This 2018 Israeli human study subject was natural killer cell epigenetic memory of pregnancies:
“Natural killer (NK) cells were first discovered for their ability to kill tumor cells, and later found to also kill pathogen-infected cells.
Different tissue-resident subpopulations of human NK cells exist throughout the body, displaying unique phenotypic and functional properties. One of the most fascinating tissue-resident subsets of NK cells, termed decidual NK cells, is found at the maternal fetal interface (decidua) in direct contact with the placenta.
We discovered a population found in repeated pregnancies, which has a unique transcriptome and epigenetic signature..have open chromatin around the enhancers of [growth factor genes] IFNG [essential for angiogenesis] and VEGFA [supporting vascular formation].
The pregnancy-related NK memory cells identified here might represent the first example of improved function of NK cells that occurs under healthy physiological conditions.”
One source for the experiments was:
“Decidual samples from healthy women who underwent elective first trimester terminations of normal pregnancies.”
https://www.sciencedirect.com/science/article/pii/S1074761318301286 “Trained Memory of Human Uterine NK Cells Enhances Their Function in Subsequent Pregnancies” (not freely available)