Chimerism and outcomes after allogeneic hematopoietic cell transplantation following nonmyeloablative conditioning

Gaining momentum: stem cell therapies for HIV cure

PURPOSE OF REVIEW

Durable HIV-1 remission has been reported in a person who received allogeneic stem cell transplants (SCTs) involving CCR5 Δ32/Δ32 donor cells. Much of the reduction in HIV-1 burden following allogeneic SCT with or without donor cells inherently resistant to HIV-1 infection is likely due to cytotoxic graft-versus-host effects on residual recipient immune cells. Nonetheless, there has been growing momentum to develop and implement stem cell therapies that lead to durable long-term antiretroviral therapy (ART)-free remission without the need for SCT.

RECENT FINDINGS

Most current research leverages gene editing techniques to modify hematopoietic stem cells which differentiate into immune cells capable of harboring HIV-1. Approaches include targeting genes that encode HIV-1 co-receptors using Zinc Finger Nucleases (ZFN) or CRISPR-Cas-9 to render a pool of adult or progenitor cells resistant to de-novo infection. Other strategies involve harnessing multipotent mesenchymal stromal cells to foster immune environments that can more efficiently recognize and target HIV-1 while promoting tissue homeostasis.

SUMMARY

Many of these strategies are currently in a state of infancy or adolescence; nonetheless, promising preclinical and first-in-human studies have been performed, providing further rationale to focus resources on stem cell therapies.

Minimal dose of hematopoietic stem cell transplantation without myelosuppressive conditioning for T-B+NK- severe combined immunodeficiency

We reviewed the medical records of five patients with T-B+NK- severe combined immunodeficiency (SCID) who received minimal dose allogeneic hematopoietic cell transplantation (HCT) (total nucleated cell count (TNC) lower than 1.0 × 10⁸/kg). Patients were administered a median of 5.0 mL of bone marrow or peripheral blood without conditioning (in four) or with anti-thymocyte globulin alone (in one). Three patients received HCT from a matched sibling donor, one from unrelated donor, and one from familial mismatched donor. The median TNC and CD34⁺ cells were 0.54 (0.29-0.84) × 10⁸/kg and 0.61 (0.35-0.84) × 10⁶/kg, respectively. Engraftment was achieved in all. Total T cell, CD4⁺ cell, and CD8⁺ cell recovery was obtained within a year in four, and immunoglobulin replacement was discontinued in all. All patients survived, exhibiting stable donor chimerism. We obtained sufficient therapeutic effects with minimal dose transplantation without intensive conditioning in patients with T-B+NK- SCID.

Immune Cell Lineage-Specific Chimerism Testing by Next-Generation Sequencing for Engraftment Monitoring After Allogeneic Hematopoietic Stem Cell Transplantation

Chimerism is an unusual state in which a person's body comprises cells from genetically different people. Chimerism testing allows monitoring for the relative proportion of recipient and donor-derived cell subsets in recipient blood and bone marrow. In the bone marrow transplant setting, chimerism testing is the standard diagnostic tool for early detection of graft rejection and the risk of malignant disease relapse. Chimerism testing enables the identification of patients with increased risk for recurrence of the underlying disease. Herein, we describe a step-by-step technical procedure of a novel, commercially available, next-generation sequencing-based chimerism testing method for use in the clinical laboratory.

Retrospective Comparison of Efficacy and Safety of Rabbit Anti-Thymocyte Globulin and Porcine Anti-Lymphocyte Globulin in Patients With Acquired Aplastic Anemia Undergoing Hematopoietic Stem Cell Transplantation From Matched Sibling Donors

We compared the efficacy and safety of porcine anti-lymphocyte globulin (pALG) (n=140) and rabbit anti-thymocyte globulin (rATG) (n=86) in patients with acquired aplastic anemia (AA) receiving hematopoietic stem cell transplantation (HSCT) from matched sibling donors (MSD) in two transplantation centers in China ranging from 2005 to 2020. The groups had similar baseline characteristics except for a higher number of infused mononuclear cells (P<0.001) and a higher proportion of peripheral blood stem cells as graft sources (P=0.003) in the pALG group. The rates of neutrophil engraftment at day 28 (P=1), platelet engraftment at day 28 (P=0.228), bloodstream infection before engraftment (P=0.867), invasive fungal diseases (P=0.362), cytomegalovirus viremia (P=0.667), and graft rejection (P=0.147) were similar in the two groups. A higher cumulative incidence of grades II-IV acute graft versus host disease (aGvHD) at 100 days occurred in the pALG group (19% vs. 8%, P=0.035) while no significant differences in grades III-IV aGvHD (P=0.572), mild to severe chronic GvHD (cGvHD) (P=0.181), and moderate to severe cGvHD (P=0.586) were observed. The actuarial 5-year overall survival (OS), failure-free survival (FFS), and GvHD-free, FFS rates of the pALG group were 87% (95% confidence interval [CI], 82-93), 85% (95% CI, 80-92), and 78% (95% CI, 72-92) versus 91% (95% CI, 86-99) (P=0.33), 88% (95% CI, 82-97) (P=0.428), and 79% (95% CI, 72-90) (P=0.824) in the rATG group, respectively. A busulfan-containing conditioning regimen was the only adverse risk factor for OS and FFS in multivariate analysis. In conclusion, pALG is an alternative to rATG in patients with severe AA receiving MSD-HSCT. A prospective, large-sample study is needed to explore this therapy further.

Digital Droplet PCR in Hematologic Malignancies: A New Useful Molecular Tool

Digital droplet PCR (ddPCR) is a recent version of quantitative PCR (QT-PCR), useful for measuring gene expression, doing clonality assays and detecting hot spot mutations. In respect of QT-PCR, ddPCR is more sensitive, does not need any reference curve and can quantify one quarter of samples already defined as "positive but not quantifiable". In the IgH and TCR clonality assessment, ddPCR recapitulates the allele-specific oligonucleotide PCR (ASO-PCR), being not adapt for detecting clonal evolution, that, on the contrary, does not represent a pitfall for the next generation sequencing (NGS) technique. Differently from NGS, ddPCR is not able to sequence the whole gene, but it is useful, cheaper, and less time-consuming when hot spot mutations are the targets, such as occurs with IDH1, IDH2, NPM1 in acute leukemias or T315I mutation in Philadelphia-positive leukemias or JAK2 in chronic myeloproliferative neoplasms. Further versions of ddPCR, that combine different primers/probes fluorescences and concentrations, allow measuring up to four targets in the same PCR reaction, sparing material, time, and money. ddPCR is also useful for quantitating BCR-ABL1 fusion gene, WT1 expression, donor chimerism, and minimal residual disease, so helping physicians to realize that "patient-tailored therapy" that is the aim of the modern hematology.

