Myeloablative Conditioning Regimen Research Articles

An Encouraging Successful Result of Allogeneic Hematopoietic Stem Cell Transplantation in a Boy Both with Juvenile Myelomonocytic Leukemia and Osteogenesis Imperfecta : A Case Report

Background: Juvenile myelomonocytic leukemia (JMML) is a rare hematologic malignancy in young children that is classified as a myelodysplastic/myeloproliferative neoplasm and not only characterized by young age, hepatosplenomegaly, thrombocytopenia and monocytosis, but also by molecular aberrations in the RAS-RAF-MEK-ERK signaling pathway and GM-CSF-hypersensitivity. Most children with JMML experience an aggressive clinical course and the only curative treatment option for these children is stem cell transplantation (SCT). Osteogenesis imperfect (OI) is also an orphan inherited monogenic bone fragility disorder that usually is caused by mutations in one of the two genes coding for collagen type I alpha chains, COL1A1 or COL1A2. A common issue associated with the molecular abnormality is a disturbance in bone matrix synthesis and homeostasis inducing bone fragility. In very early life, this can lead to multiple fractures and progressive bone deformities. Current multidisciplinary management could only improve quality of life for patients, including physical therapy, drug treatment and orthopaedic surgery. Innovative therapies, such as progenitor and mesenchymal stem cell or bone marrow transplantation, targeting the specific altered pathway rather than the symptoms, may develop new curative treatments. Here we report a 3-year-old boy who suffered from both JMML and OI, was successfully transplanted and kept presenting an encouraging outcome up to now. Aims:To investigate the possible efficacy and safety of Allogeneic Hematopoietic Stem Cell Transplantation in a boy both with Juvenile Myelomonocytic Leukemia and Osteogenesis Imperfecta. Methods:A 3-year-old boy presented with fatigue, fever, petechia and rash in Aug 2019, accompanying with loss of appetite, joint pain and severe hepatosplenomegaly. The boy had a special appearance of short stature and blue sclerae, meanwhile he suffered intermittent eczema and bone fracture twice since he was 2 years old. Similar characteristics were also positive in his grandmother, father and father's sister. The blood cell counts revealed anemia, thrombocytopenia and leukocytosis especially monocytosis. Bone marrow aspirate showed excessive proliferation of myelomonocytic cells and hypersensitivity to granulocyte-macrophage colony-stimulating factor in vitro. Somatic mutation of gene NF1, PTPN11 and COL1A1 were identified by Next Generation Sequencing.Therefore, the little boy was diagnosed with two rare diseases of Juvenile Myelomonocytic Leukemia and Osteogenesis Imperfecta at the same time. After 4 courses of hypomethylating agents therapy, the boy underwent haploidentical allogeneic bone marrow stem cell transplantation combined with allogeneic single umbilical cord blood transplant in May 2020. The myeloablative conditioning regimen was composed of Decitabine (20mg/m2/day, days -13 to -9), Cyclophosphamide (25mg/kg/day, days -8 and -7), Busulfan(100mg/m2/day, days -6 to -3), Fludarabine (40mg/m2/day, days -6 to -2) and Cytarabine (100mg/m2/day, days -6 to -2). Post-Cyclophosphamide (50mg/kg/day, days +3 and +4), tacrolimus and mycophenolate mofetil were used for prophylaxis of graft-versus-host disease (GVHD). Results:The number of infused TNCs from haplo-bone marrow and cord blood unit was 41.4×10^8/kg and 9.72×10^7/kg, respectively, while the number of infused CD34+ cells was 11.84×10^6/kg and 2.33×10^5/kg, respectively. The boy achieved sustained engraftment of both neutrophils and platelets at 16 days and 24 days, respectively, with complete haplo-donor chimerism of confirmed at 14 days. He developed grade III acute GVHD (skin, gut and liver) and recovered at 39 days after transplant. Clinical symptoms such as rash, joint pain and hepatosplenomegaly got complete remission, and the mutated genes like NF1, PTPN11 and COL1A1 all disappeared at 30 days. At the time of this report, the boy was alive with negative MRD and good quality of life with a follow-up of 3 months after HCT. Conclusion:To our knowledge, this is the first report that a child both with Juvenile Myelomonocytic Leukemia and Osteogenesis Imperfecta was cured by allogeneic hematopoietic stem cell transplantation.Our experience suggests that allogeneic bone marrow transplantation may be a novel safe and effective therapeutic strategy for OI patients. Disclosures No relevant conflicts of interest to declare.

Results of a Phase 1 Open Label Dose Escalation Trial of AB-205 (Allogeneic Engineered Endothelial Cell Therapy) in Adults with Lymphoma Undergoing High-Dose Therapy and Autologous Hematopoietic Cell Transplantation (HDT-AHCT)

Results of a Phase 1 Open Label Dose Escalation Trial of AB-205 (Allogeneic Engineered Endothelial Cell Therapy) in Adults with Lymphoma Undergoing High-Dose Therapy and Autologous Hematopoietic Cell Transplantation (HDT-AHCT)

Use of Post-Transplant Cyclophosphamide in One-Antigen Mismatched Unrelated Donor Transplantation Results in Similar Transplant Outcomes Than Haploidentical Hransplantation: A Retrospective Study on Behalf of the Acute Leukemia Working Party of the EBMT

Use of Post-Transplant Cyclophosphamide in One-Antigen Mismatched Unrelated Donor Transplantation Results in Similar Transplant Outcomes Than Haploidentical Hransplantation: A Retrospective Study on Behalf of the Acute Leukemia Working Party of the EBMT

Allogeneic Hematopoietic Cell Transplantation with Myeloablative Conditioning Regimen of Reduced Toxicity Is Associated with Favorable Survival in Patients with Secondary Acute Myeloid Leukemia

Background: Secondary or treatment-related acute myeloid leukemia (sAML) is associated with poor outcomes. Although allogeneic hematopoietic cell transplantation (alloHCT) is the treatment of choice, patient eligibility criteria and optimal conditioning regimen remain under study. We have previously shown an advantage of a myeloablative conditioning regimen with reduced toxicity (Fludarabine 150mg/m2, Treosulfan 42g/m2, FluTreo) compared to a reduced intensity regimen. However, the long-term effects of this regimen remain unknown, especially in comparison to patients not receiving alloHCT. Aims: We hypothesized that patients transplanted with FluTreo would have a long-term survival advantage over other treatment alternatives. Methods: We retrospectively studied consecutive patients treated for sAML in our center over the last two decades (1998-2018). Exclusion criteria were: age>70 years, ECOG performance status≥3 at presentation, induction regimens≤2, and autologous or haploidentical HCT because these were performed in individual patients. Since 2013, we have introduced FluTreo for patients with a suitable donor that would have been previously eligible only for reduced intensity conditioning/RIC. The following factors were studied in the whole cohort: age, type of disease (treatment-related or post myelodysplastic syndrome/MDS), previous intensive chemotherapy cycles, cytogenetic risk, overall (OS) and disease-free survival (DFS). In transplant recipients, we also recorded HCT-comorbidity index/CI score, cumulative incidence (CI) of graft-versus-host disease (GVHD), and treatment-related mortality (TRM). Follow-up was calculated from diagnosis in the whole cohort; and from date of transplant in the sub-group analysis of transplant recipients. Results: We studied 19 FluTreo recipients compared to 46 recipients of other conditioning regimens (38 myeloablative and 8 RIC), and 52 patients treated only with chemotherapy. Complete remission (CR) had been achieved in all FluTreo recipients before HCT, compared to 53% of other transplants, and 44% of chemotherapy only patients (p<0.001). As expected, median age was increased in FluTreo and chemotherapy only patients (59 and 58 years respectively), compared to other transplants (48 years, p<0.001). There was no other difference in baseline characteristics. With a median follow-up of 43 (range 13-204) months in surviving patients, 4-year OS was 40.3% in FluTreo versus 31.3% in other transplants and 11.8% in chemotherapy only patients (p<0.001, Figure 1A). In the multivariate analysis, achieving CR (p<0.001) and the FluTreo group (p<0.001) were associated with favorable OS, independently of age and cytogenetic risk. 4-year DFS was 32.3% in FluTreo, versus 29.3% in other transplants and 10.2% in chemotherapy only patients (p=0.001, Figure 1B). Within transplanted patients, there was no significant difference in GVHD, relapse and TRM between FluTreo and other transplants. Within the FluTreo group, acceptable rates of CI in severe acute and extensive chronic GVHD were observed (15.2% and 18.4%, respectively). Similarly, 4-year CI of TRM reached 30.4%, despite a median HCT-CI of 3 (0-7), age of 59 (51-67) years, 4 lines of treatment (3-6), and a majority of matched unrelated donors (13/19). Conclusion: Our real-world study confirms that alloHCT with FluTreo expands the transplant population with similar safety and efficacy to previous transplant modalities in sAML patients. Achievement of CR remains a major predictor of OS in these patients. The choice of alloHCT in this unique patient population of a rather older age and comorbidity index needs to be revisited. Figure 1 Disclosures Gavriilaki: Omeros Pharmaceuticals: Consultancy.

