How and when should we monitor chimerism after 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.

Minimal residual disease diagnostics in myeloid malignancies in the post transplant period

Allogeneic SCT is important in myelodysplastic syndrome, the BCR-ABL-negative chronic myeloproliferative diseases (CMPDs) and in poor-risk AML. Techniques to monitor the minimal residual disease, for example, by PCR or immunophenotyping gain increasing importance in the post transplantation period as basis for improved and earlier therapeutic interventions in impending relapse. Recent markers such as the NPM1 mutations in AML or the JAK2V617F mutation in the CMPD can be exactly quantified by real-time PCR and were evaluated for their prognostic value in the post transplantation phase and for their utility to plan adoptive immunotherapy in case of molecular relapse. With respect to chimerism, new and very sensitive methods were introduced, for example, quantitative assessment of genetic polymorphisms by real-time PCR, but also methods here are still highly individualized. Only in CML, where SCT focuses now on poor-risk cases or cases of tyrosine kinase inhibitor failure, follow-up schedules are standardized. Standardization of the different diagnostic techniques and of the intervals in the post transplantation period is urgently needed also in other myeloid malignancies and should be focus of future studies.

Bone marrow transplant cure for beta-thalassaemia major: initial experience from a developing country

Between July 2001 and June 2007, 48 consecutive patients with beta-thalassaemia major received allogeneic haematopoietic stem cell transplants (allo HSCT) from human-leukocyte-antigen-matched siblings at the Armed Forces Bone Marrow Transplant Centre, Rawalpindi, Pakistan, using standard conditioning regimens. The median age of the patient cohort was 4 years (range, 1-14 years). Thirty-one patients were in risk class I, 11 in class II and six patients were in class III. Engraftment was achieved in all patients. Survival was calculated from the date of transplant to death or last follow-up. Major post-transplant complications encountered were acute graft versus host disease (Ac GvHD) (grades II-IV), 35.4%; chronic GvHD, 8.3%; haemorrhagic cystitis, 12.5%; veno-occlusive disease (VOD) of the liver, 6.2%; bacterial infections, 37.5%; fungal infections, 19%; cytomegalovirus (CMV) infection, 6.2%; herpes infection, 6.2%; and tuberculosis in 2% of patients. Graft rejection was observed in five patients. Three patients received second transplants. Mortality was observed in 20.8% of patients. Major fatal complications included GvHD, VOD, intracranial haemorrhage, septicaema, CMV disease and disseminated tuberculosis. Overall survival and disease-free survival were 79% and 75%, respectively, at 6 years post-HSCT.

Fludarabine-melphalan as a preparative regimen for reduced-intensity conditioning allogeneic stem cell transplantation in relapsed and refractory Hodgkin's lymphoma: the updated M.D. Anderson Cancer Center experience

BACKGROUND

The role of reduced-intensity conditioning allogeneic stem cell transplantation in relapsed/refractory Hodgkin's lymphoma remains poorly defined. We here present an update of our single-center experience with fludarabine-melphalan as a preparative regimen.

DESIGN AND METHODS

Fifty-eight patients with relapsed/refractory Hodgkin's lymphoma underwent RIC and allogeneic stem cell transplantation from a matched related donor (MRD; n=25) or a matched unrelated donor (MUD; n=33). Forty-eight (83%) had undergone prior autologous stem cell transplantation. Disease status at transplant was refractory relapse (n=28) or sensitive relapse (n=30).

RESULTS

Cumulative day 100 and 2-year transplant-related mortality rates were 7% and 15%, respectively (day 100 transplant-related mortality MRD vs. MUD 8% vs. 6%, p=ns; 2-year MRD vs. MUD 13% vs. 16%, p=ns). The cumulative incidence of acute (grade II-IV) graft-versus-host disease in the first 100 days was 28% (MRD vs. MUD 12% vs. 39%, p=0.04). The cumulative incidence of chronic graft-versus-host disease at any time was 73% (MRD vs. MUD 57% vs. 85%, p=0.006). Projected 2-year overall and progression-free survival rates are 64% (49-76%) and 32% (20-45%), with 2-year disease progression/relapse at 55% (43-70%). There was no statistically significant differences in overall survival progression-free survival, and disease progression/relapse between MRD and MUD transplants. There was a trend for the response status pretransplant to have a favorable impact on progression-free survival (p=0.07) and disease progression/relapse (p=0.049), but not on overall survival (p=0.4)

CONCLUSIONS

Fludarabine-melphalan as a preparative regimen for reduced-intensity conditioning allogeneic stem cell transplantation in progression-free survival Hodgkin's lymphoma is associated with a significant reduction in transplant-related mortality, with comparable results in MRD and MUD allografts. Optimizing pretransplant response status may improve patients' outcome.