Establishment of Chimerism and Organ Transplant Tolerance in Laboratory Animals: Safety and Efficacy of Adaptation to Humans

The definition of immune tolerance to allogeneic tissue and organ transplants in laboratory animals and humans continues to be the acceptance of the donor graft, rejection of third-party grafts, and specific unresponsiveness of recipient immune cells to the donor alloantigens in the absence of immunosuppressive treatments. Actively acquired tolerance was achieved in mice more than 60 years ago by the establishment of mixed chimerism in neonatal mice. Once established, mixed chimerism was self-perpetuating and allowed for acceptance of tissue transplants in adults. Successful establishment of tolerance in humans has now been reported in several clinical trials based on the development of chimerism after combined transplantation of hematopoietic cells and an organ from the same donor. This review examines the mechanisms of organ graft acceptance after establishment of mixed chimerism (allo-tolerance) or complete chimerism (self-tolerance), and compares the development of graft versus host disease (GVHD) and graft versus tumor (GVT) activity in complete and mixed chimerism. GVHD, GVT activity, and complete chimerism are also discussed in the context of bone marrow transplantation to treat hematologic malignancies. The roles of transient versus persistent mixed chimerism in the induction and maintenance of tolerance and organ graft acceptance in animal models and clinical studies are compared. Key differences in the stability of mixed chimeras and tolerance induction in MHC matched and mismatched rodents, large laboratory animals, and humans are examined to provide insights into the safety and efficacy of translation of results of animal models to clinical trials.

Cell-free DNA profiling informs all major complications of hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (HCT) provides effective treatment for hematologic malignancies and immune disorders. Monitoring of posttransplant complications is critical, yet current diagnostic options are limited. Here, we show that cell-free DNA (cfDNA) in blood is a versatile analyte for monitoring of the most important complications that occur after HCT: graft-versus-host disease (GVHD), a frequent immune complication of HCT, infection, relapse of underlying disease, and graft failure. We demonstrate that these therapeutic complications are informed from a single assay, low-coverage bisulfite sequencing of cfDNA, followed by disease-specific bioinformatic analyses. To inform GVHD, we profile cfDNA methylation marks to trace the cfDNA tissues-of-origin and to quantify tissue-specific injury. To inform infection, we implement metagenomic cfDNA profiling. To inform cancer relapse, we implement analyses of tumor-specific genomic aberrations. Finally, to detect graft failure, we quantify the proportion of donor- and recipient-specific cfDNA. We applied this assay to 170 plasma samples collected from 27 HCT recipients at predetermined timepoints before and after allogeneic HCT. We found that the abundance of solid-organ-derived cfDNA in the blood at 1 mo after HCT is predictive of acute GVHD (area under the curve, 0.88). Metagenomic profiling of cfDNA revealed the frequent occurrence of viral reactivation in this patient population. The fraction of donor-specific cfDNA was indicative of relapse and remission, and the fraction of tumor-specific cfDNA was informative of cancer relapse. This proof-of-principle study shows that cfDNA has the potential to improve the care of allogeneic HCT recipients by enabling earlier detection and better prediction of the complex array of complications that occur after HCT.

Long-Term Mixed Chimerism After Ex Vivo/In Vivo T Cell-Depleted Allogeneic Hematopoietic Cell Transplantation in Patients With Myeloid Neoplasms

In patients who have undergone allogeneic hematopoietic cell transplantation (HCT), myeloid mixed donor chimerism (MC) is a risk factor for disease relapse. In contrast, several studies found favorable outcome in patients with lymphoid MC. Thus far, most studies evaluating MC focused on a short-term follow-up period. Here, we report the first case series of long-term survivors with MC. We screened 1,346 patients having undergone HCT for myeloid neoplasms at our center from 1996 to 2016; 443 patients with data on total peripheral blood mononuclear cells (PBMC)/CD4⁺/CD34⁺ short tandem repeat (STR) donor chimerism (DC) and follow-up ≥24 months post-HCT were included. We identified 10 patients with long-term MC (PBMC DC <95% at ≥12 months post-HCT). Median follow-up was 11 years. All patients had received combined ex vivo/in vivo T cell-depleted (TCD) peripheral blood stem cells; none experienced ≥grade 2 acute graft-versus-host disease (GVHD). The mean total PBMC, CD4⁺, and CD34⁺ DC of all patients were 95.88%, 85.84%, and 90.15%, respectively. Reduced-intensity conditioning (RIC) was associated with a trend to lower mean total DC. Of note, two patients who experienced relapse had lower CD34⁺ DC but higher CD4⁺ DC as compared with patients in continuous remission. Bone marrow evaluation revealed increased CD4⁺/FOXP3⁺ cells in patients with MC, which might indicate expansion of regulatory T cells (T_regs). Our results support known predictive factors associated with MC such as RIC and TCD, promote the value of CD34⁺ MC as a potential predictor of relapse, highlight the potential association of CD4⁺ MC with reduced risk of GVHD, and indicate a possible role of T_regs in the maintenance of immune tolerance post-HCT.

Primary graft failure, but not relapse, may be identified by early chimerism following double cord unit transplantation

Primary graft failure may be identified by early chimerism analysis after DUCBT with RIC.

Chimerism does not appear to be useful in predicting relapse.

Umbilical cord blood transplantation (UCBT) has increased access to potentially curative therapy for patients with life-threatening disorders of the bone marrow and immune system. The introduction of reduced intensity conditioning (RIC) regimens and double umbilical cord unit infusions (DUCBT) has broadened the applicability of UCBT to more frail or larger recipients. The kinetics of chimerism after RIC DUCBT and their clinical utility are poorly understood. The RIC CBT trial reported here sought to prospectively evaluate the role of lineage-specific chimerism after DUCBT in adult patients with hematologic malignancies in the United Kingdom. Fifty-eight patients with a median age of 52 years were recruited, with overall and progression-free survivals of 59% (95% confidence interval [CI], 45%-71%) and 52% (95% CI, 39%-64%), respectively, at 2 years. Nonrelapse mortality was 4% (95% CI, 1%-13%) at day 100, and the relapse rate was 31% (95% CI, 21%-45%) at 1 year. Peripheral blood lineage-specific chimerism was feasible from day 7 after transplant onward. Five patterns of chimerism were observed including (1) complete single unit dominance (39 patients), (2) sustained donor-donor mixed chimerism (3 patients), (3) sustained donor-recipient mixed chimerism (5 patients), (4) dominance reversion (1 patient), and (5) primary graft failure (4 patients). The RIC CBT trial enabled adult patients with high-risk hematologic malignancies to safely access UCBT in the United Kingdom and provided novel insights into the kinetics of donor and recipient chimerism after RIC DUCBT that are clinically relevant. This trial was registered at https://www.clinicaltrialsregister.eu/ctr-search/trial/2004-003845-41/GB as #NCT00959231 and EudraCT 2004-003845-41.

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.

