Engineering donor mesenchymal cells with IL-7 hastens naive T cell recruitment in vitro and supports immunologic reconstitution after HSCT in NOD/SCID mice

Key players in human T-cell development after T- cell-depleted allogeneic stem cell transplants are bone marrow stroma and interleukin-7 (IL-7). We engineered human stromal cells with the IL-7 gene and studied the effects on T cells in vitro and on in vivo immunological reconstitution in NOD/SCID mice. Transduced mesenchymal cells were negative for CD45 and CD14, positive for CD90 (98.15%), CD105 (87.6%), and STRO-1 (86.7%) and stably produced IL-7 (16.37±2SD pg/ml). In cocultures with T cells, IL-7 engineered stromal cells inhibited PHA-induced T cell proliferation (proliferation index, 3.6 vs 8.0 in untransduced cells and 65.8 in PHA alone), and in cocultures with immunoselected naive T cells, they maintained the CD45RA+CD45RO- naive phenotype (resting naive cell count, 4.2 times more than controls). In NOD-SCID mice, they homed to all organs (highest percentages in liver and lung; overlapping signals in spleen, thymus, bone marrow, heart, kidney, skin and gut; traces in brain). In a NOD/SCID model, comparing transplantation of 1× 106 CD34+ cells, cotransplantation of 5× 105 untransduced mesenchymal cells and 1× 106 CD34+ cells and cotransplantation of 5× 105 IL-7 engineered stromal cells with 1× 106 CD34+ cells, the last improved engraftment in terms of CD45+ cells and significantly increased the CD3+ cell count in peripheral blood (1.4± 1.6 vs 7.4± 3; P< .05), bone marrow (0.8± 1 vs 5.5± 2; P< .05) and spleen (0.08± 0.1 vs 6.2± 2; P< .05). No significant differences emerged in CD19+ cell recovery. IL-7 serum concentrations did not vary at any time point posttransplantation. These data demonstrate that IL-7-transduced stromal cells maintain the naive T-cell phenotype (CD45RA+/CD45RO−) in vitro and serve to improve immunologic reconstitution after HSCT in NOD/SCID mice, thus emerging as an ideal scaffold for hastening immunological recovery in T-cell-deficient hosts.