Autologous Acute Myeloid Leukemia Blasts Research Articles

Immune dysfunction signatures predict outcomes and define checkpoint blockade-unresponsive microenvironments in acute myeloid leukemia.

BackgroundImmune exhaustion and senescence are dominant dysfunctional states of effector T cells and major hurdles for the success of cancer immunotherapy. In the current study, we characterized how acute myeloid leukemia (AML) promotes the generation of senescent-like CD8+ T cells and whether they have prognostic relevance.METHODSWe analyzed NanoString, bulk RNA-Seq and single-cell RNA-Seq data from independent clinical cohorts comprising 1,896 patients treated with chemotherapy and/or immune checkpoint blockade (ICB).ResultsWe show that senescent-like bone marrow CD8+ T cells were impaired in killing autologous AML blasts and that their proportion negatively correlated with overall survival (OS). We defined what we believe to be new immune effector dysfunction (IED) signatures using 2 gene expression profiling platforms and reported that IED scores correlated with adverse-risk molecular lesions, stemness, and poor outcomes; these scores were a more powerful predictor of OS than 2017-ELN risk or leukemia stem cell (LSC17) scores. IED expression signatures also identified an ICB-unresponsive tumor microenvironment and predicted significantly shorter OS.ConclusionThe IED scores provided improved AML-risk stratification and could facilitate the delivery of personalized immunotherapies to patients who are most likely to benefit.TRIAL REGISTRATIONClinicalTrials.gov; NCT02845297.FUNDINGJohn and Lucille van Geest Foundation, Nottingham Trent University's Health & Wellbeing Strategic Research Theme, NIH/NCI P01CA225618, Genentech-imCORE ML40354, Qatar National Research Fund (NPRP8-2297-3-494).

Ex vivo isolation, expansion and bioengineering of CCR7+CD95-/or CD62L+CD45RA+ tumor infiltrating lymphocytes from acute myeloid leukemia patients' bone marrow.

T cell based immunotherapies can be applicable to acute myeloid leukemia (AML). Therefore, the selection of optimal T cells, cell manufacturing, and therapeutic T cell engineering are essential for the development of effective adoptive T cell therapies for AML. Autologous tumor-infiltrating lymphocytes (TILs) have been in clinical trials to treat solid malignancies. Herein, we assessed whether TILs can be isolated from the bone marrow (BM) of AML patients, expanded ex vivo and utilized as a novel therapeutic strategy for AML. To this end, firstly we analyzed the immunophenotypes of a series of primary BM samples from AML patients (N = 10) by flow cytometry. We observed a variable amount of CD3+ TILs (range ∼2.3–∼32.6% of mononuclear cells) among BM samples. We then developed a novel protocol that produced a three-log ex vivo expansion of TILs isolated from AML patient BM (N = 10) and peripheral blood (PB) (N = 10), including from patients with a low number of CD3+ T cells, within 3, 4 weeks. Further, we identified previously described naïve T cells (CCR7+CD95-/or CD62L+CD45RA+) in AML BM and PB samples, which seemed to be required for a successful TILs ex vivo expansion. Finally, we showed that the expanded TILs could: (1) cause cytotoxicity to autologous AML blasts ex vivo (90.6% in control without T cell treatment vs. 1.89% in experimental groups with PB derived T cells and 1.77% in experimental groups with BM derived TILs, p < 0.01), (2) be genetically engineered to express CYP27B1 gene, and (3) infiltrate the BM and reside in close proximity to pre-injected autologous AML blasts of engrafted immunodeficiency mice. Altogether, these results provide a rationale for further studies of the therapeutic use of TILs in AML.

IL-15/IL-15Rα/CD80-expressing AML cell vaccines eradicate minimal residual disease in leukemic mice

AbstractEngineered autologous acute myeloid leukemia (AML) cells present multiple leukemia-associated and patient-specific antigens and as such hold promise as immunotherapeutic vaccines. However, prior vaccines have not reliably induced effective antileukemic immunity, in part because AML blasts have immune inhibitory effects and lack expression of the critical costimulatory molecule CD80. To enhance induction of leukemia-specific cytolytic activity, 32Dp210 murine AML cells were engineered to express either CD80 alone, or the immunostimulatory cytokine interleukin-15 (IL-15) with its receptor α (IL-15Rα), or heterodimeric IL-15/IL-15Rα together with CD80 and tested as irradiated cell vaccines. IL-15 is a γc-chain cytokine, with unique properties suited to stimulating antitumor immunity, including stimulation of both natural killer and CD8+ memory T cells. Coexpression of IL-15 and IL-15Rα markedly increases IL-15 stability and secretion. Non-tumor-bearing mice vaccinated with irradiated 32Dp210-IL-15/IL-15Rα/CD80 and challenged with 32Dp210 leukemia had greater survival than did mice treated with 32Dp210-CD80 or 32Dp210-IL-15/IL-15Rα vaccines, whereas no unvaccinated mice inoculated with leukemia survived. In mice with established leukemia, treatment with 32Dp210-IL-15/IL-15Rα/CD80 vaccination stimulated unprecedented antileukemic immunity enabling 80% survival, an effect that was abrogated by anti-CD8 antibody-mediated depletion in vivo. Because, clinically, AML vaccines are administered as postremission therapy, we established a novel model in which mice with high leukemic burdens were treated with cytotoxic therapy to induce remission (<5% marrow blasts). Postremission vaccination with 32Dp210-IL-15/IL-15Rα/CD80 achieved 50% overall survival in these mice, whereas all unvaccinated mice achieving remission subsequently relapsed. These studies demonstrate that combined expression of IL-15/IL-15Rα and CD80 by syngeneic AML vaccines stimulates effective and long-lasting antileukemic immunity.

An antibody derived from a cured AML patient to identify a unique epitope on CD43 (CD43s) as a novel target for acute myeloid leukemia and myelodysplastic syndrome.

