Acute lymphoblastic leukemia (ALL) relapsed after allogeneic hematopoietic cell transplantation (allo-HCT) has a catastrophic prognosis. Blinatumomab, a CD3/CD19-directed bispecific T cell engager, is reportedly effective for advanced B-cell ALL (B-ALL), even after allo-HCT. However, the efficacy of blinatumomab in extramedullary relapse (EMR) is controversial. Donor lymphocyte infusion (DLI) is another immunological treatment worth considering for ALL relapsed after allo-HCT. We report the case of a 56-year-old woman with B-ALL. Allo-HCT was performed during the second complete remission (CR). Thirteen months after allo-HCT, isolated EMR (iEMR) of B-ALL developed without bone marrow lesions. A third CR was achieved with 2 cycles of blinatumomab. An additional four cycles each of blinatumomab and DLI were then administered. The patient did not develop graft-versus-host disease and has confirmed 2-year treatment-free remission without a second allo-HCT. Therefore, blinatumomab was considered an effective salvage therapy for iEMR of B-ALL after allo-HCT, because iEMR could have a lower tumor burden than that seen in systemic relapse, and low tumor burden was a prognostic factor for response to blinatumomab. Furthermore, immunological consolidation therapies could only provoke graft-versus-leukemia effects if the imbalanced effector/target ratio was restored and the tumor burden was lowered through immunosurveillance.

BACKGROUND: Regular monitoring of CD34 donor chimerism (DC) is a highly sensitive method of predicting relapse in allogeneic stem cell transplant (alloHSCT) recipients with AML/MDS. A fall of CD34 DC below 80% is an indicator of ensuing relapse. There are limited studies assessing the efficacy of donor lymphocyte infusion (DLI) triggered by mixed CD34 DC (MDC), in addressing falling chimerism.
METHODS: We performed a retrospective analysis of consecutive alloHSCT patients between 2012 to 2023 who received DLI (with or without azacitidine) for CD34 MDC without morphologic relapse at the time of infusion.
RESULTS: Of the 21 patients with follow up CD34 DC available, 14 (66.7%) achieved CD34 full donor chimerism (FDC) following DLI with or without azacitidine (dli-FDC), while 7 (33.3%) did not (dli-MDC). The 2-year cumulative incidence of relapse (CIR) was significantly lower in dli-FDC compared to dli-MDC (21.4% vs. 85.7%, P < 0.001), correlating with superior overall survival (OS; median years not reached vs. 0.67 years [95% CI, 0.58-ND], P < .001). Rates of grade II-IV acute GVHD post-DLI were 14.9%, and moderate-severe cGVHD was 42.8% in the dli-FDC group. The 5-year nonrelapse mortality (NRM) of the dli-FDC group was 7.1% following DLI.
CONCLUSIONS: Our study shows the restoration of CD34 FDC post-DLI is associated with reduced relapse and improved overall survival, with low NRM.

Allogeneic hematopoietic cell transplantation (alloHCT) provides a potential curative treatment for haematological malignancies. The therapeutic Graft-versus-Leukaemia (GvL) effect is induced by donor T cells attacking patient hematopoietic (malignant) cells. However, if healthy non-hematopoietic tissues are targeted, Graft-versus-Disease (GvHD) may develop. After HLA-matched alloHCT, GvL and GvHD are induced by donor T cells recognizing polymorphic peptides presented by HLA on patient cells, so-called minor histocompatibility antigens (MiHAs). The balance between GvL and GvHD depends on the tissue distribution of MiHAs and T-cell frequencies targeting these MiHAs. T cells against broadly expressed MiHAs induce GvL and GvHD, whereas those targeting MiHAs with hematopoietic-restricted expression induce GvL without GvHD. Recently, the MiHA repertoire identified in natural immune responses after alloHCT was expanded to 159 total HLA-I-restricted MiHAs, including 14 hematopoietic-restricted MiHAs. This review explores their potential relevance to predict, monitor, and manipulate GvL and GvHD for improving clinical outcome after HLA-matched alloHCT.