Nonmyeloablative allogeneic transplantation achieves clinical and molecular remission in cutaneous T-cell lymphoma

The majority of patients with refractory, advanced-stage mycosis fungoides (MF) or Sézary syndrome (SS) have a life expectancy of <5 years. Here, we report a phase 2 study of a novel nonmyeloablative allogeneic transplantation strategy tailored for this patient population. This study has completed the enrollment, and 35 patients (13 MF, 22 SS) have undergone transplant as planned. The majority (80%) of the patients had stage IV disease and received multiple previous systemic therapies. All patients had active disease at the time of conditioning using total skin electron beam therapy, total lymphoid irradiation, and antithymocyte globulin, and received allograft infusion as outpatients. Cyclosporine or tacrolimus and mycophenolate mofetil were used for graft-versus-host disease (GVHD) prophylaxis. Patients tolerated the transplant well, with 1- and 2-year nonrelapse mortality of 3% and 14%, respectively. The day +180 cumulative incidence of grade 2 to 4 acute GVHD was 16%, and the 2-year incidence of moderate/severe chronic GVHD was 32%. With a median posttransplant follow-up of 5.4 years, the 2-, 3-, and 5-year overall survival rates were 68%, 62%, and 56%. Using high-throughput sequencing of the T-cell receptor for minimal residual disease monitoring, we observed that 43% achieved molecular remission, which was associated with a lower incidence of disease progression or relapse (9% vs 87%; P = .02). Our study also showed that patients who were aged ≥65 years at the time of allotransplant had similar clinical outcomes compared with younger patients. Thus, we have developed an alternative and potentially curative nonmyeloablative allogeneic transplant regimen for patients with advanced stage MF/SS. This trial was registered at www.clinicaltrials.gov as #NCT00896493.

Safety and efficacy of a nonmyeloablative pretransplant conditioning regimen using total lymphoid irradiation with volumetric modulated arc therapy in healthy dogs: A pilot study

Allogeneic hematopoietic cell transplantation (HCT) has been an effective treatment for human patients with haematological malignancies (Baron & Storb, 2006; Bair et al., 2020; Copelan et al., 2019). However, the optimal pretransplant conditioning treatment is unclear in canine allogeneic HCT. This pilot study aimed to evaluate the safety and efficacy of total lymphoid irradiation (TLI) with volumetric modulated arc therapy (VMAT) for a nonmyeloablative HCT conditioning. Six healthy dogs were treated with 8 or 12 Gy TLI using VMAT. Haematological and physical changes were recorded over 8 weeks. To assess the effect of peripheral lymphocyte condition, lymphocyte subset and proliferative ability were examined. At the end of the experiment, necropsy was performed. All dogs showed mild‐to‐moderate neutropenia and thrombocytopenia, and these haematological changes resolved spontaneously. One dog treated with 8 Gy TLI developed transient cutaneous infection. No major complication was seen in the other seven dogs. Myelocytes and erythroblast cytopenia of bone marrow were detected in two dogs treated with 12 Gy TLI. This study is the first report of TLI using VMAT in dogs, and results suggest that this regimen is a feasible nonmyeloablative treatment.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clonal hematopoiesis and measurable residual disease assessment in acute myeloid leukemia

Current objectives regarding treatment of acute myeloid leukemia (AML) include achieving complete remission (CR) by clinicopathological criteria followed by interrogation for the presence of minimal/measurable residual disease (MRD) by molecular genetic and/or flow cytometric techniques. Although advances in molecular genetic technologies have enabled highly sensitive detection of AML-associated mutations and translocations, determination of MRD is complicated by the fact that many treated patients have persistent clonal hematopoiesis (CH) that may not reflect residual AML. CH detected in AML patients in CR includes true residual or early recurrent AML, myelodysplastic syndrome or CH that is ancestral to the AML, and independent or newly emerging clones of uncertain leukemogenic potential. Although the presence of AML-related mutations has been shown to be a harbinger of relapse in multiple studies, the significance of other types of CH is less well understood. In patients who undergo allogeneic hematopoietic cell transplantation (HCT), post-HCT clones can be donor-derived and in some cases engender a new myeloid neoplasm that is clonally unrelated to the recipient's original AML. In this article, we discuss the spectrum of CH that can be detected in treated AML patients, propose terminology to standardize nomenclature in this setting, and review clinical data and areas of uncertainty among the various types of posttreatment hematopoietic clones.

Nonmyeloablative TLI-ATG conditioning for allogeneic transplantation: mature follow-up from a large single-center cohort

Nonmyeloablative total lymphoid irradiation and antithymocyte globulin (TLI-ATG) conditioning is protective against graft-versus-host disease (GVHD), while retaining graft-versus-tumor activity across various hematologic malignancies. We report our comprehensive experience using TLI-ATG conditioning in 612 patients with hematologic malignancies who underwent allogeneic transplantation at Stanford University from 2001 to 2016. All patients received granulocyte colony-stimulating factor-mobilized peripheral blood grafts and cyclosporine and mycophenolate mofetil for GVHD prophylaxis. The median age was 60 years (range, 21-78), with a median follow-up of 6.0 years (range, 1.0-16.4). Common diagnoses included acute myeloid leukemia (AML; n = 193), myelodysplastic syndrome (MDS; n = 94), chronic lymphocytic leukemia (CLL; n = 80), non-Hodgkin lymphoma (NHL; n = 175), and Hodgkin lymphoma (HL; n = 35). Thirty-four percent of patients had a comorbidity index ≥3, 30% had a high to very high disease risk index, and 56% received unrelated donor grafts, including 15% with HLA-mismatched donors. Ninety-eight percent underwent transplant in the outpatient setting, and 57% were never hospitalized from days 0 through 100. The 1-year rates of nonrelapse mortality (NRM), grade II-IV acute GVHD, and extensive chronic GVHD were 9%, 14%, and 22%, respectively. The 4-year estimates for overall and progression-free survival were 42% and 32% for AML, 30% and 21% for MDS, 67% and 43% for CLL, 68% and 45% for NHL, and 78% and 49% for HL. Mixed chimerism correlated with the risk of relapse. TLI-ATG conditioning was well tolerated, with low rates of GVHD and NRM. Durable remissions were observed across hematologic malignancies, with particularly favorable outcomes for heavily pretreated lymphomas. Several efforts are underway to augment donor chimerism and reduce relapse rates while maintaining the favorable safety and tolerability profile of this regimen.

Early Mixed Lymphoid Donor/Host Chimerism is Associated with Improved Transplant Outcome in Patients with Primary or Secondary Myelofibrosis

We investigated risk factors for the development of mixed chimerism in 131 patients who underwent transplantation for myelofibrosis and determined the impact of lymphoid (CD3+) and myeloid (CD33+) chimerism on transplant outcome. Disease risk included DIPSS plus categories low to high. The median patient age was 58 years. Patients were conditioned with high-intensity (myeloablative) or low/reduced-intensity (nonmyeloablative) regimens and received a transplant from a related or unrelated donor. Mixed CD3⁺ chimerism was observed earlier after HCT, whereas CD33⁺ chimerism occurred later. Mixed chimerism was more frequent with low-intensity regimens than with high- intensity regimens. Mixed CD3⁺ chimerism did not lead to graft failure and was associated with a reduced incidence of acute GVHD and improved overall survival (OS) and relapse-free survival, whereas mixed CD33⁺ chimerism was associated with an increased incidence of relapse and reduced OS and relapse-free survival, independent of the CD34⁺ cell dose transplanted. Thus, mixed CD3⁺ chimerism in patients with myelofibrosis had a favorable impact on transplantation outcome and does not require therapeutic interventions.

