SARS-CoV-2 Spike protein suppresses CTL-mediated killing by inhibiting immune synapse assembly.

CTL-mediated killing of virally infected or malignant cells is orchestrated at the immune synapse (IS). We hypothesized that SARS-CoV-2 may target lytic IS assembly to escape elimination. We show that human CD8+ T cells upregulate the expression of ACE2, the Spike receptor, during differentiation to CTLs. CTL preincubation with the Wuhan or Omicron Spike variants inhibits IS assembly and function, as shown by defective synaptic accumulation of TCRs and tyrosine phosphoproteins as well as defective centrosome and lytic granule polarization to the IS, resulting in impaired target cell killing and cytokine production. These defects were reversed by anti-Spike antibodies interfering with ACE2 binding and reproduced by ACE2 engagement by angiotensin II or anti-ACE2 antibodies, but not by the ACE2 product Ang (1-7). IS defects were also observed ex vivo in CTLs from COVID-19 patients. These results highlight a new strategy of immune evasion by SARS-CoV-2 based on the Spike-dependent, ACE2-mediated targeting of the lytic IS to prevent elimination of infected cells.

NHBA is processed by kallikrein from human saliva.

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein of Neisseria meningitidis and a component of the Bexsero vaccine. NHBA is characterized by the presence of a highly conserved Arg-rich region involved in binding to heparin and heparan sulphate proteoglycans present on the surface of host epithelial cells, suggesting a possible role of NHBA during N. meningitidis colonization. NHBA has been shown to be cleaved by the meningococcal protease NalP and by human lactoferrin (hLF), a host protease presents in different body fluids (saliva, breast milk and serum). Cleavage occurs upstream or downstream the Arg-rich region. Since the human nasopharynx is the only known reservoir of infection, we further investigated the susceptibility of NHBA to human proteases present in the saliva to assess whether proteolytic cleavage could happen during the initial steps of colonization. Here we show that human saliva proteolytically cleaves NHBA, and identified human kallikrein 1 (hK1), a serine protease, as responsible for this cleavage. Kallikrein-related peptidases (KLKs) have a distinct domain structure and exist as a family of 15 genes which are differentially expressed in many tissues and in the central nervous system. They are present in plasma, lymph, urine, saliva, pancreatic juices, and other body fluids where they catalyze the proteolysis of several human proteins. Here we report the characterization of NHBA cleavage by the tissue kallikrein, expressed in saliva and the identification of the cleavage site on NHBA both, as recombinant protein or as native protein, when expressed on live bacteria. Overall, these findings provide new insights on NHBA as target of host proteases, highlights thepotential role of NHBA in the Neisseria meningitidis nasopharyngeal colonization, and of kallikrein as a defensive agent against meningococcal infection.