Safety and immunogenicity of modified vaccinia Ankara (ACAM3000): effect of dose and route of administration

Abstract

Background: We conducted a clinical trial of the safety and immunogenicity of modified vaccinia Ankara (MVA) to examine the effects of dose and route of administration.

Methods: Seventy-two healthy, vaccinia virus-naive subjects received 1 of 6 regimens of MVA (ACAM3000) or placebo consisting of 2 administrations given 1 month apart.

Results: MVA was generally well tolerated at all dose levels and by all routes. More pronounced local reactogenicity was seen with the intradermal and subcutaneous routes than with intramuscular administration. Binding antibodies to whole virus and neutralizing antibodies to the intracellular mature virion and extracellular enveloped virion forms of vaccinia virus were elicited by all routes of MVA administration and were greater for the higher dose by each route. Similar levels of neutralizing antibodies were seen at a 10-fold-lower dose given intradermally (1 x 10(7) median tissue culture infective doses [TCID(50)]), compared with responses after 1 x 10(8) TCID(50) given intramuscularly or subcutaneously. T cell immune responses to vaccinia virus were detected by an interferon gamma enzyme-linked immunospot assay but had no clear relationship to dose or route.

Conclusions: These data suggest that intradermal immunization with MVA provides a dose-sparing effect by eliciting antibody responses similar in magnitude and kinetics to those elicited by the intramuscular or subcutaneous routes but at a 10-fold-lower dose.

Trial registration: ClinicalTrials.gov NCT00133575.

Conflict of interest statement

Potential Conflict of Interest: none

Figures

Figure 1

Proportion of vaccinees experiencing (A) local or (B) systemic symptoms after first or second MVA vaccination, by dose and route. Severity of symptoms were graded by NIAID-DMID toxicity tables.

Figure 2

Binding antibody responses elicited by MVA prime/boost immunizations. Serum samples were obtained at days 0, 14, 28, 35, 42, 84, and 180 following MVA immunization. Serial dilutions were tested for antibody binding activity against (A) ACAM3000 MVA or (B) VV:WR by ELISA. Data are presented as median serum endpoint with the interquartile ranges for each dose and route-of-immunization group. The dashed line represents the limit of detection (serum endpoint titer=30), and arrows indicate days of vaccination.

Figure 3

Antibody responses to IMV and EEV associated antigens following MVA prime/boost immunizations. Serum samples were obtained two weeks following primary immunization (d.14) and two weeks following boost immunization (d.42). Serial dilutions were tested for antibody binding activity against two IMV (A27L and L1R) and two EEV (A33R and B5R) associated protein antigens by ELISA. Data are presented as individual endpoint titers with bars indicating median titer per group. PL indicates the placebo group.

Figure 4

Neutralizing antibody responses elicited by MVA prime/boost immunizations. Serum samples were obtained at days 0, 7, 14, 28, 35, 42, 56, 84, and 180 following MVA immunization. Serial dilutions were tested for neutralizing activity against (A) MVA:Luc or (B) VV:Luc. Data are presented as median ID50 titers with interquartile ranges for each dose and route-of-immunization group. The dashed line represents the limit of detection (serum ID50 titer=10), and arrows indicate days of immunization.

Figure 5

Assessment of anti-EEV neutralizing antibody responses by comet reduction assay. Serum samples were obtained two weeks following boost immunization (d. 42) and tested in a comet reduction assay at a 1:50 dilution. Data are presented as the percent comet reduction observed from individual subjects in each dose and route-of-immunization group, with bars indicating the median response. PL indicates the placebo group.

Figure 6

Cellular immune responses elicited by MVA prime/boost immunizations. PBMC were obtained at days 0, 14, 28, 35, 42, 56, 84, and 180 following MVA immunization and tested by the IFN-γ ELISPOT assay against autologous VV:WR-infected target cells. Data are presented as median SFC per 106 effector PBMC with interquartile ranges for each dose and route-of-immunization group following subtraction of responses to medium alone and pre-immune background values.