Pushing the envelope-nonmyeloablative and reduced intensity preparative regimens for allogeneic hematopoietic transplantation

Current status of conditioning regimens in haploidentical hematopoietic cell transplantation

The development of effective prophylaxis strategies against graft-versus-host disease (GVHD) has contributed to the widespread use of haploidentical related hematopoietic cell transplantation (Haplo-HCT). Currently, GVHD prophylaxis containing posttransplant cyclophosphamide (PTCY) is considered the standard of care in Haplo-HCT, and recent studies have shown comparable results for PTCY-based Haplo-HCT and HCT from other donor sources. The conditioning regimen plays an important role in eradicating tumor cells to prevent disease relapse and suppressing the recipient's immune system to facilitate engraftment. PTCY-based Haplo-HCT was initially developed using a nonmyeloablative conditioning regimen consisting of fludarabine, cyclophosphamide and low-dose total body irradiation, but high relapse rates reinforced the need to intensify the conditioning regimen. In this respect, various myeloablative and reduced-intensity conditioning regimens have been investigated. However, the optimal conditioning regimens for PTCY-based Haplo-HCT have not yet been established, and this issue needs to be addressed based on data from patients undergoing the procedure. In this article, we review the existing literature on conditioning regimens for PTCY-based Haplo-HCT and discuss future perspectives.

Efficient bone marrow irradiation and low uptake by non-haematological organs with an yttrium-90-anti-CD66 antibody prior to haematopoietic stem cell transplantation

We report the results of a Phase I radiation dose escalation study using an yttrium-90 (90Y) labelled anti-CD66 monoclonal antibody given with standard conditioning regimen for patients receiving haematopoietic stem cell transplants for myeloid leukaemia or myeloma. The 90Y-labelled anti-CD66 was infused prior to standard conditioning. In total, 30 patients entered the trial and 29 received 90Y-labelled mAb, at infused radiation activity levels of 5, 10, 25, or 37.5 megaBequerel (MBq)/kg lean body weight. A prerequisite for receiving the 90Y-labelled mAb was favourable dosimetry determined by single-photon emission computerised tomography (SPECT) dosimetry following administration of indium-111 (111In) anti-CD66. Estimated absorbed radiation doses delivered to the red marrow demonstrated a linear relationship with the infused activity of 90Y-labelled mAb. At the highest activity level of 37.5 MBq/kg, mean estimated radiation doses for red marrow, liver, spleen, kidneys and lungs were 24.6 ± 5.6 Gy, 5.8 ± 2.7 Gy, 19.1 ± 8.0 Gy, 2.1 ± 1.1 and 2.2 ± 0.9, respectively. All patients engrafted, treatment-related mortality 1-year post-transplant was zero. Toxicities were no greater than those anticipated for similar conditioning regimens without targeted radiation. The ability to substantially intensify conditioning prior to haematopoietic stem cell transplantation without increasing toxicity warrants further testing to determine efficacy. clinicaltrials.gov identifier: NCT01521611.

Comparison of reduced intensity and nonmyeloablative conditioning for adults with acute myeloid leukemia undergoing allogeneic hematopoietic cell transplantation in first or second remission

Reduced intensity conditioning (RIC) and nonmyeloablative (NMA) conditioning regimens have expanded use of allogeneic hematopoietic cell transplantation (HCT) in AML to include older and medically less-fit patients, but relative efficacies and toxicities remain poorly defined. Here, we analyzed outcomes from 343 adults transplanted in remission after RIC (n = 137) or NMA (n = 206) conditioning between 2006 and 2021. The characteristics of RIC and NMA HCT patients were similar except that RIC patients were younger and their time between most recent remission achievement and allografting was shorter. There were no significant differences in relapse risk, relapse-free survival (RFS), overall survival (OS), and non-relapse mortality (NRM) between RIC and NMA HCT patients, both overall (relapse: hazard ratio [HR] = 0.80, P = 0.27; RFS: HR = 0.93, P = 0.61; OS: HR = 0.93, P = 0.66; NRM: HR = 1.13, P = 0.59) and when patients were stratified by pre-HCT measurable residual disease (MRD) status. After multivariable adjustment, there was no statistically significant association between conditioning intensity and relapse (HR = 0.69, P = 0.088), RFS (HR = 0.86, P = 0.37), OS (HR = 0.89, P = 0.49), or NRM (HR = 1.37, P = 0.19). In this non-randomized cohort of adults undergoing allografting for AML in first or second remission at our center, we could not detect statistically significant differences in outcomes between those assigned to RIC and those assigned to NMA conditioning.

