A pilot study was performed to explore the clinical potential of Leu2a antibody in reversing acute renal allograft rejection. Anti-Leu2a, a murine IgGi monoclonal antibody (mlgGi mAb), is specific for the CD8 molecule that is expressed in high density on class I reactive T cells. Of the 6 recipients treated with anti-Leu2a, two responded with a complete reversal of rejection with long-term allograft function maintained for over a year. In two other recipients, acute rejection was initially reversed, but later rejection episodes resulted in allograft failure at 2–3 months posttreatment. Rejection in the two other recipients showed no response to Leu2a mAb treatment. Specific depletion of peripheral blood CD8+cells occurred in four of the six recipients. Even in this small series, it was evident that cell clearance