The apheresis content analysis in Allo-HSCT represents reliable influential factors on graft-versus-host disease and overall survival

BackgroundHematopoietic stem cell transplantation (HSCT) is an established treatment for hematologic malignancies. However the post-HSCT outcome can be affected by multiple pre-transplant, transplant, and post-transplant factors. The cellular content of graft could be possible factors influencing the graft-versus-host disease (GVHD) and overall survival (OS) as transplantation outcomes. PurposeThe aim of this study was to assess the impact of infused CD34+ cells, CD3+ cells, and MNC count on the patients’ survival and incidence of graft-versus-host disease (GVHD). Material and methodsWe analyzed 87 patients with hematological malignancies who underwent allogeneic hematopoietic stem cell transplantation at the Taleghani Stem Cell Transplantation and Cell therapy center, Tehran, Iran from January 2016 to December 2018. Patients were conditioned with either myeloablative conditioning regimen or reduced-intensity regimen. ResultA CD34+ cell dose < 4.35 × 106/kg and CD3+ cell dose < 365 × 106/kg was associated with higher survival and lower acute and chronic GVHD incidence, although their association was not statistically significant. Moreover, there was a significant association between MNC count < 6.15 × 108/kg and acute GVHD incidence. ConclusionGraft cell dose, lower than the cut-off level, could lead to better outcomes after allogeneic transplantation. However, this study showed that future investigations are required in a larger population of patients in order to determine the exact effect of allogeneic graft cell dose on transplantation outcome.

Alternative Donor Hematopoietic Cell Transplantation for Pediatric, Adolescent and Young Adult with Hematological Diseases

Hematopoietic cell transplantation (HCT) is the only potential curative option for many advanced hematologic diseases. Pediatrics, adolescent and young adult (PAYA) patients overall have less pre-HCT comorbidity or organ toxicity and lower transplant related morbidity and mortality risk compared to older adults. As such, a higher percentage of patients in this age group tend to receive myeloablative conditioning (MAC) over non-myeloablative regimens. Current alternative donor sources when a matched sibling donor (MSD) is not available include matched unrelated (MUD), umbilical cord blood (UCB), and haploidentical (Haplo) donors. While there are accumulating data comparing the HCT outcomes between MUD vs. Haplo or UCB in adult patients, the data are sparse in PAYA patients. In this retrospective study, we reviewed 314 consecutive patients aged 1-39 years who underwent their first allogeneic HCT using MAC at City of Hope between 1/2005-7/2018. Patients who received HCT from a matched sibling donor were excluded. Patients received HCT from either an 8/8 HLA MUD (n=196 [BM= 27%, PBSC= 73%]), UCB (n=83 [single: n=30, double: n=53]) or Haplo (n=35) donor. The most used MAC regimens were fractionated total body irradiation-based (n=234, 74%). All Haplo recipients got post-HCT cyclophosphamide (PTCy) as GVHD prophylaxis. To adjust for the difference in transplant era between UCB (predominantly performed in earlier years) and Haplo (carried out predominantly in more recent years) the comparative analyses were focused on Haplo or UCB vs. MUD. Univariate and multivariable Cox regression models were used to assess the impact of patient, disease, and treatment factors on overall survival (OS), progression-free survival (PFS), relapse/progression (RP), and non-relapse mortality (NRM). Median age of patients at the time of HCT was 24 years (range: 0.7-39), with 55% of patients being male. KPS was ≥80% in 88% of the patients and 25% had HCT-CI ≥ 2. The most common diagnoses included: ALL (48%), AML (41%), and MDS/CML (11%). DRI was high/very high in 44% of patients. Groups were balanced in general but patients in the Haplo group had higher HCT-CI (median: 2, p&amp;lt;0.01), more frequently had high/very high disease risk (49%, p&amp;lt;0.01) and higher KPS ≥80% (77%, p&amp;lt;0.01). Neutrophil engraftment was achieved at a median of 23 days (range: 10-94) in the UCB, 16 days (range: 12-32) in the Haplo and 15 days (range: 10-33) in the MUD (p&amp;lt;0.01). After a median follow up duration of 36 months (range: 5.9-36), 3-year OS was inferior among recipients of UCB-HCT (53%, 95% CI: 42-63) compared with the MUD (63%, 95% CI: 56-70; p=0.03), while similar between Haplo (62%, 95% CI:41-78) and MUD (p=0.82). The lower OS in UCB group was primarily due to the significantly higher NRM at 3 years (34%, 95% CI: 24-44) compared with the MUD (16%, 95%CI: 11-22, p&amp;lt;0.01); and 3-year NRM was not significantly different between Haplo (18%,95%CI: 6-34) and MUD (p= 0.99). On the contrary, the cumulative incidence of relapse (CIR) at 3 years was significantly lower in the UCB group (14%, 95%CI: 8-24) compared to MUD (29%, 95%CI: 23-36, p=0.01); the difference in CIR was not significant between Haplo (29%, 95% CI: 16-51) and MUD (p=0.81). PFS at 3 years was not significantly different among the three donor groups (p=0.43). Cumulative incidence of day 100 acute GvHD grade 2-4 was 61% (95% CI: 55-66) in the whole cohort, with no significant difference among the three groups (p=0.27). Cumulative incidence of chronic GVHD at 3 years was higher in the MUD group (66%: 95%CI: 59-72) compared to UCB (45%, 95%CI: 34-56, P&amp;lt;0.01) and Haplo (47%, 95% CI: 28-64, P=0.01). By multivariable analysis, patients with high/very high disease risk had worse OS (HR=1.8, 95% CI: 1.2-2.6, p&amp;lt;0.01) and PFS (HR=1.8, 95% CI: 1.3-2.5, p&amp;lt;0.01) and higher R/P (HR=2.3, 95% CI: 1.4-3.6, p&amp;lt;0.01). Neither Cord nor Haplo was significantly associated with OS compared with MUD when adjusted for Age, HCT CI, DRI, KPS, and HCT Era. In conclusion, our results indicated that in PAYA patients without a suitable MSD, outcomes of Haplo HCT are comparable to MUD HCT. By univariate analysis, UCB HCT was associated with a lower relapse rate compared to MUD. However, survival was worse in recipients of UCB HCT due to the higher NRM, possibly resulted from more infections and engraftment delays in these patients. Figure 1 Disclosures Ali: Incyte Corporation: Consultancy. Nakamura:Viracor: Consultancy; Kadmon Corporation: Other: Advisory board meeting; NapaJen Pharma: Consultancy; Celgene: Other: Support on seminar; Magenta Therapeutics: Other: Advisory board meeting; Alexion: Other: Support on a meeting presentation; Merck: Other: advisory board meeting; Kyowa-Kirin: Other: Support on a meeting presentation. Al Malki:Jazz Pharmacuticals, Inc: Consultancy; Neximmune: Consultancy; Rigel Pharma: Consultancy.

