ALBERT

Description: Background: Prognosis of diffuse large B-cell lymphoma (DLBCL) and other aggressive lymphoma entities has improved with the advent of Rituximab, and R-CHOP-21 and variants is SOC. Nevertheless, a substantial proportion of patients fail first line treatment. Salvage therapies are often effective. However, no more than 25-50% achieve a long term remission even when consolidative high dose chemotherapy (HDT) followed by hematopoietic stem cell transplantation (SCT) is applied. In case of failure or intolerance to HDT, regimen like Gemcitabine/Oxaliplatin are applied but show limited efficacy, indicating the need for new treatments. Obinutuzumab (GA101) is a type II anti-CD20 antibody. Superiority of Obinutuzumab could be demonstrated in xenograft models of mantle cell lymphoma and DLBCL. Although desirable, cumulative dose-related, progressive cardiotoxicity eliminates anthracyclins from higher treatment lines. With Pixantrone, a drug structurally related to anthracyclines and especially anthracenediones, a re-exposition against this drug class has been shown to be feasible. In 70 heavily pre-treated patients, a best ORR of 40% (20% CR/CRu) was observed (Pettengell et al). Experiences from further antibody drug combinations lead to the assumption that the effects of Pixantrone will be augmented by a monoclonal antibody without increasing toxicity. We thus initiated a trial combining both agents for the first time. The trial has opened in Q4/2015 and recruitment is ongoing. Overall, a total of up 70 patients will be enrolled for a number of 64 evaluable patients. Primary endpoint will be the objective overall response rate, with secondary endpoints being safety, PFS and OS. Methods: this is a multicenter, national, prospective trial. Inclusion criteria: patients were eligible if they had histologically proven DLBCL, FL grade IIIb or transformed indolent lymphoma, CD20 positive disease, no curative option available, relapsed disease, measurable disease, ECOG 〈 3, sufficient bone marrow reserve, no severe concomitant diseases and given informed consent. There was no upper limit or prior treatment lines. Treatment consisted of Pixantrone 50mg/m² day 1, 8 and 15 of each cycle, Obinutuzumab 1000 mg flat dose day 1, 8 and 15 of cycle one and day 1 of each subsequent cycle. A total of 6 cycles was planned with interim staging after 3 cycles. Results: 24 patients (pts) have been included until now. Concerning clinical characteristics, all were caucasian, 12 were female and the other 12 male and median age was 75 years. Most of the patients suffered from DLBCL (18 pts, 82%). Median number of prior therapies was 2 (1 to 6). Until now 55 evaluable cycles of chemotherapy (median 2 cycles (0 to 6)) have been performed. At this time, the treatment seems to be well tolerated, with no unforeseen side effects. Observed toxicity was predominantly hematologic. The following hematologic adverse events of grade 3/4 were noted: leukopenia (4 pts, 17%), neutropenia (6 pts, 25%), granulocytopenia (1 pts, 4%), as well as thrombocytopenia (2 pts). Non-hematologic grade 3/4 adverse events were observed in at least two patients: hypertension (2 pts) and pelvic pain (2 pts). Response: currently, best responses were 4 PR, 1 SD, and 8 PD in 13 patients evaluable so far. Four patients died, all after progression of lymphoma. Summary: the combination of Obinutuzumab and Pixantrone seems to be feasible and safe with early signs of efficacy. Updated results of this trial in progress with a focus on safety will be presented. Disclosures Hess: Janssen: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; Celgene: Honoraria; Roche, CTI, Pfizer, Celgene: Research Funding; Roche: Honoraria. Marks:Pfizer: Honoraria. Witzens-Harig:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Dreyling:Roche: Consultancy, Honoraria, Research Funding, Speakers Bureau. Viardot:Amgen: Consultancy; Janssen: Consultancy; BMS: Consultancy; Roche: Honoraria; Takeda: Other: travel support; Pfizer: Honoraria. Keller:Spectrum Pharmaceutical: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria.

