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Graft-versus-host disease (GVHD) is a major cause of transplant-related mortality (TRM) after allogeneic haematopoietic stem cell transplantation (HSCT) and presents a challenge in haploidentical HSCT. GVHD may be prevented by ex vivo graft T-cell depletion or in vivo depletion of proliferating lymphocytes. However, both approaches pose significant risks, particularly infections and relapse, compromising survival. A photodepletion strategy to eliminate alloreactive T cells from mismatched donor lymphocyte infusions (enabling administration without immunosuppression), was used to develop ATIR101, an adjunctive therapy for use after haploidentical HSCT. In this phase I dose-finding study, 19 adults (median age: 54 years) with high-risk haematological malignancies were treated with T-cell-depleted human leucocyte antigen-haploidentical myeloablative HSCT followed by ATIR101 at doses of 1 x 10(4)-5 x 10(6) CD3(+) cells/kg (median 31 days post-transplant). No patient received post-transplant immunosuppression or developed grade III/IV acute GVHD, demonstrating the feasibility of ATIR101 infusion for evaluation in two subsequent phase 2 studies. Additionally, we report long-term follow -up of patients treated with ATIR101 in this study. At 1 year, all 9 patients receiving doses of 0 center dot 3-2 x 10(6) CD3(+) cells/kg ATIR101 remained free of serious infections and after more than 8 years, TRM was 0%, relapse-related mortality was 33% and overall survival was 67% in these patients.

PURPOSE: Chronic myelogenous leukemia (CML) is a disorder affecting early hematopoietic stem cells (HSC) and is characterized by excessive proliferation and accumulation of myeloid progenitors and progeny in the periphery. During the chronic phase of the disease, CML patients are normally at low risk of developing infections but such complications tend to rise during the progression of the disease. Gleevec (imatinib mesylate) is currently administered as first line therapy for patients with Philadelphia chromosome-positive CML. Despite the relative high specificity of tyrosine kinase inhibitor (TKI) treatment towards the BCR-ABL fusion protein, off-target multikinase inhibitory effects occur and can interfere with normal hematopoiesis. This study was conducted to evaluate how myeloid and lymphoid immune homeostasis are affected by Imatinib mesylate. METHODS: Healthy volunteer donors (n=25) and CML patients were recruited during their first visit at our CML clinic. Seven CML patients were treated with Imatinib (400mg). The median time of Gleevec treatment was 2.9 years (range: 0.5-10.9). The median time of remission post TKI was 1.1 years (range: 0.3-3). Phenotypic analysis of dendritic cell (DCs) subsets: plasmacytoid (pDCs) and myeloid type 1, 2 and 3 (mDC1, mDC2, mDC3) were evaluated by flow cytometry. Percentage and absolute numbers of naive and memory CD4+ and CD8+ T cells, NK cells and B cells were also evaluated. DCs were differentiated from purified CD34+ cells culturedwith GM-CSF (800 U/ml) or Flt3-L (50ng/ml), IL-4 (10 U/ml) and TNFa (50 U/ml), in the presence of varying concentrations of Imatinib mesylate (0 to 5µM/mL). TCR and IL-7 signaling were evaluated based on ERK-phosphorylation (-p) and STAT5-p after incubation with 3µM of Imatinib. RESULTS AND CONCLUSION: At diagnosis, several CML patients have a deficit in DCs resulting from a severe skewing affecting BM progenitor cells. After initiating Gleevec therapy, normalization of stem cell progenitors occurs but DC counts remain well below normal levels in all CML patients. We demonstrated a direct and dose dependent interference of Imatinib on GM-CSF and Flt3-L pathways for DC differentiation from CD34+ stem cells. For T lymphocytes, Imatinib interfered with TCR and IL-7 signaling through the inhibition of ERK and STAT5 phosphorylation respectively. The failure to maintain adequate numbers of DCs combined to diminished homeostatic response to cytokines and TCR stimuli explains T cell lymphopenia in these patients. Such immune dysfunction is at least in part responsible for infectious complications that are often increased in patients treated with Imatinib. Disclosures No relevant conflicts of interest to declare.