Donor lymphocyte infusions (DLIs) are often recommended products after allogeneic hematopoietic stem cell transplant to increase graft - versus - leukemia effect. More success rate of DLI has been reported in relapsed posttransplant chronic myeloid leukemia. Whatever the indication for DLI, mortality related to post-DLI infusion is 5%-20%, and more than one-third of patients will develop acute and/or chronic graft versus host disease (GVHD) after DLI. We report two cases where DLIs were used for residual disease after posttransplant. Both of DLI went uneventful. None of the patient\'s developed signs of GVHD postinfusion. Although both patients expired with different causes, none were related to DLI infusion. Information from published literature suggests that DLI should be administered early after relapse or as a prophylactic strategy in patients receiving T-cell-depleted grafts, and patients with aggressive diseases may benefit from disease reduction before DLI. However, further evidence is required to evaluate its efficacy, especially in relapsed or residual hematological malignancies.

Background/Objectives: Relapsed B-cell acute lymphoblastic leukemia (B-ALL) remains an unresolved matter of concern regarding adverse outcomes. This case study aimed to evaluate the effectiveness of blinatumomab, with or without door lymphocyte infusion (DLI), in treating measurable residual disease (MRD)-positive B-ALL. Methods: All patients who received blinatumomab salvage therapy were included in this study. Eleven patients were included in the study. All patients were evaluated for MRD-negativity. Results: Before starting blinatumomab therapy, seven patients tested positive for MRD, three tested negative, and one had refractory disease. Hematopoietic cell transplantation (HCT) was reserved for five patients with persistent MRD. Six patients became MRD-negative and subsequent HCT was not performed. Only two patients relapsed; one patient died of relapse, and the other one received carfilzomib-based therapy and was MRD-negative thereafter. Nine patients were MRD-negative at a median follow-up of 28 months (15-52 months). Two of three MRD-positive post-transplant patients remained in complete molecular remission after preemptive DLI at the last follow-up date. In the first salvage, blinatumomab may achieve complete remission and bridging to HCT in pediatric patients with end-of-induction MRD-positive B-cell precursor ALL. Conclusions: The decision on how to treat post-transplant relapse continues to affect survival outcomes. Blinatumomab combined with DLI may extend the armamentarium of release options for high-risk pediatric patients. This approach is encouraging for high-risk ALL patients who are MRD-positive post-transplantation.

This longitudinal study was based on the outcomes of Donor Lymphocyte Infusion (DLI) for falling peripheral blood (PB) CD34+ and CD3+ donor chimerism (DC).
From 2012 to 2018, data was collected from the BMT database and electronic medical records (EMR). The primary objective was to compare the indication for DLI based on falling PB CD34+ or CD3+ DC in patients post allo-SCT for AML and MDS and their overall survival (OS).
18/70 patients met the inclusion criteria. Indications for DLI were i) falling PB CD34+ DC ≤ 80 % with morphological relapse, ii) falling PB CD34+ DC ≤ 80 % without morphological relapse and iii) falling PB CD3+ DC ≤ 80 % without falling PB CD34+ DC. Log rank analysis showed falling PB CD34+ DC and morphological relapse had significantly lower OS. Linear regression demonstrated better OS post DLI if there was PB CD34+ and CD3+ chimerism response at 30 days (p = 0.029), GVHD (p = 0.032) and tapering immunosuppression at the time of falling DC (p = 0.042).
DLI for PB CD34+ DC values ≤ 80 % and morphological relapse had the lowest OS. In this study, full DC was achieved after DLI even with a PB CD3+DC value as low as 13 %, provided the PB CD34+ DC remained > 80 %. Further research is vital in CD34+ DC as a biomarker for disease relapse and loss of engraftment.

