Evaluation of cytomegalovirus-specific T-cell reconstitution in patients after various allogeneic haematopoietic stem cell transplantation using interferon-γ-enzyme-linked immunospot and human leucocyte antigen tetramer assays with an immunodominant T-cell epitope

Cytomegalovirus (CMV) infection is a major complication for patients who received allogeneic haematopoietic stem cell transplantation (HSCT). Accurate monitoring of CMV-specific T-cell reconstitution is required for appropriate decision on treatment, such as anti-viral drugs, which have adverse effects. Although human leucocyte antigen (HLA) tetramer and interferon-γ-enzyme- linked immunospot (IFN-γ-ELISPOT) assays have been used to measure CMV-specific T cells, detailed comparison of these assays and kinetics of anti-CMV T-cell reconstitution between reduced-intensity transplantation (RIST) and conventional HSCT has not yet been performed. In this study, we performed prospective comparative monitoring of CMV-specific T cells using HLA tetramer and IFN-γ-ELISPOT assays with a single immunodominant CMV ₄₉₅ peptide in 28 HLA-A*0201 and 9 HLA-A*0206 patients after various allogeneic HSCTs. The IFN-γ-ELISPOT assay was more sensitive for evaluation of functional T cells than the HLA tetramer assay, and CMV-specific T cells were reconstituted earlier in patients who received RIST without anti-thymocyte globulin (ATG) than those receiving RIST with ATG or conventional HSCT. The threshold level for protection from CMV reactivation was estimated as over 1 × 10 ⁶ cells/l peripheral blood with the IFN-γ-ELISPOT assay. These results demonstrate that the IFN-γ-ELISPOT assay with CMV ₄₉₅ provides more accurate evaluation on CMV immunity in HLA-A*0201 and -A*0206 patients, and may be useful for determining timing of various treatments.