Abstract 3020FN2 Background: The intensive T-cell depletion of the graft accompanying haploidentical stem cell transplantation (SCT) delays immune reconstitution and results in frequent and rapidly lethal infectious complications. The ability to accelerate immune reconstitution following HLA-haploidentical-SCT would extend safe transplantation to the large number of patients who do not have an HLA-matched donor. Methods: Twenty-seven adults with very high-risk malignancy entered a Phase I clinical trial of haplo-identical T-cell depleted allogeneic SCT followed by an immunotherapeutic strategy consisting of alloreactive T-lymphocyte depleted cells to accelerate immune reconstitution (ATIR) while preventing graft-versus-host disease (GVHD). Selective elimination of host-reactive T cells was achieved using a dibromorhodamine-based photodepletion approach. All stem cell grafts underwent in vitro immunomagnetic T cell depletion using CD34+ positive cell selection (Miltenyi). The myeloablative regimen consisted of TBI (1200 cGy), thiotepa (5 mg/kg), ATG (12.5 mg/kg) and fludarabine (200 mg/m2). No GVHD prophylaxis was administered. Results: Eight patients were enrolled and subsequently removed from the study because of leukemia relapse (n=4) or late identification of an unrelated donor (n=4). All 8 patients died. Nineteen patients (11 M, 8 F) with very high-risk hematologic malignancies (mostly refractory or relapsed acute myeloid leukemia (10) and myelodysplastic syndromes (4), and refractory biphenotypic leukemia (1), CLL (2), CML (1) and NHL (1)) proceeded with the trial. Median age was 54 years (range: 20–62). Patient and disease characteristics were similar between patient cohorts. Patients received incremental doses of ATIR cells, from 1×104 to 5×106 CD3 cells/kg at a median of 30 days (range: 28–39) after SCT. Greater than 90% of activated (CD25+CD44+) CD4 and CD8 T cells (p Conclusions: Post-transplant immunotherapy with photodepleted DLI decreased the incidence and severity of infections without inducing severe GVHD. These results document the benefits of administrating selectively depleted T-cells after haploidentical transplantation. Disclosures: Roy: Kiadis Pharma: Research Funding. Mielke:Kiadis Pharma: Research Funding. Egeler:Kiadis Pharma: Employment.

The robustness of the immunostimulatory response generated by dendritic cells (DCs) has positioned these cells as central and determining cellular mediators of T cell activation. Their production in sufficient number from hematopoietic precursors is crucial in order to drive immune responses. To determine the capacity of CML clonogenic cells to generate dendritic cells expressing endogenous CML-specific epitopes, we have evaluated the generation of DCs from CD34+ progenitor cells and CD14+ monocytes isolated from patients with CML (n=28). We found that the kinetics of production of DCs, in GM-CSF 800U/ml, TNF-a 50U/ml and IL-4 10U/ml, from CD34+ progenitors of CML patients were significantly delayed in comparison to healthy controls (p 500 cells) (CML = 29 vs normal = 95 colonies, P

Graft-versus-host disease (GVHD) and impaired immune reconstitution are the primary obstacles limiting the efficacy of allogeneic stem cell transplantation (SCT). Graft-versus-host disease (GVHD) and impaired immune reconstitution are the primary obstacles limiting the efficacy of allogeneic stem cell transplantation (SCT). The purpose of this study was to determine whether selective depletion of donor alloantigen-specific T lymphocytes using photodynamic therapy (PDT) would prevent GVHD and enable immune reconstitution in the context of MHC-mismatched SCT. This question was addressed in an MHC-incompatible mouse model of GVHD. The donor (C57BL/6; H-2b) derived spleen cells were first activated against C3H/HeJ (H-2k) host spleen cells in a one-way mixed lymphocyte culture and then exposed to photodynamic treatment, using dibromorhodamine methyl ester (TH9402) as a photosensitizer. Activated T cells showed preferential retention of this photosensitizer compared to resting lymphocytes. In addition, in vitro experiments revealed that PDT eradicated a significantly higher proportion of activated than resting T cells. When lethally irradiated H-2k mice (C3H/HeJ and B10BR) were transplanted with C57BL/6 derived T cell-depleted bone marrow cells supplemented with C57BL/6 derived spleen cells activated with C3H/HeJ targets, they rapidly succumbed to acute GVHD (within 10–47 days). In contrast, both mouse strains receiving histoincompatible C57BL/6 T cells previously exposed to PDT after activation against C3H/HeJ survived until the end of the observation period (>100 days)(p