To the Editor:
We have read with interest the paper by Kotze et al. (1), reporting the retrospective analysis of 2,040 patients for the expression of soluble HLA-G (sHLA-G) by day-2 embryos after intracytoplasmic injection. The data represent further confirmation of the role of sHLA-G molecule quantification in embryo culture supernatants as a marker for embryo selection (2). In pregnancy several tolerance mechanisms have been demonstrated to counteract the maternal immune response. Among these, the expression of HLA-G by invasive cytotrophoblasts has been shown to play a fundamental role in creating a tolerogenic condition at the feto-maternal interface (2).
By now, more than 15,000 embryo culture supernatants have been evaluated for sHLA-G expression, with a positive correlation with embryo implantation rate and pregnancy outcome. However, further research is needed in HLA-G investigation in assisted reproductive technology (ART). Three aspects should be taken into consideration: 1) recognition of a common sHLA-G detection protocol; 2) necessity to identify a standardized range for positivity, as reported by Kotze et al. (1); 3) comprehension of the factors involved in the differential expression of sHLA-G between equal stage embryos originating from the same woman (3). Read the rest of this entry »