J. Brochier et al., Optimizing therapeutic strategies to inhibit circulating soluble target molecules with monoclonal antibodies: example of the soluble IL-6 receptors, EUR J IMMUN, 31(1), 2001, pp. 259-264
Therapeutic targeting of soluble molecules such as cytokines can be achieve
d with monoclonal antibodies (mAb). Anti-IL-6 mAb have been shown to form c
irculating complexes, resulting in the increase of the half-life of the cyt
okine in vivo. In IL-6-related diseases, the soluble human IL-6 receptors (
shIL-6R), which have been shown to possess strong agonist activity, circula
te in the plasma at a high concentration and must be neutralized. Their cle
arance was studied in mice that had been made to express circulating shIL-6
R after i.p. grafting of mouse thymoma cells transfected with a gene coding
for shIL-6R, treated with various anti-shIL-6R mAb recognizing different e
pitopes of the molecule. Injection of one anti-hIL-6R mAb stabilized the sh
ort-lived hIL-6R and led to their accumulation. The same result was observe
d when two mAb directed against two different epitopes of the hIL-6R were u
sed. Clearance of the receptors was only achieved when three mAb specific f
or three different epitopes were injected. A permanent clearing of the hIL-
6R could be obtained by repeated injections of the clearing mixture. No cor
relation was found between the ability of the mAb to clear the sIL-6R and t
o immunoprecipitate them in agarose gel. The F(ab')(2) fragments lost the c
learing ability of the intact mAb. These results clearly show that therapeu
tic clearance of sIL-6R by mAb need at least three mAb directed against thr
ee different epitopes of the molecule, a conclusion which is likely to appl
y for clearing any soluble target molecule.