Quantification of chimerism within peripheral blood, bone marrow and purified leukocyte subsets: comparison of singleplex and multiplex PCR amplification of short tandem repeat (STR) loci

Analysis of immunogenetics interlaboratory comparisons' success rates. External quality assurance system of the Spanish Society for Immunology GECLID-SEI

Background

For many years, transplantation outcomes were uncertain and not hopeful, until histocompatibility testing spread. Common criteria for histocompatibility assays and communications' improvement allowed an efficient organ sharing system. The possibility of organ exchanges is closely linked to the importance of interlaboratory comparisons for histocompatibility and immunogenetics methods. The external proficiency testing (EPT) systems are the most powerful quality assurance tools. They help achieve harmonization of analyses, set a standard of performance, and a common interpretation.

Methods

The external quality assurance program for diagnostic immunology laboratories (Garantía Externa de Calidad para Laboratorios de Inmunología Diagnóstica, GECLID) program nowadays runs 13 external quality assurance (EQA) histocompatibility and immunogenetics schemes, with the first of them from 2011 to date: serological and molecular: low- and high-resolution human leukocyte antigen (HLA), human platelet antigen (HPA), and killer inhibitory receptor (KIR) typing(HLA-B*27, HLA-B*57:01, and coeliac disease-related HLA), cell-dependent cytotoxicity (CDC) and flow cytometry (FC) crossmatches, anti-HLA and anti-HPA antibodies, and chimerism.

Results

A total of 85 laboratories participated in this subprogram in the last 12 years reporting over 1.69 M results: 1.46 M for anti-HLA and anti-HPA antibodies, 203.810 molecular typing data (HLA, HPA, and KIR genes), 2.372 for chimerism analyses, and 39.352 for crossmatches. Based on the European Federation for Immunogenetics (EFI) standards for EPT providers, the mean success rates ranged from 99.2% for molecular typing schemes and antibodies and 94.8% for chimerism, was 96.7% regarding crossmatches, and was 98.9% in serological typing. In 2022, 61.3% of the participating laboratories successfully passed every HLA EQA scheme, although 87.9% annual reports were satisfactory. Most penalties were due to nomenclature errors or misreporting of the risk associated to HLA and disease.

Conclusion

This EQA confirms the reliability of HLA and immunogenetics assays in routine care. There is little heterogeneity of results of different assays used by participating laboratories, even when in-house assays are used. Reliability of test results is reasonably granted.

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.

A novel multiplex tetra-primer ARMS-PCR for the simultaneous genotyping of six single nucleotide polymorphisms associated with female cancers

Background

The tetra-primer amplification refractory mutation system PCR (T-ARMS-PCR) is a fast and economical means of assaying SNP's, requiring only PCR amplification and subsequent electrophoresis for the determination of genotypes. To improve the throughput and efficiency of T-ARMS-PCR, we combined T-ARMS-PCR with a chimeric primer-based temperature switch PCR (TSP) strategy, and used capillary electrophoresis (CE) for amplicon separation and identification. We assessed this process in the simultaneous genotyping of four breast cancer–and two cervical cancer risk–related SNPs.

Methods

A total of 24 T-ARMS-PCR primers, each 5′-tagged with a universal sequence and a pair of universal primers, were pooled together to amplify the 12 target alleles of 6 SNPs in 186 control female blood samples. Direct sequencing of all samples was also performed to assess the accuracy of this method.

Results

Of the 186 samples, as many as 11 amplicons can be produced in one single PCR and separated by CE. Genotyping results of the multiplex T-ARMS-PCR were in complete agreement with direct sequencing of all samples.

Conclusions

This novel multiplex T-ARMS-PCR method is the first reported method allowing one to genotype six SNPs in a single reaction with no post-PCR treatment other than electrophoresis. This method is reliable, fast, and easy to perform.

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

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

Evaluation of the sensitivity of two recently developed STR multiplexes for the analysis of chimerism after haematopoietic stem cell transplantation

Forensic-oriented kits analysing short tandem repeat (STR) polymorphisms are widely used to determine the proportions of donor and recipient cells after haematopoietic stem cell transplantation. The sensitivity of this technology is crucial for the early detection of relapse and, in consequence, the adjustment of the treatment to enhance donor-origin haematopoiesis in transplant recipients. The objective of this study was to compare the performance of two recently developed STR multiplex kits, AmpFℓSTR(®) Identifiler(®) Plus PCR Amplification Kit (Applied Biosystems) and Investigator™ IDplex(®) (Qiagen), in the analysis of chimerism. Fifteen STR loci were amplified with both kits in 26 peripheral blood samples of transplantated patients showing chimerism. Peak amplitude threshold, detection limit (%DL), per cent donor chimerism and efficacy of each multiplex and STR were determined, and the results with both kits were compared. The %DL and the estimated per cent donor chimerism were similar with both kits. On the other hand, Identifiler(®) Plus kit allowed chimerism identification only in 24 (92%) of the 26 cases with chimerism detected by using the Investigator™ IDplex(®) when only 'type 5' allelic constellations (i.e. without potential interference by stutter peaks) were taken into account. However, IDplex(®) efficacy was somewhat lower than that of Identifiler Plus when only the most informative loci (D2S1338, D21S11, D18S51 and FGA) were considered. Therefore, although each system had some particular advantages and disadvantages, overall both STR multiplexes showed similar performance in qualitative and quantitative chimerism analysis.