Long-Term Outcomes of Busulfan, Fludarabine and 400 Cgy Total Body Irradiation Versus Busulfan and Fludarabine Reduced-Intensity Conditioning Regimens for Allogeneic Stem Cell Transplantation in Hematologic Diseases: A Large Single Center Experience

Background: Nonmyeloablative (NMA) and reduced-intensity conditioning (RIC) regimens are offered for patients with hematologic malignancies requiring allogeneic stem cell transplantation (HSCT) but are not candidates for myeloablative conditioning (MAC). The intensity of the conditioning regimen (CR) is important and contributes to the ability of HSCT to provide a cure. There is no consensus regarding the best RIC regimen and efficacy is not equal amongst RIC regimens. The combination of 2 days of intravenous Busulfan (total of 6.4 mg/Kg) and Fludarabine (total of 120-160 mg/m2) (Flu/Bu2) has been validated and widely adopted. While this regimen is well tolerated, relapses are common and remain the leading cause of death. Total body irradiation (TBI) has been widely used in the CR and provides the advantage of potent anti-cancer effect, immunosuppression and the ability to reach certain 'sanctuary sites' for chemotherapy (i.e. CNS). The 2 most commonly used TBI levels are 1200 cGy in MAC regimens and 200 cGy in NMA and RIC regimens. We hypothesize that the addition of 400 cGy (200 cGy two fractions per day, 6 hours apart) TBI to Flu/Bu2 will reduce the relapse rate without increasing its toxicity. In this retrospective study, we compared the safety and efficacy of Flu/Bu2/TBI400 with Flu/Bu2 CR amongst a diverse group of hematologic diseases. Methods: From 2006 to 2018, 137 adult patients with different hematological diseases were treated using one of two RIC regimens, either Flu/Bu2/TBI400 or Flu/Bu2 followed by HSCT from HLA-matched related or unrelated donors. The primary endpoint was OS defined as the time from the date of transplant to death from any cause. The secondary endpoints included PFS, relapse rate, cumulative incidence of relapse (CIR), non-relapse mortality (NRM), causes of death, aGVHD, cGVHD and engraftment. PFS was defined as the time from the date of transplant to disease progression as documented by the treating physician, based on pathological, imaging or clinical findings of the individual disease, or death from any cause. NRM was defined as time of death without evidence of progressive disease with relapse or progressive disease as a competing risk event (data not shown in the abstract). Relapse was defined as progression or disease relapse with NRM as a competing risk event. These endpoints were censored at the time of last follow-up. Results: A total of 137 patients were included in this study. 74 patients were treated with Flu/Bu2/TBI400 and 63 patients were treated with Flu/Bu2. The 2 groups were comparable in terms of patient-, disease- and transplant-related characteristics; however, Flu/Bu2/TBI400 patients had a higher HCT-CI score and a lower KPS. CNI-MTX GVHD prophylaxis was used in a higher proportion in Flu/Bu2/TBI400. Most of the Flu/Bu2 transplants occurred from 2006 to 2012. The median age was 62 in both groups and patients had comparable disease type distribution and DRI (Table 1). The median follow-up time was 4.62 years. Flu/Bu2/TBI400 showed improvement of PFS over Flu/Bu2; the 5-year PFS was 50% in the TBI arm vs. 34% in the no-TBI arm (p=0.06 of marginal statistical significance). There was a numerical improvement of OS in favor of the TBI arm but this was not statistically significant; The 5-year OS was 53% with TBI vs. 39% without TBI (p=0.13). Cumulative incidence of relapse was not different between the 2 groups (p=0.29), see figures 1, 2 and 3. There was no difference in aGVHD incidence between the 2 groups (p=0.21). The TBI arm had significantly lower incidence of cGVHD compared to no-TBI arm (29% vs. 54%, p=0.005). Advanced DRI, grade III-IV aGVHD, cGVHD, use of ATG and MUD were associated with worse OS (univariate analysis). The same factors, with the exception of cGVHD, were associated with worse PFS. Multivariable Cox regression model revealed that grade III-IV aGVHD was associated with worse OS (p=0.001) while advanced DRI was associated with marginally inferior OS (p=0.07) (Table 2). Conclusion: This is the largest retrospective study of RIC Flu/Bu2/TBI400 regimen for HSCT with a median follow-up approaching 5 years. Our data suggests that RIC Flu/Bu2/TBI400 is safe and efficacious for different hematological malignancies. When compared to Bu/Flu2 without TBI, Flu/Bu2/TBI400 had lower incidence of cGVHD and showed a strong trend towards improved PFS and OS though not statistically significant at this time. Grade III-IV aGVHD was associated with poor OS in both groups. Disclosures Hardy: Incyte Corporation: Other: Advisory Board Member; Kite/Gilead: Other: Advisory Board Member; American Gene Technologies: Other: DSMB Member.

Heterogeneity of Hematopoietic Stem and Progenitor Cell (HSPC) Composition in Αβ T-Cell/CD19 B-Cell Depleted Peripheral Blood Cell Stem Cell (PBSC) Transplant Grafts and Correlation with Immune and Hematopoietic Recovery

