ALBERT

Description: Abstract 2537 Introduction: Regulatory T cells (Tregs) have been shown to mitigate graft-versus-host disease (GvHD) while preserving the beneficial graft-versus-leukemia (GvL) effect in animal models of allogeneic bone marrow transplantation (BMT). However, three major obstacles prevent their use in human clinical trials: the low numbers of Tregs, loss of suppressor activity following in vitro expansion, and the lack of Treg-specific markers to purify expanded Tregs. The locus of the Foxp3 gene, the master regulator of Tregs, is unmethylated and expressed only in Tregs. We have recently reported that the hypomethylating agent azacitidine (AzaC) induces FOXP3 expression in non-Tregs, converting them into Tregs in vitro and in vivo when administered after allogeneic BMT completely mitigating GvHD without abrogating GvL (Choi, et al Blood 2010). Three possible mechanisms for these effects include: 1) AzaC induces FOXP3+ Tregs, which in turn mitigate GvHD without abrogating GvL by regulating alloreactive donor T cells, 2) AzaC directly suppresses the proliferation of alloreactive donor T cells reducing GvHD, 3) AzaC alters donor T cell trafficking to GvHD target organs to prevent GvHD without altering interaction of donor T cells with recipient leukemia or trafficking of leukemic cells. Methods: Balb/c (CD45.2+, H-2Kd) were lethally irradiated one day prior to injection of T cell-depleted BM cells isolated from B6 (CD45.1+, H-2Kb) and luciferase-expressing A20 leukemia cells derived from Balb/c. Allogeneic donor T cells isolated from B6 (CD45.2+, H-2Kb) were given 11 days after BMT. AzaC (2 mg/kg) was administrated subcutaneously every other day (4 doses total) starting 4 days after T cell injection. In vivo bioluminescence imaging (BLI) was performed to assess leukemia cell localization. For T cell proliferation/trafficking analyses, Balb/c were lethally irradiated one day prior to injection of T cell-depleted BM cells isolated from B6 (CD45.1+). Allogeneic donor T cells isolated from B6 (CD45.2+) were transduced with Click Beetle Red luciferase and were given 11 days after BMT, followed by AzaC treatment as described above. BLI was performed to track the donor T cells. Results: While neither T cell or leukemia cell trafficking was affected by the AzaC treatment, proliferation of donor T cells was significantly reduced compared to mice treated with PBS. The observed reduced T cell proliferation is not likely due to the direct effect of AzaC on T cells since the AzaC treatment preserved GvL activity comparable with the PBS control group. In addition, T cells isolated from both AzaC and PBS groups were equally reactive against third party antigen presenting cells, based on mixed lymphocyte reactions and cytotoxic T lymphocyte killing assays. These data along with our previous report demonstrating that the AzaC treatment increases Tregs in vivo strongly suggest that the therapeutic effect of AzaC on GvHD and GvL are mediated by the AzaC-induced Tregs which preferentially target alloreactive T cells while preferentially sparing anti-tumor T cells. Currently, secondary transplantation of Treg-depleted/replete T cells isolated from AzaC/PBS-treated recipient mice is underway to further confirm that donor T cells in the AzaC-treated mice are fully functional and that alloresponses of donor T cells are regulated by AzaC-induced Tregs. Conclusions: In vivo administration of AzaC after donor T cell infusion mitigates GvHD while preserving GvL via peripheral conversion of alloreactive donor T cells to FOXP3+ Tregs that preferentially inhibit alloreactive T cells while sparing anti-tumor T cells. These data provides the foundation for future clinical trials using epigenetic therapy aimed at mitigating GvHD without abrogating GvL and overcoming HLA barriers. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 2906 Background: Multiple myeloma (MM), a hematological malignancy of terminally differentiated plasma cells, is closely associated with osteolytic bone disease, caused by increased osteoclast (OC) number and resorption and suppressed osteoblast (OB) differentiation and function. Proteasome inhibitors (PIs), such as bortezomib, have become a cornerstone therapy for MM, potently reducing tumor burden and inhibiting pathologic bone destruction. In clinical trials, carfilzomib, a second generation epoxyketone-based PI, has exhibited potent anti-myeloma efficacy and decreased side effects compared to bortezomib. ONX 0912 is an orally bioavailable analog of carfilzomib. However, it is currently not known whether carfilzomib and ONX 0912, in addition to their anti-myeloma activity, may have a beneficial effect on myeloma-associated bone disease similarly to bortezomib. Here, we have conducted in vitro studies to evaluate the ability of each PI to promote osteogenic differentiation and function and to inhibit OC formation and resorption in murine and human cells. We have also studied the effects of orally administered