Impact of regulatory T cell therapy on immune cell composition and fetal survival rate in abortion prone mice.

Context: Implantation of fertilised eggs and survival of a semi-allogenic embryo rely on the interactions between the cells and molecules preparing the uterus. We investigated the effect of regulatory T cell (Treg) therapy on the mechanism of local immune tolerance of mice prone to spontaneous abortion.

Methods: Naive T cells were stimulated in vitro with 17β-oestradiol (E2), progesterone (P4) and TGF-β1 for 96h to generate induced Tregs (iTreg). The iTregs were injected into DBA/2-mated pregnant CBA/J female mice (abortion prone model). On day 14 of pregnancy, mice were killed and decidual and placental tissues were collected for cellular composition analysis.

Results: Abortion prone mice (PBS treated) showed significantly lower survival rates (P <0.0001), increased CD3+ CD8+ (P <0.05), lower IDO+ (P <0.05) and increased natural killer cells (uNK) cell numbers (P <0.001) in the uterus, as well increased NK cells in the placenta (P <0.05) than in normal pregnant mice (CBA/J×BALB/c). Adoptive transfer of iTregs increased fetal survival in abortion-prone mice (P <0.01) and histopathological evaluation revealed a significantly decreased number of uNK cells in the uterus of TGF-β1-, E2- and P4-iTregs (P<0.05, P<0.0001 and P<0.05, respectively) than in the PBS treated group. In the placenta, we found significantly lower numbers of uNK cells from TGF-β1-, E2- and P4-iTregs than in the PBS treated group (P <0.05, P <0.05 and P <0.01, respectively).

Conclusions: We propose that modulation of uterine NK cell activity through immunotherapy using Treg cells should be given more attention as an immunological strategy in the treatment of recurrent miscarriage.