Abstract: Background: Distinct from broadly acting graft-versus-host disease (GVHD) prophylaxis, JAK2 inhibition suppresses alloreactive T cells, while sparing regulatory T cells (Tregs) and graft-versus-leukemia (GVL). Early IL-6 activity via JAK2 and phosphorylated STAT3 in CD4+ T cells is associated with acute GVHD onset. In mice, we show combined JAK2/mTOR blockade synergistically prevents xenogeneic GVHD. In this first-in-human phase I/II GVHD prevention trial we combine pacritinib, a JAK2 inhibitor, with sirolimus to concurrently reduce T-cell costimulation via mTOR and IL-6 activity. With phase I complete, we demonstrate that dual JAK2/mTOR inhibition is safe, suppresses pathogenic Th1 and Th17 cells, spares Tregs and key GVL effector cells, and exhibits preliminary activity in preventing GVHD. The primary aim of phase I was to identify the lowest biologically active dose of pacritinib (defined as & lt; 35% of CD4+ pSTAT3+ T cells at day +21) that is safe when combined with sirolimus-based immune suppression. The preliminary activity of JAK2/mTOR inhibition in GVHD prevention was also investigated. Materials and Methods: This single-arm phase I/II trial (NCT02891603) tested the safety of pacritinib when administered with sirolimus plus low-dose tacrolimus (PAC/SIR/TAC) after allogeneic hematopoietic cell transplantation (alloHCT). A 3+3 dose escalation design was followed, including dose level 1 (PAC 100mg daily), level 2 (PAC 100mg twice daily), and level 3 (PAC 200mg twice daily). Clinical safety, pharmacodynamic assessments, and pharmacokinetic (PK) studies were followed during the study. Acute GVHD was scored through day +100. Patient characteristics are described in Table 1 (n=12). Allowed donor types were HLA-A, -B, -C, and -DRB1 matched-related or unrelated donors. Adequate vital organ function and Karnofsky performance status (KPS ≥ 80%) were required. Results: Dose level 2, PAC 100mg twice a day, was the lowest biologically active and safe dose, and thus the recommended phase II dose. Blood samples acquired at day +21 showed that PAC 100mg twice a day reduced the mean frequency and geometric MFI of CD4+ pSTAT3+ T cells (Figure 1A, B). Consistent with suppressed pSTAT3, PAC 100mg twice a day decreased pathogenic Th1 and Th17 cells (Figure 1C, D). pSTAT5 is critical for Tregs and effectors of GVL. PAC 100mg twice a day favored STAT5 phosphorylation in CD4+ T cells, preserved Tregs and increased the ratio of Tregs to pathogenic T helper cells, and supported CD3+ T cell and NK cell effectors (Figure 1E-J). Patients treated on dose level 2 of PAC exhibited a robust increase in Th2 cells at day +21 (29.5% v 4.87% level 1 or 4.5% baseline, P & lt;0.001 ANOVA). Additionally, neutrophil and platelet engraftment occurred without delay (Figure 1K, L). A single dose limiting toxicity was observed in dose level I only, and consisted of angioedema possibly related to PAC. CMV reactivation or disease were not observed among patients treated at dose level 2, with only a single case of CMV reactivation among dose level 1 (8 of 12 recipients were CMV seropositive). A single patient treated on dose level 2 developed grade 4 acute GVHD and died, after prematurely discontinuing TAC for acute kidney injury and electively stopping PAC. A patient died of relapsed disease in dose level 1. To test the efficacy of dual JAK2/mTOR inhibition in vivo, NSG mice were transplanted with human peripheral blood mononuclear cells (PBMCs) and treated with either vehicle, PAC, STAT3 inhibitor S3I-201, SIR, PAC/SIR, or S3I/SIR. The combination of JAK2 or downstream STAT3 inhibition plus SIR significantly reduced xenogeneic GVHD in mice (Figure 1M) and maintained donor anti-tumor activity by CD8+ T cells (data not shown). Further, dual JAK2 or STAT3 inhibition with mTOR blockade significantly increased the induction of Tregs in mice transplanted with Treg-depleted human PBMCs (62.3% PAC/SIR or 74% S3I/SIR v 29.9-38% with vehicle or inhibitors alone, P & lt;0.01 