Background. CMV infection causes significant morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HCT). CMV cell mediated immunity, as assessed by T cells production of interferon gamma (IFN-γ) and other cytokines, is considered as a major pathway to control CMV replication. We aimed to evaluate the ability of a CMV-specific ELISPOT assay to predict the outcome of low-level CMV reactivation in allo-HCT recipients. Methods. In this prospective observational study, we

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... enrolled allo-HCT recipients with low level of CMV viral loads (VL) <1000 IU/mL or <500 IU/mL if they had graftversus-host disease or were receiving systemic corticosteroids. Patients were serially monitored with a CMV-specific ELISPOT assay (T-SPOT ® .CMV, Oxford Diagnostics Laboratories ® , Memphis, TN) on a weekly basis and up to 8 weeks from the date of first CMV reactivation. Progression from low level reactivation was defined as either ≥50% increase in CMV VL and/or CMV end-organ disease. Data from 25 patients who reached 4 weeks of follow-up were analyzed. Results. Majority of the patients were white (43%), males (70%), with a median age of 58 (18-68) years, and had unrelated (52%) or matched related (30%) HCT. Progression of CMV infection occurred in 12 (52%) allo-HCT recipients. We observed an inverse correlation of peak CMV VL with CMV specific pp65 spot counts (SPC) (Co-efficient= -0.44, P = 0.01). Mean (±SD) pp65 SPC was significantly lower in patients who progressed from low level CMV reactivation when compared to patients who did not (10 (± 20) versus 183 (± 138) SPC; P = 0.0003, respectively). The risk of CMV progression was 52% for a decline of 10 pp65 SPC by next time point of