Relapse after bone marrow transplantation: evidence for distinct immunological mechanisms between adult and paediatric populations

Impaired Hematopoiesis after Allogeneic Hematopoietic Stem Cell Transplantation: Its Pathogenesis and Potential Treatments

Impaired hematopoiesis is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Bone marrow aplasia and peripheral cytopenias arise from primary and secondary graft failure or primary and secondary poor graft function. Chimerism analysis is useful to discriminate these conditions. By determining the pathogenesis of impaired hematopoiesis, a timely and appropriate treatment can be performed. Hematopoietic system principally consists of hematopoietic stem cells and bone marrow microenvironment termed niches. Abnormality in hematopoietic stem and progenitor cells and/or abnormality in the relevant niches give rise to hematological diseases. Allo-HSCT is intended to cure each hematological disease, replacing abnormal hematopoietic stem cells and bone marrow niches with hematopoietic stem cells and bone marrow niches derived from normal donors. Therefore, treatment for graft failure and poor graft function after allo-HSCT is required to proceed based on determining the pathogenesis of impaired hematopoiesis. Recent progress in this area suggests promising treatment manipulations for graft failure and poor graft function.

Comparison of chimerism and minimal residual disease monitoring for relapse prediction after allogeneic stem cell transplantation for adult acute lymphoblastic leukemia

Little data are available on the relative merits of chimerism and minimal residual disease (MRD) monitoring for relapse prediction after allogeneic hematopoietic stem cell transplantation (HCT). We performed a retrospective analysis of serial chimerism assessments in 101 adult HCT recipients with acute lymphoblastic leukemia (ALL) and of serial MRD assessments in a subgroup of 22 patients. All patients had received myeloablative conditioning. The cumulative incidence of relapse was significantly higher in the patients with increasing mixed chimerism (in-MC) compared with those with complete chimerism, low-level MC, and decreasing MC, but the sensitivity of in-MC detection with regard to relapse prediction was only modest. In contrast, MRD assessment was highly sensitive and specific. Patients with MRD positivity after HCT had the highest incidence of relapse among all prognostic groups analyzed. The median time from MRD positivity to relapse was longer than the median time from detection of in-MC, but in some cases in-MC preceded MRD positivity. We conclude that MRD assessment is a powerful prognostic tool that should be included in the routine post-transplantation monitoring of patients with ALL, but chimerism analysis may provide additional information in some cases. Integration of these tools and clinical judgment should allow optimal decision making with regard to post-transplantation therapeutic interventions.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: report from the Committee on Disease-Specific Methods and Strategies for Monitoring Relapse following Allogeneic Stem Cell Transplantation. Part I: Methods, acute leukemias, and myelodysplastic syndromes

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

The graft-versus-tumor effect in pediatric malignancy

Because severe forms of the graft-versus-host reaction directed against normal tissues (also termed graft-versus-host disease [GVHD]) also contribute to morbidity and mortality following allogeneic hematopoietic stem cell transplantation, major efforts have focused on strategies to separate GVHD from the potentially beneficial immune reactivity against tumor (also called the graft-versus-tumor [GVT] effect). This article focuses on the data supporting the contribution of the GVT effect to cure of malignancy, what is known about the biology of the GVT reaction, and, finally, strategies to manipulate the GVT effect to increase the potency of HSCT.

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.

Prediction of graft-versus-host disease in humans by donor gene-expression profiling

BACKGROUND

Graft-versus-host disease (GVHD) results from recognition of host antigens by donor T cells following allogeneic hematopoietic cell transplantation (AHCT). Notably, histoincompatibility between donor and recipient is necessary but not sufficient to elicit GVHD. Therefore, we tested the hypothesis that some donors may be "stronger alloresponders" than others, and consequently more likely to elicit GVHD.

METHODS AND FINDINGS

To this end, we measured the gene-expression profiles of CD4(+) and CD8(+) T cells from 50 AHCT donors with microarrays. We report that pre-AHCT gene-expression profiling segregates donors whose recipient suffered from GVHD or not. Using quantitative PCR, established statistical tests, and analysis of multiple independent training-test datasets, we found that for chronic GVHD the "dangerous donor" trait (occurrence of GVHD in the recipient) is under polygenic control and is shaped by the activity of genes that regulate transforming growth factor-beta signaling and cell proliferation.

CONCLUSIONS

These findings strongly suggest that the donor gene-expression profile has a dominant influence on the occurrence of GVHD in the recipient. The ability to discriminate strong and weak alloresponders using gene-expression profiling could pave the way to personalized transplantation medicine.

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

SUMMARY

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

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

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

P-glycoprotein targeting: a unique strategy to selectively eliminate immunoreactive T cells

T lymphocytes have been found to harbor P-glycoprotein (Pgp) and to demonstrate modulation of its ion channel transporter function according to the state of activation of T lymphocytes. We hypothesized that cytotoxic chemicals that are extruded by Pgp could be used to specifically eliminate immunoreactive T-cell populations. In this study, we evaluated the capacity of 4,5-dibromorhodamine methyl ester (TH9402), a photosensitizer structurally similar to rhodamine, a dye transported by Pgp, and which becomes highly cytotoxic on activation with visible light to selectively deplete alloreactive T lymphocytes. Stimulation of T cells with mitogens or allogeneic major histocompatibility complex-mismatched cells resulted in the preferential retention of the TH9402 rhodamine-derivative in activated T cells, both CD4+ and CD8+. Photodynamic cell therapy of TH9402-exposed T cells led to the selective elimination of immunoreactive T-cell populations. In addition, this treatment preserved resting T cells and their capacity to respond to third-party cells. Inhibition of Pgp enhanced cellular trapping of the dye in nonactivated T cells and resulted in their depletion after exposure to light. Targeting of Pgp-deficient cells may therefore represent an appealing strategy for the prevention and treatment of graft-versus-host disease and other alloimmune or autoimmune disorders.

Second allogeneic peripheral blood stem cell transplantation with fludarabine-based low-intensity conditioning regimen for relapsed myelodysplastic syndrome after allogeneic bone marrow transplantation

We describe the case of a 51-year-old patient with relapsed myelodysplastic syndrome after allogeneic bone marrow transplantation (BMT), who underwent allogeneic peripheral blood stem cell transplantation (PBSCT) after conditioning with a novel regimen consisting of fludarabine, busulfan, and antithymocyte globulin. The second PBSCT was performed early, at 3 months after the initial allogeneic BMT, but it was well tolerated and complete hematologic remission was documented. The patient did not experience any early transplantation-related organ toxicity but died from opportunistic infection 6 months after the second transplantation. Our experience suggests that this novel regimen may induce remission and could be offered to patients relapsing after the first transplantation; however, the fludarabine-containing regimen might be accompanied by profound immunosuppression.