Immunization with stallion lymphocytes for treatment of recurrent spontaneous abortion in thoroughbred mares

The incidence of recurrent spontaneous abortion within the human population in the Western world is low (2-5%) but significant, and a proportion of these pregnancy losses are thought to have an underlying immunological cause. Immunization of women who have a history of recurrent spontaneous abortion with lymphocytes isolated from their husband or a third party donor is one of several forms of immunotherapy used to treat the problem. Early pregnancy loss in Thoroughbred mares is also significant and, as in women, a small number of mares undergo repeated pregnancy losses. Two trials have been performed in which Thoroughbred mares suffering from recurrent spontaneous abortion before day 150 of gestation were immunized with lymphocytes isolated from the mating stallion or from an unrelated stallion. The first trial, which was conducted without control mares, resulted in a very high live birth rate (97%) for the mares (n=24) treated. Therefore, a second controlled double-blinded trial was established in which randomly selected mares (n=17) were treated with stallion (heterologous) lymphocytes and control mares (n=13) were injected with their own (autologous) lymphocytes. The live birth rates after these treatments were 88 and 77%, respectively. Thus, immunization with stallion lymphocytes had no effect on the incidence of abortion in mares suffering from recurrent spontaneous abortion.