Abstract: Introduction Dozens of secondary mutations in BCR-ABL have been identified in CP-CML patients (pts) whose disease becomes resistant to imatinib. Four TKIs (dasatinib, nilotinib, bosutinib and ponatinib) are potentially available as second (2L) or later line treatment, but no comprehensive clinical dataset or validated preclinical methodology exists to inform the choice of therapy based on BCR-ABL mutation status. While an extensive clinical dataset is available that describes response rates observed with dasatinib 2L treatment according to the specific BCR-ABL mutation present at baseline (eg cytogenetic response rates based on at least 10 pts available for 15 mutants), minimal data are available for the other TKIs, including, nilotinib and, especially, bosutinib and ponatinib. 1A generally more practicable approach is to compare sensitivities of BCR-ABL mutants to each TKI based on in vitro assessments. We have previously compared the in vitro potencies of all approved BCR-ABL TKIs against 21 BCR-ABL mutants, with preliminary results suggesting that TKI potency in vitro could be related to clinical efficacy if clinical pharmacokinetic parameters, and functional effects of protein binding, were taken into account. 2However, confirmation that this, or an alternative, methodology can produce reliable associations between in vitro data and clinical efficacy across all TKIs requires a more extensive clinical dataset than is currently available. To address this gap, we sought to leverage the combined resources of multiple institutions to collect outcome data for all available TKIs being used 2L in CP-CML pts who had a single BCR-ABL mutation detected at baseline. Uniform inclusion criteria were used to enhance the chance that the mutant BCR-ABL clone is the predominant driver of disease, so clinical outcomes could be optimally associated with preclinical data. Here we describe the design and initial results of this effort. Methods De-identified data were collected retrospectively based on chart review of appropriately consented pts. Key inclusion criteria include chronic phase disease being treated 2L and the presence of a single BCR-ABL mutation detected by Sanger sequencing. Additional demographic data collected include the 1L TKI and cytogenetic and molecular response status at baseline. Clinical outcome data collected include whether specific cytogenetic (MCyR or CCyR) and/or molecular (MR1, MR2, MMR) responses were achieved on 2L TKI treatment. To facilitate integration of data across multiple institutions, we examined the concordance between cytogenetic and molecular response outcomes. Univariate and multivariate regression will be used to examine associations between clinical responses and in vitro data. Results Results are reported as of July 24, 2015, based on data compiled from 157 pts who met all of the inclusion criteria (collected from 5 of the more than 10 institutions participating in this study). The median duration of prior TKI treatment was 3.0 years, with the vast majority of pts having received imatinib 1L (154 pts). Pts had 37 unique mutations at baseline, with the most common being T315I (N=19), M244V (N=18), M351T (N=13), G250E (N=12), and F359V (N=12). Cytogenetic and/or molecular response data were available for all 157 pts according to treatment 2L with dasatinib (N=81), nilotinib (N=61), ponatinib (N=14), and bosutinib (N=1). The use of MR2 as a surrogate for CCyR was examined in 121 pts evaluable for this comparison: 59 pts achieved both MR2 and CCyR, 58 achieved neither, and 4 achieved MR2, but not CCyR. MR2 demonstrated 100% sensitivity and 93.5% specificity at determining CCyR in the interim data. Conclusion A broad collaborative effort has been successfully initiated to greatly expand the available clinical data relating response outcomes to TKI treatment in CP-CML pts according to baseline mutation status. Analysis of a substantially expanded clinical dataset and the association with preclinical data will be presented. References: 1. Baccarani, M., et al, Molecular monitoring and mutations in chronic myeloid leukemia: how to get the most out of your tyrosine kinase inhibitor. Am Soc Clin Oncol Educ Book, 2014: p. 167-75. 