Abstract: Abstract 2771 Introduction: We have previously shown that 5-azaC inhibits T-cells proliferation and favours the development of Tregs which decreases the risk of GVHD after allogeneic transplantation. This is at least in part due to the effect of the drug on the expression of genes such as FOXP3. Nevertheless, considering the unspecific effect of 5-azaC, it could also favour the overexpression of other genes related to the regulation of the immune response such as TBET, GATA3, IFNg or IL-2, which in turn would favour the development of a Th1, Th2 or Th17 polarization instead of a Treg expansion. In the current study we have evaluated the effect of 5-azaC on these genes in order to know the mechanisms involved in the effect of the drug on the immune response. Methods: We analyzed TBET, GATA3, FOXP3, IFNg and IL-2 mRNA expression of T lymphocytes by RT-PCR after exposure to 1mM 5-azaC during eleven days of culture. These T cells were cultured in medium alone or stimulated with plate-bound anti-CD3 (5 mg/ml) plus soluble anti-CD28 (2.5 mg/ml). Furthermore, we analyzed the methylation status of the promoters of these genes before and after 5-azaC treatment. Results: The expression of TBET, GATA3 and RORγ is not significantly affected by the exposure to the drug whereas the expression of FOXP3 significantly increases along the culture. Regarding IFNg and IL-2 expression no increased expression was observed after exposure to the drug at different time-points along the 11 days of culture. Upon analyzing the mathylation status of the promoter of these genes, we observed that in steady state the promoter of TBET and GATA is demethylated, which is in contrast to FOXP3 promoter. For this reason, the exposure to the drug decreases the methylation status of the promoter of FOXP3 while there is no effect on the promoters of TBET or RORg, thus justifying the absence of effect on the expression of these genes. By contrat, the promoter of both IFNg and IL-2 is methylated prior to the exposure to 5-azaC and it is demethylated after exposure to the drug, which is in contrast to the absence of increased expression of these genes. Accordingly, other mechanisms in addition to the epigenetic regulation of the promoter of IFNg and IL-2 are responsible for their expression in this model. Conclusions: In the current study we show by the first time the effect of 5-azaC on the promoters of genes which regulate the immune response. While no effect was observed for TBET, and GATA3 5-azaC induces a strong demethylation in the promoter of IFN or IL-2. In spite of this effect there is no increase in their expression which could be due to the overexpression of FOXP3 or to additional mechanisms involved in their regulation which are currently being evaluated. Disclosures: Cañizo: Celgene: Membership on an entity's Board of Directors or advisory committees. San Miguel:Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Jangssen-cilag: Membership on an entity's Board of Directors or advisory committees; millennium: Membership on an entity's Board of Directors or advisory committees. Off Label Use: The drug used in this study is the demethylating agent 5-azacytidine (5-azaC) and the purpose is the inhibition of graft versus host disease.