ONX 0912 in both non-myelomatous mice and mice bearing bone marrow (BM) disseminated human myeloma. Patient samples, material and methods: The human MM cell lines MM.1S, U266 and RPMI-8226 were employed. Mesenchymal stem cells from BM samples of healthy donors, MM patients and mice were used for OB studies, whereas PBMCs from healthy volunteers and murine BM macrophages were used to generate OCs. Viability, proliferation and apoptosis were respectively assessed by MTT assay, BrdU incorporation and Annexin V/7-AAD staining. OB differentiation and function were investigated by alkaline phosphatase activity, quantitative mineralization assay and real-time quantitative RT-PCR. Osteoclastogenesis was assessed by enumeration of mutinucleated (≥3) tartrate resistant acid phosphatase-positive cells, whereas OC resorption was assessed on calcium-coated slides. Immunoflurescence analyses and flow cytometry were used to further evaluate OC function. Micro-CT analysis of myelomatous and non-myelomatous bone, bioluminescence imaging of tumor burden, calcein labeling and determination of serum levels of Igλ, CTX and P1NP were used in in vivo models. Results: Carfilzomib and ONX 0912 effectively decreased MM cell viability in vitro following continual or physiologic brief pulse treatment. These PIs were also able to overcome the growth advantage conferred by co-culture with human BM stromal cells or OCs. During their differentiation from mesenchymal stem cell precursors of mice and myeloma patients, physiologic concentrations of carfilzomib and ONX 0912 stimulated osteogenic differentiation and matrix mineralization and enhanced OB activity. In a similar manner, carfilzomib and ONX 0912 inhibited osteoclastogenesis from mouse and human progenitors and inhibited OC resorption. Importantly, the effects of these new PIs were exerted without being cytotoxic to OC/OB precursors. Daily oral administration of ONX 0912 to non-tumor bearing mice increased trabecular bone volume and enhanced bone formation. Finally, in a mouse model of disseminated human MM, ONX 0912 decreased human RPMI-8226 tumor burden and prevented bone loss, with serum markers evidencing both bone anti-catabolic and anabolic effects. Conclusion: In vitro and at physiologic concentrations and dosing, carfilzomib and ONX 0912 not only exert cytotoxic effects on myeloma cells, but also directly enhance OB formation and function and inhibit OC differentiation and resorption. In a disseminated human MM mouse model, orally administered ONX 0912 showed anti-resorptive and bone-anabolic effects in addition to its anti-tumor properties. Our data demonstrate that carfilzomib and ONX 0912 exert combined beneficial effects of anti-myeloma activity and on associated-myeloma bone disease, with favorable pharmacologic and tolerability profiles being reported in patients. This work was supported by funding from the Spanish MICINN-ISCIII (PI081825), Fundación de Investigación Médica Mutua Madrileña 2008, Centro en Red de Medicina Regenerativa y Terapia Celular de Castilla y León, the National Institutes of Health (T32CA113275; P01CA100730; P50CA94056), the St. Louis Mens' Group Against Cancer, and the Holway Myeloma Fund. Disclosures: Kirk: Onyx Pharmaceuticals: Employment. San Miguel:Onyx Pharmaceuticals: Consultancy.

Description: Abstract 455 Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative treatment for patients with relapsed/refractory leukemia, and marrow failure states such as myelodysplasia and aplastic anemia. However, allo-HSCT is complicated by allogeneic donor T cell-mediated graft-versus-host disease (GvHD) which can be life-threatening especially in recipients of unrelated or HLA-mismatched hematopoietic stem cell products. These same alloreactive donor T cells also mediate a beneficial graft-versus-leukemia (GvL) effect. Thus, the clinical goal in allo-HSCT is to minimize GvHD while maintaining GvL. Recent studies have suggested that this might be achieved by infusing regulatory T cells (Tregs) which in some preclinical models suppress GvHD-causing alloreactive donor T cells but have only limited effects on GvL-promoting alloreactive donor T cells. Unfortunately, Tregs exist in low frequency in the peripheral blood, are costly to purify and expand, and after expansion are difficult to isolate due to the lack of cell surface markers, all of which prevent their routine use in the clinic. Thus, alternative therapeutic approaches that do not require Tregs are needed. We have found that interferon gamma receptor deficient (IFNγR−/−) allogeneic donor T cells induce significantly less GvHD in both a MHC fully-mismatched (B6 (H-2b) → Balb/c (H-2d)) and a minor-mismatched (B6 (H-2b) → B6×129(H-2b)) allo-HSCT models compared to WT T cells. In addition, IFNγR−/− donor T cells maintain a beneficial GvL effect, which has been examined in both systemic leukemia and solid tumor models using luciferase-expressing A20 cells derived from Balb/c. We find that IFNγR−/− T cells