Although several (chemotherapeutic) protocols to treat acute myeloid leukemia (AML) are available, high rates of relapses in successfully treated patients occur. Strategies to stabilize remissions are greatly needed. The combination of the (clinically approved) immune-modulatory compounds Granulocyte-Macrophage-Colony-Stimulating-Factor (GM-CSF) and Prostaglandine E1 (PGE-1) (Kit-M) converts myeloid blasts into dendritic cells of leukemic origin (DC_leu). After stimulation with DC_leu ex vivo, leukemia-specific antileukemic immune cells are activated. Therefore, Kit-M treatment may be an attractive immunotherapeutic tool to treat patients with myeloid leukemia. Kit-M-mediated antileukemic effects on whole bone marrow (WBM) were evaluated and compared to whole blood (WB) to evaluate the potential effects of Kit-M on both compartments. WB and WBM samples from 17 AML patients at first diagnosis, in persisting disease and at relapse after allogeneic stem cell transplantation (SCT) were treated in parallel with Kit-M to generate DC/DC_leu. Untreated samples served as controls. After a mixed lymphocyte culture enriched with patients’ T cells (MLC), the leukemia-specific antileukemic effects were assessed through the degranulation- (CD107a⁺ T cells), the intracellular IFNγ production- and the cytotoxicity fluorolysis assay. Quantification of cell subtypes was performed via flow cytometry. In both WB and WBM significantly higher frequencies of (mature) DC_leu were generated without induction of blast proliferation in Kit-M-treated samples compared to control. After MLC with Kit-M-treated vs. not pretreated WB or WBM, frequencies of (leukemia-specific) immunoreactive cells (e.g., non-naive, effector-, memory-, CD3⁺β7⁺ T cells, NK- cells) were (significantly) increased, whereas leukemia-specific regulatory T cells (T_reg, CD152⁺ T cells) were (significantly) decreased. The cytotoxicity fluorolysis assay showed a significantly improved blast lysis in Kit-M-treated WB and WBM compared to control. A parallel comparison of WB and WBM samples revealed no significant differences in frequencies of DC_leu, (leukemia-specific) immunoreactive cells and achieved antileukemic processes. Kit-M was shown to have comparable effects on WB and WBM samples regarding the generation of DC_leu and activation of (antileukemic) immune cells after MLC. This was true for samples before or after SCT. In summary, a potential Kit-M in vivo treatment could lead to antileukemic effects in WB as well as WBM in vivo and to stabilization of the disease or remission in patients before or after SCT. A clinical trial is currently being planned.

Background: Allogeneic hematopoietic stem cell transplantation (allo-HCT) is a potentially curative treatment for high-risk acute myeloid leukemia and myelodysplastic neoplasms (AML/MDS). However, AML/MDS relapse post-transplant is driven by immune escape mechanisms, limiting treatment options and contributing to poor prognosis. Granulocyte–Macrophage Colony-Stimulating Factor (GM-CSF) and Prostaglandin-E1 (PGE-1) (termed “Kit M”) induce dendritic cells of leukemic origin (DC_leu) that have been shown to induce antileukemic immune responses. Methods: Using flow cytometry, we analyzed ICM/ICML-expressing uncultured T-cells/blasts in whole blood (WB) samples from patients with AML/MDS relapse post-allo-HCT who had received salvage treatment. Using Kit M, DC_leu were generated ex vivo. T-cell-enriched mixed-lymphocyte cultures (MLC) were performed for functional assessment of DC/DC_leu to stimulate (leukemia specifically) patients’ immune cells. After MLC, ICM/ICML-expressing cells and immune activation were assessed. The experimental results were correlated with patients’ clinical responses to salvage treatment. Results: WB samples from 15 patients were analyzed. On average, high frequencies of ICM (CTLA4/PD1)-co-expressing blasts and high frequencies of ICM (CTLA4/PD1/TIGIT/TIM3/2B4)-co-expressing T-cells were found in uncultured WB, compared to the frequencies of healthy ICM-expressing T-cells. Treatment with Kit M induced DC/DC_leu, which, after MLC, downregulated ICM-expressing T-cells and enhanced activated and memory T-cells. High frequencies of ICM-co-expressing uncultured T-cells/blasts correlated negatively with the blast lysis capacity and patients’ clinical response to relapse treatment. However, post-MLC, Kit-mediated modulation of ICM-expressing T cells did not correlate with blast lysis, nor with patients’ clinical response to treatment. Conclusions: We conclude that Kit M contributes to overcoming impaired antileukemic reactions, independent of the presence of ICM-expressing T-cells in relapsed AML patients after allo-HCT ex vivo.