Abstract: A method of reducing the chance of disease resulting from mononuclear cells in a body attacking desirable cell antigens in the body, such as antigens expressed by normal body cells or desirable engrafted cells, comprises reducing the number of mononuclear cell in the body that are likely to attack such desirable cell antigens. This is done by obtaining cell derived antigens subject to attack by mononuclear cells in the body and also obtaining mononuclear cells to be placed in the body. The mononuclear cells may be from a donor or may be removed from the subject body. The mononuclear cells are reacted, in vitro, with the cell derived antigens, such as by passing the mononuclear cells over a layer of fibroblast cells from the body expressing the desirable antigens, and recovering the mononuclear cells that do not bind to the antigens. These recovered cells are then infused into the body.