Abstract: Abstract 3615 Introduction: Preferentially expressed antigen of melanoma (PRAME) was first isolated as a human melanoma antigen by cDNA expression cloning using melanoma-reactive cytotoxic Tcells (CTL). PRAME is a tumor associated antigen (TAA) of particular interest since it is widely expressed by lymphoid and myeloid malignancies and solid tumors. Several studies have associated high PRAME RNA levels with good prognosis in acute myeloid leukemia (AML). In addition, several authors have suggested that PRAME could be used as a target for anticancer T-cell therapy. PRAME expression is regulated at the epigenetic level. For this reason inhibitors of DNA methylation, such as 5-azacytidine, can modulate the expression of this TAAs. In the current study we analyzed the effect of 5-azaC on the expression of PRAME in blasts versus CD34+ cells from healthy donors in an attempt to increase its expression, thus inducing a potential target for therapeutic strategies. Methods: We analyzed PRAME mRNA expression of blast cells from AML patients at diagnosis versus CD34+ stem cells from healthy donors by RT-PCR without treatment or after exposure to 1mM 5-azaC during the four days of culture and correlated the expression of PRAME with the methylation status of the promoter. Results: PRAME is significantly over-expressed in blasts from AML patients (n=11) compared with normal CD34+ cells (n=8) ((700±1102 vs. 1.8±2.5 p=0.002). Interestingly, we found an inverse correlation between PRAME expression and the degree of methylation in the promoter among both AML samples and healthy donors (r=-0.77 p=0.010). In order to evaluate the effect of 5-azaC on PRAME gene expression, we treated blast cells and CD34+ cells from healthy donors with the drug and we observed that the exposure to the drug induced a decrease in the percentage of methylation in the promoter and subsequently increased the expression of PRAME but, interestingly, the higher the basal methylation of the promoter the more intense the effect of the drug among AML cells. By contrast, CD34+ cells from healthy donors were resistant to the effect of the drug so that no significant changes were observed neither in terms of methylation status of the promoter nor in the expression of PRAME prior to or after exposure to the drug among healthy donors. Conclusions: The promoter region is highly methylated in normal CD34+ cells compared to AML cells and this pattern correlates with a higher expression of PRAME in blasts. Furthermore, the level of PRAME methylation was reduced in AML patients after exposure to 5-azaC which correlated with an increase in the expression of PRAME. By contrast, the effect of 5-azaC on the methylation pattern of the promoter was significantly lower in CD34+ cells from healthy donors. Disclosures: Cañizo: Celgene: Membership on an entity's Board of Directors or advisory committees. San Miguel:Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Jangssen-cilag: Membership on an entity's Board of Directors or advisory committees; millennium: Membership on an entity's Board of Directors or advisory committees. Off Label Use: The drug used in this study is the demethylating agent 5-azacytidine (5-azaC) and the purpose is to increase PRAME expression in blasts from AML patients and generate CTL CD8+ specific response against tumor cells.

Abstract: Background: Evaluation of MRD is standard in patients with AML. However, the role of decentralized MRD assessment for risk stratification in AML remains largely unknown, and so it does which methodological aspects are critical to empower the evaluation of MRD with prognostic significance, particularly if using MFC. Aim: To evaluate the role of decentralized MRD assessment using MFC for risk stratification and putative treatment individualization of patients with AML. Methods: This study was performed on 1,076 AML patients in complete remission (CR) after 7+3 induction chemotherapy, in whom MRD was evaluated by MFC in local laboratories over a period of 20 years in the PETHEMA group. We conducted a survey of technical aspects of MFC based MRD testing in the laboratories of the 60 participating Hospitals, to determine the impact of methodological heterogeneity in the