Conditioning regimens for allogeneic hematopoietic cell transplantation in acute myeloid leukemia: Real-world data from the Japanese registry studies

Conditioning regimens play a crucial role in preventing relapse of acute myeloid leukemia (AML) following allogeneic hematopoietic cell transplantation (HCT). In early times, myeloablative conditioning was used exclusively, but it was associated with significant toxicity. However, the advent of reduced-intensity conditioning has allowed allogeneic HCT to be performed more safely, leading to an expansion of our choices for conditioning regimens. As the transplantation methods have become highly diversified, it is reasonable to determine an optimal conditioning regimen in consideration of patient-, disease-, and transplantation-related factors. In this context, large-scale registry-based studies provide real-world data to allow for a detailed evaluation of the utility of individual conditioning regimens in specific clinical settings. The Japanese Society for Transplantation and Cellular Therapy has been conducting a nationwide survey for HCT since 1993 that currently covers >99% of all the transplantation centers nationwide, and >1,000 allogeneic HCTs performed for adults with AML are registered per year. We have been using the registry data to implement a number of studies focusing on adults with AML, and the large number of patients registered consecutively from nearly all transplantation centers nationwide represent real-world practice in Japan. This article reviews and discusses the results obtained from our registry-based studies pertaining to various conditioning regimens.

Case Report: Graft Versus Tumor Effect After Non-Myeloablative Allogeneic Stem-Cell Transplantation in a Patient With Brentuximab-Vedotin Refractory Sezary Syndrome

Sezary Syndrome (SS) is a rare leukemic variant of primary cutaneous T-cell lymphoma. Relapsed or refractory disease is generally considered incurable by conventional therapeutic approaches, although durable responses can be achieved with novel monoclonal antibodies. Allogeneic hematopoietic stem cell transplantation (alloHSCT) may have potential value by inducing graft vs-lymphoma (GvL) effects, but there is currently no consensus regarding the timing of alloHSCT or type of conditioning regimen. Here we present the case of a male patient who achieved a complete remission (CR) of primary refractory SS after non-myeloablative alloHSCT. Patient: Two years prior to HSCT, the patient had been refractory to CHOEP-based chemotherapy, interferon, extracorporeal photopheresis (ECP), and bexarotene. Directly prior to alloHSCT brentuximab-vedotin (BV) was applied resulting in a partial remission of the skin compartment and overall in a stable disease. Prior to HSCT, flow cytometry of the bone marrow and peripheral blood showed an infiltration with T-cells positive for CD5, CD4, low CD3, low CD2 and negative for CD7, CD38, HLA-DR and CD8. The trephine biopsy showed a 7% infiltration of SS cells. The CD4:CD8 ratio in peripheral blood (pb) was massively increased at 76.67, with 63.5% of white blood cells expressing a SS immune phenotype. The conditioning regimen included 30 mg/m2 fludarabine on days -5, -4 and -3 and total body irradiation with 2 Gy on day -1. Immunosuppression consisted of cyclosporine A from day-1 and mycophenolate mofetil from day 0. The patient received 6.55x106 CD34+ cells and 1.11x108 CD3+ cells/kg body weight. Bone marrow evaluation on day 28 still showed persistent SS cells by flow cytometry. After tapering immunosuppression until day 169, the CD4:CD8 ratio in pb normalized. CR was documented on day 169 after alloHSCT and is now ongoing for almost 3 years after alloHSCT. Conclusions: We confirm that an alloHSCT can be a curative option for refractory patients with SS. The achievement of a CR after tapering the immunosuppressive therapy indicates a significant role of the GvL effect. In present treatment algorithms for patients with SS, the timing of an alloHSCT and the intensity of conditioning should be further explored.

