Leukemia-associated Antigens Research Articles

Therapeutic vaccination against leukaemia via the sustained release of co-encapsulated anti-PD-1 and a leukaemia-associated antigen.

Therapeutic leukaemia vaccines have shown modest potency. Here, we show that the co-encapsulation of a leukaemia-associated epitope peptide highly expressed in leukaemia patients and of the immune checkpoint inhibitor anti-programmed-cell-death-protein-1 (anti-PD-1) in degradable poly(lactic acid) microcapsules resulted in the sustained release of the peptide and of the antibody, which led to the recruitment of activated antigen-presenting cells to the injection site, their uptake of the peptide and the transportation of the anti-PD-1 antibody to lymph nodes, enhancing the expansion of epitope-specific T cells and the activation of cytotoxic T cells. After single subcutaneous injections of vaccine formulations with different epitope peptides, mice bearing leukaemia xenografts derived from humanized cell lines or from primary cells from patients showed better therapeutic outcomes than mice receiving repeated injections of free antigen, antibody and a commercial adjuvant. The sustained release of a tumour-associated peptide and of anti-PD-1 may represent a generalizable strategy for boosting antitumour immune responses to leukaemia.

Utility of immunohistochemistry on bone marrow trephine biopsy for the diagnosis and classification of acute leukemia

Abstract Background: Bone marrow examination is an essential diagnostic tool in acute leukemia for the determination of lineage of blasts by flow cytometry or immunophenotyping. In cases of dry tap or where facilities of flow cytometry is not available, immunohistochemistry (IHC) on trephine biopsy sections can be used as a supportive tool to diagnose and classify acute leukemia. Materials and Methods: The giemsa-stained peripheral smears and bone marrow aspirate/imprints smears were retrospectively evaluated. IHC was done on trephine biopsy sections using a panel of antibodies which included CD34, MPO, CD117, Tdt, CD3, CD20, PAX5, and CD10 Results: Of the 29 cases diagnosed by IHC on trephine sections, 25 cases could be accurately classified based on the expression of myeloid and lymphoid markers. Majority of the acute lymphoblastic leukemia (ALL) were of B-cell lineage (81.25%), and almost half of the B-ALL were common acute lymphoblastic leukemia-associated antigen positive. Conclusion: IHC on trephine biopsy facilitates the confirmation and subtyping of leukemia in more than 85% cases. A limited panel of antibodies using CD34, MPO, TdT, CD3 CD20, PAX 5, and CD10 can be used for subtyping of leukemias in trephine biopsy sections, especially in centers with limited resources. It obviates the need for a repeat bone marrow procedure where material is not available for flow cytometry.

Abstract 874: Adoptive transfer of cytotoxic lymphocytes generated by engineered human dendritic cells for AML treatment

Abstract Introduction: Acute myeloid leukemia (AML) is a devastating blood cancer. The clinical benefit of allogeneic stem cell transplantation (alloSCT) greatly relies on the graft-versus-leukemia (GVL) effect mediated by donor T cells, but it may also cause graft-versus-host disease (GVHD). One strategy to improve GVL without promoting GVHD is to adoptive transfer of cytotoxic T cells (CTLs) against leukemia-associated antigen (LAA). Generating potent CTLs is challenging. Stimulating naïve T cells with monocyte-derived dendritic cells loaded with LAA is commonly used, but it is severely limited due to low efficacy. We have developed a novel DC methodology and established immortalized human primary blood DC lines (ihv-DCs) by transducing human peripheral blood mononuclear cells (PBMCs) with a viral protein Tax. The constitutively activated ihv-DCs expand efficiently in vitro and can potently prime naïve T cells. They can be genetically modified to deliver given tumor antigens and stimulate antigen-specific CTLs in high efficiency. Here, we generate CTLs by stimulating donor PBMCs with ihv-DCs that carry HLA-A2 restrict human telomerase reverse transcriptase (hTERT), a known LAA. We investigate, in vitro and in vivo, the CTL killing efficacy. Methods: ihv-DCs that carry HLA-A2 restrict hTERT was engineered as previously described (Wu et al., PNAS 2018). HLA-A2 restrict hTERT-specific CTLs were generated by co-culturing ihv-DCs in the presence of IL-2 with donor PBMCs. In vitro cytotoxicity was performed by culturing CTLs with target cells that labeled with cell-track dye at different E:T ratio. Cell lysis was tested by flow-cytometry-based cell apoptosis analysis. In vivo cytotoxicity was examined by adoptive transfer CTLs into xenograft AML model. Flow cytometry was used to detect the leukemia burden. Results: Although variable, THP-1 cell line and blasts from all HLA-A2+ AML patients (11/11) in our study express significant intracellular hTERT. CTLs were successfully established by co-culturing ihv-DCs carrying hTERT with PBMCs from HLA-A2+ healthy donors. We observed an increasing proportion of effector memory T cells over time. We observed significant cytotoxic activities of purified CD8 T cells to U2OS that engineered to express hTERT, THP-1 cells, and primary leukemia blasts from AML patients in vitro. The cytotoxicity is predominantly hTERT specific as the killing to the primary U2OS cell line (negative for hTERT) is minimal. In addition, the cytotoxic effect was significantly diminished upon adding blockade antibody against HLA-A2, indicating the killing is through an HLA-A2 restrict manner. To study whether the CTLs can eradicate AML in vivo, we adoptively transferred CTLs into a xenograft AML model generated by engrafting primary AML into NSG mice (n=5), 5 × 106 cells were injected every 5 days for 4 times. Mice injected with PBS were set as control. On day 20, we found significant reduction of leukemia burden in blood and bone marrow from mice treated with CTLs. Importantly, no GVHD was observed. Persistent CTLs were detected in all organs (blood, bone marrow, liver, spleen, and lungs). Conclusion: Using a novel ihv-DC delivering LAA, we established CTLs that are highly efficient in killing primary leukemia blasts derived from AML patients both in vitro and in vivo. Our study provides a proof of principle for applying the novel DC methodology to AML treatment. Citation Format: Chenchen Zhao, Bei Jia, Yixing Jiang, Hiroko Shike, David F. Claxton, W Christopher Ehmann, Todd D. Schell, Hua Cheng, Bei Liu, Hong Zheng. Adoptive transfer of cytotoxic lymphocytes generated by engineered human dendritic cells for AML treatment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 874.

