Clinical Characteristics and Outcome Analysis for HLA Loss Patients Following Partially Mismatched Related Donor Transplantation Using HLA Chimerism for Loss of Heterozygosity Analysis by Next-Generation Sequencing

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.

[Relapse with HLA loss after hematopoietic stem cell transplantation with non-HLA identical donor: Guidelines from the Francophone society of bone marrow transplantation and cellular therapy (SFGM-TC)]

Loss of heterozygosity or HLA loss is a genomic-type escape mechanism highlighted in certain types of relapses after allogeneic hematopoietic stem cell transplantation with a non-HLA identical donor, and especially after haplo-identical transplantation. The diagnosis must be made with certainty because the result conditions the therapy. In this article, the different mechanisms and techniques that can be used for the diagnosis of loss of heterozygosity, as well as the therapeutic options are reviewed, making it possible to establish clinico-biological recommendations for the diagnosis confirmation and management of the patients in relapse.

Acute myeloid leukaemia relapse after allogeneic haematopoietic stem cell transplantation: Mechanistic diversity and therapeutic directions

Emerging biological and clinical data, along with advances in new technologies, have exposed the mechanistic diversity in post-haematopoietic stem cell transplant (HCT) relapse. Post-HCT relapse mechanisms are relevant for guiding sophisticated selection of therapeutic interventions and identification of areas for further research. Clonal evolution and emergence of resistant leukemic strains is a common mechanism shared by relapse post-chemotherapy and post-HCT, other mechanisms such as leukemic immune escape and donor T cell exhaustion are unique entities to post-HCT relapse. Due to diversity in the mechanisms behind post-HCT relapse, the subsequent clinical approach relies on clinician discretion, rather than objective evidence. Lack of standardized selection based on post-HCT relapse mechanism(s) could be a contributing factor to observed poor outcomes. Therapeutic strategies including donor lymphocyte infusion (DLI), second transplant, immunotherapies, hypomethylating agents, and targeted strategies are supported options and efficacy may be enhanced when post-HCT AML relapse mechanism is established and guides treatment selection. This review aims, through compilation of supporting studies, to describe mechanisms of post-HCT relapse and their implications for subsequent treatment selection and inspiration for future research.

Relapse of acute myeloid leukemia after allogeneic stem cell transplantation: immune escape mechanisms and current implications for therapy

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by the expansion of immature myeloid cells in the bone marrow (BM) and peripheral blood (PB) resulting in failure of normal hematopoiesis and life-threating cytopenia. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is an established therapy with curative potential. Nevertheless, post-transplant relapse is common and associated with poor prognosis, representing the major cause of death after allo-HCT. The occurrence of relapse after initially successful allo-HCT indicates that the donor immune system is first able to control the leukemia, which at a later stage develops evasion strategies to escape from immune surveillance. In this review we first provide a comprehensive overview of current knowledge regarding immune escape in AML after allo-HCT, including dysregulated HLA, alterations in immune checkpoints and changes leading to an immunosuppressive tumor microenvironment. In the second part, we draw the line from bench to bedside and elucidate to what extend immune escape mechanisms of relapsed AML are yet exploited in treatment strategies. Finally, we give an outlook how new emerging technologies could help to improve the therapy for these patients, and elucidate potential new treatment options.