1. Results Background Study outlineKey findings Printed by Dynamics of cytotoxic T cell subsets during immunotherapy with HDC/IL-2 prognosticates outcome in acute myeloid leukemia Frida Ewald Sander 1, Anna Rydström 1, Elin Bernson 1, Roberta Kiffin 1, Rebecca Riise 1, Johan Aurelius 1, Harald Anderson 2, Mats Brune 1, Robin Foà 3, Kristoffer Hellstrand 1, Fredrik B. Thorén 1 and Anna Martner 1* 1 TIMM Laboratory, Sahlgrenska Cancer Center, University of Gothenburg, Sweden, 2 Department of Cancer Epidemiology, University of Lund, Sweden, 3 Department of Cellular Biotechnology, Sapienza University of Rome, Italy Immunotherapy with histamine dihydrochloride and low-dose interleukin-2 (HDC/IL-2) is approved within the EU for relapse prevention in the post- consolidation phase of acute myeloid leukemia (AML) (Brune et al., Blood 108:88, 2006). We performed a phase IV trial (Re:MISSION) to assess the immunomodulatory properties of this regimen and to correlate potential biomarkers with clinical outcome. Altered distribution of CD8 + in non-relapsing patients during immunotherapy with HDC/IL-2. Blood was drawn from AML patients in complete remission immediately before the onset of immunotherapy (C1D1) and at the end of the first HDC/IL-2 treatment cycle (C1D21). The frequency of naïve (T N ; CD45RA + CCR7 + ), central memory (T CM ; CD45RO + CCR7 + ), effector memory (T EM ; CD45RO + CCR7 - ) and effector (T eff ; CD45RA + CCR7 - ) cells within the CD8 + T cell compartment in blood was determined using the outlined gating strategy. In non-relapsing (n=18), but not in relapsing (n=26), patients the frequency of CD8 + T EM cells was significantly reduced while the frequency of T eff cells was increased. Statistical analyses were performed using Student’s paired t-test. 1. In non-relapsing patients, we observed a reduction of cytotoxic T cells with effector memory (T EM ) phenotype with a concomitant increase of effector cells (T eff ) during the first cycle of mmunotherapy with HDC/IL-2. 2. The T EM to T eff transition heralded maintained CR and survival and remained significantly predictive also in multivariable analysis. 3. T cell transition was a strong predictor of outcome in older patients (>60 years old) with high relapse risk. Eighty-four patients (age 18-79) with AML in complete remission received HDC (0.5 mg sc bid) and human recombinant IL-2 (1MIU sc bid) in repeated three-week cycles (n=10) for 18 months. Patients were followed for leukemia-free survival (LFS) and overall survival (OS) for at least 2 years after the initiation of immunotherapy. Mononuclear cells, recovered from blood samples before and after the first 3-week cycle of immunotherapy, were analyzed for CD8 + T cell phenotypes. The dynamics of cytotoxic T cell subsets during immunotherapy were correlated to clinical outcome in terms of LFS and OS. Altered distribution of CD8 + T cell subsets during immunotherapy impacts on clinical outcome. A reduction of the frequency of CD8 + T effector memory cells (T EM ; CD8 + 45RO + CCR7 - phenotype) during the first cycle of HDC/IL-2 prognosticated LFS and OS. Similarly, induction of T effector cells (T eff ; CD8 + 45RO - CCR7 - ) during cycle 1 impacted favorably on outcome. The altered distribution of cytotoxic T cells during treatment with HDC/IL-2 was a stong predictor of outcome within the group of older patients (>60 years old). P-values were obtained by the logrank test. T EM to T eff cell transition during immunotherapy heralds favorable clinical outcome. Patients showing a concomitant reduction of T EM cells and induction of T eff cells ("T EM to T eff transition”, as indicated in the red square below) in blood during the first cycle of immunotherapy showed favorable outcome in terms of LFS and OS. The altered distribution of cytotoxic T cells during treatment with HDC/IL-2 significantly prognosticated LFS and OS within the group of older patients (>60 years old). P-values were obtained by the logrank test. The reported predictors of clinical outcome remained significant when taking potential confounders into account in multivariable analysis. C1D21-C1D1 % of T EM cells C1D21-C1D1 % of T eff cells Supported by The Swedish Research Council, The Swedish Cancer Society, The Swedish Society for Medical Research, Meda Pharma and Immune Pharmaceuticals