2. Gozgit, M.J., et al., Comprehensive Analysis of the In Vitro Potency of Ponatinib, and all Other Approved BCR-ABL Tyrosine Kinase Inhibitors (TKIs), Against a Panel of Single and Compound BCR-ABL Mutants. ASH, 2013: p. Abstract: 3992. Disclosures Rivera: ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Branford:BMS: Honoraria, Research Funding; ARIAD Pharmaceuticals Inc.: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Nicolini:Novartis: Honoraria, Other: Consulting & Advisory Role, Research Funding, Speakers Bureau; BMS: Other: Travel/Accommodations/Expenses; Novartis: Other: Travel, Accommodations, Expenses; ARIAD: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Consulting or Advisory Role, Speakers Bureau. Pritchard:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time/Part-time Employee & Stock Shareholder (self-managed). Gozgit:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Milojkovic:Pfizer: Honoraria; ARIAD Pharmaceuticals Inc.: Honoraria; BMS: Honoraria; Novartis: Honoraria. Muller:ARIAD Pharmaceuticals Inc.: Honoraria, Other: Consulting & Advisory Role, Research Funding; BMS: Honoraria, Other: Consulting or Advisory Role, Research Funding; Novartis: Honoraria, Other: Consulting or Advisory Role, Research Funding. Deininger:Novartis: Other: Consulting or Advisory Role, Research Funding; Celgene: Research Funding; ARIAD Pharmaceutical Inc.: Other: Consulting or Advisory Role; Incyte: Other: Consulting or Advisory Role; BMS: Other: Consulting & Advisory Role, Research Funding; Genzyme: Research Funding; Gilead: Research Funding; Pfizer: Other: Consulting or Advisory Role. Heinrich:MolecularMD: Other: Consulting or Advisory Role; MolecularMD: Other: Stock/Shareholder; Onyx: Other: Consulting or Advisory Role; Novartis: Other: Expert Testimony; Blueprint Pharmaceuticals: Consultancy, Other: CONSULTING OR ADVISORY ROLE; ARIAD Pharmaceuticals Inc.: Consultancy, Other: Consulting or Advisory Role, Research Funding; Novartis: Consultancy, Other: Consulting & Advisory Role, Research Funding; Pfizer: Consultancy, Other: Consulting or Advisory Role; BMS: Research Funding; Bayer: Research Funding. Soverini:Novartis, Briston-Myers Squibb, ARIAD: Consultancy. Baccarani:BMS: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses, Speakers Bureau; Novartis: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses, Speakers Bureau; Pfizer: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses, Speakers Bureau; ARIAD Pharmaceuticals Inc.: Consultancy, Other: Travel/Accommodations/Expenses, Speakers Bureau. Cortes:Teva: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; BMS: Consultancy, Research Funding; ARIAD Pharmaceuticals Inc.: Consultancy, Research Funding. Etienne:Novartis: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses, Research Funding, Speakers Bureau; BMS: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses, Speakers Bureau; ARIAD Pharmaceuticals Inc.: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Abstract: Introduction: The introduction of the tyrosine kinase inhibitors (TKIs) into clinical practice in the late 1990s has considerably improved both survival and quality of life for patients with CML. Imatinib was the only TKI available for several years with no useful drug treatment for patients with resistance and/or intolerance. Despite the lack of alternative agents the 8-year follow-up of the IRIS trialshowed that only 55% of patients were still on imatinib. The majority of those who discontinued did so for lack or loss of response rather than intolerance, suggesting that imatinib is very well tolerated in the long-term. This is particularly pertinent today as controversy persists as to the best agent for newly diagnosed patients. There is not only increasing evidence that the second and third generation TKIs are associated with more severe adverse events, but generic imatinib is now available in many countries at considerably less expense. We report our experience of treating 45 patients with continuous imatinib for more than 10 years. Methods: We interrogated our single centre database of all patients treated with TKIs for CML at our centre from June 2000 to March 2015. From a total of 832 patients we identified 188 CML who had received only imatinib. Of these, 45 patients had received treatment for more than 10 years. Results: The median duration of imatinib therapy was 6 years in the total cohort of imatinib only patients and 11 years (range 10-14.7) in the study group. All 45 patients were in chronic phase at diagnosis: the median age was 45.4 years (range 26-72). Forty patients were evaluable for Sokal scoring, with 19, 13 and 8 identified as low, intermediate and high risk respectively. The median imatinib starting dose was 400 mg daily. The proportions of patients who achieved optimal responses (OR), as defined by the ELN at 3, 6 and 12 months from start of imatinib, were 88.2%, 78.8 and 56.1% respectively. At 10 years the probabilities of CCyR, MR3, MR4, MR4,5 and MR5 were 100%, 100%, 100%, 100%, 75.6% respectively. The 10 year probability of obtaining a sustained (at least 2 years) molecular response was 100%, 64.4%, 35.6% and 15.6% for MR3, MR4, MR4.5 and MR5 respectively. In patients who were not optimal responders at one or more time points (n=21), the median dose of imatinib was ≥400 mg in the first 12 months of treatment; for 13/21 higher dosages (range 600-800 mg daily) were prescribed. We found a significant correlation between a low or intermediate Sokal score at diagnosis and OR at 3 months (p=0.012). No correlation was found between Sokal score and OR at 6 or 12 months. No statistically significant association was found between an optimal response at 6 or 12 months and the future depth of responses. In fact, the overall rates of sustained MR4.5 for patients optimal responders at 6 and 12 months were 52% and 52% versus 41.6% and 50% for non optimal responders at the same time points. Grade 4 toxicities and secondary malignancies were not observed during the follow-up. Seven pts (15.5%) experienced grade 3 events, including 1 each of supraventricular tachycardia and anemia, and neutropenia, fatigue and hypophosphataemia were each seen in 2 patients. The most frequent adverse event of any grade was fatigue (36% of pts), followed by anemia (27%) and neutropenia (18%). The cumulative probability of common side effects increased over the time. Cardiovascular events were mostly grade 1-2 palpitations and hypertension. At last follow-up, all pts were alive. Conclusions: Our patient cohort analysis confirms long term safety and tolerability of imatinib after 10 years of therapy. The majority of side effects were grade 1-2 and some increased in incidence over the time. The most frequent adverse events were hematological. Imatinib continues to provide an excellent therapeutic outcome granting deep molecular responses even in some patients deemed to be poor risk at diagnosis. ELN optimal response status at 6 and 12 months was not associated with prediction of the future depth of response, in this very good risk population (majority of patients in optimal response at 3 months). Disclosures Milojkovic: BMS: Honoraria; ARIAD Pharmaceuticals Inc.: Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Apperley:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; ARIAD: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Abstract: Background: While chronic myeloid leukaemia (CML) originates from a single genetic aberration (BCR-ABL1) remarkably heterogeneity characterises treatment response and outcome. Most CML patients respond well to tyrosine kinase inhibitors (TKI), particularly 2nd generation (2G) TKI but a significant minority shows resistance and a proportion experience progression. At diagnosis there are currently no biomarkers for patients at higher risk of progression who could be treated with more effective treatment or be selected for BMT at an early stage of therapy. Such biomarkers may also provide useful prognostic information in addition to the most valid biomarker to date, the BCR-ABL1 IS ratio during the first 3-6-12 months of TKI therapy. Aims: The aim of our study is to analyse a panel of mutations in epigenetic modifiers in pre-treatment CML-CP using Ion Torrent next-generation sequencing (IONT-NGS) to assess the prognostic value of potential mutations as novel biomarkers of response to 1st and 2G TKI and risk of progression to advanced phase disease. Methods: 100 samples from untreated patients with newly diagnosed CML-CP were included in the study, 62 from patients treated frontline with imatinib (IM) and 38 with a 2G-TKI (31 dasatinib, 4 nilotinib, 3 bosutinib). The patients were classified as TKI responders (R) (34 IM, 22 2G-TKI) or non-responders (NR) (28 IM, 16 2G-TKI) based on BCR-ABL1 IS ratio at 3 months. DNA was extracted from CD34+ cells isolated from diagnostic samples, while DNA from T cells was used as constitutional non-leukemic control to exclude