Can immune therapy cure acute myeloid leukemia?

There is considerable progress in immune therapy of diverse cancers. In haematology these advances are mostly limited to lymphoid cancers. Effective therapies include monoclonal antibodies and chimeric antigen receptor (CAR)-T-cells to lymphoid lineage-antigens such as CD19, CD20 and B-cell maturation antigen (BCMA). Gemtuzumab ozogamicin (Myelotarg®) is the only FDA-approved immune-based therapy for acute myeloid leukemia (AML). Several clinical trials of antibodies to CD38 and CD123 are reported with unimpressive efficacy and safety concerns. Reasons are higher daily production rates of myeloid cells and unacceptable collateral damage to normal haematopoietic cells because of imperfect specificity for AML cells. Potential targets of anti-AML immune therapy are (1) HLA antigens; (2) minor histocompatibility antigens; (3) leukemia-associated antigens; and (4) leukemia-specific antigens. Data supporting an effective allogeneic anti-AML effect come from studies in recipients of haematopoietic cell transplants with graft-versus-host disease (GvHD) and recipients of donor lymphocyte infusions (DLI). A special problem is a relative paucity of neo-antigens in AML compared with solid cancers because of a low cumulative mutation frequency. Cell immune therapy trials are in progress including CAR-T-cells, CAR-NK-cells and allogeneic NK-cells. Approaches using synthetic biology are being developed. Presently, except for gemtuzumab ozogamicin there are no convincing data of efficacy of immune therapy in AML.

T cell optimization for graft-versus-leukemia responses.

Protection from relapse after allogeneic hematopoietic cell transplantation (HCT) is partly due to donor T cell-mediated graft-versus-leukemia (GVL) immune responses. Relapse remains common in HCT recipients, but strategies to augment GVL could significantly improve outcomes after HCT. Donor T cells with αβ T cell receptors (TCRs) mediate GVL through recognition of minor histocompatibility antigens and alloantigens in HLA-matched and -mismatched HCT, respectively. αβ T cells specific for other leukemia-associated antigens, including nonpolymorphic antigens and neoantigens, may also deliver an antileukemic effect. γδ T cells may contribute to GVL, although their biology and specificity are less well understood. Vaccination or adoptive transfer of donor-derived T cells with natural or transgenic receptors are strategies with potential to selectively enhance αβ and γδ T cell GVL effects.

Identification and generation of tumor antigen-specific T cells directed against AML

