Vaccination with an HIV T-Cell Immunogen (HTI) Using DNA Primes Followed by a ChAdOx1-MVA Boost Is Immunogenic in Gut Microbiota-Depleted Mice despite Low IL-22 Serum Levels

Abstract

Despite the important role of gut microbiota in the maturation of the immune system, little is known about its impact on the development of T-cell responses to vaccination. Here, we immunized C57BL/6 mice with a prime-boost regimen using DNA plasmid, the Chimpanzee Adenovirus, and the modified Vaccinia Ankara virus expressing a candidate HIV T-cell immunogen and compared the T-cell responses between individuals with an intact or antibiotic-depleted microbiota. Overall, the depletion of the gut microbiota did not result in significant differences in the magnitude or breadth of the immunogen-specific IFNγ T-cell response after vaccination. However, we observed marked changes in the serum levels of four cytokines after vaccinating microbiota-depleted animals, particularly a significant reduction in IL-22 levels. Interestingly, the level of IL-22 in serum correlated with the abundance of Roseburia in the large intestine of mice in the mock and vaccinated groups with intact microbiota. This short-chain fatty acid (SCFA)-producing bacterium was significantly reduced in the vaccinated, microbiota-depleted group. Therefore, our results indicate that, although microbiota depletion reduces serum levels of IL-22, the powerful vaccine regime used could have overcome the impact of microbiota depletion on IFNγ-producing T-cell responses.

Keywords: HIV; IFNγ; IL-22; Roseburia; T-cell; microbiota; vaccine.

Figure 1

Animal treatments, vaccination, and sampling schedule. All groups received a fecal microbiota transplant (FMT) from the same donor pool prior to vaccination. Afterward, mock animals were vaccinated with PBS while DDDCM and DDDCM-ATB groups received three DNA.HTI primes and ChAdOx1.HTI-MVA.HTI boost regimen. The DDDCM-ATB group also received antibiotic treatment (ATB) in drinking water throughout the vaccination period. Feces were collected before and after FMT as well as before each vaccination. At the last study time point (week 21), the intestinal content, serum, and spleen were collected. Created with BioRender.com.

Figure 2

Magnitude and breadth of IFNγ-producing, HTI-specific T-cell responses after vaccination without (DDDCM) and with (DDDCM-ATB) microbiota depletion. Median and interquartile ranges of the magnitude and breadth are indicated. Data are shown by groups (a) and segregated by sex (b). DDDCM (n = 16, 8 females and 8 males) and DDDCM-ATB (n = 13, 6 females and 7 males) groups were compared. The Mann–Whitney U test and Kruskal–Wallis (KW) test with a false discovery rate (FDR) for multiple comparisons were used to compare groups. Statistically significant differences were set at p < 0.05 and q < 0.05 when FDR was used. Trends (p < 0.05 and q < 0.1) are indicated in grey.

Figure 3

Serum levels of cytokines showing at least one significant difference between study groups (p < 0.05 in the Kruskal–Wallis (KW) test with an FDR correction for multiple comparisons) when comparing mock (n = 10)-vaccinated mice (DDDCM, n = 17) and mice vaccinated with depleted microbiota (DDDCM-ATB, n = 12). The lower limit of quantification is indicated by a dotted line, and median and interquartile ranges are shown. The statistically significant threshold was set at p < 0.05 and q < 0.05, and trends (p < 0.05, q > 0.05) are indicated in grey.

Figure 4

(a) Relative abundance of Roseburia in the caecum, large, and small intestine sections for the three different groups: the mock (n = 10 per sample type), vaccinated DDDCM (n = 10 per sample type), and vaccinated with depleted microbiota DDDCM-ATB (n = 16 per sample type) groups. Comparisons were performed using the Kruskal–Wallis test, boxplots, and statistically significant differences were indicated (p < 0.05). (b) Spearman’s correlation between IL-22 levels in serum and Roseburia abundance in the large intestine of DDDCM (n = 9) and mock (n = 5) groups. Correlation coefficient and p-value are indicated.