Reduced-intensity stem cell transplantation for acute myeloid leukemia with fludarabine-based conditioning with intravenous busulfan versus melphalan

Reduced-intensity conditioning (RIC) has been facilitating allogeneic hematopoietic cell transplantation (allo-HCT) for patients originally considered ineligible for HCT with myeloablative conditioning. Fludarabine (Flu) with reduced doses of busulfan (Bu) (Flu + Bu) and Flu with reduced doses of melphalan (Mel) (Flu + Mel) are widely used RIC regimens for acute myeloid leukemia (AML). A nationwide retrospective study comparing clinical outcomes of adult patients with AML receiving first allo-HCT after RIC between 2001 and 2010 was performed. Cumulative incidences of relapse were not significantly different among the Flu + ivBu-based (FBiv), Flu + poBu-based (FBpo), and Flu + Mel-based (FM) groups (p = 0.29). Non-relapse mortality (NRM) was significantly lower in patients receiving FBiv compared with FBpo (p = 0.003) and FM (p < 0.001). On multivariate analysis, there was no significant difference in overall survival, but FM was associated with a significantly lower risk of relapse (hazard ratio (HR) = 0.65, 95% confidence interval (CI): 0.50-0.85, p = 0.002), higher NRM (HR = 1.60, 95% CI: 1.10-2.33, p = 0.013) and better leukemia-free survival (HR = 0.77, 95% CI: 0.63-0.95, p = 0.015) compared with FBiv. These results suggest that Flu + Mel has a more intense disease control potential and Flu + ivBu is less toxic than the other. Both RIC regimens provide similar survival outcomes and are effective and useful regimens for patients with AML who received allo-HCT.

Outstanding questions in transplantation: Tolerance

In 2017, the American Society of Transplantation (AST) launched the Outstanding Questions in Transplantation Research forum to stimulate a community-wide discussion of how the field is evolving and to help identify areas where a better dialogue between clinicians and researchers could result in great advancements. Tolerance emerged as a topic of great interest to the AST community. This minireview provides an overview of clinical transplantation tolerance. Historical background followed by a review of the current status of attempts to establish tolerance in the clinic, highlighting the dynamic online discussion surrounding this important topic from the AST Transplantation Research forum, is provided.

Summary of Scientific and Statistical Methods, Study Endpoints and Definitions for Observational and Registry-Based Studies in Hematopoietic Cell Transplantation

Due to the increasingly strict word/character restrictions enforced by most scientific publications, we identified a need for a master document illustrating the "Scientific Methods" that may be applicable to the majority of observational and registry-based studies in hematopoietic cell transplantation (HCT). The purpose of this study is to serve as a reference document that describes the data source, study endpoints and statistical analyses utilized most commonly in retrospective studies in HCT. To this end we compile, define and reference the methodology commonly used in HCT research. While it is recognized that the scientific methodology may periodically require updates due to the evolving landscape of transplant research, such as newer study endpoints and statistical methods, this manuscript describes frequently used methodologies.

[Prognostic value of donor chimerism at +90 days after allogeneic hematopoietic stem cell transplantation in young patients with intermediate-risk acute myeloid leukemia]

Objective: To investigate the relationship between donor chimerism and relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . Methods: The clinical data of 105 patients with acute myeloid leukemia (AML) who underwent allo-HSCT and recurrence-free survival>90 days from January 2010 to January 2019 were retrospectively analyzed. The bone marrow samples were collected at 15, 30, 60, 90, 180, 270, 360 days after transplantation. Donor chimerism was detected by single nucleotide polymorphism (SNP) -PCR. Results: Of the 105 patients, 43 cases were male and 62 cases were female, with a median age of 38 (16-60) years. Till April 2019, the median follow-up was 843 (94-3 261) days. Ninety days after transplantation, 18 cases relapsed, 33 cases died, and 72 cases survived. The 3-year overall survival (OS) rate was (66.8±5.1) %, and the recurrence-free survival (RFS) rate was (65.1±5.0) %. Pre-transplant disease status, pre-transplant minimal residual disease (MRD) , and 90 day post-transplantation chimerism were independent risk factors related to RFS. The risk of recurrence was significantly increased in patients with a donor chimerism rate ≤97.24% at 90 days after transplantation[HR=6.921 (95%CI 2.669-17.950) , P<0.001], which was considered as a sign of early relapse. Conclusion: SNP-PCR is an applicable method for detecting donor chimerism in patients after allo-HSCT. Chimerism rate equal or less than 97.24% at 90 days after transplantation predicts a higher risk of relapse.

Digital droplet PCR-based chimerism analysis for monitoring of hematopoietic engraftment after allogeneic stem cell transplantation

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a curative approach for multiple hematologic diseases. The success of alloHSCT is evaluated by analyzing the proportion of living donor cells in blood and bone marrow samples of the recipient (chimerism analysis). To monitor the engrafted cells, donor's individual genetic markers are analyzed in peripheral blood and bone marrow samples, usually by using short tandem repeat (STR) analysis. An alternative method to measure chimerism is based on insertion and deletion markers (InDels) analyzed by digital droplet PCR (ddPCR); however, this approach is rarely evaluated in clinical practice.

METHODS

In this study, we examined the usefulness of ddPCR-based chimerism analysis against the standard STR analysis in samples around day+30 after alloHSCT in clinical practice using peripheral blood and bone marrow samples.

RESULTS

The median absolute difference between ddPCR and STR analysis was 0.55% points for bone marrow chimerisms and 0.25% points for peripheral blood chimerisms, respectively, including variation in the range of maximum 2% for both methods. The results of every single sample gave the same clinical message.

CONCLUSION

According to our data, chimerism analysis by ddPCR has an excellent correlation with STR-based analyses. Due to its fast and easy applicability, the ddPCR technique is suitable for chimerism monitoring in clinical practice.

[Comparison of the efficacy of decitabine combined with micro-transplantation or priming regimen as consolidation treatment for older patients with acute myeloid leukemia]

目的

探索老年急性髓系白血病（AML）第1次完全缓解（CR₁）后采用地西他滨联合微移植巩固治疗的疗效与安全性。

方法

回顾性分析2012年11月至2015年9月诊治的37例CR₁老年（≥60岁）AML患者病例资料，比较分析地西他滨联合微移植（微移植组，19例）与地西他滨联合预激方案巩固治疗（化疗组，18例）的疗效和不良反应。

结果

两组患者起病时的年龄、WBC水平、疾病状态差异均无统计学意义（P值均>0.05）。两种巩固治疗方案的耐受性均良好，微移植组与化疗组的CTC 3~4级非血液学不良反应发生率差异无统计学意义[36.8%（7/19）对27.8%（5/18），χ²=0.347，P=0.728]。微移植组与化疗组中性粒细胞恢复的中位时间分别为12和13 d（z=1.599，P=0.110），血小板恢复的中位时间分别为14和12 d（z=−1.314，P=0.189）。微移植组患者均未发生移植物抗宿主病。微移植组与化疗组的2年无白血病生存率分别为50.7%和24.3%（P=0.047），2年总生存率分别为54.9%和30.0%（P=0.071）。

结论

对于老年AML患者，地西他滨联合微移植可能是一种安全有效的巩固方案。

Allogeneic Hematopoietic Cell Transplantation in Patients with Primary Immunodeficiencies in Korea: Eleven-Year Experience in a Single Center

PURPOSE

We aimed to report our single-center experience of allogeneic hematopoietic cell transplantation (HCT), which has been the only curative option for certain patients with lethal primary immunodeficiencies (PIDs).

