To cite R/npem in publications use:

  Broman et al. (1996) Estimation of antigen-responsive T cell
  frequencies in PBMC from human subjects. J Immunol Meth 198:119-132
  doi:10.1016/S0022-1759(96)00136-6

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Estimation of antigen-responsive {T} cell frequencies in {PBMC} from human subjects},
    author = {Karl Broman and Terry Speed and Michael Tigges},
    journal = {J. Immunol. Meth.},
    year = {1996},
    volume = {198},
    pages = {119-132},
    doi = {10.1016/S0022-1759(96)00136-6},
    url = {https://doi.org/b54v33},
    eprint = {https://www.biostat.wisc.edu/~kbroman/publications/jim.pdf},
  }