7009 Background: Immunotherapy for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) is hampered by the lack of tumor-specific targets. Methods: We took advantage of the tumor-immunotherapeutic effect of allogeneic hematopoietic stem cell transplantation (HSCT) and searched the B cell repertoire of a patient with a lasting and potent graft versus AML response for AML-specific antibodies. Results: We identified a donor-derived B cell clone that produced an IgG1 antibody, AT1413, that specifically interacted with AML cell lines, with the patient’s autologous AML blasts, but not with lymphocytes or with cells from liver, colon, skin and other tissues. AT1413 recognized a unique, not previously described, sialylated epitope on CD43 (CD43s). CD43s is overexpressed on all types of AML and MDS, as illustrated by its reactivity with freshly isolated blasts of each of more than 60 randomly selected AML and MDS patients in our clinic, representing all WHO 2008 AML and MDS classes. AT1413 induced antibody-dependent cell-mediated cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC) of target cells in vitro. To investigate the effect of AT1413 in vivowe first generated mice populated with human effector cells (NK cells, CTL and myeloid cells) by injecting human hematopoietic stem cells into new born immunodeficient mice. After establishment of a human immune system in these mice we inoculated luciferase labeled AML cells via tail vein injection. Following engraftment of the tumor we dosed the mice biweekly with AT1413 or a control antibody. We observed strongly reduced numbers of AML cells in AT1413- but not in control antibody treated mice. Importantly, AT1413 treatment was tolerated well and did not affect numbers of non-malignant human myeloid cell in these mice. Conclusions: We have obtained an antibody from a cured AML patient which recognizes a unique sialylated epitope on CD43 (CD43s) that is selectively over-expressed on all WHO 2008 types of AML and MDS. This antibody was able to eliminate AML cells in vivo and therefore has high therapeutic potential.

Identification of Naturally Presented HLA Ligands of Enriched Leukemic Progenitor Cells for Peptide-Based Immunotherapy in Acute Myeloid Leukemia (AML)

Several studies demonstrated that peptide-based cancer immunotherapy can induce specific immune responses and affect clinical outcome in a variety of different cancer entities. We recently conducted a study, which directly characterized the antigenic landscape of acute myeloid leukemia (AML) by mass spectrometric analysis of naturally presented HLA ligands and identified a panel of AML-specific CD4+ as well as CD8+ T-cell epitopes as suitable targets for T-cell based immunotherapy (Berlin et al. Leukemia 2015). One main reason for the high relapse rates in AML patients after standard polychemotherapy and allogeneic stem cell transplantation is the presence of minimal residual disease (MRD), which is associated with the persistence of leukemic stem cells (LSCs) in the bone marrow of patients. For clinically effective immunotherapy it is therefore indispensable to target the highly chemotherapy resistant LSCs.Here we present a mass spectrometry-based study, which for the first time analyzes the naturally presented HLA ligandome of stem cell enriched (LSCenr) fractions of primary AML samples to identify novel LSC-associated antigens using the approach of direct peptide isolation and identification. The enrichment of LSCs was performed using fluorescence-activated cell sorting of the originally described phenotype of lineage-negative CD34+CD38- cells of PBMCs from eight AML patients. The original stem cell containing population of 1-3% within the PBMCs of most patients was enriched to >90% purity with cell counts of 20-200x106 for the LSCenr fraction per sample. Consistent with our own previous results, all samples showed comparable expression levels of HLA class I molecules on primary leukemia blasts as well as for the LSCenr fractions, with HLA class I molecule counts ranging from 145,000 to 175,000 molecules/cell for the LSCenr fractions.To specifically identify leukemia-associated antigens on LSCenr cells, the HLA ligandome results obtained from the sorted LSCenrfractions were combined with data acquired from AML blasts of 20 AML patients (HLA class I n=19, HLA class II n=20) in previous studies as well as our normal tissue database that comprises 153 HLA class I and 82 HLA class II ligandomes of various healthy tissues (e.g. blood, bone marrow, spleen, kidney, liver, brain, skin, ovary, bowl).We identified more than 14,600 different naturally presented HLA class I ligands representing ~6,500 source proteins on LSCenr fractions of primary AML samples (n=8) and their autologous blast cells by mass spectrometry. Overlap analysis of the HLA class I ligandomes of LSCenr fractions and autologous AML blasts with the benign peptidome revealed 45.4% (3,132/6,896) and 40.2% (4,922/12,244) of the LSCenr fraction and the autologous AML blast ligandomes to be represented in the benign-associated HLA ligandome, respectively. 79.1% (5,458/6,896) of the mapped LSCenr fraction ligandome was also presented on autologous AML blasts. 1,029 (14.9%) of these identified HLA class I ligands were presented exclusively on LSCenr fractions and not found on autologous AML blasts, previously analyzed AML blasts or any benign tissue.Furthermore, we were able to identify more than 8,000 different naturally presented HLA class II ligands representing ~1,700 source proteins. Overlap of the HLA class II ligandomes revealed 45.0% (2,800/4,624) and 39.9% (2,706/6,790) of the LSCenr fraction and autologous AML blast ligandomes to be represented in the benign-associated HLA ligands, respectively. The HLA ligandomes of the LSCenr fraction and the autologous AML blasts showed an overlap of 69.7% (3,224/4,624). 941 (11.5%) HLA class II ligands showed exclusive representation in the LSCenr fraction ligandomes and were never identified on AML blast or benign tissue.These LSC-associated peptides represent highly interesting targets for immunotherapeutic approaches in AML patients and will be further evaluated for their potential to elicit a specific T-cell response.Taken together these preliminary results prove the feasibility of our approach to enrich leukemic progenitor cells of primary AML samples for the successful isolation and identification of HLA presented peptides associated with enriched leukemic progenitor cells. DisclosuresSchuster:Immatics Biotechnologies GmbH: Employment. Kowalewski:Immatics Biotechnologies GmbH: Employment.

Generating Peripheral Blood Derived Lymphocytes Reacting Against Autologous Primary AML Blasts.

Expanding on our prior studies with cord blood T cells, we hypothesized that primary acute myeloid leukemia (AML)-reactive autologous T cells could be generated ex vivo under immunomodulatory conditions. We purified AML and T cells from 8 newly diagnosed high-risk patients. After 2 weeks expansion, T cells were stimulated with interferon-γ-treated autologous AML weekly × 3, interleukin-15, and agonistic anti-CD28 antibody. Cytotoxic T cells and ELISpot assays tested functionality; reverse transcriptase quantitative polymerase chain reaction tested AML and T-cell gene expression profiles. On the basis of combined positive ELIspot and cytotoxic T cells assays, T cells reactive against AML were generated in 5 of 8 patients. Treg proportion declined after cocultures in reactive T-cell samples. AML-reactive T cells displayed an activated gene expression profile. "Resistant" AML blasts displayed genes associated with immunosuppressive myeloid-derived suppressor cells. We discuss our approach to creating primary AML-reactive autologous T cell and limitations that require further work. Our study provides a platform for future research targeting on generating autologous leukemia-reactive T cells.