ANOVA). Conclusions: We demonstrate that PAC/SIR/TAC (RP2D: PAC 100mg twice a day) is safe and effectively reduces IL-6 signal transduction, pathogenic Th1 and Th17 cells, and preserves Tregs and effectors necessary for GVL and antiviral immunity. Preliminarily, adding pacritinib limits acute GVHD, preserves donor CMV immunity, and permits timely engraftment. The efficacy of PAC/SIR/TAC will be tested in our ongoing phase II GVHD prevention trial. Disclosures Pidala: Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Takeda: Research Funding; Janssen: Research Funding; Johnson and Johnson: Research Funding; Pharmacyclics: Research Funding; Abbvie: Research Funding; BMS: Research Funding. Bejanyan:Kiadis Pharma: Membership on an entity's Board of Directors or advisory committees. Nishihori:Karyopharm: Other: Research support to institution; Novartis: Other: Research support to institution. Lawrence:Patent Pending: Patents & Royalties: Dr. Lawrence has a patent WO2014070859A1: Stat3 dimerization inhibitors. . Lawrence:Patent Pending: Patents & Royalties: Dr. Lawrence has a patent WO2014070859A1: Stat3 dimerization inhibitors. . Sebti:Patent Pending: Patents & Royalties: Dr. Sebti has a patent WO2014070859A1: Stat3 dimerization inhibitors. . Betts:Patent Pending: Patents & Royalties: Dr. Betts has a pending patent WO2017058950A1: Methods of treating transplant rejection. This includes the use of JAK inhibitors. Neither he nor his institution have received payment related to claims described in the patent.. OffLabel Disclosure: Pacritinib and its use in GVHD prevention as part of a phase I trial

Abstract: Peripheral blood stem cell (PBSC) as a graft source compared to bone marrow has been reported to result in lower risk of relapse after haploidentical hematopoietic cell transplantation (haplo-HCT) with use of post-transplant cyclophosphamide (PTCy) as a graft-versus-host-disease (GvHD) prophylaxis. However, cytokine release syndrome (CRS) is a common complication of this platform that can affect the outcomes of patients after PBSC haplo-HCT. CRS occurs due to rapid activation and proliferation of alloreactive donor T cells resulting in the elevated secretion of inflammatory cytokines. In this study, we sought to examine the risk factors for CRS and the effect of CRS severity on outcomes of PBSC haplo-HCT. We identified total of 271 consecutive patients with hematological malignancies who received their first PBSC haplo-HCT with PTCy-based GVHD prophylaxis at City of Hope (n=157) or Moffitt (n=114) Cancer Centers between 2014 and 2019. The median patient age at HCT was 54 years (INQ range, 37-64) for the entire cohort and 48% of the patients had HCT-CI ³3. Close to 70% of the study cohort had acute leukemia and 33% of all patients had high/very high-risk disease risk index. Myeloablative conditioning was used in 52% of the cases and 81% of all HCT recipients were CMV seropositive. The median donor age at HCT was 33 years (INQ range, 26-43). The HLA -A, -B, -C, -DRB1, -DQB1, or -DPB1 mismatch between the recipient and the donor in the GVH direction was 5/10 in 51%, 4/10 in 29% and £3/10 in 20% of cases. Offspring donors were used in 54% of the patients, sibling donors in 35%, and parent/other relative donors in 11%. Female donors to male recipients were used in only 22% of patients. The median infused CD34 dose was 5.25 x106 cells/kg (range, 2.3-22.4x106) and the CD3 dose was 2.48x108 cells/kg (range, 0.002-8.88 x108). CRS of any grade by ASTCT criteria was observed in 92% of study patients within first 7 days of HCT: 54% had grade 1, 39% grade 2, and 5.2% grade 3-4. Infused cell doses of CD34 & gt;5x106 cells/kg and of CD3 & gt;2.5x108 cells/kg had no significant effect on grade 3-4 CRS. On multivariable analysis, the use of reduced-intensity conditioning (RIC) was associated with increased grade 2-4 CRS (HR = 1.6, 95% CI: 1.11.