Pathogenic human coronavirus infections, such as severe acute respiratory syndrome CoV (SARS-CoV) and Middle East respiratory syndrome CoV (MERS-CoV), cause high morbidity and mortality 1,2 . Recently, a severe pneumonia-associated respiratory syndrome caused by a new coronavirus was reported at December 2019 (2019-nCoV) in the city Wuhan, Hubei province, China [3][4][5] , which was also named as pneumonia-associated respiratory syndrome (PARS) 6 . Up to 9th of February 2020, at least 37, 251 cases have been reported with 812 fatal cases according to the report from China CDC. However, the immune mechanism that potential orchestrated acute mortality from patients of 2019-nCoV is still unknown. Here we show that after the 2019-nCoV infection, CD4 + T lymphocytes are rapidly activated to become pathogenic T helper (Th) 1 cells and generate GM-CSF etc. The cytokines environment induces inflammatory CD14 + CD16 + monocytes with high expression of IL-6 and accelerates the inflammation. These aberrant and excessive immune cells may enter the pulmonary circulation in huge numbers and play an immune damaging role to causing lung functional disability and quick mortality. Our results demonstrate that excessive non-effective host immune responses by pathogenic T cells and inflammatory monocytes may associate with severe lung pathology. Therefore, we suggest that monoclonal antibody that targets the GM-CSF or interleukin 6 receptor may potentially curb immunopathology caused by 2019-nCoV and consequently win more time for virus clearance.Coronavirus, including SARS and MERS, has caused two large-scale pandemic in the last two decades 1,2 . Although viral evasion of host immune responses and virus-induced cytopathic effects are believed to be critical in disease severity, studies from humans who died of SARS and animal models suggested that an excessive and aberrant host immune response resulting in an exuberant immunopathology and lethal disease [7][8][9] . Similarly, patients infected with 2019-nCoV, that have been reported recently, have increased plasma concentrations of preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

Checkpoint blockade enhances effector T cell function and has elicited long-term remission in a subset of patients with a broad spectrum of cancers. TIGIT is a checkpoint receptor thought to be involved in mediating T cell exhaustion in tumors; however, the relevance of TIGIT to the dysfunction of natural killer (NK) cells remains poorly understood. Here we found that TIGIT, but not the other checkpoint molecules CTLA-4 and PD-1, was associated with NK cell exhaustion in tumor-bearing mice and patients with colon cancer. Blockade of TIGIT prevented NK cell exhaustion and promoted NK cell-dependent tumor immunity in several tumor-bearing mouse models. Furthermore, blockade of TIGIT resulted in potent tumor-specific T cell immunity in an NK cell-dependent manner, enhanced therapy with antibody to the PD-1 ligand PD-L1 and sustained memory immunity in tumor re-challenge models. This work demonstrates that TIGIT constitutes a previously unappreciated checkpoint in NK cells and that targeting TIGIT alone or in combination with other checkpoint receptors is a promising anti-cancer therapeutic strategy.

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