Biology-Driven Approaches to Prevent and Treat Relapse of Myeloid Neoplasia after Allogeneic Hematopoietic Stem Cell Transplantation

Strategies to reduce relapse risk in patients undergoing allogeneic stem cell transplantation for acute myeloid leukaemia

Allogeneic stem cell transplantation is a centrally important curative strategy in adults with acute myeloid leukaemia; however, relapse occurs in a significant proportion of patients and remains the leading cause of treatment failure. The prognosis for patients who relapse post-transplant remains poor, and the development of new strategies with the ability to reduce disease recurrence without increasing transplant toxicity remains a priority. In this review, within the context of our understanding of disease biology and the graft-versus-leukaemia (GVL) effect, we will discuss established, evolving and novel approaches for increasing remission rates, decreasing measurable residual disease pretransplant, future methods to augment the GVL effect and the opportunities for post-transplant maintenance. Future progress depends upon the development of innovative trials and networks, which will ensure the rapid assessment of emerging therapies in prospective clinical trials.

Risk factors and survival analysis of human leukocyte antigen loss in relapsed acute myeloid leukaemia/myelodysplastic syndrome patients after allogeneic haematopoietic stem cell transplantation

To investigate the clinical characteristics and risk factors of specific human leukocyte antigen loss (HLA loss) in relapsed acute myeloid leukaemia (AML)/myelodysplastic syndrome (MDS) patients after allogeneic haematopoietic stem cell transplantation (allo-HSCT), and compare the responses of patients with HLA loss relapse with those without HLA loss (non-HLA loss) to different treatment regimens. Clinical data of traceable patients with AML/MDS after myeloablative allo-HSCT in our centre between January 2010 and June 2021, who experienced disease relapse after the transplantation, were collected. The patients were divided into the HLA loss relapse group and the non-HLA loss relapsed group based on HLA loss gene test findings by next-generation sequencing. The patients' median overall survival (OS) after the relapse were compared, and univariate and multivariate analyses were performed using the Kaplan-Meier survival curve and Cox proportional hazard model to explore the responses to different treatments after relapse. A total of 2359 patients were selected. Retrospective HLA gene loss gene detection was performed for the deoxyribonucleic acid in 179 relapsed patients, including 47 patients in the HLA loss group (27.2%), 126 patients in the non-HLA loss group (72.8%) and 6 patients were excluded due to a lack of confirmed results. There was no significant statistical difference in the baseline characteristics of patients between the two groups, but as to transplantation-related characteristics, the donor-recipient relationship and HLA mismatched loci were statistically different between the two groups (both p < 0.001). Multivariate Cox analysis showed that more HLA mismatched loci ≥3 (HR = 3.66; 95% CI: 1.61-8.31; p = 0.002), time (≤6 months) from HSCT to relapse (HR = 7.92; 95% CI: 3.35-18.74; p < 0.001) and donor chimerism (CD3) in bone marrow at relapse (HR = 1.02; 95% CI: 1.00-1.03; p = 0.036) were independent factors affecting HLA loss relapse. The ratio of negative conversion of FLT3-ITD or CEBPA mutation was significantly lower in patients with post-transplantation HLA loss relapse than in the non-HLA loss group (0.0% vs. 45.5%, p = 0.003; 0.0% vs. 80.0%, p = 0.035), with none of the patients with FLT3-ITD or CEBPA mutation turned negative in the HLA loss group. The number of gene mutations turned negative when relapse in the non-HLA loss group was remarkably higher than that in the HLA loss group (p = 0.001). Using donor lymphocyte infusion (DLI) could not prolong OS for the HLA loss group (p = 0.42). Nevertheless, second transplantation had a significant positive impact on OS in the HLA loss group (p = 0.017), although only five patients in the HLA loss group underwent second transplantation. However, patients in the non-HLA loss group using DLI had a relatively longer OS time than those without DLI (p = 0.017). Second transplantation could also prolong OS in the non-HLA loss group, but the effect was not as significant as in the HLA loss group (p = 0.053). In summary, HLA loss detection is essential for patients with recurrence after transplantation, especially for those with more HLA mismatched loci and non-sibling donor. Furthermore, the detection of HLA loss has a guiding role in choosing subsequent therapy when relapsed, as secondary transplantation is more suitable than DLI for those with HLA loss.

Metabolic instruction of the graft-versus-leukemia immunity

Allogeneic hematopoietic cell transplantation (allo-HCT) is frequently performed to cure hematological malignancies, such as acute myeloid leukemia (AML), through the graft-versus-leukemia (GVL) effect. In this immunological process, donor immune cells eliminate residual cancer cells in the patient and exert tumor control through immunosurveillance. However, GVL failure and subsequent leukemia relapse are frequent and associated with a dismal prognosis. A better understanding of the mechanisms underlying AML immune evasion is essential for developing novel therapeutic strategies to boost the GVL effect. Cellular metabolism has emerged as an essential regulator of survival and cell fate for both cancer and immune cells. Leukemia and T cells utilize specific metabolic programs, including the orchestrated use of glucose, amino acids, and fatty acids, to support their growth and function. Besides regulating cell-intrinsic processes, metabolism shapes the extracellular environment and plays an important role in cell-cell communication. This review focuses on recent advances in the understanding of how metabolism might affect the anti-leukemia immune response. First, we provide a general overview of the mechanisms of immune escape after allo-HCT and an introduction to leukemia and T cell metabolism. Further, we discuss how leukemia and myeloid cell metabolism contribute to an altered microenvironment that impairs T cell function. Next, we review the literature linking metabolic processes in AML cells with their inhibitory checkpoint ligand expression. Finally, we focus on recent findings concerning the role of systemic metabolism in sustained GVL efficacy. While the majority of evidence in the field still stems from basic and preclinical studies, we discuss translational findings and propose further avenues for bridging the gap between bench and bedside.

Considerations regarding maintenance therapy for acute myeloid leukemia in remission

INTRODUCTION

For most adult patients with acute myeloid leukemia, relapse is characteristic of the disease. When allotransplant in first complete remission is administered as consolidative therapy, relapse is still common, affecting 20-40% of recipients. Maintenance of remission with low-dose treatments may hold promise in preventing relapse.