migrate primarily to the spleen while WT T cells to GI tract and peripheral lymph nodes (LNs) using bioluminescence imaging (BLI), suggesting that altered T cell trafficking of IFNγR−/− T cells to GvHD target organs might be the major reason for the reduced GvHD. We further demonstrate that the IFNγR-mediated signaling in alloreactive donor T cells is required for expression of CXCR3 which has been implicated in trafficking of T cells to areas of inflammation and target organs, commonly known to be the sites of GvHD. Indeed, CXCR3−/− T cells recapitulate the reduced GvHD potential of IFNγR−/− T cells. In addition, forced overexpression of CXCR3 in IFNγR−/− T cells via retroviral transduction partially rescues the GvHD defect observed in IFNγR−/− T cells. We next examine if inhibition of IFNγR signaling using a small molecule inhibitor can recapitulate the anti-GVHD effects seen in IFNγR−/− T cells. We find that INCB018424, an inhibitor of JAK1/JAK2 which are the mediators of IFNγR signaling, blocks CXCR3 expression in vitro. Most importantly, in vivo administration of INCB018424 after allo-HSCT alters T cell trafficking and significantly reduces GvHD. Thus, the IFNγR signaling pathway represents a promising therapeutic target for future efforts to mitigate GvHD while maintaining GvL after allo-HSCT. Moreover, this pathway can be exploited in other diseases besides GvHD such as those from organ transplantation, chronic inflammatory diseases and autoimmune diseases. Disclosures: DiPersio: genzyme: Honoraria.

Description: Abstract 2971 Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative treatment for patients with relapsed/refractory leukemia, and marrow failure states such as myelodysplasia and aplastic anemia. However, allo-HSCT is complicated by allogeneic donor T cell-mediated graft-versus-host disease (GvHD) which can be life-threatening especially in recipients of unrelated or HLA-mismatched hematopoietic stem cell products. These same alloreactive donor T cells also mediate a beneficial graft-versus-leukemia (GvL) effect. Thus, the clinical goal in allo-HSCT is to minimize GvHD while maintaining GvL. Recent studies have suggested that this might be achieved by infusing regulatory T cells (Tregs) which in some preclinical models suppress GvHD-causing alloreactive donor T cells but have only limited effects on GvL-promoting alloreactive donor T cells. Unfortunately, Tregs exist in low frequency in the peripheral blood, are costly to purify and expand, and after expansion are difficult to isolate due to the lack of cell surface markers, all of which prevent their routine use in the clinic. Thus, alternative therapeutic approaches that do not require Tregs are needed. Using a MHC-mismatched GvHD model, B6 (H-2b) → Balb/c (H-2d), we demonstrated that infusion of IFN γR deficient allogeneic donor T cells induce significantly less GvHD, compared to WT T cells, determined by survival (74% vs. 0 % in overall survival; p =0.0004), weight and percentages of B220+ B cells (12.4% vs. 3.8%; p =0.0205), CD3+ T cells (14.3% vs. 4.3%; p =0.0025) in blood. Of note was that the IFN γR deficient donor T cells maintained a beneficial GvL effect, which was examined in both a systemic leukemia and a solid tumor model using luciferase-expressing A20 cells derived from Balb/c. We found that IFN γR deficient donor T cells responded normally to allogeneic antigens as measured by in vitro mixed lymphocyte reaction analyses, and express similar levels of granzyme B, compared to WT T cells. However, IFN γR deficient T cells trafficked predominantly to the spleen while WT T cells trafficked to gastrointestinal tract and peripheral lymph nodes, which are major GvHD target organs, based on in vivo bioluminescence imaging. All of these findings suggest that the reduced GvHD was not due to reduced function, altered subsets or relative deficiency of allogeneic donor T cells but from modification of in vivo trafficking of IFN γR deficient donor T cells compared to WT T cells. We further demonstrated that the IFN γR-mediated signaling in alloreactive donor T cells was required for expression of CXCR3 which has been implicated in trafficking of T cells to areas of inflammation and target organs, commonly known to be the sites of GvHD. CXCR3−/− T cells demonstrated a reduction in GvHD while maintenance of the same robust GvL effect using the same MHC mismatched transplant model. Thus, the IFN γR-CXCR3 axis represents a promising therapeutic target for future efforts to mitigate GvHD while maintaining GvL after allo-HSCT. Current studies are focused on 1) whether forced expression of CXCR3 rescues the GvHD-inducing potential of IFN γR deficient donor T cells and 2) if inhibition of IFN γR signaling (IFN γR, JAK1 and/or JAK2, CXCR3 and STAT1) using both neutralizing antibodies and small molecule inhibitors can recapitulate the anti-GvHD and pro-GvL effects seen in IFN γR−/− and CXCR3−/− T cells. Disclosures: No relevant conflicts of interest to declare.