Donor Myeloid Engraftment Research Articles

Allogeneic Hematopoietic Cell Transplant For Bone Marrow Failure or Myelodysplastic Syndrome in Dyskeratosis Congenita/Telomere Biology Disorders: Single-Center, Single-Arm, Open-Label Trial of Reduced-Intensity Conditioning Without Radiation

BackgroundDyskeratosis congenita/Telomere biology disorders (DC/TBD) often manifest as bone marrow failure (BMF) or myelodysplastic syndrome (MDS). Allogeneic hematopoietic cell transplant (alloHCT) rescues hematologic complications, but radiation and alkylator-based conditioning regimens cause diffuse whole-body toxicity and may expedite DC/TBD-specific non-hematopoietic complications. Optimization of conditioning intensity in DC/TBD to allow for donor hematopoietic cell engraftment with the least amount of toxicity remains a critical goal of the alloHCT field. Objectives/Study DesignWe report prospectively collected standard alloHCT outcomes from a single-center single-arm open-label clinical trial of bone marrow or peripheral blood stem cell alloHCT for DC/TBD-associated BMF or MDS. Conditioning was reduced intensity (RIC) including alemtuzumab 1mg/kg, fludarabine 200 mg/m2, and cyclophosphamide 50 mg/kg. A previous single-arm open-label phase II clinical trial for the same patient population conducted at the same center, differing only by inclusion of 200 centigray of total body irradiation (TBI), served as a control cohort. ResultsThe Non-TBI cohort included 10 patients (ages 1.7-65.9 years, median follow-up of 3.9 years) compared to the control TBI cohort which included 12 patients (ages 2.2-52.2 years, median follow-up of 10.5 years). Baseline characteristics differed only in total CD34+ cells received, with a median of 5.6 (Non-TBI) compared to 2.6 (TBI) x 106/kg (p=0.02; no difference in total nucleated cells). The cumulative incidence of day +100 grade II-IV acute and 4-year chronic graft-versus-host disease (GvHD) were low at 0 and 10% (Non-TBI) and 8 and 17% (TBI), respectively (acute, p=0.36; chronic, p=0.72). Primary graft failure was absent. Secondary non-neutropenic graft failure occurred in one (Non-TBI cohort). The Non-TBI cohort demonstrated delayed achievement of full donor chimerism but superior lymphocyte recovery. There was no difference in 4-year overall survival at 80% (Non-TBI) and 75% (TBI; p=0.78).MDS as an indication for alloHCT was uncommon, but overall associated with poor outcomes. There were 3 MDS patients in the Non-TBI cohort: 1 relapsed and died at day+387; 1 relapsed at day+500 and is alive 5.5 years later following salvage with a 2nd alloHCT; 1 relapsed at day+1093 and is alive at day +100 after a 2nd alloHCT. There was 1 MDS patient in the TBI cohort who achieved 100% donor myeloid engraftment without relapse but died at day+827 from a bacterial infection in the setting of immune mediated cytopenia. ConclusionElimination of TBI from the RIC regimen for DC/TBD was not associated with significant changes in rates of graft failure, GvHD, and overall survival, but was associated with delayed achievement of full donor chimerism and improved lymphocyte reconstitution. For DC/TBD-associated BMF, TBI appears to be dispensable. Optimal approaches to DC/TBD-associated MDS remain unclear. Larger cohorts are needed to better assess the unique contribution of TBI and donor CD34+ cell dose. Longer follow-up is required to assess differences in DC/TBD complications and late effects.

Non-Myeloablative Transplant in Severe Sickle Cell Disease Is Safe & Effective. Single Center Experience from Saudi Arabia

Background:Sickle cell disease (SCD) is a severe monogenic disorder in the world with >300,000 newly born afflicted children per year. Prevalence of this disorder is high in sub-Saharan Africa, Mediterranean basin, Middle East and India. Patients with severe disease phenotype manifested with stroke or other complications may benefit from allogeneic hematopoietic stem cell transplant (SCT). Recent reports in pediatric patients using myeloablative regimen showed excellent outcomes but similar progress in adults has been hampered by higher rates of transplant related mortality (TRM) and infertility.Methods:We conducted a study of adult patients at our institution with SCD whom underwent a matched related SCT during the period of 2014-2017. Medical records of eligible patients were retrospectively reviewed and extracted. All patients received hydroxyurea (HU) at maximally tolerated doses with hyper-transfusion 2-3 months prior to SCT. Iron chelation was given for patients with ferritin > 1000 ug/L. The preperative regimen was non-myeloablative (NMA) consisting of alemtuzumab 1 mg/kg divided over 5 days (day -7 to -3) followed by Total Body Irradiation (TBI) 300 cGy on day -1. Stem cells were collected from peripheral blood via apheresis after 5 days of GCSF with target CD34 cells of 10×106/kg. Graft vs. host disease (GVHD) prophylaxis consisted of sirolimus starting from day -2 and continued for one year post SCT with dose modification based on chimerism. Event free survival (EFS) was defined from time to SCT to graft failure, development of GVHD or death from any cause. EFS and overall survival (OS) via time to end point analysis was computed using the Kaplan-Meir test.Results:A total of 18 adults patients were eligible and further analysed. Median age was 23.5 (14 - 39) years with 14 males and 4 females. All patients were on HU prior to SCT. Median ECOG performance status was 1 (0-1). Indications for transplant were recurrent vaso-occlusive crisis (VOC) refractory to standard therapy in 61%, stroke or other central nervous system (CNS) complication in 38%, recurrent avascular necrosis of joints in 38%, recurrent acute chest syndrome in 22% and severe disease requiring recurrent intensive care unit admission (ICU) in 17%. All donors were related siblings fully matched at 10/10 human leucocyte antigen (HLA) loci with median age of 23.6 years. A total of 11 (61%) of donors were sickle cell carriers with average Hgb S 33%. Stem cell mobilization was with 5 ug/kg GCSF in all donors and the average stem cell collected 11.6 x 106/kg. No significant complications resulted from GCSF use in donors with sickle cell trait.17 patients were conditioned with alemtuzumab / TBI regimen and GVHD prophylaxis with sirolmus. One patient who failed prior transplant received fludarabine, busulfan and thymoglobulin with GVHD prophylaxis as cyclosporine and methotrexate. Median duration of neutrophil engraftment was 20 days and platelet engraftment 2.6 days with half of patient's platelet nadir > 20. Average hemoglobin (Hb) pre- and post-SCT was 83 g/L and 142 g/L respectively. Average hemoglobin (Hb) S pre- and post-SCT was 77% and 13% respectively. Peri-SCT adverse events were 9 (50%) patients experienced neutropenic fever, 12 (67%) mucositis, 6 (33%) diarrhea. None of the patients developed acute or chronic GVHD. No SCD crises developed post SCT. One patient developed aplastic anemia while retaining 71% donor cell chimerism and underwent a second successful SCT from the same donor with fludarabine, cyclophosphamide and thymoglobulin. All patients have stable mixed chimerism resulting in full donor myeloid engraftment and normalization of blood count. With a median follow up of 9.1 months (2.3-32), all patients are alive and free of sickle cell crises. At last follow up, OS and EFS were 100% and 88.9%, respectively as shown in Figure 1.Conclusion:Herein, we report that SCT in adults with severe SCD using NMA regimen is safe, feasible and results in amelioration of disease severity. These excellent results are encouraging given the high prevalence and debilitating nature of SCD in our region. Follow up is on-going to assess the feasibility of sirolimus tapering and sustainability of donor chimerism status over time. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Excellent outcomes following hematopoietic cell transplantation for Wiskott-Aldrich syndrome: a PIDTC report