Description: Introduction Starvation of tumor cells from the amino acid arginine has recently gained particular interest because of the downregulation of the rate-limiting enzyme argininosuccinate synthethase 1 (ASS1) in various cancer entities. ASS1-deficient cells cannot resynthesize arginine from citrulline and are therefore considered arginine auxotrophic. The arginine depleting enzyme arginine deiminase (ADI-PEG20, Polaris Pharmaceuticals) is currently tested in phase I-III clinical trials for different arginine auxotrophic cancers. The natural arginine analogue canavanine can compete with arginine for arginyl-tRNA-binding sites and consequently be incorporated into nascent proteins instead of arginine. Canavanine could therefore potentially further disturb intracellular protein homeostasis, especially under arginine deprivation. The sensitivity of myeloma cells towards arginine depletion strategies has not been analyzed so far. Methods Human myeloma cell lines and CD138-sorted primary human myeloma cells from patient bone marrow were screened for ASS1 expression by western blotting (WB). The cells were cultured in arginine free medium and assessed for proliferation and metabolic activity (CFSE/MTT assays), apoptosis (caspase-3 cleavage) and cell death (annexinV/propidium iodide). Canavanine was supplied in both arginine-sufficient and -deficient conditions. The level of intracellular protein stress was determined by WB and/or flow cytometry analysis for ubiquitinated proteins, phosphorylated eukaryotic initiation factor 2α (peIF2α) and the spliced isoform of the X-Box binding protein 1 (Xbp1s). Repetitive ADI-PEG20 ± canavanine application i.p. were tested in vivo in an U266 myeloma xenograft model in NOD/SCID/IL2Rcg-/- (NSG) mice. Arginine and canavanine levels in plasma were determined by HPLC. Tumor growth was measured, mice were assessed for survival, weight and side effects. Tumor tissues were analyzed for caspase-3 cleavage and Ki67 expression by immunohistochemistry. Results 5 of 6 myeloma cell lines were negative for ASS1. Also, ASS1 was either not or only weakly expressed in the majority of primary CD138+ myeloma patient samples. Arginine starvation induced an arrest of cell proliferation and/or metabolic activity of primary myeloma cells and myeloma cell lines after 18-24 h. Addition of citrulline could only rescue ASS1 positive myeloma cells due to the intracellular resynthesis of arginine. Arginine starvation alone led to delayed induction of apoptosis (e.g. 35% cell death of NCI-H929 cells after 72 h of treatment). Addition of 100 mM canavanine strongly increased cell death specifically in the context of arginine deficiency (e.g. cell death in NCI-H929 cells: 87% after 24 h, 100 % after 48h) while it was non-toxic and had no effect on cell viability under physiological arginine conditions. Co-application of canavanine induced ubiquitination of cellular proteins and led to the prolongation of a fatal unfolded protein response (UPR) as measured by markedly elevated Xbp1s levels. Prolonged UPR ultimately led to the induction of apoptosis as reflected by annexin V binding and caspase-3 cleavage. In an U266 myeloma NSG xenograft model, systemic arginine depletion by ADI-PEG20 suppressed tumor growth in vivo and significantly prolonged median survival of mice when compared with the control group (22±3 vs. 15±3 days). Canavanine treatment alone had no influence on viability (13±0 days). However, the combination of ADI-PEG20 and canavanine demonstrated the longest median survival (27±7 days). Histological examination of explanted tumors showed the highest rates of caspase-3 cleavage in the ADI-PEG20/canavanine group. Conclusion Myeloma cells are mostly arginine auxotrophic and can be selectively targeted by arginine starvation. Combination of arginine depletion with the arginine analogue canavanine leads to a highly efficient and specific tumor cell eradication and should be further optimized in multiple myeloma preclinical models. Disclosures Bomalaski: Polaris Pharmaceuticals Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Description: Background Acute myeloid leukemia (AML) is a heterogeneous disease of the hematopoietic progenitor cell driven by the subsequent acquisition of genetic alterations. Approximately 20% of AML patients show strong expression of CD56 (neural