METHODS

We summarized the results of HCT performed for patients with PIDs for 11 consecutive years from 2006 to 2016 at Samsung Medical Center, Seoul, Korea. Twenty-six patients with PIDs received HCT. Most had chronic granulomatous disease (42.3%), Wiskott Aldrich syndrome (15.4%), or severe combined immunodeficiency (11.5%).

RESULTS

Nine patients (34.6%) received HCT during the former half period and 17 patients (65.4%) during the latter half period. Donor types were categorized as: matched sibling donor (n = 5), unrelated donor (n = 17), and familial mismatched donor (FMMD) (n = 4). Unrelated HCT and FMMD transplantation were increasingly performed in the latter half period compared to the first (5 vs. 16, P = 0.034). Five patients experienced initial engraftment failure, but all of them were eventually engrafted after additional HCTs. The 3-year probability of overall survival was 72.0%. Seven patients (26.9%) died, and the causes of death were bacterial sepsis (n = 4), pneumonia (n = 1), chronic graft-versus-host disease (GVHD) (n = 1), and diffuse alveolar hemorrhage (n = 1). Two patients with bacterial sepsis and a patient with pneumonia also had chronic GVHD. Unrelated HCT and use of methotrexate were associated with poor outcome. Complete chimerism was attained in 85.0% at 1 year after HCT.

CONCLUSION

PID candidates have been increasingly identified for allogeneic HCT in Korea, and the majority of them could be cured by HCT. Establishment of a systematic registry of PID patients for HCT is needed.

Droplet Digital PCR-Based Chimerism Analysis for Primary Immunodeficiency Diseases

OBJECTIVE

In the current study, we aimed to accurately evaluate donor/recipient or male/female chimerism in samples from patients who underwent hematopoietic stem cell transplantation (HSCT).

METHODS

We designed the droplet digital polymerase chain reaction (ddPCR) for SRY and RPP30 to detect the male/female chimerism. We also developed mutation-specific ddPCR for four primary immunodeficiency diseases.

RESULTS

The accuracy of the male/female chimerism analysis using ddPCR was confirmed by comparing the results with those of conventional methods (fluorescence in situ hybridization and short tandem repeat-PCR) and evaluating dilution assays. In particular, we found that this method was useful for analyzing small samples. Thus, this method could be used with patient samples, especially to sorted leukocyte subpopulations, during the early post-transplant period. Four mutation-specific ddPCR accurately detected post-transplant chimerism.

CONCLUSION

ddPCR-based male/female chimerism analysis and mutation-specific ddPCR were useful for all HSCT, and these simple methods contribute to following the post-transplant chimerism, especially in disease-specific small leukocyte fractions.

Inosine Monophosphate Dehydrogenase Pharmacogenetics in Hematopoietic Cell Transplantation Patients

We evaluated inosine monophosphate dehydrogenase (IMPDH) 1 and IMPDH2 pharmacogenetics in 247 recipient-donor pairs after nonmyeloablative hematopoietic cell transplant (HCT). Patients were conditioned with total body irradiation + fludarabine and received grafts from related or unrelated donors (10% HLA mismatch), with postgraft immunosuppression of mycophenolate mofetil (MMF) with a calcineurin inhibitor. Recipient and donor IMPDH genotypes (rs11706052, rs2278294, rs2278293) were not associated with day 28 T cell chimerism, acute graft-versus-host disease (GVHD), disease relapse, cytomegalovirus reactivation, nonrelapse mortality, or overall survival. Recipient IMPDH1 rs2278293 genotype was associated with a lower incidence of chronic GVHD (hazard ratio, .72; P = .008) in nonmyeloablative HCT recipients. Additional studies are needed to confirm these results with the goal of identifying predictive biomarkers to MMF that lower GVHD.

HLA-mismatched unrelated donor transplantation using TLI-ATG conditioning has a low risk of GVHD and potent antitumor activity

Many patients lack a fully HLA-matched donor for hematopoietic cell transplantation (HCT), and HLA mismatch is typically associated with inferior outcomes. Total lymphoid irradiation and antithymocyte globulin (TLI-ATG) is a nonmyeloablative conditioning regimen that is protective against graft-versus-host disease (GVHD), and we hypothesized that the protective effect would extend beyond HLA-matched donors. We report outcomes for all consecutively transplanted patients at Stanford University from December 2001 through May 2015 who received TLI-ATG conditioning and HCTs from 8 to 9 out of 10 HLA-mismatched unrelated donors (MMUDs, N = 72) compared with 10 out of 10 HLA-matched unrelated donors (MUDs, N = 193). The median age of the patients was 60 years with a median follow-up of 2 years, and there was a similar distribution of lymphoid and myeloid malignancies in both cohorts. There were no significant differences between MMUD and MUD cohorts in overall survival (46% vs 46% at 5 years, P = .86), disease-free survival (38% vs 28% at 5 years, P = .25), nonrelapse mortality (17% vs 12% at 2 years, P = .34), acute GVHD grades III-IV (6% vs 3% at day +100, P = .61), or chronic GVHD (39% vs 35% at 5 years, P = .49). There was a trend toward less relapse in the MMUD cohort (45% vs 60% at 5 years, hazard ratio: 0.71, P = .094), which was significant for patients with lymphoid malignancies (29% vs 57% at 5 years, hazard ratio: 0.55, P = .044). Achieving full donor chimerism was strongly associated with lower relapse rates. TLI-ATG conditioning may overcome the traditionally poorer outcome associated with HLA-mismatched donors and may be particularly well suited for patients with lymphoid malignancies who lack HLA-matched donors.

Antibacterial Resistance in Patients with Hematopoietic Stem Cell Transplantation

Recipients of hematopoietic stem cell transplantation (HSCT) are at substantial risk of bacterial, fungal, viral, and parasitic infections depending on the time elapsed since transplantation, presence of graft-versus-host disease (GVHD), and the degree of immunosuppression. Infectious complications in HSCT recipients are associated with high morbidity and mortality. Bacterial infections constitute the major cause of infectious complications, especially in the early post-transplant period. The emergence of antibacterial resistance complicates the management of bacterial infections in this patient group. Multidrug-resistant bacterial infections in this group of patients have attracted considerable interest and may lead to significant morbidity and mortality. Empirical antibacterial therapy in patients with HSCT and febrile neutropenia has a critical role for survival and should be based on local epidemiology. This review attempts to provide an overview of risk factors and epidemiology of emerging resistant bacterial infections and their management in HSCT recipients.