AREAS COVERED

Improvements in the detection of clinical and biological variants of disease allow the practitioner to identify which patients, based on disease features, may benefit from therapy directed at residual clonal elements that might contribute to relapse. Along with improvements in methods of detecting residual disease, novel agents are under investigation as a platform in order to maintain remission and may contribute to prolonged survival. In this manuscript, we review literature available through PubMed regarding the use of maintenance therapy, described as post-remission or post-transplant treatment intended to delay or prevent relapse.

EXPERT OPINION

Although results of randomized studies are limited, a role for maintenance therapy, particularly directed at molecular targets, in distinct settings of post-remission management is recommended. We also advise that randomized studies of immune therapy along with opportunities for further evaluation of risk-agnostic interventions be a focus of cooperative groups.

Phase II trial of hypomethylating agent combined with nivolumab for acute myeloid leukaemia relapse after allogeneic haematopoietic cell transplantation-Immune signature correlates with response

Acute myeloid leukaemia (AML) relapse after allogeneic haematopoietic cell transplantation (allo-HCT) is often driven by immune-related mechanisms and associated with poor prognosis. Immune checkpoint inhibitors combined with hypomethylating agents (HMA) may restore or enhance the graft-versus-leukaemia effect. Still, data about using this combination regimen after allo-HCT are limited. We conducted a prospective, phase II, open-label, single-arm study in which we treated patients with haematological AML relapse after allo-HCT with HMA plus the anti-PD-1 antibody nivolumab. The response was correlated with DNA-, RNA- and protein-based single-cell technology assessments to identify biomarkers associated with therapeutic efficacy. Sixteen patients received a median number of 2 (range 1-7) nivolumab applications. The overall response rate (CR/PR) at day 42 was 25%, and another 25% of the patients achieved stable disease. The median overall survival was 15.6 months. High-parametric cytometry documented a higher frequency of activated (ICOS+ , HLA-DR+ ), low senescence (KLRG1- , CD57- ) CD8+ effector T cells in responders. We confirmed these findings in a preclinical model. Single-cell transcriptomics revealed a pro-inflammatory rewiring of the expression profile of T and myeloid cells in responders. In summary, the study indicates that the post-allo-HCT HMA/nivolumab combination induces anti-AML immune responses in selected patients and could be considered as a bridging approach to a second allo-HCT. Trial-registration: EudraCT-No. 2017-002194-18.

Younger Matched Unrelated Donors Confer Decreased Relapse Risk Compared to Older Sibling Donors in Older Patients with B Cell Acute Lymphoblastic Leukemia Undergoing Allogeneic Hematopoietic Cell Transplantation

Although allogeneic hematopoietic cell transplantation (alloHCT) offers cure for older patients with acute lymphoblastic leukemia (ALL), disease relapse remains a major issue. Whether matched sibling donors (MSDs) are still the preferred donor choice compared to younger matched unrelated donors (MUDs) in the contemporary era of improved transplantation practices remains unknown. This retrospective cohort registry study queried the Center for International Blood and Marrow Transplant Research (CIBMTR) database in patients with B cell ALL (B-ALL) age ≥ 50 years undergoing alloHCT from older MSDs (age ≥ 50 years) or younger MUDs (age ≤ 35 years) between 2011 and 2018. The study included common allograft types, conditioning regimens, and graft-versus-host disease (GVHD) prophylaxis strategies. The primary outcome was relapse risk, and secondary outcomes included nonrelapse mortality (NRM), GVHD, leukemia-free survival (LFS), and overall survival (OS). Among 925 eligible patients in the study cohort, 386 underwent alloHCT with an older MSD (median donor age, 58 years) and 539 underwent alloHCT from a younger MUD (median donor age, 25 year). In multivariable analysis, younger MUDs conferred a significantly decreased risk of relapse (hazard ratio [HR], .68; P = .002) compared with older MSDs. The adjusted cumulative incidence of relapse at 5 years was significantly lower with younger MUDs than with older MSDs (26% versus 37%; P = .001). Younger MUDs were associated with a greater risk of chronic GVHD compared to older MSDs (HR, 1.33; 95% confidence interval [CI], 1.10 to 1.61; P = .003). Compared to older MSDs, younger MUDs conferred an increased NRM (HR, 1.38; P = .02) and higher adjusted cumulative incidence of NRM at 5 years (31% versus 22%; P = .006). There were no differences in post-alloHCT OS or LFS rates between younger MUDs and older MSDs (OS: HR, 1.09; [P = .37]; LFS: HR, .95 [P = .57]). The use of younger MUDs could be considered as a possible way to prevent relapse after alloHCT in older adults with ALL. Combining the use of younger MUDs with improved strategies to reduce GVHD merits further exploration to improve outcomes.

Impact of Donor Age on Allogeneic Hematopoietic Cell Transplantation Outcomes in Older Adults with Acute Myeloid Leukemia

Allogeneic hematopoietic cell transplantation (alloHCT) provides cure for older patients with acute myeloid leukemia (AML); however, disease relapse remains a major concern. Based on recent data suggesting that younger donor age confers the greatest benefit for alloHCT with matched unrelated donors (MUDs), we attempted to answer a practical question: which donor type provides the best outcomes when an older patient with AML has a matched sibling donor (MSD, also older) versus the best MUD? This retrospective cohort registry study accessed data from the Center for International Blood and Marrow Transplant Research (CIBMTR) in patients with AML age ≥ 50 years undergoing alloHCT from older MSDs (age ≥ 50 years) or younger MUDs (age ≤ 35 years) between 2011 and 2018. The study included common allograft types, conditioning regimens, and graft-versus-host disease (GVHD) prophylaxis. The primary outcome was relapse risk. Secondary outcomes included nonrelapse mortality (NRM), GVHD, disease-free survival (DFS), and overall survival. Among 4684 eligible patients, 1736 underwent alloHCT with an older MSD (median donor age, 60 years), and 2948 underwent alloHCT from a younger MUD (median donor age, 25 years). In multivariable analysis, compared to older MSDs, the use of younger MUDs conferred a decreased relapse risk (hazard ratio [HR], .86; P = .005) and a significantly lower adjusted 5-year cumulative incidence of relapse (35% versus 41%; P = .003), but was associated with an increased risk for chronic GVHD (HR, 1.18; 95% confidence interval [CI], 1.08 to 1.29; P = .0002) and greater NRM only in the earlier period of 2011 to 2015 (HR, 1.24; P = .016). The corresponding NRM rates were significantly lower in the more recent period of 2016 to 2018 (HR, .78; P = .017). The adjusted 5-year DFS probability was 44% (95% CI, 42% to 46%) with an alloHCT from younger MUDs compared to 41% (95% CI, 38% to 43%) with older MSDs (P = .04). In summary, for older patients with AML undergoing alloHCT, the use of younger MUDs is associated with decreased relapse risk and improved DFS compared with the use of older MSDs.

