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

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+CD56dimNK 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+CD56brightNK 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.