Low serum levels of total rabbit-IgG is associated with acute graft-versus-host disease after unrelated donor hematopoietic stem cell transplantation: results from a prospective study.

In a prospective study we determined rabbit-IgG (r-IgG) levels in serum samples before (day 0) and after (days 1 and 7) unrelated donor hematopoietic stem cell transplantation (HSCT). Most patients suffered from a hematologic malignancy. All patients received rabbit antithymocyte globulin (ATG) as part of the conditioning for 2-4 days (2 mg/kg/day). We found a good correlation (r = 0.34, r = 0.42 and r = 0.46) between the dose of ATG and serum r-IgG levels at all 3 time points. The cumulative incidence of acute graft-versus-host disease (aGVHD) grades II-IV in patients given the 4, 6, and 8 mg/kg ATG dose was 50%, 34%, and 15% (P = .04), respectively. In patients with r-IgG < or = 70 microg/mL (n = 54) the cumulative incidence of grades II-IV aGVHD was 33% compared with only 6% in those with r-IgG >70 microg/mL (n = 18), P = .023. Low serum levels of r-IgG seem to be a strong predictor for aGVHD grades II-IV in patients treated with Thymoglobulin before unrelated donor HSCT.