INTRODUCTION. While total CD34 counts in PBSC graft products have correlated with overall likelihood of hematopoietic recovery after allogeneic hematopoietic stem cell transplantation (HSCT), analyses of the HSPC composition and its relationship to relevant post-transplant clinical outcomes are lacking. In fact, the biological basis for different dynamics of hematopoietic/immune recovery, the risk of infection, and graft-versus-host disease (GvHD) is not fully understood. We have performed the first analysis of HSPC graft composition in 6 αβ T-cell/CD19 B-cell depleted haploidentical (αβhaplo) HSCT. Additionally, we correlated the HSPC graft composition with the distribution of the same HSPC subsets in serial post-HSCT bone marrow aspirates performed at Days 30, 60, and 90, with the peripheral blood counts [neutrophils, monocytes, platelet (PLT)] and with the immune recovery (CD3+, CD3+CD4+, CD3+CD8+, αβT, γδT, NK cells) at the same time points. The patients were divided in two groups: 3 patients had a robust and sustained hematopoietic recovery (Group 1) while 3 patients experienced mild cytopenia after Day 60 (Group 2). All patients were transplanted for acute leukemia and received a myeloablative TBI-based conditioning regimen. See Table 1 for details about patients and graft composition. METHODS. All patients were enrolled in the Stanford IRB approved BMT Protocols 179/351/361 and had peripheral blood (PB) and bone marrow (BM) evaluated at Day 30, 60 and 90 post HSCT for the primitive CD34+ Lin- HSPC subsets: HSC (CD38-CD45RA-CD90+), MPP (CD38+CD45RA+), CMP (CD38+CD45RA-CD123+), GMP (CD38+CD45RA+CD123+), MEP (CD38+CD45RA-CD123+) and CLP (CD38+CD127+). Aliquots of αβhaplo-HSCT grafts were cryopreserved for later analyses. Mononuclear cells were isolated from PBSC, PB and BM by Ficoll-Hypaque (Sigma-Aldrich) density gradient centrifugation. FACS analyses were performed on either fresh or frozen cells on Becton Dickinson (BD) Aria II flow cytometer. At least 5x105 events were acquired and analyzed using FlowJo software (BD). RESULTS. Despite consistent levels of αβT-cell depletion and CD34 enrichment, the frequency of the HSPC subsets varied between the grafts. Notably, while CMP and GMP were very consistent across the 6 grafts, the frequency of HSC, CLP, MEP and MPP showed a 2-fold range of variation (Fig1A). No significant correlation was observed between the HSC frequency in the graft and the hematopoietic/immune recovery. However, the frequency of HSC in the BM at Day 30 is statistically correlated (P=0.027) with the PLT at Day 90 (Fig1B). In these preliminary results, the different distribution of CMP, GMP, MEP and MPP did not impact on the hematopoietic/immune recovery. However, there was a significant correlation (P=0.02) between CLP and γδ T cells reconstitution at Day 90 in Group 1 patients (Fig1C). Additionally, the neutrophils, monocytes and phagocytic cells recovery at Day 90 is statistically correlated with the GMP frequency in the BM at Day 30 (P=0.017; P=0.018; P=0.0132, respectively) (Fig1D). Interestingly, the same strong correlation is observed between the CMP in the BM at Day 60 and the recovery of neutrophils and phagocytic cells (P=0.016, P=0.019) at Day 90 (Fig1E), but the CMP at day 30 are already predictive of a robust engraftment in the Group 1 patients (data not shown). CONCLUSIONS. In αβhaplo-HSCT, previously identified factors influencing hematopoietic recovery have been mainly limited to the enumeration of bulk CD34 counts and of mature effector cells, such as αβ/γδ T and NK cells. On the other hand, the presence of GvHD and thymic injury have been correlated to the kinetics of immune reconstitution. We hypothesized that the HSPC composition of the graft would impact lymphohematopoietic recovery in αβhaplo-HSCT recipients. Although preliminary, our data indicate that even with a consistent method of graft manipulation, the HSPC graft composition is heterogeneous. Variations in HSPC subsets frequency and number can contribute to significant differences in lymphohematopoietic recovery and, therefore, clinical outcome. The evaluation of a larger number of patients with longer follow up after HSCT are required. Comparative studies with unmanipulated T-cell replete and cord blood grafts are ongoing. Such analyses will be instrumental not only for prediction of clinical outcome, but also for optimization of novel graft engineering strategies. Disclosures No relevant conflicts of interest to declare.

Reduced-Intensity Versus Myeloablative Conditioning for Allogeneic Hematopoietic Cell Transplantation in Patients with Myelodysplastic Syndrome: A Systematic Review and Meta-Analysis of Randomized Clinical Trials & Cohort Studies

Background: Conditioning regimen given before allogeneic hematopoietic stem cell transplantation (allo-HSCT) contributes significantly to the outcomes following transplant for myelodysplastic syndrome (MDS). Myeloablative conditioning (MAC) regimens are often associated with a lower risk of relapse; however, their use is often limited by toxicity and a higher risk of non-relapse mortality (NRM). Reduced-intensity conditioning (RIC) regimens are associated with a higher risk of relapse, a lower NRM, a lower incidence of graft versus host disease (GVHD), and hence is feasible in patients with advanced age or comorbidities. This study highlights the importance of the difference between the two interventions used in allo-HSCT for myelodysplastic syndrome (MDS). Methods: We conducted a comprehensive literature search using PubMed, Clinicaltrial.gov, Embase, Cochrane, and Web of Science on 5th May 2020 with no restriction of language or period. Initial research revealed 1698 articles. After excluding review articles, duplicates, and non-relevant articles, we included two randomized clinical trials and three cohort studies, which reported overall survival (OS), relapse-free survival (RFS), relapse incidence (RI), and incidence of acute and chronic (GVHD). Based on inclusion criteria, two randomized clinical trials (BMT CTN 0901 Trial Scott et al. 2017 &amp; EBMT RICMAC Trial Kroger et al. 2017) and three cohort studies (BBMT 55226 Park et al. 2018, BBMT Orozco et al. 2019, BMT Alatrash et al. 2019) were included. Results: Among combined MDS and acute myeloid leukemia (AML) patients (n=1188) enrolled in 5 studies, 651 patients had MDS. Patients underwent MAC (n=484) or RIC (n=692) followed by either a matched related donor (MRD), n=236, or matched unrelated donor (MUD), n=236, allo-HCT. The median age range at the time of transplant was 50-54 years The use of RIC causes statistically non-significant trend of improved overall survival (OS) (OR 1.11: 95% CI: 0.74-1.67, p-value= 0.61) along with more risk of relapse incidence (RI) (R 1.34: 95% CI: 0.56-3.18, p value= 0.51), and reduced relapse free survival (RFS) (OR 0.88, 95% CI: 0.55-1.44: p value= 0.59). Differences were found in terms of safety of both conditioning regimens. MAC allo-HCT have more acute GVHD, grade 3 and 4 (OR 0.66: 95% CI: 0.29-1.52, p value= 0.33) and chronic GVHD, grade 3 and 4 (OR 0.72: 95% CI: 0.41-1.27: p value= 0.26) and treatment-related mortality (TRM) (OR 0.83, 95% CI: 0.37-1.86, p value= 0.65). The meta-analysis results are shown in figure-1. Conclusion: In adult MDS patients undergoing allo-HSCT, RIC is associated with improved overall survival, but at the cost of reduced RFS, and a higher risk of relapse. MAC, on the other hand, is associated with more treatment-related mortality and GVHD. Results of our analysis point out these trends but these are not statistically significant Figure 1 Disclosures Anwer: Incyte, Seattle Genetics, Acetylon Pharmaceuticals, AbbVie Pharma, Astellas Pharma, Celegene, Millennium Pharmaceuticals.: Honoraria, Research Funding, Speakers Bureau.

Myeloablative Fractionated Busulfan with Fludarabine in Older Patients: Long Term Outcomes of Prospective Phase II Clinical Trial

Myeloablative Fractionated Busulfan with Fludarabine in Older Patients: Long Term Outcomes of Prospective Phase II Clinical Trial

Improvement in Survival of AML and MDS Patients Following Allogeneic Transplant: A Long-Term Institutional Experience

Improvement in Survival of AML and MDS Patients Following Allogeneic Transplant: A Long-Term Institutional Experience

Prognostic Value of Refined Disease Risk Index (rDRI) and Conditioning Regimen in Adult Patients Receiving Unrelated Cord Blood Transplantation (UCBT) for Haematological Malignancies - 15-Year Follow-up of Multicenter Study in Singapore