Pharmacokinetics, Pharmacodynamics and Pharmacogenomics of Immunosuppressants in Allogeneic Haematopoietic Cell Transplantation: Part I

Although immunosuppressive treatments and target concentration intervention (TCI) have significantly contributed to the success of allogeneic haematopoietic cell transplantation (alloHCT), there is currently no consensus on the best immunosuppressive strategies. Compared with solid organ transplantation, alloHCT is unique because of the potential for bidirectional reactions (i.e. host-versus-graft and graft-versus-host). Postgraft immunosuppression typically includes a calcineurin inhibitor (cyclosporine or tacrolimus) and a short course of methotrexate after high-dose myeloablative conditioning, or a calcineurin inhibitor and mycophenolate mofetil after reduced-intensity conditioning. There are evolving roles for the antithymyocyte globulins (ATGs) and sirolimus as postgraft immunosuppression. A review of the pharmacokinetics and TCI of the main postgraft immunosuppressants is presented in this two-part review. All immunosuppressants are characterized by large intra- and interindividual pharmacokinetic variability and by narrow therapeutic indices. It is essential to understand immunosuppressants' pharmacokinetic properties and how to use them for individualized treatment incorporating TCI to improve outcomes. TCI, which is mandatory for the calcineurin inhibitors and sirolimus, has become an integral part of postgraft immunosuppression. TCI is usually based on trough concentration monitoring, but other approaches include measurement of the area under the concentration-time curve (AUC) over the dosing interval or limited sampling schedules with maximum a posteriori Bayesian personalization approaches. Interpretation of pharmacodynamic results is hindered by the prevalence of studies enrolling only a small number of patients, variability in the allogeneic graft source and variability in postgraft immunosuppression. Given the curative potential of alloHCT, the pharmacodynamics of these immunosuppressants deserves to be explored in depth. Development of sophisticated systems pharmacology models and improved TCI tools are needed to accurately evaluate patients' exposure to drugs in general and to immunosuppressants in particular. Sequential studies, first without and then with TCI, should be conducted to validate the clinical benefit of TCI in homogenous populations; randomized trials are not feasible, because there are higher-priority research questions in alloHCT. In Part I of this article, we review the alloHCT process to facilitate optimal design of pharmacokinetic and pharmacodynamics studies. We also review the pharmacokinetics and TCI of calcineurin inhibitors and methotrexate.

Bone marrow chimerism as a strategy to produce tolerance in solid organ allotransplantation

PURPOSE OF REVIEW

Clinical transplant tolerance has been most successfully achieved combining hematopoietic chimerism with kidney transplantation. This review outlines this strategy in animal models and human transplantation, and possible clinical challenges.

RECENT FINDINGS

Kidney transplant tolerance has been achieved through chimerism in several centers beginning with Massachusetts General Hospital's success with mixed chimerism in human leukocyte antigen (HLA)-mismatched patients and the Stanford group with HLA-matched patients, and the more recent success of the Northwestern protocol achieving full chimerism. This has challenged the original view that stable mixed chimerism is necessary for organ graft tolerance. However, among the HLA-mismatched kidney transplant-tolerant patients, loss of mixed chimerism does not lead to renal-graft rejection, and the development of host Foxp3+ regulatory T cells has been observed. Recent animal models suggest that graft tolerance through bone marrow chimerism occurs through both clonal deletion and regulatory immune cells. Further, Tregs have been shown to improve chimerism in animal models.

SUMMARY

Animal studies continue to suggest ways to improve our current clinical strategies. Advances in chimerism protocols suggest that tolerance may be clinically achievable with relative safety for HLA-mismatched kidney transplants.

Indiscernible Benefit of Double-Unit Umbilical Cord Blood Transplantation in Children: A Single-Center Experience from Hong Kong

Double-unit umbilical cord blood (DU-UCB) may extend the use of UCB transplantation and improve clinical outcomes. Data in the literature show that single-unit dominance happened in a vast majority of recipients, and the mechanism is unknown. We examined the clinical relevance and engraftment kinetics of DU-UCB transplant in 65 consecutive children who underwent unrelated single-unit ( n = 25) and double-unit ( n = 40) UCB transplantation for various hematological malignancies ( n = 45) and nonmalignant disorders ( n = 20). Our result showed no discernible benefit to children receiving double-unit transplant over those receiving single-unit transplant when the total nucleated cell (TNC) doses are ≥2.5 × 107/kg, in terms of the hastening of the engraftment of neutrophils and platelets, reduction of nonengraftment, disease recurrence, early mortality, and graft-versus-host disease, despite significantly higher numbers of TNCs in double units. Further analyses demonstrated that the phenomena were not associated with underlying disease, duration of UCB storage, postthaw viability, HLA disparity, ABO incompatibility, gender, or doses of TNCs, CD34+ cells, CD3+ cells, or colony-forming units. Engrafting units in DU-UCB transplants were notably associated with higher CD34+ cell dose. Chimerism studies demonstrated that single-unit dominance started before neutrophil engraftment in DU-UCB transplants. Data from the study suggested no advantage of infusing double-unit UCB, if an adequately dosed single-unit UCB is available. Successful prediction of the dominant graft would optimize algorithms of UCB selection and maximize the long-term engraftment of chosen units.

Long-Term Stable Mixed Chimerism after Hematopoietic Stem Cell Transplantation in Patients with Non-Malignant Disease, Shall We Be Tolerant?

Long-term stable mixed chimerism is a rare and poorly understood phenomenon post hematopoietic stem cell transplantation. This study aims to shed light on whether the two hematopoietic systems in patients with mixed chimerism remain functional. Additionally, we investigate possible immunologic differences in these individuals compared to patients with only donor derived immune cells. Patients with donor and mixed chimerism, at median 10 (5–16) years post-HSCT for non-malignant diseases, were assessed regarding clinical situation and immune system (phenotypical and functional). No difference in long-term outcome was seen in terms of general wellbeing, central phenotypic immune system features (e.g., differentiation status, CD4/CD8 ratio, B and NK-cell frequency) and antibody responses to immunizations. At a median of 10 years post transplantation, patients with mixed chimerism had significantly higher IgG3 and platelet levels. Additionally, these patients had higher NKT-cell levels (CD94+CD8+ and CD56+CD8+) than patients with donor chimerism. In depth phenotypic analysis of patients with mixed chimerism demonstrated recipient-derived fractions in most immune cell lineages (e.g., T-cell, B-cell and NK-cell subsets). Recipient cells were also capable of responding to mitogenic stimulation with production of several cytokines. In conclusion, long-term mixed chimerism did not negatively affect patient wellbeing and long-term outcome. Moreover, recipient-derived immunity may still be functional in these patients, suggesting an active state of tolerance and immunologic dependence on both hematopoietic systems.

Kinetics of Langerhans cell chimerism in the skin of dogs following 2 Gy TBI allogeneic hematopoietic stem cell transplantation

Background

Langerhans cells (LC) are bone marrow-derived cells in the skin. The LC donor/recipient chimerism is assumed to influence the incidence and severity of graft-versus-host disease (GVHD) after hematopoietic stem cell transplantation (HSCT). In nonmyeloablative (NM) HSCT the appearance of acute GVHD is delayed when compared with myeloablative conditioning. Therefore, we examined the development of LC chimerism in a NM canine HSCT model.