-2.33, p=0.01) and grade 3-4 CRS (HR = 14.7, 95% CI: 1.97-109.5, p=0.009) compared with the myeloablative conditioning. Donor 5/10 HLA-mismatch was also associated with increased grade 2-4 CRS (HR = 1.5, 95% CI: 1.05-2.18; p=0.03) and grade 3-4 CRS (HR = 3.50, 95% CI: 1.00-12.32; p=0.05) compared with £4/10 HLA-mismatch. Non-relapse mortality (NRM) at day 100, and 1-year overall survival (OS) by CRS severity is shown in Figure. Comparing with the grade 0-1 CRS in multivariable analysis (Table), increase in CRS severity was associated with lower probability of neutrophil engraftment (HR = 0.9 for grade 2 and HR = 0.4 for grade 3-4; p=0.03). Increased CRS severity as compared to the grade 0-1 was also predictive of higher risks of NRM (HR = 1.6, 95% CI: 0.95-2.79 for grade 2 and HR = 6.6, 95% CI: 3.12-13.78 for grade 3-4; p & lt;0.001), lower disease-free survival (DFS; HR = 1.3 for grade 2 and HR = 4.5 for grade 3-4; p & lt;0.001) and lower OS (HR = 1.2 for grade 2 and HR = 4.1 for grade 3-4; p & lt;0.001) after HCT. We observed no association between CRS severity and risk of relapse or the incidence and severity of acute GvHD after transplant. We conclude that CRS is a common complication after PB haplo-HCT/PTCy. CRS severity is associated with post-HCT outcomes with grade 3-4 CRS associated with the highest risk of NRM and overall mortality after HCT. Infused CD34 or CD3 cell doses effect on CRS is unclear. RIC and higher degree of HLA-mismatch are predictive of higher-grade CRS. Identification of modifiable risk factors can help to mitigate the risk for serious CRS and subsequent mortality after PB haplo-HCT/PTCy. Figure 1 Disclosures Nishihori: Karyopharm: Other: Research support to institution; Novartis: Other: Research support to institution. Pidala:CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Takeda: Research Funding; Janssen: Research Funding; Johnson and Johnson: Research Funding; Pharmacyclics: Research Funding; Abbvie: Research Funding; BMS: Research Funding; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees. Nakamura:Merck: Other: advisory board meeting; Alexion: Other: Support on a meeting presentation; Kyowa-Kirin: Other: Support on a meeting presentation; Celgene: Other: Support on seminar; Magenta Therapeutics: Other: Advisory board meeting; Viracor: Consultancy; Kadmon Corporation: Other: Advisory board meeting; NapaJen Pharma: Consultancy. Al Malki:Rigel Pharma: Consultancy; Jazz Pharmacuticals, Inc: Consultancy; Neximmune: Consultancy. Bejanyan:Kiadis Pharma: Membership on an entity's Board of Directors or advisory committees.

Abstract: BACKGROUND: Outcomes of patients with acute promyelocytic leukemia (APL) have improved; however, a number of patients, particularly those with high-risk APL, still relapse despite all-trans-retinoic acid (ATRA) and arsenic-based therapies. We present single institution outcomes of autologous (auto) and allogenic (allo) hematopoietic cell transplantation (HCT) in patients with relapsed APL. PATIENTS AND METHODS: We retrospectively reviewed outcomes in patients with relapsed APL who underwent either auto- or allo- HCT at Moffitt Cancer Center from 1990 to 2018 utilizing the clinical data obtained from BMT Research & Analysis Information Network (BRAIN). Survival data were analyzed using Kaplan-Meier estimates. RESULTS: Autologous HCT Cohort: A total of 15 received auto-HCT with a median age at HCT of 39 (range, 21-60) years. Disease status at HCT were first complete remission (CR1) in 5 (33%) and CR2 in 10 (67%). Majority of patients (13/15, 87%) received busulfan/cyclophosphamide (Bu/Cy) conditioning and remaining (2/15, 13%) Bu/Cy/etoposide. All (n=15) patients received peripheral blood (PB) stem cell grafts. Median time to neutrophil engraftment was 11 (range, 10-14) days and platelet recovery was 14 (range 9-44) days. The median progression-free survival (PFS) for auto HCT was 12.9 (95% confidence interval (CI): 1.2-24.8) months. With a median follow up of 45.1 months for surviving patients, overall survival (OS) for auto HCT was 12.9 (95%CI: 0-27.8) years. At the time analysis, 8 patients were