You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["RNA", "CellLine", "Protein", "DNA", "CellType"].

Please return the output as a JSON object of the format: {"DNA" : ["TAL1", ...], "RNA": ["mRNAs", ...], "CellLine": ["T cells", ...], "CellType": ["monocytes", ...], "Protein": ["IL-2", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Immune response of peripheral blood mononuclear cells to HBx-antigen of hepatitis B virus. The hepatitis B virus genome encodes a transcriptional transactivator protein designated HBxAg. We have investigated whether this antigen is a target structure for human T-lymphocytes. Using recombinant HBxAg protein, we found HBxAg-specific stimulation of peripheral blood mononuclear cells in patients with acute hepatitis B virus infection (6 of 6) and chronic hepatitis B virus infection (6 of 17) but not in healthy individuals. With HBxAg-specific synthetic polypeptides, several T-cell epitopes were identified. Most were located in the carboxyterminal half of the HBxAg protein. Five T-cell clones specific for a T-cell epitope located at the carboxyterminal region of HBxAg were established and found to belong to the CD2 / CD4-positive, CD8-negative subtype. These data establish for the first time HBxAg as an antigen in the cellular immune response.
{"CellLine": ["CD2 / CD4 - positive , CD8 - negative subtype", "T - cell clones"], "CellType": ["peripheral blood mononuclear cells", "T - lymphocytes", "human T - lymphocytes"], "DNA": ["The hepatitis B virus", "hepatitis B virus", "hepatitis B virus genome"], "Protein": ["HBxAg", "recombinant HBxAg protein", "T - cell epitope", "carboxyterminal half", "carboxyterminal region", "HBx - antigen", "the HBxAg protein", "HBxAg protein", "transcriptional transactivator protein", "T - cell epitopes"], "RNA": []}