AbstractWiskott-Aldrich syndrome (WAS) is an X-linked disease caused by mutations in the WAS gene, leading to thrombocytopenia, eczema, recurrent infections, autoimmune disease, and malignancy. Hematopoietic cell transplantation (HCT) is the primary curative approach, with the goal of correcting the underlying immunodeficiency and thrombocytopenia. HCT outcomes have improved over time, particularly for patients with HLA-matched sibling and unrelated donors. We report the outcomes of 129 patients with WAS who underwent HCT at 29 Primary Immune Deficiency Treatment Consortium centers from 2005 through 2015. Median age at HCT was 1.2 years. Most patients (65%) received myeloablative busulfan-based conditioning. With a median follow-up of 4.5 years, the 5-year overall survival (OS) was 91%. Superior 5-year OS was observed in patients <5 vs ≥5 years of age at the time of HCT (94% vs 66%; overall P = .0008). OS was excellent regardless of donor type, even in cord blood recipients (90%). Conditioning intensity did not affect OS, but was associated with donor T-cell and myeloid engraftment after HCT. Specifically, patients who received fludarabine/melphalan-based reduced-intensity regimens were more likely to have donor myeloid chimerism <50% early after HCT. In addition, higher platelet counts were observed among recipients who achieved full (>95%) vs low-level (5%-49%) donor myeloid engraftment. In summary, HCT outcomes for WAS have improved since 2005, compared with prior reports. HCT at a younger age continues to be associated with superior outcomes supporting the recommendation for early HCT. High-level donor myeloid engraftment is important for platelet reconstitution after either myeloablative or busulfan-containing reduced intensity conditioning. (This trial was registered at www.clinicaltrials.gov as #NCT02064933.)

Reduced-Toxicity (BuFlu) Conditioning Is Better Tolerated but Has a Higher Second Transplantation Rate Compared to Myeloablative Conditioning (BuCy) in Children with Inherited Metabolic Disorders.

Hematopoietic stem cell transplantation (HCT) is a primary treatment for various inherited metabolic disorders (IMDs). Achieving stable and sustained engraftment while minimizing transplantation-related morbidity and mortality is critical to optimizing outcomes for IMDs. Traditional regimens have used myeloablative approaches, primarily busulfan and cyclophosphamide (BuCy), which is associated with significant regimen-related toxicity. Alternatively, reduced-toxicity regimens, such as busulfan and fludarabine (BuFlu), have been proposed to offer similar efficacy with reduced toxicities. We compared transplantation-related outcomes with BuCy-based and BuFlu-based conditioning in patients with IMDs. We retrospectively analyzed the University of Minnesota's transplantation database for patients with IMDs who underwent HCT using a BuCy (with alemtuzumab) or BuFlu (with antithymocyte globulin) preparative regimen between March 2008 and September 2017. Overall survival (OS), event-free survival (EFS), and incidence of neutrophil and platelet recovery were determined using standard definitions. Complications such as graft failure, sinusoidal obstruction syndrome, hemorrhagic cystitis, and respiratory failure were compared. Graft failure includes primary and secondary aplastic graft failure with and without autologous recovery. The incidence of viral infections post-transplantation in the 2 regimens was also determined. A total of 99 patients underwent HCT for IMDs during the study period. Sixty-four patients received BuCy conditioning, and the other 35 received BuFlu. Hurler syndrome (46%) and adrenoleukodystrophy (43%) were the most common IMDs, and umbilical cord blood was the most common graft source (74%). One-year OS was similar in the 2 groups (81.2% in BuCy versus 85.5% in BuFlu; P=.8), with an EFS of 75% versus 63%, respectively. The 2 groups also had similar incidences of grade III-IV acute GVHD (9% versus 6%; P=.5) and chronic GVHD (9% versus 7%; P=.67). Neutrophil and platelet recovery were similar in the 2 groups, with a significantly shorter duration of hospital stay noted in the BuFlu cohort (median, 21 days versus 34 days; P=.002). The cumulative incidence of graft failure was significantly higher in the BuFlu group (29% versus 14%; P=.08), as was the rate of second HCT (27% versus 3%; P=.001). The incidences of adenoviral infection (14% versus 0%; P=.02) and hemorrhagic cystitis (23% versus 3%; P=.01) were higher in the BuCy group. T cell engraftment occurred significantly sooner with BuCy conditioning until 1-year post-transplantation, but donor myeloid engraftment was similar in the 2 groups. Our data indicate that reduced-toxicity conditioning is associated with lower rates of infection and other transplantation-related complications but is concerning for a higher rate of graft failure in patients with IMDs. Alternate immunosuppressive agents and novel techniques should be considered to minimize toxicities and reduce complications.

Non-Genotoxic Anti-CD117 Antibody Conditioning Results in Successful Hematopoietic Stem Cell Engraftment in Patients with Severe Combined Immunodeficiency

Non-Genotoxic Anti-CD117 Antibody Conditioning Results in Successful Hematopoietic Stem Cell Engraftment in Patients with Severe Combined Immunodeficiency

Rheological Assessments of Sickle Cell Patients Post Allogeneic Hematopoietic Cell Transplant

