Back in 2014 the National Institutes of Health (NIH) announced that it would be taking steps to ensure that research involving lab animals and research cells would reflect the same gender standards required for research involving human subjects. At the time there were no official changes made to research regulations, but the NIH started a process of communication and discussion with researchers and other stakeholders about how to better account for both males and females in their research.
Now things are being formalized. Effective with grant applications due on or after January 25, the NIH is requiring projects be evaluated for how the proposals treat sex as a biological variable. If the project is focusing on only one sex the proposal must provide a strong justification based on the scientific literature, preliminary research data or other relevant factors. The NIH has provided guidance, with pointer to relevant sources, for complying with the new policy.
It has taken nearly two years to move from initial announcement from NIH to first requirements that sex as a biological variable is important in research. While some of this time can be accounted for by the typical time required in developing policy I think it also highlights the challenges in confronting and mitigating a longstanding bias against systematic consideration of sex in biomedical research. As noted in this 2015 GAO report, the agency has had trouble in effectively integrating data from women in clinical trials. I think it plausible that similar challenges face the integration of both sexes in animal and cell research.