Immunologic Monitoring after Allogeneic Stem Cell Transplantation: T-SPOT.CMV and QuantiFERON-CMV, Are They the Same?

Despite prophylactic and preemptive strategies, cytomegalovirus (CMV) reactivation and disease remains major concerns after allogeneic hematopoietic stem cell transplantation (allo-HSCT). In recent years, immunologic monitoring using CMV commercially available IFN-γ release assays (IGRAs) has gained interest to better risk-stratify immunocompromised patients or to guide prophylactic therapy. CMV-IGRA can quantify CMV cell-mediated immunity by measuring the IFN-γ that is released by CD4⁺ and CD8⁺ T lymphocytes in the presence of CMV antigens. However, the 2 most widely used CMV-IGRAs, T-SPOT.CMV and QuantiFERON-CMV, had not yet been compared in the setting of an allo-HSCT. In the present study, we performed a method comparison between T-SPOT.CMV and QuantiFERON-CMV at 28 days and 100 days post-allo-HSCT, and to assess predictive values of both tests for CMV reactivation. Twenty-seven patients were included in a bicentric prospective trial. Samples were obtained on days +28 and +100 post-allo-HSCT, and patients' clinical information was collected up to day +270 post-HSCT. Comparisons of methods were performed using Cohen's κ. On day +28 (n = 26) post-allo-HSCT, T-SPOT.CMV yielded 3 positive test results and QuantiFERON-CMV yielded 2 positive results. On day +100 (n = 24), T-SPOT.CMV produced 7 positive test results, and QuantiFERON-CMV produced 9. One discordant result was obtained at day +28 (n = 26), and 6 discordant results were obtained at day +100 (n = 24). Method comparison showed a strong agreement on day +28 (κ = .780; 95% confidence interval [CI], .366 to 1.000) but only a moderate agreement on day +100 (κ = .442; 95% CI, .070 to .814) and in pooled data from both time points (κ = .578; 95% CI, .300-.856). Four clinically significant CMV infections (CS-CMVi) were observed, all occurring after discontinuation of letermovir prophylaxis. None of those 4 patients had a positive result with either test at day +100 (or day +28). Thus, the negative predictive value (NPV) and sensitivity were very high, at 100% for both tests measured at day +100. Positive predictive values (PPVs) and specificity were considerably lower at day +100 (T-SPOT.CMV: PPV, 23.5%; specificity, 35%; QuantiFERON-CMV: PPV, 26.7%; specificity, 45%). T-SPOT.CMV and QuantiFERON-CMV had only moderate agreement (at day +100) after allo-HSCT. Although these IGRAs are very promising, as shown by their very high NPVs for protection against CS-CMVi, they are not interchangeable. Future research should stipulate which IGRA was used, and future guidelines preferably should be assay-specific. As QuantiFERON-CMV still lacks a large post-allo-HSCT validation study, the moderate agreement with T-SPOT.CMV poses a significant hurdle in the routine implementation of this test.