Murine liver-resident group 1 innate lymphoid cells regulate optimal priming of anti-viral CD8⁺ T cells

The liver contains 2 transcriptionally distinct group 1 ILC subsets: CD49a⁺ ILC1s and CD49b⁺ NK cells. However, little is known about how group 1 ILCs contribute to hepatic immune responses. Therefore, we characterized murine liver-resident group 1 ILCs and found that CD49a⁺ ILC1s express high levels of the inhibitory receptor NKG2A and localize near DCs in perivascular spaces surrounding the portal triads. Upon hepatic viral infection, NKG2A signaling in group 1 ILCs, especially in CD49a⁺ ILC1s, inhibits CXCL9 expression required for robust accumulation of IFN-γ⁺CD49b⁺ NK cells. As a consequence, NKG2A^-/- mice showed increased numbers of IFN-γ-producing NK cells that preferentially activate liver CD103⁺ DCs, leading to the sustained proliferation of adoptively transferred, virus-specific CD8⁺ T cells. Collectively, these data suggest that group 1 ILCs play a role in maintaining the liver as a tolerogenic site by limiting the recruitment of peripheral NK cells during the early phase of viral infection. Furthermore, our findings implicate that the inhibition of NKG2A signaling on group 1 ILCs may be a novel vaccine strategy to induce robust CD8⁺ T cell responses against persistent liver pathogens.