Monitoring neutrophil engraftment in allogeneic stem cell transplantation by flow cytometric analysis of neutrophil-specific antigens NA1 and NA2

Neutrophil-specific antigen (NA) expression on neutrophils was analysed in 18 Japanese children before and after allogeneic stem cell transplantation (allo-SCT) with myeloablative regimen. Donor-recipient NA-incompatibility was present in one of eight NA1/NA2 heterozygous patients and eight of 10 NA1/NA1 or NA2/NA2 homozygous patients. After allo-SCTs from NA-incompatible donors, a neutrophil recipient-to-donor conversion was confirmed in all cases. Conversion to donor NA type was complete before the absolute neutrophil count reached 0.1 x 10(9)/l. These observations indicate that flow cytometric analysis of NA antigens is a simple and useful method for monitoring neutrophil engraftment in NA-incompatible allo-SCT.

The Impact of Chimerism Patterns and Predonor Leukocyte Infusion Lymphopenia on Survival following T Cell-Depleted Reduced Intensity Conditioned Transplants

Donor leukocyte infusions (DLI) are frequently required following reduced intensity conditioned (RIC) allografts to convert mixed chimerism (MC) to full donor chimerism (FDC). The rationale is to break tolerance and maximize the graft-versus-leukemia responses. We analyzed the impact of chimerism in 125 recipients of RIC (Alemtuzumab containing) transplants. Four patterns of chimerism were seen: (1) always 100% donor chimerism (54%), (2) persisting MC (22%), (3) MC with subsequent development of FDC (18%), (4) lost donor chimerism (6%). Forty-five (36%) patients received DLI. Chimerism patterns and pre-DLI lymphocyte counts (pDLI[Ly]) were significantly associated with DLI responsiveness. Complete disease responses were seen in 6 of 17 (35%) group A patients, 9 of 10 (90%) group C patients, and 0 of 6 group B patients (P = .027), supporting reports that chimerism response is a surrogate marker for disease response. In those with MC, pDLI(Ly) were significantly lower in DLI responsive than nonresponsive patients (P = .044). At 2 years, group C patients had a significant survival advantage (P = .009) compared to all other groups. In conclusion, the chimerism pattern was the best indicator of improved survival in this cohort (ie, MC later converting to FDC). In those with MC, response to DLI therapy was associated with a low lymphocyte count pre-DLI.

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.

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.

Assessing quantitative chimerism longitudinally: technical considerations, clinical applications and routine feasibility

In this review, we describe the current laboratory approach to quantitative chimerism testing based on short tandem repeats (STRs), focusing on a longitudinal analysis. The latter is based on relative changes appearing in the course of sequential samples, and as such exploits the ultimate potential of this intrinsically semiquantitative platform. Such an analysis is more informative than single static values, less likely to be confused with platform artifacts, and is individualized to the particular patient. It is particularly useful with non-myeloablative conditioning, where mixed chimerism is common. Importantly, longitudinal monitoring is a routinely feasible laboratory option because multiplex STR-polymerase chain reaction kits are available commercially, and modern software can be used to perform computation, reliability testing and longitudinal tracking in a rapid, easy to use format. The ChimerTrack application, a shareware, user friendly program developed for this purpose, produces a report that automatically summarizes and illustrates the quantitative temporal course of the patient's chimeric status. Such a longitudinal perspective enhances the value of quantitative chimerism monitoring for decisions regarding immunomodulatory post transplant therapy. This information also provides unique insights into the biological dynamics of engraftment underlying the fluctuations in the temporal course of a patient's chimeric status.