Introduction: Mixed donor chimerism (MDC) occurs in nearly 35% of patients with sickle cell disease (SCD) post allogeneic hematopoietic cell transplant (alloHCT). Donor myeloid engraftment of &amp;gt;20% is considered necessary to support disease resolution. However, in a disease known for its clinical variability, we hypothesize that patients (pts) with a severe pre-HCT phenotype may have abnormal RBC rheology at a level of chimerism and %HbS believed to be consistent with a cure. RBC rheology is markedly abnormal in SCD; these abnormalities are associated with SCD related clinical complications. Even fully oxygenated, sickle RBC are less deformable than those of HbAA or HbAS individuals; upon deoxygenation, deformability further declines. Sickle RBC morphology reflects the tendency to polymerize, with characteristic sickle forms. Sickle RBC are more adherent to the endothelial cell lining of the vasculature than HbAA or HbAS RBCs. The goal of any cell-based therapy of curative intent should be normalize the red cell rheology. To determine if the rheology of blood from SCD pts post-HCT with varying degrees of donor chimerism fall into the HbSS range of values, we propose to functionally assess the peripheral blood from a series of 6 post alloHCT SCD patients using a battery of rheological tests measuring deformability, sickling, adherence, percent dense cells (%DRBC), and RBC morphology. Methods: Peripheral blood samples (EDTA) from 6 SCD pts post alloHCT with a matched sibling donor were collected and immediately analyzed using oxygenscan (Lorrca), artificial microvascular network (AMVN), microfluidic image acquisition, and an ADVIA hematology analyzer. The Lorrca with oxygenscan measures RBC deformability (elongation index EI), under a range of pO2 (150-0 mmHg). EImax is the deformability of the oxygenated sickle RBC; EImin is the deformability of deoxygenated RBCs. The point of sickling (PoS) is the pO2 at which RBC deformability rapidly declines. RBC adhesiveness is measured by the difference in rate of perfusion of RBC through the AVMN coated with adhesive proteins (adherent AVMN) and a non-adherent, uncoated AVMN. %DRBC was measured by an ADVIA hematology analyzer. Microscopic RBC images were acquired and classified to determine the fraction of sickled RBCs in well-oxygenated samples. Additional clinical data including Hb profile, donor chimerism, and symptoms were obtained via chart review. Reference ranges were generated as described above using n=45 HbSS samples ages 2-21, on hydroxyurea, chronic transfusion, or untreated; n=14 HbAS, and n=43 HbAA. Results: In Figure 1, we show the measurements obtained by the Lorrca with oxygenscan on 5 pts post-alloHCT with a range of donor chimerism, as well as typical values for HbAA, HbAS, and HbSS patients. Patient 1 and 3 exhibit normal rheology; both were transplanted with a HbAA donor, with high chimerism and no detectable HbS. Patient 2 has 40% whole blood chimerism, well above the 20% threshold described with myeloid chimerism, and a HbS less than 50%, yet their plot resembles that of an untransplanted HbSS pt; the donor to Patient 2 exhibits the expected HbAA deformability. Patients 5 and 6 exhibit rheology in the HbAS range; they have intermediate chimerism from a HbAS donor. Clinical details and biomarker panel values for all 6 pts analyzed are in Table 1, as well as ranges of values for HbSS and HbAS subjects generated in the Sheehan and Shevkoplyas labs. Patient 2 is the only subject with values in the HbSS range, and the only subject with SCD symptoms. Conclusions: Our rheological tests identified a pt with values consistent with a HbSS pt of moderate severity or treated with hydroxyurea despite variable donor chimerism above the 20% threshold and HbS &amp;lt;50% thought to be sufficient for cure. The pt reported pain events beginning two years prior, indicating a clinical correlation supporting the validity of the rheological tests we propose to use to distinguish cure from persistent SCD. Current post-HCT evaluation depends on chimerism and hemoglobin profiles, and would not detect the significant functional abnormalities visible by Lorrca with oxygenscan biomarkers that indicate that Patient 2 is at risk for SCD related complications. Our results suggest that this functional analysis may help with management of post alloHCT SCD pts, and may be even more essential to assessing new gene-based therapy approaches to curing patients with SCD. Disclosures Rab: RR Mechatronics: Research Funding. van Wijk:Agios Pharmaceuticals: Consultancy, Research Funding; RR Mechatronics: Research Funding. Shevkoplyas:SSS: Research Funding; New Health Sciences: Consultancy.

Reduced Toxicity Conditioning Is Better Tolerated but Has Higher Graft Failure Compared to Myeloablative Conditioning in Children with Inherited Metabolic Disorders

Introduction Hematopoietic stem cell transplantation (HSCT) is a primary treatment for various inherited metabolic diseases (IMDs). Achieving stable and sustained engraftment while minimizing transplant related morbidity and mortality is critical in optimizing outcome for IMDs. Traditional regimens have used myeloablative approaches, primarily Busulfan and Cyclophosphamide (BuCy), which is associated with significant regimen related toxicity (RRT). Alternatively, reduced toxicity regimens, such as Busulfan and Fludarabine (BuFlu), have been proposed to offer similar efficacy with reduced toxicities. Objective To compare outcomes with BuCy and BuFlu based conditioning in patients with IMDs. Methods We retrospectively analyzed University of Minnesota's transplant database for patients with IMDs who underwent HSCT using BuCy (with alemtuzumab) or BuFlu (with ATG) preparative regimen from March, 2008 to September,2017. Overall survival (OS) and incidence of neutrophil and platelet recovery was determined using standard definitions. Complications such as graft failure, sinusoidal obstruction syndrome, hemorrhagic cystitis and respiratory failure were compared. Graft failure includes primary and secondary aplastic graft failure, with and without autologous recovery. Incidence of viral infections post-transplant comparing two regimens were also determined. Results Total of 99 patients underwent HSCT for IMDs during the study period. Sixty-four received BuCy conditioning and 35 received BuFlu. Hurler syndrome (46%) and adrenoleukodystrophy (43%) were most common IMDs and umbilical cord blood was the most common graft source (74%). One-year OS was similar in both groups (81.2% in BuCy vs. 85.5% in BuFlu; p=0.8) with a similar incidence of grade 3-4 acute GVHD(9% vs. 6%; p=0.5) and chronic GVHD(9% vs. 7%; p=0.67). Neutrophil and platelet recovery were similar in both groups with significantly shorter duration of hospital stay noted in BuFlu cohort (median 21 d vs. 34 d, p = 0.002). Cumulative incidence of graft failure was higher with BuFlu group (29% vs 14%, p= 0.08). Significantly higher rates of second HCT was noted following BuFlu cohort (27% vs. 3%, p= 0.001). Incidence of adenoviral infection (14% vs. 0%, p=0.02) and hemorrhagic cystitis (23% vs. 3%, p=0.01) were higher in the BuCy group. T-cell engraftment occurred significantly sooner with BuCy conditioning until 1-year post transplant, donor myeloid engraftment was similar in both groups. Conclusions Reduced toxicity conditioning leads to lower rates of infections and other transplant related complications, but is associated with higher rate of graft failure in patients with IMDs. Alternate immune suppressive agents should be considered to reduce graft failure and minimize toxicities. Alternate donor options, including expanded UCB, should also be considered to improve engraftment in patients with IMDs.

