Innate immune defects correlate with failure of antibody responses to H1N1/09 vaccine in HIV-infected patients

Abstract

Background: Mechanisms underlying the failure of influenza vaccine-induced antibody responses in HIV-infected persons are poorly understood.

Objective: To investigate innate immune factors regulating B-cell function in HIV-infected persons and to correlate them with serologic responses to H1N1/09 vaccine.

Methods: We evaluated immunologic characteristics of 17 HIV-infected patients and 8 healthy controls (HCs) at 0, 7, and 28 days (designated T0, T1, and T2) following a single 15-μg dose of nonadjuvanted H1N1/09 influenza vaccine by using flow cytometry, ELISpot, and ELISA. All HCs and 9 patients (53%) seroconverted with >1:40 hemagglutination inhibition antibody titer at T2.

Results: In vaccine responders and HCs, serum levels of BAFF (B cell-activating factor) and APRIL (a proliferation-inducing ligand) increased from T0 to T2 in conjunction with increases in frequencies of memory B cells. Concurrently, receptors for these factors showed changes, with increases in expression of TACI (transmembrane activator and calcium modulator and cyclophilin ligand interactor) and decreases in BAFF receptor in memory B cells. IL-2 secreting cells and IgG antibody-secreting cells increased at T2 in vaccine responders and HCs in ex vivo H1N1 antigen-stimulated cultures. These immunologic responses were not evident at T1 and were deficient in vaccine nonresponder patients at T2. At T0, vaccine nonresponders had lower frequencies of BAFF receptor and TACI-expressing memory B cells than did responders.

Conclusion: Impaired memory B-cell responses, deficiencies in serum BAFF and APRIL, and alterations in their receptors on B cells were associated with failure of H1N1/09 influenza vaccine responses among virologically controlled HIV-infected patients.

Figure 1. H1N1/09 vaccine responders show expansion of memory B cells

Frequencies of (A), Frequencies of memory B cells (CD20⁺CD27⁺CD10⁻) in total (CD20⁺) B cells. (B), KI67⁺ memory B cells and (C), IgG producing ASC following ex-vivo stimulation with H1N1 antigen.

Figure 2. Serum BAFF and APRIL are increased in H1N1/09 vaccine responder patients

Serum levels of BAFF and APRIL were measured by ELISA. (A), Serum levels of BAFF. (B), Serum levels of APRIL.

Figure 3. Differential expression of BAFF-R and TACI in vaccine responder and non-responder patients

Representative histograms showing frequency of (A) BAFF-R, (D) TACI in total B cells at T0 (grey) and T2 (black) compared to isotype controls (filled). Expression of BAFF-R⁺ in (B), total B cells; (C), memory B cells. TACI expression in (E), total B cells; (F), memory B cells. Correlation between the H1N1 Ab titer with (G), BAFF-R⁺ B cells and (H), TACI⁺ B cells.

Figure 4. H1N1 antigen-stimulated IL-2, IFNγ and IgG responses in healthy controls and HIV-infected patients pre- and post- H1N1 vaccination

Frequencies of H1N1-stimulated (A), IFN-γ and (B), IL-2 producing SFU in PBMC at T0 and T2. (C), Correlation between the H1N1 Ab titer and IL-2 SFU in PBMC ELISPOT assay. (D), Mean H1N1-stimulated IgG ASC with and without exogenous IL-2 at T0 and T2.