prognostic value of MFC. Results: We first investigated the most effective MRD cutoff to stratify patients' risk at first remission. Patients were segmented into progressively higher cutoffs, starting at 0.01% followed by 0.05%, 0.1%, 0.5% and 1%. Our results showed that 0.1% reached higher statistical significance to discriminate patients with different relapse-free survival (RFS, HR: 0.77; P = .001) and overall survival (OS, HR: 0.73; P = .001). In multivariate analyses together with patients' age, WBC, genetic risk and post-consolidation therapy, MRD status was selected as an independent prognostic factor for OS. To further define the utility of "real-world" MRD assessment using MFC in risk stratification of AML, recursive partitioning was performed using the prognostic and treatment related factors selected in the multivariate Cox model for OS. Of the four variables evaluated, hematopoietic stem cell transplantation (HSCT, regardless of autologous or allogeneic source) vs no transplant emerged as the best single discriminator for OS, followed by genetic risk, age and MRD status. There were two branching points defined by MRD status; the first in patients ≤60 years with intermediate genetic risk who were not transplanted and the second in patients with adverse genetics who were not transplanted, in whom & lt;0.1% MRD faintly improved the dismal outcome of this subgroup. Overall, patients not referred to HSCT had dismal RFS regardless of MRD levels. Forty-nine of the 60 hospitals (82%) responded to the survey on questions regarding the measurement of MRD using MFC in the PETHEMA LMA 1999, 2007 and 2010 protocols, providing information corresponding to 966 of the 1,076 (90%) patients regarding the number of markers, preparation of samples, instruments, approach (ie, LAIP, DfN or LAIP+DfN), number of cells to define a cluster, etc. The survey revealed significant heterogeneity intra- and inter-protocols that reflected improvement in MFC assessment of MRD over time, in the absence of harmonization nor standardization at the national level. Accordingly, we investigated if the heterogeneity in methodological, interpretation and reporting aspects of MFC based MRD testing were hampering its ability to predict outcome independently of other patient and treatment related factors. Strikingly, our results showed that except for the denominator used to calculate MRD burden (ie, total nucleated cells vs leukocytes), lack of standardization in all other parameters had an impact on the ability of MFC to predict outcomes in AML (Figure). Namely, panels with ≤4 markers or ≤2 combinations failed to identify patients with significantly different RFS according to MRD status, and MFC-based MRD monitoring was prognostic only when & gt;500,000 cells were measured. Only MRD assessment using patient-specific panels was predictive of outcome. Conclusions: We report here one of the largest studies investigating the role of MRD monitoring using MFC. Our results confirmed that detection of MRD identifies patients in CR/CRi with inferior survival, but uncovered that decentralized MRD testing lacks significance when compared to other baseline risk factors and in the context of risk-adapted post-consolidation strategies. Thus, while this study demonstrated that "real-world" decentralized assessment of MRD using MFC does provide prognostic information in AML patients at first remission, our results question its readiness for risk stratification towards clinical decisions outside trials, at least until adequate standardization of this technique is achieved. Figure Disclosures Paiva: SkylineDx: Consultancy; Takeda: Consultancy, Honoraria, Research Funding; Roche: Research Funding; Adaptive: Honoraria; Amgen: Honoraria; Janssen: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Kite: Consultancy; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding. Alonso Dominguez:Celgene: Research Funding; Incyte: Research Funding; Pfizer: Research Funding. Martinez-Lopez:Janssen: Speakers Bureau; Altum: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; Hosea: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; Roche: Speakers Bureau; Amgen: Speakers Bureau; Takeda: Speakers Bureau; Vivia Biotech: Honoraria; Novartis: Research Funding; BMS: Research Funding, Speakers Bureau; Incyte: Research Funding, Speakers Bureau. Sossa:Astellas: Honoraria; Roche: Honoraria; Takeda: Honoraria; Novo: Honoraria. San-Miguel:Roche, AbbVie, GlaxoSmithKline, and Karyopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb, Celgene, Novartis, Takeda, Amgen, MSD, Janssen, and Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Abstract: Chronic Graft-versus-Host disease (cGVHD) remains a major cause of morbidity and mortality in long-term survivors after allogeneic hematopoietic stem cell transplantation (ASCT). Among the major risk factors previously noted is sex-mismatch, acute GVHD and peripheral hematopoietic blood stem cell grafts (PBSC). Our aim in this study was to determine risk factors for cGVHD and evaluate the impact of ATG on cGVHD in a multi-centre setting. Methods Patients from three centers (Stockholm, Sant Pau, Barcelona and Salamanca) were included. Retrospective data analysis was conducted for all patients (n=820) transplanted between 2000 and 2006. In our cohort 91% had malignant disease, 57% received HLA-identical sibling donor grafts, 13% received grafts with one HLA-A, -B or –DR antigen mismatch and 30% received grafts from HLA-A, -B and –DR matched unrelated donors. Reduced intensity conditioning was given to 65% of the patients. Chronic GVHD was classified according the National Institute of Health consensus criteria. Results Overall incidence of cGVHD was 46% for patients surviving more than three months after ASCT (n=747). Older patient age HR 1.15 (95% CI 1.07-1.24), p 〈 0.001, acute GVHD HR 1.30 (95% CI: 1.04-1.63), p=0.024, and reduced intensity conditioning (RIC) HR 1.36 (95% CI 1.04-1.79) p=0.028 were shown to significantly increase the risk of overall cGVHD in multivariate analysis. In addition, female donor to male recipient HR 1.43 (95% CI 1.07-1.92), p=0.02, RIC HR 1.65 (95% CI 1.18-2.30) p=0.003, and PBSC HR 1.90 (95% CI 1.14-3.16), p=0.01 significantly influenced the risk of moderate-to-severe cGVHD in multivariate analysis. For both overall and moderate-to-severe cGVHD, ATG had a protective effect with HR 0.41 (95% CI 0.32-0.52) p 〈 0.001 and HR 0.32 (95% CI 0.23-0.46) p 〈 0.00, respectively. Accordingly, we developed a scoring system including all variables influencing the risk of cGVHD in multivariate analysis allowing us to distinguish patient cohorts with 12% to 71% incidence of cGVHD (figure 1). Relapse free survival (RFS) was significantly impaired in the group with severe cGVHD. RFS was not affected significantly by the addition of ATG. All three centers had similar overall survival for patients with cGVHD. Conclusion RIC increases the risk for both overall and moderate to severe cGVHD. Acute GVHD and older recipient age are significant risk-factors for overall cGVHD and female donor to male recipient and PBSC for moderate to severe cGVHD. ATG significantly reduces the risk of all grades of cGVHD without having a negative outcome on RFS. Therefore, in order to prevent overall and moderate-extensive cGVHD it should be added to the RIC regimen in older patients and in male patients with female donors after PBSC grafts. Disclosures: Ringden: Gilead : Invited to Gilead on July 28, 2011, to participate in an Advisory Board Meeting on Treatment of invasive fungal infection. Other. San Miguel:Jansen, Celgene, Onyx, Novartis, Millenium: Consultancy, Membership on an entity’s Board of Directors or advisory committees.

Abstract: Abstract 3025 Introduction: Although allogeneic stem cell transplantation (allo-SCT) is the only curative treatment for MM, it is associated to a high morbility and mortality. Moreover, relapses are common after allo-RIC. Accordingly, new strategies are required to reduce both the risk of relapse and the toxicity of the procedure. As we have previously demonstrated, Bz induces a selective depletion of alloreactive T-cells and has immunomodulatory properties which might be of potential benefit for GVHD control. The primary end point of this study was to evaluate the efficacy of allo-RIC in terms of response when Bz was added as part of a reduced intensity conditioning prior to allo-SCT. Secondary end points included incidence of GVHD