Introduction: Umbilical cord blood (UCB) is an established stem cell source for transplantation in patients with hematological diseases who lack suitable related or unrelated donors. Refined Disease Risk Index (rDRI) is a prognostic tool used in hematopoietic cell transplant (HCT), solely based on disease type and status. Its value in patients undergoing UCB transplants (UCBT) with different conditioning regime intensity is unclear. We sought to evaluate the predictive value of rDRI in patients undergoing UCBT. Methods: We performed a retrospective analysis of 107 adult patients with various hematological malignancies who underwent 4-6/6 HLA-matched UCBT using single unit UCB (n=14) or double unit UCB (n=93) between Aug 2006 and Nov 2019 at 2 academic tertiary hospitals in Singapore. Patients received pre-transplant conditioning with either myeloablative conditioning (MAC, n=63) regimen consisting of Fludarabine (Flu) 75mg/m2, Cyclophosphamide (Cy) 120mg/kg and total body irradiation (TBI) 12- 13.2Gy , intensified reduced intensity conditioning (i-RIC, N=22) regimen consisting of Flu 150 mg/m2, Cy 50mg/kg, thiotepa 10mg/kg and TBI 4 Gy, or nonmyeloablative conditioning (NM, n=22) regimen, consisting of Flu 200 mg/m2, Cy 50mg/kg and TBI 2 Gy. The median total nucleated cell dose infused was 5.07 x 107/kg (range, 2.61 to 11.5) Results: Median follow-up was 84 months (range, 6 to 167 months).. Kaplan-Meier estimates of overall (OS) and event-free (EFS) survival at 10 years were 40 % (95% CI, 31-50) and 37% (95% CI, 28-47) respectively. At 2 years, cumulative incidence (CI) of relapse-related mortality (RRM) and non-relapse mortality (NRM) were 27% (95% CI, 18-35) and 35 % (95% CI, 25-45), respectively. In multivariate analysis (MVA), rDRI showed significant correlation with OS (HR 2.41; 95% CI 1.41-4.11; p=0.001), EFS (HR 2.54; 95% CI 1.51-4.28; p=0.0004) and RRM (HR 2.71; 95% 1.36-5.41; p=0.005). Conditioning regimen intensity was found to have significant impact on NRM (p=0.047) and RRM (p=0.002) in MVA. When patients were further stratified into 4 risk groups incorporating both rDRI and conditioning regimen intensity, significant differences in OS (p=0.002) and EFS (p=0.001) were seen. 5-year OS (Figure 1) in patients receiving MAC/i-RIC and NM conditioning with low-intermediate risk rDRI were 52% and 36% respectively, compared with 24% and 13% in patients with high-very high risk rDRI (p=0.002). The corresponding ES were 50%, 29%, 20%, and 13%, respectively (Figure2). Conclusions: Our results confirm that rDRI has good predictive value for relapse and survival in UCBT recipients. Conditioning regime intensity was also found to have a significant impact on patient outcomes when evaluated together with rDRI. Prognostic scoring systems in HSCT are revised constantly with further studies needed to potentially incorporate the intensity of the conditioning regime into the rDRI. Outcomes in rDRI high risk patients remain poor and further studies are needed to define the best strategy that can induce sustained engraftment without increasing risk of relapse and toxicity death. Disclosures No relevant conflicts of interest to declare.

A Single Dose of a Novel Anti-Human CD117-Amanitin Antibody Drug Conjugate (ADC) Engineered for a Short Half-Life Provides Dual Conditioning and Anti-Leukemic Activity and Extends Survival Compared to Standard of Care in Multiple Preclinical Models of Acute Myeloid Leukemia (AML)

Hematopoietic stem cell transplant (HSCT) can be a highly effective, and often curative, treatment for patients with AML. At present, myeloablative conditioning (MAC) regimens are associated with severe acute and long-term toxicities. A subset of transplant-eligible AML patients undergoes reduced-intensity conditioning (RIC) regimens; while reducing toxicities, RIC regimens have higher incidence of post-transplant relapse and graft failure vs MAC. Thus, the need for safe and effective targeted conditioning agents for a broader use in transplant in both malignant as well as non-malignant settings is critical. We developed MGTA-117, an anti-human CD117 (c-kit)-targeted antibody (Ab) engineered for a short-half life (t1/2) conjugated to amanitin, an RNA polymerase II inhibitor, to enable ADC clearance prior to HSCT. MGTA-117 has a t1/2 of 91 hours in humanized NSG (hNSG) mice compared to the parental wild type (WT) Ab with a t1/2 of 217 hours in human FCRN mice. Via optimization of the linker-toxin moiety, the maximum tolerated dose (MTD) in C57BL/6 mice was improved 17-fold compared to previous generations of the ADC. The antibody component specifically binds CD117, which is expressed on hematopoietic stem and progenitor cells (HSPC) and in ~80% of patient cells with AML and MDS (Gao et al. PLOS One. 2015). When conjugated to amanitin, this ADC robustly depletes both CD117+ HSPCs and leukemic blasts. This targeted and optimized approach not only broadens the therapeutic window across preclinical models, but also provides the dual benefit of effective conditioning for HSCT and reduction of target-expressing tumor cells. Previously we have shown MGTA-117 elicits potent cytotoxicity on both primary human CD34+ cells and a CD117+ AML cell line in vitro. In hNSG mice, a single dose (0.1 mg/kg) of MGTA-117 selectively depleted ≥95% human HSPCs (Figures 1A and B). To demonstrate anti-leukemic activity of MGTA-117, we studied it in multiple human leukemic xenograft murine models that mimic untreated and refractory AML, including both cell line derived (Kasumi-1, CD117-expressing leukemia cell line, in NSG mice) and patient derived (AML PDX 1: J000106134, treatment naïve AML PDX and AML PDX 2: J000106132, heavily pretreated relapsed refractory AML PDX in NSG-SGM3 mice) xenograft models. MGTA-117 was well-tolerated in all three AML xenograft models both as a single dose (1-10 mg/kg) and as a multi-dose (3 mg/kg QODx2) regimen. In the Kasumi-1 model (Figure 1C), MGTA-117, both as a single dose (3 &amp; 10 mg/kg) and as a multi-dose (3 mg/kg QODx2), resulted in a 2.4-2.7-fold increase in median survival compared to vehicle (PBS), isotype-ADC, or standard of care (SOC) cytarabine (ARA-C, 30 mg/kg QDx5). Furthermore, a single dose of MGTA-117 significantly decreased peripheral tumor burden leading to delayed tumor growth resulting in a 2-3.3 fold and 1.3-1.8 fold increase in median survival in the treatment naïve AML PDX 1 and highly pretreated AML PDX 2 models (respectively) compared to vehicle, isotype-ADC and SOC. ARA-C treatment demonstrated a modest improvement in survival in both the AML PDX 1 (1.3 fold), AML PDX 2 (1.3 fold) models compared to control. These data demonstrate that MGTA-117 has potential to be a potent targeted conditioning and anti-leukemia agent. Together with prior reports demonstrating MGTA-117 as an effective conditioning agent in an animal model, this targeted ADC approach has the potential to improve HSCT outcomes in AML by reducing leukemic burden peri-transplant and may decrease the toxicities associated with current conditioning regimens. Disclosures Lanieri: Magenta Therapeutics: Current Employment. Lamothe:Magenta Therapeutics: Current Employment. Miske:Magenta Therapeutics: Current Employment. McDonough:Magenta Therapeutics: Current Employment. Sarma:Magenta Therapeutics: Ended employment in the past 24 months. Bhattarai:Magenta Therapeutics: Current Employment. Latimer:Magenta Therapeutics: Current Employment. Dushime:Magenta Therapeutics: Current Employment. Jain:Magenta Therapeutics: Current Employment. Palchaudhuri:Magenta Therapeutics: Current Employment. Knihtila:Magenta Therapeutics: Current Employment. Pearse:Magenta Therapeutics: Ended employment in the past 24 months. Proctor:Magenta Therapeutics: Current Employment. Boitano:Magenta Therapeutics: Ended employment in the past 24 months, Patents &amp; Royalties. Cooke:Magenta Therapeutics: Ended employment in the past 24 months, Patents &amp; Royalties. Davis:Magenta Therapeutics: Current Employment, Current equity holder in publicly-traded company.