Blasts in context: the impact of the immune environment on acute myeloid leukemia prognosis and treatment

Acute myeloid leukemia (AML) is a cancer that originates from the bone marrow (BM). Under physiological conditions, the bone marrow supports the homeostasis of immune cells and hosts memory lymphoid cells. In this review, we summarize our present understanding of the role of the immune microenvironment on healthy bone marrow and on the development of AML, with a focus on T cells and other lymphoid cells. The types and function of different immune cells involved in the AML microenvironment as well as their putative role in the onset of disease and response to treatment are presented. We also describe how the immune context predicts the response to immunotherapy in AML and how these therapies modulate the immune status of the bone marrow. Finally, we focus on allogeneic stem cell transplantation and summarize the current understanding of the immune environment in the post-transplant bone marrow, the factors associated with immune escape and relevant strategies to prevent and treat relapse.

Targeting MDM2 enhances antileukemia immunity after allogeneic transplantation via MHC-II and TRAIL-R1/2 upregulation

Patients with acute myeloid leukemia (AML) often achieve remission after allogeneic hematopoietic cell transplantation (allo-HCT) but subsequently die of relapse driven by leukemia cells resistant to elimination by allogeneic T cells based on decreased major histocompatibility complex II (MHC-II) expression and apoptosis resistance. Here we demonstrate that mouse-double-minute-2 (MDM2) inhibition can counteract immune evasion of AML. MDM2 inhibition induced MHC class I and II expression in murine and human AML cells. Using xenografts of human AML and syngeneic mouse models of leukemia, we show that MDM2 inhibition enhanced cytotoxicity against leukemia cells and improved survival. MDM2 inhibition also led to increases in tumor necrosis factor-related apoptosis-inducing ligand receptor-1 and -2 (TRAIL-R1/2) on leukemia cells and higher frequencies of CD8+CD27lowPD-1lowTIM-3low T cells, with features of cytotoxicity (perforin+CD107a+TRAIL+) and longevity (bcl-2+IL-7R+). CD8+ T cells isolated from leukemia-bearing MDM2 inhibitor-treated allo-HCT recipients exhibited higher glycolytic activity and enrichment for nucleotides and their precursors compared with vehicle control subjects. T cells isolated from MDM2 inhibitor-treated AML-bearing mice eradicated leukemia in secondary AML-bearing recipients. Mechanistically, the MDM2 inhibitor-mediated effects were p53-dependent because p53 knockdown abolished TRAIL-R1/2 and MHC-II upregulation, whereas p53 binding to TRAILR1/2 promotors increased upon MDM2 inhibition. The observations in the mouse models were complemented by data from human individuals. Patient-derived AML cells exhibited increased TRAIL-R1/2 and MHC-II expression on MDM2 inhibition. In summary, we identified a targetable vulnerability of AML cells to allogeneic T-cell-mediated cytotoxicity through the restoration of p53-dependent TRAIL-R1/2 and MHC-II production via MDM2 inhibition.

Thiotepa-fludarabine-treosulfan conditioning for 2nd allogeneic HCT from an alternative unrelated donor for patients with AML: a prospective multicenter phase II trial

Therapeutic options for patients with AML relapsing after allogeneic HCT range from chemotherapy or hypomethylating agents with or without donor lymphocyte infusions to a 2nd allogeneic HCT. Available data are based on retrospective single center or registry studies. The aim of this multicenter trial was to investigate prospectively intensive conditioning with Thiotepa, Fludarabine and Treosulfan (TFT) for 2nd allogeneic HCT from an alternative unrelated donor in patients with AML relapse > 6 months after a 1st allogeneic HCT. Primary endpoint was disease-free survival (DFS) at one year after 2nd HCT. 50 patients median age 53.5 years, in CR/PR (34%) or active relapse (66%) were included. 33 of 38 patients (86.8%) with available data achieved CR 100 days post transplant. 23 patients were alive and free of relapse at primary endpoint one year after 2nd HCT (DFS rate 0.46, 95%-CI (0.32-0.61). Three-year rates of DFS, relapse, non-relapse mortality, and overall survival were 0.24, 95%-CI (0.13-0.36); 0.36 (0.25-0.52); 0.40 (0.29-0.57); and 0.24 (0.13-0.37). Second HCT with TFT conditioning is feasible and has high anti-leukemic efficacy in chemosensitive or refractory AML relapse after prior allogeneic HCT. Still, relapse rates and NRM after 2nd allogeneic HCT remain a challenge. The trial is registered in the German Clinical Trials Registry (number DRKS00005126).

Monitoring of Measurable Residual Disease Using Circulating DNA after Allogeneic Hematopoietic Cell Transplantation

Simple Summary

The major cause of treatment failure after allogeneic stem cell transplantation (allo-HSCT) is due to relapse of the underlying disease. Novel methods and strategies are needed to detect early relapse after allo-HSCT. The present study reports the clinical utility of monitoring measurable residual disease (MRD) and mixed chimerism (MC) by droplet-digital PCR in circulating cell-free DNA (cfDNA) in 62 patients with myeloid malignancies undergoing allo-HSCT. MC in circulating cfDNA at an optimal threshold of 18% discriminated patients with hematological relapse from patients in complete remission after allo-HSCT. Most of the mutations identified using a targeted next-generation sequencing (NGS) panel were detected in cfDNA at relapse and were suitable for the monitoring of MRD. In several cases, mutations were detected earlier in cfDNA than in peripheral blood mononuclear cells. In conclusion, longitudinal analysis of cfDNA for MRD and MC can be used as a complementary tool for early detection of relapse in patients after allo-HSCT and could be used to guide clinical interventions.