Background & Aim Acute myeloid leukemia (AML) is an aggressive hematological malignancy characterized by aberrant expression of leukemia associated antigens (LAA) that can be presented in context of HLA molecules, to elicit anti-tumor T cell response and improve clinical outcomes. This study aimed to 1) identify targets of endogenous LAA-specific T cells in AML patients post allogeneic hematopoietic stem cell transplant (allo-HSCT) and whose detection was associated with favorable clinical outcomes and 2) assess the feasibility of generating LAA-specific T cells targeting these antigens for adoptive immunotherapy. Methods, Results & Conclusion We obtained blood from patients (n=8) with relapsed and/or refractory AML who were in remission post allo-HCST, and measured the frequency of T cells reactive against known LAAs (e.g. WT1, CCNA1, survivin, PRAME). These patients were followed for 1 year post-sampling. Of the tested antigens, we identified that the best predictor of those who would eventually relapse was the magnitude CCNA1-directed T cell activity (clinical remission vs relapse: 171 vs 7.13 mean spot forming colonies/1 × 10e5; p=0.03). We next hypothesized that outcomes for AML could be improved by the ex vivo preparation and adoptive transfer of stem cell donor-derived CCNA1-specific T cells to patients at risk of relapse post allo-HSCT. Thus, we exposed autologous peripheral blood mononuclear cells from healthy donors (n=14) with CCNA1 pepmix and were able to induce specific responses in 13 of 14 donors tested. The cultures expressed both central (30±3%) and memory markers (30±6%) and were polyclonal though the dominant CCNA1-directed response was CD8-mediated. Reactive cells were polyfunctional (dual IFNg+/TNFa+ secretion), and capable of lysing HLA-matched CCNA1+ myeloid leukemia cell lines and primary AML blasts, while CCNA1 negative and/or HLA mismatched targets were spared (mean±SEM %lysis =42.6±10 vs 4.3±1.7; p=0.03) Thus, by measuring endogenous immune activity and correlating this data with clinical outcomes we identify clinically relevant target antigens that may be suitable for future T cell therapy studies in AML. As a proof of principle, this study demonstrated the importance of CCNA1-targeted T cells and established the preclinical feasibility of expanding Th1-polarized reactive cells from healthy donors that are suitable for adoptive transfer. Our future studies involve identification of other novel targets in AML including neoantigens and clinical translation of these findings.

Discovery and Differential Processing of HLA Class II-Restricted Minor Histocompatibility Antigen LB-PIP4K2A-1S and Its Allelic Variant by Asparagine Endopeptidase.

Minor histocompatibility antigens are the main targets of donor-derived T-cells after allogeneic stem cell transplantation. Identification of these antigens and understanding their biology are a key requisite for more insight into how graft vs. leukemia effect and graft vs. host disease could be separated. We here identified four new HLA class II-restricted minor histocompatibility antigens using whole genome association scanning. For one of the new antigens, i.e., LB-PIP4K2A-1S, we measured strong T-cell recognition of the donor variant PIP4K2A-1N when pulsed as exogenous peptide, while the endogenously expressed variant in donor EBV-B cells was not recognized. We showed that lack of T-cell recognition was caused by intracellular cleavage by a protease named asparagine endopeptidase (AEP). Furthermore, microarray gene expression analysis showed that PIP4K2A and AEP are both ubiquitously expressed in a wide variety of healthy tissues, but that expression levels of AEP were lower in primary acute myeloid leukemia (AML). In line with that, we confirmed low activity of AEP in AML cells and demonstrated that HLA-DRB1*03:01 positive primary AML expressing LB-PIP4K2A-1S or its donor variant PIP4K2A-1N were both recognized by specific T-cells. In conclusion, LB-PIP4K2A-1S not only represents a novel minor histocompatibility antigen but also provides evidence that donor T-cells after allogeneic stem cell transplantation can target the autologous allelic variant as leukemia-associated antigen. Furthermore, it demonstrates that endopeptidases can play a role in cell type-specific intracellular processing and presentation of HLA class II-restricted antigens, which may be explored in future immunotherapy of AML.

Two unique HLA-A*0201 restricted peptides derived from cyclin E as immunotherapeutic targets in leukemia.

Immunotherapy targeting leukemia-associated antigens has shown promising results. Because of the heterogeneity of leukemia, vaccines with a single peptide have elicited only a limited immune response. Targeting several peptides together elicited peptide-specific cytotoxic T lymphocytes (CTLs) in leukemia patients, and this was associated with clinical responses. Thus, the discovery of novel antigens is essential. In the current study, we investigated cyclin E as a novel target for immunotherapy. Cyclin E1 and cyclin E2 were found to be highly expressed in hematologic malignancies, according to reverse transcription polymerase chain reaction and western blot analysis. We identified two HLA-A*0201 binding nonameric peptides, CCNE1M from cyclin E1 and CCNE2L from cyclin E2, which both elicited the peptide-specific CTLs. The peptide-specific CTLs specifically kill leukemia cells. Furthermore, CCNE1M and CCNE2L CTLs were increased in leukemia patients who underwent allogeneic hematopoietic stem cell transplantation, and this was associated with desired clinical outcomes. Our findings suggest that cyclin E1 and cyclin E2 are potential targets for immunotherapy in leukemia.

