Some researchers have hypothesized that the fetus can be exposed to and mount an immune response against allergens to which the mother has been exposed, and this may have an effect on the development of allergic sensitivity (e.g. eczema and asthma) later in an infant’s life. However this hypothesis has remained controversial because of an inability to detect antigen-specific T cells in cord blood. Recently, a newly developed technique known as MHC tetramer staining has facilitated the detection of antigen-specific T cells.