cell adhesion molecule; NCAM). Expression of NCAM is associated with poor overall survival; however, the functional role of aberrant NCAM expression has not been investigated to date. The goal of this study is to examine the biological role of NCAM in AML and to explore whether NCAM represents a potential therapeutic target. Results In order to evaluate the clinical significance of elevated NCAM expression in AML, we screened a panel of human cell lines for CD56 expression. Most cell lines were positive and cell surface expression correlated with mRNA levels. Knockdown of NCAM with three different doxycycline-inducible shRNAs suppressed cell growth and MTT activity in all positive cell lines. Propidium iodide staining demonstrated an increase in G1 arrest. Importantly, there was a marked apoptosis after NCAM suppression and this effect was proportional to the knockdown efficiency. Survival of NOD-SCIDgamma chain mice in a leukemia engraftment model was significantly prolonged upon NCAM knockdown. Suppression of NCAM sensitized leukemic blasts to treatment with Ara-C or Daunorubicin in vitro and in xenotransplantation experiments. To test the consequences of NCAM overexpression in negative leukemic cell lines we transduced the NCAM transcript from Nomo-1 into HL60 and K562 cells. HL60 cells had a significantly lower sensitivity towards Ara-C or Daunorubicin treatment. IC50 for the BCR-ABL inhibitor Dasatinib in K562 cells increased from 0.95 nM (EV, empty vector) to 2.2 nM in NCAM overexpressing cells. To dissect possible upstream regulation mechanisms of NCAM expression we performed DNAseI hypersensitivity assays coupled to qRT-PCR mapping of known putative sites in the NCAM promoter and observed open chromatin for the binding sites of Meis1, Mef2 and Stat1. shRNA-mediated knockdown of MEIS1, MEF2c and MLL-AF9 resulted in significant suppression of NCAM cell surface expression, suggesting an upstream regulatory role for MLL-AF9. To gain insights into the mechanisms underlying the NCAM function in AML we performed gene expression comparisons of the 30 highest versus 30 lowest expressing samples in the GSE8043 dataset. Fifty-seven Biocharta pathways were differentially expressed between NCAMhigh and NCAMlow samples, while expression changes predicted abnormal cell-cycle regulation, stress and DNA damage response, cell survival, renewal and adhesion. Western blot, protein array and qRT-PCR analyses of candidate downstream signaling pathways upon knockdown of NCAM demonstrated enhanced degradation of BetaCatenin, decreased expression of BCL-2 and increased levels of p21 and p27. The upstream regulation mechanism described above revealed MLL-AF9 (M/A9) as a top candidate for NCAM regulation. Subsequent analysis of M/A9 L-GMPs (Lin- cKit+ CD34+ FcgR+) demonstrated strong surface expression of NCAM, whereas normal HSCs (Lin-cKit+ Sca1+) were NCAM-negative. This could be validated by gene expression analyses of M/A9 L-GMPs compared with normal HSCs. In order to elucidate the role of NCAM on leukemic cell function in a mouse model, NCAM-/- and control wildtype (WT) bone marrow cells were transformed with a retroviral construct of M/A9 and transplanted into lethally irradiated littermates. Recipients of NCAM-/- M/A9 cells developed acute leukemia with prolonged disease latency. NCAM-/- M/A9 cells had lower CD117 and Gr-1 expression, but higher expression of Mac-1 and, in some samples, aberrant B220 co-expression. Importantly, there was a reduced representation of L-GMPs in the NCAM-/- M/A9 group and limited dilution retransplantation assays revealed a significantly prolonged survival of NCAM-/- M/A9 mice. Replating activity in methylcellulose was diminished and could be eradicated with sublethal doses of Cytarabine. Summary Targeting aberrant expression of NCAM demonstrated strong antileukemic activity in vitro and sensitized leukemic blasts to genotoxic stress. In vivo, depletion of NCAM resulted in prolonged disease survival in syngeneic and xenotransplantation experiments and diminished self-renewal capacities. Our data suggest that NCAM represents a promising therapeutic strategy and likely targets AML cells at the LSC level. