Anti-CD4 MoAb therapy in kidney transplantation--a pilot study in early prophylaxis of rejection.

B-F5, a mouse IgG1 anti-CD4 MoAb, was used in recipients of a first cadaveric kidney allograft. Eighteen patients received 30 mg/day MoAb with a quadruple sequential therapy. All but one kidney were functioning at 6 months, with a mean serum creatinine of 153 micromol/L. However, 50% of the patients had an acute rejection episode within the first three months, and most of the early episodes (i.e., < 1 month) occurred in patients with low levels of circulating MoAb. The biological analysis showed a strong depleting effect on the CD4+ cell counts, a saturation by the MoAb of the remaining circulating CD4+ cells, and no detectable immunization against B-F5. Although the biological parameters indicate an action of B-F5 in vivo, the clinical data associated with poor MoAb bioavailability suggest the need for an improved pharmacokinetic behavior of the MoAb to determine its use for prophylaxis of early rejection.