Recent advances in quantitative chimerism analysis

Quantitative chimerism analysis is a diagnostic tool used to monitor engraftment kinetics after allogeneic stem cell transplantation. It reflects the proportion of recipient and donor genotypes and is based on the identification of genetic markers characteristic to a given transplant pair. Currently, PCR amplification of short tandem repeats and single-nucleotide polymorphism-specific quantitative real-time PCR are the most widely used techniques for this purpose. In this review, we will address advances as well as technology-specific imperfections, of both techniques that have emerged over the recent years. We will discuss new principles that may simplify assay design, and improve its robustness and reliability. A better chimerism assay could then guide clinical interventions and may, eventually, improve the outcome of allogeneic stem cell transplantation.

Recipient-derived cells after cord blood transplantation: dynamics elucidated by multicolor FACS, reflecting graft failure and relapse

Although umbilical cord blood has been increasingly used as an alternative donor source to treat hematologic malignancies, cord blood transplantation (CBT) is frequently complicated by graft failure and relapse of primary diseases. Because persistence or increase of recipient-derived hematopoietic or malignant cells has pathogenic import under these conditions, analysis of recipient-derived cells should be useful to understand the pathogenesis of graft failure and relapse of primary disease. Because most CBT involves human leukocyte antigen (HLA)-mismatched transplantation, we developed a 9-color fluorescence activated cell sorter (FACS)-based method of mixed chimerism (MC) analysis using anti-HLA antibodies to detect mismatched antigens (HLA-Flow method). Among CD4(+) T cells, CD8(+) T cells, B cells, NK cells, monocytes, and granulocytes, donor- and recipient-derived cells alike could be individually analyzed simultaneously in a rapid, quantitative and highly sensitive manner, making the HLA-Flow method very valuable in monitoring the engraftment process. In addition, this method was also useful in monitoring recipient-derived cells with leukemia-specific phenotypes, both as minimal residual disease (MRD) and as early harbingers of relapse. Leukemia relapse can be definitively diagnosed by cytogenetic or PCR studies using recipient-derived cells sorted for leukemia markers. Multicolor HLA-fFlow analysis and cell sorting in early diagnosis of graft failure and relapse was confirmed as valuable in 14 patients who had received HLA-mismatched CBT.

Mixed chimerism in SCT: conflict or peaceful coexistence?

Stem cell transplants that follow both myeloablative and non-myeloablative conditioning regimens can result in states of mixed chimerism, which can be stable over time. With widespread availability of Y chromosome FISH in sex-mismatched transplantation and DNA-based methodologies for analysis of chimerism in other donor-recipient pairs, further insights have been gained regarding the implications of the mixed chimeric state. In transplants performed for inherited and acquired marrow failure disorders, disease status can be improved with only 10-20% donor cells, and it appears that stable mixed chimerism at that level is an acceptable outcome often leading to a state of tolerance, but an increasing level of recipient cells often precedes graft rejection. In transplants performed for malignant conditions, increasing levels of mixed chimerism may indicate disease relapse, but some cases with stable levels of mixed chimerism have been compatible with prolonged remission states. Understanding when mixed chimerism is an indication of secondary graft failure or impending graft rejection vs a state of tolerance and ongoing propensity for the establishment of a graft-vs-tumor effect is often difficult with currently available technologies and immunologic assays. The ability to understand the implication of mixed chimerism of multiple cell lineages and of varied lymphocyte subsets will remain important areas for future research to best harness the immunologic and other therapeutic benefits of allogeneic transplantation.

Donor cell leukemia: a critical review

Approximately 40 cases of DCL have been reported in the literature; cases have been reported after allografts from bone marrow, peripheral blood and cord blood. The study of these cases may provide new insights into the mechanisms of leukemogenesis. Some data suggest that the prevalence of this complication has been under-estimated. Most cases of DCL have occurred following transplantation for leukemia, but there have also been cases reported after transplantation for non-malignant conditions. Various mechanisms have been proposed to explain how DCL arise and are briefly discussed. Additional studies are needed to define with more detail both the true prevalence of this complication and its precise pathogenetic mechanism.

Epstein-barr virus-associated posttransplant lymphoproliferative disorder of donor origin after simultaneous pancreas-kidney transplantation limited to pancreas allograft: A case report

A 45-year-old man was admitted with fever and elevated pancreas enzymes 6 months after simultaneous pancreas-kidney transplantation (SPKT). Function of the allografts was normal. Bacterial and fungal infections were excluded, while Epstein-Barr virus (EBV)-polymerase chain reaction (PCR) was positive. However, screening for EBV-associated lymphoma was negative. EBV infection did not respond to antiviral therapy. After an 18F-Fluorodeoxyglucose positron emission tomography positive signal and an abnormal computed tomography scan of the pancreas transplant, a biopsy revealed a diffuse large monomorphic B-cell lymphoma, which was confined to the grafted organ. Its origin was assigned to the donor by microsatellite analysis. Reduction of immunosuppression and immunotherapy with rituximab was unsuccessful. After 10 weeks, the patient developed an acute hemolytic uremic syndrome which required explantation of the allografts. Subsequent to the intervention, fever disappeared, EBV DNA became undetectable and lymphoma screening remained negative. In posttransplant lymphoproliferative disorder of donor origin after SPKT, transplantectomy may be a curative therapy.