Significant Long-Term Benefits of CAR T-Cell Therapy Followed By a Second Allo-HSCT for Relapsed/Refractory (R/R) B-Cell Acute Lymphoblastic Leukemia (B-ALL) Patients Who Relapsed after an Initial Transplant

Introduction Current available treatments are limited once patients with B-ALL relapse following allogeneic hematopoietic stem cell transplantation (allo-HSCT). While chimeric antigen receptor (CAR) T-cell therapy offers a chance of remission, long-term outcomes for these patients remain poor. The benefit of bridging into a second transplant after CAR T-cell therapy remains inconclusive and available data are limited. Here, we report the long-term outcomes of 23 B-ALL patients who chose to undergo a second allo-HSCT after achieving complete remission (CR) from CAR T-cell therapy. Methods From April 2017 to April 2020, 23 R/R B-ALL patients (median age of 20 years, ranging from 3 to 58 years) who relapsed after first allo-HSCT received CAR T-cell therapy. The data were aggregated from seven different clinical trials (www.clinicaltrials.gov NCT03173417, NCT02546739 NCT03825718, NCT03825731, NCT03952923, NCT04100187 and www.chictr.org.cn ChiCTR1800016541). Patients' first transplant sources were HLA-identical sibling (n=5), matched-unrelated donor (MUD) (n=1), and haploidentical donors (haplo) (n=17). Eight of the 23 patients had disease relapse within 6 months following the first transplant. The median time from first transplant to CAR T-cell infusion was 261days (range: 117~2181 days). Before CAR T-cell infusion, patients' median bone marrow (BM) blasts by morphology were about 72.5% (1.5%-94.5%) including 12 patients with BM blasts &amp;gt;70% (5 with BM blasts &amp;gt;90%). Three of the 23 patients (13%) had received at least one prior donor lymphocyte infusion. No patients had active graft-versus-host disease (GVHD) prior to CAR T-cell therapy. Second generation CAR T-cells were generated by using purified T-cells from transplant donors (n=15) or patients (n=8). Twenty-two patients received T-cells modified with CD19-targeting CAR T-cells containing either a 4-1BB (n=18) or a CD28 co-stimulatory domain (n=4), and one patient received CD19-CD22 dual specificity CAR T-cells. All patients received a conditioning regimen of IV fludarabine (30mg/m2/d) and cyclophosphamide (250mg/m2/d) for 3 days followed by a single CAR T-cell infusion with a median dose of 3×105 cells/kg (1×105-6×105 cells/kg) in 21 patients. Two patients received a second CAR T-cell infusion in 2-3 months (1/3×105 cells/kg dose). Post CAR-T therapy, all patients bridged into a consolidation second transplantation with conventional myeloablative pre-transplantation conditioning regimens including 15 patients who received total body irradiation-based and 7 patients that received a busulfan-based conditioning regimen. Cyclosporin A, short-term methotrexate, and mycophenolate mofetil were used for GVHD prophylaxis. Results Patients' characteristics are shown in Table 1. On Day 30 post CAR-T-cell infusion, 23/23 (100%) patients achieved minimal residual disease (MRD)-negative CR. A total of 16/23 (69.6%) patients developed cytokine release syndrome (CRS) of which 14/23 (60.9%) had Grade I-II and 2/23 (8.7%) had Grade III CRS. Two patients had Grade III neurotoxicity. All patients with MRD-negative status subsequently bridged into a second transplant (2 from MUD and 21 from haplo donors) with a median interval time of 67 days (39- 329 days) from CAR T-cell therapy to a second transplant. At a median follow-up time of 258 days (84-978 days), no patients relapsed, which was encouraging. Five of 23 patients (21.7%) died from transplant-related mortality (TRM) at a median time of 295 days (103-372 days) (1 from GVHD and 4 from infection). The 1-year overall survival (OS) was 68.0% and 2-year OS was 54.4% (Fig.1). While there was a trend towards a more efficacious OS for patients whose CAR T-cells were derived from donors rather than from patients themselves but the number are too small to reach statistical significance (1-year OS 83.9% vs. 64.3%, 2-year OS 83.9% vs. 42.9%, P=0.739. Fig.2). After the 2nd transplant, four patients developed GVHD. Conclusions Our study demonstrates that even for R/R B-ALL patients who have relapsed following a first allo-HSCT , an MRD-negative CR status can still be achieved through CAR T-cell cell therapy without increasing CRS or neurotoxicity, making consolidation second allo-HSCT feasible for these patients. CAR T-cell therapy combined with a consolidation second HSCT are effective for these heavily pre-treated patients with an encouraging prospect for long-term survival. Disclosures No relevant conflicts of interest to declare.

Healthcare Resource Utilization in Transplant Patients Who Are at a Higher-Risk to Develop Cytomegalovirus Infection during Their Primary Transplant-Related Hospitalization

Healthcare Resource Utilization in Transplant Patients Who Are at a Higher-Risk to Develop Cytomegalovirus Infection during Their Primary Transplant-Related Hospitalization

Impact of Two Different Types of Rabbit ATG on Immune Reconstitution and Overall Results after Allogeneic Hematopoetic Stem Cell Transplantation for Acute Lymphoblastic Leukemia in Children

Introduction Thymoglobulin® and Grafalon® are 2 polyclonal rabbit anti-thymocyte globulin (ATG) used in allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent graft rejection and graft-versus-host disease (GvHD). Differences in manufacturing lead to different types and concentrations of antibodies in each product. Few studies compare their effects on post-transplant immune reconstitution: indeed, the latter is essential to prevent post-transplant infections as well as relapse (in case of hematological malignancies). Methods We conducted a retrospective study on children or adolescents who received a first unrelated allo-HSCT for an Acute Lymphoblastic Leukemia (ALL) between 2007 and 2018, in the department of pediatric hematology of the Robert Debré Hospital in Paris, France. During this time period, 2 types of ATG were used: Thymoglobulin® at 7.5mg/kg or Grafalon® at 60mg/kg. We included patients with a B or T phenotype ALL aged 2 to 18 years at the time of HSCT indication. Stem cell source could be from unrelated matched or mismatched bone marrow, peripheral blood or cord blood. All patients received a myeloablative conditioning regimen consisting of 12 grays total body irradiation and etoposide (60mg/kg). We compared patients for engraftment, counts of total lymphocytes, B and T lymphocytes, T CD4+ and CD8+ lymphocytes and their sub-types (naïve, effector memory, central memory and effector memory RA+), regulatory T cells, NK cells, and compared lymphocyte proliferation assays at 1, 3, 6 and 12 months after transplant. We used joint models of longitudinal and survival data to further analyze evolution of total lymphocytes, B and T cells, T CD4+ and T CD8+ cells, and NK cells. Finally, we compared clinical outcomes between the 2 groups. Statistical analyses were performed according to EBMT guidelines (Iacobelli, 2013). Results 76 children were included: 23 received Thymoglobulin® and 53 received Grafalon®. Stem cell source was peripheral blood or bone marrow for 61 patients and cord blood for 15 patients. Initial characteristics of patients, disease status and HSCT were similar between the two groups except for the median total nucleated cells and CD34+ progenitor cells of the graft, that were significantly higher in the Grafalon® group. We found a delayed cumulative incidence of engraftment in patients who received Grafalon® compared to those who received Thymoglobulin®: 29 days [interquartile range 22-36] versus 22 days [19.5-29.5], p=0.004. We observed significantly higher counts of total and T CD4+ lymphocytes 1 month after transplant in patients who received Thymoglobulin® as compared to those who received Grafalon®: 238/mm3 [172-466] versus 137/mm3 [51-306] respectively (p=0.005), and 40/mm3 [31.5-70.5] versus 16/mm3 [2.5-41.5], respectively (p=0.011). No differences in immune cell population counts were found 3, 6 and 12 months after transplant (figure 1). However, joint models found no difference in the evolution of lymphocyte subsets analyzed depending on the ATG used, except a non-significant difference in slopes over time for CD8+ cells (p=0.13). In patients given Thymoglobulin® compared to those given Grafalon®, we found a higher proliferation in response to stimulation by CD3 3 month after HSCT (CD3 index 20.4 [12.4;41] versus 5.9 [3.3;6.4] respectively, p=0.0039), and a higher proliferation in response to stimulation by adenovirus (ADV) antigen 1 year after HSCT (ADV index 78.6 [58.8;163.1] versus 15.7 [2.8;59.3] respectively, p=0.027). We found no effect of ATG type on overall survival (OS), disease-free survival (DFS), treatment-related mortality and chronic GvHD. In a multivariate analysis, we observed no effect of the type of ATG on OS and DFS. Conclusions We found a higher count of total and T CD4+ lymphocytes 1 month after unrelated allo-HSCT for ALL in children who received Thymoglobulin® at 7.5mg/kg compared to those who received Grafalon® at 60mg/kg. From 3 months after HSCT, we found no difference in immune reconstitution. Joint models for longitudinal data and survival found no significant difference in evolution of the lymphocyte subsets analyzed. Clinical outcomes were similar between the two groups. However, we compared an intermediate dose of Thymoglobulin® to a high dose of Grafalon® that is not still the standard in clinical practice. A prospective study comparing Thymoglobulin® to a lower dose of Grafalon® would be needed. Disclosures Baruchel: Novartis: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Bellicum: Consultancy. Dalle:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi-Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bellicum: Consultancy, Honoraria; Medac: Consultancy, Honoraria; Orchard: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria; AbbVie Pharmacyclics: Membership on an entity's Board of Directors or advisory committees.