Microrna 29b Mediates Immune Evasion of Natural Killer Cells in Acute Myeloid Leukemia

Natural killer (NK) cells are innate effector cells that can spontaneously recognize and kill cancer cells. While important in inducing long-term disease free survival (DFS) in the setting of killer immunoglobulin-like receptor (KIR) mismatch for acute myeloid leukemia (AML), harnessing NK cells to kill autologous or self AML blasts to extend DFS has had no success. In this study, we uncover one potential mechanism by which AML blasts can evade NK cell cytotoxicity. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that has now been shown to be expressed in immature human NK cells. Furthermore, activation of AHR in these immature cells suppresses human NK cell maturation and function. We and others have shown that human AML blasts secrete ligands that can activate AHR, leading us to hypothesize that AML may evade autologous NK cell cytotoxicity in part by inhibiting NK cell maturation. Expression of microRNA (miR)-29b has previously been shown to suppress the expression of transcription factors Tbx21 (TBET) and Eomesodermin (EOMES), both of which are critical for terminal NK cell differentiation and function. Here we show that AHR is able to directly regulate the expression of miR-29b and thus may serve as the link between AML and immune evasion of NK cells. We first identified putative AHR binding sites within the proximalpromoter of miR-29b, suggesting that AHR may directly regulate miR-29b expression. To test this, we transfected the AHR responsive HepG2 human cell line with a miR-29b promoter driven luciferase reporter and measured luciferase activity after treatment with the known AHR agonist, FICZ, compared to vehicle control. We discovered that cells treated with 6-formylindolol[3,2-b]carbazole (FICZ) had increased luciferase activity compared to cells treated with vehicle control (P<0.05). This effect was subsequently shown to be directly mediated by AHR, as mutation of the putative AHR binding site as well as siRNA targeting of AHR mRNA both significantly diminished the induced luciferase activity (P<0.01). We then established the importance of miR-29b in human NK cell development by transducing immature NK cells, characterized as Lin(-)CD117(+)CD94(-), with a miR-29b knockdown virus and testing for the ability of these cells to become mature [i.e., Lin(-)CD117(-)CD94(+)] NK cells, after two weeks in IL-15 and FICZ. Indeed, in early experiments, knockdown of miR-29b resulted in increased percentages of mature NK cells compared to cells transduced with control virus (16.8% compared to 3.6%, respectively), despite being cultured with an AHR agonist. Finally, utilizing a translational in vivo murine AML model developed by our laboratory that recapitulates human AML, we have found that AML blasts harvested from these leukemic mice release an AHR agonist (P < 0.01), similar to previous reports that have described AHR ligands being produced by human AML blasts. In addition,NK cells isolated from these mice have increased levels of miR-29b when leukemic, compared to NK cells from wild type control littermates, consistent with our hypothesis that AHR regulates miR-29b expression. Thus, we propose that AHR, when activated by AML-derived ligands, upregulates miR-29b in NK cells to ultimately suppress the primary regulators of NK cell maturation and function, resulting in immune evasion (See Figure). [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Development of a Bispecific Antibody-Releasing Stem Cell System for the Eradication of Acute Myeloid Leukemia Blasts Via Redirected Immune Effector Cells

Despite many years of research and great advances in the field, acute myeloid leukemia (AML) still remains one of the most challenging battle fields in the context of hematologic malignancies treatment. Although AML patients initially respond to conventional chemotherapy, a complete remission is rarely achieved and 5-year survival rates remain low especially in elderly patients. Hence, there is a pressing need for novel effective strategies for AML treatment to prevent relapse and treat minimal residual disease (MRD).The use of recombinant bispecific antibodies (bsAbs) for retargeting effector T lymphocytes towards cancer cells is recently emerging as a promising immunotherapeutic approach for tumor treatment. This class of small molecules is designed to bind simultaneously to a pre-defined tumor-associated antigen (TAA) on tumor cells and the activating CD3 complex on T cells. The cross-linkage of immune effector cell and tumor cell leads to a tumor-specific T cell activation and efficient target cell killing independently of the T cell receptor specificity.However, due to their low molecular mass, bsAbs have a short life span in vivo and consequently have to be continuously administrated to patients over prolonged time spans of several weeks to achieve clinical responses. As an alternative to continuous exogenous infusions of short-lived Abs we examined the use of engineered bone marrow-derived human mesenchymal stem cells (hMSCs) as cellular vehicles for the constant production and secretion of a fully humanized anti-CD33-anti-CD3 bsAb that targets the surface molecule CD33, which is widely overexpressed on AML blasts. Our studies demonstrate that gene-modified hMSCs are effective in releasing the bsAb at sufficient amounts to activate and redirect both human primary CD4+ and CD8+T cells from healthy donors against AML cells expressing varying levels of the CD33 antigen, leading to an efficient T cell-mediated tumor cell killing at low effector to target cell ratios and Ab concentrations. Most importantly, we could demonstrate that patient-derived T cells were able to suppress autologous AML blasts upon Ab-mediated cross-linkage over prolonged period of time without being affected by the presence of the modified hMSCs. Additional improvement of this system was achieved by the artificial expression of T cell co-stimulatory 4-1BB ligand (CD137L) on the hMSCs surface. The additional co-stimulatory signal provided by the engineered hMSCs resulted in an enhanced T cell proliferation, a higher pro-inflammatory cytokine release, and consequently in a more pronounced specific tumor cell killing already at earlier time-points.Taken together, our data could demonstrate that continuous in situ delivery of the anti-CD33-anti-CD3 bsAb by genetically modified hMSCs facilitates efficient activation of T cells for specific and efficient killing of AML blasts over prolonged period of time.Furthermore, as promising perspective of this approach for future in vivo application we are currently investigating on the development of biocompatible synthetic scaffolds as transplantable biomaterial-based production platforms for genetically engineered hMSCs as locally confined vehicle of immunotherapeutics. The implantation of these small engineered devices would ensure that the delivery of the anti-cancer agents can be controlled and stopped after tumor clearance by removing the scaffold at a desired time point. In this way, administration of ex vivo gene-modified hMSCs embedded in appropriate scaffolds would result in a continuous in situ production of recombinant Abs for effective and persistent levels of these therapeutic agents over time with low risk of side effects. DisclosuresCartellieri:Cellex Patient Treatment GmbH, Dresden, Germany: Employment. Ehninger:GEMoaB Monoclonals GmbH, Dresden, Germany: Employment, Patents & Royalties. Ehninger:GEMoaB Monoclonals GmbH, Dresden, Germany: Consultancy, Patents & Royalties. Bachmann:GEMoaB Monoclonals GmbH, Dresden, Germany: Consultancy, Patents & Royalties.