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: Transcutaneous immunization (TCI) is a novel vaccination strategy to induce strong therapeutic cytotoxic T-lymphocyte (CTL) responses by directly targeting skin-resident professional antigen-presenting cells (APC). This vaccination approach is very promising to overcome current limitations of standard vaccination approaches that are mostly effective in prophylaxis, but not in the treatment of diseases. In this context, we have developed a TCI method based on a synthetic TLR7 agonist imiquimod that partial tumor protection in experimental rodent models. In our present work, we describe a novel optimized formulation of imiquimod in a solid suspension of crystalline imiquimod (IMI-Sol) that induces superior CTL responses and enhanced tumor protection. Methods: We determined imiquimod-penetration into the skin as well as systemic distribution by HPLC in C57BL/6 mice (at 6-12 weeks). For TCI, C57BL/6, Tlr7 (TLR7-/-) or Myd88 (MyD88-/-) gene deficient mice IMI-sol or imiquimod (in the commercially available formulation Aldara®) together with the CTL epitope SIINFEKL (derived from chicken ovalbumin) was applied on two consecutive days on the dorsum of the animals after hair removal by electric clippers. Induction of CTL responses was characterized after 7 days by the analysis of peptide-specific CTLs (ELISpot, tetrameric MHC I complexes) and in vivo cytolytic activity by flow cytometry. Tumor protection was assessed using the B16OVA tumor model. Results: Despite equal imiquimod penetration into the skin, we found superior vaccination capacity of IMI-Sol compared to Aldara® leading to enhanced tumor-protection. Using TLR7-/- or MyD88-/- mice, we confirmed that the induction of CTL responses with IMI-Sol was completely dependent on the TLR/MyD88 pathway. The enhanced immune response are due to more efficiently activated skin-derived DCs upon IMI-Sol treatment found in skin-draining lymph nodes. Conclusions: We developed of a superior imiquimod formulation for transcutaneous vaccination that boosts vaccination efficacy by the enhanced activation of skin-resident APCs leading to the induction of therapeutic CTL responses underscoring the importance of pharmaceutical aspects affecting vaccination potency beyond understanding of the underlying basic mechanisms. Combined efforts are necessary to establish TCI as a promising novel next generation vaccination platform that can be used for the treatment of persistent infections and cancer. Disclosures No relevant conflicts of interest to declare.

Description: Introduction:Even in the era of novel targeted therapies for the treatment of Chronic Lymphocytic Leukemia (CLL) patients, such as BTK, PI3K and BCL2 inhibitors, allogeneic hematopoietic stem cell transplantations (alloHCT) will remain an important treatment option for a subset of patients with very high risk CLL. The current study focused on the impact of center and procedure-related factors on outcomes after alloHCT, taking into account the impact of patient- and disease-related risk factors. Patients and Methods:Data of 684 CLL patients who received a first alloHCT between 2000 and 2011 were analyzed. Their data were collected as part of the EBMT CLL Data Quality Initiative. Outcomes of interest were Event-Free Survival (EFS) up to 5 years after transplantation and mortality in the first 100 days after alloHCT. Outcomes were analyzed by means of the Kaplan-Meier method and Cox proportional hazards models with a frailty (random effects) component to take into account unexplained center heterogeneity. The following factors describing center characteristics or the transplant procedure were analyzed: experience in alloHCT in general and, for CLL specifically, accreditation by the Joint Accreditation Committee-ISCT & EBMT (JACIE), Gross National Income (GNI)/capita based on purchasing power parity (PPP) (GNI/cap), donor type, donor-patient sex-match, type of conditioning, stem cell source and T-cell depletion (TCD). Results:Five-year EFS of the whole cohort was 37% (95% Confidence Interval, 33%-42%), Day-100 survival was 90% (88%-92%). Experience of the transplant center was measured by the number of all alloHCTs, and alloHCTs for patients with CLL respectively. The median total number of alloHCTs per center per year was 45 (range 0-169) and the median number of CLL alloHCTs was only 2 per center per year (range 0-19). Greater experience with transplantation of patients with CLL (Hazard Ratio (HR) 0.96 per additional