Development and Function of Innate Polyclonal TCRαβ+ CD8+ Thymocytes

Abstract

Innate CD8 T cells are found in mutant mouse models, but whether they are produced in a normal thymus remains controversial. Using the RAG2p-GFP mouse model, we found that ∼10% of TCRαβ+ CD4−CD8+ thymocytes were innate polyclonal T cells (GFP+CD44hi). Relative to conventional T cells, innate CD8 thymocytes displayed increased cell surface amounts of B7-H1, CD2, CD5, CD38, IL-2Rβ, and IL-4Rα and downmodulation of TCRβ. Moreover, they overexpressed several transcripts, including T-bet, Id3, Klf2, and, most of all, Eomes. Innate CD8 thymocytes were positively selected, mainly by nonhematopoietic MHCIa+ cells. They rapidly produced high levels of IFN-γ upon stimulation and readily proliferated in response to IL-2 and IL-4. Furthermore, low numbers of innate CD8 thymocytes were sufficient to help conventional CD8 T cells expand and secrete cytokine following Ag recognition. This helper effect depended on CD44-mediated interactions between innate and conventional CD8 T cells. We concluded that innate TCRαβ+ CD8 T cells represent a sizeable proportion of normal thymocytes whose development and function differ in many ways from those of conventional CD8 T cells.

Differential effects of γc cytokines on postselection differentiation of CD8 thymocytes

“…This observation is consistent with previous work showing that innate TCR␣␤ CD8 T cells are IL-4 dependent 15 and that they diverge from classic CD8 T cells during or shortly after positive selection. 16 The CD69 ϩ Foxo1 lo Klf2 lo S1pr1 lo phenotype of IL-4-induced CD8 T cells suggests that their migration toward the medulla and their export from the thymus might be delayed relative to classic CD8 T cells. Considering that only 10% of TCR␣␤ CD8 thymocytes are innate T cells in vivo, 16 For personal use only.…”

“…16 The CD69 ϩ Foxo1 lo Klf2 lo S1pr1 lo phenotype of IL-4-induced CD8 T cells suggests that their migration toward the medulla and their export from the thymus might be delayed relative to classic CD8 T cells. Considering that only 10% of TCR␣␤ CD8 thymocytes are innate T cells in vivo, 16 For personal use only. on May 10, 2018. by guest www.bloodjournal.org From is produced by a rich network of TECs, particularly at the corticomedullary junction and in the medulla, whereas IL-4 is produced by rare PLZF ϩ NKT cells in the medulla.…”

“…on May 10, 2018. by guest www.bloodjournal.org From polyclonal TCR␣␤ CD8 T cells 15,16 and was more conspicuous in the presence of EIINFEKL than other peptides. These CD8 int CD69 hi PD-L1 hi CD44 hi cells did not bind TL tetramers (supplemental Figure 6A), suggesting that they do not express CD8␣␣ homodimers.…”

“…In fact, the generation of a specific subset of "innate polyclonal" CD8 thymocytes was recently found to be dependent on IL-4 provision in addition to TCR signals. 15,16 The fetal thymic organ culture model and its variants have been invaluable for dissecting the mechanisms of positive selection in vitro. 17 However, these systems are hampered by several technical intricacies and cannot be used for high-throughput studies required to gain further insights into the role of specific peptides and cytokines in positive selection and T-cell differentiation.…”

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

“…S1A). The use of the RAG2p‐GFP model allows to easily assess de novo thymopoiesis as expression of the GFP transgene, marking newly developed T cells, is controlled by the Rag2 promoter activity (Monroe et al ., 1999; Yu et al ., 1999; Rafei et al ., 2011). Thymic analysis 1 week following the last injection revealed a progressive increase in total thymocyte count in 15M but not 2M‐old rIL‐21‐treated mice with an optimal response rate achieved at a dose of 50 μg kg −1 (Fig.…”