Immunomodulatory Effect of SGI-110, a Novel Hypomethylating Agent in Acute Myeloid Leukemia (AML)

Introduction: We have developed a promising leukemia vaccine in which patient derived AML cells are fused with autologous dendritic cells (DCs) effectively presenting a broad array of antigens that capture the heterogeneity of the leukemia cell population. A major challenge of developing effective immunotherapy is overcoming the immunosuppressive milieu that characterizes patients with AML. AML cells evade immune targeting, in part, through the limited presentation of antigen by primitive leukemia progenitors. In contrast, induction of differentiation through upregulation of reactive oxygen species may enhance antigen presentation and the capacity to target AML cell by a tumor vaccine. Hypomethylating agents have been shown to be effective therapeutic agents for patients with AML and MDS, in part due to immunomodulatory effects. In the current study, we have examined the immunomodulatory properties of the novel DNA hypomethylating agent SGI-110, a dinucleotide of decitabine (DAC) and deoxyguanosine, which is resistant to in-vivo inactivation by cytidine deaminase. We have explored the in-vitro effect of treatment with SGI-110 on ROS, AML immunogenicity and efficacy of the AML/DC fusion vaccine.Methods and results: AML blasts were isolated by ficoll density centrifugation of bone marrow mononuclear cells (BMMCs) from patients with AML at presentation. AML blasts were cultured for 4 days in the presence or absence of 1 uM SGI-110, added twice daily on days 1 and 2 of culture. ROS as detected by levels of H2O2 expression demonstrated a 40% increase after treatment with SG1-110 (n=2). We subsequently evaluated whether the increase in ROS levels correlated with enhanced targeting by immune effector cells. SGI-110 or control treated AML cells were assessed for their susceptibility to T cell mediated targeting, using a standardized flourochrome CTL assay. Remarkably, a 72% increase in autologous cytotoxic T lymphocyte-mediated lysis as measured by Granzyme B activity, was demonstrated following SGI-110 treatment of AML blasts (n=3). The expression of co-stimulatory molecules CD80 and CD86, were unchanged following treatment with SGI-110 (n=3). In contrast, exposure to SGI-110 resulted in increased expression of the antigen processing TAP proteins by immunocytochemical analysis.We have previously demonstrated that DC/AML fusion cells potently stimulate the expansion of leukemia specific T cells. The effect of SGI-110 on T cell response to DC/AML fusion vaccine stimulation in vitro was assessed. Autologous Dendritic cells (DCs) were generated by culture of adherent peripheral mononuclear cells obtained from AML patients following remission in the presence of GM-CSF, IL-4 and TNF-α. DCs were fused with AML blasts by co-culture at a 1:1 ratio in the presence of polyethylene glycol (PEG). DC/AML fusions were cultured at a 1:10 ratio with autologous T cells for 5-6 days in the presence and absence of 1uM of SGI-110. Exposure of fusion stimulated autologous T cells to SGI-110 resulted in an increase in T cell expression of IFN-γ, with mean fold increase of 2.2 and 2.3 for CD4 and CD8 T cells respectively (n=4). The percentage of CD4+CD25+FOXP3+ regulatory T cells (TRegs) and T cell expression of PD1 was not significantly changed in the presence of SGI-110. The effect of SGI-110 on CTL mediated killing by vaccine stimulated T cells was assessed. Following stimulation with the DC/AML fusion vaccine, T cells mediated killing of autologous AML blasts increased to 11% from 4% following co-culture with unstimulated T cells. Interestingly, exposure of the AML cells to SGI-110 led to a further increase in T cells mediated killing with mean levels of 20% tumor lysis (n=2).Conclusions: The results demonstrate that treatment with SGI-110 results in increased ROS levels and an associated enhanced susceptibility of AML blasts to immune mediated targeting. The addition of SGI-110 to T cell stimulation by an autologous DC/AML fusion vaccine results in an increase in interferon gamma and increased susceptibility of AML cells to T cell mediated killing. The immunomodulatory properties of SGI-110, combined with its favorable pharmacologic and pharmacokinetic features, identify SGI-110 as a useful agent to implement novel combined epigenetic–immunotherapeutic strategies in AML. A clinical trial evaluating SGI-110 in combination with DC/AML fusion cell vaccination is planned. DisclosuresTaverna:Astex Pharmaceuticals, Inc.: Employment. Avigan:Astex Pharmaceuticals: Research Funding.

Immune Surveillance By Autoreactive Helper But Not Cytolytic T Cells Is a Common Phenomenon In Patients With Acute Myeloid Leukemia