confounding germline mutations. Samples from healthy donors (n=14) and CML blast crisis (BC) (n=5) patients were used as negative and positive controls, respectively. We used a custom panel covering the coding region of 71 epigenetic enzymes. After sequencing data processing was performed excluding variants of low quality, common in the general population with minor allele frequency (maf) 〉 1% or present in the healthy controls, we analysed the genomic data and integrated them with annotated clinical data. Results: After using a variant reduction pipeline, 164 non-synonymous variants that affected protein function were identified: 52 somatic and 112 germline. The somatic mutations (including missense, nonsense, frameshift insertions and splice site variants) were confined to 30 genes, with ASXL1, IKZF1, CREBBP beingthe most frequently mutated (n=9, 7 and 4 respectively). The mutations were detected in 34/100 (34%) CML-CP patients (19/62 IM and 15/38 2G-TKI), in higher proportion in NR (19/44, 43%) compared to R (15/56, 27%; p=0.027). We next correlated the presence of mutations with overall survival (OS), TKI failure free survival (TFFS) and progression free survival (PFS). IM patients carrying somatic mutations demonstrated a poorer response to IM [HR=2.1 (1-4.4 95% CI), p=0.05] and were more likely to progress to advanced phase [HR=3.1 (1-9.4 95% CI), p=0.03] (Figure 1). Nonsense mutations in particular (in ASXL1, IKZF1, DNMT3A, EP300) were found in 4 IM NR vs 1 R and their presence led to poor OS [HR= 6.1 (1.6-23 95% CI), p=0.002] and PFS [HR= 5.4 (1.4-21 95% CI), p=0.006] . As these were observed in 5 patients, further testing is required to corroborate this initial observation. Multivariate analysis revealed that both increased Sokal score and occurrence of somatic mutations negatively influenced outcome: somatic mutations detected in 6/24 low and in 8/13 high Sokal IM patients were associated with worse OS and PFS compared to unmutated patients with the same Sokal score. Among 38 patients treated with 2G-TKI, neither somatic mutations (including nonsense variants) nor combination of somatic mutations with Sokal score had any influence on OS, TFFS, PFS, neither did the presence of germline mutations in either IM or 2G-TKI patients. Summary/Conclusion: Somatic mutations identified using IONT-NGS on 71 epigenetic modifiers potentially predict 1st generation (IM) patient poor survival, drug failure and progression to advance phase disease. However, the more effective therapeutic effect of 2G-TKI seems to overcome the poor prognostic influence of such mutations though further validation on larger cohort of patients may be required to validate preliminary data. Our results suggest that occurrence of somatic mutations at diagnosis have the potential to identify patients who would benefit from upfront treatment with 2G-TKI. Disclosures Apperley: Incyte: Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Ariad: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; Bristol Myers Squibb: Honoraria, Speakers Bureau.

Abstract: Introduction: Ex-Vivo T-Cell Depletion (EX-TCD) has been shown, in multiple cohorts, to markedly decrease the incidence of graft-versus-host-disease (GvHD). This conditioning regime however, has been associated with high incidence of disease relapse. This single center, observational 34 year study, demonstrates outcomes of patients who underwent EX-TCD Allogeneic Hematopoietic Stem Cell Transplant (AHSCT) for Chronic Myeloid Leukemia (CML). The total cohort consisted of 62 patients; all underwent EX-TCD AHSCT between 1984 and 1988. 58% (n=36) of the total cohort relapsed and 53% of relapsed patients (n=19) went on to have a second AHSCT (non-T-cell depleted) or donor lymphocyte infusion (DLI) with the remaining 47% (n=17) receiving conservative management. Given these differences in management, we used a competing risk model to adjust for the second AHCST or DLI on survival outcomes (using a second AHSCT or DLI as a competing risk). The aim of this study was to determine from this cohort, which factors were associated with overall survival and survival following disease relapse. Methods: Within the relapsed cohort, univariate and multivariate standard Cox proportional hazard regression models were used to analyse various factors, which were hypothesized to be associated with survival. These included; age at