Heterovariant cross-reactive B-cell responses induced by the 2009 pandemic influenza virus A subtype H1N1 vaccine

Abstract

Background: The generation of heterovariant immunity is a highly desirable feature of influenza vaccines. The goal of this study was to compare the heterovariant B-cell response induced by the monovalent inactivated 2009 pandemic influenza A virus subtype H1N1 (A[H1N1]pdm09) vaccine with that induced by the 2009 seasonal trivalent influenza vaccine (sTIV) containing a seasonal influenza A virus subtype H1N1 (A[H1N1]) component in young and elderly adults.

Methods: Plasmablast-derived polyclonal antibodies (PPAb) from young and elderly recipients of A(H1N1)pdm09 vaccine or sTIV were tested for binding activity to various influenza antigens.

Results: In A(H1N1)pdm09 recipients, the PPAb titers against homotypic A(H1N1)pdm09 vaccine were similar to those against the heterovariant seasonal A(H1N1) vaccine and were similar between young and elderly subjects. The PPAb avidity was higher among elderly individuals, compared with young individuals. In contrast, the young sTIV recipients had 10-fold lower heterovariant PPAb titers against the A(H1N1)pdm09 vaccine than against the homotypic seasonal A(H1N1) vaccine. In binding assays with recombinant head and stalk domains of hemagglutinin, PPAb from the A(H1N1)pdm09 recipients but not PPAb from the sTIV recipients bound to the conserved stalk domain.

Conclusion: The A(H1N1)pdm09 vaccine induced production of PPAb with heterovariant reactivity, including antibodies targeting the conserved hemagglutinin stalk domain.

Figures

Figure 1.

Homotypic vaccine-specific plasmablast responses to 2009 pandemic influenza A virus subtype H1N1 (A[H1N1]pdm09) vaccine and 2009 seasonal trivalent influenza vaccine (sTIV; containing seasonal influenza A virus subtype H1N1) in young and elderly recipients. The P values in each panel were determined by an unpaired t test for comparison between the young and elderly groups. A, A(H1N1)pdm09-specific and seasonal A(H1N1)-specific plasmablast-derived polyclonal antibody (PPAb) immunoglobulin G (IgG) binding activity in the A(H1N1)pdm09 vaccine and sTIV recipients, respectively. Enzyme-linked immunosorbent assay titers of individual PPAb samples were normalized to a B-cell density of 3 × 106 B cells/mL in PPAb culture. B, Minimum binding concentrations of each PPAb sample were calculated as the IgG concentration (in ng/mL) divided by titer. C, Homotypic vaccine-specific IgG avidity of PPAb. Avidity is defined as the ratio of specific antibody-secreting cell frequency to the normalized PPAb titer (A) (Supplementary Materials). A smaller value indicates higher avidity.

Figure 2.

Relative heterovariant avidity of PPAb IgG induced by 2009 pandemic inuenza A virus subtype H1N1(A[H1N1]pdm09, or pH1N1) vaccine and 2009 seasonal trivalent inuenza vaccine (sTIV, containing seasonal inuenza A virus subtype H1N1, or sH1N1) vaccine. Relative heterovariant avidity is defined as the ratio of avidity for the heterovariant strain to avidity for the homotypic immunizing strain, which is equal to the ratio of titer, T, against the vaccine strain to the titer against the heterovariant strain. A smaller value indicates higher heterovariant avidity. The P values were determined by an unpaired t test.

Figure 3.

Homotypic and heterovariant binding activity of indicated PPAb pools to recombinant hemagglutinin (HA) protein of seasonal influenza A virus subtype H1N1 (sH1) and 2009 pandemic influenza A virus subtype H1N1 (A[H1N1]pdm09; pH1). A plasmablast-derived polyclonal antibody (PPAb) pool was assembled for each vaccine/age group by combining an equal quantity of immunoglobulin G from individual PPAb samples. All subjects with a sufficient amount of available PPAb samples were included in the pools, without selection on the basis of their response to the vaccination. The pools and the number of subjects included in each pool were P18, young A(H1N1)pdm09 vaccine recipients, n = 15; P70, elderly A(H1N1)pdm09 vaccine recipients, n = 16; S18, young 2009 seasonal trivalent influenza vaccine (sTIV) recipients, n = 20; S70, elderly sTIV recipients, n = 19. The number in each panel indicates the ratio of the area under the curve (AUC) for heterovariant HA to AUC for homotypic vaccine HA. Abbreviation: OD, optical density.

Figure 4.

Binding activity of plasmablast-derived polyclonal antibody (PPAb) pools to recombinant HA1 and HA2 domains of the hemagglutinin (HA) protein of 2009 pandemic influenza A virus subtype H1N1 (pH1). The table lists the areas under the curve (AUCs) for each titration curve and the ratios of AUCs between different PPAb pools (P18/S18 and P70/S70) and between different domains (HA1/HA2) for each pool.

Figure 5.

Binding activity of plasmablast-derived polyclonal antibody pools P18 and S18 to the full-length and headless HA proteins of seasonal influenza A virus subtype H1N1 (sH1). The ratios of areas under the curve (to the right of the dotted lines) are shown in each graph.

Figure 6.

Binding activity of plasmablast-derived polyclonal antibody pools P18 and S18 to the full-length hemagglutinin (HA) protein of an avian influenza A virus subtype H5N1 strain (H5) and to the HA1 and HA2 domains of H5.

Figure 7.

Domain-specific avidity of plasmablast-derived polyclonal antibody pools P18 and P70 for the full-length hemagglutinin (HA; HA0) or HA1 and HA2 domains. The avidity was assessed by enzyme-linked immunosorbent assay, with or without 7 M urea. The bar graph shows the percentage of 7 M urea-resistant high-avidity binding activity.