DC Vaccination Induces Antigen Specific Immune Responses in AML Patients: A 1-Year Interim Assessment

Acute myeloid leukemia (AML) is a lethal hematological malignancy characterized by high rates of relapse (50%). Studies of immune responses in AML patients led to identification of two leukemia-associated antigens (Wilms' tumor protein 1 (WT1) and preferentially expressed antigen of melanoma (PRAME) for which cellular and humoral immune responses were detected. Based on expression profiles in AML and normal tissues, WT1 and PRAME were selected as target antigens for a DC vaccine, aiming to elicit adaptive and innate immune responses in AML patients. The primary objective of the trial (EudraCT No.: 2014-003520-44) is to evaluate safety and feasibility of active immunotherapy with antigen-loaded autologous DCs. The secondary objectives are to assess DC vaccination-induced T cell responses against WT1 and PRAME and to evaluate the clinical outcome over a period of 2 years or until disease progression/relapse. WT1-positive AML patients, with or without PRAME positivity were included, if they had a morphological remission with or without hematological recovery (CRi) after induction chemotherapy and were not eligible for allogeneic hematopoietic stem cell transplantation. DCs were administered intradermally (2.5x106 WT1 plus 2.5x106 PRAME DCs) on a weekly basis for 4 consecutive weeks, followed by administration on week 6 and then every 4 weeks until 2 years, tumor progression or patient withdrawal. This report focusses on the immune-monitoring data collected during the first year of treatment. Multiple parameters were evaluated, including WT1- and PRAME specific T cell responses in peripheral blood (IFN-g ELISPOT), the recurrence of WT1- and/or PRAME-positive AML blasts in bone marrow (qRT-PCR) and peripheral blood (flow cytometry), and occurrence of AML-specific mutations in bone marrow (NGS). DCs were assessed for expression of WT1 and PRAME and costimulatory molecules by flow cytometry, while secretion of IL10 and IL12 was evaluated by double-color ELISPOT. Twenty CR/CRi AML patients were vaccinated, and vaccination was well tolerated, and no signs of autoimmunity were observed. 12/20 patients remained stable throughout the first year of treatment, while 8/20 relapsed. 2/8 relapsed patients died due to progression of disease during the first year. In patients in stable remission, 7/12 patients had no detectable IFN-γ ELISPOT response in peripheral blood, 3/12 mounted a response and 2/12 were not evaluable due to high background production of IFN-γ. Positive IFN-γ ELISPOT responses were observed within 1-30 weeks of treatment and associated with a decrease over time in levels of WT1 (3/3) and/or PRAME mRNA (1/3) expression. Except for 2 patients who remained MRD-negative throughout the first year of treatment, ELISPOT-negative patients in remission (5/7) exhibited low, relatively stable levels of target antigens. Stable remissions were associated with one (3/12) or no (8/12) AML-related mutations while one patient was not evaluable. AML relapses were observed within 50 days in 4 patients, within 51-100 days in 1 patient, and after more than 150 days in 3 patients. Overall, 6/8 relapsing patients exhibited positive IFN-γ ELISPOT responses, while 2 patients relapsing in <50 days failed to respond and one patient relapsing on day 77 exhibited an IFN-γ response at baseline. In all other relapsing patients, IFN-γ ELISPOT responses were detected within 6-30 weeks after vaccination, in association with rapid and progressive increases in levels of WT1 and/or PRAME. AML-related gene mutations were detected in 6/8 relapses, while one patient was not evaluable, and one had no mutation; In 4 of the relapsing patients, 3 to 6 mutations were detected, while in 2/8 a single mutation was observed. In conclusion, IFN-γ responses to WT1 and/or PRAME were detected in peripheral blood of 75% (6/8) of relapsing patients, but only 25% (3/12) of the patients in remission. It is tempting to speculate that detection of IFN-γ response in peripheral blood is linked to the concomitant presence of AML blasts in the periphery of relapsing patients. Stable or decreasing levels of WT1 and/or PRAME mRNA in bone marrow of most patients in remission is compatible with the hypothesis that a local response against AML antigens may be ongoing, despite a negative IFN-γ response in peripheral blood. Monitoring of the patients currently in remission may shed some light on the role of DC vaccination on the prevention of AML recurrence. Disclosures Eckl: Medigene Immunotherapies GmbH: Employment. Raffegerst:Medigene Immunotherapies GmbH: Employment. Schnorfeil:Medigene Immunotherapies GmbH: Employment. Prinz-Schulz:Medigene Immunotherapies GmbH: Employment. Fingerhut:Medigene Immunotherapies GmbH: Employment. Bigalke:BioNTech Innovative Manufacturing Services GmbH: Employment. Pinkernell:Medigene AG: Employment. Schendel:Medigene AG: Employment, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Tafuri:Medigene Immunotherapies GmbH: Employment.

RUNX1 Mutation Accompanied with Dysregulated Cellular Senescence in Lower-Risk Myelodysplastic Syndrome Patients Is Associated with Disease Progression

