text: Cellular Tropism of SARS CoV 2 across Human Tissues and Age related Expression of ACE2 and TMPRSS2 in Immune inflammatory Stromal Cells Recently emerging evidence has indicated that COVID 19 represents a major threat to older populations but the underlying mechanisms remain unclear The pathogen causing COVID 19 is acute respiratory syndrome coronavirus 2 SARS CoV 2 SARS CoV 2 infection depends on the key entry factors angiotensin converting enzyme 2 ACE2 and transmembrane serine protease 2 TMPRSS2 Recognizing the importance of ACE2 and TMPRSS2 for the cellular tropism of SARS CoV 2 we analyzed and presented the landscape of cell type identities for ACE2 sup sup TMPRSS2 sup sup cells across different human tissues and the age related alterations in ACE2 and TMPRSS2 expression across different cell types Additionally most of the post acute COVID 19 sequelae could attribute to the ACE2 expressing organ systems Therefore these SARS CoV 2 tropism data should be an essential resource for guiding clinical treatment and pathological studies which should draw attention toward the prioritization of COVID 19 research in the future Notably we discovered the age related expression of ACE2 and TMPRSS2 in the immune inflammatory stromal cells implying the potential interplay between COVID 19 stromal cells and aging In this study we developed a novel and practical analysis framework for mapping the cellular tropism of SARS CoV 2 This approach was built to aid the identification of viral specific cell types and age related alterations of viral tropism highlighting the power of single cell RNA sequencing scRNA seq to address viral pathogenesis systematically With the rapid accumulation of scRNA seq data and the continuously increasing insight into viral entry factors we anticipate that this scRNA seq based approach will attract broader interest in the virus research communities 