don't need to be US citizens or PR.The following is directly copied from an NIH grant page:

Eligible Project Director/Principal Investigator (PD/PI): Also referred to as the Applicant or Candidate, individuals with the skills, knowledge, and resources necessary to carry out the proposed research and career activities are invited to with their mentor (if applicable) and sponsoring institution to develop an application for support. They must have a health professional or science doctoral degree and be: 1) already proficient in general epidemiology, behavioral sciences, or other relevant disciplines, and now want to make use of these proficiencies in cancer-focused research careers in prevention, control, population and/or the behavioral sciences; or 2) already trained in cancer epidemiology, etiology, prevention, control, and the behavioral and population sciences, but are not yet fully independent investigators. Individuals from underrepresented racial and ethnic groups, individuals with disabilities, and individuals from disadvantaged backgrounds are always encouraged to apply for NIH support. Applicants must be U.S. citizens, non-citizen nationals, or permanent residents, who hold a research or health-professional doctoral degree and can commit the minimum required effort to relevant career activities.