Adjuvant potential of low dose all-trans retinoic acid during oral typhoid vaccination in Zambian men

Abstract

There is an urgent need to identify ways of enhancing the mucosal immune response to oral vaccines. Rotavirus vaccine protection is much lower in Africa and Asia than in industrialized countries, and no oral vaccine has efficacy approaching the best systemic vaccines. All-trans retinoic acid (ATRA) up-regulates expression of α4β7 integrin and CCR9 on lymphocytes in laboratory animals, increasing their gut tropism. The aim of this study was to establish the feasibility of using ATRA as an oral adjuvant for oral typhoid vaccination. In order to establish that standard doses of oral ATRA can achieve serum concentrations greater than 10 nmol/l, we measured ATRA, 9-cis and 13-cis retinoic acid in serum of 14 male volunteers before and 3 h after 10 mg ATRA. We then evaluated the effect of 10 mg ATRA given 1 h before, and for 7 days following, oral typhoid vaccine in eight men, and in 24 men given various control interventions. We measured immunoglobulin (Ig)A directed against lipopolysaccharide (LPS)and protein preparations of vaccine antigens in whole gut lavage fluid (WGLF) and both IgA and IgG in serum, 1 day prior to vaccination and on day 14. Median [interquartile range (IQR)] C(max) was 26·2 (11·7-39·5) nmol/l, with no evidence of cumulation over 8 days. No adverse events were observed. Specific IgA responses to LPS (P = 0·02) and protein (P = 0·04) were enhanced in WGLF, but no effect was seen on IgA or IgG in serum. ATRA was well absorbed, well tolerated and may be a promising candidate oral adjuvant.

Keywords: IgA; oral vaccines; retinoic acid; retinoid pharmacokinetics; typhoid vaccine.

Figure 1

Pharmacokinetics. (a–c) Serum concentrations of (a) all-trans retinoic acid (ATRA), (b) 13-cis retinoic acid (RA) and (c) 9-cis RA just before or 3 h after an oral dose 10 mg ATRA on day 1. Although pure ATRA was given, immediate isomerization occurs and the peak concentration of 13-cis RA exceeds that of ATRA. (d) Serum concentration of ATRA before and after 10 mg ATRA on the eighth day; there is no evidence of accumulation, but C_max appears to be reduced compared with day 1, probably reflecting induction of degradative enzymes. (e,f) Serum concentrations of (e) ATRA and (F) 13-cis RA before and 3 h after a single dose of 60 mg retinyl palmitate, and then on day 8 at the same time as the baseline sample was taken for the volunteers shown in (d). Dotted lines show the polynomial smoothed curve, and the shaded band the 95% confidence limits.

Figure 2

Summary of changes in specific immunoglobulin (Ig)A in Vivotif recipients. Responses are shown measured as change in optical density (OD) values at 405 nm, in response to vaccination with or without 10 mg all-trans retinoic acid (ATRA) daily for 8 days (P = 0·02 for lipopolysaccharide (LPS), P = 0·04 for protein extract).

Figure 3

Secretory immunoglobulin (Ig)A concentrations in whole gut lavage fluid. Total IgA (ng/ml) in men in different groups was not statistically significant (P = 0·07).

Figure 4

Correlations between whole gut lavage fluid (WGLF) and serum specific and total immunoglobulin (Ig)A responses. (a) Specific IgA responses to lipopolysaccharide (LPS) and protein extract in WGLF were closely correlated (ρ = 0·71; P < 0·0001). (b) Specific IgA responses to LPS and protein extract in serum were very closely correlated (ρ = 0·91; P < 0·0001). (c) Specific IgA to LPS in WGLF against total IgA in WGLF were correlated (ρ = 0·58; P = 0·0001). (d) Specific IgA to protein extract in WGLF against total IgA in WGLF were correlated (ρ = 0·60; P = 0·0001). (e) WGLF and serum-specific IgA to LPS were correlated moderately (ρ = 0·34; P = 0·006). (f) WGLF and serum-specific IgA to LPS were correlated moderately (ρ = 0·28; P = 0·03). Specific IgA concentrations given as optical density (OD) values at 1:200 dilution, and total IgA in WGLF as ng/ml.

Figure 5

Changes in serum immunoglobulin (Ig)A and IgG in Vivotif recipients. No difference in serum responses to the vaccine antigens was seen in the vaccinees given 10 mg all-trans retinoic acid (ATRA)daily for 8 days alongside vaccination.