Abstract: Provided is a tetanus toxin protein variant, the tetanus toxin protein variant comprising a C fragment of the tetanus toxin protein and a partial fragment of a translocation region of the tetanus toxin protein. Further provided is a proteoglycan conjugate, the proteoglycan conjugate comprising a polysaccharide from Streptococcus pneumoniae and a truncated tetanus toxin protein. Also provided is a method for improving immunogenicity, the method comprising the following steps: providing a proteoglycan conjugate comprising a polysaccharide from Streptococcus pneumoniae and a truncated tetanus toxin protein.