Incidence, Risk Factors and Outcomes of Cardiac Toxicity in Haploidentical Peripheral Stem Cell Transplantation with High Dose Cyclophosphamide

Introduction: Haploidentical donor transplant (HIDT) with high dose post-transplant cyclophosphamide (PTcy) has shown promising results in terms of GVHD and survival. PTcy when given on day +3 and +4 is associated with considerable morbidity. In our previous analysis, we demonstrated that when compared to matched donor allogeneic stem cell transplant, HIDT with PTcy was associated with significantly higher rates of hypoxia, grade 3-4 mucositis and hemorrhagic cystitis (Modi et al, JCO 2020). PTcy is known to cause cardiomyopathy. However, a comprehensive analysis of cardiac toxicity occurring from PTcy is limited. Methods: We retrospectively evaluated adult patients (pt) who underwent HIDT with PTcy to evaluate incidence and risk factors of cardiac toxicities. Source of stem cell was peripheral blood in all patients, and all received PTcy-based GVHD prophylaxis. We aimed to evaluate impact of cardiac toxicity on NRM and OS. We compared outcomes between two groups: cardiac toxicity and no-cardiac toxicity. Results: Between June 2012 and June 2019, 98 pt underwent HIDT. Of these, 21 (21.4%) developed cardiac toxicity and 77 (78.6%) did not. Median day to onset of cardiac toxicity from HIDT was 7 days, and median duration of cardiac toxicity was 14 days. Fourteen pt (67%) had resolution of the cardiac toxicity. Median age of the patient was significantly higher in the cardiac toxicity than no-cardiac toxicity (65 vs 57 years, p=0.007). Following cardiac toxicities were observed: systolic heart failure (n=7, 34%), diastolic heart failure (n=2, 10%), atrial fibrillation (n=10, 48%), pericardial effusion (n=2, 9%) one of which required pericardial window, pericarditis (n=1, 5%) and supraventricular tachycardia (n=1, 5%). In patients with congestive heart failure, the median LVEF was 45% (range, 20-60). Majority of the cardiac toxicities were de-novo in origin, while sepsis-induced cardiac toxicity was present in one pt. The proportion of male patients was higher in the cardiac toxicity than no-cardiac toxicity (81% vs 55%, p=0.04). Median KPS was marginally lower (70% vs 80%, p=0.08) and median donor age was marginally higher (59 vs 51 years, p=0.08) in the cardiac toxicity group compared to no-cardiac toxicity. Median Co-morbidity index was 1 for both groups. Patients in the cardiac toxicity had higher rate of pre-transplant coronary artery disease compare to no-cardiac toxicity group (24% vs 6%, p=0.03). No difference in the pre-transplant cardiac function was noted between both groups (LVEF 55% vs 60%, p=0.76). Six pt (29%) in the cardiac toxicity and 30 pt (39%) in the no-cardiac toxicity received myeloablative conditioning regimen (p=0.45). Grade 3-4 cytokine release syndrome was higher in the cardiac toxicity compared to the other group (20% vs 6%, p=0.04). Median follow-up of surviving patients was 1.9 years in both groups. For cardiac toxicity and no-cardiac toxicity, 1-year OS was 38.1% and 76.4% (HR 0.25, 95% CI 0.13-0.48, p≤0.001), respectively; and 1-year NRM was 57.1% and 13.1%, respectively (P≤0.001). Multivariable analysis was performed to evaluate risk factors associated with cardiac toxicity, and older age (OR 1.05, 95% CI 1.00-1.10, p=0.08) and male sex (OR 0.34, 95% CI 0.08-1.13, p=0.096) were marginally associated with higher risk of cardiac toxicity. No impact of intensity of conditioning regimen was noted. Multivariable analysis revealed adverse OS (HR 0.20, 95% CI 0.09-0.43, p&amp;lt;0.001) and significantly higher NRM (SHR 0.19, 95% CI 0.09-0.40, p&amp;lt;0.001) in patients with cardiac toxicity than the other group. Conclusion: Cardiac toxicity was associated with worse OS and higher NRM. Older age and male sex may have higher risk of developing cardiac toxicity. Early supportive care and aggressive cardiac management may help improve outcomes. Figure Disclosures Deol: Kite, a Gilead Company: Consultancy; Novartis: Consultancy. Modi:MorphoSys: Membership on an entity's Board of Directors or advisory committees.

Outcome of Hematopoietic Stem Cell Transplantation in Children with Primary Hemophagocytic Lymphohistiocytosis: A Single Institution Experience Using Reduced Intensity Conditioning

