Long term T cell response and safety of a tetravalent dengue vaccine in healthy children

Abstract

As robust cellular responses are important for protection against dengue, this phase 2 study evaluated the kinetics and phenotype of T cell responses induced by TAK-003, a live-attenuated tetravalent dengue vaccine, in 4-16-year-old living in dengue-endemic countries (NCT02948829). Two hundred participants received TAK-003 on Days 1 and 90. Interferon-gamma (IFN-γ) enzyme-linked immunospot assay [ELISPOT] and intracellular cytokine staining were used to analyze T cell response and functionality, using peptide pools representing non-structural (NS) proteins NS3 and NS5 matching DENV-1, -2, -3, and -4 and DENV-2 NS1. One month after the second TAK-003 dose (Day 120), IFN-γ ELISPOT T cell response rates against any peptide pool were 97.1% (95% CI: 93.4% to 99.1%), and similar for baseline dengue seropositive (96.0%) and seronegative (98.6%) participants. IFN-γ ELISPOT T cell response rates at Day 120 were 79.8%, 90.2%, 77.3%, and 74.0%, against DENV-1, -2, -3, and -4, respectively, and remained elevated through 3 years post-vaccination. Multifunctional CD4 and CD8 T cell responses against DENV-2 NS peptides were observed, independent of baseline serostatus: CD8 T cells typically secreted IFN-γ and TNF-α whereas CD4 T cells secreted ≥ 2 of IFN-γ, IL-2 and TNF-α cytokines. NAb titers and seropositivity rates remained substantially elevated through 3 years post-vaccination. Overall, TAK-003 was well tolerated and elicited durable T cell responses against all four DENV serotypes irrespective of baseline serostatus in children and adolescents aged 4-16 years living in dengue-endemic countries. TAK-003-elicited CD4 and CD8 T cells were multifunctional and persisted up to 3 years post-vaccination.

Fig. 1. Participant flow.

Numbers of participants who completed the study in each country, and reasons for discontinuation. ^aParticipants enrolled in Panama; ^bsix participants enrolled in the Philippines and two participants enrolled in Panama.

Fig. 2. T cell response rates against DENV induced by TAK-003.

Percentage (error bars: 95% CI) of participants with a positive T cell response to any DENV peptide pool from first vaccination to Day 1185, by baseline serostatus (per protocol set). The percentage of positive responders is represented as the overall percentage and corresponding 95% CI, with a number of responders/total number of participants with samples included in the table. Peptide pools evaluated: DENV-2 NS1; DENV-1, -2, -3, and -4 NS3, and DENV-1, -2, -3, and -4 NS5. A positive T cell response was defined as IFN-γ ELISPOT response >3 times higher than baseline and ≥5 spot forming cells [SFCs]/10⁶ peripheral blood mononuclear cells [PBMCs]). LOD: 5 SFC/10⁶ PBMC. The terms “seropositive” and “seronegative” refer to baseline dengue serostatus. Seropositivity was defined as a neutralizing titer MNT ≥ 10 for at least one DENV serotype. ELISPOT enzyme-linked immunospot, IFN-γ interferon-gamma.

Fig. 3. T cell response rates against individual DENV serotypes induced by TAK-003.

Percentage (error bars: 95% CI) of participants with a positive T cell response to peptide pools matching DENV-1, DENV-2, DENV-3, and DENV-4 from first vaccination to Day 1185, by baseline serostatus (per protocol set). A positive T cell response was defined as IFN-γ ELISPOT response >3 times higher than baseline and ≥5 spot forming cells [SFCs]/10⁶ peripheral blood mononuclear cells [PBMCs]). LOD: 5 SFC/10⁶ PBMC. The terms “seropositive” and “seronegative” refer to baseline dengue serostatus. Seropositivity was defined as a neutralizing titer MNT ≥ 10 for at least one DENV serotype. Peptide pools evaluated: DENV-1, -2, -3, and -4 NS3, and DENV-1, -2, -3, and -4 NS5. The table indicates the number of participants with samples for each time point. ^an = 103 for DENV-1; ^bn = 100 for DENV-2 and -3; ^cn = 72 for DENV-3; ^dn = 96 for DENV-4. ELISPOT enzyme-linked immunospot, IFN-γ interferon-gamma.

Fig. 4. Magnitude of T cell responses against DENV induced by TAK-003.

Boxplot of median magnitude (error bars: interquartile range) of T cell responses to any DENV peptide pool and peptide pools matching DENV-1, DENV-2, DENV-3, and DENV-4 in participants with a positive T cell response from first vaccination to Day 1185, by baseline serostatus (per protocol set). A positive T cell response was defined as IFN-γ ELISPOT response >3 times higher than baseline and ≥5 SFC/10⁶ peripheral blood mononuclear cells [PBMCs]. Seropositivity was defined as a neutralizing titer MNT ≥ 10 for at least one DENV serotype. Limit of detection (LOD): 5 SFC/10⁶ PBMC. Peptide pools evaluated for “any” serotype: DENV-2 NS1, DENV-1, -2, -3, and -4 NS3, and DENV-1, -2, -3, and -4 NS5. Peptide pools evaluated for individual serotypes included NS3 and NS5 only for the corresponding serotype. Magnitude estimates for individual serotypes were calculated by adding together negative control-subtracted magnitude measures against individual peptides. The table indicates the number of participants with samples for each time point. ELISPOT enzyme-linked immunospot, IFN-γ interferon-gamma, PBMC peripheral blood mononuclear cells, SFC spot-forming cells. Boxplot elements: center line, median; box limits, upper and lower quartiles; whiskers, 1.5× interquartile range; points, outliers.

Fig. 5. Cytokine profiles of T cell responses against DENV NS proteins induced by TAK-003.

Heat maps of cytokine profiles for individual participants for a CD4 and b CD8 T cell response against DENV-2 NS1, NS3, and NS5 proteins one month after the second vaccination (Day 120) (ICS subset). The legend maps colors for individual subjects and cytokine profiles to magnitudes expressed as % cytokine-secreting CD4 or CD8 T cells. Data are shown for each of the tested peptide pools. IFNg interferon-gamma, IL2 interleukin 2, NS non-structural protein, TNFa tumor necrosis factor-alpha.

Fig. 6. Multifunctional T cell responses against DENV NS proteins induced by TAK-003.

Percentage (error bars: 95% CI) of CD4 and CD8 T cells secreting ≥2 cytokines against DENV-2 NS1, NS3, and NS5 from first vaccination to Day 1185, by baseline dengue serostatus (ICS subset). p Values represent the frequency of antigen-specific T cell subsets vs baseline using paired t-tests *p < 0.05; **p < 0.01; ***p < 0.001. Data are truncated at 0.07% for CD4 T cells and 0.5% for CD8 T cells for clarity. The terms “seropositive” and “seronegative” refer to baseline dengue serostatus. Seropositivity was defined as a neutralizing titer MNT ≥ 10 for at least one DENV serotype. The table indicates the number of participants with samples for each time point.

Fig. 6. Multifunctional T cell responses against DENV NS proteins induced by TAK-003.

Percentage (error bars: 95% CI) of CD4 and CD8 T cells secreting ≥2 cytokines against DENV-2 NS1, NS3, and NS5 from first vaccination to Day 1185, by baseline dengue serostatus (ICS subset). p Values represent the frequency of antigen-specific T cell subsets vs baseline using paired t-tests *p < 0.05; **p < 0.01; ***p < 0.001. Data are truncated at 0.07% for CD4 T cells and 0.5% for CD8 T cells for clarity. The terms “seropositive” and “seronegative” refer to baseline dengue serostatus. Seropositivity was defined as a neutralizing titer MNT ≥ 10 for at least one DENV serotype. The table indicates the number of participants with samples for each time point.