The role of monoclonal antibodies in the prevention of graft versus host disease.

We have previously reported that the elimination of T-lymphocytes (greater than 99%) from the donor bone marrow prevents significant graft versus host disease (GvHD). This has been confirmed by other centres. Many of these groups have applied monoclonal antibodies with cytolytic rabbit complement. In some of these studies mostly patients with fully matched sibling donors have been studied and no further immunosuppression has been given during the regeneration period. The experience here shows that the haemopoietic regeneration (to recover a total leucocyte count of 1.0 X 10(9)/l) has only been minimally delayed (mean 25 days) when compared to patients receiving standard methotrexate (Mtx) GvHD prophylaxis (22 days). The incidence of cytomegalovirus (CMV) infections (14%; none fatal) was lower than that in our previous 54 patients (43% CMV infections, 13% fatal). Furthermore, no fatal pneumonitis was seen. The regeneration of T-cells in our patients has shown normal values of T8-positive cells in the circulation from 45 to 50 days onwards, as opposed to the previous groups of patients whose T8-positive cells regenerated to 3-4 times higher than normal values. These observations indicate that T-cell depletion with monoclonal antibodies is an effective method for preventing GvHD, but further studies are necessary to investigate the cause(s) of a new occasional complication, the rejection of the newly established bone marrow.