Jurkat cell-reactive anti-thymocyte globulin assessed ex vivo by flow cytometry persists three weeks in circulation

Rabbit anti-thymocyte globulin (ATG-Fresenius) is a polyclonal anti-serum r aised against the lymphoblastic T cell line Jurkat. It is used for in vivo depletion of host and donor T cells for allogeneic stem cell transplantatio n. After administration of 90 mg/kg prior to transplant, rabbit immunoglobu lin G (IgG) remains present for 4-5 weeks, but it is unknown how long T cel l-reactive antibodies persist. Therefore, we measured anti-Jurkat antibodie s by flow cytometry. The detection limit for Jurkat-reactive antibodies was 0.1 mg/ml rabbit IgG; half-maximal labeling of Jurkat cells required 183 m ug/ml rabbit ATG. The mean half-life of Jurkat-reactive antibodies in 7 pat ients was 4 days. Detectable levels persisted up to 3 weeks with antibody l evels equivalent to 0.2-4.1 mug/ml rabbit ATG. Jurkat-reactive antibodies w ere eliminated two-fold faster than rabbit IgG, as assessed by enzyme-linke d immunosorbent assay (ELISA). The results suggest that in patients pretrea ted with ATG before transplantation, residual anti T-cell antibodies may ef fectively modulate recovery of T cells generated after transplantation, the reby lowering the incidence of severe GVHD.