Background and Aims A part of lower-risk myelodysplastic (LR-MDS) patients progress to higher-risk MDS or acute myeloid leukemia (AML). The progression may be predicted in some of these patients by determining mutations associated with myeloid malignancies at the time of diagnosis. We focused to find out dysregulated pathways caused by a well-defined mutation associated with disease progression. Methods We examined 158 samples from LR-MDS patients at diagnosis using TruSight Myeloid Sequencing Panel containing 54 genes (Illumina) to identify the mutational profile. We applied RNA-seq (NEB; Illumina) on bone marrow CD34+ cells of 5 LR-MDS patients with RUNX1 mutation and 6 LR-MDS patients without mutations. We performed differential gene expression analysis, gene set enrichment analysis (GSEA), Reactome biological pathway and Gene Ontology (GO) annotations. Results Forty out of 158 patients (25%) progressed during the follow-up period (median: 45.1 months). Mutation in RUNX1 gene was detected in 10 patients. Using RNA-seq, significantly dysregulated expression was observed in 986 genes (FDR<0.05; FC >2). Patients with mutation in RUNX1 gene had significant down regulation of expression genes involved in cellular senescence induced by DNA Damage/Telomere Stress (FDR=1.4e-11) and Oxidative Stress (FDR=3.6e-9), HDACs deacetylate histones (FDR =1.1e-13) and Senescence Associated Secretory Phenotype (FDR=1.4e-11) according to Reactome pathway database. There were 21 genes involved in the regulation of these pathways, of which 10 were part of all described pathways and belonged to the Nucleosome Assembly according to GO biological process with 33 down regulated genes (FDR=6.3e-28). According to GSEA, GO chromatin silencing gene set (Figure 1) was down regulated in the patients with RUNX1 mutation (p<0.001; NES=-1.8) same as Reactome apoptosis (p<0.001; NES-1.7). In these patients, expression of 750 genes was up-regulated (FDR<0.05; FC >2); however, they did not form a specific pathway. The up-regulated genes were classified as so-called leukemia-associated antigens (LAAs) such as PRAME (adjusted p=6.9e-09; logFC=6.8), WT1AS (adjusted p=4.4e-07; logFC=5.7), BAALC (adjusted p=3.5e-06; logFC=2.1), WT1 (adjusted p=6.8e-07; logFC=3.2), FLT3 (adjusted p=0.004; logFC=1.3) and LEF1 (adjusted p=5.3e-08; logFC=-4.2). Conclusions To study the transcriptome of the hematopoietic stem cells of LR-MDS patients, we used gene expression profiling and identified biological processes in relation to mutations in RUNX1 gene that were detected in patients with disease progression. According to our results, we suppose that cells of LR-MDS patients with no mutations are maintained in senescent state or apoptosis in opposite to RUNX1 mutated cells. Finding out of dysregulated senescence was reinforced by other dysregulated pathways such as HDACs deacetylate histones, chromatin structural changes and senescence-associated secretory phenotype. About cellular senescence is known that may act as a strong tumor suppression mechanism that restrains proliferation of cells at risk for malignant transformation. We suppose that in precancerous cells of LR-MDS patients apoptosis or cellular senescence limits the replicative capacity of cells, thus preventing the proliferation. The disturbed state of cellular senescence in RUNX1 gene mutated hematopoietic stem cell can escape proliferation control and then can contribute to the disease progression in these patients. Supported by grants NV18-03-00227 and 00023736 from the Ministry of Health of the Czech Republic. Disclosures No relevant conflicts of interest to declare.

HLA class I-restricted T cell epitopes isolated and identified from myeloid leukemia cells

Leukemia-associated antigens (LAAs) and HLA-I epitopes published previously have shown promise in inducing leukemia-specific T cell responses. However, the clinical responses are limited, and clinical effectiveness is yet to be achieved. Limitations, among others, being the LAAs themselves, the indirect approach to HLA-I epitope identification by reverse immunology, and the use of single or few LAAs and HLA-I epitopes, which limits the spectrum of inducible tumor-specific T cells. Use of a direct approach to identify naturally processed and presented HLA-I epitopes from LAAs, and higher numbers of antigens for T cell-mediated immunotherapy for leukemia may enhance clinical responses and broaden clinical effectiveness. In a prior study we used immunoaffinity purification of HLA-I peptide complexes from the differentiated myeloid tumor cell lines MUTZ3 and THP1 coupled to high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). From this we identified in the current study seven new HLA-I epitopes and the corresponding LAAs for myeloid leukemia. In comparison, the myeloid HLA-I epitopes reported here were generally stronger HLA-binders that induce stronger T cell responses than those previously published, and their source LAAs had higher immunogenicity, higher expression levels in myeloid tumors cells compared to normal hemopoietin and other major normal tissues, and more protein interaction partners, and they are targeted by CD8 T cells in CML patients. This study analyses and compares the LAAs and HLA-I epitopes based on various immunotherapeutic targets selection criteria, and highlights new targets for T cell-mediated immunotherapy for leukemia.

Skuteczność zastosowania ruksolitynibu u chorej z wtórnym włóknieniem szpiku w przebiegu wieloletniej czerwienicy prawdziwej powikłanej zakrzepicą w układzie wrotnym

The effect of leukaemia-associated antigens prepared from leukaemic lymphoblasts and myeloblasts has been studied on the migration of peripheral leucocytes obtained from children with Down's syndrome. Membrane extract from leukaemic lymphoblasts had no effect, while that from leukaemic myeloblasts was slightly inhibitory, i.e. it was "recognized" as antigen by the lymphocytes of children with Downs syndrome.

