The CD8 (+) T-cell response comprises terminally differentiated effector cells and antigen-experienced memory T cells. The latter encompass central (TCM) and effector (TEM) memory cells. TCM cells are superior in their protection against viral and bacterial challenges and mediation of antitumor immunity due to their higher proliferative ability upon antigen re-encounter. Defining a mechanism to enhance TCM cells and delay terminal differentiation of CD8 (+) T cells is crucial for cancer immune therapy, as it can promote a better tumor immune response. The differentiation of CD8 (+) memory T cells is thought to be coordinated by the phosphoinositide 3-kinase (PI3K)/Akt pathway. We, therefore, investigated the role of Akt isoforms in the differentiation and proliferation of memory CD8 (+) T cells. We found that Akt1 and Akt2, but not Akt3, drive the terminal differentiation of CD8 (+) T cells, and their inhibition enhances the therapeutically superior TCM phenotype. Furthermore, the inhibition of Akt1 and Akt2, but not Akt 3, delays CD8 (+) T-cell exhaustion and preserves naïve and TCM CD8 (+) T cells, thus enhancing their proliferative ability and survival and prolonging their cytokine and Granzyme B production ability. Here, we define a mechanism in which proliferative potential, function, and survival of CD8 (+) T cells are enhanced by maintaining a reservoir of TCM and naïve cells using only Akt1 and Akt2 inhibition. Therefore, our findings strongly suggest the utility of using Akt1 and Akt2 inhibitors to modulate CD8 (+) T cells, both for adoptive cell transfer and vaccine-based cancer immune therapies.
Bibliographical noteThe authors thank Dr Esteban Celis and Dr Rhea-Beth Markowitz for reviewing the manuscript and for their valuable suggestions and also thank Dr Lei Huang for his suggestions.
- central memory
- effector memory
- T cells