(233) ELISpot Assay for Fetus-Specific T Cell Response in Human Pregnancy

Objective: Evidence from mouse models show that healthy pregnancies induce T cell hypofunction against fetus-specific antigens (FSA) as a mechanism of tolerance to the fetus. Inappropriate regulation of fetus-specific T cells is implicated in obstetric complications such as preterm birth, preeclampsia, miscarriage. Our hypothesis is that maternal T cells are tolerized (hyporesponsive) against FSA in successful human pregnancy, and produce less IFN-gamma (IFNg) when exposed to matched (mDCs) compared to unmatched/3rd-party fetal dendritic cells (uDCs).

Study Design: This is a prospective, proof of concept, pilot study. IRB approval and patient consent was obtained. Maternal peripheral blood and umbilical cord blood (UCB) was collected at delivery. DCs were matured from UCB, and used as stimulators of maternal peripheral blood mononuclear cells (PBMC). ELISpot assay was used to measure IFNg production by maternal T cells against mDC and uDC. The frequency of IFNg-producing cells was normalized against positive control stimulation with anti-CD3/CD28. Additional controls included influenza vaccine ± DCs.

Results: A total of 27 participants were included in analysis. The majority (n=14 of 27; 55.6%) exhibited no or very low response to mDC, significantly lower than to uDCs. Notably a subset of patients (n=5 of 12, 41.7%) with high gravidity (≥5 pregnancies) exhibited hyper responsiveness to mDCs compared to uDCs, suggesting aberrant T cell response.

Conclusion: We developed an IFNg ELISpot assay to quantify the magnitude of maternal T cell responses to FSA. T cell IFNg responses to mDC were lower compared to uDCs in a majority of pregnancies. Higher gravidity was associated with sensitized responses to mDCs. In some pregnancies, increased gravidity may override pregnancy-induced T cell tolerance. This suggests that additional mechanisms constrain memory T cell responses to ensure successful pregnancy. Future directions include measuring T cell responses to paternal antigens in patients with obstetric complications, as well as investigating how therapeutically targeting aberrant T cells may treat these complications.