Expression of T cell activation antigen CD134 (OX40) has no predictive value for the occurrence or response to therapy of acute graft-versus-host disease in partial T cell-depleted bone marrow transplantation.

CD134 (OX40) is a member of the tumor necrosis factor family which is expressed by activated T lymphocytes. CD134 expression on T cells was monitored during the first 35 days post-transplant in 14 patients, receiving either an HLA-identical sibling bone marrow transplant (BMT), a matched unrelated transplant (MUD-BMT) or an autologous peripheral blood progenitor cell transplant (PBPCT). The sibling and unrelated grafts were partially depleted of T cells. CD134 expression on CD4+ T cells peaked between 7 and 14 days after BMT, with a mean peak value of 45% of CD4+ cells (range 26-70%) over all three patient groups. The observed pattern of CD4+ CD134+ expression, an increase during the first 2 weeks post-BMT followed by a gradual decline towards values of 15-40%, was similar in all groups. No difference in the kinetics of CD134 expression by CD4+ T cells was observed between the patients that did or did not develop graft-versus-host disease (GVHD), nor did the clinical effect of any treatment given for GVHD correlate with alterations in CD134 expression by CD4+ T cells. Absolute CD4+,CD134+ T cell numbers showed a more rapid increment after autologous PBPCT than after sibling or MUD transplants. We conclude that expression of CD134+ by CD4+ T lymphocytes cannot serve as a surrogate marker for allo-reactivity. CD134+ expression may reflect lymphocyte regeneration, rather than alloreactivity.