Both mesenchymal stem cells (MSCs) and their corresponding small extracellular vesicles (sEVs, commonly referred to as exosomes) share similar immunomodulatory properties that are potentially beneficial for the treatment of acute graft versus host disease (aGvHD). We report that clinical grade Wharton's Jelly‐derived MSCs (WJMSCs) secrete sEVs enriched in programmed death‐ligand 1 (PD‐L1), an essential ligand for an inhibitory immune checkpoint. A rapid increase in circulating sEV‐associated PD‐L1 was observed in patients with aGvHD and was directly associated with the infusion time of clinical grade WJMSCs. In addition, in vitro inhibitory antibody mediated blocking of sEV‐associated PD‐L1 restored T cell activation (TCA), suggesting a functional inhibitory role of sEVs‐PD‐L1. PD‐L1‐deficient sEVs isolated from WJMSCs following CRISPR‐Cas9 gene editing fail to inhibit TCA. Furthermore, we found that PD‐L1 is essential for WJMSC‐derived sEVs to modulate T cell receptors (TCRs). Our study reveals an important mechanism by which therapeutic WJMSCs modulate TCR‐mediated TCA through sEVs or sEV‐carried immune checkpoints. In addition, our clinical data suggest that sEV‐associated PD‐L1 may be not only useful in predicting the outcomes from WJMSC clinical administration, but also in developing cell‐independent therapy for aGvHD patients.

Autologous stem cell transplant (ASCT) is an effective treatment for multiple myeloma (MM). However the timing of ASCT in the era of novel agents (lenalidomide, thalidomide, bortezomib) is unknown. We retrospectively reviewed the outcome of MM patients who received novel agent based induction treatment and received first ASCT within 12 months of diagnosis (early ASCT, N = 102), or at a later date (late ASCT, N = 65). Median time to ASCT was 7.9 months vs. 17.7 months in the early vs. late ASCT. The 3 and 5 yr overall Survival (OS) from diagnosis was 90 and 63% versus 82 and 63% in early and late ASCT respectively (P=0.45). Forty-one and 36 patients in the early and late ASCT have relapsed or progressed with median time to relapse of 28 and 23 mos (p=0.055). On multivariable analysis, factors predictive of increased risk for progression were ISS stage III (p=0.007), and < VGPR post-ASCT (p<0.001). Factor predictive of worst outcomes for OS was being on hemodialysis (p=0.037). No superiority of one agent was seen. In summary, early or late ASCT is a viable option for MM patients receiving induction treatment with novel targeted therapies.

Background Because of their well-described immunosuppressive properties, allogeneic adult human mesenchymal stromal cells (MSC) derived from bone marrow have demonstrated safety and efficacy in steroid refractory acute graft versus host disease (SR aGVHD). Clinical trials have resulted in variable success and an optimal source of MSC has yet to be defined. Based on the importance of maternal-fetal interface immune tolerance, extraembryonic fetal tissues, such as the umbilical cord, may provide an superior tissue source of MSC to mediate immunomodulation in aGVHD. Methods A two-dose cohort trial allogeneic Wharton's Jelly-derived mesenchymal stromal cells (WJMSC, referred to as MSCTC-0010, here) were tested in 10 patients with de novo high risk (HR) or SR aGVHD post allogeneic hematopoietic stem cell transplantation (allo-HCT). Following Good Manufacturing Practices isolation, expansion and cryostorage, WJMSC were thawed and administered via intravenous infusions on days 0 and 7 at one of two doses (low dose cohort, 2 × 10 6 /kg, n = 5; high dose cohort, 10 × 10 6 /kg, n = 5). To evaluate safety, patients were monitored for infusion related toxicity, Treatment Related Adverse Events (TRAE) til day 42, or ectopic tissue formation at day 90. Clinical responses were monitored at time points up to 180 days post infusion. Serum biomarkers ST2 and REG3α were acquired 1 day prior to first MSCTC-0010 infusion and on day 14. Results Safety was indicated, e.g., no infusion-related toxicity, no development of TRAE, nor ectopic tissue formation in either low or high dose cohort was observed. Clinical response was suggested at day 28: the overall response rate (ORR) was 70%, 4 of 10 patients had a complete response (CR) and 3 had a partial response (PR). By study day 90, the addition of escalated immunosuppressive therapy was necessary in 2 of 9 surviving patients. Day 100 and 180 post infusion survival was 90% and 60%, respectively. Serum biomarker REG3α decreased, particularly in the high dose cohort, and with REG3α decrease correlated with clinical response. Conclusions Treatment of patients with de novo HR or SR aGVHD with low or high dose MSCTC-0010 was safe: the infusion was well-tolerated, and no TRAEs or ectopic tissue formation was observed. A clinical improvement was seen in about 70% patients, with 4 of 10 showing a complete response that may have been attributable to MSCTC-0010 infusions. These observations indicate safety of two different doses of MSCTC-0010, and suggest that the 10 × 10 6 cells/ kg dose be tested in an expanded randomized, controlled Phase 2 trial.

