Darrell R Anderson

Elimination of Fc receptor-dependent effector functions of a modified IgG4 monoclonal antibody to human CD4.

Several CD4 mAbs have entered the clinic for the treatment of autoimmune diseases or transplant rejection. Most of these mAbs caused CD4 cell depletion, and some were murine mAbs which were further hampered by human anti-mouse Ab responses. To obviate these concerns, a primatized CD4 mAb, clenoliximab, was generated by fusing the V domains of a cynomolgus macaque mAb to human constant regions. The heavy chain constant region is a modified IgG4 containing two single residue substitutions designed to ablate residual Fc receptor binding activity and to stabilize heavy chain dimer formation. This study compares and contrasts the in vitro properties of clenoliximab with its matched IgG1 derivative, keliximab, which shares the same variable regions. Both mAbs show potent inhibition of in vitro T cell responses, lack of binding to complement component C1q, and inability to mediate complement-dependent cytotoxicity. However, clenoliximab shows markedly reduced binding to Fc receptors and therefore does not mediate Ab-dependent cell-mediated cytotoxicity or modulation/loss of CD4 from the surface of T cells, except in the presence of rheumatoid factor or activated monocytes. Thus, clenoliximab retains the key immunomodulatory attributes of keliximab without the liability of strong Fcγ receptor binding. In initial clinical trials, these properties have translated to a reduced incidence of CD4+ T cell depletion.

Human monoclonal antibodies isolated from spontaneous Epstein-Barr virus-transformed tumors of Hu-SPL-SCID mice and specific for fusion protein display broad neutralizing activity toward respiratory syncytial virus.

Two human monoclonal antibodies, RF-1 and RF-2, specifically recognize the fusion protein of the human respiratory syncytial virus (RSV). These were isolated from spontaneous tumors in SCID mice reconstituted with human splenocytes and boosted with fusion protein. The tumors consisted of Epstein-Barr virus-transformed human B cells in animals with antigen-specific antibody titers>105. The binding affinity of RF-1 and RF-2 to the fusion protein is 1010 and 109 M-1, respectively. The antibodies bind specifically to a conformational epitope of the fusion protein on RSV-infected HEp-2 cells. Both antibodies display virus-neutralizing properties in vitro at concentrations varying between 8 and 1000 ng/mL. Virus neutralization applies to a broad variety of wild and laboratory-adapted virus strains belonging to both virus types A and B. These antibodies are potential candidates for passive immunotherapy of severe RSV infections.