The present invention relates to methods of using lactoferrin (LF) to treat, prevent or reduce the incidence of organ transplant rejection and graft-versus-host-disease. More particularly, the present invention relates to methods of reducing an immune response against miss-matched transplanted organs such as kidney, heart, lung, liver, pancreas and stem cells by administering a composition of lactoferrin to the recipient patients. In addition, this invention relates to the treatment of bone marrow transplant (BMT) donors with lactoferrin to attenuate the development of graft-versus-host-disease in the recipients. Moreover, this invention relates to the treatment of xenograft organ donors with lactoferrin to attenuate the development of graft rejection in the recipients.