The presence of immune surveillance as a mechanism to prevent the development of malignancies and/or to eradicate small numbers of developing tumor cells has been described by many researchers in the past. The development of an overt malignancy may therefore be seen as failure of immune surveillance. In previous studies we demonstrated the existence of autoreactive CD4 T cells showing HLA-restricted reactivity against myeloid cells as a common phenomenon in healthy individuals. These autoreactive T cells show a profound cytokine response, but do not exert significant cytotoxic effects. To investigate whether such autoreactive T cell responses could play a role in immune surveillance against myeloid malignancies, we investigated the functional reactivity and cell lineage specificity of autologous T cell responses mounted against mature acute myeloid leukemia (AML) blasts. T cells were isolated using the pan T isolation kit and magnetic bead separation (MACS) from peripheral blood of patients with AML in remission after induction chemotherapy and labeled with the fluorescent dye PKH26. These T cells were stimulated with autologous AML blasts at a 1/2 responder to stimulator ratio and cultured for 14 days in medium containing heat-inactivated human serum and 1 ng/mL IL7 and 0.01 ng/mL IL-15 (Miltenyi). At day 14, proliferating CD4 and CD8 T cells comprising 7.3% +/- 2.5% and 0.8 +/- 0.5% of the total T cell populations, respectively, were isolated single cell/well using flowcytometric cell sorting based on PKH dilution. T cell clones were expanded and tested against a panel of autologous and HLA-matched or HLA-mismatched allogeneic target cells, comprising AML blasts, EBV-LCL, monocytes, monocyte-derived dendritic cells (DCs), B cells and primary skin fibroblasts. The isolated CD4 clones produced interferon-gamma (IFNg) and/or interleukin 4 (IL-4) in response to stimulation with autologous AML blasts. This cytokine production could be blocked using pan-HLA-class-II and allele-specific blocking antibodies. HLA-DR, -DP, as well as –DQ restricted clones were found and these clones displayed an oligoclonal T cell receptor V-beta (TCR-VB) usage. Interestingly, these clones exerted also reactivity against autologous EBV-LCL, monocytes, DCs, HLA-class II expressing (IFNg pretreated) fibroblasts and to a lesser extend against autologous B cells, as well as to the same target cell populations (including AML blasts) obtained from allogeneic third party individuals that were matched for the HLA-molecules presenting the T cell epitopes. These results indicate recognition of common antigens, not restricted to the malignant cell populations. No reactivity was observed against HLA-mismatched target cells. In addition, a limited number of CD8 clones was isolated that showed a similar HLA-restricted cytokine production profile. Similar experiments were performed in serumfree X-vivo15 medium to exclude recognition of serum components. In contrast to the profound cytokine response, none of the isolated clones exerted substantial cytotoxicity against one of the targets. Some CD8 clones exerted a maximum of 17% lysis at a 10/1 effector to target ratio against AML blasts. Since no direct cytotoxicity by the autoreactive T cells could be demonstrated, we investigated whether crosstalk between the autoreactive T cells and the AML blasts may render the AML cells more sensitive to subsequent immune attack. The expression of costimulatory markers (CD40, CD80 and CD86) and adhesion (ICAM-1 /CD54) on the AML blasts was significantly increased after co-incubation with the autoreactive T cells. Similar AML responsive autoreactive T cell clones were obtained using T cells from HLA-matched healthy donors as responder cells, illustrating that these autoreactive T cells are part of the normal T cell repertoire and were not induced by the high dose chemotherapy that the patients had been subjected to. In conclusion, we here demonstrate that the presence of autoreactive helper T cells is a common phenomenon in patients with AML. We hypothesize that the large burden of myeloid cells at presentation of AML may result in the amplification of an autoreactive AML directed CD4 T cell response. This response does not result in a direct effective anti-AML immune surveillance, but the immune-modulatory effect on the AML phenotype upon crosstalk may pave the way for other immunological interventions. Disclosures:No relevant conflicts of interest to declare.

T cells expressing CD123-specific chimeric antigen receptors exhibit specific cytolytic effector functions and antitumor effects against human acute myeloid leukemia

AbstractInduction treatments for acute myeloid leukemia (AML) have remained largely unchanged for nearly 50 years, and AML remains a disease of poor prognosis. Allogeneic hematopoietic cell transplantation can achieve cures in select patients and highlights the susceptibility of AML to donor-derived immunotherapy. The interleukin-3 receptor α chain (CD123) has been identified as a potential immunotherapeutic target because it is overexpressed in AML compared with normal hematopoietic stem cells. Therefore, we developed 2 chimeric antigen receptors (CARs) containing a CD123-specific single-chain variable fragment, in combination with a CD28 costimulatory domain and CD3-ζ signaling domain, targeting different epitopes on CD123. CD123-CAR–redirected T cells mediated potent effector activity against CD123+ cell lines as well as primary AML patient samples. CD123 CAR T cells did not eliminate granulocyte/macrophage and erythroid colony formation in vitro. Additionally, T cells obtained from patients with active AML can be modified to express CD123 CARs and are able to lyse autologous AML blasts in vitro. Finally, CD123 CAR T cells exhibited antileukemic activity in vivo against a xenogeneic model of disseminated AML. These results suggest that CD123 CAR T cells are a promising immunotherapy for the treatment of high-risk AML.Key Points

Defective Natural Killer (NK) Receptor Expression and Effector Function in Acute Myeloid Leukemia Partially Normalize At Remission and Predict Response to Chemotherapy.

AbstractAbstract 2591▪▪This icon denotes a clinically relevant abstractDespite favorable initial responses to induction chemotherapy, most patients with acute myeloid leukemia (AML) will relapse. We hypothesized that just as cancers evade immunosurveillance by suppressing the immune response (“immunoediting”), remission and relapse in AML may be determined by similar immune interactions. After stem cell transplantation natural killer (NK) cells exert powerful allogeneic graft vs. leukemia effects. To explore immunosurveillance by autologous NK cells and immunoediting by AML blasts, we prospectively analyzed NK surface phenotype and function in AML patients at presentation and following remission induction. Using multi-color flow cytometry, we analyzed the surface expression of natural cytotoxicity receptors (NCRs), killer immunoglobulin receptors (KIRs) and C-type lectins directly ex-vivo in 32 consecutive patients at presentation and following complete remission (CR) in 12 patients for whom remission samples were available. Results were compared with 15 healthy controls. NK effector function in AML was measured against K562 leukemia targets and autologous AML blasts by CD107a degranulation and interferon-gamma (IFNγ) and TNF-alpha (TNFα) production.NK cells from 32 patients with AML at diagnosis had an abnormal phenotype compared to controls, with downregulation of the activatory receptor NKp46 (MFI 187± 15 vs. 266± 24, p=0.007) and upregulation of the inhibitory receptor NKG2A (mean 45%± 4.2 vs. 32%± 2.7, p=0.046). Moreover, AML-NK cells were defective in their effector function with significantly reduced CD107a degranulation (5% vs. 11%, p=0.0002), TNFα (1% vs. 3%, p=0.008) and IFNγ production (1% vs. 5%, p=<0.0001). In the 12 patients who achieved remission following induction chemotherapy NKp46 expression normalized from an MFI 122 at presentation to 242 (p=0.01); however, NKG2A expression continued to increase (45% vs. 61%, p=0.008). At remission AML-NK cells displayed CD107a degranulation levels comparable to that of healthy donor NK cells (9% vs. 11%, p=0.4). In contrast, TNFα and IFNγ production only partially normalized (2% vs. 3%, p=0.3) and (3% vs. 5%, p=0.04), respectively.AML patients with NKG2A overexpression (> median of 32.6%) at diagnosis were significantly less likely to achieve CR post chemotherapy compared to those with lower NKG2A expression (78% vs. 32% p= 0.041). Furthermore, patients who failed to respond to induction chemotherapy had significantly reduced NK effector function at diagnosis compared to normal controls (mean TNFα production 1% cf. 5% p=0.019).We then sought for evidence of immunoediting by AML on NK cell phenotype and function. Co-incubation of healthy donor NK cells with primary AML blasts for 24 hours resulted in significant reduction in TNFα production (p=0.02), IFNγ production (p=0.01) and a trend to reduced CD107a degranulation (p=0.07) against K562 leukemia targets. Our results indicate that AML blasts can produce long-lasting changes in NK cell subsets and impair their effector function and favouring immune escape from NK cell control. This work justifies larger prospective analyses to relate NK-based prognostic factors to classical predictive factors for remission and relapse, and should guide the development of NK cell based immunotherapy to improve outcome in AML. Disclosures:No relevant conflicts of interest to declare.