transplant, p=0.002), JACIE accreditation (HR 0.7, p=0.045) and a higher GNI/cap (HR 0.4, 95% CI 0.2-0.96, p=0.04) showed a protective impact on 5-year EFS in the Cox model. In vivo TCD with alemtuzumab (HR 1.5 compared to no TCD, p=0.03) and a female donor for a male patient (HR 1.4 compared to a male donor for a male patient, p=0.02) were the only procedure-related factors significantly associated with EFS. Event-Free Survival after in vivo TCD with Anti-Thymocyte-Globulin or after ex vivo TCD was comparable to EFS without TCD (HR 0.9, 0.7-1.3, p=0.6; HR 0.9, 0.5-1.6, p=0.8). Non-myeloablative conditioning did not have a negative impact on 5-year EFS, and exposed patients to a lower risk of non-relapse mortality. Measured and unmeasured center characteristics did not have a significant impact on 100-day mortality. Even when correcting for patient-, procedure- and center-related characteristics, there was still significant variation in center outcome, expressed by center-specific HRs derived from the frailty models, ranging from 0.6 to 1.2. Their impact is illustrated in a model-based plot for EFS (see Figure) which shows outcomes for three reference patients with the same characteristics who would be transplanted in three centers with the same measured characteristics but with the highest, average and lowest HRs in the dataset. These unexplained center effects likely represent a mixture of differences which could apply to the location of the transplant center, unmeasured characteristics of the patient population transplanted at this center, selection criteria which were not reported and factors determining the success of the transplant procedure which might differ between centers. Conclusion: We have confirmed that both center- and procedure-related factors have a significant impact on the EFS of patients with CLL undergoing alloHCT. Our results may help to interpret outcomes of single or multicenter studies better. Since non-myeloablative conditioning did not have a negative impact on EFS and exposed patients to a lower risk of non-relapse mortality, this approach should be favored for future alloHCT for CLL. Probability of Event-Free Survival up to Five Years Post-HCT for three Reference Patients Contribution: J.S. designed the research and wrote the paper. L.C.d.W conducted the statistical analysis and produced the figure. Figure Figure. Disclosures Schetelig: Sanofi: Honoraria. Gramatzki:Janssen: Other: Travel/Accommodation/Expenses, Research Funding. Dreger:Gilead: Consultancy; Gilead: Speakers Bureau; Janssen: Consultancy; Novartis: Speakers Bureau; Novartis: Consultancy; Roche: Consultancy.

Description: Background and Aims: In immunosuppressed individuals Aspergillus (A.) fumigatus is a frequent cause of invasive pulmonary aspergillosis (IPA) which is highly associated with relevant morbidity and mortality. Moreover, it often occurs in patients suffering from leukocyte-adhesion deficiency type 1 (LAD1) which is triggered by a functional loss of CD18 in ß2 integrin receptors as these receptors consist of an alpha subunit (CD11a-CD11d) and CD18 as the common beta subunit. ß2 integrin receptors are differentially expressed by leukocytes, and are required for cell-cell interaction, transendothelial migration, uptake of opsonized pathogens, and cell signaling processes. Here, we asked for the importance of CD11b/CD18 also termed MAC-1 which is required for phagocytosis of opsonized A. fumigatus conidia by polymorphonuclear neutrophils (PMN) for control of pulmonary A. fumigatus infection. Methods: We used a murine IPA model (C57BL/6) and challenged CD11b deficient (CD11b-/-) or wild type (WT) mice with A. fumigatus conidia intratracheally. Afterwards, some mice were sacrificed 24h after infection. In these mice PMN recruitment and cytokine patterns were examined by analyzing bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) using flow cytometry, cytospin analysis, and cytometric bead array. Additionally, pulmonary fungal clearance and inflammation in murine lungs were analyzed by fungal culture assays and histopathologic examination using a scoring system. Furthermore, survival was studied with neutropenic animals serving as positive controls. To determine PMNs phagocytic activity and fungal killing capacity ex vivo, PMN were purified from bone marrow of CD11b-/- or WT mice