Lymphatic coagulation and neutrophil extracellular traps in lung-draining lymph nodes of COVID-19 decedents

Clinical manifestations of severe COVID-19 include coagulopathies that are exacerbated by the formation of neutrophil extracellular traps (NETs). Here, we report that pulmonary lymphatic vessels, which traffic neutrophils and other immune cells to the lung-draining lymph node (LDLN), can also be blocked by fibrin clots in severe COVID-19. Immunostained tissue sections from COVID-19 decedents revealed widespread lymphatic clotting not only in the lung but also in the LDLN, where the extent of clotting correlated with the presence of abnormal, regressed, or missing germinal centers (GCs). It strongly correlated with the presence of intralymphatic NETs. In mice, tumor necrosis factor α induced intralymphatic fibrin clots; this could be inhibited by DNase I, which degrades NETs. In vitro, TNF-α induced lymphatic endothelial cell upregulation of ICAM-1 and CXCL8, among other neutrophil-recruiting factors, as well as thrombomodulin downregulation; in decedents, lymphatic clotting in LDLNs. In a separate cohort of hospitalized patients, serum levels of Myeloperoxidase-DNA (MPO-DNA, a NET marker) inversely correlated with antiviral antibody titers, but D-dimer levels, indicative of blood thrombosis, did not correlate with either. Patients with high MPO-DNA but low D-dimer levels generated poor antiviral antibody titers. This study introduces lymphatic coagulation in lungs and LDLNs as a clinical manifestation of severe COVID-19 and suggests the involvement of NETosis of lymphatic-trafficking neutrophils. It further suggests that lymphatic clotting may correlate with impaired formation or maintenance of GCs necessary for robust antiviral antibody responses, although further studies are needed to determine whether and how lymphatic coagulation affects adaptive immune responses.

Tumor Cell-Surface Binding of Immune Stimulating Polymeric Glyco-Adjuvant via Cysteine-Reactive Pyridyl Disulfide Promotes Antitumor Immunity

Immune stimulating agents like Toll-like receptor 7 (TLR7) agonists induce potent antitumor immunity but are limited in their therapeutic window due to off-target immune activation. Here, we developed a polymeric delivery platform that binds excess unpaired cysteines on tumor cell surfaces and debris to adjuvant tumor neoantigens as an in situ vaccine. The metabolic and enzymatic dysregulation in the tumor microenvironment produces these exofacial free thiols, which can undergo efficient disulfide exchange with thiol-reactive pyridyl disulfide moieties upon intratumoral injection. These functional monomers are incorporated into a copolymer with pendant mannose groups and TLR7 agonists to target both antigen and adjuvant to antigen presenting cells. When tethered in the tumor, the polymeric glyco-adjuvant induces a robust antitumor response and prolongs survival of tumor-bearing mice, including in checkpoint-resistant B16F10 melanoma. The construct additionally reduces systemic toxicity associated with clinically relevant small molecule TLR7 agonists.

Persistent antigen exposure via the eryptotic pathway drives terminal T cell dysfunction

Although most current treatments for autoimmunity involve broad immunosuppression, recent efforts have aimed to suppress T cells in an antigen-specific manner to minimize risk of infection. One such effort is through targeting antigen to the apoptotic pathway to increase presentation of the antigen of interest in a tolerogenic context. Erythrocytes present a rational candidate to target because of their high rate of eryptosis, which facilitates continual uptake by antigen-presenting cells in the spleen. Here, we develop an approach that binds antigens to erythrocytes to induce sustained T cell dysfunction. Transcriptomic and phenotypic analyses revealed signatures of self-tolerance and exhaustion, including up-regulation of PD-1, CTLA4, Lag3, and TOX. Antigen-specific T cells were incapable of responding to an adjuvanted antigenic challenge even months after antigen clearance. With this strategy, we prevented pathology in a mouse experimental autoimmune encephalomyelitis model. CD8⁺ T cell education occurred in the spleen and was dependent on cross-presenting Batf3⁺ dendritic cells. These results demonstrate that antigens associated with eryptotic erythrocytes induce lasting T cell dysfunction that could be protective in deactivating pathogenic T cells.