Chimerism analysis within 6 months of allogeneic stem cell transplantation predicts relapse in acute myeloid leukemia

The role of chimerism analysis as a prognostic indicator of relapse after hematopoietic stem cell transplantation (SCT) is controversial. We monitored chimerism status by short tandem repeat-based polymerase chain reaction (PCR) in T- and non-T-cell subsets and retrospectively evaluated clinical outcome in 96 patients with acute myeloid leukemia after myeloablative (MA) or reduced-intensity conditioning SCT. Fifty-six percent of 80 patients in the MA group demonstrated complete donor chimerism (CC) at all time points, whereas 6% had decreasing mixed chimerism (MC), 8% stable MC, 25% increasing MC and 3% increasing and decreasing MC. In 16 RIC patients, these percentages were 12, 50, 6, 6 and 19, respectively, together with 6% nonengraftment. Forty-three out of 96 patients experienced relapse. The last chimerism evaluation before relapse revealed increasing MC in only eight patients. In samples taken between 1 and 6 months post SCT, CC/decreasing MC was significantly related with a lower risk of relapse (31 versus 83%, P<0.000) and mortality (38 versus 83%, P<0.000) than with MC/increasing MC. However, the development of relapse was very rapid. Only very frequent monitoring of chimerism status by highly sensitive methods might identify impending relapse and allow early immunological intervention.

Quantitative analysis of chimerism after allogeneic stem cell transplantation by real-time polymerase chain reaction with single nucleotide polymorphisms, standard tandem repeats, and Y-chromosome-specific sequences

We compared the results of chimerism analyses with real-time SNP-PCR to those obtained by the classical STR-PCR method in 135 hematopoietic stem cell transplantation recipients. Using 10 different SNP gene loci, the SNP-PCR method was able to discriminate patient from donor cells in 125 of 135 cases (93%), whereas the use of 11 different STR gene loci with the STR-PCR analysis using agarose or polyacrylamide gel resolution resulted in accurate donor-host discrimination in all patients. Of the 470 analyzed samples we found in 74% concordant results for both chimerism methods. In all 26% discordant cases the SNP-chimerism method showed mixed chimerism (MC), whereas the STR-method found complete chimerism (CC). As a consequence, the SNP-PCR chimerism analysis method detected a MC prior to the occurrence of relapse significantly earlier than the STR-PCR chimerism method (120 vs. 30 days, P < 0.007). The probability of relapses was significantly higher in patients with increasing MC (70%) compared to 30% in patients with CC (P < 0.00001) associated with a significantly shorter overall survival in patients with increasing MC. The multivariate Cox model showed that chimerism analsis with SNP-PCR was the only significant risk factor predicting relapse (RR 6.08, P < 0.0001).Furthermore, we analyzed the chimerism status in male recipients with a female donor in 580 samples of 134 patients using quantitative real-time PCR of Y-chromosome-specific sequences and compared the results with interphase XY-fluorescent in situ hybridization (FISH). MC without signs of relapse was detected in 35% of samples using quantitative real-time PCR of Y-chromosome-specific sequences. The detected Y-DNA amounts were low compared to the amounts detected in 104 samples of 42 patients with leukemic relapse at the time of analysis (P < 0.0001). Quantitative real-time PCR of Y-chromosome-specific sequences detected therefore an increasing MC with high residual host DNA amounts approximately 143 days (mean) prior to the occurrence of relapse. By comparing the results of Y-chromosome PCR with the XY-FISH analysis we found concordant results in 73% in patients with myeloablative regimens. The XY-FISH could detect 12 relapses, whereas the Y-chromosome PCR detect 36 relapses by MC (P < 0.005). Residual host cells gradually decreased during the posttransplant period from a mean of 5.4 ng (first months) to 0.5 ng (above 5 years) without evidence of relapses. The probability of relapses was significantly higher in patients with increasing MC (100%) compared to 8% in patients with CC (P < 0.00001) associated with a significantly shorter overall survival in patients with increasing MC. The multivariate Cox model showed that chimerism analysis of Y-chromosome-specific sequences is an important risk factor for relapse (RR 17.0, P < 0.0001). We conclude that the use of real-time SNP or Y-PCR may be superior to the STR-PCR or interphase XY-FISH methods in detecting patients who are at high risk for relapse after transplant.