Human acute myeloid leukemia blast-derived exosomes in patient-derived xenograft mice mediate immune suppression

Exosomes are virus-size membrane-bound vesicles of endocytic origin present in all body fluids. Plasma of AML patients is significantly enriched in exosomes, which carry a cargo of immunosuppressive molecules and deliver them to recipient immune cells, suppressing their functions. However, whether these exosomes originate from leukemic blasts or from various normal cells in the bone marrow or other tissues is unknown. In the current study, we developed an AML PDX model in mice and studied the molecular cargo and immune cell effects of the AML PDX exosomes in parallel with the exosomes from plasma of the corresponding AML patients. Fully engrafted AML PDX mice produced exosomes with characteristics similar to those of exosomes isolated from plasma of the AML patients who had donated the cells for engraftment. The engrafted leukemic cells produced exosomes that carried human proteins and leukemia-associated antigens, confirming the human origin of these exosomes. Furthermore, the AML-derived exosomes carried immunosuppressive proteins responsible for immune cell dysfunctions. Our studies of exosomes in AML PDX mice serve as a proof of concept that AML blasts are the source of immunosuppressive exosomes with a molecular profile that mimics the content and functions of the parental cells.

PF783 TREG DOWNREGULATION IS ASSOCIATED WITH INCREASE OF T CELL RESPONSES AGAINST IMMUNOGENIC ANTIGENS AND CLINICAL RESPONSES IN PATIENTS WITH HEMATOLOGICAL MALIGNANCIES AFTER DONOR LYMPHOCYTE INFUSION

Background:Cytotoxic T‐cell responses against malignant cells play a pivotal role in maintaining remission and prolonging overall‐survival after allogeneic stem cell transplantation (allo‐SCT) and donor lymphocyte infusion (DLI), however they are not well characterized so far.Aims:In this study, we focused on the detection of immune responses in patients before and after DLI. A broader epitope‐specific T cell activity is associated with clinical response of patients treated with DLI and additionally reduced regulatory T cell frequency may contribute to clinical response in patients after DLI.Methods:For a better characterization of the T cell responses, frequency and diversity of leukemia‐associated antigen (LAA)‐specific cytotoxic T cells was assessed using ELISpot and pMHC multimer assays. Furthermore, the frequency of regulatory T cells (Treg) before and after DLI was analyzed. Results were correlated to the clinical course of the patients.Results:Independently of their clinical response, over the course of DLI 7/11 patients (63.6%) showed an immunological response through an increase in the number of recognized epitopes. Comparing early screening and maximum response after DLI there was a significant increase (p = 0.02) in epitope recognition. A significant increase in the mean augmentation from 1 to 4 of the spotted epitopes in the course of DLI was detected in the cohort of clinical responders (R) compared to non‐responders (NR) who did not show any dynamics in epitope recognition with a median of 3 to 4 recognized LAA.The proportion of the CD4+CD25highFoxP3+ Treg within the CD4+CD25high T cell fraction decreased significantly in R from a median of 72.9% to 54.6% when comparing the variation at the time points before and after DLI (p = 0.04). In NR there was no significant change in the Treg fraction in the course of DLI.In general, significantly more LAA‐derived T cell epitopes (p = 0.02) were recognized in R when compared to NR. Moreover, the frequency of Treg in R decreased significantly (p = 0.008) while remaining stable in NR.Summary/Conclusion:Taken together, an increase of specific CTL responses against several LAA after DLI was detected. This study suggests that decreasing numbers of Treg as well as enhanced LAA diversity in T cell responses contribute to clinical outcome of patients treated with DLI.

The HLA ligandome landscape of chronic myeloid leukemia delineates novel T-cell epitopes for immunotherapy

AbstractAntileukemia immunity plays an important role in disease control and maintenance of tyrosine kinase inhibitor (TKI)-free remission in chronic myeloid leukemia (CML). Thus, antigen-specific immunotherapy holds promise for strengthening immune control in CML but requires the identification of CML-associated targets. In this study, we used a mass spectrometry–based approach to identify naturally presented HLA class I– and class II–restricted peptides in primary CML samples. Comparative HLA ligandome profiling using a comprehensive dataset of different hematological benign specimens and samples from CML patients in deep molecular remission delineated a panel of novel frequently presented CML-exclusive peptides. These nonmutated target antigens are of particular relevance because our extensive data-mining approach suggests the absence of naturally presented BCR-ABL– and ABL-BCR–derived HLA-restricted peptides and the lack of frequent tumor-exclusive presentation of known cancer/testis and leukemia-associated antigens. Functional characterization revealed spontaneous T-cell responses against the newly identified CML-associated peptides in CML patient samples and their ability to induce multifunctional and cytotoxic antigen-specific T cells de novo in samples from healthy volunteers and CML patients. Thus, these antigens are prime candidates for T-cell–based immunotherapeutic approaches that may prolong TKI-free survival and even mediate cure of CML patients.

