Lymphocyte Immunization Therapy (LIT) is a fertility treatment that involves injecting white blood cells from the father-to-be into the skin of the prospective mother. LIT is often done after many failed IVF cycles and suspected immunologic reasons for failed implantation. The growing embryo and fetal tissues are derived from both the mother and father’s genes, and it is theorized that the mother’s immune system is recognizing proteins derived from the husband’s part of the genome as foreign and attacking the growing fetus. LIT is thought to mitigate this harmful reaction to the growing embryo/fetus by providing a “friendly” introduction to paternal proteins, antigens, and cellular structures that could be classified as harmful and thus trigger the termination of an early-stage pregnancy.