Current strategies in immunotherapy for acute myeloid leukemia.

The prognosis of acute myeloid leukemia, particularly when associated with adverse chromosomal or molecular aberrations, is poor due to a high relapse rate after induction chemotherapy. Postremission therapy for elimination of minimal residual disease remains a major challenge. Allogeneic hematopoietic stem cell transplantation has proven to provide a potent antileukemic effect. Novel strategies are needed for patients ineligible for this treatment. Here current immunotherapeutic concepts in acute myeloid leukemia in a nonallogeneic hematopoietic stem cell transplantation setting are reviewed. Data gathered with different monoclonal antibodies are discussed. Adoptive transfer of NK and T cells is reviewed, including evolving data on T-cell engineering. Results of systemic cytokine administration and of therapeutic vaccinations with peptides, modified leukemic cells and dendritic cells are presented. One particular focus of this review is the integration of currently running clinical trials. Recent immunotherapeutic studies have been encouraging and further interesting results are to be expected

T cells are functionally not impaired in AML: Increased PD-1 expression is only seen at time of relapse and correlates with a shift towards the memory T cell compartment.

BACKGROUND: T cell function is crucial for the success of several novel immunotherapeutic strategies for the treatment of acute myeloid leukemia (AML). However, changes in phenotype and function of T cells have been described in various hematologic malignancies, mimicking T cell exhaustion known from chronic viral infections. Detailed knowledge about phenotype and function of T cells in AML patients at different stages of the disease is indispensable for optimal development and application of immunotherapeutic strategies for this disease. METHODS: We used flow cytometry-based assays to characterize T cell phenotype and function in peripheral blood and bone marrow of AML patients at diagnosis, at relapse after intensive chemotherapy, and at relapse after allogeneic stem cell transplantation (SCT). Surface expression of CD244, PD-1, CD160, and TIM-3 was determined, and proliferation and production of IFN-γ, TNF-α, and IL-2 were measured. RESULTS: We detected similar expression of inhibitory molecules on T cells from patients at diagnosis and from age-matched healthy controls. At relapse after SCT, however, PD-1 expression was significantly increased compared to diagnosis, both on CD4(+) and CD8(+) T cells. This pattern was not associated with age and cytomegalovirus (CMV) status but with a shift towards effector memory cells in relapsed AML patients. Proliferation and cytokine production assays did not reveal functional defects in T cells of AML patients, neither at diagnosis nor at relapse. CONCLUSION: We thus conclude that T cell exhaustion does not play a major role in AML. Immunotherapeutic strategies targeting autologous T cells thus have particularly good prospects in the setting of AML. &nbsp

Next-generation dendritic cell vaccination in postremission therapy of AML: Results of a clinical phase I trial.

Postremission therapy for acute myeloid leukemia (AML) is critical for elimination of minimal residual disease (MRD). In patients not eligible for allogeneic stem cell transplantation, alternative treatment options are needed. Therapeutic vaccination with autologous dendritic cells (DCs) loaded with leukemia-associated antigens (LAAs) is a promising treatment strategy to induce anti-leukemic immune responses and to eradicate chemorefractory cells. We have developed a GMP-compliant 3-day protocol including a TLR7/8 agonist to differentiate monocytes of intensively pretreated AML patients into next-generation DCs. A phase I/II proof-of-concept study has been initiated using next-generation DCs as postremission therapy of AML patients with a non-favorable genetic risk profile in CR after intensive induction therapy (NCT01734304). DCs are loaded with in vitro transcribed RNA encoding the LAAs WT1 and PRAME as well as CMVpp65 as adjuvant and surrogate antigen. Patients are vaccinated intradermally with 5x106 DCs of each antigen species up to 10 times within 26 weeks. The primary endpoint of the phase I/II trial is feasibility and safety of the vaccination. Secondary endpoints are immunological responses and disease control. Based on the safety and toxicity profile of the phase I trial (n=6), phase II has been initiated. In total, 10 patients have been enrolled into the study. DCs of sufficient number and quality were generated from leukapheresis in 8/9 cases. DCs exhibited an immune-stimulatory profile based on high surface expression of positive costimulatory molecules, the capacity to secrete IL-12p70, the migration towards a chemokine gradient and processing and presentation of antigen. 5 patients have completed the vaccination schedule; the 6th and 7th patient have received 7/10 and 4/10 vaccinations, respectively. We observed delayed-type hypersensitivity (DTH) responses at the vaccination site in 6/6 patients, accompanied by slight erythema and indurations at the injection site, but no grade III/IV toxicities. TCR repertoire analysis by next-generation sequencing revealed an enrichment of particular clonotypes at DTH sites. Limited by HLA restriction, we have so far analyzed 4 patients by multimer staining. All of them mounted DC vaccination-specific T cell responses: We detected an increase of WT1-specific T cells in one patient and strong expansion/induction of CMVpp65-specific T cells in one CMV-seropositive and two CMV-seronegative patients. In an individual treatment attempt, an enrolled patient with impending relapse was treated with a combination of DC vaccination and 5-azacytidine, resulting in MRD conversion. Long-term disease control and immunological responses are studied in the ongoing phase II trial. We conclude that vaccination with next-generation LAA-expressing DCs in AML is feasible, safe and induces anti-leukemia-specific immune responses in vivo