Stem cell transplantation is used widely in the management of a range of diseases of the hemopoietic system. Patients are immunosuppressed profoundly in the early posttransplant period, and reactivation of cytomegalovirus (CMV) remains a significant cause of morbidity and mortality. Adoptive transfer of donor-derived CMV-specific CD8+ T cell clones has been shown to reduce the rate of viral reactivation; however, the complexity of this approach severely limits its clinical application. We have purified CMV-specific CD8+ T cells from the blood of stem cell transplant donors using staining with HLA–peptide tetramers followed by selection with magnetic beads. CMV-specific CD8+ cells were infused directly into nine patients within 4 h of selection. Median cell dosage was 8.6 × 103/kg with a purity of 98% of all T cells. CMV-specific CD8+ T cells became detectable in all patients within 10 d of infusion, and TCR clonotype analysis showed persistence of infused cells in two patients studied. CMV viremia was reduced in every case and eight patients cleared the infection, including one patient who had a prolonged history of CMV infection that was refractory to antiviral therapy. This novel approach to adoptive transfer has considerable potential for antigen-specific T cell therapy.

Immune function in the elderly is associated with a number of phenotypic and functional abnormalities, and this phenomenon of immune senescence is associated with increased susceptibility to infection. The immune response to pathogens frequently declines with age, but the CD8 ؉ T-cell response to cytomegalovirus (CMV) is unusual, as it demonstrates a significant expansion over time. Here we have documented the CD4 ؉ T-cell immune response to CMV in healthy donors of different ages. The magnitude of the CMV-specific CD4 ؉ T-cell immune response increases from a mean of 2.2% of the CD4 ؉ T-cell pool in donors below 50 years of age to 4.7% in donors aged over 65 years. In addition, CMV-specific CD4 ؉ T cells in elderly donors demonstrate decreased production of interleukin-2 and less dependence on costimulation. CMV seropositivity is associated with marked changes in the phenotype of the overall CD4؉ T-cell repertoire in healthy aged donors, including an increase in CD57؉ expression and a decrease in CD28 and CD27 expression, a phenotypic profile characteristic of immune senescence. This memory inflation of CMV-specific CD4 ؉ T cells contributes to evidence that CMV infection may be damaging to immune function in elderly individuals.Healthy aging is associated with the development of a number of phenotypic and functional abnormalities of the immune system. These include the accumulation of memory T cells, impaired functional responses in vitro, and a reduction in the response rate to vaccinations (5, 8). These findings are associated with the phenomenon of immune senescence and are thought to underlie the increased rate of infectious disease that is seen in elderly individuals (7).The magnitude of the cellular immune response to a number of pathogens has been studied in donors of different ages and has revealed that cellular immunity to viruses such as influenza virus and varicella-zoster virus decreases with advancing age (3). In marked contrast to these findings, the CD8 T-cell response to cytomegalovirus (CMV) increases markedly with age, such that it may represent over 40% of the CD8 ϩ T-cell pool (14,15). A similar observation has been seen with the CD8 T-cell immune response to murine cytomegalovirus (13). There has been speculation that this accumulation of memory CD8 T cells may itself contribute to features of immune senescence, and this idea has gained support from studies of elderly donors in whom CMV seropositivity is associated with the development of an immunological phenotype associated with impaired survival (16,29).CD4 T cells are important in the induction and regulation of the cellular immune response to pathogens, and an impaired CMV-specific CD4 T-cell immune response has been correlated with prolonged viral secretion following neonatal infection (10). Currently little is known with regard to how the magnitude or functional properties of the CD4 T-cell immune response to CMV are influenced by aging. Here we have studied the CMV-specific CD4 T-cell response to CMV viral lysate in a cohort of 30 ...

Reactivation of CMV is a common complication following allogeneic haematopoietic SCT and is associated with significant morbidity and mortality. The relative importance of the CD4 þ and CD8 þ components of the CMVspecific immune response in protection from reactivation is unclear. The CMV-specific CD4 þ and CD8 þ immune response was measured at serial time points in 32 patients following allogeneic HSCT. Intracellular cytokine staining following CMV lysate stimulation and HLA-peptide tetramers were used to determine CMV-specific CD4 þ and CD8 þ responses, respectively. A deficient CMVspecific CD4 þ T-cell immune response within the first 30-50 days post transplant was associated with high risk of viral reactivation. Patients with combined impairment of the CD4 þ and CD8 þ immune response within the first 100 days were susceptible to late viral reactivation. The frequency of CMV-specific CD4 þ T cells correlated with CMV-specific CD8 þ T cells, comprising 10% of the whole T-cell repertoire. Early CMV-specific CD4 þ T-cell reconstitution was dominated by effector memory cells with normal levels of IL-2 resuming 6 months following transplantation. In summary, both CD4 and CD8 CMV-specific immune reconstitution is required for protection from recurrent activation. Measurement of the magnitude of the CMV-specific CD4 þ immune response is useful in managing viral reactivation following HSCT.