Engineering Mesenchymal Cells with Interleukin 7 Gene: In Vitro Effects on Naive T Cell Population.

T cell homeostasis is regulated by several molecules among which Interleukin 7 (IL-7) plays an essential role for survival and homeostatic proliferation of peripheral naive T cells. In a previous study we demonstrated whether human mesenchymal cells could be engineered with IL-7 gene to produce functional level of this cytokine. Now we analysed the impact of different quantities of IL-7 produced by mesenchymal cells on survival and proliferation of a negative immunoselected naive (CD3⁺/CD45RA⁺) T cell population. Co-cultivation of peripheral naive T cells with mesenchymal cells producing low (16 pg/ml) or high (1000 pg/ml) IL-7 levels or in presence of exogenous IL-7 (0,01 ng/ml and 100 ng/ml) maintained the CD3⁺/CD45RA⁺ naive T cell phenotype. The chemokine receptor CCR7⁺ expression was also maintained among this T cell population. Naive T cell molecular characteristics were maintained as assessed by the Vβ spectratyping complexity score which shows the maintenance of a broad T cell repertoire. No Th1 or Th2 differentiation was observed as assessed by IFNγ or IL-4 accumulation. In contrast only mesenchymal cells producing high IL-7 amount caused increases in the activation (CD25 31.2%±12 vs 10%±3.5, p<0.05), proliferation (CD71 17.8±7% vs 9.3%±3, p<0.05), apoptosis (assessed by annexin V: 18.6%±5 vs 14.9%±2.6, p>0.05) and phase S cell cycle (15% vs 6.9%, p>0.05). Exogenous IL-7 did not exert any significant effect. In conclusion, we demonstrated that IL-7 produced by mesenchymal cells has a dose-independent effect on naive T cell survival while exerts a dose-dependent effect on activation/proliferation. Due to continuous production of IL-7 by engineered cells, our system emerge as more efficacious than the exogenous IL-7.