The clinical outcome for patients with severe COVID-19 remains poor due to the lack of highly efficacious treatment for such individuals. Finding a better remedy for them is an important niche and immediate unmet need. The aim of this pre-clinical project is to substantiate the therapeutic effect of combined alpha-1- antitrypsin (AAT) + enoxaparin (a low molecular weight heparin) against SARS-CoV-2 infection and its consequences. Establishing the efficacy of AAT + enoxaparin combination will provide a necessary foundation for future clinical trials with the goal of employing effective therapy for those with severe COVID-19. We have novel biological evidence supported by Artificial Intelligence-based molecular modeling that enoxaparin synergizes with AAT to inhibit TMPRSS2 (a cell surface protease that activates the spike protein of SARS-CoV-2) and to reduce SARS-CoV-2 burden in primary human airway epithelial cells (hAEc) and monocyte-derived macrophages (MDM). Because both AAT and enoxaparin embrace a panoply of activities that antagonize other pathogenic mechanisms of severe COVID-19 – including anti-inflammatory, anti-thrombotic, pro-autophagy (known to kill MERS-CoV), and endothelial cell protection – we hypothesize that the AAT + enoxaparin combination will be most effective (compared to each alone) in mitigating SARS- CoV-2 infection and its consequences. We will use three complementary models to elucidate the efficacy of AAT, enoxaparin, and combination of both against SARS-CoV-2 infection: (i) primary hAEc since they express high ACE2 levels, fulminant airway disease occurs, and infection of ciliated hAEc and breach of their defense initiates a portal of entry into the lower airways / alveoli to cause COVID-19 pneumonia; (ii) MDM + plasma derived from AAT-deficient individuals immediately before and immediately after receiving routine intravenous AAT since macrophages are key orchestrators of the hyper-inflammatory response seen with COVID-19; and (iii) two murine models, one with wildtype AAT and another with AAT knocked out. Aim 1: Determine in primary hAEc the mechanisms by which AAT, enoxaparin, and both reduce SARS- CoV-2 infection and its consequences. Approach: hAEc will be infected with SARS-CoV-2 followed by no treatment or treatment with AAT, enoxaparin, or combination of both and assayed for viral load, autophagic flux, pro-inflammatory cytokines, and hAEc viability and barrier integrity. Aim 2: Determine in macrophages the mechanisms by which AAT (given in vivo) ± enoxaparin mitigate SARS-CoV-2 infection. Approach: infect human MDM cultured in autologous plasma – prepared from AAT- deficient individuals before and after AAT infusions ± ex vivo enoxaparin – with SARS-CoV-2 and determine viral load, autophagic flux, and pro-inflammatory cytokine / macrophage extracellular trap (METs) production. Aim 3: Determine if SARS-CoV-2 infection of mice is mitigated by AAT, enoxaparin, and combination of both. Approach: transgenic (Tg) ...