Single-cell RNA-sequencing highlights a curtailed NK cell function in convalescent COVID-19 pregnant women.

Introduction: During gestation the immune system undergoes dramatic remodelling to protect the maternal-fetal dyad from infections whilst also preventing fetal rejection. We investigated how SARS-CoV-2 modifies the immune landscape during infection and in recovered pregnant women.

Methods: We immunophenotyped our two independent geographical cohorts using a 14-colour flow cytometry panel (surface and intracellular staining). We estimated cytokines and SARS-CoV-2 IgG antibodies in validation cohort using a multiplexd flow cytometry panel. Single-cell RNA sequencing (scRNA-seq) was performed using a Chromium Single Cell 3' Gel Bead Chip and Library Kit from 10x Genomics (Drop-seq method). Furthermore, we estimated the cytotoxic functions of natural killer (NK) cells by flow cytometry using surface and intracellular staining.

Results: Using two independent geographical cohorts, we identified that NK cells had a sustained reduction during active infection and after recovery. Further, scRNA-seq data revealed that infection with SARS-CoV-2 rewired the gene expression profile of NK, monocytes, CD4, CD8 effector T cells and antibody producing B cells in convalescent pregnant women. Several gene pathways associated with cytotoxic function, interferon signalling type I & II, and pro- and anti-inflammatory functions in NK and CD8 cytotoxic T cells were attenuated in recovered pregnant patients compared with healthy pregnancies. We validated our scRNA-seq of NK cells from convalescent pregnant women and confirmed that NK cells had diminished levels of cytotoxic proteins; perforin, CD122 and granzyme B.

Discussion: Overall, our study uncovers that SARS-CoV-2 infection deranges the adaptive immune response in pregnant women even after recovery and may contribute to post-COVID19 sequalae of symptoms.