Human proT-cells generated in vitro facilitate hematopoietic stem cell-derived T-lymphopoiesis in vivo and restore thymic architecture

Abstract

• Intrathymic T-cell regeneration is facilitated by human proTcells generated in vitro.• In vitro-generated human proT-cells home to the thymus, wherein they restore thymic structure.Hematopoietic stem cell transplantation (HSCT) is followed by a period of immune deficiency due to a paucity in T-cell reconstitution. Underlying causes are a severely dysfunctional thymus and an impaired production of thymus-seeding progenitors in the host. Here, we addressed whether in vitro-derived human progenitor T (proT)-cells could not only represent a source of thymus-seeding progenitors, but also able to influence the recovery of the thymic microenvironment. We examined whether co-transplantation of in vitro-derived human proT-cells with hematopoietic stem cells (HSCs) was able to facilitate HSC-derived T-lymphopoiesis posttransplant. A competitive transfer approach was used to define the optimal proT subset capable of reconstituting immunodeficient mice. Although the 2 subsets tested (proT1,1 ) showed thymus engrafting function, proT2-cells exhibited superior engrafting capacity. Based on this, when proT2-cells were coinjected with HSCs, a significantly improved and accelerated HSC-derived T-lymphopoiesis was observed. Furthermore, we uncovered a potential mechanism by which receptor activator of nuclear factor kb (RANK) ligand-expressing proT2-cells induce changes in both the function and architecture of the thymus microenvironment, which favors the recruitment of bone marrow-derived lymphoid progenitors. Our findings provide further support for the use of Notch-expanded progenitors in cellbased therapies to aid in the recovery of T-cells in patients undergoing HSCT. (Blood. 2013;122(26):4210-4219)

The role of the thymus in T-cell immune reconstitution after umbilical cord blood transplantation

“…More importantly, these in vitro-derived proT2 cells could also restore thymic architecture and when coinfused with HSCs, were able to promote HSC-derived T-cell lymphopoiesis. 95 These findings suggest that Notch-based ex vivo culture of human progenitor T cells might represent a clinically applicable novel method to support T-cell reconstitution in UCBT recipients.…”

Chemokine treatment rescues profound T-lineage progenitor homing defect after bone marrow transplant conditioning in mice

“…Interestingly, improved donor settling in the thymus increased the numbers of host thymocyte populations (data not shown), similar to previous observations. 49,50 The facilitated reconstitution of host-derived cells may be through the restoration of thymic architecture due to lymphocyte-stromal interactions. 50 As expected, LSK engraftment in the BM was equivalent between untreated and pretreated cells ( Figure 6D), consistent with the absence of CCR7 and CCR9 on HSCs and MPPs.…”

“…49,50 The facilitated reconstitution of host-derived cells may be through the restoration of thymic architecture due to lymphocyte-stromal interactions. 50 As expected, LSK engraftment in the BM was equivalent between untreated and pretreated cells ( Figure 6D), consistent with the absence of CCR7 and CCR9 on HSCs and MPPs. Another chemokine receptor, CXCR4, although insufficient for efficient thymic homing physiologically, is broadly expressed on hematopoietic progenitor populations.…”

T cell progenitor therapy–facilitated thymopoiesis depends upon thymic input and continued thymic microenvironment interaction

“…An allogeneic BMT model was used to show that proTs enhanced thymic reconstitution and produced a broad repertoire of functional mature peripheral T cells, which protected against immunological challenges (32,33). Furthermore, human in vitro-generated proTs have demonstrated the ability to enhance thymopoiesis after transplant in mice (44). These studies have set the foundation for future clinical trials using human proT protocols.…”