Methods

2 Gy conditioned dogs received bone marrow from dog leukocyte antigen identical littermates. Skin biopsies were obtained pre- and post-transplant. LC isolation was performed by immunomagnetic separation and chimerism analysis by PCR analyzing variable-number-of-tandem-repeat markers with subsequent capillary electrophoresis.

Results

All dogs engrafted. Compared to peripheral blood chimerism the development of LC chimerism was delayed (earliest at day +56). None of the dogs achieved complete donor LC chimerism, although two dogs manifested a 100 % donor chimerism in peripheral blood at days +91 and +77. Of interest, one dog remained LC chimeric despite loss of donor chimerism in the peripheral blood cells.

Conclusion

Our study indicates that LC donor chimerism correlates with chimerism development in the peripheral blood but occurs delayed following NM-HSCT.

Peripheral blood late mixed chimerism in leucocyte subpopulations following allogeneic stem cell transplantation for childhood malignancies: does it matter?

The impact of persistent mixed chimerism (MC) after haematopoietic stem cell transplantation (HSCT) remains unclarified. We investigated the incidence of MC in peripheral blood beyond day +50 after HSCT and its impact on rejection, chronic graft-versus-host disease (c-GvHD) and relapse in 161 children receiving allogeneic HSCT for haematological malignancies. The 1-year incidence of late MC was 26%. Spontaneous conversion to complete donor chimerism (CC) occurred in 43% of patients as compared to 62% after donor lymphocyte infusions. No graft rejection occurred. The 1-year incidence of c-GvHD was 20 ± 7% for MC, and 18 ± 4% for CC patients (P = 0·734). The 3-year cumulative incidence of relapse (CIR) according to chimerism status at days +50 and +100 was 22 ± 4% for CC patients vs. 22 ± 8% for MC patients (day +50; P = 0·935) and 21 ± 4% vs. 20 ± 7% (day +100; P = 0·907). Three-year CIRs in patients with persistent MC and patients with CC/limited MC were comparable (8 ± 7% vs. 19 ± 4%; P = 0·960). HSCT for acute leukaemia or myelodysplastic syndrome as secondary malignancies (hazard ratio (HR) 4·7; P = 0·008), for AML (HR 3·0; P = 0·02) and from mismatched donors (HR 3·1; P = 0·03) were independent factors associated with relapse. Our data suggest that late MC neither protects from c-GvHD nor does it reliably predict impending disease relapse.

Use of hematopoietic cell transplants to achieve tolerance in patients with solid organ transplants

The goals of tolerance in patients with solid organ transplants are to eliminate the lifelong need for immunosuppressive (IS) drugs and to prevent graft loss due to rejection or drug toxicity. Tolerance with complete withdrawal of IS drugs has been achieved in recipients of HLA-matched and mismatched living donor kidney transplants in 3 medical centers using hematopoietic cell transplants to establish mixed or complete chimerism.

Insurance approval of mesenchymal stem cell for acute GVHD in Japan: need of follow up for some remaining concerns

Acute graft-versus-host disease (aGVHD) is a major obstacle following allogeneic hematopoietic stem cell transplantation. Steroid is the standard treatment for aGVHD grade II-IV; however, nearly half of patients do not respond to the therapy. Many drugs have been proposed, but no standard therapy has been determined. This is because of the resistance to these drugs and of infections due to prolonged immunosuppressive states. Over the past decade a new approach using mesenchymal stem cells (MSCs) has been emerging in Japan and western countries. MSCs have unique characteristics such as specific immunosuppressive properties, no immunogenicity on their own and supportive activity for hematopoiesis. Most of the published trials have reported a favorable effect in acute GVHD, but a phase III trial failed to reach the primary endpoint, although, subgroup analyses found significant effects on gut and liver GVHD in the patients with MSCs infusion. In Japan several institutes are trying to develop MSC for clinical use in post HSCT patients. However, several limitations make it difficult to use MSC in clinical practice. Recently we conducted a phase II/III study using MSC (JR-031) for patients with steroid-refractory grade III or IV aGVHD. From the feasible clinical results, JR-031 was approved by PMDA as the first product which meets the Act to Revise the Pharmaceutical Affairs Act and the Act to Ensure the Safety of Regenerative Medicine. The cost of one series of the treatment is more than ten million yen. Now we encounter new issues such as cost, indication, safety and efficacy. The mechanism of MSC is still unclear and potential concerns about ectopic tissue formation and MSC related malignancy in vivo remain. In conclusion, MSC infusions are well tolerated and show benefit in some patients without adverse safety effects; however, long-term follow-up is needed to be more certain of this.

Risk factors and outcomes of cytomegalovirus viremia in pediatric hematopoietic stem cell transplantation patients

BACKGROUND

Cytomegalovirus (CMV) is a major pathogen causing significant mortality and morbidity in immunocompromised hosts. It is important to find risk factors associated with CMV viremia and its outcome.

METHODS

We investigated the incidence, time of onset, risk factors for CMV viremia, and characteristics of CMV diseases in 57 pediatric patients receiving hematopoietic stem cell transplantation (HSCT). Between August 2011 and March 2014, cases of pediatric HSCT patients at the National Taiwan University Children's Hospital were reviewed. Viremia was identified by plasma CMV real-time polymerase chain reaction (RT-PCR) assay.

RESULTS

Eighteen (32%) of the 57 patients developed CMV viremia at a median of 23 days post-HSCT (range -3 to +721 days). Eighty-nine percent (16/18) of CMV viremia occurred within 100 days posttransplantation. Four patients finally had CMV diseases (1 with CMV colitis and 3 with CMV pneumonitis) and one patient died of CMV pneumonitis complicated with pulmonary hemorrhage and sepsis. Significant risk factors associated with CMV viremia via univariate analysis include older age (p = 0.03), leukemic patients [odds ratio (OR): 5.2, 95% confidence interval (CI): 1.52∼17.7, p = 0.008), allogeneic HSCT (OR: 14.57, 95% CI: 1.76∼120.5, p = 0.002), antithymoglobulin (ATG) use before transplantation (OR: 5.09, 95% CI: 1.52∼16.9, p = 0.007), graft-versus-host disease (GvHD) (OR: 10.1, 95% CI: 2.7∼38.7, p < 0.001), and gastrointestinal GvHD (OR: 10.9, 95% CI: 2.72∼43.9, p = 0.001).

CONCLUSION

In pediatric posttransplantation patients, CMV viremia mostly occurred within 100 days after transplantation. Risk factors associated with CMV viremia include older diagnostic age, leukemic patients, unrelated donor HSCT, pretransplant ATG use, GvHD, and gastrointestinal GvHD.

