Ex Vivo Generation of Human T-Cell Precursors from CD34 super(+) Hematopoietic Progenitors Exposed to Notch Ligand Delta-like 4

The prolonged immune T cell compartment after transplantation of hematopoietic stem cells represents a major clinical obstacle. The acceleration of the recovery of the compartment through the injection of T lymphoid precursors generated ex vivo represents an innovative strategy to shorten the duration of immunosuppression post-transplant. Recently it was shown that exposure of CD34 super(+) cells derived from cord blood to Notch delta4 ligand induced commitment of these progenitors in the T cell differentiation pathway. We modified this technique to characterize and improve the development of T precursors ex vivo, in pursuing the objective of adapting this method to a clinical application. The CD34 super(+) hematopoietic progenitors isolated from cord blood or adult human bone marrow were cultured in the presence of delta4 for 3 weeks. A population of lymphoid precursors CD34 super(+) CD7 super(+) appears at D3, followed at day 7 by CD34-7 super(++), consisting of CD1a super(+) T committed precursors and CD56 super(+) NK cells. After D14, the T precursors do not expand anymore unlike NK cells. The number of T precursors increases by a factor of 90 between DO and D7. T-cell differentiation stops early because no immature CD4 super(+) cells and no rearrangement of T cell receptors loci are observed. T precursors generated after 7 day culture on delta4 are now grafted into mice NOD/SCID/gc super(-/-) to test their ability to generate T cells in vivo. These tests will allow us to estimate whether a passage can be considered clinically.