Although recent observations implicate the importance of telomerase activity in acute myeloid leukaemia (AML), the roles of epigenetic regulations of the TERT gene in leukaemogenesis, drug resistance and clinical prognosis in AML are not fully understood. We developed a quantitative pyrosequencing-based methylation assay covering the TERT proximal promoter and a partial exon 1 (hTERTpro/Ex1) region and tested both cell lines and primary leukaemia cells derived from AML and AML with preceding myelodysplastic syndrome (AML/MDS) patients (n = 43). Prognostic impact of methylation status of the upstream TERT promoter region was assessed by the Kaplan-Meier method. The activity of the telomerase inhibitor, imetelstat, was measured using leukaemia cell lines. The TERTpro/Ex1 region was highly methylated in all cell lines and primary leukaemia cells showed diverse methylation profiles. Most cases showed hypermethylated regions at the upstream TERTpro/Ex1 region that were associated with inferior patient survival. TERTpro/Ex1 methylation status was correlated with the cytotoxicity to imetelstat and its combination with hypomethylating agent enhanced the cytotoxicity of imetelstat. AML cell lines and primary blasts harbour distinct TERTpro/Ex1 methylation profiles that could serve as a prognostic biomarker of AML. However, validation in a large cohort of patients is necessary to confirm our findings.

After more than a decade of preclinical and clinical development, therapeutic infusion of mesenchymal stromal cells is now a leading investigational strategy for the treatment of acute graft-versus-host disease (GVHD). While their clinical use continues to expand, it is still unknown which of their immunomodulatory properties contributes most to their therapeutic activity. Herein we describe the proposed mechanisms, focusing on the inhibitory activity of mesenchymal stromal cells (MSCs) at immunologic checkpoints. A deeper understanding of the mechanism of action will allow us to design more effective treatment strategies.

