Vaccines derived from chimpanzee adenovirus Y25 (ChAdOx1), human adenovirus type 26 (HAdV-D26), and human adenovirus type 5 (HAdV-C5) are critical in combatting the severe acute respiratory coronavirus 2 (SARS-CoV-2) pandemic. As part of the largest vaccination campaign in history, ultrarare side effects not seen in phase 3 trials, including thrombosis with thrombocytopenia syndrome (TTS), a rare condition resembling heparin-induced thrombocytopenia (HIT), have been observed. This study demonstrates that all three adenoviruses deployed as vaccination vectors versus SARS-CoV-2 bind to platelet factor 4 (PF4), a protein implicated in the pathogenesis of HIT. We have determined the structure of the ChAdOx1 viral vector and used it in state-of-the-art computational simulations to demonstrate an electrostatic interaction mechanism with PF4, which was confirmed experimentally by surface plasmon resonance. These data confirm that PF4 is capable of forming stable complexes with clinically relevant adenoviruses, an important step in unraveling the mechanisms underlying TTS.

Human papillomavirus subtype 16 (HPV16) is the primary cause of an increasing number of head and neck squamous cell carcinomas (HNSCC), providing strong rationale for T-cell immune therapies against HPV HNSCC. Here we assess immunogenicity of HPV16-specific CD8 T cells (CTL) and characterize HPV-specific mechanisms of T-cell dysfunction. We identified 16 strong and 29 moderately immunogenic CTL-epitopes from HPV16 E2, E6, and E7 antigens restricted by 12 common HLA class I alleles. E2-specific CTL-reactivity was higher in patients with HPV HNSCC than in healthy controls (>3-fold; = 0.026). Patient-derived E2, E6, and E7 peripheral CTLs exhibited heterogeneity in dysfunctional phenotypes. Immunogenomic analyses of 119 HNSCC transcriptomes revealed high T-cell infiltration and dysfunction in HPV HNSCC and correlation of HPV antigen expression with T-cell exhaustion gene signatures. Indoleamine 2,3-dioxygenase (IDO-1) was strongly expressed in HPV HNSCC versus HPV HNSCC ( = 0.001) and correlated with E7 expression ( = 0.84; = 0.033). Combination treatment with PD-1 blockade and IDO-1 inhibition overcame profound CTL-dysfunction, enhancing HPV HNSCC sensitivity to CTL-cytotoxicity (up to 10-fold in E7-CTLs, = 0.011). Our findings implicate mechanisms of T-cell escape in HPV HNSCC, wherein high tumoral HPV-antigen load results in high expression of immune dysfunction genes on tumor cells (e.g., IDO-1), and dysfunction of HPV-specific CTLs (e.g., E7, E2-CTLs). The HPV16 CTL-epitopes identified in this study, in combination with blockade of HPV HNSCC-specific PD-1/IDO-1 checkpoints, may be useful for targeted immunotherapy. This study evaluates the HPV antigen T-cell immunogenicity role of inhibitory receptors and other exhaustion markers in the cytotoxic function of HPV antigen-specific CTLs and identifies combined inhibition of PD-1/IDO-1 as a strategy to enhance CTL targeting of HPV HNSCC. .

Adenovirus derived vectors, based on chimpanzee adenovirus Y25 (ChAdOx1) and human adenovirus type 26 are proving critical in combating the 2019 SARS-CoV-2 pandemic. Following emergency use authorization, scale up in vaccine administration has inevitably revealed vaccine related adverse effects; too rare to observe even in large Phase-III clinical trials. These include vaccine-induced thrombotic thrombocytopenia (VITT), an ultra-rare adverse event in which patients develop life-threatening blood clots 5-24 days following vaccination. To investigate vector-host interactions of ChAdOx1 underpinning VITT we solved the structure of the ChAdOx1 capsid by CryoEM, and the structure of the primary receptor tropism determining fiber-knob protein by crystallography. These structural insights have enabled us to unravel key protein interactions involved in ChAdOx1 cell entry and a possible means by which it may generate misplaced immunity to platelet factor 4 (PF4), a protein involved in coagulation. We use in vitro cell binding assays to show that the fiber-knob protein uses coxsackie and adenovirus receptor (CAR) as a high affinity binding partner, while it does not form a stable interface with CD46. Computational simulations identified a putative mechanism by which the ChAdOx1 capsid interacts with PF4 by binding in the spaces between hexon proteins, with downstream implications for the causes of VITT.

Polymorphisms in MHC-I protein sequences across human populations significantly impacts viral peptide binding capacity and thus alters T cell immunity to infection. In the present study, we assess the relationship between observed SARS-CoV-2 population mortality and the predicted viral binding capacities of 52 common MHC-I alleles. Potential SARS-CoV-2 MHC-I peptides are identified using a consensus MHC-I binding and presentation prediction algorithm, called EnsembleMHC. Starting with nearly 3.5 million candidates, we resolve a few hundred highly probable MHC-I peptides. By weighing individual MHC allele-specific SARS-CoV-2 binding capacity with population frequency in 23 countries, we discover a strong inverse correlation between predicted population SARS-CoV-2 peptide binding capacity and mortality rate. Our computations reveal that peptides derived from the structural proteins of the virus produce a stronger association with observed mortality rate, highlighting the importance of S, N, M, E proteins in driving productive immune responses.

Transporters of the Nramp (Natural resistance-associated macrophage protein) family import divalent transition metal ions into cells of most organisms. By supporting metal homeostasis, Nramps prevent diseases and disorders related to metal insufficiency or overload. Previous studies revealed that Nramps take on a LeuT fold and identified the metal-binding site. We present high-resolution structures of Deinococcus radiodurans (Dra)Nramp in three stable conformations of the transport cycle revealing that global conformational changes are supported by distinct coordination geometries of its physiological substrate, Mn2+, across conformations, and by conserved networks of polar residues lining the inner and outer gates. In addition, a high-resolution Cd2+-bound structure highlights differences in how Cd2+ and Mn2+ are coordinated by DraNramp. Complementary metal binding studies using isothermal titration calorimetry with a series of mutated DraNramp proteins indicate that the thermodynamic landscape for binding and transporting physiological metals like Mn2+ is different and more robust to perturbation than for transporting the toxic Cd2+ metal. Overall, the affinity measurements and high-resolution structural information on metal substrate binding provide a foundation for understanding the substrate selectivity of essential metal ion transporters like Nramps.