Characterization of new monoclonal antibodies that discriminate between soluble and membrane CD4 and compete with human anti-CD4 autoimmune sera

In this report we present results on immunization of hu-CD4 C57Black/6J transgenic mice with HIV-1 gp120₄₅₁ complexed with its receptor protein, CD4. In addition to development of anti-gp120 antibodies, these mice also produced two anti-CD4 monoclonal antibodies, designated T6 and T9. Both these antibodies recognize soluble CD4 but not membrane associated CD4. Their corresponding epitopes map to the D3-D4 domains of CD4. These characteristics are very similar to the HIV related anti-CD4 autoimmunity found in 10-15% of HIV-1 infected people. Therefore, 208 HIV-1 positive patients were screened for anti-CD4 humoral response of which 27 were found positive (13%). Sixteen of these patients were then tested for their ability to compete with the T6 and T9 anti-CD4 monoclonal antibodies. In such experiments saturating amounts of either T6 or T9 antibodies were able to prevent 20-80% of the human serum binding to immobilized soluble CD4 in competitive ELISA tests. The T6 and T9 antibodies therefore help to define distinct CD4 epitopes associated with clinical anti-CD4 autoimmunity.