relapse, gender and relapse grade. Competing risk model was used to analyse the contribution of a second AHSCT or DLI to survival. Results: The cohort underwent EX-TCD AHSCT for CML between 1984 and 1988. Age range of recipients was 15 to 53 years and all were sibling donors. At the 34 year follow-up mark, there was no difference in overall survival between those who relapsed (and received a second AHSCT or DLI) and those patients who did not relapse (p-value 0.86). Of the 26 % (n=16) of patients who remain alive, 50% (n=8) relapsed and received a second AHSCT or DLI. Most recent BCR-ABL polymerase chain reaction (PCR) confirm all patients remain in molecular remission (MR4 or below). For the whole cohort, relapse was not affected by; donor gender, recipient age, CMV status, GvHD grade, duration of disease prior to AHSCT, Sokal score at diagnosis or duration to relapse following AHSCT. No parameter had a statistically significant association with survival or relapse, suggesting heterogeneity of disease could be an important consideration. 22 % (n=2) of the non-relapsed group and 17% (n=6) of the relapsed group developed acute GvHD. 37% (n= 23) of patients from the whole cohort developed chronic GvHD. Known causes of death included; relapse (36%, n=22), infection (16%, n=10), chronic GvHD (11%, n=7), other (8%, n=5). 26% (n=16) of patients remain alive today and 3% (n=2) were lost to follow-up. Relapse was graded into 5 categories, mirroring monitoring methods at the time of relapse (prior to the development of BCR-ABL PCR). 6% (n=2) of patients developed a molecular relapse (grade 1), 58% (n=21) developed cytogenetic relapse (grade 2), 25% (n=9) developed hematological relapse (grade 3), 3% (n=1) relapsed as accelerated phase CML (grade 4) and 8% (n=3) relapsed with blast phase CML (grade 5). We divided patients into two groups; relapse grade 〈 2 (cytogenetic or molecular relapse only) and grade 〉 3 (hematological relapse or above). In a multivariate Cox proportional model, relapse grades were significantly associated with subsequent survival (log rank p-value 0.0057). Relapse grade 〉 3 had an 11% increased hazard of death compared to relapse grade 〈 2 (Hazard ratio (HR) 1.11; p-value 0.0068). 46% (6/13) of patients with relapse grade 〉 3 underwent a second AHSCT or received DLI, compared with 56% (13/23) of patients with grade 〈 2. In the competing risk analysis, those patients with relapsed grade 〈 2 had a significantly improved survival with a second AHSCT or DLI (HR 1.34; 95% CI 1.06-13.70; p-value 0.03) whereas patients with a relapse grade 〉 3 had no improvement in survival. (HR 0.96; 95% CI 0.93 to 6.8; p-value 0.07, Figure 1). Conclusion: In this cohort, EX-TCD was associated with high rates of relapse. However, patients remain alive from both the non-relapsed and relapsed cohorts. In the relapsed cohort, patients who received a second AHSCT or DLI had improved survival outcomes compared to conservative management. A competing risk analysis demonstrated that patients with lower relapse grades had a statistically significant improvement in survival after a second AHSCT or DLI. Disclosures Milojkovic: Incyte: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau. Apperley:Novartis: Honoraria, Research Funding, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau.

Abstract: June 2018 was the 20th anniversary of the clinical use of the first tyrosine kinase inhibitor (TKI), imatinib, for chronic myeloid leukemia. Since then, the change in prognosis for patients with this disease is one of the major success stories of modern cancer medicine. The dilemmas that face physicians and patients are no longer only those concerned with delaying inevitable progression to the terminal blastic phase or selecting the individuals most likely to benefit from allogeneic stem-cell transplantation; rather, they are now focused also on the choice of TKI, the management of comorbidities and adverse effects, strategies to improve quality of life, and the appropriateness of a trial of therapy discontinuation. Interestingly, with 4 TKIs approved for frontline use, the choice of initial therapy continues to cause controversy, a situation made more complicated by the tantalizing prospect of treatment-free remission. In this manuscript, we will explore the factors influencing this decision and try to provide a pragmatic and clinically applicable solution.

