The impact of incomplete vaccination schedules on the magnitude and duration of protective antigen-specific IgG responses in recipients of the US licensed anthrax vaccine

The anthrax vaccine adsorbed vaccine generates protective antigen (PA)-Specific CD4+ T cells with a phenotype distinct from that of naive PA T cells

Cellular immune responses against protective antigen (PA) of Bacillus anthracis in subjects that received the anthrax vaccine adsorbed (AVA) vaccine were examined. Multiple CD4(+) T-cell epitopes within PA were identified by using tetramer-guided epitope mapping. PA-reactive CD4(+) T cells with a CD45RA(-) phenotype were also detected by direct ex vivo staining of peripheral blood mononuclear cells (PBMC) with PA-specific tetramers. Surprisingly, PA-specific T cells were also detected in PBMC of nonvaccinees after a single cycle of in vitro PA stimulation. However, PA-reactive CD4(+) T cells in nonvaccinees occurred at lower frequencies than those in vaccinees. The majority of PA-reactive T cells from nonvaccinees were CD45RA(+) and exhibited a Th0/Th1 cytokine profile. In contrast, phenotyping and cytokine profile analyses of PA-reactive CD4(+) T cells from vaccinees indicated that vaccination leads to commitment of PA-reactive T cells to a Th2 lineage, including generation of PA-specific, pre-Th2 central memory T cells. These results demonstrate that the current AVA vaccine is effective in skewing the development of PA CD4(+) T cells to the Th2 lineage. The data also demonstrated the feasibility of using class II tetramers to analyze CD4(+) cell responses and lineage development after vaccination.

Rapid point-of-care test to detect broad ranges of protective antigen-specific immunoglobulin G concentrations in recipients of the U.S.-licensed anthrax vaccine

Currently, there is no routine monitoring of an immune response to the anthrax vaccine. Simple on-site tests are needed to evaluate the antibody response of anthrax-vaccinated individuals in the Armed Forces and others at high risk. Using a prototype lateral flow assay (LFA) (R. E. Biagini, D. L. Sammons, J. P. Smith, B. A. MacKenzie, C. A. F. Striley, J. E. Snawder, S. A. Robertson, and C. P. Quinn, Clin. Vaccine Immunol. 13:541-546, 2006), we investigated the agreement between a validated anthrax protective antigen (PA) immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and the LFA for 335 unvaccinated and vaccinated subjects. We also investigated the performance of the LFA under the following conditions: thermal shock (i.e., thermal cycling between temperature extremes), high temperature/high relative humidity, high temperature/low relative humidity, and low temperature/low relative humidity. With the anti-PA ELISA used as a standard, the LFA was shown to be optimally diagnostic at 11 microg/ml anti-PA-specific IgG. At this concentration, the LFA specificity and sensitivity were 98% (95% confidence interval [CI], 97% to 100%) and 92% (CI, 88% to 97%), respectively. Receiver operating characteristic curve analysis yielded an area under the curve value of 0.988 (CI, 0.976 to 1.00), suggesting that the LFA is an extremely accurate diagnostic test. For < or = 4 or > or = 50 microg/ml PA-specific IgG, the LFA results for each environmental condition were identical to those obtained in the laboratory. These data indicate that this rapid point-of-care test would be a feasible tool in monitoring the serological antibody responses of individuals that have been vaccinated against anthrax.

Serum IgG antibody response to the protective antigen (PA) of Bacillus anthracis induced by anthrax vaccine adsorbed (AVA) among U.S. military personnel

The seroconversion rates and geometric mean concentrations (GMC) of IgG anti-PA for stored sera from U.S. military personnel immunized 3, 4, and 6 times with the U.S. licensed anthrax vaccine adsorbed were studied. Anti-PA IgG concentrations were measured by ELISA. All 246 vaccinees had low but detectable pre-immunization anti-PA IgG (GMC 1.83 microg/mL). Three doses elicited a GMC of 59.92 microg/mL and a seroconversion rate of 85.3%, four doses elicited a GMC of 157.44 microg/mL and 67.9% and the sixth of 276.95 microg/mL and 45.5%, respectively. The forth dose elicited 100% seroconversion compared to the pre-immunization level. These results should facilitate comparison between different immunization schedules and new vaccines.

Detection of anti-protective antigen salivary IgG antibodies in recipients of the US licensed anthrax vaccine

The immune response of anthrax vaccine recipients is not routinely monitored. For field use, a noninvasive test would be beneficial to evaluate the antibody response of anthrax-vaccinated individuals working within a high-risk area of possible exposure. The aim of this cross-sectional study was to determine whether whole saliva can be used as a surrogate matrix for the detection of 83 kDa protective antigen (PA)-specific immunoglobulin G (IgG). An enzyme-linked immunosorbent assay was used for the detection of PA-specific IgG in matched samples (serum and saliva) that were collected from vaccinated and unvaccinated participants. Specimens from 180 individuals revealed a positive correlation (r=0.73; P<0.0001) between the level of PA-specific antibody detected in the saliva and serum. The number of vaccinations influenced both the saliva and serum antibody response. On average, the concentration of serological PA-specific antibodies in the vaccinated group was nearly 1600-fold greater than that in saliva. The magnitude of the salivary anti-PA antibody response was not significantly affected by the consumption of food, beverage, or tobacco products or other factors, which could potentially affect oral fluid properties. These results suggest that an oral fluid-based immunoassay may be a feasible alternative to monitoring the serological antibody response of individuals that have been vaccinated against anthrax.