UM171-Expanded Cord Blood Transplants Support Robust T-Cell Reconstitution with Low Rates of Severe Infections

Abstract

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. <40 years old) also showed a more pronounced increase in naïve T cells and recent thymic emigrants (RTE) between 3- and 12-months post-transplant compared to age-matched unmanipulated CB patients, suggesting that UM171-expansion improves thymopoiesis at least in the young patients. This also correlated with the demonstration that UM171 expands common lymphoid progenitors in vitro. ELISpot assays revealed that UM171 patients showed early virus-specific T cell reactivity, at 2- and 3-months post-transplant. Most importantly, UM171 patients had a 2-fold lower frequency of severe (i.e. grade 2-3) infections at 1 year post-transplant, even though time to engraftment of 500 neutrophils was similar between the two cohorts (17 and 20 days for the UM171-expanded and unmanipulated CB cohorts respectively, p=0.94). Conclusion Our data show that the relative T-cell paucity of the UM171 graft is rapidly compensated after transplant with no significant difference observed between the two cohorts in terms of numbers and phenotypes of T cells at 3, 6 or 12 months post-transplant. Although it is difficult to dissect the relative contribution of homeostatic expansion and de novo thymopoiesis, recipients of UM171 grafts had a greater TCR diversity at one year, which was more evident among patients younger than 40 years of age. The prompt immune reconstitution observed in UM171 patients translated into a low rate of severe (grade 2-3) infections and no infection-related mortality. These results support rapid and functional T cell reconstitution following UM171 expanded CB transplantation, which likely contributes to the absence of moderate/severe cGVHD, infection-related mortality and late TRM observed in this cohort. Figure legend: Mean cumulative counts of infectious events in patients transplanted with UM171-expanded (blue) or unmanipulated (red) CB. Mean cumulative counts are shown for all infectious events (A), bacterial (B) and viral (C) infections. Events were categorized by type and severity as per BMT CTN guidelines (Appendix 4A). Infectious events of grade 1-3 are shown in pale colors, while more severe events (grade 2-3) are shown in dark colors. Censored patients (including those who relapsed) are indicated with white circles. Figure 1 Disclosures Dumont-Lagacé: ExCellThera: Current Employment. Busque:Novartis: Honoraria; BMS: Honoraria; Pfizer: Honoraria. Sauvageau:ExCellThera: Current equity holder in private company, Other: CEO, Patents & Royalties. Cohen:ExCellThera: Consultancy, Other: principal investigator of an ongoing UM171 clinical trial.

Optimizing Blood Stem Cell Transplants Through Cellular Engineering

“…In one of the studies, 20 patients received a single UM171-expanded UCB transplant, while 12 patients received transplants with single or double unmanipulated UCB. The results showed a 17-fold larger CD34+ cell dose and a 2-fold lower CD3+ T cell dose in UM171 patients, as well as a shorter median time to immunosuppression withdrawal for the UM171 cohort, compared to the control cohort 13 . A novel azole small molecule, C7, was used in the ex vivo expansion of UCB HSPC, and the results showed that the addition of C7 could boost the expansion of hematopoietic progenitor cells (HPCs) by large amounts.…”

“…Patients who had received HSC 835 all demonstrated neutrophil recovery, which was achieved faster than the control group 12 . Another expansion technique involves the use of UM171, an HSPC agonist, which has been shown in several studies to successfully expand UCB units 13,14 . In one of the studies, 20 patients received a single UM171-expanded UCB transplant, while 12 patients received transplants with single or double unmanipulated UCB.…”

“…In fact, several cellular engineering methods have been used to date, including UCB expansion, cell selection, infusion of immune regulatory cells, including MSCs and Tregs, and immune effector cell therapy, which includes DLIs, CAR T cells, NK cells, and γδ T cells. UCB expansion has been mostly successful, with several of the molecules used causing large increases in the number of HSPCs and improved outcomes in patients 10,12,13,15 . In haploidentical transplantations, two cell selection methods are TCR αβ+/CD19+ cell depletion and naïve CD45RA+ cell depletion, both of which have been shown to contribute to a lower GvHD rate in patients 28,31 .…”

Effect of expansion of human umbilical cord blood CD34 + cells on neurotrophic and angiogenic factor expression and function

“…These expanded cells also showed the ability for long-term repopulation in vivo either in combination with SR-1 or when added alone (Fares et al 2014). The discovery of these small molecules has led to advances in the clinical use of small molecule expanded HSCs for use in haematological indications (Wagner et al 2016;Cohen et al 2020;Dumont-Lagacé et al 2020).…”

“…Furthermore, UM171 added to SCF, FLT-3, TPO and low-density lipoprotein (LDL) containing media has been shown to enable expansion of HSCs by up to 100-fold over 7 days of culture (Fares et al 2014). Thus, the addition of these small molecules has led to progress in the clinical application of small molecule expanded HSCs for haematological uses (Wagner et al 2016;Cohen et al 2020;Dumont-Lagacé et al 2020). It is, however, unknown if the addition of small molecules used during ex vivo expansion affects the production and expression of angiogenic and neurotrophic factors which, in turn, could impact the efficacy of expanded HSCs in neuroregenerative medicine.…”