In vitro monitoring of in vivo development of human anti-thymoglobulin antibodies by ELISA.
Thymoglobulin (rATG), polyclonal immunoglobulin, is prepared from rabbits immunized with human thymocytes. It is effective in prevention and treatment of renal allograft rejection. Human antibodies against antilymphocyte preparations can reduce efficacy by accelerating drug clearance or by inducing serum sickness. We developed an enzyme-linked immunosorbent assay (ELISA) to study posttreatment development of anti-rATG. In an Institutional Review Board-approved trial, we tested 101 allograft recipients for anti-rATG antibodies. Patients received rATG intravenously at 1.25 to 2.0 mg/kg/d for 2 to 14 days. Serum samples were obtained pretreatment and at weeks 1, 2, 4, 6, and months 3 and 6 post-rATG. ELISA plates were coated with rATG (10 microg/mL). Samples were diluted 1:100 and tested in quadruplicate. Positive samples were titrated. Horseradish peroxidase-conjugated (HRPO) affinity-purified goat anti-human immunoglobulin G (H&L) antibody reacted with bound human antibody. A chromagenic substrate for HRPO was added and optical density (OD, 490 nm) was read. An OD of twice the negative control was considered positive. Mean ODs of negative and positive controls were 0.113 +/- 0.030 and 1.042 +/- 0.196, respectively. Ten patients had detectable anti-rATG before rATG administration (1:100). Thirty-five of 101 patients (35%) developed anti-rATG antibody. Patients showed an initial positive anti-rATG antibody from days 8 to 59 after infusion and titers from 1:100 to 1:4000. In spite of rATG's postulated anti-B-cell activity, this study confirms that rATG induces sensitization at a frequency and titer seen with other xenogeneic antilymphocyte antibodies. Formation of such antixenoantibodies can have a negative impact on treatment response and hence warrant monitoring.