Abstract

Relapse of the underlying disease is a frequent complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). In this study, we describe the clinical utility of measurable residual disease (MRD) and mixed chimerism (MC) assessment in circulating cell-free DNA (cfDNA) analysis to detect earlier relapse in patients with hematological malignancies after allo-HSCT. A total of 326 plasma and peripheral blood mononuclear cell (PBMCs) samples obtained from 62 patients with myeloid malignancies were analyzed by droplet-digital PCR (median follow-up: 827 days). Comparison of MC in patients at relapse and in complete remission identified an optimal discriminating threshold of 18% of recipient-derived cfDNA. After performing a targeted next-generation sequencing (NGS) panel, 136 mutations in 58 patients were detected. In a total of 119 paired samples, the putative mutations were detected in both cfDNA and PBMCs in 73 samples (61.3%). In 45 samples (37.8%) they were detected only in cfDNA, and in only one patient (0.9%) were they detected solely in DNA from PBMCs. Hence, in 6 out of 23 patients (26%) with relapse after allo-HSCT, MRD positivity was detected earlier in cfDNA (mean 397 days) than in DNA derived from PBMCs (mean 451 days). In summary, monitoring of MRD and MC in cfDNA might be useful for earlier relapse detection in patients with myeloid malignancies after allo-HSCT.

[Efficacy and safety of Venetoclax in the treatment of 25 patients with recurrent hematologic malignancies after an allogeneic hematopoietic stem cell transplantation]

Objegtive: To investigate the efficacy and safety of preemptive/salvage therapy with venetoclax (VEN) in patients with recurrence after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . Methods: Retrospective analysis the clinical data of 25 patients with minimal residual disease (MRD) positive or morphological recurrence after allo-HSCT treated with VEN in the hematological Hospital of Chinese Academy of Medical Sciences from 2021.2 to 2021.11, there were 15 MRD positive patients (preemptive treatment group) and 10 morphological recurrence patients (salvage treatment group) . The dose of VEN in both groups was 400 mg/d, which was reduced to 100 mg/d when combined with azole antifungal drugs. Results: ①In the preemptive group, there were 7 males and 8 females, with a median age of 32 (18-52) years; There were 13 cases of acute myeloid leukemia (AML) , 1 case of acute lymphoblastic leukemia (ALL) and 1 case of primary myelofibrosis (PMF) ; the median time from MRD positive to the application of VEN was 2.5 (0-12.5) months. The median course of treatment was 2 (1-4) . On the 7th day of the first course of treatment, the median concentration of VEN was 1945 (688-5383) μg/L. After one course of VEN treatment, MRD in 8 patients turned negative (major responses) , MRD in 4 patients decreased by 50% compared with that before treatment, 3 cases were ineffective, and the overall response rate (ORR) was 80% (12/15) . On the 7th day of treatment, 3 of the 9 patients with VEN blood concentration <1 000 μg/L or >3 000 μg/L turned negative for MRD (33.3%) , and 5 of the 6 patients with VEN blood concentration between 1000 and 3000 μg/L turned negative for MRD (83.3%) . Grade 3/4 neutropenia occurred in 5 patients (33%) and grade 3/4 thrombocytopenia occurred in 5 patients (33%) , there were no new cases of severe infection and death. ②In the salvage group, there were 7 males and 3 females, with a median age of 44 (28-59) years; there were 6 cases of AML, 2 cases of ALL, 1 case of atypical chronic myeloid leukemia (aCML) , 1 case of refractory hemopenia with multiline dysplasia (MDS-RCMD) ; the median time from relapse to application of VEN was 0 (0-1) months. The median treatment was 1 (1-2) course. The median concentration of VEN on the 7th day of the first course of treatment was 2 419 (1 200-6 155) μg/L. After one course of VEN treatment, 3 cases achieved complete remission (CR) (major responses) and 3 cases achieved partial remission (PR) , 4 cases were ineffective and the ORR was 60% (6/10) . On the 7th day of treatment, 1 of the 4 patients with VEN blood concentration >3 000 μg/L achieved CR (25%) , and 2 of the 6 patients with VEN blood concentration between 1 000 and 3 000 μg/L achieved CR (33.3%) . Grade 3/4 neutropenia and grade 3/4 thrombocytopenia occurred in 10 patients (100%) . One patient died of severe pulmonary infection. ③The median follow-up was 4.5 (1-8.5) months. The overall survival rate (OS) of the preemptive group and the salvage group were (70.2±12.7) % and (50.0± 15.8) %, respectively (χ(2)=1.873, P=0.171) . The OS of patients with and without primary response to one course of VEN were (90.9±8.7) % and (36.2±14.7) % respectively (χ(2)=6.843, P=0.009) . Three patients with TP53 mutation achieved the major responses after VEN treatment. Conclusion: Preemptive/salvage therapy with VEN after allo-HSCT in patients with hematological malignancies is effective and well tolerated, monitoring the concentration of VEN is expected to improve the curative effect. The prognosis of patients who fail to reach the major responses after one course of preemptive/salvage treatment with VEN is poor, so they need to switch to other treatment schemes as soon as possible.

Epigenetic Regulation to Enhance Graft-versus-Leukemia Activity

SUMMARY

Accumulating evidence supports that loss of HLA expression contributes to relapse after allogeneic hematopoietic cell transplantation (allo-HCT), but the mechanisms behind this evasion strategy are unclear. The groups of Luca Vago and Raffaella Di Micco identified the polycomb repressive complex 2 (PRC2) as a key epigenetic driver of immune escape after allo-HCT by reducing the chromatin accessibility of HLA class II molecules, which could be targeted by pharmacologic inhibition of PRC2 subunits. See related article by Gambacorta et al., p. 1449 (10).

