(P24) Role of cervicovaginal microbiome in HIV-1 transmission in HIV-exposed seronegative (ESN) women
Aswathy Narayanan  , Sivasankaran Munusamy Ponnan  , Chaitanya Tellapragada  , Anoop T Ambikan , Sujitha Kathirvel  Kailapuri G.Murugavel  , Srikanth Prasad Tripathy  , Soumya Swaminathan  , Luke Elizabeth Hanna , Ujjwal Neogi 
 Division of Clinical Microbiology, ANA Futura, Karolinska Institute, Stockholm, Sweden  National Institute for Research in Tuberculosis (Indian Council of Medical Research), Chennai, India. YRG Center for AIDS Research and Education, Chennai, India.
Background: The female genital tract (FGT) is the major site of HIV infection and understanding the nature of virus-specific local immune responses are required to identify its role in disease prevention in HIV exposed seronegative (ESN) individuals. The vaginal microbiota plays an essential role in protecting the host against pathogens, including HIV. With the advancement in the sequencing techniques, it is possible to understand the role of the vaginal microbiota and its association with HIV-transmission.
Methods: The current study was performed on exposed seronegative (ESN, n=37) and HIV- Unexposed seronegative (UH, n=35). The V3-V4 region of the 16s rRNAs was sequenced using Illumina HiSeq2500 with 2×250 cycles chemistry. Preprocessing of the obtained raw data was performed for removing adapters, contaminants, and primers. Further, QIIME2 was used for the next generation microbiome analysis, and taxonomic classification was done using the SILVA database. The flora was Cervicotype 1-4 (CT-1 to CT-4) as per standard classification.
Results: Bacteria belonging to the phyla Proteobacteria, Epsilonbacteria, Acidobacteria, and Chloroflexi were relatively more abundant (p <0.001) in the ESN group as compared to the HIV unexposed seronegative group. At the species level, the majority (51%) of the UH women had a predominance of L. inners (CT-2 flora), followed by Gardnerella vaginalis (CT-3 flora) in 29% and mixed anaerobic bacteria (CT-4 flora) in 11%. Among the ESN group, CT2, CT3, and CT4 flora were observed in 32, 47, and 11% of the women respectively. Put together, the proportion of women with higher diversity (abnormal flora belonging to CT-3 and CT-4) was observed to be 40% and 58% in the UH and ESN groups respectively in our study population. Statistically significant differences in the relative abundances of Vellionella montpellerensis (ESN, p=0.028), L. gasseri (ESN, p=0.005), L. crispatus (ESN, p=0.023), Prevotella amnii (UH, p=0.025), Sneathia amnii (UH, p=0.039) and Streptococcus agalactiae (UH, p=0.010) were observed between the study groups. The richness and diversity of the microbiome composition in ESN females were higher than unexposed seronegative females. Results showed a significant high abundance of L. inners in ESN relative to UH and this leads to microbiome dysbiosis with reduced susceptibility to HIV infection in ESN women.
Conclusion: The study concluded that highly diverse microbiome especially, the significantly enriched Lactobacillus could play an important role in protecting against HIV infection. Thus, it is important to examine the role of vaginal microbiota in mediating HIV resistance/susceptibility. These data demonstrated that a highly diverse cervicovaginal microbiome could play an important role in protecting against HIV infection.