The invention relates to chimeric proteins comprising an antigen and a trimer forming portion or a trimer and virus-like particle forming portion of foamy virus envelope protein (FV TM). The trimer or trimer and virus-like particle forming portion comprises i) full length foamy virus transmembrane protein； ii) foamy virus transmembrane protein absent a functional cytoplasmic domain； iii) foamy virus transmembrane protein absent a functional cytoplasmic domain and transmembrane domain； iv) foamy virus ectodomain comprising N-terminal heptad repeat region and cysteine rich region between N-terminal heptad repeat region and C-terminal α-helical region； v) N-terminal heptad repeat region； vi) a functional variant of any one of i) to v)； or vii) any one of i) to vi) lacking an FV fusion peptide domain. In particular, the antigen is an antigen of a virus envelope protein, such as HIV gp 120. Soluble and membrane bound forms of trimeric and higher oligomeric forms of the chimeric proteins are provided as well as nucleic acid molecules encoding and expressing same, viral-like particles comprising same, compositions including pharmaceutical compositions, host cells and kits. Methods are described for producing immune responses including antibodies determined by the chimeric protein or VLP, as well as methods of screening using the chimeric protein, VLP and/or antibodies.
