Thymosin fraction 5 does not accelerate reconstitution of immunologic reactivity after human marrow grafting.

More than 1 year is required for immunologic function to recover following human marrow grafting. In an attempt to shorten the time required for immunologic reconstitution, 14 patients were treated with thymosin fraction 5 after transplantation. Two died before administration of thymosin could be completed. In the remaining 12 patients, immunologic studies were compared to those of patients who were transplanted but did not receive thymosin. While five patients had transient elevation of in vitro lymphocyte blastogenesis during thymosin treatment, results of other immunologic studies from patients treated with thymosin were similar to those from patients not treated. The subsequent development of graft-versus-host disease, major or minor infection, and leukaemic relapse was not different between the groups. Six patients are alive and five are well without problems; one has chronic graft-versus-host disease. We conclude that thymosin fraction 5 administered as described was not toxic. Although modifying some immunological parameters, thymosin did not appear to alter the incidence of graft-versus-host disease, infection or leukaemic relapse or to accelerate immunologic reconstitution.