There is a high medical need to develop new strategies for the treatment of patients with acute myeloid leukemia (AML) refractory to conventional therapy. In vitro, the combinations of the blast-modulatory response modifiers GM-CSF + Prostaglandin E1, (summarized as Kit M) have been shown to convert myeloid leukemic blasts into antigen-presenting dendritic cells of leukemic origin (DC_leu) that were able to (re-)activate the innate and adaptive immune system, direct it specifically against leukemic blasts, and induce memory cells. This study aimed to investigate the immune modulatory capacity and antileukemic efficacy of Kit M in vivo. Brown Norway rats suffering from AML were treated with Kit M (twofold application). Blasts and immune cells were monitored in peripheral blood (PB) and spleen. Upon the observation of promising immune modulatory effects in the treated animals, two patients with AML refractory to multiple lines of therapy were offered treatment with Kit M on an individualized basis. Safety, as well as immunological and clinical effects, were monitored. Samples obtained from a third patient in similar clinical conditions not receiving Kit M were used as controls for immune monitoring tests. Animal experiments: Drugs were well tolerated by the treated animals. After 9 days of treatment, DC_leu and memory-like T cells increased in the peripheral blood, whereas regulatory T cells, especially blasts, decreased in treated as compared to untreated control animals. Clinical courses: No severe side effects were observed. In patient 1482, PB blasts remained under the detection threshold during 27 days of treatment, thrombocytes were normalized, and (leukemia specific) immune effector cells of the adaptive and innate immune system increased up to 800-fold compared to the start of treatment. Patient 1601 responded with a 12% reduction in blasts in PB immediately after Kit M treatment. Several subtypes of (leukemia-specific) immune effector cells in PB increased up to four-fold during the 19 days of treatment. In contrast, immune-reactive cells decreased under mild chemotherapy in the PB of control patient 1511 with comparably refractory AML. Within the limitation of low numbers in both animal experiments and clinical applications, our data suggest that Kit M treatment of AML-diseased rats and patients is feasible and may induce leukemia-specific immune reactions and clinical improvement. A larger series and a prospective clinical trial will be required to confirm our observations. Beyond optimized doses and schedules of the applied compounds, the combination with other antileukemic strategies or the application of Kit M in less proliferative stages of the myeloid diseases need to be discussed. If effects are confirmed, the concept may add to the armamentarium of treatments for highly aggressive blood cancer.

Background/Objectives: Acute myeloid leukemia (AML) is characterized by impaired anti-leukemic immune responses, and the ex vivo or in vivo generation of dendritic cells (DCs), including leukemic dendritic cells (DC_leu), represents a promising strategy to stimulate immune cells and improve anti-leukemic activity. Methods: This study examined the generation, phenotype and functional relevance of DCs and DC_leu produced ex vivo from blast-containing PBMNCs and whole blood (WB) in AML. Using both standard DC/DC_leu-generating protocols and available Kits. Results: We show that DC/DC_leu can be reliably generated with both methods. Generated DC/DC_leu effectively activated T cells during mixed lymphocyte cultures (MLCs), resulting in enhanced anti-leukemic cytotoxicity. Improved blast lysis correlated with specific immunological features, including higher frequencies of generated DC_leu and mature DC subsets, as well as a certain cytokine pattern after DC/DC_leu cultures or MLC. In addition, the frequencies of proliferating T cells after MLC strongly correlated with the degree of achieved blast lysis, underscoring the importance of efficient DC/DC_leu-mediated T cell stimulation. Both the frequencies of generated DC/DC_leu and the resulting blast lytic activity were linked to overall survival (OS) in AML patients. Individuals who failed to demonstrate improved blast lysis exhibited significantly reduced OS, suggesting inadequate immune responsiveness of patients in vivo. Conclusions: These findings identify phenotypic and functional immune parameters as predictors of clinical outcome and highlight the prognostic relevance of ex vivo immune profiling. This approach may help to optimize and personalize future immunotherapeutic strategies in AML.

Background /Objectives: Novel (immune) therapies are needed to stabilize the disease or achieve remissions in AML. We already demonstrated that DCleus can be generated ex vivo from AML patients’ blasts in WB using approved drugs (GM-CSF and PGE-1 (Kit-M) or GM-CSF and Picibanil (OK-432), Kit-I). The generated DCleus induce antileukemia-directed immune cells of the adaptive and innate immune system, enabling leukemia-specific immune activation after MLC. Methods: We compared the effects of Kit-I vs. Kit-M by quantifying (1) their potential to produce DCs/DCleus from WB samples from 6 healthy individuals and 28 AML patients’ WB in different stages of the disease and (2) the activation of adaptive and innate leukemia-specific IFNγ-producing or degranulating antileukemic cells after MLC with and without Kit-I/Kit-M-pretreated WB. Furthermore, we correlated the obtained results with the achieved improved cells’ antileukemic functionality and patients’ clinical data. Results: In AML samples we found significantly higher frequencies of (mature) DCleus generable without induction of blast proliferation in Kit-M as well as (although less pronounced) in Kit-I-treated vs. untreated samples, a significant increase in the frequency of (leukemia- specific) immunoreactive cells, and improved blast cytotoxicity after MLC with Kit-M and with Kit-I-treated vs. untreated samples (potentially with higher induction of CD4 and CIK IFNγ + cells in Kit-I-pretreated samples). These data might suggest that both Kits work via different pathways. Conclusions: We show that Kit-M and Kit-I produce DCs/DCleus and subsequently enhance (potentially via a different mode of action) antileukemic immune cell activation after MLC. Our findings point to a possibility to enhance antileukemic treatment in vivo by combining agents or identifying criteria for selecting an appropriate agent (combination) for the respective patient in the course of a personalized treatment strategy.