Reduced Toxicity Conditioning Is Better Tolerated but Has Higher Graft Failure Compared to Myeloablative Conditioning in Children with Inherited Metabolic Disorders

Background: Hematopoietic stem cell transplantation (HCT) is a primary treatment option for various inherited metabolic diseases (IMDs). Successful engraftment is crucial for favorable survival and functional outcomes and correlates with optimal conditioning in these patients with an intact immune system. Traditional regimens have used myeloablative Busulfan and Cyclophosphamide (BuCy) which is associated with significant potential morbidity. Alternate reduced toxicity regimens, like Busulfan and Fludarabine (BuFlu), are often utilized to reduce treatment related toxicities.Objective: To compare outcomes and complications with BuCy and BuFlu based conditioning regimens in patients with IMDs.Methods: This is the largest single institution retrospective analysis of University of Minnesota's transplant database for patients with IMDs who underwent HCT using BuCy + campath or BuFlu + ATG based preparative regimen from March 2008 to September 2017. Incidence of neutrophil and platelet recovery were determined using standard definitions. Complications such as graft failure, sinusoidal obstruction syndrome, hemorrhagic cystitis and respiratory failure were compared. Graft failure includes primary aplastic graft failure, primary graft failure with autologous recovery, secondary aplastic failure and secondary graft failure with autologous recovery. Incidence of viral infections post-transplant comparing two regimens were also determined.Results: Total of 99 patients were studied who underwent HCT for IMDs during the study period. Sixty-four received BuCy conditioning and 35 received BuFlu. Hurler syndrome (46%) and adrenoleukodystrophy (43%) were most common IMDs transplanted and umbilical cord blood was the most common donor source (74%). One-year overall survival was similar in both groups (81.2% in BuCy vs. 85.5% in BuFlu; p=0.8) with a similar incidence of grade 3-4 acute GVHD (9% in BuCy vs. 6% in BuFlu; p=0.5) and chronic GVHD (9% in BuCy vs. 7% in BuFlu; p=0.67) in the two groups. Neutrophil and platelet recovery were similar in both groups with significantly shorter duration of hospital stay noted in BuFlu group (median 21 d vs. 34 d, p = 0.002). The cumulative incidence of graft failure was higher with BuFlu conditioning (29% vs 14%, p= 0.08, Figure 1a). Significantly higher rates of second HCT was noted following BuFlu conditioning (27% vs. 3%, p= 0.001; Figure 1b). The incidence of adenoviral infection (14% vs. 0%, p=0.02) and hemorrhagic cystitis (23% vs. 3%, p=0.01) were notably higher in the BuCy group. Though donor myeloid engraftment was similar in both groups, donor T-cell engraftment occurred sooner with BuCy conditioning until 1-year post transplant (Figure 2).Conclusions: Reduced toxicity conditioning leads to lower rates of infections and other transplant related complications, but is associated with a high rate of graft failure in patients with IMD. Alternate immune suppressive agents should be considered to reduce graft failure and minimize toxicities. Alternate donor options, including expanded UCB, should also be considered to improve engraftment in patients with IMDs. [Display omitted] DisclosuresShanley:Magenta Therapeutics: Research Funding. Miller:Sangamo Therapeutics: Employment. Orchard:Magenta Therapeutics: Research Funding.

Epidermal Growth Factor Rejuvenates Aging Hematopoietic Stem Cells

Aging hematopoietic stem cells display distinct abnormalities such as myeloid skewing, decreased repopulating capacity, and leukemia predisposition. Radiation exposure potentiates aging of the hematopoietic system, as evidenced by premature and persistent senescence of HSCs in mice exposed to moderate dose irradiation (Blood, 2014. 123(20): p. 3105-15). Our laboratory demonstrated that EGF promotes hematopoietic stem cell (HSC) regeneration after radiation injury (Nat Med, 2013. 19(3): p. 295-304). Based on these results, we hypothesized that EGF and EGFR signaling may have rejuvenating effects on aging HSCs.For comparisons of young and aged mice, we utilized 2-4 month old mice and >18-24 month old female C57BL/6 mice, respectively. We discovered that aged C57BL/6 mice have decreased levels of EGF in the peripheral blood compared to young mice (p= 0.02) and decreased expression of EGFR on bone marrow (BM) ckit+sca-1+lin- (KSL) stem/progenitor cells (p= 0.03). BM KSL cells from aged mice displayed increased DNA damage in culture with thrombopoietin, SCF and Flt-3 ligand (TSF) compared to young KSL cells (p< 0.0001). Aged BM KSL cells treated with 100 ng/ml EGF had decreased DNA damage compared to aged BM KSL cells treated with TSF only (p< 0.01) Treatment with EGF for 7 days increased the colony forming capacity of aged BM KSL cells (p< 0.01). Importantly, competitive repopulation assays revealed that 7 day in vitro treatment of aged BM KSL cells with EGF significantly increased primary donor cell engraftment (p< 0.01) at 16 weeks compared to aged BM KSL cells cultured with TSF alone.Based on these in vitro observations, we next tested whether systemic administration of a recombinant, pegylated EGF (pEGF), 20 mcg three times weekly for 4 weeks could alter the hematopoietic characteristics of aged C57BL/6 mice. pEGF treatment decreased BM myeloid skewing (p< 0.01) and increased CD3 T cell content (p< 0.01) in aged mice compared to saline-injected controls. Furthermore, competitive repopulation assays revealed that pEGF treatment of aged mice caused a significant increase in functional HSCs capable of competitive engraftment in recipient congenic mice. Total primary donor cell (p< 0.01), myeloid cell (p< 0.01), T cell (p< 0.01) and B cell (p= 0.01) engraftment were significantly increased in recipient mice transplanted with BM cells from aged, pEGF-treated donors compared to recipients of aged, saline-treated donors at 20 weeks. Additionally, secondary transplantation also resulted in increased donor engraftment (p< 0.01) and increased donor myeloid engraftment (p< 0.05) at 12 weeks. These results suggested that systemic administration of pEGF rejuvenates the repopulating ability of aged HSCs.We next sought to determine if deficiency in EGFR signaling could accelerate hematopoietic aging in mice. For this purpose, we utilized a doxycycline-inducible, hematopoietic cell specific EGFR dominant negative mutant model (SCL-tTA;EGFR-DN mice). Interestingly, adult (13 month old) SCL-tTA;EGFR-DN mice displayed increased myeloid skewing in the peripheral blood (p< 0.05) and BM cells from SCL-tTA;EGFR-DN mice generated significantly decreased colony forming cells, compared to age-matched, EGFR-expressing mice (p< 0.01). Mechanistically, BM KSL cells from 13 month old SCL-tTA;EGFR-DN mice demonstrated increased senescence (p< 0.01) and increased expression of p16 (p< 0.05) compared to young mice. In contrast, BM KSL cells from aged C57BL/6 mice that were treated with 100 ng/ml EGF (plus TSF) for 7 days displayed decreased senescence and decreased p16 expression compared to BM KSL cells from aged mice treated with TSF alone. Taken together, these studies suggest that EGF/EGFR signaling declines with age and that reactivation of EGFR signaling via EGF treatment can ameliorate clinically relevant features of hematopoietic aging, including HSC self-renewal capacity. DisclosuresNo relevant conflicts of interest to declare.