relapse-free. Allogeneic HCT Cohort: A total of 10 patients received allo HCT with a median age of 46 (range, 22-56) years at HCT. Disease status at allo HCT was CR2 in 2, CR3 in 6, and two had refractory disease. Two patients had prior auto HCT. Donor type was HLA-identical sibling=5; one antigen-mismatched sibling=1; HLA-matched unrelated donor=3; related haploidentical=1. Seven patients received peripheral blood graft and 3 received bone marrow graft. Conditioning regimen intensity was myeloablative in 7 (fludarabine/busulfan +/- anti-thymocyte globulin=3; Bu/Cy=3; cyclophosphamide/total body irradiation=1), and reduced intensity in 3 (fludarabine/melphalan=2; fludarabine/cyclophosphamide/total body irradiation=1). Seven patients received tacrolimus-based graft-versus-host disease (GVHD) prophylaxis. Median time of neutrophil engraftment was 15 (range, 12-22) days, and platelet engraftment was 22 (range, 15-28) days. The median PFS for allo HCT was 11.9 (95%CI: 2.1-21.6) months. With a median follow up of 48.2 months for surviving patients, median OS for allo HCT was 12.4 (95%CI: 4.8-19.9) months. At the time of analysis 4 patients were relapse-free. CONCLUSIONS: In our single center analysis, auto HCT for APL resulted in a durable remission and prolonged survival. Outcomes after allo HCT were suboptimal primarily due to their heavily pretreated condition and chemotherapy resistant disease. Further research on novel conditioning regimen and relapse prevention is needed to improve the outcomes of allo HCT in APL. Figure Disclosures Lancet: Jazz Pharmaceuticals: Consultancy; Agios Pharmaceuticals: Consultancy; Daiichi-Sankyo: Consultancy; Pfizer: Consultancy. Sweet:Pfizer: Consultancy; Celgene: Speakers Bureau; Jazz: Speakers Bureau; Incyte: Research Funding; Stemline: Consultancy; Astellas: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Komrokji:JAZZ: Speakers Bureau; Novartis: Speakers Bureau; Agios: Consultancy; JAZZ: Consultancy; Incyte: Consultancy; pfizer: Consultancy; DSI: Consultancy; celgene: Consultancy. Bejanyan:Kiadis Pharma: Other: advisory board. List:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Nishihori:Novartis: Research Funding; Karyopharm: Research Funding.

Abstract: The introduction of posttransplant cyclophosphamide (PTCy) made performing allogeneic hematopoietic cell transplantation (HCT) from HLA haplotype–incompatible donors possible. In a setting of PTCy and tacrolimus/mycophenolate mofetil (MMF) as a graft-versus-host disease (GVHD) prophylaxis, a peripheral blood (PB) graft source as compared with bone marrow reduces the relapse rate but increases acute GVHD (aGVHD) and chronic GVHD (cGVHD). This phase 2 trial assessed sirolimus and MMF efficacy following PTCy as a GVHD prophylaxis after PB haploidentical HCT (haplo-HCT). With 32 evaluable patients (≥18 years) enrolled, this study had 90% power to demonstrate a reduction in 100-day grade II-IV aGVHD to 20% from the historical benchmark of 40% after haplo-HCT using PTCy/tacrolimus/MMF. At a median follow-up of 16.1 months, the primary end point of the trial was met with a day-100 grade II-IV aGVHD cumulative incidence of 18.8% (95% confidence interval [CI], 7.5% to 34.0%). There were no graft-failure events and the 1-year probability of National Institutes of Health (NIH) moderate/severe cGVHD was 18.8% (95% CI, 7.4% to 34.0%), nonrelapse mortality was 18.8% (95% CI, 7.4% to 34.0%), relapse was 22.2% (95% CI, 9.6% to 38.2%), disease-free survival was 59.0% (95% CI, 44.1% to 79.0%), GVHD-free relapse-free survival was 49.6% (95% CI, 34.9% to 70.5%), and overall survival was 71.7% (95% CI, 57.7% to 89.2%) for the entire cohort. These data demonstrate that GVHD prophylaxis with sirolimus/MMF following PTCy effectively prevents grade II-IV aGVHD after PB haplo-HCT, warranting prospective comparison of sirolimus vs tacrolimus in combination with MMF following PTCy as GVHD prophylaxis after PB HCT. This trial was registered at www.clinicaltrials.gov as #NCT03018223.