Immunodeficiency: primary or acquired
We improved the classical OP9-DeltaLigand culture system for in vitro differentiation of CD34+ hematopoietic stem and progenitor cells (HSPC) into the mature T cell lineage so as to render it robust and amenable for smaller quantities of HSPC (minimum of 300 CD34+ cells) that can be isolated from as few as 1-5 ml of peripheral blood. In turn, we applied this functional test in order to demonstrate that it could be successfully used to distinguish cell-autonomous from non-cell-autonomous defects in T cell differentiation of HSPC taken from SCID patients. Particularly, we confirmed that CD34+ cells obtained from peripheral blood of one IL2Rgc SCID patient were stalled early in their differentiation, as they could not produce any CD34-CD7+CD1a+ double-negative (DN), CD4+CD8+CD3+/- double-positive (DP) or CD3+ single-positive (SP) cells after three weeks of culture, although CD34+CD7+ proT cells were abundantly present. On the other hand, CD34+ cells obtained from peripheral blood of patients with primary thymic defects (22q11 deletion and TBX1 SCID) differentiated normally up to the CD3 single-positive stage, with the major progenitor intermediates (proT, DN, DP) being present in similar fashion as to controls. Therefore, such tools could be used to facilitate clinical decisions facing unknown SCID, where doubt exists as to whether bone marrow or thymus transplantation is appropriate.