Abstract A072: Calreticulin exposures by malignant blasts correlate with robust anticancer immunity and improved clinical outcome in AML patients

Abstract Cancer cell death can be perceived as immunogenic by the host only when malignant cells emit immunostimulatory signals (so-called “damage-associated molecular patterns,” DAMPs), as they die in the context of failing adaptive responses to stress. Accumulating preclinical and clinical evidence indicates that the capacity of immunogenic cell death to (re-)activate an anticancer immune response is key to the success of various chemo- and radiotherapeutic regimens. Malignant blasts from patients with acute myeloid leukemia (AML) exposed multiple DAMPs, including calreticulin (CRT), heat-shock protein 70 (HSP70), and HSP90 on their plasma membrane irrespective of treatment. In these patients, high levels of surface-exposed (ecto)-CRT correlated with an increased proportion of natural killer cells and effector memory CD4+ and CD8+ T-cells in the periphery. Moreover, CRT exposure on the plasma membrane of malignant blasts positively correlated with the frequency of circulating T-cells specific for leukemia-associated antigens, indicating that ecto-CRT favors the initiation of anticancer immunity in patients with AML. Finally, although the levels of ecto-HSP70, ecto-HSP90, and ecto-CRT were all associated with improved relapse-free survival, only CRT exposure significantly correlated with superior overall survival. Thus, CRT exposure represents a novel powerful prognostic biomarker for patients with AML, reflecting the activation of a clinically relevant AML-specific immune response. Citation Format: Jitka Fucikova. Calreticulin exposures by malignant blasts correlate with robust anticancer immunity and improved clinical outcome in AML patients [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A072.

A Phase I/II Clinical Trial of Type 1 Interferon for Reduction of Relapse after HCT in High Risk AML

Introduction Relapse remains a significant challenge towards improving survival after allogeneic hematopoietic transplantation (HCT) for Acute Myeloid Leukemia (AML) not in remission or possessing poor cytogenetic/molecular features. Insights from murine pre-clinical studies demonstrate a central role for CD8+ dendritic cells in cross-presentation of leukemia associated antigens (LAA) in mediating GVL without aggravating acute Graft-versus-Host Disease (aGVHD)(Toubai, Blood 2013). We posited that enhancing LAA cross-presentation with exogenous Type I Interferon (pegIFNα) would promote GVL response and reduce rates of relapse after HCT. Methods We initiated a prospective, phase I/II, clinical trial of pegIFNα administration after myeloablative conditioning for prevention of relapse in pts with detectable AML at time of HCT (resistant to induction) or with cytogenetic/molecular features conferring high relapse risk and poor survival. Pts received up to four doses of 90mcg or 180mcg pegIFNα SubQ on d -1 and d 14, 28, 42 after PBSC or BMT. aGVHD prophy was tacrolimus + MTX or MMF. The primary endpoint was to determine the incidence of relapse in pts receiving the phase II dosage of pegIFNα. We hypothesized that 30 pts assigned to the same dose would provide 80% power to detect a difference between a promising day 180 relapse rate of 40% versus a rate of 60%. Results A total of 30 pts received study treatment at a median age of 60 years (17-72). Conditioning was myeloablative FluBu (n=9), CloBu (n=20) or FluCyTBI (n=1). At time of HCT, AML was detected in 28 pts and 2 pts enrolled for poor cytogenetic/molecular risk, complex/monosomal karyotype (n=1) and FLT3-ITD+ (n=1). There was no DLT at 90mcg (n=3) and one DLT (graft failure) after escalation to 180mcg (n=27). pegIFNα was well tolerated with ≥3 doses administered to 87% of pts. ≥Grade 3 SAEs during treatment include acute kidney injury(n=1), engraftment failure(n=1), bone pain/weakness(n=1), hypotension(n=1) and hypoxemia (n=1). 29 pts (97%) experienced primary engraftment and bone marrow exam at d 30 revealed CR in 100% of pts. Thirteen pts (43%) experienced infection. Grade II-IV aGVHD and grade III-IV aGVHD occurred in 35% (20 – 56%) and 11% (4 – 30%) by day 180. The incidence of TRM was 11% (3-30%) at day 180 and 19% (8-41%) at 1-yr. The day 180 (and 1-yr) incidence of relapse was 39% (24 – 60%) in the overall cohort and 36% (20 – 58%) in 27 pts treated at the phase II dose. At a median follow up of 19 months, the 1-yr OS was 42% (27 – 65%). Conclusion These data provide initial evidence of clinical translation for pegIFNα when administered prophylactically in an AML cohort at high risk for relapse. Type I Interferon did not significantly alter toxicity or aGVHD risk and produced relatively low rates of relapse suggesting a robust GVL response. The role of type 1 IFN in reducing clinical relapse and its underlying biological mechanisms warrants additional study.

