ALBERT

Description: Background Immune checkpoint (IC) inhibitors (ICI) is a promising group of agents with potential effect in myelodysplastic syndrome (MDS). However, there is not enough data on the pattern of IC expression in MDS bone marrow, though this can guide future therapies with ICI. Methods We prospectively included 57 patients with high risk MDS during 2019-2020 years after signing informed consent for participation in research. We used 7 eight-colored panels in each patient to define IC expression on T- and NK-cells (CD3, CD8, CD4, CD56, CD16), myeloid precursors (CD117, CD34), T-regulators (CD25, CD4), myeloid-derived suppressor cells (CD15, CD11b, CD14, HLA-DR, CD33). In each population we assessed expression of CD279, CD152, CD223, TIM3, CD273, CD274, CD275, CD80. Results In lymphoid populations we observed an extremely high percentage of PD-1 positive lymphocytes (10.5 ± 8.0% of all nucleated cells), including PD-1 positive CD4 lymphocytes (6.3 ± 3.7%) and CD8 lymphocytes (4.7 ± 3.5%). Interestingly, on average 63 ± 34% of all lymphocytes were PD-1 positive (Figure 1A), which indicates an extreme degree of T-cell exhaustion and significant exploitation of the PD-1 system by a malignant tumor. Among the PD-1 ligands PD-1L predominated, however it was present only on a small percentage of myeloid precursors (2.2 ± 0.39% of nucleated cells), but most of the PD-1L ligand expression was observed on granulocytes in the process of their differentiation from myeloid precursors (5.8 ± 4.1% of nucleated cells), and in some patients the proportion of such granulocytes reached more than 20%. Moreover, on the cells of the monocytic series, PD-1L is practically not expressed, but CD80 is expressed, a ligand for CTLA4 (1.6 ± 0.7% of nucleated cells). Interestingly, despite the presence of expression of CD80 on monocytic and dendritic cells, the receptor for this ligand on T-lymphocytes was practically absent. The proportion of such cells was only 0.02 ± 0.01%, i.e. the expression of CD80 facilitates the activation of lymphocytes through interaction with CD28 rather than the suppression of the immune response through CD152. Thus, it can be suggested that CTLA4 does not have a clinically significant role in MDS. At the same time, a certain number of TIM3 positive lymphocytes were observed, the proportion of which was 0.42 ± 0.16%, and the percentage of lymphocytes carrying this receptor was 3.6 ± 1.2% (Figure 1A). However, significantly greater TIM3 expression was detected on NK cells. The proportion of such cells was 1.3 ± 0.6% of all nucleated cells, while 30% of all NK cells carried the TIM3 receptor (Figure 1A). Only 0.1% of cells from early myeloid progenitors that expressed TIM3 receptor were detected during flow cytometry, while the proportion of TIM3 positive myeloid cells increased during maturation just in the same way as the PD-1L. Expression of Gal9 was negligible, as it is a protein secreted into the intercellular space. Only a small percentage is associated with cell membranes. The analysis of the correlation matrix showed synchronous changes in the number of most bone marrow T-cell populations. A negative correlation of the level of myeloid tumor precursors actively expressing IC ligands and activated T cells, expressing CD223, NK cells, NKT was observed. The total number of myeloid tumor precursors positively correlated with the number of PD-1 positive lymphocytes (Figure 1B). Conclusion It was found that IC system plays a role in high-risk MDS. Moreover, the expression of ligands is mainly realized during maturation of blast cells into granulocytes, which are the main population expressing these inhibitory molecules. The leading role in the suppression of the T-cell response in MDS is played by the PD-1-PD-1L system, the CTLA4 system plays a minor role in our study cohort. The second most important system is GAL9-TIM3, effecting predominantly NK cells, while T cell are less affected. Thus, the data obtained justify the trials of dual blockade with anti-PD-1 and anti-TIM3 agents in high-risk MDS. Figure 1 Disclosures No relevant conflicts of interest to declare.

Description: Introduction: In spite of the widespread use of second- and third-generation tyrosine kinase inhibitors (TKIs) the prognosis of patients with advanced phase CML (accelerated phase (AP) or blast crisis (BC)) is still dismal. The aim of this study was to compare outcomes in advanced phase CML cohorts based on whether or not these patients received allogeneic hemopoietic stem cell transplantation (allo-HSCT). Patients and methods: A total of 162 patients with AP/BC-CML with (allo-HSCT+TKIs, n=20/62,) or without (n=10/70, TKI) history of allo-HSCT were included in this retrospective study. All patients received allo-HSCT with a reduced-intensity conditioning regimen with fludarabine 180 mg/m2 and busulfan 8-12 mg/kg or melphalan 140 mg/m2. Forty-two patients received TKIs for post-transplant relapse prophylaxis. In the majority of cases dasatinib was used (n=36). In the remaining 80 patients alloHSCT was not performed due to refusal for personal reasons or delay in referral to transplant center. They were included in TKI-group and were treated with chemotherapy+TKIs (60) or TKIs only (20). Eighty-one percent received second or third line TKIs. There were no significant differences in age, sex, comorbidity status, disease phase, and additional chromosomal aberrations incidence between allo-HSCT+TKI and TKI groups (Table 1). Overall survival (OS) was defined as the time from the start of treatment (allo-HSCT/TKI, chemotherapy) to death, event-free survival (EFS) - as the time between commencement of treatment and loss of response or post-transplant relapse, death. Response was defined according to European Leukemia Net and National Comprehensive Cancer Network recommendations. All patients signed an informed consent for processing of personal data; the trial was approved by Pavlov University local ethical committee. Results: The median follow-up was 44 months (1-344). The engraftment was documented in 71 (86%) patients. The cumulative incidence of non-relapse mortality at day 100 and 1 year after allo-HSCT were 10% and 18%, respectively. Grade 2-4 acute graft versus host disease (GVHD) was documented in 21 (29%), grade 3-4 acute GVHD - 14 (20%), chronic GVHD - 18 (27%) including mild, moderate and severe form in 6 (9%), 8 (12%) and 4 (6%) patients, respectively. Two-year cumulative incidence of relapse was 39%. Twenty-four patients received donor lymphocyte infusions and TKIs after relapse, in 4 cases chemotherapy was added. In four cases only TKIs were administered to treat relapse. Nine patients achieved sustained complete molecular response (CMR), in 19 cases disease progression was documented. The data on response was available for 71 patients in TKI group. Among patients with BC 36 (59%) patients did not respond to therapy, while complete hematological response (CHR), complete cytogenetic response (CCR) and CMR were achieved in 22 (34%), 1 (2%) and 2 (3%) cases, respectively. Nine patients (90%) without BC history achieved response to therapy (CHR 5, CCR 2, CMR 2), while 1 patient failed to respond. Sixty-nine patients died; all deaths were CML-related. Four-year OS was 58% in allo-HSCT+TKIs versus 33% in TKI group (p=0.032) (Figure 1A). However, there was no significant difference in 4-year EFS between groups: 35% vs. 17% (p=0.5), accordingly. BC at the moment of allo-HSCT significantly worsened 4-year OS: 23% vs. 63% (p=0.007). The 4-year OS in patients transplanted in BC (n=10) was comparable to one in TKI group: 23% vs. 33% (p=0.3) (figure 1B). Conclusions: Allo-HSCT still has an advantage as potentially curative treatment for part of advanced phase CML patients even in the presence of new generation TKIs. Allo-HSCT in BC is associated with worse outcome. An earlier referral of these patients to the transplant center can improve the outcome of allo-HSCT and prognosis.. Disclosures No relevant conflicts of interest to declare.