Human Vγ9Vδ2 T Cells Specifically Recognize and Kill Acute Myeloid Leukemic Blasts

Vγ9Vδ2 T cells are attractive candidates for antileukemic activity. The analysis of Vγ9Vδ2 T cells in newly diagnosed acute myeloid leukemia (AML) patients revealed that their absolute cell numbers were normal in the blood as well as in the bone marrow but showed a striking imbalance in the differentiation subsets, with preponderance of the effector memory population. This unusual phenotype was restored after removal of leukemic cells in patients, which reached complete remission after chemotherapy, suggesting that leukemic cells might be involved in the alteration of γδ T cell development in AML. Accordingly, coculture between AML cells and Vγ9Vδ2 T cells induced selection of effector cells. In accordance with their effector memory status, in vitro proliferation of Vγ9Vδ2 T cells was reduced compared with normal controls. Nevertheless, Vγ9Vδ2 T cells efficiently killed autologous AML blasts via the perforin/granzyme pathway. The ligands for DNAM-1 were expressed by AML cells. We showed that killing of AML blasts was TCR and DNAM-1 dependent. Using a xenotransplantation murine model, we showed that Vγ9Vδ2 T cells homed to the bone marrow in close proximity of engrafted leukemic cells and enhanced survival. These data demonstrate that Vγ9Vδ2 T cells are endowed with the ability to interact with and eradicate AML blasts both in vitro and in a mouse model. Collectively, our data revealed that Vγ9Vδ2 T cells have a potent antileukemic activity provided that optimal activation is achieved, such as with synthetic TCR agonists. This study enhances the interest of these cells for therapeutic purposes such as AML treatment.

Impaired Natural Killer Cells Immune Synapse Formation in Acute Myeloid Leukemia.

Abstract 2663Poster Board II-639Natural killer (NK) cells are an important component of the innate immune surveillance of tumor cells. Defective NK cell function has been correlated with poor prognosis in acute myeloid leukemia (AML). It is well established that NK cell-mediated cytolytic activity is significantly diminished in AML patients; the mechanisms of this hypo-function are not well understood. Identifying mechanisms of tumor-induced immune suppression of lymphocytes function will aid the development of effective immunotherapeutic strategies. In the present study we examined the molecular basis for impaired NK cell responses in AML and demonstrate impaired NK cell immunological synapse formation. Confocal microscopy was used to visualize F-actin polymerization at the immune synapse between CD56+ CD3- NK cells and autologous AML blasts. We identified a significant reduction in formation of the NK cell immune synapse (NKIS) (p<0.001) from AML patients compared healthy donors (> 70% reduction). This defect was induced by direct tumor contact since NK cell defects were induced in healthy NK cells when they were co-cultured (in direct contact) for 48 hr with allogeneic AML blasts, but not with healthy allogeneic monocytes (P < 0.01). In control transwell co-culture experiments, where the NK cells and AML blast were not in direct contact, we did not observe the induced defect. We examined the molecular nature of the AML blast induced defect by quantifying recruitment of a number of these NK cell adhesion and cytoskeletal signaling proteins to the immune synapse. Following primary co-culture with AML blasts, healthy NK cells showed significantly reduced recruitment of integrin LFA-1, CD2, Lck, WASP, and tyrosine-phosphorylated protein to the NK-AML target interactions synapse (P < 0.001). These studies demonstrate a role for the tumor induced immune suppression of NK cells and will aid in the development of immunotherapeutic approaches targeting AML. Disclosures:No relevant conflicts of interest to declare.

A Dendritic Cell Based Vaccination Strategy Geared towards Eradication of Leukemic Stem Cells.

Abstract 2046Poster Board II-23 Introduction:In the majority of cases, initial remission of acute myeloid leukemia (AML) is reached but unfortunately relapse rates remain high and therefore novel treatments are needed. It is thought that recurrent AML originates from chemotherapy resistant quiescent leukemic stem cells (LSC). The application of immunotherapeutic approaches to eradicate LSC remaining after first line chemotherapy may contribute to improved disease outcome. Vaccination strategies have often used dendritic cells (DC) ex vivo pulsed with tumor-derived whole lysates or peptides as modalities to present a broad range of tumor antigens to T cells to stimulate effective anti-tumor T-cell immunity in vivo. It is likely that certain proteins expressed by LSC have a distinct antigenicity as compared to more mature AML blasts and thus provide targets for specific T-cells. Even without identification of specific antigens, LSC can be a useful source of tumor antigens in DC vaccination-based immunotherapy. CD34+CD38- LSC can be identified using malignant stem cell associated cell surface markers including CLL-1 and lineage markers such as CD7, CD19 and CD56. However, the low frequency of these cells precludes the use of LSC derived apoptotic cells or lysates for DC loading. Alternatively, mRNA isolated from LSC can be amplified and subsequently transfected into DC. Materials and Methods:We have made use of the CD38- AML derived cell line MUTZ-3 which contains a subpopulation of CD34+CLL1+ cells which resembles the phenotype of a putative LSC. CLL1+CD34+ and CLL1-CD34- cells were isolated by FACS sorting and total RNA was isolated. mRNA was converted to cDNA and amplified by PCR using the SMART system. Subsequently, mRNA was in vitro transcribed from the amplified cDNA. Mature monocyte derived DC (MoDC) were generated from healthy donor blood and transfected with amplified CLL1+CD34+ derived mRNA and used to stimulate autologous CD8β+ T-cells. After three weekly re-stimulations with CLL1+CD34+ mRNA transfected DC, specificity of the T-cells was analyzed by intracellular IFNγ staining upon 5 hour stimulation with autologous immature MoDC transfected with GFP mRNA, mRNA amplified from unsorted, CLL1+CD34+ or CLL1-CD34- MUTZ-3 subpopulations. Results:Amplification of CLL1 and survivin (also expressed by MUTZ-3) transcripts was confirmed by RT-PCR. After 3 weekly re-stimulations with CLL1+CD34+ amplified RNA transfected DC, 0.04% (range 0.01-0.12%) of the T-cells were positive for IFNγ upon a 5 hr re-stimulation with GFP transfected DC. 0.44% (range 0.04-0.69%) of the T-cells responded to DC transfected with unsorted MUTZ-3 amplified mRNA (p<0.00005 versus GFP control, 2-sided student's T-test), 0.51% (range 0.24-1.35%) responded to DC transfected with CLL1+CD34+ amplified mRNA (p<0.005 versus GFP control) and 0.46% (range 0.24-0.94%) responded to DC transfected with CLL1-CD34- amplified mRNA (p<0.0001 versus GFP control). Conclusion:We show that MoDC transfected with RNA amplified from one MUTZ-3 sub-population resembling the phenotype of LCS cells are capable of inducing T-cells which recognize both cells transfected with mRNA from the LSC resembling MUTZ-3 subset as well as the CLL1-CD34- subset. We are currently testing the efficacy and feasibility of this approach in an autologous setting in vitro. CD8β+ T-cells are stimulated with autologous MoDC from AML patients transfected with amplified mRNA isolated from their own LSC enriched populations. The capacity of these T-cells to kill autologous AML blasts and LSC is subsequently analysed in a 6-colour FACS based cytotoxicity assay. Disclosures:No relevant conflicts of interest to declare.

