TGF-Beta Signaling Favors Central Memory Phenotype Expression By Ex-Vivo Stimulated Human T Cells

Adoptive immunotherapy using ex vivo differentiated and expanded T cell lines can be remarkably efficient to treat cancer and infections. Unfortunately, the process of ex vivo T cell stimulation can lead to terminal effector differentiation and functional exhaustion thereby limiting the persistence and therapeutic effects of these T cells after transfer. Accumulating evidence suggests that, owing to their proliferative capacity, self-renewal ability and long term persistence in vivo, T cells bearing a central memory (CD45RO⁺/CD62L⁺ - Tcm) instead of an effector memory (CD45RO⁺/CD62L^- - Tem) phenotype before adoptive transfer can mediate more significant therapeutic activity. Transforming-growth factor-beta (TGF-β) is a pleiotropic cytokine that influences several aspects of T-cell biology and that is best known for its growth suppression and immunosuppressive activity. We show that TGF-β signaling can have a profound impact on the number of CD4 and CD8 T cells expressing the Tcm and Tem phenotype after anti-CD3e and anti-CD28 stimulation without altering the number of cells recovered at the end of the culture and without inducing regulatory T cells. By enhancing the percentage of the lymph-node homing receptors, L-selectin (CD62L) and CC-chemokine receptor 7 (CCR7) expressing cells, exogenous TGF-β, added to the culture medium to a concentration of 5 ng/ml, favors Tcm over Tem cell accumulation at 7 days (CD4⁺: 55.80 vs 35.51% (P= 0.0074); CD8⁺: 56.9 vs 40.3% (P= 0.0063)). Reciprocally, the inhibition of TGF-β signaling with a TGF-β receptor kinase inhibitor (GW788388) accentuated Tem phenotype acquisition. Importantly, these effects of TGF-β on Tcm marker expression were maintained in the presence of exogenous cytokines commonly used in ex-vivo cultures for adoptive immunotherapy (IL-2, IL-7 and IL-15). The manipulation of TGF-β signaling did not increase the expression of exhaustion markers (KRLG-1, CD57) but exogenous TGF-β decreased interferon-gamma (IFN-γ) expression. No effect was noted on TNF-α and IL-2 expression as well as on the percentage of polyfunctional cells generated. We also found that modulating TGF-β signaling during the course of clinically relevant cultures capable of expanding T-cells specific for Epstein-Barr virus LMP2 protein antigens, in the presence of IL-7 and IL-15, could increase the number of CD4 Tcm cells, even 2 weeks after the withdrawal of TGF-β from the culture (38.24 vs 27.82, N=3) without compromising antigen-specific IFN-γ release. In conclusion, the modulation of TGF-β signaling can significantly alter Tcm and Tem phenotype acquisition and may therefore be used to optimize Tcm phenotype expression by ex-vivo pathogen/antigen-specific T cells expanded for adoptive immunotherapy.