by magnetic cell sorting using Ly6G specific antibodies. Afterwards, isolated PMN were stimulated with pacific blue-labeled tomato red-fluorescent modified A. fumigatus conidia and analyzed by flow cytometry. Results: We found that lung homogenates from CD11b-/- mice obtained 24h after infection showed an enhanced fungal burden as compared to lungs from WT mice. In contrast, lung tissue from infected CD11b-/- mice displayed impaired pulmonary inflammation as assessed by Hematoxilin-Eosin (HE) staining. Furthermore, the number of mucus-producing cells in bronchi of A. fumigatus infected CD11b-/- mice was decreased compared to cells in bronchi of WT mice. However, we observed markedly higher numbers of PMN in BALF of infected CD11b-/- mice compared to corresponding WT mice samples. In contrast, BALF derived from infected CD11b-/- mice contained lower levels of three different proinflammatory cytokines (TNF-α, IL-1α, IL-1β) compared to BALF from WT mice while levels of other cytokines and chemokines (IL-5, IL-6, IL-10, GM-CSF, CXCL1, CCL2) were comparable. In contrast, we measured higher levels of the chemokine CCL5 known as a relevant chemoattractant in innate and adaptive immune cells in BALF obtained from CD11b-/- mice. Interestingly, numbers of PMN, lymphocytes, and monocytes in the peripheral blood of A. fumigatus infected mice did not differ in a genotype-dependent manner. However, CD11b-/- mice PMN showed lower phagocytic activity than WT PMN, indicating an impaired capability to clear A. fumigatus. Nevertheless, CD11b-/- mice were finally characterized by similar long-term survival as WT mice after IPA induction while the PMN-depleted control mice died as expected. Conclusions: Our study demonstrates, that CD11b deficiency on myeloid cells affects the early course of IPA. This may be due to the importance of MAC-1 for PMN effector functions, and their interplay with DC and other leukocytes. Further work is necessary to elucidate the long-term course of IPA in CD11b-/- mice with regard to the interplay of PMN with dendritic cells, the efficacy of adaptive immune responses, and the potential pulmonary overexpression of CCL5. Beyond patients with LAD1 syndrome, we suggest our findings as being clinically relevant in other immunocompromised patients suffering from severe opportunistic infections. Disclosures Radsak: Celgene: Honoraria, Other: Travel grant; Jazz Pharmaceuticals: Other: Travel grant; TEVA: Consultancy; Gilead: Other: Travel grant; Takeda: Consultancy; Novartis: Consultancy, Honoraria; Daiichi Sankyo: Honoraria, Other: Travel grant.

Description: Neural cell adhesion molecule 1 (NCAM1; CD56) is expressed in up to 20% of acute myeloid leukemia (AML) patients. NCAM1 is widely used as a marker of minimal residual disease; however, the biological function of NCAM1 in AML remains elusive. In this study, we investigated the impact of NCAM1 expression on leukemogenesis, drug resistance, and its role as a biomarker to guide therapy. Beside t(8;21) leukemia, NCAM1 expression was found in most molecular AML subgroups at highly heterogeneous expression levels. Using complementary genetic strategies, we demonstrated an essential role of NCAM1 in the regulation of cell survival and stress resistance. Perturbation of NCAM1 induced cell death or differentiation and sensitized leukemic blasts toward genotoxic agents in vitro and in vivo. Furthermore, Ncam1 was highly expressed in leukemic progenitor cells in a murine leukemia model, and genetic depletion of Ncam1 prolonged disease latency and significantly reduced leukemia-initiating cells upon serial transplantation. To further analyze the mechanism of the NCAM1-associated phenotype, we performed phosphoproteomics and transcriptomics in different AML cell lines. NCAM1 expression strongly associated with constitutive activation of the MAPK-signaling pathway, regulation of apoptosis, or glycolysis. Pharmacological inhibition of MEK1/2 specifically inhibited proliferation and sensitized NCAM1+ AML cells to chemotherapy. In summary, our data demonstrate that aberrant expression of NCAM1 is involved in the maintenance of leukemic stem cells and confers stress resistance, likely due to activation of the MAPK pathway. Targeting MEK1/2 sensitizes AML blasts to genotoxic agents, indicating a role for NCAM1 as a biomarker to guide AML treatment.