Role of Radiation Based Conditioning Regimens in Patients With High-Risk AML Undergoing Allogenic Transplantation in Remission or Active Disease and Mechanisms of Post-Transplant Relapse

In the two decades there has been a consistent improvement in the clinical outcomes of patients diagnosed with acute leukemia undergoing allogenic stem cell transplantation. These improvements have been made possible by advancements in supportive care practices, more precise risk stratification of leukemia patients by genetic testing at diagnosis, accurate disease assessment by measurable residual disease (MRD) in pretransplant marrow and attempts to clear residual disease clones prior to transplant. Availability of targeted therapies, immunotherapies, and approval of novel drug combinations with BCL-2 inhibitors has also improved remission rates for patients who are undergoing transplant. For patients who are unable to achieve a morphologic or MRD^- remission prior to transplant, the risk of relapse post-transplant remains high. Total body irradiation (TBI) based intensification of transplant conditioning may be able to overcome risk of increased relapse rate in this clinical setting by improving clearance of leukemic clones. However, in the past increased nonrelapse mortality (NRM) associated with escalation of conditioning intensity has neutralized any potential benefit of decreasing relapse rate in HCT patient resulting in no significant improvement in overall survival. In this review we discuss incorporation of newer radiation techniques such as total marrow irradiation (TMI) to safely deliver targeted doses of radiation at higher doses to improve outcomes of patients with active leukemia. We also discuss the mechanisms associated with leukemia relapse and treatment options available in post allo-HCT relapse setting despite use of intensified conditioning regimens.

Time-dependent analysis of adoptive immunotherapy following sequential FLAMSA-reduced intensity conditioning and allogeneic hematopoietic stem cell transplantation in patients with high-risk myeloid neoplasia

Prophylactic donor lymphocyte infusions (DLI) are part of the sequential FLAMSA-reduced intensity conditioning (RIC) regimen to cure high risk myeloid neoplasia with allogeneic hematopoietic stem cell transplantation (HSCT). Although DLI themselves carry significant risks, their prophylactic use has not been analyzed in a time-dependent manner. One hundred and fourteen patients underwent FLAMSA-RIC HSCT between 2013 and 2020. Next to Kaplan-Meier estimation of overall, disease-free, and graft-versus-host relapse-free survival (OS, DFS, GRFS), cumulative incidences of relapse and death in remission were calculated in a competing risk model. Additionally, the contribution of prophylactic and preemptive DLI as time-dependent covariates was assessed using a time-varying model toward DFS (Simon-Makuch method, Mantel-Byar test). At 2 years, OS was 45.2% [95% CI 36.7-55.7%], DFS 31.8% [95% CI 24-42.2%] and GRFS 11.3 [95% CI 6.5-19.8]. Neither prophylactic nor preemptive DLI showed a significant influence on DFS when considered time-dependent covariates (Mantel-Byar, p = .3). This was further corroborated in competing risk analysis with DLI as time-dependent covariates. Both prophylactic and preemptive DLI miss significance in their impact on survival within a high-risk cohort in a time-varying model. Controlled trials to address the impact of postgrafting immunotherapy approaches are needed.

Long-term results and GvHD after prophylactic and preemptive donor lymphocyte infusion after allogeneic stem cell transplantation for acute leukemia

We report on 318 patients with acute leukemia, receiving donor lymphocyte infusion (DLI) in complete hematologic remission (CHR) after allogeneic stem cell transplantation (alloSCT). DLI were applied preemptively (preDLI) for minimal residual disease (MRD, n = 23) or mixed chimerism (MC, n = 169), or as prophylaxis in high-risk patients with complete chimerism and molecular remission (proDLI, n = 126). Median interval from alloSCT to DLI1 was 176 days, median follow-up was 7.0 years. Five-year cumulative relapse incidence (CRI), non-relapse mortality (NRM), leukemia-free and overall survival (LFS/OS) of the entire cohort were 29.1%, 12.7%, 58.2%, and 64.3%. Cumulative incidences of acute graft-versus-host disease (aGvHD) grade II-IV°/chronic GvHD were 11.9%/31%. Nineteen patients (6%) died from DLI-induced GvHD. Age ≥60 years (p = 0.046), advanced stage at transplantation (p = 0.003), shorter interval from transplantation (p = 0.018), and prior aGvHD ≥II° (p = 0.036) were risk factors for DLI-induced GvHD. GvHD did not influence CRI, but was associated with NRM and lower LFS/OS. Efficacy of preDLI was demonstrated by decreasing MRD/increasing blood counts in 71%, and increasing chimerism in 70%. Five-year OS after preDLI for MRD/MC was 51%/68% among responders, and 37% among non-responders. The study describes response and outcome of DLI in CHR and helps to identify candidates without increased risk of severe GvHD.

Maintenance therapy after allogeneic hematopoietic transplant for acute myeloid leukemia: a systematic review and meta-analysis

BACKGROUND

For patients undergoing allogeneic hematopoietic stem cell transplant (HSCT) for acute myeloid leukemia (AML), disease relapse remains the most common reason for transplant failure and patient death. Recent randomized controlled trials (RCTs) have aimed to reduce the risk of relapse by means of post-transplant maintenance therapy.

METHODS

We performed a systematic review and meta-analysis of RCTs comparing the efficacy and safety of maintenance with observation or placebo in patients with AML after allogeneic HSCT. We searched Cochrane Library, PubMed and conference proceedings up to Febuary 2021.

RESULTS

Our search yielded five trials including 736 patients. Maintenance therapy consisted of tyrosine kinase inhibitors (TKIs) in 3 studies (sorafenib 2 studies; midostaurin 1 study) and hypomethylating agents (HMAs) in 2 studies (decitabine and azacytidine 1 study each). Maintenance therapy was associated with an improved overall survival (OS), HR = 0.61 (95% CI 0.47-0.80). Subgroup analysis revealed advantage in OS with either TKI or HMA maintenance. Relapse free survival (RFS) was also improved in the maintenance arm compared with the control arm HR = 0.51(95% CI 0.40 - 0.66). There was no difference between the two arms in overall grade 3/4 adverse events or overall infections, in grade 3/4 infections, or in acute and chronic graft versus host disease.

CONCLUSIONS

Our meta-analysis shows that post-transplant maintenance therapy in AML patients is effective in improving RFS and OS, with a satisfactory safety profile.