Abstract: SARS-CoV-2 infection, and resulting disease, COVID-19, has a high mortality amongst patients with haematological malignancies. Global vaccine rollouts have reduced hospitalisations and deaths, but vaccine efficacy in patients with haematological malignancies is known to be reduced. The UK-strategy offered a third, mRNA-based, vaccine as an extension to the primary course in these patients. The MARCH database is a retrospective observational study of serological responses in patients with blood disorders. Here we present data on 381 patients with haematological malignancies. By comparison with healthy controls, we report suboptimal responses following two primary vaccines, with significantly enhanced responses following the third primary dose. These responses however are heterogeneous and determined by haematological malignancy sub-type and therapy. We identify a group of patients with continued suboptimal vaccine responses who may benefit from additional doses, prophylactic extended half-life neutralising monoclonal therapies (nMAB) or prompt nMAB treatment in the event of SARS-CoV-2 infection.

Abstract: Abstract 4438 BACKGROUND: Graft Failure (GF) occurs in 5–27% of patients (pts) after allogeneic hamatopoietic stem cell transplant (HSCT) and is associated with high morbidity and mortality related to infections and hemorrhagic events. Graft function may be poor as result of graft rejection, primary disease relapse or Poor Graft Function (PGF). The incomplete recovery of blood counts is defined primary PGF and the decreasing blood counts after successful engraftment secondary PGF. Several factors may determine GF: disease risk and status, conditioning regimen, HSC source, HLA compatibility, T cell content, immunosuppression, GvHD, viral infections, drugs. GCSF and Rhu-EPO are readily available and effective in PGF but with no effects on platelets. Second transplantation from the same donor, with or without conditioning therapy, can boost the haematopoietic recovery in pts with GF. Unfortunately, both a second peripheral CD34+ mononuclear cells (MNC) mobilization and a marrow harvest in the operating room may be contraindicated early after the first donation as not safe for donors. Intrabone SCT can overcome the risk of graft failure even with a low number of CD34+ MNC, as it has been demonstrated in cord blood transplant. Here we investigate in three adult pts with GF a bone-to-bone boost (BBB) with a small marrow harvest from respective donors, unfit for a second conventional donation. AIM: to evaluate the feasibility of the BBB technique in 3 pts with graft failure. METHODS: pts were 2 males (57, 53 y) with PGF with a diagnosis of AML and CMML, respectively, and a female (44 y) with graft rejection and AML relapse. In the first two patients prolonged pancytopenia and hypoplastic marrow were documented, with diagnosis of primary PGF and secondary PGF, respectively, donor chimerism ranging from 80–100% (STR and HLA), without evidence of leukemia. In the third patient, after prolonged pancytopenia an AML relapse was documented with 89% blasts on bone marrow aspirate. In PGF patients no conditioning regimen was administered before the boost at day 30 and 72 after SCT, respectively. In the patient with AML relapse Melphalan 200 mg/mq was given 48 h before the infusion, at day 35 after SCT. The 3 donors were related, haploidentical. For the BBB procedure small quantities of bone marrow ( 〈 200ml) were collected from the posterior iliac crest bilaterally of the donors, at the bedside, during deep sedation and analgesya. Shortly after the unmanipulated marrow harvested was infused in superior-posterior iliac crest mono- or bilaterally, depending on the volume, during deep sedation and analgesya. In pt 1 Mononucleated cell (MNC) dose was 0.9 × 10^8/Kg for a volume of 166 ml. In pt 2 MNC dose was 0.4 × 10^8/Kg for a volume of 88 ml. In pt 3 MNC dose was 0.3 × 10^8/Kg for a volume of 140 ml. RESULTS AND CONCLUSION: In this cases the BBB technique proved feasible and safe for both the donor and the patient. Patient 1 received a second PBSC boost, without conditioning, 3 months after the BBB, and he's now alive, in CR, 13 months after the first transplant. Patient 2 died 3 months after the first transplant for pneumonia and sepsis. Patient 3 is alive, in CR, 4 months after the first HSCT. This practice can give the chance of HSC boost to patients with GF without the need of a GCSF mobilization for donors, with a minimal invasive operation. This can give the option to overcome and resolve infectious and hemorrhagic complications, bridging patients to further therapies and procedures. The intra-bone SCT may be a facilitating tool for microenvironment reconstitution, seeding and subsequent differentiation and may as well have a tolerogenic effect, through the mesenchymal stromal cells infused with the harvest. Further studies are necessary to assess the efficacy of this procedure. Disclosures: No relevant conflicts of interest to declare.