Allogeneic hematopoietic cell transplantation after failed autologous transplant for lymphoma using TLI and anti-thymocyte globulin conditioning

We describe 47 patients with lymphoma and failed prior autologous hematopoietic cell transplantation (HCT) who received TLI-ATG conditioning followed by allogeneic HCT. Thirty-two patients had non-Hodgkin lymphoma (NHL; diffuse large B cell lymphoma [n=19], T-cell NHL [n=6], mantle cell lymphoma [n= 4], or other B-cell subtypes [n=3]), and 15 had Hodgkin lymphoma. The median follow-up was 4.9 (range, 2.1–11.9) years. The cumulative incidence of grade II–IV acute GVHD at day +100 was 12%, and the cumulative incidence of extensive chronic GVHD at 1 year was 36%. The 3-year cumulative incidences of overall survival, progression-free survival (PFS), and non-relapse mortality (NRM) were 81%, 44%, and 7%, respectively. Fifteen patients died (relapse, n=10; NRM, n=5). Among the 25 patients with relapse after allogeneic HCT, 11 (44%) achieved durable (>1 year) complete remissions following donor lymphocyte infusion or chemoradiotherapy. The majority of surviving patients (75%; n=24) were able to discontinue all immunosuppression. For patients with relapsed lymphoma after autologous HCT, allogeneic HCT using TLI-ATG conditioning is a well-tolerated, predominantly outpatient therapy with low NRM (7% at 3 years), a low incidence of GVHD, durable disease control, and excellent overall survival (81% at 3 years).

Association of fludarabine pharmacokinetic/dynamic biomarkers with donor chimerism in nonmyeloablative HCT recipients

PURPOSE

Fludarabine monophosphate (fludarabine) is an integral component of many reduced-intensity conditioning regimens for hematopoietic cell transplantation (HCT). Fludarabine's metabolite, 9-β-D-arabinofuranosyl-2-fluoroadenine (F-ara-A), undergoes cellular uptake and activation to form the active cytotoxic metabolite fludarabine triphosphate (F-ara-ATP), which inhibits cellular DNA synthesis in CD4(+) and CD8(+) cells. In this study, we evaluated whether fludarabine-based pharmacologic biomarkers were associated with clinical outcomes in HCT recipients.

METHODS

Participants with hematologic diseases were conditioned with fludarabine and low-dose total body irradiation (TBI) followed by allogeneic HCT and post-grafting immunosuppression. After fludarabine administration, we evaluated pharmacological biomarkers for fludarabine-F-ara-A area under the curve (AUC) and the ratio of circulating CD4(+) and CD8(+) cells (CD4(+)/CD8(+) ratio) after fludarabine administration-in 102 patients; F-ara-ATP accumulation rate in enriched CD4(+) and CD8(+) cells was evaluated in 36 and 34 patients, respectively.

RESULTS

Interpatient variability in the pharmacological biomarkers was high, ranging from 3.7-fold (F-ara-A AUC) to 39-fold (F-ara-ATP in CD8(+) cells). Circulating CD8(+) cells were more sensitive to fludarabine administration. A population pharmacokinetic-based sampling schedule successfully allowed for estimation of F-ara-A AUC in this outpatient population. There was a poor correlation between the F-ara-AUC and the F-ara-ATP accumulation rate in CD4(+) (R (2) = 0.01) and CD8(+) cells (R (2) = 0.00). No associations were seen between the four biomarkers and clinical outcomes (day +28 donor T cell chimerism, acute graft-versus-host disease (GVHD), neutrophil nadirs, cytomegalovirus reactivation, chronic GVHD, relapse, non-relapse mortality, or overall mortality).

CONCLUSIONS

Considerable interpatient variability exists in pharmacokinetic and fludarabine-based biomarkers, but these biomarkers are not associated with clinical outcomes in fludarabine/TBI-conditioned patients.

FISH Detection of X and Y Chromosomes in Combination with Immunofluorescence to Study Contribution of Transplanted Cells to Skeletal Muscle Fibers

During the past decades, several studies in animals have displayed the ability of cells from the bone marrow (BM) to participate in regeneration of various tissues including skeletal muscle tissue. Studies in mice have demonstrated that regular physical activity is sufficient to induce contribution of BM derived cells to the skeletal muscle tissue, suggesting that this is part of the physiological remodeling of skeletal muscle. To analyze whether BM-derived cells participate in skeletal muscle remodeling in human, we developed a protocol of immunofluorescence in combination with fluorescence in situ hybridization (FISH) that enables the detection of male donor bone marrow cell contribution to female skeletal muscle tissue.

Preferential depletion of host over donor T cells through in vivo decay of active rabbit-anti-thymocyte globulin levels during reduced intensity conditioning

Inadequate T-cell chimerism following reduced-intensity conditioning transplantation may contribute to graft rejection and disease relapse. Anti-thymocyte globulin (ATG) enhances early donor T-cell chimerism, but may also deplete donor T cells, increasing risks of infection and relapse. We prospectively tested administration of rabbit ATG (rATG) ⩾14 days before the infusion of the graft, followed by in vivo decay of active rATG levels, to selectively deplete host T cells. Twenty-three patients received rATG total dose 4.5 mg/kg on days -16 and -15, fludarabine 30 mg/m(2) per day on day -7 through -3, IV busulfan 130 mg/m(2) per day on days -4 and -3 and cyclophosphamide 1500 mg/m(2) on day -2. rATG levels were therapeutic in all patients on day -14, but were sub-therapeutic (<1 μg/mL) by day 0 in 82% of patients. Median donor T-cell chimerisms on days 30 and 180 were 100% (75-100%) and 100% (90-100%), respectively. Non-relapse mortality and relapse/progression at 48 months were 17 and 30%. Cumulative incidences of acute GvHD grades II-IV and III-IV were 39 and 9%. Median follow-up is 64 months (46-79 months). Survival and disease-free survival at 48 months were 70 and 52%. These data suggest that selective depletion of host T cells using this regimen is a feasible and effective strategy.

Recipient pretransplant inosine monophosphate dehydrogenase activity in nonmyeloablative hematopoietic cell transplantation

Mycophenolic acid, the active metabolite of mycophenolate mofetil (MMF), inhibits inosine monophosphate dehydrogenase (IMPDH) activity. IMPDH is the rate-limiting enzyme involved in de novo synthesis of guanosine nucleotides and catalyzes the oxidation of inosine 5'-monophosphate to xanthosine 5'-monophosphate (XMP). We developed a highly sensitive liquid chromatography-mass spectrometry method to quantitate XMP concentrations in peripheral blood mononuclear cells (PMNCs) isolated from the recipient pretransplant and used this method to determine IMPDH activity in 86 nonmyeloablative allogeneic hematopoietic cell transplantation (HCT) patients. The incubation procedure and analytical method yielded acceptable within-sample and within-individual variability. Considerable between-individual variability was observed (12.2-fold). Low recipient pretransplant IMPDH activity was associated with increased day +28 donor T cell chimerism, more acute graft-versus-host disease (GVHD), lower neutrophil nadirs, and more cytomegalovirus reactivation but not with chronic GVHD, relapse, nonrelapse mortality, or overall mortality. We conclude that quantitation of the recipient's pretransplant IMPDH activity in PMNC lysate could provide a useful biomarker to evaluate a recipient's sensitivity to MMF. Further trials should be conducted to confirm our findings and to optimize postgrafting immunosuppression in nonmyeloablative HCT recipients.