Unmanipulated haploidentical transplantation conditioning with busulfan, cyclophosphamide and anti-thymoglobulin for adult severe aplastic anaemia.

We conducted a retrospective analysis to evaluate outcomes of haploidentical transplantation in adult severe aplastic anaemia (SAA) patients. Fifty-one adults received haploidentical transplantation between May 2011 and December 2016. Patients were administered busulfan (Bu), cyclophosphamide (Cy) and anti-thymoglobulin (ATG) as conditioning regimens, followed by bone marrow and peripheral blood transplantation. The patients' median age was 25 years. Forty-nine patients survived for more than 28 days and all achieved donor myeloid engraftment. The median time for myeloid engraftment and platelet recovery was 13 days (range, 10-21) and 17.5 (range, 7-101) days. The cumulative incidence (CI) of grade II-IV and III-IV acute GvHD) was 20.00±0.33% and 6.00±0.12%, respectively. The incidence of chronic GvHD was 14.00±0.36% and 25.90±0.71%, and that of moderate-severe chronic GvHD was 2.51±0.06% and 6.92±0.25% at 1 and 3 years, respectively. The 3-year estimated overall survival and failure-free survival were both 83.5±5.4% with a median follow-up of 21.1 months. Multivariate analysis showed hematopoietic cell transplantation-specific comorbidity index (HCT-CI) score of ⩾3 was significantly associated with worse outcome. Haploidentical transplantation conditioning including Bu/Cy/ATG was a safe and effective strategy for adult SAA patients, and HCT-CI might be an outcome predictor in these patients.

Reticular dysgenesis: international survey on clinical presentation, transplantation, and outcome

AbstractReticular dysgenesis (RD) is a rare congenital disorder defined clinically by the combination of severe combined immunodeficiency (SCID), agranulocytosis, and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 were identified to cause the disorder. Hematopoietic stem cell transplantation (HSCT) is the only option to cure this otherwise fatal disease. Retrospective data on clinical presentation, genetics, and outcome of HSCT were collected from centers in Europe, Asia, and North America for a total of 32 patients born between 1982 and 2011. Age at presentation was <4 weeks in 30 of 32 patients (94%). Grafts originated from mismatched family donors in 17 patients (55%), from matched family donors in 6 patients (19%), and from unrelated marrow or umbilical cord blood donors in 8 patients (26%). Thirteen patients received secondary or tertiary transplants. After transplantation, 21 of 31 patients were reported alive at a mean follow-up of 7.9 years (range: 0.6-23.6 years). All patients who died beyond 6 months after HSCT had persistent or recurrent agranulocytosis due to failure of donor myeloid engraftment. In the absence of conditioning, HSCT was ineffective to overcome agranulocytosis, and inclusion of myeloablative components in the conditioning regimens was required to achieve stable lymphomyeloid engraftment. In comparison with other SCID entities, considerable differences were noted regarding age at presentation, onset, and type of infectious complications, as well as the requirement of conditioning prior to HSCT. Although long-term survival is possible in the presence of mixed chimerism, high-level donor myeloid engraftment should be targeted to avoid posttransplant neutropenia.

High-Exposure, Targeted Daily Busulfan and Fludarabine-Based Conditioning for Children Undergoing Hematopoietic Stem Cell Transplantation for Inherited Metabolic Disorders: Outcomes at a Single Center

Allogeneic hematopoietic stem cell transplantation (HSCT) has emerged as standard therapy for children suffering from various life-threatening inherited metabolic disorders (IMD). Historically, successful outcomes have been limited by high rates of both graft failure and regimen-related toxicity. Real-time busulfan pharmacokinetic monitoring, combined with once daily dosing, has allowed for more precise delivery of targeted exposures during transplant conditioning. Recently, the Utrecht group reported highly favorable outcomes following a high-dose busulfan and fludarabine-based preparative regimen in patients with a variety of diagnoses, particularly in comparison to historical regimens that employ two or more alkylating agents. We report our experience using the same regimen specifically in patients with IMD. Since July 2014, 24 children undergoing first HSCT for IMD were conditioned with once daily IV busulfan (4 days; total regimen exposure of 90 mg x h/L) and once daily IV fludarabine (40 mg/m2/day x 4 days). Busulfan pharmacokinetic monitoring was performed on each of the first 3 doses (days); subsequent doses were altered to achieve the desired total regimen exposure. Serotherapy use was donor-dependent: HLA-matched related donor (MRD, n = 5), none; unrelated UCB (n = 16), thymoglobulin (2.5 mg/kg/day, days - 8 to -5); HLA-matched unrelated donor (MUD, n = 1), thymoglobulin (2.5 mg/kg/day, days - 5 -to -2); and, related HLA haploidentical marrow (n = 2), alemtuzumab (0.5 mg/kg divided days -11 and -10), +/- rituximab (375 mg/m2, day -12). All patients received CSA for GvHD prophylaxis. Additional GvH prophylaxis depended upon the allograft source: UCB, prednisolone; MRD/MUD, MMF; related haploidentical, MMF and post-transplant cyclophosphamide. Growth factor support was administered to recipients of UCB or haploidentical grafts. IMD diagnoses were as follows: Hurler syndrome (n = 10); cerebral adrenoleukodystrophy (n = 9); metachromatic leukodystrophy (n = 1); osteopetrosis (n = 1); fucosidosis (n = 1); alpha-mannosidosis (n = 1); and, beta-mannosidosis (n = 1). At a median follow-up of 229 days (range, 15 - 743), 22 of 24 patients survive, with a Kaplan Meier estimate of survival at one year of 86%. Causes of death were pulmonary bronchiolitis obliterans (BOS, n = 1) and graft failure (n = 1). Twenty-two patients had initial donor neutrophil recovery at a median day +14 (range, +11 to +21); for these patients, the median duration of severe neutropenia (ANC < 500/μL) was 7.5 days (range, 4 to 16 days). Of 20 patients who at the time of analysis are ≥ 30 days from HSCT, 18 had platelet engraftment (≥20,000/μL, transfusion unsupported) at a median day +22.5 (range, +10 to +94). One patient developed Grade II aGvHD (haploidentical marrow graft) which was successfully treated; no patients developed Grade III-IV aGvHD. One patient developed chronic GvHD with fatal BOS (UCB). Regimen-related complications were as follows: veno-occlusive disease, n = 0; hemorrhagic cystitis, n = 1; diffuse alveolar hemorrhage n = 1; idiopathic pneumonia syndrome, n = 1; immune-mediated cytopenias, n = 2; CMV viremia, n = 3; and, adenovirus infection, n = 1. Twenty patients (83%) have demonstrated durable, complete donor myeloid engraftment following the regimen. Of these, all have demonstrated mixed donor-recipient T-cell chimerism. Four patients, (all UCB grafts), have experienced graft failure: aplastic graft failure, n = 3, and autologous hematopoietic recovery, n = 1. Three of these patients underwent second HSCT and 2 are alive and engrafted while the other died of complications following second transplant. One patient awaits second transplant. In summary, this regimen of high-exposure, targeted daily busulfan and fludarabine in children with IMD provides favorable engrafted survival with minimal toxicities. DisclosuresNo relevant conflicts of interest to declare.

