Ikaros, Helios, and Aiolos protein levels increase in human thymocytes after β selection

Abstract

In human T cell development, the mechanisms that regulate cell fate decisions after TCRβ expression remain unclear. We defined the stages of T cell development that flank TCRβ expression and found distinct patterns of human T cell development. In half the subjects, T cell development progressed from the CD4−CD8− double negative (DN) stage to the CD4+CD8+ double positive (DP) stage through an immature single positive (ISP) CD4+ intermediate. However, in some patients, CD4 and CD8 were expressed simultaneously and the ISP population was small. In each group of patients, CD3− ISP and DP thymocytes were subdivided into ISP1, ISP2, DP1, DP2, DP3, DP4, and DP5 developmental stages according to their expression of CD28, CD44, CD1a, CD7, CD45RO, and CD38. The ISP2, DP2, and DP3 thymocyte populations proliferated more robustly than ISP1 and DP1 and expressed markers consistent with TCRβ expression. After the DP3 stage, proliferation returned to baseline levels. We then analyzed protein levels of Ikaros, Helios, and Aiolos, the three Ikaros family members most abundantly expressed in human thymocytes. Ikaros and Helios expression increased transiently at the ISP2, DP2, and DP3 populations. Aiolos expression also increased at the ISP2, DP2, and DP3 stages, but its expression remained elevated throughout the DP4 and DP5 stages. In summary, we propose a model of human T cell development that reflects the asynchronous nature of TCRβ expression and we define the subpopulations of thymocytes that are highly proliferative and express Ikaros family members.

Expression patterns of Ikaros family members during positive selection and lineage commitment of human thymocytes

“…Nearly all TSP CD8 + thymocytes were CD38 hi CD45RO hi . These observations extend our previous findings that thymocytes progress from CD38 lo CD45RO lo to CD38 hi CD45RO hi as they mature through the CD3 − developmental stages and continue to up‐regulate these markers as the cells advance through the CD3 lo stages.…”

“…Ikaros, Helios and Aiolos protein levels increase when TCR‐ β is first expressed . For Ikaros and Helios, the increase in expression was transient whereas the increase in Aiolos was sustained throughout the CD3 – DP populations.…”

“…b). For comparison, we also analysed CD38 and CD45RO expression among CD3 − DP thymocytes, which we previously used to define the CD3 − DP developmental stages . Among CD3 − DP thymocytes, 27 ± 4·6% of cells were CD38 hi CD45RO hi and 67 ± 4·5 of CD3 lo DP thymocytes were CD38 hi CD45RO hi .…”

“…c). We previously used CD38, CD45RO, CD44 and CD7 expression to define the DP1 through DP5 subsets of CD3 − DP thymocytes; the DP3, DP4 and DP5 populations are shown in Fig. (c).…”

The checkpoint for agonist selection precedes conventional selection in human thymus

“…In addition to CD8αα, these thymocytes also express PD-1 and CD28, both markers induced by pre-TCR signaling (Fig. 5b) (14, 33–35). Together, these observations indicate that among the DP progenitors, the expression of CD8αα, PD-1 and CD28 marks a subset that we will refer to as ‘TP blasts’.…”