Molecular Targeted Therapy and Immunotherapy for Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) is a heterogeneous, clonal hematological disorder characterized by ineffective hematopoiesis, cytopenia, morphologic dysplasia, and predisposition to acute myeloid leukemia (AML). Stem cell genomic instability, microenvironmental aberrations, and somatic mutations contribute to leukemic transformation. The hypomethylating agents (HMAs), azacitidine and decitabine are the standard of care for patients with higher-risk MDS. Although these agents induce responses in up to 40-60% of patients, primary or secondary drug resistance is relatively common. To improve the treatment outcome, combinational therapies comprising HMA with targeted therapy or immunotherapy are being evaluated and are under continuous development. This review provides a comprehensive update of the molecular pathogenesis and immune-dysregulations involved in MDS, mechanisms of resistance to HMA, and strategies to overcome HMA resistance.

Donor lymphocyte infusions after first allogeneic hematopoietic stem-cell transplantation in adults with acute myeloid leukemia: a single-center landmark analysis

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is potentially curative for acute myeloid leukemia (AML). The inherent graft-versus-leukemia activity (GvL) may be optimized by donor lymphocyte infusions (DLI). Here we present our single-center experience of DLI use patterns and effectiveness, based on 342 consecutive adult patients receiving a first allo-HSCT for AML between 2009 and 2017. The median age at transplantation was 57 years (range 19-79), and the pre-transplant status was active disease in 58% and complete remission (CR) in 42% of cases. In a combined landmark analysis, patients in CR on day +30 and alive on day +100 were included. In this cohort (n=292), 93 patients received cryopreserved aliquots of peripheral blood-derived grafts for DLI (32%) and median survival was 55.7 months (2-year/5-year probability: 62%/49%). Median survival for patients receiving a first dose of DLI "preemptively," in the absence of relapse and guided by risk marker monitoring (preDLI; n=42), or only after hematological relapse (relDLI; n=51) was 40.9 months (2-year/5-year: 64%/43%) vs 10.4 months (2-year/5-year: 26%/10%), respectively. Survival was inferior when preDLI was initiated at a time of genetic risk marker detection vs mixed chimerism or clinical risk only. Time to first-dose preDLI vs time to first-dose relDLI was similar, suggesting that early warning and intrinsically lower dynamics of AML recurrence may contribute to effectiveness of preDLI-modified GvL activity. Future refinements of the preemptive DLI concept will benefit from collaborative efforts to diagnose measurable residual disease more reliably across the heterogeneous genomic spectrum of AML.

Myelodysplastic syndrome and immunotherapy novel to next in-line treatments

Patients with Myelodysplastic syndromes (MDS) have few therapy options for sustainable responses in the frontline setting, and even less after hypomethylating agent (HMA) failure in relapsed and refractory setting. The only potential cure is an allogeneic hematopoietic stem cell transplant which is an unrealistic option for the majority of MDS patients. Immunotherapy with checkpoint inhibition, CAR-T cells, and vaccine therapy few have shown promise in a variety cancer and have now been tested in patients with MDS. Most trials have focused on AML patients and included small numbers of MDS patients. Until now, a dedicated review of immunotherapy outcomes in MDS patients has been lacking. Thus, herein we review outcomes of MDS patients after immunotherapies on a variety of clinical trials reported to date.

Prophylactic or Preemptive Low-Dose Azacitidine and Donor Lymphocyte Infusion to Prevent Disease Relapse following Allogeneic Transplantation in Patients with High-Risk Acute Myelogenous Leukemia or Myelodysplastic Syndrome

Because of the persistently high rates of relapse of patients with high-risk acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) following allogeneic hematopoietic stem cell transplantation (allo-HSCT), post-transplantation maintenance therapy has been proposed. We previously initiated a Phase II trial in which epigenetic therapy was combined with immunotherapy in an attempt to reduce disease relapse. In that study, low-dose azacitidine (AZA) and escalating doses of donor lymphocyte infusion (DLI) were given as post-allo-HSCT maintenance treatment. In the present study, we retrospectively analyze a larger cohort of patients receiving post-transplantation maintenance therapy and provide updates on some patients of the earlier study. The objectives of the present study were to analyze the cumulative incidence of relapse (CIR), overall survival (OS), and progression-free survival (PFS) and the incidence of acute and chronic graft-versus-host disease (GVHD) of patients with high-risk AML or MDS receiving post-transplantation maintenance treatment with AZA with or without DLI. We retrospectively analyzed 77 patients (54 with AML, 23 with MDS) considered at high risk based on either their genomic or clinical status at transplantation. Following allogeneic transplantation, they received at least 1 cycle of prophylactic or preemptive low-dose AZA with or without escalating doses of DLI to prevent disease relapse. Almost one-half of the patients (47%) were able to receive the full 12 cycles of scheduled AZA, and a majority (79%) received at least 1 DLI. With a median follow-up of 24 months, 19 patients (25%; 16 with AML, 3 with MDS) relapsed, at a median of 9.8 months (range, 4 to 58.6 months), giving a 22% CIR at 24 months. OS and PFS at 24 months were 70.8% and 68.3%, respectively. The cumulative incidences of grade II-IV acute GVHD and chronic GVHD were 27.4% and 45%, respectively. Only a minority of patients (11%) required delayed administration of AZA. These findings confirm that AZA-DLI maintenance is both tolerable and effective in reducing the risk of post-transplantation relapse.

Dose intensity for conditioning in allogeneic hematopoietic cell transplantation: can we recommend "when and for whom" in 2021?

Allogeneic hematopoietic stem-cell transplantation is a potentially curative therapy for various hematologic diseases. An essential component of this procedure is the pre-transplant conditioning regimen, which should facilitate engraftment and reduce or eliminate tumor cells. The recognition of the substantial association of a graft-versus- tumor effect and the high toxicity of the commonly used conditioning regimen led to the introduction of more differentiated intensity strategies, with the aim of making hematopoietic stem-cell transplantation less toxic and safer, and thus more applicable to broader populations such as older or unfit patients. In general, prospective and retrospective studies suggest a correlation between increasing intensity and nonrelapse mortality and an inverse correlation with relapse incidence. In this review, we will summarize traditional and updated definitions for conditioning intensity strategies and the landscape of comparative prospective and retrospective studies, which may help to find the balance between the risk of non-relapse mortality and relapse. We will try to underscore the caveats regarding these definitions and analyses, by missing complex differences between intensity and toxicity as well as the broad influences of other factors in the transplantation procedure. We will summarize evidence regarding several confounders which may influence decisions when selecting the intensity of the conditioning regimen for any given patient, according to the individual risk of relapse and non-relapse mortality.