Haplo-identical transplantation for acquired severe aplastic anaemia in a multicentre prospective study.

We conducted a prospective, multicentre study to confirm the feasibility of haplo-identical transplantation in treatment of severe aplastic anaemia (SAA) as salvage therapy, by analysing the outcomes of 101 patients who received haplo-identical transplantation between June 2012 and October 2015. All cases surviving for more than 28d achieved donor myeloid engraftment. The median time for myeloid engraftment was 12 (range, 9-25) days and 15 (range, 7-101) days for platelets, with a cumulative platelet engraftment incidence of 94·1±0·1%. With a median follow-up of 18·3 (3·0-43·6) months, recipients from haplo-identical transplantation had more cumulative incidence of grade II-IV acute graft-versus-host disease (aGVHD, 33·7% vs. 4·2%, P<0·001), more chronic GVHD (22·4% vs. 6·6%, P=0·014) at 1year, but similar grade III-IV aGVHD (7·9% vs. 2·1%, P=0·157), 3-year estimated overall survival (OS, 89·0% vs. 91·0%, P=0·555) and failure-free survival (FFS, 86·8% vs. 80·3%, P=0·659) when compared with 48 patients who received contemporaneous transplantation from matched related donors. Multivariate analysis showed no significant difference in engraftment and survival between the two cohorts. Both OS and FFS for the entire population correlated significantly with grades III-IV aGVHD. In conclusion, haplo-identical transplantation is a feasible choice for SAA with favourable outcomes.

Full Donor Myeloid Engraftment with Minimal Toxicity in Dyskeratosis Congenita Patients Undergoing Allogeneic Bone Marrow Transplantation without Radiation or Alkylating Agents

Dyskeratosis congenita (DC) is an inherited bone marrow failure (BMF) syndrome caused by defects in telomere biology genes. BMF occurs in approximately 80% of patients by 30 years of age and, in addition to pulmonary failure and malignancies, remains a major contributor to mortality. Hematopoietic cell transplantation (HCT) cures BMF in DC patients but is associated with a high incidence of graft failure and transplant-related mortality. Radiation and/or alkylating agents (e.g. cyclophosphamide, busulfan, melphalan) used in conditioning may have a role in the poor outcomes in DC patients following HCT. Recently, reduced-intensity conditioning approaches have improved short-term outcomes, but concerns remain about the long-term effects of DNA damaging agents in these regimens, given the multisystem disease and lifelong predisposition to malignancy conferred by telomere dysfunction.Radiation and alkylating agents are mainstays of allogeneic HCT preparative regimens: their highly effective myeloablative and immunosuppressive properties provide a niche for donor hematopoietic progenitors and decrease graft rejection. Based on a rationale that presumes (1) niche availability in DC patients with BMF, and (2) an intrinsic replicative defect in DC hematopoietic cells, we hypothesized that engraftment would be feasible in DC patients using a regimen of immunosuppressive therapy alone.Here, we report that in a single-institution prospective study, 4 consecutive patients with DC have undergone successful HCT using a radiation- and alkylator-free preparative regimen. Patients received alemtuzumab and fludarabine, followed by bone marrow transplantation (BMT) from unrelated donors. Cyclosporine A and mycophenolate mofetil were used for graft versus host disease (GVHD) prophylaxis. The primary outcome measures were neutrophil engraftment at day +30 and overall survival at day +100. Secondary outcome measures included acute toxicities and rates of graft failure, infections, and GVHD.The first two patients were 18 month-old twins with TINF2 mutations and transfusion-dependent BMF who received a BMT from a fully HLA-matched unrelated donor. The third patient was an 18 year-old female with CTC1 mutations and transfusion-dependent BMF, who underwent a B-mismatched unrelated donor BMT. The fourth patient, a 22 year-old male with clinical DC and short telomeres, had significant pulmonary disease (diffusing capacity of lung for carbon monoxide 28% of predicted) and BMF, and underwent a fully HLA-matched unrelated donor BMT.All 4 patients engrafted neutrophils by day +30, and are alive and well with follow-up ranging from 6 months (1 patient) to 2 years (3 patients). Platelet transfusion-independence occured between day +4 to +18, and red cell transfusion-independence occured between day 0 to +90. No patients required transfusions thereafter. All patients showed full donor myeloid chimerism by day +60. 3 of 4 patients showed full donor lymphoid chimerism by year 2; the fourth patient has high and increasing mixed donor lymphoid chimerism (60%) at day +180. There were no significant, unexpected toxicities, bacterial or fungal bloodstream or tissue infections. All patients were monitored weekly by serum PCR for CMV, EBV, adenovirus and HHV6 until day +100; only one patient showed CMV reactivation which was controlled with pre-emptive ganciclovir therapy. There was no acute GVHD. Only one patient developed chronic GVHD with limited skin involvement controlled with topical steroids.These results provide promising early data for engraftment and a favorable short-term toxicity profile using a radiation- and alkylator-free conditioning regimen in HCT for BMF due to DC. This approach could spare DC patients the acceleration of non-hematologic complications and malignancies, which has been attributed to HCT, and improve long-term survival. The limited toxicity of the alemtuzumab/fludarabine regimen may also allow patients with severe disease-related co-morbidities such as pulmonary dysfunction to safely undergo HCT. To our knowledge, this is the first prospective HCT study to achieve full donor myeloid engraftment in a series of patients following conditioning without radiation or alkylating agents. DisclosuresOff Label Use: alemtuzumab - conditioning for bone marrow transplantation fludarabine - conditioning for bone marrow transplantation cyclosporine A - graft versus host disease prophylaxis in bone marrow transplantation mycophenolate mofetil - graft versus host disease prophylaxis in bone marrow transplantation.

A trial of plerixafor adjunctive therapy in allogeneic hematopoietic cell transplantation with minimal conditioning for severe combined immunodeficiency.