and analysis of the toxicity of the procedure when Bz is also administered post-infussion as part of the GVHD prophylaxis. Method: Prior to allo-RIC, patients received two cycles of Bz plus dexamethasone. Conditioning consisted of fludarabine (30 mg/m2 intravenously on days -9 to -5) and melphalan (70 mg/m2 intravenously on days -4, -3) plus Bz 1, 3mg/m2 on day - 11 and -2. GVHD prophylaxis included cyclosporine (CsA) and methotrexate for the first 9 patients and CsA plus MTX and Bz on days +3 and +7 for the remaining 7 patients. From day +50 post allo-RIC 7 cycles of Bz (+1, +8, +15) were administered, the first two cycles every 28 days and the rest every 56. Results: 16 patients from the Twenty-one initially enrolled, were evaluable. All 16 patients had received at least 2 lines of therapy including autologous-SCT. Disease status was CR or nCR in 4 patients, 9 had PR and the remaining 3 patients had relapsed / progressive disease. 15 patients maintained or improved status at transplant including all × patients with active disease at transplant. Eight patients (50%) relapsed, four with extramedullary involvement. No patient developed grade 4 aGVHD.Grades 2–3 aGVHD occurred in 6 patients (37%). Interestingly, two out of the nine (29%) patients who received Bz on days +3 and 7 developed grades 2–3 acute GVHD as compared to four of the nine (44%) who did not receive it. In terms of toxicity, one patient did not achieve platelet engraftment and 2 patients developed peripheral neuropathy requiring treatment withdrawal. 8 patients died, four of them due to relapse (MRT: 25%). With a median follow-up of 457 days overall survival was 46%. Conclusions: The current trial is the first evaluating the efficacy and safety of Bz as part of a reduced intensity conditioning regimen among patients with high risk MM undergoing allogeneic transplantation. Regarding the efficacy of the procedure all but one patient improved disease status post-alloRIC although relapse rate was still high in this heavily pretreated population. In addition, Bz post-alloSCT is well tolerated and may decrease the incidence of GVHD. Disclosures: Perez-Simón: Janssen-Cilag: Patents & Royalties. Off Label Use: This study evaluates the efficacy of Bortezomib as part of a reduced intensity conditioning regimen among patients with high risk MM undergoing allogeneic transplantation. Rosiñol:Celgene: Honoraria; Janssen: Honoraria. San Miguel:Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees.

Abstract: Introduction: Allogeneic haematopoietic stem cell transplantation (alloHCT) is a potentially curative approach for patients (pts) with multiple myeloma (MM). The high transplant related mortality (TRM) rate with myeloablative conditioning has resulted in a shift to reduced intensity conditioning regimens (RIC). However, most MM pts who receive an alloRIC ultimately relapse and their treatment remains a challenge. Since alloHCT can modify the biology of the disease, including the immune environment, responses after alloHCT to rescue therapies previously used before alloHCT could be improved. Our main objective was to evaluate the efficacy of regimens including new drugs in MM pts relapsing after alloHCT comparing the efficacy achieved before and after alloHCT. Material and Methods: We report a retrospective multicenter analysis of 126 consecutive pts that underwent alloHCT for MM from 2010 to 2013 at 8 Spanish centers. Results: Baseline pts and transplant characteristics are shown in Table I. The median of prior therapies prior to alloHCT was 3 (1-9), 83% had received previous autologous HCT and 26% had high risk cytogenetic. 71 (56%) and 48 pts (38%) had been treated with regimens containing proteasome inhibitors (PI) and immunomodulatory drugs (IMIDs) before transplantation, respectively. Disease status at transplant was complete remission (CR) in 16 (13%) pts, partial response (PR) or very good PR in 86 (68%) and 24 (18.5%) had relapsed/progressive disease. 35 pts (28%) had active extramedullary disease at transplant. The majority of pts received peripheral blood HCT (90%), RIC (90%) with fludarabine plus melphalan based conditioning regimen (61%) and calcineurin inhibitor plus MTX as GVHD prophylaxis (68%). 