Chimerism and outcomes after allogeneic hematopoietic cell transplantation following nonmyeloablative conditioning

Allogeneic hematopoietic cell transplantation (HCT) following nonmyeloablative conditioning has been extensively evaluated in patients with hematologic malignancies who are ineligible for conventional HCT because of age or medical comorbidities. Nonmyeloablative regimens have led to an initial state of mixed hematopoietic chimerism defined as coexistence of donor- and host-derived hematopoiesis. While nonmyeloablative regimens have been associated with reduced regimen-related toxicities in comparison with conventional myeloablative conditioning, graft rejection, graft-versus-host disease (GVHD), and disease progression have remained significant challenges. In this article, after briefly introducing current techniques for chimerism assessment, we describe factors affecting donor chimerism levels after nonmyeloablative conditioning, and then review data suggesting that chimerism assessment early after HCT might help identify patients at risk for graft rejection, GVHD and relapse/progression. Finally, we discuss how these observations have opened the way to further research protocols evaluating manipulation of postgrafting immunosuppression, and/or infusion of donor immune cells.

Major ABO-incompatible hematopoietic stem cell transplantation: study of post-transplant pure red cell aplasia and endothelial cell chimerism

BACKGROUND

In contrast to human leukocyte antigen (HLA) matching, ABO-blood group incompatibility plays a minor role in the success of allogeneic hematopoietic stem cell transplantation (HSCT). Incompatible ABH histo-blood group antigens, expressed on recipient endothelial cells (EC) and donor erythroid progenitor cells, may represent targets for graft-versus-host disease (GVHD) and host-versus-graft reactions, respectively. The aims of the current study were to investigate: (1) red blood cell (RBC) engraftment and (2) EC chimerism as a potential result of replacement of recipient EC by donor bone marrow (BM)-derived EC in a patient following major ABO-incompatible (A to O) and gender-mismatched HSCT, who died at day 350 of severe acute GVHD.

METHODS

Blood counts and anti-A/B isoagglutinin titers were analyzed repeatedly. Heart and BM specimens were obtained at autopsy. The expression of ABH histo-blood group antigens was examined by immunhistochemistry, X/Y chromosomes were detected by chromogen in situ hybridization (CISH).

RESULTS

RBC engraftment defined as appearance of 1% reticulocytes in the peripheral blood was delayed and correlated with anti-donor isoagglutinin titers. Circulating hematopoietic cells were exclusively of donor origin demonstrating full donor hematopoietic chimerism, whereas EC in heart and BM blood vessels were exclusively of the recipient type.

CONCLUSIONS

Pure red cell aplasia (PRCA) after major ABO-incompatible HSCT was caused by anti-A/B isoagglutinins produced by recipient-type plasma cells. Using ABO and gender mismatch for discrimination, heart and BM blood vessels demonstrated no evidence for EC chimerism 11 months after ABO-incompatible HSCT. These findings suggest that EC replacement and chimerism do not represent major mechanisms responsible for tolerance induction after HSCT.

Developing an algorithm of informative markers for evaluation of chimerism after allogeneic bone marrow transplantation

Analysis of chimerism by polymerase chain reaction amplification of STR or VNTR has become a routine procedure for the evaluation of engraftment after allogeneic stem cell transplantation. Knowledge of the frequency of different STR or VNTR alleles in unrelated individuals in a population is useful for forensic work. In the context of HLA identical sibling bone marrow transplantation the informativeness of these markers needs to be evaluated. We evaluated five STRs (THO1, VWA, FES, ACTBP2, and F13A1) and 1 VNTR (APOB) for informativeness in stem cell transplants from HLA identical sibling donors. All four markers used individually allowed us to discriminate 20-56% of the patient donor pairs. Using a combination of all these markers along with a polymorphic marker in the beta-globin gene and the sex chromosome specific amelogenin marker, we were able to discriminate 99% of the patient donor pairs. We have established an algorithm for evaluating chimerism following HLA identical sibling donor transplants in the Indian population using molecular markers in 310 patients. Analysis of heterozygote frequencies in different populations is similar suggesting that this algorithm can be used universally for transplant centers to evaluate chimerism following allogeneic bone marrow transplantation.

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

OBJECTIVE AND METHODS

Chimerism analysis has become a routine diagnostic procedure after haematopoietic allogeneic stem cell transplantation for early detection of relapse of disease or graft failure. Whereas some centres developed individual in-house short tandem repeat (STR) systems, others prefer commercial multiplex PCR systems. However, little is known about inter-assay variation, which could have a significant impact on treatment decision. We therefore compared two commercial multiplex PCR kits with our in-house STR system using different sample sources, such as peripheral blood (PB), bone marrow (BM) and specific leukocyte subsets.