Preclinical characterization of 1-7F9, a novel human anti–KIR receptor therapeutic antibody that augments natural killer–mediated killing of tumor cells

AbstractInhibitory-cell killer immunoglobulin-like receptors (KIR) negatively regulate natural killer (NK) cell–mediated killing of HLA class I–expressing tumors. Lack of KIR-HLA class I interactions has been associated with potent NK-mediated antitumor efficacy and increased survival in acute myeloid leukemia (AML) patients upon haploidentical stem cell transplantation from KIR-mismatched donors. To exploit this pathway pharmacologically, we generated a fully human monoclonal antibody, 1-7F9, which cross-reacts with KIR2DL1, -2, and -3 receptors, and prevents their inhibitory signaling. The 1-7F9 monoclonal antibody augmented NK cell–mediated lysis of HLA-C–expressing tumor cells, including autologous AML blasts, but did not induce killing of normal peripheral blood mononuclear cells, suggesting a therapeutic window for preferential enhancement of NK-cell cytotoxicity against malignant target cells. Administration of 1-7F9 to KIR2DL3-transgenic mice resulted in dose-dependent rejection of HLA-Cw3–positive target cells. In an immunodeficient mouse model in which inoculation of human NK cells alone was unable to protect against lethal, autologous AML, preadministration of 1-7F9 resulted in long-term survival. These data show that 1-7F9 confers specific, stable blockade of KIR, boosting NK-mediated killing of HLA-matched AML blasts in vitro and in vivo, providing a preclinical basis for initiating phase 1 clinical trials with this candidate therapeutic antibody.

Generation of T-cell lines to autologous acute myeloid leukemia cells by competitive limiting dilution culture of acute myeloid leukemia mononuclear cells

To develop a novel method of generating multiple autologous acute myeloid leukemia (AML) reactive T-cell lines as a step toward adoptive immunotherapy for AML. AML peripheral blood mononuclear cells (MNC), including >90% AML blasts and 1% to 3% T cells, were seeded in limiting dilution culture in which AML blasts were induced to undergo dendritic cell (DC) differentiation. T cells were primed and activated with the addition of a cytokine combination. Highly reactive anti-AML T-cell lines (both CD4(+) and CD8(+)) were generated, selected, and expanded. The estimated average frequency of AML-reactive T cells or precursors was 6 +/- 3/1,000,000 AML peripheral blood mononuclear cells (n = 11). Robust intracellular interferon-gamma (IFN-gamma) release from T-cell lines was demonstrated by flow cytometry after stimulation by autologous AML cells, but not an autologous B-lymphoblastoid cell line (LCL). These T-cell lines caused specific lysis of autologous AML cells, but not autologous LCL or allogeneic AML cells, and they depleted autologous AML colony-forming cells (CFC), but not normal CFC. Most CD4(+) T-cell lines exerted strong proapoptotic effects on AML cells. AML cell apoptosis by CD4(+) T-cell lines correlated with IFN-gamma secretion. This study demonstrates a methodology for generating large numbers of AML-reactive cytotoxic T cell lines (either class I or II restricted) that may be useful clinically in adoptive immunotherapy. This study also provides estimates of AML-reactive T-cell frequency in patients with AML.

Phase III Trial of Immunotherapy with Recombinant Interleukin-2 (rIL-2) Versus Observation in Patients < 60 Years with Acute Myeloid Leukemia (AML) in First Remission (CR1): Preliminary Results from Cancer and Leukemia Group B (CALGB) 19808.

