γδ T lymphocyte regeneration after T lymphocyte-depleted bone marrow transplantation from mismatched family members or matched unrelated donors

The recovery of γδ T lymphocytes was studied in 31 recipients of T cell-depleted allogeneic bone marrow (BMT) to determine if the dynamics of reconstitution could be related to graft-versus-host disease (GVHD) or other complications of marrow transplantation. Two distinct patterns of regeneration were apparent. In 12 patients, there was a progressive rise in both the percentage and the absolute number of peripheral blood γδ T cells over the first year post-transplantation, but these increases never breached levels found in 14 healthy donors. Each of the 19 remaining patients had abnormally high proportions and numbers of γδ T cells on at least two occasions following transplantation. The clinical factor that best explained these observations was the frequency of intercurrent infections. Of 19 patients with abnormally increased percentages and numbers of γδ T lymphocytes, 18 had one or more episodes of confirmed viral or fungal infection, contrasted with only two of 12 in the comparison group (P < 0.001). There was no significant association of γδ T cell recovery patterns with the presence of GVHD (P = 0.33). We conclude that the recovery of γδ T lymphocytes after marrow transplantation may vary. Supranormal levels of this T cell subset are associated with infection and may contribute significantly to cellular immune defenses against fungal or viral disease.