STING and transplantation: can targeting this pathway improve outcomes?

Stimulator of interferon genes (STING) is an innate immune sensor of cytoplasmic dsDNA originating from microorganisms and host cells. STING plays an important role in the regulation of murine graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and may be similarly activated during other transplantation modalities. In this review, we discuss STING in allo-HSCT and its prospective involvement in autologous HSCT (auto-HSCT) and solid organ transplantation (SOT), highlighting its unique role in nonhematopoietic, hematopoietic, and malignant cell types.

Total Body Irradiation for Hematopoietic Stem Cell Transplantation: What Can We Agree on?

Total body irradiation (TBI), used as part of the conditioning regimen prior to allogeneic and autologous hematopoietic cell transplantation, is the delivery of a relatively homogeneous dose of radiation to the entire body. TBI has a dual role, being cytotoxic and immunosuppressive. This allows it to eliminate disease and create “space” in the marrow while also impairing the immune system from rejecting the foreign donor cells being transplanted. Advantages that TBI may have over chemotherapy alone are that it may achieve greater tumour cytotoxicity and better tissue penetration than chemotherapy as its delivery is independent of vascular supply and physiologic barriers such as renal and hepatic function. Therefore, the so-called “sanctuary” sites such as the central nervous system (CNS), testes, and orbits or other sites with limited blood supply are not off-limits to radiation. Nevertheless, TBI is hampered by challenging logistics of administration, coordination between hematology and radiation oncology departments, increased rates of acute treatment-related morbidity and mortality along with late toxicity to other tissues. Newer technologies and a better understanding of the biology and physics of TBI has allowed the field to develop novel delivery systems which may help to deliver radiation more safely while maintaining its efficacy. However, continued research and collaboration are needed to determine the best approaches for the use of TBI in the future.

Comparative study of micro-transplantation from HLA fully mismatched unrelated and partly matched related donors in acute myeloid leukemia

Micro-transplantation (MST) by chemotherapy, combined with granulocyte colony-stimulating factor-mobilized peripheral blood stem cell (GPBSC) infusion, from an HLA partial matched related donor has shown some encouraging effective therapy for acute myeloid leukemia (AML). However, the outcome of human leukocyte antigen (HLA) fully mismatched unrelated donor-derived MST in such patients is still unknown. In the present study, we compared the efficacy of HLA fully mismatched unrelated donor-derived MST, and partly matched related donor-derived MST, in AML of 126 patients from two centers in China, These patients, aged 16 to 65 years, were given three or four courses of MST, which consisted of a high dosage cytarabine followed by GPBSC from unrelated donor or related donor. There was a statistically significant difference in 3-year leukemia-free survival (LFS) and 3-year overall survival (OS) between the unrelated and the related group. The non-treatment-related mortality (NRM) rates of patients, and other adverse complications, were no different in the two groups. In conclusion, unrelated donor-derived MST is believed to be a safe treatment, with efficacy similar to or higher than related donor-derived MST. This result provides support for the potential of MST for expanding the donor selection. However, the specific mechanism of action needs further study.

Donor Evaluation for Hematopoietic Stem and Progenitor Cell Collection

With the increasing incidence of hematopoietic allogeneic cell transplantation (allo-HCT), the importance of securing a cellular product, safely from a donor, and ensuring that the product is without additional risk to the recipient, continues to be of paramount importance. The evaluation of the donor’s medical eligibility and suitability is designed to identify and limit the risk of transmitting infectious, genetic, or neoplastic diseases to the recipient through the product. It also aims to ensure a maximum level of safety for the donor and informs them of the risks of donation. Several regulatory agencies, national and international registries, and accreditation bodies have facilitated the availability and safe provision of human cells, tissues, and cellular- and tissue-based products not only at local institutions but also through international exchange.