For infants with SCID, the ideal conditioning regimen before allogeneic HCT would omit cytotoxic chemotherapy to minimize short- and long-term complications. We performed a prospective pilot trial with G-CSF plus plerixafor given to the host to mobilize HSC from their niches. We enrolled six patients who received CD34-selected haploidentical cells and one who received T-replete matched unrelated BM. All patients receiving G-CSF and plerixafor had generally poor CD34(+) cell and Lin(-) CD34(+) CD38(-) CD90(+) CD45RA(-) HSC mobilization, and developed donor T cells, but no donor myeloid or B-cell engraftment. Although well tolerated, G-CSF plus plerixafor alone failed to overcome physical barriers to donor engraftment.

Heme oxygenase-1 derived carbon monoxide permits maturation of myeloid cells

Critical functions of the immune system are maintained by the ability of myeloid progenitors to differentiate and mature into macrophages. We hypothesized that the cytoprotective gas molecule carbon monoxide (CO), generated endogenously by heme oxygenases (HO), promotes differentiation of progenitors into functional macrophages. Deletion of HO-1, specifically in the myeloid lineage (Lyz-Cre:Hmox1flfl), attenuated the ability of myeloid progenitors to differentiate toward macrophages and decreased the expression of macrophage markers, CD14 and macrophage colony-stimulating factor receptor (MCSFR). We showed that HO-1 and CO induced CD14 expression and efficiently increased expansion and differentiation of myeloid cells into macrophages. Further, CO sensitized myeloid cells to treatment with MCSF at low doses by increasing MCSFR expression, mediated partially through a PI3K-Akt-dependent mechanism. Exposure of mice to CO in a model of marginal bone marrow transplantation significantly improved donor myeloid cell engraftment efficiency, expansion and differentiation, which corresponded to increased serum levels of GM-CSF, IL-1α and MCP-1. Collectively, we conclude that HO-1 and CO in part are critical for myeloid cell differentiation. CO may prove to be a novel therapeutic agent to improve functional recovery of bone marrow cells in patients undergoing irradiation, chemotherapy and/or bone marrow transplantation.

Haploidentical hematopoietic stem cell transplantation for the treatment of severe aplastic anemia in children

This study was purposed to assess the effectiveness of haploidentical hematopoietic stem cell transplantation (HSCT) without in vitro T cell depletion for the treatment of severe aplastic anemia (SAA) in children. Two children with SAA/very SAA (VSAA) received T cell-depleted HSCT from their fathers with 2 loci mismatched in our center between October 2010 and March 2013. During 4 months after onset, both failed in treatment of cyclosporine (CsA)+ granulocyte colony stimulating factor (G-CSF), had active or serious infections, were transfusion dependent and lacked HLA-identical sibling donors and unrelated donors. The conditioning regimen before HSCT included fludarabine, cyclophosphamide and thymoglobulin. The source of grafts was a combination of G-CSF mobilized peripheral blood hematopoietic stem cells and BM. The recipients received CsA, mycophenolate mofetil (MMF) and short-term MTX for GVHD prophylaxis. Both children with SAA achieved 100% donor myeloid engraftment. Neutrophil engraftment occurred at day 12 and day 18 after transplant respectively. Platelet engraftment occurred at day 17 and day 26 after transplantation respectively. Two patients all developed grade I acute graft versus host disease (GVHD), one of which evolved into chronic limited GVHD well-controlled. Both have survived for two years after transplantation with 100% donor myeloid engraftment and effective lymphoid reconstitution. In conclusion, these limited cases suggest that haploidentical HSCT for children with SAA without a HLA-identical sibling donor and unrelated donor may be feasible. Further prospective clinical study is required to increase the overall survival (OS) by decreasing GVHD while maintaining stable engraftment.

A novel protocol for haploidentical hematopoietic SCT without in vitro T-cell depletion in the treatment of severe acquired aplastic anemia

Mismatched related donors of hematopoietic SCT (HSCT) for severe aplastic anemia (SAA) present challenges mainly associated with graft failure and GVHD. The greater the HLA disparity, the poorer the OS. About 19 consecutive SAA/very SAA (VSAA) patients who received HSCT from haploidentical family donors in our center are reported in this study, 18/19 pairs had 2-3 loci mismatched. All 19 cases failed to respond to previous therapy and were heavily transfused before transplantation. The conditioning regimen before HSCT included BU, CY and thymoglobulin. The recipients received CsA, mycophenolate mofetil (MMF) and short-term MTX for GVHD prophylaxis. The source of stem cell grafts was a combination of G-CSF-primed BM and G-CSF-mobilized peripheral blood stem cells. All patients achieved 100% donor myeloid engraftment; the median time for myeloid engraftment was 12 days (ranging from 10-29 days) and for platelets was 18 days (ranging from 8-180 days) with a cumulative platelet engraftment incidence of 84.21 ± 10.53%. The cumulative incidence was 42.1 ± 11.3% for grade II-IV acute GVHD and 56.2 ± 12.4% for chronic GVHD. The OS was 64.6 ± 12.4% with a median 746-day (90-1970) follow-up for surviving patients. These limited retrospective analysis data suggest that HLA-haploidentical HSCT for SAA patients without an HLA-identical sibling donor might be feasible. Further research to increase OS by decreasing GVHD while maintaining stable engraftment will be needed in the future.

Infusion of “off-the-shelf” Third Party Ex Vivo Expanded Cord Blood Progenitor Cells As Supportive Care Following Clofarabine with High Dose Cytarabine and Granulocyte Colony-Stimulating Factor Priming for the Treatment of AML,