Description: Introduction Although the therapeutic armamentarium against multiple myeloma has tremendously increased in recent years, it still remains an incurable disease. A highly promising novel anti-tumoral treatment strategy is to target specific non-redundant metabolic achilles heels of individual cancer entities. The semi-essential amino acid arginine can be synthesized from citrulline in most physiological tissues due to expression of the rate-limiting enzyme argininosuccinate synthetase 1 (ASS1). Various tumor entities do not express ASS1, therefore depend on the exogenous availability of arginine and pharmacological approaches to systemically deplete arginine are in phase I-III clinical development for such arginine-auxotrophic cancers. Cell death induction by arginine depletion can be dramatically enhanced by co-application of the arginine analogue canavanine. Canavanine can be used by the respective aminoacyl tRNA synthetase instead of arginine during protein translation and this leads to a highly toxic intracellular accumulation of misfolded proteins. In preliminary work we have seen that myeloma cells are largely arginine-auxotrophic and can be killed by arginine depletion and canavanine supplementation within hours, while ASS1 expressing cells are completely protected by their endogenous arginine rescue capability. Encouraging results of tumor control have already been seen in a murine myeloma model. Methods Human myeloma cell lines (NCI-H929_A2 and FD50, developed in our laboratory) were cultured and treated in RPMI-1640 medium with or without arginine. Protein levels were determinded by western blot analysis. Cell viability was measured by propidium iodide staining and flow cytometry analysis. RNA quantification was done by qRT-PCR. For autophagosome and aggresome quantification we used immunofluorescence staining (IF) and laser scanning microscopy (LSM). Results Arginine depletion and canavanine supplementation led to misfolded protein accumulation which was followed by massive apoptotic cell death. Both processes were further enhanced by co-treatment with the proteasome inhibitor bortezomib, indicated by an increase in intracellular polyubiquitinated proteins as well as higher cleaved caspase 3 levels and propidium-iodide positive cells after only 8-12 h in both tested cell lines. Unexpectedly, the endoplasmic reticulum (ER)-stress response was activated only very moderately. Expression of CHOP, a pro-apoptotic transcription factor that is highly translated under toxic ER stress, was not altered compared to control conditions. Tunicamycin-mediated induction of enhanced ER stress significantly improved the viability of arginine-starved and canavanine treated cells. This suggests that protein accumulation mainly takes place in the cytoplasm rather than the ER and tunicamycin might alleviate cell death by reduction of total protein translation. Despite severe arginine deficiency and induction of misfolded protein stress, the cells were not able to respond by an adequate upregulation of macroautophagy, as determined by an altered LC3 metabolism. The autophagic flux was significantly reduced compared to control conditions after 4-8 h of treatment. There was a strong induction of BAG3 and p62 proteins, which are both associated with chaperone-assisted autophagy as well as aggresome formation and are normally cleared via macroautophagy. Cytoplasmic aggresome formation was not detectable until onset of apoptosis. Also, no relevant modulation of phosphorylation of the autophagy inducer mTORC and the downstream kinase p70S6K1 was noted upon arginine depletion and canavanine co-treatment. Finally, ER stress induction via tunicamycin did not improve autophagic protein turnover, as determined by IF staining, LSM and western blot. Conclusions Arginine starvation in combination with canavanine supplementation induces fast and highly efficient cell death in arginine-auxotrophic myeloma cells. This novel strategy interferes with myeloma cellular metabolism by induction of misfolded protein accumulation. A relevant upregulation of potentially protective cellular strategies like ER stress responses, aggresome formation and autophagy are either not detectable or they remain insufficient. We hypothesize that our novel metabolic anti-tumor strategy is either too potent or too fast for the tumor cells to cope with its consequences. Disclosures No relevant conflicts of interest to declare.

