Inhibition of contact sensitivity in human CD4(+) transgenic mice by humanCD4-specific monoclonal antibodies: CD4(+) T-cell depletion is not required

Clenoliximab and keliximab are monkey/human chimeric monoclonal antibodies (mAbs) of the immunoglobulin G4 (IgG4) and IgG1 isotypes, respectively, tha t recognize the same epitope on human CD4. The two mAbs possess identical i diotypes and exhibit equal affinities for CD4. Upon administration of these mAbs to mice that express a human CD4 transgene, but not mouse CD4 (HuCD4/ Tg mice), clenoliximab and keliximab exhibited similar kinetics of binding to CD4, and induced the same degree of CD4 modulation from the cell surface , although only keliximab mediated CD4(+) T-cell depletion. Epicutaneous se nsitization and challenge of HuCD4/Tg mice with the hapten oxazolone result ed in a contact sensitivity response characterized by tissue swelling, and the presence of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in th e local tissue. Administration of a single 2-mg dose of either clenoliximab or keliximab to HuCD4/Tg mice prior to sensitization significantly reduced post-challenge tissue swelling, and levels of IFN-gamma and IL-4, indicati ng that CD4(+) T-cell depletion is not required for anti-CD4 mAb-mediated i nhibition of contact sensitivity. Administration of either mAb prior to cha llenge failed to inhibit the contact sensitivity response, indicating diffe rential sensitivity of the afferent and efferent phases of the response to inhibition by CD4-specific mAbs. Collectively, these data indicate that CD4 functions as a positive regulatory molecule in the contact sensitivity res ponse.