Oncolytic virotherapy in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a curative option for various hematologic malignancies. However, fatal complications, such as relapse and graft-versus-host disease (GVHD) hampered favorable HSCT outcomes. Cancer cells remained in the body following the conditioning regimen, or those contaminating the autologous graft can cause relapse. Although the relapse is much lesser in allogeneic HSCT, GVHD is still a life-threatening complication in this type of HSCT. Researchers are seeking various strategies to reduce relapse and GVHD in HSCT with minimum effects on the engraftment and immune-reconstitution. Oncolytic viruses (OVs) are emerging anti-cancer agents with promising results in battling solid tumors. OVs can selectively replicate in the malignant cells in which the antiviral immune responses have defected. Hence, they could be used as a purging agent to eradicate the tumoral contamination of autologous grafts with no damages to hematopoietic stem cells. Moreover, they have been shown to alleviate GVHD complications through modulating alloreactive T cell responses. Primary results promise using OVs as a strategy to reduce both relapse and GVHD in the HSCT without affecting hematologic and immunologic engraftment. Herein, we provide the latest findings in the field of OV therapy in HSCT and discuss their pros and cons.

Relapse after Allogeneic Stem Cell Transplantation of Acute Myelogenous Leukemia and Myelodysplastic Syndrome and the Importance of Second Cellular Therapy

Patients with acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS) who relapse after allogeneic hematopoietic cell transplantation (allo-HCT) generally have poor overall survival (OS). Interventions that result in improved OS after relapse are not well established. The efficacy of second cellular therapy and specific indications are matters of debate. This study was conducted to evaluate factors associated with postrelapse survival and the efficacy of a second course of cellular therapy. We retrospectively analyzed consecutive patients with AML and MDS who underwent a first allo-HCT between 2010 and 2017 at our center but subsequently relapsed. One hundred and four patients with AML and 44 patients with MDS were included (total n = 148). Bone marrow (BM) and peripheral blood stem cell grafts were either unmodified or T cell-depleted (TCD) by CD34⁺ selection ex vivo. Forty-five patients (30.4%) received a second cellular therapy after relapse, either a second allo-HCT (n = 28; 18.9%) or donor leukocyte infusion (DLI) (n = 17; 11.5%). The median age at transplantation was 60 years (range, 24 to 78 years). The median time to relapse (TTR) after transplantation was 6.5 months (range, 1 to 60.9 months), and the ensuing median OS was 6 months (95% confidence interval [CI], 4.8 to 8.9 months). In univariable analysis, longer TTR, relapse type (measurable residual disease versus morphologic), relapse occurring in the most recent years, and receipt of cellular therapy after relapse were associated with better outcomes, whereas adverse cytogenetics and/or abnormality of TP53, as well as NPM1 mutation in patients with AML, were associated with adverse outcomes. Relapse type, year of relapse, and a variable resulting from the combination of TTR and receipt of second cellular therapy remained significantly associated with postrelapse survival in multivariable analysis. In a separate multivariable model, adjusted only for TTR, relapse type, and receipt of second cellular therapy, an adverse effect of NPM1 mutation on survival was confirmed. We could not show an effect of post-transplantation maintenance on survival after relapse. In both univariable and multivariable analysis, we found a positive association for second cellular therapy with survival after relapse in patients who relapsed early (<6 months) after allo-HCT and a similar trend in patients who relapsed late (>12 months) after transplantation. Two-year OS after a second cellular therapy was 44.9% (95% CI, 28.5% to 61.4%), and it was significantly better in patients with <5% BM blasts before cell infusion. We could not show different effects on survival after second cellular therapy for DLI versus second allo-HCT in univariable analysis. Survival after relapse is improving over time, but this remains a challenging event, especially for patients who relapse early after transplantation. We found that a second cellular therapy could offer a benefit even in these cases. Nonetheless, more research is needed to clarify the most appropriate treatment choices after relapse. These are probably driven by underlying genetic and immunologic conditions, which should be the focus of future studies.

Establishment of a cell processing laboratory to support hematopoietic stem cell transplantation and chimeric antigen receptor (CAR)-T cell therapy

Cell processing laboratories are an important part of cancer treatment centers. Cell processing laboratories began by supporting hematopoietic stem cell (HSC) transplantation programs. These laboratories adapted closed bag systems, centrifuges, sterile connecting devices and other equipment used in transfusion services/blood banks to remove red blood cells and plasma from marrow and peripheral blood stem cells products. The success of cellular cancer immunotherapies such as Chimeric Antigen Receptor (CAR) T-cells has increased the importance of cell processing laboratories. Since many of the diseases successfully treated by CAR T-cell therapy are also treated by HSC transplantation and since HSC transplantation teams are well suited to manage patients treated with CAR T-cells, many cell processing laboratories have begun to produce CAR T-cells. The methods that have been used to process HSCs have been modified for T-cell enrichment, culture, stimulation, transduction and expansion for CAR T-cell production. While processing laboratories are well suited to manufacture CAR T-cells and other cellular therapies, producing these therapies is challenging. The manufacture of cellular therapies requires specialized facilities which are costly to build and maintain. The supplies and reagents, especially vectors, can also be expensive. Finally, highly skilled staff are required. The use of automated equipment for cell production may reduce labor requirements and the cost of facilities. The steps used to produce CAR T-cells are reviewed, as well as various strategies for establishing a laboratory to manufacture these cells.