A Novel T-Cell Engaging Bi-specific Antibody Targeting the Leukemia Antigen PR1/HLA-A2

Despite substantial advances in the treatment of acute myeloid leukemia (AML), only 30% of patients survive more than 5 years. Therefore, new therapeutics are much needed. Here, we present a novel therapeutic strategy targeting PR1, an HLA-A2 restricted myeloid leukemia antigen. Previously, we have developed and characterized a novel T-cell receptor-like monoclonal antibody (8F4) that targets PR1/HLA-A2 and eliminates AML xenografts by antibody-dependent cellular cytotoxicity (ADCC). To improve the potency of 8F4, we adopted a strategy to link T-cell cytotoxicity with a bi-specific T-cell-engaging antibody that binds PR1/HLA-A2 on leukemia and CD3 on neighboring T-cells. The 8F4 bi-specific antibody maintained high affinity and specific binding to PR1/HLA-A2 comparable to parent 8F4 antibody, shown by flow cytometry and Bio-Layer Interferometry. In addition, 8F4 bi-specific antibody activated donor T-cells in the presence of HLA-A2+ primary AML blasts and cell lines in a dose dependent manner. Importantly, activated T-cells lysed HLA-A2+ primary AML blasts and cell lines after addition of 8F4 bi-specific antibody. In conclusion, our studies demonstrate the therapeutic potential of a novel bi-specific antibody targeting the PR1/HLA-A2 leukemia-associated antigen, justifying further clinical development of this strategy.

Prognostic Impact of WT-1 and Survivin Gene Expression in Acute Myeloid Leukemia Patients.

Wilms Tumor 1 (WT1) and Survivin genes are important leukemia-associated antigens (LAAs) in AML with potential prognostic impact. We investigated WT1 and Survivin expression levels by RT-PCR in 61 AML patients in correlation with clinical characteristics and outcomes. WT1 was overexpressed in 45 patients (73.8%), associated with higher BM blasts (p = 0.017), lower incidence of favorable-prognosis cytogenetics (p = 0.035), and higher incidence of Flt3-ITD mutations (p = 0.026). Survivin was overexpressed in 17 patients (27.9%) with higher mean WBC count (p = 0.049). Patients with overexpression of either gene showed inferior complete remission (CR) rates and survival rates, patients with overexpression of both genes showed higher mean WBCs (p = 0.035) and higher BM blasts (p = 0.029) while the double negative group showed higher incidence of favorable cytogenetic events (p = 0.021), better CR rates and survival rates. Our findings support the introduced prognostic impact of WT1 and Survivin genes in AML patients and its potential use in MRD monitoring and immunotherapy.

Treg Downregulation Was Associated with Augmentation of T Cell Responses Against Immunogenic Antigens and Clinical Responses in Patients with Hematological Malignancies after Donor Lymphocyte Infusion (DLI)

In order to maintain remission and to prolong overall-survival after allogeneic stem cell transplantation (allo-SCT) and donor lymphocyte infusion (DLI), cytotoxic T-cell responses against malignant cells play a pivotal role, however they are not well characterized so far. In this study, we focused on the detection of immune responses in patients before and after DLI. A broader epitope-specific T cell activity is associated with clinical response of patients treated with DLI and a concurrent reduction of regulatory T cell frequency may contribute to clinical response in patients after DLI.For a better characterization of the T cell responses, frequency and diversity of leukemia-associated antigen (LAA)-specific cytotoxic T cells was assessed using ELISpot and pMHC multimer assays. Furthermore, the frequency of regulatory T cells (Treg) before and after DLI was analyzed. Results were correlated to the clinical course of the patients.Independently of their clinical response, 7/11 patients (63.6%) showed an immunological response through an increase in the number of recognized epitopes over the course of DLI. There was a significant increase (p=0.02) in epitope recognition comparing early screening and maximum response after DLI and a significant increase in the mean augmentation from 1 to 4 of the spotted epitopes in the course of DLI was detected in the cohort of clinical responders (R) compared to non-responders (NR) who did not show any dynamics in epitope recognition with a median of 3 to 4 recognized LAA.The proportion of the CD4+CD25highFoxP3+ Treg within the CD4+CD25high T cell fraction decreased significantly in R from a median of 72.9% to 54.6% when comparing the variation at the time points before and after DLI (p=0.04). In NR there was no significant change in the Treg fraction in the course of DLI.In general, significantly more LAA-derived T cell epitopes (p=0.02) were recognized in R when compared to NR. Moreover, the frequency of Treg in R decreased significantly (p=0.008) while remaining stable in NR.Taken together, an increase of specific CTL responses against several LAA after DLI was detected. This study suggests that decreasing numbers of Treg as well as enhanced LAA diversity in T cell responses contribute to clinical outcome of patients treated with DLI. DisclosuresDöhner:AbbVie: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding; AROG Pharmaceuticals: Research Funding; Agios: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; Agios: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Pfizer: Research Funding; Seattle Genetics: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Pfizer: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Celator: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding.