Dengue, a mosquito-borne acute viral illness, is a growing threat to public health. Dengue virus (DENV) exposure and infection prevalence is typically assessed using serological measurements. However, antibody titers may wane to undetectable levels over time, and serology alone may miss prior DENV infection, consequently underestimating true disease burden. In contrast, virus-specific T cell responses are more long-lived, and may tthus provide a more accurate indicator of DENV exposure and immune status. However, the extent to which DENV-specific cellular immunity is detectable in the absence of serological responses remains poorly defined.
To investigate this, we recruited two independent adult cohorts from Singapore (n = 37) and Vietnam (n = 49), both dengue-endemic countries, to characterize DENV-specific T cell immunity in relation to serostatus. Individuals in the Singapore cohort were sampled cross-sectionally, while those in the Vietnam cohort were followed longitudinally over a one-year period. Serostatus was determined using anti-dengue IgG ELISA followed by confirmation with plaque reduction neutralization testing (PRNT); Seropositivity was defined as a PRNT titer > 1:10. DENV-specific T cell responses were assessed using two complementary assays: IFN-γ ELISpot and whole-blood cytokine release assay, following stimulation with DENV-derived peptide pools. At enrollment, 19/37 individuals in Singapore and 43/49 individuals in Vietnam were DENV-seropositive. As expected, DENV-specific T cell responses were detected in the majority of seropositive individuals in both cohorts (94.7% [n = 18/19] in Singapore; 76.7% [n = 33/43] in Vietnam). Remarkably among seronegative individuals, DENV-specific T cell responses were detected in 50% (n = 9/18) and 33.3% (n = 2/6) of the Singapore and Vietnam cohorts respectively, albeit at lower levels compared to seropositive individuals. In the Vietnam cohort, a significant and continued expansion in DENV-specific T cell responses were observed over time even among individuals who remained seronegative at all time-points throughout the one-year period, suggesting persistent or repeated DENV exposure despite lack of seroconversion.
Collectively, our findings demonstrate that DENV-specific cellular immunity can be detected even in the absence of detectable serological responses, suggesting that reliance on serology alone may miss prior dengue exposure. Incorporating measurements of cellular immunity with serological studies would provide a more comprehensive assessment of DENV immune status, with important implications for both disease surveillance and vaccine-response evaluation.