Additionally, immunology testing to measure the effect of the new 6MP formulation on immunological FACS analysis will be performed on peripheral blood lymphocytes at 0, 12 and 24 hours post-dosing of each formualtion. Lymphocytes will be tested for surface marker expression (ex: CD3, CD4, CD8, CD25, NKT, etc.), with anticipated results a greater lowering of immune parameters after even 1 dose of 40 mg delayed release test drug, as compared to 100 mg Purinethol.