Autologous hematopoietic cell transplantation for acute myeloid leukemia in adults: 25 years of experience in Japan

Autologous hematopoietic cell transplantation (HCT) has not gained universal popularity in the treatment of acute myeloid leukemia (AML), and its status remains unclear. To determine the implementation status and outcomes of autologous HCT for adults with AML in Japan, we analyzed data from 1,174 patients (including 446 with acute promyelocytic leukemia [APL]) who underwent autologous HCT between 1992 and 2016 consecutively reported to the Japanese nationwide transplantation registry. The annual number of transplantations peaked at 82 cases in 1997, and has recently remained at around 40 cases. The percentage of APL has increased sharply since 2004, and currently exceeds 70%. While most non-APL patients underwent autologous HCT during first complete remission (CR), transplantation during second CR has become mainstream for APL patients since the early 2000s. The 5-year survival, relapse, and non-relapse mortality rates were 55.3%, 42.1%, and 8.6% for non-APL patients, and 87.6%, 12.9%, and 3.4% for APL patients, respectively. Patients transplanted in the later period showed better survival than those transplanted in the earlier period, both for non-APL (P < 0.001) and APL (P = 0.036). These results clearly show the various changes in transplantation practice and post-transplant outcomes in Japan over the past 25 years.

The effect of melphalan dose and total body irradiation as reduced-intensity conditioning for acute lymphoblastic leukemia patients undergoing allogeneic stem cell transplantation

To evaluate the prognostic impact of melphalan dose and total body irradiation (TBI) in acute lymphoblastic leukemia (ALL) patients undergoing reduced-intensity allogeneic transplantation, we retrospectively compared the outcomes between higher-dose melphalan (120-140 mg/m²) with (HDM/TBI+, n = 118) or without 2-4 Gy TBI (HDM/TBI-, n = 152) and lower-dose melphalan (80-110 mg/m²) with TBI (LDM/TBI+, n = 237). At 3 years, the overall survival was 49.6% in the HDM/TBI+, 51.7% in the HDM/TBI-, and 47.3% in the LDM/TBI + groups (p = .67). The relapse rate and non-relapse mortality were comparable among the three groups. Multivariate analysis revealed that conditioning regimen was not associated with overall survival, relapse, and non-relapse mortality; however, central nervous system complication was less frequent with LDM/TBI + than with HDM/TBI+. Our findings suggest reduced-intensity conditioning with LDM/TBI + might be a reasonable option, especially in vulnerable ALL patients, with similar transplant outcomes to HDM with or without TBI.

Prognostic impact of melphalan dose and total body irradiation use in patients with acute myeloid leukemia undergoing allogeneic stem cell transplantation with reduced-intensity conditioning

To evaluate the prognostic impact of melphalan dose and total body irradiation (TBI) use in acute myeloid leukemia patients undergoing reduced-intensity allogeneic transplantation, we retrospectively compared outcomes of patients receiving a higher-dose (120-140 mg/m², n = 379) or lower-dose melphalan (80-110 mg/m², n = 128) with or without TBI of ≤4 Gy. At 3 years, overall survival was 48.9% in the higher-dose group versus 40.3% in the lower-dose group (p = .013). This survival benefit was attributed to lower tumor-related mortality (23.9% vs. 31.7%; p = .049). Non-relapse mortality did not differ (24.8% vs. 23.5%, p = .59). The beneficial effect of a higher-dose melphalan was more evident when combined with TBI in younger patients, those not in complete remission, and those with good performance status. Our findings support the use of a higher-dose melphalan in combination with TBI for reduced-intensity conditioning in physically fit patients.

Diagnosis and management of AML in adults: 2017 ELN recommendations from an international expert panel

The first edition of the European LeukemiaNet (ELN) recommendations for diagnosis and management of acute myeloid leukemia (AML) in adults, published in 2010, has found broad acceptance by physicians and investigators caring for patients with AML. Recent advances, for example, in the discovery of the genomic landscape of the disease, in the development of assays for genetic testing and for detecting minimal residual disease (MRD), as well as in the development of novel antileukemic agents, prompted an international panel to provide updated evidence- and expert opinion-based recommendations. The recommendations include a revised version of the ELN genetic categories, a proposal for a response category based on MRD status, and criteria for progressive disease.

