Provided herein are, inter alia, antibodies, antigen-binding antibody fragments, cells, polynucleotides, compositions, kits, and methods relating to the detection of HBV protein X (HBx), e.g., in vitro and in vivo. Included are antibodies and fragments thereof that bind HBx, as well as kits, cells, and compositions comprising such antibodies and fragments.

The present disclosure relates to a cytosol-penetrating antibody and the use thereof, and more specifically to identification of a structural mechanism that induces escape from endosomes into the cytosol after cellular internalization into living cells through a cell membrane protein, a light-chain variable region and/or heavy-chain variable region, which is based on this identification and has a significantly improved ability to escape from endosomes into the cytosol, a cytosol-penetrating antibody comprising the same, a method for producing the same, and the use thereof.

Compositions are provided, which can be used as frameworks for the creation of very stable and soluble single-chain Fv antibody fragments. These frameworks have been selected for intracellular performance and are thus ideally suited for the creation of scFv antibody fragments or scFv antibody libraries for applications where stability and solubility are limiting factors for the performance of antibody fragments, such as in the reducing environment of a cell. Such frameworks can also be used to identify highly conserved residues and consensus sequences which demonstrate enhanced solubility and stability.

The present application provides PEI compounds comprising a linker, PEI-polypeptide conjugates (e.g., PEI-antibody conjugates), and complexes thereof comprising a biologically active molecule. Methods of preparing and using the compounds, conjugates and complexes are further provided. The PEI-polypeptide conjugates and complexes are useful for delivering biologically active molecules to the cytoplasm of cells and promoting release of the biologically active molecules from the endo-lysosomal pathway.

Compositions are provided, which can be used as frameworks for the creation of very stable and soluble single-chain Fv antibody fragments. These frameworks have been selected for intracellular performance and are thus ideally suited for the creation of scFv antibody fragments or scFv antibody libraries for applications where stability and solubility are limiting factors for the performance of antibody fragments, such as in the reducing environment of a cell. Such frameworks can also be used to identify highly conserved residues and consensus sequences which demonstrate enhanced solubility and stability.

The invention relates generally to polypeptides, such as antibody molecules, that demonstrate high stability and solubility. In particular, the invention relates to polypeptides comprising paired V.sub.L and V.sub.H domains that demonstrate soluble expression and folding in a reducing or intracellular environment. The invention also relates to polynucleotides encoding such polypeptides, to libraries of such polypeptides or polynucleotides, and to methods of using such polypeptides in research, diagnostic and therapeutic applications.

It has been established that cancer cells with oncogenic mutants in the small GTPase K-Ras are susceptible to antibodies that bind intracellular guanosine, but delivery of antibodies into cells can be challenging. A subset of lupus autoantibodies is associated with anti-guanosine activity, and is capable of cellular penetration. These antibodies have potential as therapeutic agents targeted towards K-Ras associated malignancies.

The present invention relates to active form specific anti-Rho GTPase conformational single domain antibodies and their uses in particular in the therapeutic and diagnostic fields. In particular, the present invention relates to a single domain antibody wherein the amino acid sequences of CDR1-IMGT, CDR2-IMGT and CDR3-IMGT have at least 90% of identity with the amino acid sequences of the CDR1-IMGT, CDR2-IMGT and CDR3-IMGT of the H12, B6, 4P75, 4SP1, 4SNP36, 4SNP61, 5SP10, 5SP11, 5SP58, 5SNP47, 5SNP48, 5SNP65, B20, B15, B5, B71, E3, A6, G12, NB61, 212B, 111B or 404F (hs2dAb) single domain antibody which are defined in Table B.

The present invention provides an antibody or antigen-binding fragment thereof that: (a) specifically binds 4R tau protein isoforms in a physiological sample; or (b) specifically binds 3R tau protein isoforms in a physiological sample. The present invention further provides nucleic acids and vectors encoding such an antibody or antigen-binding fragment, as well as host cells comprising such nucleic acids and vectors. The antibodies and fragments may be used in treating and diagnosing tauopathies.

Compositions are provided, which can be used as frameworks for the creation of very stable and soluble single-chain Fv antibody fragments. These frameworks have been selected for intracellular performance and are thus ideally suited for the creation of scFv antibody fragments or scFv antibody libraries for applications where stability and solubility are limiting factors for the performance of antibody fragments, such as in the reducing environment of a cell. Such frameworks can also be used to identify highly conserved residues and consensus sequences which demonstrate enhanced solubility and stability.