Hematopoietic stem cell transplantation (HSCT) is the only curative therapy for primary hemophagocytic lymphohistiocytosis (HLH). Conventional myeloablative conditioning regimen using busulfan, cyclophosphamide with or without etoposide was associated with high rate of transplant-related mortality (Horne et al. BJH 2005). Reduced intensity conditioning (RIC) is used in HLH to minimize transplant-related toxicities. The use of alemtuzumab, fludarabine, and melphalan in HLH was associated with low mortality; however, mixed donor chimerism and graft failure were frequent (Allen et al. Blood 2018). A recent report in 25 HLH patients who underwent HSCT from HLA matched donors using targeted busulfan (45-65 mg/L X h), fludarabine, and serotherapy resulted in adequate stable donor chimerism, no graft rejection, and no mortality (Felber et al. Blood Adv. 2020). In this study, we reviewed the outcome of 16 HLH patients who underwent HSCT from HLA matched donors using RIC. All patients were initially treated using HLH-2004 protocol. They subsequently underwent HSCT from 10/10 HLA matched related or unrelated donor using RIC regimens. We initially used AFM conditioning regimen that included alemtuzumab (1 mg/kg), fludarabine (150 mg/m2), and melphalan (140 mg/m2) with or without thiotepa (10 mg/kg). GVHD prophylaxis included cyclosporine (CSA) and steroids. Given the high rate of low donor chimerism with AFM regimen, we subsequently used BF conditioning regimen that included busulfan (weight-based dosing for total of 16 doses) and fludarabine (160 mg/m2). Therapeutic drug monitoring of busulfan was performed. Thymoglobulin (10 mg/kg) was added in matched unrelated donor (MUD). GVHD prophylaxis included CSA and steroids in matched related donors (MRD) and CSA and methotrexate in MUD. Bone marrow was the stem cell source in all patients except one who underwent second transplant using peripheral blood stem cells. Supportive care was consistent among all patients. Defibrotide prophylaxis was administered to prevent sinusoidal obstruction syndrome (SOS). Donor chimerism &amp;lt;5% from whole blood or &amp;lt;20% in T-cell, graft failure, and death from any cause were considered as events. A total of 16 HSCT transplants were performed, 5 received AFM regimen and 11 received BF regimen. Patient and transplant characteristics are shown in Table. All patients had successful neutrophil and platelet engraftments. Among the five patients who underwent AFM conditioning, one patient with SH2D1A mutation is 8 years post transplant with stable full donor chimerism and another patient with PRF1 mutation who received AFM with thiotepa has stable sufficient donor chimerism 3 years post transplant. Both patients did not require donor leukocyte infusions (DLI). The remaining 3 patients had declining donor chimerism beyond the first year of transplant despite the frequent use of DLI, one of them had disease reactivation and underwent second HSCT using BF regimen. Event free survival (EFS) at 3 years was 60% and overall survival (OS) was 100%. Among the 11 patients who underwent BF regimen, 7 were transplanted using MRD and 4 MUD. The median cumulative area under the curve of busulfan was 64 mg/L X h (range, 56-73). Median donor myeloid chimerism was 97% (range, 83-100) and median T-cell chimerism was 78% (range, 40-93). One patient who underwent MUD had grade III acute GVHD and none had chronic GVHD. Two patients had mild SOS. There were no events among BF group with median follow up duration of 393 days (151-2080). The use of BF regimen in HLH was associated with excellent outcome and stable donor chimerism with no graft failure in comparison to AFM regimen. Longer follow up is needed to confirm our findings. Disclosures No relevant conflicts of interest to declare.

Hemorrhagic Cystitis in Patients Undergoing Allogeneic Hematopoietic Cell Transplant with Post Transplant Cyclophosphamide As GvHD Prophylaxis

Hemorrhagic Cystitis in Patients Undergoing Allogeneic Hematopoietic Cell Transplant with Post Transplant Cyclophosphamide As GvHD Prophylaxis

Comparison of Fixed Vs ALC-Based Doses of Thymoglobulin® (ATG) in Pediatric Patients with Acute Leukemia Given αβhaplo-HSCT: Impact on Immune Reconstitution at Day 90

INTRODUCTION: Allogeneic hematopoietic stem cell transplantation (HSCT) remains the treatment of choice for pediatric patients with high risk or refractory leukemia. In the absence of related or unrelated HLA-matched donors, alternative approaches such as HLA-haploidentical HSCT have been implemented. Our group has developed one such approach, αβ T-cell/CD19 B-cell depletion (αβhaplo-HSCT), and demonstrated its clinical efficacy (Bertaina A, Blood 2018). In αβhaplo-HSCT, anti-thymocyte globulin (ATG) is used for preventing graft rejection and graft-versus-host disease (GvHD). However, the optimal dose still needs to be elucidated. Here, we present the first analysis comparing 2 different Thymoglobulin® ATG doses: one fixed at 3.75 mg/Kg, as established in previous European studies with the closely related ATG Grafalon®, and one based on a newly developed algorithm that also integrates absolute lymphocyte count (ALC). METHODS: Between March 2017 and April 2020, 27 pediatric patients (median age 12 years) with hematological malignancies were transplanted at Stanford University's Lucile Packard Children's Hospital. Importantly, 60% of these patients were in CR2 or greater and 2/27 had active disease at the time of HSCT. All children received a fully myeloablative conditioning regimen. On days -9/-8/-7 before αβhaplo-HSCT, patients were given a regimen of Thymoglobulin® ATG. No patient received post-HSCT pharmacological GvHD prophylaxis. The fixed dosage was given to 14 patients in cohort 1 (ATG: 3.75 mg/Kg) and the novel ALC-based dosage to 13 in cohort 2 (ATG ranging between 3-6 mg/Kg). All patients enrolled in this study (BMT Protocol 179 and 351 approved from our IRB) had a minimum follow-up of 100 days, evaluated at Day 30 and 90. Following Admiraal R (Lancet Hematology 2015), we defined CD4 immune reconstitution (IR) as more than 50 CD4 T-cells/ul twice within the first 100 days after HSCT. PBMC were enriched by Ficoll-Hypaque (Sigma Aldrich) density gradient centrifugation. Flow analyses were performed on fresh cells resuspended in PBS 2% FBS on Cytek DxP 10 flow-cytometer. At least 5x104 events of total cells were acquired and analyzed using FloJo software. RESULTS: With a median follow-up of 555 and 124 days for cohort 1 and 2 respectively, 12 patients (85.7%) in cohort 1 and 7 patients (54%) in cohort 2 achieved CD4 immune reconstitution. In cohort 2, CD3 αβ T cells were significantly lower at both Day 30 and Day 90 (P=0.0003, Figure 1A). At Day 90, both the CD4 and CD8 subpopulations were significantly depressed (P=0.01 and P=0.056, respectively, Figure 1C). In both subpopulations, the memory compartment was the most reduced (Figure 1D). The absolute numbers of CD3 γδ T cells did not differ between the cohorts at either Day 30 or 90 (Figure 1B). Viral reactivations were higher in cohort 1 (10/14, 71%) than in cohort 2 (6/13, 46%, P=NS). Half of the reactivations were CMV reactivations, but no patient developed organ disease. There was no statistically significant difference in overall survival and the incidence of relapse in the two cohorts. Three patients developed grade III-IV aGvHD: 2 in cohort 1 (14%) and 1 in cohort 2 (8%, P=NS). Remarkably, the only patient, who developed grade IV aGvHD in cohort 2, did not experience symptoms until Adenovirus reactivation 138 days after HSCT. CONCLUSION: Our analysis confirms that the optimal dose of ATG Thymoglobulin® before αβhaplo-HSCT remains elusive. There were no significant clinical differences between the 2 ATG regimens. However, the ALC-based regimen resulted in the more pronounced reduction of donor-derived memory T cells. Our analysis suggests two intriguing explanations for the observed pattern of results. First, the selective depletion of the memory compartment in both CD4 and CD8 T cells may well be due to a priming effect of ATG Thymoglobulin® on the few αβ T cells left over in the graft. Second, the equivalent reconstitution of naive T cells in the 2 cohorts is likely because the ATG has no impact on the thymus-dependent IR. Remarkably, in our overall cohort, 70% of the patients achieved CD4 IR by 90 days after αβhaplo-HSCT. This result is superior to the best results from other ex vivo T-cell depleted approaches 54%, recently reported by Van Roessel (Cytotherapy 2020). In vivo studies of the pharmacokinetics of ATG in αβhaplo-HSCT recipients and a comparison with the use of Grafalon® are required to shed more light on this crucial topic. Disclosures No relevant conflicts of interest to declare.