Description: Background: Adoptive transfer of genetically modified T lymphocytes with tumor antigen-specific receptor has proven efficacy in cancer immunotherapy. However, in many patients the overall benefit is still limited due to various tumor escape mechanisms. Cell damage and metabolic/hypoxic stress in the tumor microenvironment (TME) can lead to a dysfunctional anti-tumor T cell response called T cell senescence. The tumor suppressor TP53 is a master molecule in the regulation of cell cycle and senescence. Few studies have demonstrated the critical role of p53 isoforms in the regulation of cellular senescence mainly in tumor cells. However, their role in tumor infiltrating lymphocytes (TILs) remains largely unexplored. Aims: Strategies to prevent T cell senescence in the TME could improve T cell function and thus anti-tumor response. To better understand the role of D133p53 isoform in regulating the cell cycle and senescence we studied the cellular and metabolic/energetic phenotype as well as the effector function of the D133p53-modified tumor-antigen (TA) specific human T cells. We further aimed at identifying the mechanism that may regulate this phenotype. Methods: T cells form healthy donors were retrovirally co-transduced with a TA-specific T cell receptor (TCR) together with the D133p53 isoform or an empty control vector. Modified T cells were characterized for the expression of key activating/inhibitory molecules, homing markers and for their proliferation capacity by flow cytometry. Additionally, we determined the metabolic and energetic phenotype of the cells with an Agilent Seahorse XFp Analyzer. The effector functions i.e. cytokine secretion and antigen-specific killing capacity were assessed by Luminex immunoassay and long-term tumor colony-forming assay, respectively. In an attempt to identify molecules/pathway contributing to this phenotype we performed quantitative proteomic-based analysis. Results: Our analyses of human T cells simultaneously engineered with D133p53a-isoform and a TA-specific TCR revealed reduced cell surface expression of T-cell inhibitory molecules (i.e. PD-1 or TIGIT), senescence markers (CD57, CD160) and increased expression of the homing receptor CD62L upon TA stimulation. First comparative analyses between D133p53a-modified and control T-cells revealed changes in the cell's metabolic and energetic program similar to quiescent/naïve T cells. D133p53a-T cells exhibited lower ATP production, oxygen consumption as well as lower glucose utilization. Upon antigen-specific stimulation, however, they increased their metabolic activity up to the levels of control cells. Importantly, while control T cells exhibited replicative senescence after chronic antigen stimulation, D133p53a-expressing T cells remained highly proliferative, showed superior cytokine secretion and enhanced tumor-specific killing capacity. Comparative proteomic analysis revealed significant differences in more than 100 proteins. Detailed pathway and network analysis as well as validation of the most significantly changing proteins is currently performed. Conclusion: By providing insights in the regulation of T cell metabolic changes and underlying mechanisms that limit immunosenescence, genetic modification with p53 isoforms could be a promising strategy to circumvent tumor-mediated T cell dysfunction and represents a novel approach with high potential for cancer immunotherapy. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: The combination of reduced-intensity conditioning (RIC) with in vivo T-cell depletion by alemtuzumab prior to hematopoietic stem cell transplantation (HSCT) has demonstrated efficient engraftment and reduced graft-versus-host disease (GVHD). However, this regimen is associated with slow lymphocyte recovery leading to a delayed anti-infectious and anti-malignant immunity. DLI can be used to improve immune reconstitution. Here we investigate on the impact of different DLI: prophylactic CD8-depleted DLI vs preemptive non-depleted DLI. Methods: 256 patients with different hematologic malignancies were planned for treatment with DLI after allogeneic HSCT following reduced intensity conditioning (Fludarabin, Melphalan, in vivo Alemtuzumab). All patients received PBSC. Donors were HLA-identical siblings or HLA-matched unrelated donors. The calcineurin-inhibitor used for GVHD-prophylaxis (Cyclospron A) was intended to be tapered until day 50. 134 patients should receive CD8deplDLI prophylactically after day +60 (Group A). 122 patients were planned for non-depleted DLI after day +100 in a preemptive setting. Trigger for preemptive DLI were mixed donor chimerism or MRD positivity. Both groups received DLI in escalating doses with an interval of 60 to 90 days. DLI application was stopped when GVHD occurred (Group A and B), or a full donor chimerism was achieved / MRD became negative (Group B). Both patient-groups did not differ in median age. The majority of patients either suffered from an acute leukemia / MDS (n=42%), lymphoma (n=28%), myeloma (n=17%), or myeloproliferative neoplasms (n=12%) and these diseases were equally distributed among the groups. All patients were treated at the university medical center in Mainz, Germany. Results: Of 134 patients (Group A) 41% received CD8deplDLI prophylactically (GVHD was the main cause for withholding DLI). In group B, 32% of 122 patients received preemptive non-depleted DLI. 2 Year-Overall survival (OS) significantly increased in all patients (both groups) after DLI (74% with DLI, 37% without DLI, p