Abstract 3640Regardless of patient age, prolonged neutropenia and infectious complications are common side effects of AML induction and salvage chemotherapy, requiring intensive supportive care and contributing to treatment failure. Thus, novel therapies that can abrogate prolonged pancytopenia and facilitate more rapid hematopoietic recovery are needed. Previously, we have demonstrated that the absolute number of repopulating cord blood (CB) hematopoietic stem/progenitor cells (HSPC) can be increased by culture with Notch ligand; recent data from a Phase I double CB transplant trial utilizing ex vivo expanded CB HSPC has suggested more rapid neutrophil recovery (Delaney et al, Nat med). We hypothesize that this expanded cell product, which is devoid of T cells, could be cryopreserved and then infused as an off-the-shelf non-HLA matched product to provide rapid but temporary donor myeloid engraftment and might also facilitate autologous hematopoietic recovery following AML therapy, thus reducing the infectious complications associated with therapy.In a cohort of 50 patients, Becker et al at the Fred Hutchinson Cancer Research Center have reported on the use of clofarabine and high dose ara-c, in combination with G-CSF (GCLAC) in a phase I/II trial for the treatment of relapsed/refractory AML (Becker et al, Br. J. Haematol, in press). GCLAC is profoundly immunosuppressive and myelosuppressive, with periods of prolonged neutropenia post-GCLAC ranging from 17 to 35 days (median time to ANC >500 is 21 days) in this cohort. Infection was the most frequent adverse event, with ≥ grade 3 bacterial and fungal infections seen in 40% of patients (including 1st and ≥ 2nd salvage patients). We now herein report the preliminary results of a phase I safety trial investigating the use of GCLAC plus infusion of off-the-shelf expanded and cryopreserved CB HSPC for patients with AML.To date, 12 adult patients with relapsed (n=8), primary refractory (n=2) or de novo high risk (n=2) AML have been enrolled and received GCLAC as their first salvage or initial induction therapy. The median age and weight was 55 years (range, 38 to 59 years) and 79.5 kg (range, 63.8 to 126) respectively. Patients received cycle 1 of GCLAC followed by infusion of off-the-shelf expanded CB HSPC 24 hours after completion of chemotherapy. Patients who achieved a complete morphologic remission and did not experience any toxicities associated with the expanded cell product were eligible to receive a 2nd cycle of GCLAC with cells if not proceeding directly to stem cell transplant. A total of 15 products have been infused in 12 patients. Five of the 12 patients were refractory to GCLAC and therefore non-evaluable for neutrophil recovery. The median time to achieve an ANC > 500 in the evaluable patients was 19 days (range 18 to 27) after cycle 1, as compared to 21 days (range 17 to 35) in the historical cohort of patients receiving GCLAC only without expanded cells. Importantly, in this phase I study, there have been no infusional toxicities from the expanded cells or adverse events attributed to the expanded cell product. Alloimmunization has not been observed as monitored by pre- and post-infusion panel reactive antibody assays to determine the presence of donor directed antibodies.Four of the 12 enrolled patients have experienced clinically significant infections (e.g., bacteremia, fungal infections) compared to 40% in the comparison cohort, and no infectious deaths have been observed. Finally, in contrast to the first cycle of chemotherapy where donor cells were detected in only one patient, 4 out of 4 patients who received a 2nd cycle of GCLAC with expanded cells were found to have transient donor contribution to myeloid recovery (by peripheral blood cell sorted DNA chimerism assay) one week after infusion of the cells ranging from 85 to 100% donor in the CD33/CD14 cell lineages. Expanded cells were also able to home to the marrow as evidenced by transient donor engraftment (range, 3 to 15%) in recipient marrows one week after expanded cell infusion. It is unclear whether this is related to increased marrow “space” or increased host immunosuppression following cycle 2. With this encouraging data, we are continuing accrual of newly-diagnosed patients. This approach may decrease complications of pancytopenia and allow delivery of more dose-intense therapy, particularly in patients with intermediate/favorable cytogenetics who are already relatively sensitive to GCLAC. Disclosures:Delaney:Sanofi-Oncology (formerly Genzyme): Clofarabine for the study supplied by Sanofi-Oncology (formerly Genzyme). Becker:Sanofi-Oncology (formerly Genzyme): Research Funding.

HLA Alloantibody Persistence and De Novo Production of HLA Alloantibodies of Donor Origin Following Reduced Intensity Allogeneic Hematopoietic Stem Cell Transplantation.

AbstractAbstract 1109▪ Background:Platelet refractoriness as a consequence of HLA alloimmunization complicates allogeneic hematopoietic stem cell transplantation (HSCT). Little is known regarding the affects of reduced intensity HSCT on the incidence and duration of HLA alloimmune-mediated platelet refractoriness following reduced intensity HSCT. Methods:We retrospectively studied HLA alloimmunization in 16 patients with malignant and non-malignant hematological disorders, who underwent an allogeneic HSCT from an HLA matched relative using reduced intensity, non-myeloablative conditioning. All patients received a G-CSF mobilized, lymphocyte replete, peripheral blood stem cell (PBSC) allograft following cyclophosphamide (120 mg/kg) and fludarabine (125 mg/m2) based conditioning (+/− equine ATG 40 mg/kg × 4 days) with cyclosporine (CSA; beginning on day −4) and IV methotrexate (5 mg/m2 × 3 days) given as GVHD prophylaxis. Eight patients known to be HLA alloimmunized pre-transplant were compared to 8 control patients who were HLA alloantibody negative pre-transplant. Stored patients' serum samples from pre-transplant (day -30) and post-transplant intervals (days +30, +60, +100, +180, and ≥ 365) were analyzed for the presence of IgG antibodies to HLA class I antigens using a membrane-independent solid phase assay involving color-coded microbeads coated with HLA antigens and analysis with a flow analyzer (LABScan 100; One Lambda, Canoga Park, CA). Panel reactive antibody (PRA) and mean fluorescent intensity (MFI) were analyzed for all samples to measure HLA antibody strength and specificity, respectively. HLA alloantibodies were analyzed and compared with the degree of donor myeloid and T-cell engraftment measured on post-transplant blood samples by PCR of short tandem repeats (STRs). Results:Among the 8 alloimmunized patients who required HLA matched platelets pre-transplant, the median time until HLA antibodies disappeared was 100 days post HSCT. Remarkably, among these patients, 3/8 (37%) had HLA class I antibodies detectable for more than 100 days post-transplant including one patient who continued to show high level alloreactivity greater than 1 year after HSCT. Among the 8 control patients who tested negative for HLA alloantibodies pre-transplant, 3 acquired HLA alloantibodies after HSCT which were first detected at day +30 in all 3 cases. In 2 of the 3 cases, the donors for these patients were found to have pre-existing HLA antibodies of equivalent specificity to those found in the patient post-transplant suggesting patient acquisition of HLA antibodies was mediated by passenger donor lymphocytes that were transplanted in the allograft. Overall, HLA antibodies were detectable for more than 100 days after transplantation in 6/16 (37%) patients analyzed with 3/16 (18%) having alloantibodies detectable for more than 1 year post-transplant despite chimerism being 100% donor in myeloid and T cell lineages. Conclusions:Prolonged production of HLA alloantibodies leading to platelet refractoriness can occur following reduced intensity allogeneic HSCT and may persist even after full donor myeloid and T-cell chimerism have been achieved. Remarkably, we observed that transplantation of passenger donor lymphocytes can result in de novo HLA alloimmunization, complicating post-transplant transfusion management. Screening patients and their donors for HLA antibodies before HSCT would identify the majority of subjects at risk for alloimmune-mediated platelet refractoriness after transplantation. This new screening strategy would not only assist in transfusion support after allogeneic HSCT but could also play a role in the decision analysis for selecting optimal stem cell donors. Disclosures:No relevant conflicts of interest to declare.