A positive ReceptivaDx result for BCL6 does not correlate with abnormal ERA results or decreased expression of receptivity-associated markers: two sides of the endometrial receptivity coin in fertility evaluation and treatment.

Objective: To investigate if a positive result on ReceptivaDx for evaluation of B-cell lymphoma 6 (BCL6), a proposed marker of progesterone resistance associated with impaired uterine receptivity, correlates with a suboptimal profile of receptivity-associated markers in the window of implantation using the endometrial receptivity array and single-nucleus transcriptomic analysis.

Design: Retrospective clinical cohort study; pilot study of single-nucleus RNA sequencing of prospectively collected window of implantation endometrium undergoing ReceptivaDx BCL6 evaluation.

Setting: Academic center.

Patients: Patients with infertility who underwent endometrial biopsy for concurrent endometrial receptivity array analysis (ERA; Igenomix, Valencia, Spain) and BCL6 immunostaining (ReceptivaDx; Cicero Diagnostics, Inc., Huntington Beach, CA).

Intervention: Positive BCL6 result on ReceptivaDx (histologic score >1.4).

Main outcome measures: Prereceptive ERA result; relative expression levels of endometrial receptivity-associated epithelial genes by single-nucleus sequencing.

Results: One hundred and seventy-two patients with concurrent ERA and ReceptivaDx evaluation were included in the analysis: 40 were BCL6-positive and 132 were BCL6-negative. One patient (2.5%) in the BCL6-positive group had a prereceptive ERA result, compared with 29 patients (22.0%) in the BCL6-negative group (P<.01). BCL6 positivity was associated with decreased odds of a prereceptive ERA result (odds ratio, 0.09; 95% confidence interval, 0.01-0.69; P=.02). Single-nucleus transcriptomic analysis of 5,718 epithelial cell nuclei from four individuals showed significant cell type-specific transcriptomic changes associated with a positive ReceptivaDx BCL6 result in both natural cycle (NC) and programmed cycle (PC) endometrium: there were 2,801 significantly differentially expressed genes comparing NC BCL6-positive with -negative, and 1,062 differentially expressed genes comparing PC BCL6-positive with -negative. Of the 34 receptivity-associated epithelial markers evaluated, 16 were significantly upregulated in NC BCL6-positive vs. -negative endometrium epithelial nuclei. In PC epithelial nuclei, 12 of the 34 receptivity-associated genes were significantly upregulated, whereas only one was significantly downregulated in BCL6-positive vs. -negative endometrium.

Conclusions: A positive ReceptivaDx BCL6 result does not correlate with a prereceptive ERA. Epithelial cells from BCL6-positive endometrium did not show significantly decreased expression in most of the receptivity markers evaluated. These findings demonstrate discordance between the interpretation of "endometrial receptivity" by ReceptivaDx and ERA, and highlight the need for further validation of endometrial evaluation methods in fertility treatment.