Prolonged immune deficiency following allogeneic stem cell transplantation: risk factors and complications in adult patients.

To evaluate the long-term immune reconstitution after allogeneic haematopoietic stem cell transplantation (SCT), we prospectively screened standard immune parameters in a series of 105 patients, at a median time of 15 months after SCT. Analysing lymphoid phenotypes, in vitro immune functions and immunoglobulin levels, we found that, more than 1 year post SCT, cellular and humoral immunity was still altered in a significant number of patients. CD4+ T cells were < 200/microl in one third of patients, and the CD4/CD8 ratio was still reversed in 78% of patients. Almost all patients showed positive T-cell responses against mitogens, but antigen-specific proliferation assays identified 20% to 80% of non-responders. B-cell counts were reconstituted in 61% of the patients, but levels of total immunoglobulins were still low in 59%. In multivariate analyses, human leucocyte antigen (HLA) disparity between donor and recipient and chronic graft-versus-host disease were the leading causes affecting immune reconstitution. Interestingly, cytomegalovirus (CMV) infections were strongly associated with normal CD8+ T-cell counts. Studying the impact of impaired immune reconstitution on the rate of infections occurring in the 6 years following screening, we identified three parameters (low B-cell count, inverted CD4/CD8 ratio, and negative response to tetanus toxin) as significant risk factors for developing such late infections.