BACKGROUND: Disease relapse after allogeneic stem cell transplantation (allo-SCT) is the main challenge for curing acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). We investigated the overall survival (OS) after allo-SCT relapse according to different therapeutic approaches.
METHODS: We analyzed 134 patients who relapsed after allo-SCT performed between 2015 and 2021 at Saint-Antoine University Hospital, Paris and Spedali Civili di Brescia, Brescia. Of these, 103 (77%) were treated, comprising 69/103 (67%) who received therapy in overt relapse and 34/103 (33%) who were treated in a pre-emptive manner when molecular/cytogenetics recurrence or mixed chimerism occurred. The treatment was donor lymphocyte infusion (DLI)-based for 40/103 (39%) patients.
RESULTS: The 1-, 2-, and 5-year OS of patients treated with DLI (n = 40) was 67%, 34%, and 34%, respectively, for those treated preventively (n = 20) and 43%, 20%, and 20%, respectively, for those treated in overt relapse (n = 20) (p < 0.01). The 1-, 2-, and 5-year OS of patients treated without DLI (n = 63) was 54%, 40%, and 26%, respectively, for those treated preventively (n = 14) and 17%, 5%, and 0%, respectively, for those treated in overt relapse (n = 49) (p < 0.01).
CONCLUSIONS: Relapse treatment with a pre-emptive strategy was associated with improved outcomes, particularly when DLI was employed.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many hematologic malignancies as well as non-malignant conditions. Part of the curative basis underlying HSCT for hematologic malignancies relies upon induction of the graft versus leukemia (GVL) effect in which donor immune cells recognize and eliminate residual malignant cells within the recipient, thereby maintaining remission. GVL is a clinically evident phenomenon; however, specific cell types responsible for inducing this effect and molecular mechanisms involved remain largely undefined. One of the best examples of GVL is observed after donor lymphocyte infusions (DLI), an established therapy for relapsed disease or incipient/anticipated relapse. DLI involves infusion of peripheral blood lymphocytes from the original HSCT donor into the recipient. Sustained remission can be observed in 20-80% of patients treated with DLI depending upon the underlying disease and the intrinsic burden of targeted cells. In this review, we will discuss current knowledge about mechanisms of GVL after DLI, experimental strategies for augmenting GVL by manipulation of DLI (e.g. neoantigen vaccination, specific cell type selection/depletion) and research outlook for improving DLI and cellular immunotherapies for hematologic malignancies through better molecular definition of the GVL effect.

Unmodified donor lymphocyte infusions (DLI) after allogeneic stem cell transplantation (alloSCT) can boost the beneficial Graft-versus-Leukemia (GvL) effect but may also induce severe Graft-versus-Host-Disease (GvHD). To improve the balance between GvL and GvHD, it is crucial to identify factors that influence the alloreactivity of DLI.
We investigated the effects of the presence of patient-derived antigen-presenting cells at time of DLI as estimated by the bone marrow (BM) chimerism status, lymphopenia as measured by the absolute lymphocyte count (ALC) at time of DLI, and the presence of a viral infection (de novo or reactivation) close to DLI on the risk of GvHD after DLI. The cohort consisted of patients with acute leukemia or myelodysplastic syndrome who prophylactically or pre-emptively received DLI as standard care after alemtuzumab-based alloSCT. In patients at high risk for relapse, DLI was administered at 3 months after alloSCT (n=88) with a dose of 0.3x106 or 0.15x106 T cells/kg in case of a related or unrelated donor, respectively. All other patients (n=76) received 3x106 or 1.5x106 T cells/kg, respectively, at 6 months after alloSCT.
For both DLIs, patients with reduced-intensity conditioning and an unrelated donor had the highest risk of GvHD. For DLI given at three months, viral infection within 1 week before and 2 weeks after DLI was an additional significant risk factor (hazard ratio (HR) 3.66 compared to no viral infection) for GvHD. At six months after alloSCT, viral infections were rare and not associated with GvHD. In contrast, mixed BM chimerism (HR 3.63 for ≥5% mixed chimerism compared to full donor) was an important risk factor for GvHD after DLI given at six months after alloSCT. ALC of <1000x106/l showed a trend for association with GvHD after this DLI (HR 2.05 compared to ≥1000x106/l, 95% confidence interval 0.94-4.45). Furthermore, the data suggested that the presence of a viral infection close to the DLI at three months or ≥5% mixed chimerism at time of the DLI at six months correlated with the severity of GvHD, thereby increasing their negative impact on the current GvHD-relapse-free survival.
These data demonstrate that the risk factors for GvHD after DLI depend on the setting of the DLI.

Extramedullary (EM) relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acute myeloid leukemia (AML) is rare and causes systemic relapse. Consequently, the prognosis is very poor because limited treatment is feasible in post-transplant patients. The efficacy and safety of venetoclax (VEN), a newly developed oral inhibitor of B-cell leukemia/lymphoma-2, plus azacytidine (AZA) in patients newly diagnosed with AML who are ineligible for intensive chemotherapy have been reported. We report a case in which VEN + AZA salvage treatment following radiation therapy and donor lymphocyte infusion afforded promising results in a patient with AML who showed post-allo-HSCT EM relapse.