The CALGB evaluated the use of rIL-2 for immunotherapy of minimal residual disease in a phase III trial in patients with AML in first CR after completing all planned chemotherapy. The rationale supporting the use of rIL-2 in this setting includes its ability to effect antigen-independent cytotoxicity against AML blasts, its non-cross resistance with cytotoxic agents, and its ability to expand cytotoxic T and natural killer (NK) cells. Pts < 60 years with untreated non-M3 AML were eligible. 734 patients were enrolled. The first 302 patients were randomized between 2 induction regimens: Ara-C, Daunorubicin, and Etoposide (ADE) or ADEP with the P-glycoprotein modulator PSC-833 (Kolitz et al, ASH 2005). The remaining 432 patients received ADE induction. Post-remission therapy was based on cytogenetic risk factors: patients with Core Binding Factor (CBF) AML received 3 courses of High-Dose Ara-C (HiDAC), while all others were assigned to receive a 2 step autologous transplant (ASCT) regimen (Linker et al, Biol Blood Marrow Transpl 2000). Randomization between rIL-2 and observation was to occur no later than 120 days after day 1 of the last HiDAC cycle or day 0 of ASCT, as soon as the neutrophil count > 750/μl, platelets > 50,000/μl with bone marrow showing a leukemia-free state and trilineage maturation and recovery from non-hematological toxicity to < grade 2. The 90 day immunotherapy regimen consisted of low-dose rIL-2 sequences for expanding cytotoxic effector cells and brief, higher dose bolus treatments aimed at activating them. rIL-2 was given SC at 1 x 106 IU/m2 on days 1–14, 19–28, 33–42, 47–56, 61–70 and 75–90, and 12–15 x 106 IU/m2 on days 15–17, 29–31, 43–45, 57–59 and 71–73. CR was achieved in 77% of evaluable patients. After HiDAC consolidation or ASCT, patient refusal, early relapse, and delayed blood count recovery accounted for nearly all failures to undergo randomization to IL-2 or observation. The distribution of patients with CBF and non-CBF AML was comparable between the randomized arms. The median follow-up time from the post-remission randomization date for the surviving patients is 29 months. By intention-to-treat, for the 214 randomized patients, the 3-year disease-free survival rate is 45% (95% CI: 35%, 56%) on the observation arm and 56% (47%, 67%) on the rIL-2 arm (p=0.11; logrank test); the 3-year overall survival rate is 61% (52%, 72%) for patients randomized to observation and 68% (58%, 79%) for the rIL-2 arm (p=.0.09). Twenty-nine of the 107 patients randomized to rIL-2 therapy either refused to receive rIL-2 or were unable to start because of unresolved toxicities; another 28 patients started treatment but failed to complete their 90-day course. Grade 4 toxicities were neutropenia (17%), thrombocytopenia (11%), febrile neutropenia (FN, 1%), increased bilirubin (1%) and hypocalcemia (1%). Grade 3 toxicities, observed in 10%–14% of patients, were hypotension, fatigue, dehydration and FN. We conclude that post-consolidation immunotherapy with 90 days of rIL-2 is tolerable but not well accepted by patients and/or physicians. Further follow-up and additional analyses are planned, correlating outcomes with clinical subsets, amount of rIL-2 therapy received, as well as measurements of ex vivo cytotoxicity mediated by patients' effector cells against cryopreserved autologous AML blasts.

Depletion of Regulatory T Cells Dramatically Improves DC-Based Immunization Against Acute Myeloid Leukemia.

Dendritic cell (DC)-based vaccination is a promising approach to enhance anti-tumor immunity that could be considered for patients with high risk acute myeloid leukemia (AML). We have already shown in human that DC pulsed with eluted peptides (EP) from autologous AML blasts (DC/EP) are able to induce CD4+ and CD8+ anti-leukemic immune response in vitro (Delluc S, Haematologica, 2005). In order to optimize this vaccination strategy for AML patients we developed a pre-clinical murine model. C57/Bl6 mice were vaccinated by DC pulsed or not with peptides eluted from the syngenic C1498 myelomonocytic leukemic cell line in a prophylactic setting. Injection of DC/EP induced an anti-leukemic response as shown by the cytotoxic activity of CD4 T cells, whereas the injection of unpulsed DC induced a NK cell-mediated cytotoxicity against C1498 cells. In vivo depletion of CD4 T cells or NK cells abrogated the protective effect induced by DC/EP (p=0.02) or DC (p=0.06) vaccination, respectively, confirming their critical role in preventing leukemic outgrowth. However, late C1498 re-challenge showed that the anti-leukemic immune response was insufficient to protect DC/EP vaccinated mice from death, suggesting an ineffective or absent long-lived memory response. Since several populations of T cells have regulatory properties potentially inhibiting anti-tumor responses, we hypothesized that CD25+ cell-depletion in vivo could enhance the protection induced by vaccination. Indeed, we observed a dramatic improvement of the survival of mice treated by an anti-CD25 antibody before vaccination compared to mice vaccinated by DC/EP alone (p<0.01). More interestingly, CD25 depletion allowed the generation of long-lived immune responses since mice were protected from a late re-challenge by C1498 cells. Our results strongly suggest that depletion of regulatory CD25 T cells before DC-based vaccination should be considered for immunotherapy of weakly immunogenic tumors such as AML.

Identification and Characterization of T Cell Epitopes Deduced from RGS5, a Novel Broadly Expressed Tumor Antigen.

Identification of tumor-associated antigens (TAA) has resulted in the development of therapeutic vaccines for the treatment of cancer. We applied an integrated functional genomics approach to identify TAA in malignant tissues of patients with renal cell carcinoma (RCC). A comparative DNA chip analysis of tumor and the corresponding non-malignant tissue from patients with RCC followed by sequencing of peptides bound to the HLA-class I molecules by mass spectrometry was applied to identify novel TAA in RCC. To confirm the immunogenicity of identified epitopes cytotoxic T lymphocytes (CTL) were generated using dendritic cells (DC). Utilizing this approach, two peptides derived from RGS5 binding to either HLA-A*02 or 03 were identified. The key function of regulators of G protein-signalling (RGS) is to bind to G protein α subunits and to stimulate their intrinsic GTPase activity. The hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) thereby is accelerated and the inactive heterotrimer more rapidly restored. Thus, RGS proteins inhibit the biological activity of G proteins. Interestingly, it was recently shown that RGS5 is overexpressed in pericytes of newly developing tumor vessels, indicating that RGS5 plays an important role during tumor angiogenesis.Using RT-PCR analysis we found that RGS5 is expressed on a broad variety of tumor cells including RCC, colorectal, breast and ovarian cancer, malignant melanoma and multiple myeloma as well as in acute and chronic leukemias making this protein an interesting candidate for the development of vaccination strategies to target the tumor cells and the tumor vessels. CTL that were induced using the RGS5 peptides lysed autologous DC pulsed with the cognate peptide or transfected with in vitro transcribed RGS5 RNA as well as HLA-matched tumor cell lines. The specificity and HLA restriction was confirmed using blocking monoclonal antibodies and in cold-target inhibition assays. We next utilized DC transfected with RGS5 RNA to generate specific CTL. Using this approach we confirmed the processing and presentation of the identified peptides by malignant cells. These CTL lysed tumor cells in an antigen specific manner while sparing non-malignant cells. To analyze the induction of RGS5 specific CTL in an autologous setting in patients with malignant diseases, we used blood samples from a patient with acute myeloid leukemia (AML) in complete remission after chemotherapy and were able to generate specific CTL capable of recognizing autologous AML blasts while sparing non-malignant cells.Our results demonstrate that RGS5 is a novel tumor rejection antigen expressed in a wide range of malignancies that can be applied to target malignant cells and tumor angiogenesis.