Suppressive characteristics of the cultured umbilical cord blood lymphocytes: enhanced suppression of non specific MLR by short term cultured peripheral blood and rosetted lymphocytes.

We have used the mixed leukocyte reaction assay (MLR) to compare the non-specific suppressor activity of fresh and short-term cultured peripheral blood rosetted lymphocytes from human umbilical cord blood. To a one way MLR between adult responders and irradiated adult stimulator cells, we added adult or cord blood mononuclear cells. Cord-blood derived mononuclear cells were more potent suppressors of the MLR than the adult peripheral blood mononuclear cells. When the fresh cord blood T cell fraction was separated from non-T cells by rosetting, the frequency and capacity of suppression fell, suggesting a role of non-T cells in this phenomenon. However, short-term culture (up to nine days) of cord blood derived T cells in the absence of mitogen resulted in a significant increase in their suppressive characteristics. Maternal cells were not used in any of these assays and the suppression was non specific. There was no HLA restriction to the response. The cord blood lymphocytes responded poorly to alloantigen when compared to the adult lymphocytes. In addition, there was a correlation between the allogeneic proliferative response and the suppressive capacity of the cord blood cells. Such a correlation was not found with the adult peripheral blood lymphocytes.