Background
In 2022, Clade IIb human monkeypox virus (MPXV) led to Mpox outbreaks in many non-endemic countries. Modified vaccinia Ankara vaccines (Imvamune®) are used to curb MPXV transmission. However, vaccine effectiveness is limited and Mpox immunity is not well characterized, especially in persons living with HIV (PLWH). We hypothesized that T cell responses to MPXV antigens produced early in infection may be effective in immune clearance.
Methods
Using the Immune Epitope Database, we created a panel of 46 peptides derived from proteins produced early in poxvirus infection also present in MPXV Clade IIb. 28 male participants from Toronto, Canada (mean age = 41 years; range = 21-75) were enrolled: 15 (53%) were PLWH all on anti-retroviral therapy (ART), 10 individuals recovered from Mpox (MPXV-R; median = 376 days post symptom onset), 9 received two doses of Imvamune® (MPXV-V; median time since second dose = 5 mo), and 9 were poxvirus-naïve individuals (MPXV-N). Peptide specific interferon gamma (IFN-g) and granzyme B (GB) responses were determined using ex vivo peripheral blood mononuclear cells (PBMC) by enzyme-linked immunosorbent spot assays in spot-forming cells per million PBMC (SFC/106 PBMC). Peptide responses were considered positive if SFC/106 PBMC were at least twice the average MPXV-N response and ≥ 20. We compared responses among MPXV-R, -V, and -N groups using Kruskal-Wallis tests, and HIV status with Mann-Whitney U tests.
Results
18/19 (95%) of MPXV-R and MPXV-V participants responded to at least 3 peptides, with IFN-g responses being more frequent than GB. The median total IFN-g responses using our peptides were 1794 vs 1078 vs 328 SFC/106 PBMC in MPXV-R, MPXV-V, MPXV-N, respectively (p<0.01). IFN-g responses tended to be greater in PLWH than people without HIV in MPXV-R (median = 2389 vs. 389 SFC/106 PBMC, p=0.067). Total GB responses were much lower than IFN-g responses (e.g. MPXV-R median = 185 SFC/106 PBMC) and significant differences were not observable between the 3 groups (p=0.53). 13 peptides failed to induce GB in any individual.
Conclusions
We find potent MPXV-specific IFN-g responses in MPXV-R and -V individuals. In PLWH who recovered from Mpox, we observed elevated IFN-g responses which suggests immune imprinting. The etiology of low GB responses in MPXV-R and -V is unclear but could suggest loss of circulating effector cytotoxic T cell responses after recovery of Mpox or vaccination. Further epitope characterization of these peptides will inform future MPXV vaccines.
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