Glycoprotein B vaccine is capable of boosting both antibody and CD4 T-cell responses to cytomegalovirus in chronically infected women

Abstract

Traditionally, vaccines have been utilized to generate immune responses to a pathogen in a naive population. In the setting of congenital cytomegalovirus (CMV) infection, a vaccine that, when administered to women already infected with CMV, could boost the mother's immunity to CMV would most likely be beneficial in diminishing in utero transmission of CMV. However, the ability to boost an immune response in a population of individuals seropositive for a pathogen of interest is not well studied. This study examines the ability of a recombinant CMV glycoprotein B vaccine with MF59 adjuvant to boost both antibody (neutralizing and enzyme-linked immunosorbent assay end point dilution titer) and CD4+ T-cell responses in previously CMV-seropositive women by way of natural infection. These data suggest that this vaccine is capable of boosting immunity in a population of CMV-infected women and warrants additional evaluation to determine whether these boosted responses may prevent mother to child transmission of CMV.

Figure 1.

Immunization schedule. Arrows indicate day of vaccination (day 0, day 28, and day 180). Boxed dates are time points for blood collection days for both antibody titers and CD4+ T-cell assays. Bolded dates are time points for blood collection days for antibody titer measurements, and dates in italics are for CD4+ T-cell assays.

Figure 2.

CD4+ T cells proliferate in response to glycoprotein B (gB) protein. Peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with gB protein, a pool of peptides from cytomegalovirus pp65, or staphylococcal enterotoxin B (SEB). A, The frequency of proliferating CD3+CD4+ T cells was determined by labeling PBMCs with 5, 6-carboxyflourescein diacetate succinimidyl ester (CFSE) at prevaccination (day 0) and 2 weeks after vaccination (day 14) and is shown for a selected individual. Percentage of CFSE^lo cells is indicated in the upper left hand quadrant. CD4+ T cell proliferative responses are shown in response to gB protein (B) or pP65 protein (C) at the indicated time points. Data for all vaccine-naive subjects (placebo recipients and individuals at the prevaccination time point of day 0) are combined. Net responses (ie, with unstimulated responses subtracted) are plotted. The median response is shown by the horizontal line. Vaccination time points are indicated by an arrow.

Figure 3.

Induction of glycoprotein B (gB)–specific CD4+ T cells measured by intracellular cytokine staining. A, interferon (IFN) γ secretion from CD4+ T cells from a vaccinated volunteer at day 0 (prevaccination), day 14 (2 weeks after the first vaccination), day 180 (5 months after the second vaccination), day 194 (2 weeks after the third vaccination), and day 360 (6 months after the third vaccination). Peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with gB protein, and the frequency of IFN-γ producing CD3+CD4+ T cells was determined by intracellular cytokine staining assay. Percentage of CD4+ IFN-γ+ cells is indicated in the upper right hand quadrant. B, The generation of gB-specific CD4+ T cells from all vaccinees at the indicated time points is shown. Net responses (ie, with unstimulated responses subtracted) are plotted. C, Upregulation of CD154 on PBMCs from vaccinees in response to gB stimulation after vaccination. D, The proportion of gB-specific CD4+ T cells that are IFN-γ⁺CD127^hi is shown. Only responder individuals, as defined by a positive response to gB by IFN-γ secretion, are shown. Net responses (ie, with unstimulated responses subtracted) are plotted. The median responses are shown by horizontal line. Vaccination time points are indicated by an arrow.