Research article
Efficacy of tacrolimus treatment in two-dose single-group controlled trial for patients with refractory infertility
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Keywords
Tacrolimus
; Unexplained refractory infertility
; Maternal immune environment
; Th1-dominant cytokine pattern
; Th1/Th2 cell ratio
Introduction
Infertility refers to a reproductive system disorder characterized by the inability to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse. A World Health Organization report that analyzed 133 studies reporting on infertility prevalence between 1990 and 2021 revealed that globally approximately one in six persons experiences infertility at some point during their lives (World Health Organization, 2023). Major underlying factors of infertility are categorized as ovulatory dysfunction, tubal occlusion, endometriosis, diminished ovarian reserve, uterine factors, and male factors (Carson and Kallen, 2021). Approximately 85% of couples experiencing infertility have one or more of these identified factors, while the remaining couples suffer physically and mentally from unexplained refractory infertility. In a portion of women with refractory infertility, maternal immune system is implicated, potentially impairing immunological tolerance toward semi-allogeneic conceptus (Abdolmohammadi-Vahid et al., 2016, Yamaguchi, 2019, Kwak-Kim et al., 2022). Immune cells such as T cells, dendritic cells, macrophages, and natural killer (NK) cells in the endometrium and peripheral blood may provide insights into the elucidation of immunological factors in infertility. Immune factors regarding the occurrence of recurrent pregnancy loss include a shift toward T-helper (Th)1 in the Th1/Th2 ratios in CD4+ T cells, a decrease in the number of regulatory T cells (Treg), an imbalance in the Th17/Treg cell ratios, and an increase in the number and activity of NK cells (Yu et al., 2023), representing noteworthy findings.
Tacrolimus (FK506) inhibits calcineurin by forming the complex of FK506 and FK506 binding protein 12, leading to suppression of the cytoplasmic nuclear factor of T cell pathway. In Japan, it has been approved as immunosuppressants for patients with solid organ transplantation, rheumatoid arthritis, lupus nephritis, and active ulcerative colitis. FK506 is a 23-membered macrolide lactone produced by the original strain of Streptomyces tsukubaensis, which was isolated from a soil sample collected from Mount Tsukuba, Ibaraki, Japan (Muramatsu and Nagai, 2013). FK506 is known to suppress T cell-mediated immune responses in vitro, including the generation of cytotoxic T cells and the production of IL-2 and IFN-γ, and its suppressive activity is 50–100 times more potent than that of cyclosporine. These inhibitory effects on cellular immunity may contribute to modulating the maternal immune environment in patients with infertility exhibiting a Th1-dominant cytokine pattern.
This clinical trial aimed to evaluate the efficacy and safety of tacrolimus treatment in patients with unexplained refractory infertility who failed to achieve a chemical pregnancy after multiple in-vitro fertilization (IVF) and embryo transfer (ET) cycles with morphologically good-quality embryos.
Section snippets
Study design
We conducted two-dose, single-group controlled trial across four facilities in Japan to evaluate the efficacy, safety, and appropriate dosage of tacrolimus (Tacrolimus hydrate; Astellas Pharma Inc., Tokyo, Japan) in patients with unexplained refractory infertility. Patients completed a screening period followed by randomization to oral administration of either low- or high-dose tacrolimus, a 16-day randomized intervention period, and a post-intervention observation period. In accordance with
Population
From May 2023 to October 2024, a total of 26 patients underwent randomization, of which 17 were assigned to the low-dose group and nine to the high-dose group. All patients received tacrolimus treatment and were included in the SAS. Two patients in the low-dose group were excluded from the FAS because they met the exclusion criteria for hepatic dysfunction and blood abnormality with neutrophil count < 1500 /μL, respectively. Additionally, three patients in the low-dose group and one patient in
Discussion
According to an analysis of patients who experienced repeated implantation failures prior to the introduction of preimplantation genetic testing for aneuploidy, the clinical pregnancy proportion following the fourth IVF treatments after three previously failed attempts was approximately 20% (Yovel et al., 1994). In our trial, patients with unexplained refractory infertility were defined as those who had repeatedly failed conventional IVF treatments and for whom all known underlying factors had
Conclusion
This trial confirmed the safety and efficacy of tacrolimus treatment at two doses for patients with infertility exhibiting a Th1-dominant cytokine pattern. Tacrolimus is currently used off label in Japan for females with infertility, and its clinical management is left to the discretion of individual fertility clinics and physicians. This tacrolimus treatment was determined to be safe and effective by the 180th Advanced Medical Technology Review Subcommittee of the Ministry of Health, Labor and
Funding
This trial was supported by funding from the National Center for Child Health and Development (2021E-1, 2022S-3, 2024S-1, 2025C-22) and the Japan Agency for Medical Research and Development (AMED) (grant numbers: 20lk0201108h0001, 22lk0201158h0001, 23lk0201158h0002, 24lk0201158h0003).
CRediT authorship contribution statement
Yasushi Hirota: Methodology, Investigation. Eisuke Inoue: Writing – review & editing, Methodology, Formal analysis, Data curation. Osamu Yoshino: Methodology, Investigation. Takakazu Saito: Methodology, Investigation. Koji Nakagawa: Methodology, Investigation. Masanori Ono: Methodology, Investigation. Koushi Yamaguchi: Writing – review & editing, Supervision, Methodology, Conceptualization. Michi Hisano: Writing – original draft. Nakamura Hidehumi: Writing – review & editing, Supervision,
Declaration of Competing Interest
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Koushi Yamaguchi has patent licensed to Licensee. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank all investigators and staff who were involved in this trial. The authors also thank Yoko Yamashita of the Women’s Health Center, National Center for Child Health and Development, Japan for her support in conducting this trial.
. Study design
| Section | Screening | Enrollment | Study drug administration | Observation | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Date | −84 to −21 | −5 to −2 | −2 | 0 | 13 | 14 | 21 | 28 | 41 | |
| Eligibility assessment | ▼ | |||||||||
| Randomization (2:1) | ▼ | |||||||||
| Embryo transfer | ▼ | |||||||||
| Outcome assessment | ||||||||||
| Primary outcome | ▼ | (▼)* | ||||||||
| Secondary outcome | ▼ | (▼)* | ||||||||
| Safety outcomes | ▶ | ▶ | ▶ | ▶ | ▶ | ▶ | ▶ | |||
*If
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