• Response [ Time Frame: at 6months ] [ Designated as safety issue: No ]
  

• Failure free and overall survival [ Time Frame: at 2 years ] [ Designated as safety issue: No ]
  

Traditionally horse antithymocyte globulin (ATG) has been the preferred animal source of ATG as first line treatment for acquired aplastic anaemia (AA) patients who are ineligible for bone marrow transplantation (BMT). For severe AA (SAA) the combination of ATG and Ciclosporin (CSA) results in response in 60-75% of patients and the response is superior to using either agent alone. The addition of granulocyte colony stimulating factor (G-CSF) to the combination of ATG and CSA has so far shown no significant benefit in terms of response and survival, but an EBMT prospective study is currently evaluating this further in a larger number of patients. For patients with NSAA who are transfusion dependent, the combination of ATG and CSA was shown to be superior to CSA alone in an EBMT prospective randomised study, with a higher response rate, superior blood counts and improved disease free survival using the combination of ATG with CSA.

There have been no phase II studies of rabbit ATG (Thymoglobuline®) in the treatment of AA as first line therapy. Preliminary results from a small single centre study compared horse ATG (ATGAM) with rabbit ATG (Fresenius) in children and showed response rates of 93% and 47%, respectively, but it is likely that different preparations of rabbit ATG will vary in their efficacy. Rabbit ATG is more commonly used for a second course following relapse or lack of response to a first course of horse ATG. Rabbit ATG in combination with CSA and G-CSF was used in patients with SAA who had failed to respond to a course of horse ATG with CSA and G-CSF. Overall response (transfusion independence) was seen in 23/30 (77%) of patients after a median of 95 days and complete response (neutrophils > 2.0, haemoglobin > 11, and platelets > 100) in 9/30 (30%). Rabbit ATG was well tolerated; no anaphylaxis or severe side effects were reported. Another study of 43 patients treated with rabbit ATG and CSA following non-response or relapse after horse ATG and CSA, showed 30% response rate among non-responding patients and 65% response rate for relapsing patients.

Studies comparing the antibody specificities between Thymoglobuline® and Lymphoglobuline® are in broad agreement, but (a) Lymphoglobuline® has fewer studies and those reported are older, because the product is older and has been less extensively developed (b) antibodies against certain epitopes are inconsistently present (c) not all antibody specificities have been examined in some studies and (d) different methods of testing have been used. There is a view that it is the immunogen and not the animal species which is most important in creating differences between different ATGs.