19% receiving allo-HCT from an unrelated donor (91% 10/10 HLA matched). All pts engrafted. Grade II-IV acute GVHD occurred in 54% pts (grade IV 8%) and chronic GVHD in 45% (moderate 15%, severe 12%). TRM within the first 100 days after transplant was 6% (overall TRM 28%). 60% pts improved their pre-transplant response, with an overall response rate of 74% (56% CR). After a median follow-up of 92 months for pts alive (22-197), the OS was 51 and 43% at 2 and 5 years respectively. 75 pts (59.5%) relapsed after alloHCT, 57 of them with extramedullary involvement. Median time to relapse was 8 months post-transplant (1-141). The cumulative incidence of relapse was 79% at 3 years. Median OS after relapse was 22 months (8-33). Seventeen out of 75 pts who relapsed received IP both in the pre-transplant and in the post-transplant period. Sixteen pts out of 17 who received IP achieved at least PR pre-transplant while 10 out of these 16 pts responded again to PI post-HCT. Moreover, 1 patient reached a deeper response (CR) post as compared to pre alloHCT (PR) and 1 patient who was refractory pre-alloHCT did respond post-alloHCT. In addition, 6 out of 7 pts who did not respond to IP post-transplant reached stable disease with time to progression (TTP) lasting 4 to 12 months. Twelve out of 75 pts who relapsed received IMIDs both pre and post-alloHCT. Ten pts out of 12 who received IMID pre-alloHCT achieved at least PR, and 8 out of these 10 pts responded again to IMIDs post-alloHCT. Moreover, 1 patient who had been refractory to IMIDs in the pre-transplant period reached CR after alloHCT. In addition, 2 out of 4 pts who were refractory to IMIDs in the post-transplant period reached stable disease with TTP of 8 to 13 months. Remarkably, among pts who respond both in the pre and the post-transplant period to IP or IMIDs, the time to response (TTR) and time to progression (TTP) was similar despite the regimens used in the pre-transplant setting were more aggressive (TTR 3 vs 3.5 and TTP 9 vs 7 months before and after alloHCT for IP, and TTR 4 both before and after alloHCT and TTP 10 vs 9.5 months before and after alloHCT for IMIDs). All but 2 pts received first generation IP pre and post-alloHCT (two pts received carfilzomib) and all but 5 received first generation IMIDs (5 pts were treated with pomalidomide). Conclusions: MM pts relapsing after alloHCT should be considered candidates to receive new drugs, as they can achieve response rates at least in a similar proportion and durability to those observed in the pre-transplant setting. This finding is in contrast to the usual course of the disease outside the alloHCT setting, where response rates and TTP decreases with consecutive lines of treatment. Disclosures Mateos: Janssen: Honoraria; Celgene: Honoraria; Takeda: Honoraria; Amgen: Honoraria.

Abstract: Cytokine genes are targets of multiple epigenetic mechanisms in T lymphocytes. 5-azacytidine (5-azaC) is a nucleoside-based DNA methyltransferase inhibitor that induces demethylation and gene reactivation. In the current study, we analyzed the effect of 5-azaC in T-cell function and observed that 5-azaC inhibits T-cell proliferation and activation, blocking cell cycle in the G0 to G1 phase and decreasing the production of proinflammatory cytokines such as tumor necrosis factor-α and interferon-γ. This effect was not attributable to a proapoptotic effect of the drug but to the down-regulation of genes involved in T-cell cycle progression and activation such as CCNG2, MTCP1, CD58, and ADK and up-regulation of genes that induce cell-growth arrest, such as DCUN1D2, U2AF2, GADD45B, or p53. A longer exposure to the drug leads to demethylation of FOXP3 promoter, overexpression of FOXP3, and expansion of regulatory T cells. Finally, the administration of 5-azaC after transplantation prevented the development of graft-versus-host disease, leading to a significant increase in survival in a fully mismatched bone marrow transplantation mouse model. In conclusion, the current study shows the effect of 5-azaC in T lymphocytes and illustrates its role in the allogeneic transplantation setting as an immunomodulatory drug, describing new pathways that must be explored to prevent graft-versus-host disease.

