Early transient suppression of immune checkpoint proteins T-cell immunoglobulin mucin-3 and programmed cell death-1 in peripheral blood lymphocytes after blastocyst transfer is associated with successful implantation

Abstract

Objective: To compare the changing peripheral levels of immune checkpoint proteins T-cell immunoglobulin mucin-3 (Tim-3)/galectin-9 (Gal-9), and programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) over a 9-day period after blastocyst transfer between women who did and did not conceive.

Design: Prospective observational study.

Setting: University teaching hospital.

Patients(s): Fifty-one infertile women undergoing day-5 blastocyst transfer.

Intervention(s): Serial blood samples obtained on the day of embryo transfer (ET), and 3, 6, and 9 days afterward for measurement of membranous Tim-3 and PD-1 expression on various peripheral lymphocytes by flow cytometry, and serum concentrations of ligands Gal-9 and PD-L1 by ELISA.

Main outcome measure(s): Membranous Tim-3 and PD-1 expression on lymphocytes and serum Gal-9 and PD-L1 concentrations and comparison of results between pregnant and nonpregnant women.

Result(s): In women who conceived, the measurements exhibited three different types of response: [1] a transient and statistically significant reduction of Tim-3⁺NK-like T cells, Tim-3⁺/PD-1⁺CD8⁺ T cells, and Tim-3⁺/PD-1⁺CD4⁺ T cells that returned back to baseline level 9 days after ET; [2] a reduction followed by steady increase to above baseline level on day 9 (Tim-3⁺CD56^dimNK cells); [3] a steady increase in expression after ET to reach a level statistically significantly higher than that of the baseline by day 9 (Tim-3⁺CD56^brightNK cells). Women who did not conceive showed no statistically significant fluctuation in any of the parameters measured across the four time pointswith exception of increased Tim-3 expression on NK cells on day 9.

Conclusion(s): Successful blastocyst implantation is associated with a reduction of Tim-3 and PD-1 expression in peripheral lymphocytes on days 3 and 6 that is no longer apparent on day 9.

Keywords: Implantation; PD-1; Tim-3; immune checkpoint; natural killer (NK) cells.