RESULTS

Fifty samples of eighteen paediatric patients were analysed. For neither material, PB, BM and leukocyte subtypes, a significant difference between the STR systems tested was observed. Chimerism analyses of each single STR primer, which is component of both the in-house and the commercial STR system, did not reveal significant differences.

CONCLUSION

Our analysis demonstrates that similar results can be obtained with both assays, even when using various sample sources. Further evaluation of different test systems will help to increase interlaboratory standardisation of chimerism analyses for early clinical intervention.

Analysis of donor-type chimerism in lineage-specific cell populations after allogeneic myeloablative and nonmyeloablative stem cell transplantation

We analyzed donor-type chimerism in CD3+, CD14.15+ and CD56+ cells from 36 patients who had undergone conventional-intensity allogeneic stem cell transplantation (CST) and 34 patients who had undergone non-myeloablative allogeneic stem cell transplantation (NST) for hematological malignancies. On day 28 after transplantation, all fractions in NST patients and CD3+ cells in CST patients who received a non-total body irradiation (TBI) regimen showed more frequent mixed chimerism (<90% donor cells) than those in patients who had received TBI. NST patients with acute graft-versus-host disease (grade II-IV) frequently showed more than 50% donor-type chimerism in CD3+ cells on day 14 (P=0.029). NST patients with <50% donor-type chimerism on day 14 and with <90% donor-type chimerism on day 28 in CD56+ cells had significantly poor 1-year overall survival (0 vs 91%, P<0.001 and 20 vs 74%, P=0.002, respectively). Both NST and CST patients with <90% donor-type chimerism in CD14.15+ cells on day 28 had significantly poor 1-year overall survival (14 vs 70%, P=0.005 and 0 vs 66%, P=0.002, respectively). Our data show that the extent of donor-type chimerism in lineage-specific cells appears to have an impact on outcome after allogeneic stem cell transplantation.

Reduced intensity transplants (RIT) in pediatrics: a review

We describe the experience with reduced intensity transplants (RIT) in pediatric patients and review the basis for this approach using adult examples and series of patients. We report the experience with RIT in two pediatric studies.

Present and future of rapid and/or high-throughput methods for nucleic acid testing

BACKGROUND

Behind the success of 'completing' the human genome project was a more than 30-year history of technical innovations for nucleic acid testing.

METHODS

Discovery of specific restriction endonucleases and reverse transcriptase was followed shortly by the development of the first diagnostic nucleic acid tests in the early 1970s. Introduction of Southern, Northern and dot blotting and DNA sequencing later in the 1970s considerably advanced the diagnostic capabilities. Nevertheless, it was the discovery of the polymerase chain reaction (PCR) in 1985 that led to an exponential growth in molecular biology and the introduction of practicable nucleic acid tests in the routine laboratory. The past two decades witnessed a continuing explosion of technological innovations in molecular diagnostics. In addition to classic PCR and reverse transcriptase PCR, numerous variations of PCR and alternative amplification techniques along with an ever-increasing variety of detection chemistries, closed tube (homogeneous) assays, and automated systems were developed. Discovery of real-time quantitative PCR and the development of oligonucleotide microarrays, the 'DNA chip', in the 1990s heralded the beginning of another revolution in molecular biology and diagnostics that is still in progress.

Evaluation and Automation of Hematopoietic Chimerism Analysis Based on Real-Time Quantitative Polymerase Chain Reaction

Abstract Chimerism analysis is an essential tool in the follow-up of patients after allogeneic stem cell transplantation. High-resolution methods for chimerism analysis based on real-time quantitative polymerase chain reaction (RQ-PCR) with a detection limit of 0.1% marker-specific cells are especially valuable in the detection of patient-derived subpopulations for the monitoring of minimal residual disease. Using artificial chimeric mixtures of genotypically different cells, we optimized and evaluated the intrasample variation, accuracy, and detection limit of chimerism analysis based on RQ-PCR of short insertion and deletion polymorphisms. Furthermore, automated setup by robot was evaluated. The results were accurate, with acceptable intrasample variation at and above 0.1% marker-specific cells. The sensitivity was mainly limited by background values. Chimerism results based on RQ-PCR were similar to results based on PCR of short tandem repeats when samples from recipients of transplants with nonmyeloablative conditioning were analyzed. Furthermore, automated setup was feasible in a time-, labor-, and reagent-conserving manner.