Abstract: Introduction: Although survival rates have improved over the years, chronic graft-versus-host disease (cGvHD) remains the most frequent and severe complication in the long term after allogeneic hematopoietic stem cell transplantation (allo-HSCT). All the strategies developed to reduce its incidence are based on procedures aimed to decrease the risk of acute GvHD that, consequently, can also reduce the risk of cGvHD, mainly using immunosuppression in the early post-transplant period. These strategies induce apoptosis of donor T lymphocytes, responsible for a/cGvHD but also for graft-versus-tumor response. In the present project, we have evaluated a new strategy aimed to reduce the risk of cGvHD by manipulating the immune response not in the early post-transplant period, but in later phases. cGvHD develops via a complex cellular and molecular network involving thymus damage and unusual antigen presentation leading to aberrant T- and B-cell reactions characterized by Th17/Tc17 differentiation, macrophage sequestration in tissue, alloantibody formation, and fibrosis. Most of these cell populations are dependent on NF-kB for their activation. Ixazomib is a second-generation proteasome inhibitor for oral administration, representing an ideal candidate for prophylaxis in GvHD. Objective: We propose to develop a murine model of cGVHD and progressive onset cGvHD to test the efficacy of delayed administration of ixazomib as a novel strategy to decrease the risk of cGvHD. Methods: For in vitro studies, peripheral blood mononuclear cells from healthy donors were stimulated in the presence of different concentrations of ixazomib. After 48h and 120h, apoptosis was analyzed, and activation markers were evaluated. For in vivo studies, a murine model of progressive cGvHD (pcGvHD - allowing the recipient to survive to mild aGvHD, thus favoring autoreactive T cells to expand and cause cGvHD) and a scleroderma model of cGvHD were used. Ixazomib at 0.75mg/Kg/twice weekly, 2X from day +21 in the pcGvHD, with or without cyclosporine A (CyA) at 5mg/Kg/day from day 0 until the end of the study. For scleroderma cGvHD group, 3mg/Kg/2X from day +30 was used up to 120 days post-transplant. Flow cytometry was used to evaluate the different lymphocyte populations in the different target organs of the GvHD. Results: In vitro results showed that activated T lymphocytes are sensitive to the proapoptotic effect of ixazomib ( 〉 100nM), while high concentrations of the drug are necessary to cause apoptosis in the non-activated cells (5000nM). Through CD27 and CD45 expression, we verified that ixazomib has a proapoptotic effect mainly on naïve and effector cells. We also verified a decrease in the activation markers of CD3+CD25+INF-γ+ cells (p˂0.01, 1000nM, n = 4). In the animal trial, the survival of the pcGvHD model mice treated with ixazomib was significantly higher as compared to untreated mice, with a significant decrease in the signs of pcGvHD (Figure 1A). In addition, the combination of CyA and ixazomib improved survival as compared to those mice receiving CyA or ixazomib alone as well as untreated controls (Figure 1B). In the scleroderma cGvHD model, we observed that the animals treated with ixazomib showed significantly less signs of GvHD (p˂0.0001) (Figure 2). Multiparametric flow cytometer analyses showed that in the pcGvHD model, mice treated with ixazomib had a decrease of effector CD4 T-cells in bone marrow (p=0.06) and spleen (p=0.015) when compared to untreated mice. Also an increase of CD19+ cells in the colon (p=0.04), liver (p=0.035), lymph nodes (LN) (p=0.037) and lungs (p=0.03) was observed. Regarding the regulatory T cells (Foxp3+), the treated mice had a significant increase in LN (p=0.02), Peyer patches (p=0.015) and thymus (p=0.028) as compared to untreated mice. Conclusion: In vitro studies show that ixazomib induces apoptosis on activated T lymphocytes and decreases the expression of activation markers. Our in vivo model indicates that the combination of CyA and ixazomib for the prevention of pcGvHD and cGVHD after allogeneic HSCT is promising and merits further investigation in clinical trials. Figure 1. Survival of pcGvHD. Figure 2. Score graphic of scleroderma cGvHD. BM - Bone marrow, mice that were transplanted with BM from BALBc mice (Syngeneic). Disclosures Ramos: Takeda Oncology: Research Funding.

