766 and R21CA162002, the Aubrey Fund, the Claire Tow Foundation, the Major Family Foundation, the Max Cure Foundation, the Richard "Rick" J. Eisemann Pediatric Research Fund, the Banbury Foundation, the Edith Robertson Foundation, and the Larry Smead Foundation. Atara Biotherapeutics licensed the bank of third-party EBV-CTLs from Memorial Sloan Kettering Cancer Center in June 2015.