Repository logo

First do no harm: uterine natural killer (NK) cells in assisted reproduction.

Change log


Shreeve, Norman 


Natural killer (NK) cells are a type of lymphocyte circulating in peripheral blood named because of their effector functions in killing target cells. Immune cells that share similar phenotypic characteristics but are poor killers populate the uterine lining at implantation and during early pregnancy when the placenta is established. The functions of these uterine NK (uNK) cells are essentially unknown but available data point to a role in regulating placentation in concert with other elements of the decidua and invading trophoblast cells. Despite the lack of scientific rationale and advice from clinical governing bodies, such as the Human Fertilisation and Embryology Authority, an increasing range of tests and therapies are still offered to women undergoing IVF or attending recurrent miscarriage clinics based on the myth that uterine NK cells need suppressing to prevent damage to the embryo. New treatments can be introduced at whim with subsequent demands for expensive trials to prove/disprove their efficacy. The evidence that targeting uNK or peripheral blood NK cells assists women with recurrent pregnancy failure is lacking. Healthcare professionals and patients should very carefully evaluate the practice of immunomodulation to enhance pregnancy outcome. A discussion on how to move towards stricter regulation of immunotherapy in non-hospital settings is now needed because it is clear that the potential risks and costs of these therapies outweigh any benefits.



assisted reproduction, embryo, immunotherapy, miscarriage, uterine natural killer cells, Adult, Female, Humans, Immunotherapy, Killer Cells, Natural, Reproductive Techniques, Assisted, Uterus

Journal Title

Hum Reprod

Conference Name

Journal ISSN


Volume Title



Oxford University Press (OUP)
A.M. acknowledges funding support from the Wellcome Trust and Centre for Trophoblast Research, University of Cambridge, UK. Funding to pay the Open Access publication charges for this article was provided by the University of Cambridge.