Treatment of myeloid malignancies relapsing after allogeneic hematopoietic stem cell transplantation with venetoclax and hypomethylating agents-a retrospective multicenter analysis on behalf of the German Cooperative Transplant Study Group

Treatment of relapse after allogeneic hematopoietic stem cell transplantation (alloHSCT) remains a great challenge. Aiming to evaluate the combination of venetoclax and hypomethylating agents (HMAClax) for the treatment of relapse of myeloid malignancies after alloHSCT, we retrospectively collected data from 32 patients treated at 11 German centers. Venetoclax was applied with azacitidine (n = 13) or decitabine (n = 19); 11 patients received DLI in addition. HMAClax was the first salvage therapy in 8 patients. The median number of cycles per patient was 2 (1–19). All but 1 patient had grade 3/4 neutropenia. Hospital admission for grade 3/4 infections was necessary in 23 patients (72%); 5 of these were fatal. In 30 evaluable patients, overall response rate (ORR) was 47% (14/30, 3 CR MRD^neg, 5 CR, 2 CRi, 1 MLFS, 3 PR). ORR was 86% in first salvage patients versus 35% in later salvage patients (p = 0.03). In 6 patients with molecular relapse (MR), ORR was 67% versus 42% in patients with hematological relapse (HR) (n = 24, p = n.s.). After a median follow-up of 8.4 months, 25 patients (78%) had died and 7 were alive. Estimated median overall survival was 3.7 months. Median survival of patients with HMAClax for first versus later salvage therapy was 5.7 and 3.4 months (p = n.s.) and for patients with MR (not reached) compared to HR (3.4 months, p = 0.024). This retrospective case series shows that venetoclax is utilized in various different combinations, schedules, and doses. Toxicity is substantial and patients who receive venetoclax/HMA combinations for MR or as first salvage therapy derive the greatest benefit.

Randomized trials with checkpoint inhibitors in acute myeloid leukaemia and myelodysplastic syndromes: What have we learned so far and where are we heading?

The treatment of acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS) has seen dramatic advances with the approval of multiple novel agents in recent years. However, unlike solid malignancies, immune checkpoint inhibitors have yet to garner regulatory approval in AML and MDS with recent randomized clinical trials yielding only underwhelming results. Novel targets have been explored in early phase clinical trials with impressive results leading to ongoing subsequent controlled trials. However, major challenges in the field remain such as the validation of predictive genetic, molecular, and immunophenotypic biomarkers, optimization of clinical trial design, and the identification of novel synergistic combination therapies. Herein, we review recent clinical trial data focusing on randomized clinical trials and highlight limitations of the currently available evidence in an effort to suggest options for advancing the field.

Novel Biomarkers for Outcome After Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a well-established curative treatment for various malignant hematological diseases. However, its clinical success is substantially limited by major complications including graft-vs.-host disease (GVHD) and relapse of the underlying disease. Although these complications are known to lead to significant morbidity and mortality, standardized pathways for risk stratification of patients undergoing allo-HSCT are lacking. Recent advances in the development of diagnostic and prognostic tools have allowed the identification of biomarkers in order to predict outcome after allo-HSCT. This review will provide a summary of clinically relevant biomarkers that have been studied to predict the development of acute GVHD, the responsiveness of affected patients to immunosuppressive treatment and the risk of non-relapse mortality. Furthermore, biomarkers associated with increased risk of relapse and subsequent mortality will be discussed.

The FLAMSA concept-past and future

The FLAMSA reduced intensity (RIC) concept, also known as "sequential therapy", is a conceptual platform for the treatment of leukemia separated in several parts: induction therapy, a sequence of antileukemic and immunosuppressive conditioning for allogeneic stem cell transplantation, and immune restitution supported by donor lymphocyte transfusions. The antileukemic part consists of fludarabine, cytosine arabinoside, and amsacrine (FLAMSA); non-cross reactive agents like fludarabine and amsacrine have been successfully used in cases of refractoriness and relapse. Immunosuppressive conditioning and transplantation follow after only 3 days of rest. This way, the toxicity of allogeneic transplantation could be reduced and the anti-leukemia effects by using allogeneic immune cells could be optimized. This review summarizes available data on efficacy and toxicity of this approach. Further, possible strategies for improvements are discussed in order to provide better chances for elderly and frail patients and patients with advanced and high-risk disease. Among others, several new agents are available that target molecular changes of leukemia for induction of remission and allow for bridging the time after transplantation until adoptive immunotherapy becomes safe and effective.

Successful Treatment of Early Relapsed High-Risk AML After Allogeneic Hematopoietic Stem Cell Transplantation With Biomodulatory Therapy

Early relapse of acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an often unsuccessful therapeutic challenge. Since treatment options are few and efficacy is low, new approaches such as de novo allo-HSCT, targeted therapies and biomodulatory drugs have been developed, albeit prognosis is very poor. In this manuscript we present an unusual case of a patient with high-risk AML with an unbalanced jumping translocation and FLT3-TKD (low) mutation who presented with early relapse (FLT3 negative) after allo-HSCT, refractory to one cycle of azacytidine and discontinuation of immunosuppression (IS). As salvage therapy, the patient received a biomodulatory therapy consisting of low-dose azacytidine 75 mg/day (given s.c. d1-7 of 28), pioglitazone 45 mg/day orally, and all-trans-retinoic acid (ATRA) 45 mg/m2/day orally achieving a complete remission after two cycles of therapy. Even after cessation of treatment after 5 cycles, the patient remained in complete remission with full chimerism in peripheral blood and bone marrow for another 7 months. In conclusion, we report about an unusual case of long-lasting complete remission of early relapsed high-risk AML after allo-HSCT treated with azacytidine, pioglitazone and ATRA after standard of care treatment with HMA and discontinuation of IS failed.

The road map of cancer precision medicine with the innovation of advanced cancer detection technology and personalized immunotherapy

The advancement of cancer genomics research due to the development of next generation sequencing technologies is going to bring the promise of cancer precision medicine, in turn revolutionizing cancer detection and treatment. In this review, we will discuss the possible road map for implementation of cancer precision medicine into the clinical practice by mainly focusing on the role of liquid biopsy, particularly circulating tumor DNA, as a potential tool for cancer screening, selection of an appropriate drug(s), surveillance of minimal residual diseases, and early detection of recurrence. We will also review the current status of genome-driven oncology and emerging field of immunotherapies that could be provided to patients to improve their clinical outcome and quality of life. Lastly, we will discuss the usefulness of artificial intelligence that facilitate complex data integration in our health care/medical care system.