Detection of DBY and UTY antibodies after stem cell transplantation. Sixteen F → M HSCT patients had 5 or more serial plasma samples tested for DBY and UTY antibodies. All had one or more samples test H-Y antibody-negative before later samples tested positive, and 12 had at least 2 negative samples. Eleven patients developed both DBY and UTY antibodies. Four developed only DBY antibody, and one developed only UTY antibody. Smoothing spline curves are superimposed on the scatterplots for anti-DBY and anti-UTY.²⁸