Interleukin-5 (IL-5) Therapy Prevents Allograft Rejection by Promoting CD4 + CD25 + Ts2 Regulatory Cells That Are Antigen-Specific and Express IL-5 Receptor.

CD4 ⁺ CD25 ⁺ Foxp3 ⁺ T cell population is heterogenous and contains three major sub-groups. First, thymus derived T regulatory cells (tTreg) that are naïve/resting. Second, activated/memory Treg that are produced by activation of tTreg by antigen and cytokines. Third, effector lineage CD4 ⁺ CD25 ⁺ T cells generated from CD4 ⁺ CD25 ^- T cells' activation by antigen to transiently express CD25 and Foxp3. We have shown that freshly isolated CD4 ⁺ CD25 ⁺ T cells are activated by specific alloantigen and IL-4, not IL-2, to Ts2 cells that express the IL-5 receptor alpha. Ts2 cells are more potent than naïve/resting tTreg in suppressing specific alloimmunity. Here, we showed rIL-5 promoted further activation of Ts2 cells to Th2-like Treg, that expressed foxp3, irf4, gata3 and il5. In vivo , we studied the effects of rIL-5 treatment on Lewis heart allograft survival in F344 rats. Host CD4 ⁺ CD25 ⁺ T cells were assessed by FACS, in mixed lymphocyte culture and by RT-PCR to examine mRNA of Ts2 or Th2-like Treg markers. rIL-5 treatment given 7 days after transplantation reduced the severity of rejection and all grafts survived ≥60d whereas sham treated rats fully rejected by day 31 (p<0.01). Treatment with anti-CD25 or anti-IL-4 monoclonal antibody abolished the benefits of treatment with rIL-5 and accelerated rejection. After 10d treatment with rIL-5, hosts' CD4 ⁺ CD25 ⁺ cells expressed more Il5ra and responded to specific donor Lewis but not self. Enriched CD4 ⁺ CD25 ⁺ cells from rIL-5 treated rats with allografts surviving >60 days proliferated to specific donor only when rIL-5 was present and did not proliferate to self or third party. These cells had more mRNA for molecules expressed by Th2-like Treg includin g Irf4, gata3 and Il5. These findings were consistent with IL-5 treatment preventing rejection by activation of Ts2 cells and Th2-like Treg.
Competing Interests: BH and SH hold patents related to production of antigen specific Treg and tests of tolerance related to this work. The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.
(Copyright © 2021 Hall, Hall, Tran, Robinson, Wilcox, Rakesh, Wang, Sharland, Verma and Hodgkinson.)