ALBERT

Description: Cord blood (CB) transplants have fallen into disfavor in large part due to low cell dose leading to prolonged hospitalizations and high transplant related mortality (TRM). UM171, a novel and potent agonist of hematopoietic stem cell (HSC) self-renewal could solve this major limitation, allowing for CB's important qualities of lower risk of chronic GVHD and relapse to prevail. In addition, UM171 could permit transplantation of smaller, better HLA matched cords, associated with lower TRM. Hence, we initiated a clinical trial to test the safety and efficacy of UM171 expanded CB (eCB). Our goal was to design a clinically viable eCB transplant with a TRM as low or lower than other HSC sources all the while maintaining CB's low relapse rate. Patients (pts) received a myeloablative conditioning regimen. On day (D)-7 of transplant, CB was thawed and CD34+ selected. The CD34- lymphocyte containing fraction was cryopreserved and infused on D+1. The CD34+ component was placed in a closed culture system with UM171 and media was injected once a day until D0, when cells were washed and infused. This fed-batch culture system allowed for small culture volumes, saving cost and labor. Between 7/16-6/18, 21 adult pts (median age 44 years) were transplanted with an eCB. Median final culture volume and net viable CD34 fold expansion were 670 mL and 35, respectively. Median 1st day of 100 and 500 neutrophils were D+10 and D+18, respectively. Achieving 100 neutrophils was 5 days faster than seen with our pts receiving peripheral blood (PB) or marrow (BM) and appeared cell dose independent, suggesting that clinically meaningful expansion of an early repopulating myeloid progenitor is at saturation even with smaller CBs. In contrast, attaining 500 neutrophils was accelerated but dependent on cell dose. More importantly, pts appeared to derive clinical benefit beyond neutrophil engraftment (defined as 500 neutrophils). Pts' median last day of fever prior to 500 neutrophils was D+8, much earlier than engraftment and 4 days earlier than seen with our PB-BM pts. We offer 2 hypotheses as explanation: i) 100 neutrophils, which are attained early, provide significant defense against infection, ii) the graft contains a significant proportion of dendritic cell precursors (30-40%) which offer mucosal protection during severe neutropenia. Duration of hospitalization was shorter by 12 days and longer by 2 days compared to our non eCB and PB-BM transplants, respectively. In addition, because cell dose requirements were lower, 12/21 pts received a better HLA matched CB, thus 〉80% of patients were transplanted with a ≥6/8 HLA matched eCB. As a result of lower minimal cell dose criteria, we can now use ∼half the CBs in the banks instead of only 5% for a 70 kg patient. Platelet engraftment occurred at a median of 42 days. With a median follow up of 14 months, there has been no CMV disease, no PTLD, 2 adenovirus cystitis, 2 (10%) grade 3-4 acute GVHD, no moderate/severe chronic GVHD and 1 TRM (5%) despite a median comorbidity index of 2 (0-5). Full donor chimerism was achieved in all cell subsets. Immune recovery was faster than seen in our unrelated donor transplants who routinely receive ATG prophylaxis with 196, 300 and 413 CD4+/µL at 3, 6 and 12 months, respectively. Interestingly, transcriptome analysis of UM171-eCB cells shows an enhanced lymphoid progenitor-associated gene signature when compared to DMSO exposed cells. Animals transplanted with UM171-eCB cells showed a 20 to 35-fold increase in thymic cellularity at 8 weeks post-transplant. Despite some very high risk pts in our trial, only 3 relapsed. Overall, progression free, and GVHD/relapse free survival (GRFS) are excellent at 95, 77 and 67%, respectively, at 12 months. A 7 day UM171 single eCB protocol is feasible and provides clinical benefits beyond faster engraftment with fewer infectious complications, better HLA matching and very low TRM, all the while saving production and hospitalization costs. Nevertheless, longer follow up will be required to better assess relapse howbeit encouraging preliminary results. Furthermore, patients' quality of life is paramount and best evaluated by GRFS which is excellent thanks to a very low rate of significant chronic GVHD all the while maintaining a low risk of relapse. In conclusion, this 1st trial documents the potency of UM171 and positions UM171-eCB as a promising HSC source which could compete with the current standard of care. Figure. Figure. Disclosures Cohen: ExCellThera: Patents & Royalties: Royalities from sales of UM171. Roy:ExCellThera: Patents & Royalties: Royalities from sales of UM171. Lachance:ExCellThera: Patents & Royalties: Royalities from sales of UM171. Roy:Hopital Maisonneuve Rosemont: Patents & Royalties: Author on patent; Kiadis Pharma: Other: Travel support; University of Montreal: Patents & Royalties: Author on patent. Busque:BMS: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; Paladin: Consultancy. Kiss:Alexion: Membership on an entity's Board of Directors or advisory committees, Research Funding; Otsuka: Membership on an entity's Board of Directors or advisory committees, Research Funding. Caudrelier:ExCellThera: Employment. Zandstra:ExCellThera: Equity Ownership. Sauvageau:ExCellThera: Employment, Equity Ownership.

Description: Introduction Rapid T cell reconstitution following hematopoietic stem cell transplantation is essential for protection against infections and has been associated with lower incidence of chronic graft-vs-host disease (cGVHD), relapse and transplant-related mortality (TRM). While cord blood (CB) transplants are associated with lower rates of cGVHD and relapse, their low stem cell content results in slower immune reconstitution and higher risk of graft failure, severe infections and TRM. Recently, results of a Phase I/II trial revealed that single UM171-expanded CB transplant allowed the use of smaller CB units without compromising engraftment. We now report on T cell reconstitution and immune function in patients transplanted with UM171-expanded CB grafts. Methods We performed a retrospective analysis of 20 patients treated with UM171-expanded CB and compared it to a contemporary cohort of 12 patients treated in the same institution who received unmanipulated CB transplant with similar conditioning regimens. Of note, no patient received ATG as part of the conditioning in either cohort. We used flow cytometry and TCR sequencing to evaluate T cell reconstitution, and virus-specific ELISpot assays to evaluate T cell function in the first year post-transplantation. We also categorized infectious events as per definitions of infection severity in the BMT CTN Technical MOP Version 3.0 and report the mean cumulative count of infectious events for each cohort. Results While median T cell dose in graft was at least 2-3x lower for the cohort of patients treated with UM171-expanded CB due to the selection of smaller cords and to cell loss occurring during CD34 selection process, numbers and phenotype of T cells at 3, 6 and 12 months post-transplant were similar in patients treated with UM171-expanded or unmanipulated CB transplant. TCR sequencing analyses revealed that UM171 patients had greater T cell diversity and higher numbers of T cell clonotypes at 12 months post-transplant compared to patients who received unmanipulated CB. Younger UM171 patients (i.e.