3564 Background: Autologous stem cell transplant (ASCT) with high-dose therapy (HDT) is an effective treatment modality for multiple myeloma (MM). MM is the leading indication for ASCT in North America. It was shown in a recent meta-analysis that a strategy of using ASCT early in the course of myeloma improves progression free survival (PFS) and quality of life. However, this study addressed only patients who had received conventional chemotherapy. Over the last decade, novel agents (thalidomide, bortezomib, and lenalidomide) have replaced conventional chemotherapy for induction in myeloma. These agents have demonstrated superior response rates when compared to conventional chemotherapy, and there is some indication that using novel therapies for induction before ASCT improves the duration of response and overall survival (OS). However, the question of whether early ASCT is the best strategy in the era of novel agents remains unanswered. We performed a retrospective analysis in order to compare the outcomes of patients with newly diagnosed MM treated with novel agents who received an early versus late ASCT. Methods: 179 newly diagnosed MM patients were treated or referred to The Ohio State University for ASCT between October 2006 and December 2009. All patients in the analysis received either thalidomide, bortezomib, or lenalidomide as part of their induction regimen and went on to receive HDT and ASCT. We compared the outcomes of patients who received ASCT within 12 months of diagnosis (early group, N=134) to those who received ASCT at a later date (late group, N=45). All patients received melphalan 140mg/m2 or 200mg/m2 as preparative regimen. Kaplan-Meier estimates were used to compare PFS and OS. Result: In our sample of 179 subjects there were no statistically significant differences in age, sex, race, performance status, comorbidity index score, disease stage at diagnosis, genetic risk and preparative regimen dose between the two groups. The median time from diagnosis to transplant was 7.2 months in the early group (N=134) and 17.7 months in the late group (N=45). In the early group, 81% of patients had received one line of treatment before transplant vs. 49% in the late group (p < 0.001). The overall response rate (ORR) prior to transplant was 90% (9% complete (CR), 31% very good (VGPR), 45% partial (PR)) in the early group, and 83% (9% CR, 22% VGPR, 47% PR) in the late group (p = 0.277). The ORR post transplant was 92% in the early group and 82% in the late group (p = 0.082), with a statistically significant proportion of patients in the early group obtaining CR (52% vs. 27%, p = 0.003). One year non-relapse mortality was 2% for both groups. At a median follow up of 22 months, 36% vs. 47% of patients had progressed (p = 0.29) and 7.5% vs. 24% had died due to disease progression (p = 0.005) in the early vs. late group. Median PFS was 30 months vs. 27 months with 1 year and 3 years PFS of 83% vs. 75% and 64% vs. 55% in the early vs. late group respectively (p = 0.851, Fig. 1). Of patients who had only one therapy pre transplant, results trended toward equivalent PFS in the two groups (p = 0.090), however more than 1 line of therapy and late transplant resulted in a progression hazard ratio of 2.43 (p = 0.050). OS was significantly better in the early group vs. the late group (p = 0.005, Fig. 2). On Cox regression analysis, a late ASCT resulted in a mortality hazard ratio of 3.30. Conclusion: An early ASCT in newly diagnosed MM patients receiving novel agents for induction resulted in an improved OS but not PFS. Patients who are responding well to their first line treatment may have equivalent PFS regardless of time to ASCT. Patients who have had ≥ 2 lines of treatment and underwent ASCT within 12 months had significantly improved PFS compared to those who received ≥ 2 lines of treatment but were transplanted later. Therefore, patients who have not responded to their first line regimen and are within 12 months of diagnosis may have the greatest benefit from ASCT. An extended analysis will be presented at the meeting. A multicenter randomized study comparing early vs. late transplant is underway. Disclosures: Phillips: NCI/NIH: Research Funding; NCCM Grant: Research Funding; ARRA RC2 Grant: Research Funding. Byrd:Genzyme Corporation: Research Funding.

Chronic pulmonary inflammation (CPI) gives rise to serious lung injuries in rheumatoid arthritis (RA) patients. However, the molecular mechanism underlying the pathogenesis of RA-associated CPI remains little understood. Here we established a novel tree shrew-based collagen-induced arthritis (TsCIA) model to study RA-associated CPI. Our results showed that typical CPI but not fibrosis developed pathologically in the TsCIA model. Furthermore, abnormal up-regulation of pulmonary chemokine CXCL10 was directly associated with lung damage. Specific blockage of CXCR3 (a CXCL10 receptor) significantly decreased the severity of CPI by decreasing the recruitment of inflammatory cells. Therefore, CXCL10 is proposed as a key player responsible for the development of TsCIA-associated CPI. Our findings also suggest that CXCR3 could be developed as a potential diagnosis biomarker for RA-associated CPI.

p97 is an ATPase that works in concert with histone deacetylase 6 (HDAC6), to facilitate the degradation of misfolded proteins by autophagosomes. p97 has also been implicated in DNA repair and maintaining genomic stability. In this study we determined the effect of combined inhibition of p97 and HDAC6 activities in mantle cell lymphoma (MCL) cells. We report that treatment with p97 inhibitors induces dose-dependent apoptosis in MCL cells. The p97 inhibitor CB-5083 induces ER stress markers GRP78 and CHOP and results in the accumulation of polyubiquitylated proteins. Co-treatment with CB-5083 and the HDAC6 inhibitor ACY-1215 result in marked downregulation of CDK4, Cyclin D1 and BRCA1 levels without inhibiting autophagic flux. Consequently, treatment with CB-5083 accentuates DNA damage in response to treatment with ACY-1215 resulting in enhanced accumulation of H2AX-γ and synergistic apoptosis. Furthermore, ATM loss severely impairs phosphorylation of 53BP1 following co-treatment with CB-5083 and ACY-1215 in response to gamma irradiation. Finally, co-treatment CB-5083 and ACY-1215 results in reduced tumor volumes and improves survival in Z138C and Jeko-1 xenografts in NSG mice. These observations suggest that combined inhibition of p97 and HDAC6 abrogates resolution of proteotoxic stress and impairs DNA repair mechanisms in MCL cells.