Abstract: Introduction Autologous adoptive T cell therapies, based on the use of tumor infiltrating lymphocytes (TILs), have made great progress in recent years for the treatment of solid tumors, especially melanoma. However, further work is needed to isolate tumor-reactive T cells among patients diagnosed with hematologic malignancies. The dynamics of the interaction between T cells and antigen presenting cells (APC) dictate the quality of the immune responses. While stable joints between target cells and T lymphocytes lead to the induction of T cell activation and immune response, brief contacts contribute to the induction of immune-tolerance. Taking advantage of the strong interaction between target cell and activated T-cells, we show the feasibility to identify and isolate tumor-specific cytotoxic T lymphocytes (CTLs) from acute myeloid leukemia (AML) patients. Using this approach, CTLs stably bound through T cell receptor to tumor cells (doublet forming T-cells) can be identified in peripheral blood and bone marrow and subsequently selected and isolated by FACS-based cell sorting. Methods Co-cultures between PBMC from AML patients in complete remission and AML tumor cells (PKH-stained) from the same patient were performed to study the percentage of doublet-forming T cells (CD3+PKH+) (T cell bound to a tumor cell). After 15 hours of co-culture, cells were stained and sorted. Secondary co-cultures with autologous tumor cells (used in primary co-culture) were performed to study the cytotoxic activity and cytokine production of T-cells capable or not to form stable joints with the leukemic cells (doublet population vs non-doublet population). Results Doublet-forming T cells from AML patients were identified in a range of 2% to 6% (mean=3.83%, n=5). Immunophenotyping analysis showed differences between doublet-forming T cells (CD3+PKH+) and those T cells which did not form stable and strong interactions with target cells (CD3+PKH-). Doublet T cells displayed a higher percentage of CD8+ T cells and higher percentage of effector CD4+ and CD8+ T cells compared to non-doublet T cells. Next, we explored, among effector CD4+ and CD8+ cells, those with cytotoxic phenotype. As expected, a high percentage of effector CD8+ doublet T cells showed Granzyme B and perforin expression, thus corresponding with a cytotoxic immune-phenotype (n=3, mean 65.51%). Within effector CD4+ doublet T cells, a mean of 9.053 % showed expression of both Granzyme B and perforin corresponding with CD4+ CTL (n=3). Regarding CD57 and CD16 markers, a mean of 18.62% of effector CD4+ doublet T cells were positive for both markers, compared to 65.84% of effector CD8+ doublet T cells (n=3). Further, we performed secondary co-cultures to analyze the CD69 activation marker after 24h of co-culture. A high percentage of CD69+ cells was observed in co-cultures with doublet-forming T cells against target cells as compared to non-doublet T cells (n=3, p=0.0053). Finally, analysis of supernatants of co-culture of doublet T cells and non-doublet T cells with target cells revealed specific secretion of IFNγ and IL-2 (n=3, p=0.0001; p=0.0005, respectively). The cytolytic activity was evaluated comparing the viability of tumor cells cultured alone or with doublet-forming T cells or non-doublet T cells from the same patient. A significant increase of the specific lysis of AML cells was observed when doublet T cells were co-cultured as compared to non-doublet T cells (p=0.0424, n=5). This encouraged us to examine whether we were able to identify doublet-forming T cells from bone marrow of AML patients at diagnosis. Analyses of bone marrow by flow cytometry reveled a small percentage of CD3+CD34+ population corresponding with bone marrow-doublet-forming T cells (n=3, mean=2.9%). Interestingly, bone marrow-doublet-forming T cells show a higher percentage of CD4+ T cells, whereas bone marrow-non-doublet T cells show a higher percentage of CD8+ T cells. Conclusions Our data demonstrate that when T cells from AML patients are co-cultured with tumor cells, a "doublet T cell" population appears. This population consists of T cells capable to bind tumor cells. These CTLs display higher percentage of effector cells and a marked cytotoxic activity against AML blasts. In conclusion, we have developed a new procedure to identify and select specific cytotoxic T cells in both bone marrow and peripheral blood from patients diagnosed with acute myeloid leukemia. Figure. Figure. Disclosures Sanchez-Abarca: Virgen del Rocio University Hospital: Patents & Royalties. Ramos:Takeda Oncology: Research Funding.