Immediately following her completion of education, she began working at a private practice in NB, Canada as a veterinary surgeon for two years.
In addition, Simpson has done work for the National Cancer Institute, was the Deputy Director of the Clinical Sciences Centre at Imperial College, London, and continues to spend many summers at the Jax Laboratory in Maine.
Her studies in the area of minor histocompatibility antigens showed that male-specific cytotoxic T cells recognize self-MHC and products of genes on the Y chromosome.
Simpson's work has led to an increased understanding of immunological tolerance and graft acceptance/rejection, leading organ transplantation to become safer and more successful for patients.
[4] She is now using information to address fundamental questions, such as T cell-repertoire selection and immunodominance, and to devise models for investigating the modulation of in vivo haematopoietic stem cells.