PD-1-PD-L1 immune-checkpoint blockade in B-cell lymphomas

Cancer cells can escape T-cell-mediated cellular cytotoxicity by exploiting the inhibitory programmed cell-death protein 1 (PD-1)/programmed cell death 1 ligand 1 (PD-L1) immune checkpoint. Indeed, therapeutic antibodies that block the PD-1-PD-L1 axis induce durable clinical responses against a growing list of solid tumours. B-cell lymphomas also leverage this checkpoint to escape immune recognition, although the outcomes of PD-1-PD-L1 blockade, and the correlations between PD-L1 expression and treatment responses, are less-well elucidated in these diseases than in solid cancers. Nevertheless, in patients with Hodgkin lymphoma, amplification of the gene encoding PD-L1 is commonly associated with increased expression of this protein on Reed-Sternberg cells. Correspondingly, PD-1 blockade with nivolumab has been demonstrated to result in response rates as high as 87% in unselected patients with relapsed and/or refractory Hodgkin lymphoma, leading to the FDA approval of nivolumab for this indication in May 2016. The PD-1/PD-L1 axis is probably also important for immune evasion of B-cell lymphomas with a viral aetiology, including those associated with human immunodeficiency virus (HIV) and Epstein-Barr virus (EBV). This Review is focused on the role of PD-1-PD-L1 blockade in unleashing host antitumour immune responses against various B-cell lymphomas, and summarizes the clinical studies of this approach performed to date.

Host Foxp3+CD4+ Regulatory T Cells Act as a Negative Regulator of Dendritic Cells in the Peritransplantation Period

Host Foxp3+CD4+ regulatory T cells (Tregs) have been shown to suppress graft-versus-host disease (GVHD) in experimental bone marrow transplantation (BMT) models; however, the detailed mechanism is unknown. To address this issue, we established a murine MHC-haploidentical BMT model (BDF1 (H-2b/d) → B6C3F1 (H-2b/k)), in which transplantation following conditioning with high-dose (13 Gy) or low-dose (5 Gy) total body irradiation corresponds to myeloablative stem cell transplantation (MAST) or reduced-intensity stem cell transplantation (RIST) BMT. All MAST recipients died of GVHD within 70 d, whereas RIST recipients developed almost no GVHD and survived for at least 3 mo. In this BMT model, we investigated the kinetics of immune cells in the mesenteric lymph nodes because GVHD was most prominent in the intestines. Host Tregs that survived after total body irradiation could proliferate transiently by day 4. Comparing the kinetics of immune cells among MAST, RIST, and anti-CD25 mAb-treated RIST, we found that the transiently surviving host Tregs were fully functional, closely contacted with host dendritic cells (DCs), and significantly restrained the maturation (CD80 and CD86 expression) of DCs in a dose-dependent manner. There was a positive correlation between the ratio of DCs to host Tregs and the extent of maturation of DCs. Host Tregs suppressed alloresponse mainly by contact inhibition. Host Tregs are already active in lymph nodes before transplantation and restrain the maturation of host DCs, thereby dampening the ability of DCs to activate allogeneic donor T cells and consequently reducing the magnitude of graft-versus-host reaction. Thus, host Tregs are negative regulators of host DCs that act in the peritransplantation period.

Alterations in Memory and Impact on Academic Outcomes in Children Following Allogeneic Hematopoietic Cell Transplantation

The prevalence of late effects following allogeneic hematopoietic cell transplantation (HCT), a curative treatment for pediatric leukemia, is high: 79% of HCT recipients experience chronic medical conditions. The few extant studies of cognitive late effects have focused on intelligence and are equivocal about HCT neurotoxicity. In an archival study of 30 children (mean transplant age = 6 years), we characterize neuropsychological predictors of academic outcomes. Mean intellectual and academic abilities were average, but evidenced extreme variability, particularly on measures of attention and memory: ∼25% of the sample exhibited borderline performance or lower. Medical predictors of outcome revealed paradoxically better memory associated with more severe acute graft-versus-host disease (GVHD) and associated with steroid treatment. Processing speed and memory accounted for 69% and 61% of variance in mathematics and reading outcomes, respectively. Thus, our findings revealed neurocognitive areas of vulnerability in processing speed and memory following HCT that contribute to subsequent academic difficulties.