Interleukin-21 administration to aged mice rejuvenates their peripheral T-cell pool by triggering de novo thymopoiesis

The vaccination efficacy in the elderly is significantly reduced compared to younger populations due to thymic involution and age-related intrinsic changes affecting their naive T-cell compartment. Interleukin (IL)-21 was recently shown to display thymostimulatory properties. Therefore, we hypothesized that its administration to ageing hosts may improve T-cell output and thus restore a competent peripheral T-cell compartment. Indeed, an increase in the production of recent thymic emigrants (RTEs) attributable to intrathymic expansion of early thymic progenitors (ETPs), double-negative (DN), and double-positive (DP) thymocytes as well as thymic epithelial cell (TEC) was observed in recombinant (r)IL-21-treated aged mice. In sharp contrast, no alterations in the frequency of bone marrow (BM)-derived progenitors were detected following rIL-21 administration. Enhanced production of naive T cells improved the T-cell receptor (TCR) repertoire diversity and re-established a pool of T cells exhibiting higher levels of miR-181a and diminished amounts of the TCR-inhibiting phosphatases SHP-2 and DUSP5/6. As a result, stimulation of T cells derived from rIL-21-treated aged mice displayed enhanced activation of Lck, ZAP-70, and ERK, which ultimately boosted their IL-2 production, CD25 expression, and proliferation capabilities in comparison with T cells derived from control aged mice. Consequently, aged rIL-21-treated mice vaccinated using a tyrosinase-related protein 2 (Trp2)-derived peptide exhibited a substantial delay in B16 tumor growth and improved survival. The results of this study highlight the immunorestorative function of rIL-21 paving its use as a strategy for the re-establishment of effective immunity in the elderly.