As a unique approach to cancer therapy, cancer vaccines exert an anti-tumor effect by engaging the host immune response and have the advantages of exquisite specificity, low toxicity, potentially durable treatment effect and ability to circumvent the intrinsic drug resistance that currently underlies therapeutic failure [19]. Unlike the case of infectious agents where the target is clearly foreign, the host immune system must be able to differentiate tumor cells from their normal non-malignant counterpart before it can mount an SPP immune response against them. is a new promising immunogenic molecule for the development of an anti-hCG-based cancer vaccine. Keywords:-Subunit of human chorionic gonadotropin (hCG), -Subunit of ovine luteinizing hormone (oLH), Recombinant protein, Tetanus toxoid (TT), Immunogenicity == Introduction == Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein secreted by trophoblastic cells during normal gestation. It consists of an subunit and a subunit. The subunit, which contains 92 amino acid residues, is common to all glycoprotein hormones including hCG, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH). The subunit of hCG (hCG) determines Kinesin1 antibody the biological activity of hCG and shows a low degree of homology with FSH and TSH. However, the substantial homology with the first 115 amino acids between hCG and LH that make up the -subunit of hLH is approximately 80%. The additional 30 carboxy-terminl amino acid (C-terminal peptide, CTP) of hCG (hCG-CTP) is unique to hCG [1]. As hCG is essential for the establishment and maintenance of early pregnancy, it presents an ideal target for the development of a contraceptive vaccine. Several different immunogenic types of hCG-based contraceptive vaccines have been designed and evaluated successfully [2]. One of the developed immunogen is a heterospecies dimer (HSD) protein prepared by non-covalently SPP linking native hCG with the native -subunit of ovine LH (oLH). The phase II clinical trial of the anti-hCG SPP contraceptive vaccine using HSD as the immunogen was carried out in India [3]. hCG, especially hCG, is also produced in a number of tumor cells such as malignant trophoblastic tumors, ovarian cancer, cervical cancer, bladder cancer, colorectal cancer and lung cancer [49]. In addition, the elevated amount of hCG detected in serum, urine or tumor tissue was usually associated with the adverse prognosis in many non-trophoblastic tumors [10], indicating that hCG might play a pathogenic role in these tumor cells [11]. Thus, hCG has been also recognized as a target antigen for anti-tumor vaccines. Previously, an hCG-based anti-tumor vaccine, hCG-CTP/DT, was prepared by conjugating hCG-CTP with diphtheria toxoid (DT) [12]. Studies indicate that there was a positive correlation between the survival time and anti-hCG antibody titers in some patients who suffered from colorectal cancer in a clinical trial, although the antibodies induced by this kind of vaccine were of relatively low affinity and titer [12]. Given that HSD immunogen has been demonstrated as an efficient and safe contraceptive vaccine in clinical trials, it could be expected that the HSD/DT(TT) vaccine might be more effective than the hCG-CTP/DT vaccine for anti-tumor immunotherapy. However, since both hCG and oLH used to prepare the HSD immunogen were separated from the native hCG and oLH as reported [3], the preparation of HSD/DT(TT) vaccine was considerably complicated and expensive, and it was difficult to ensure quality control. We therefore constructed a single chain of chimeric cDNA encodinghCG-oLHand expressed this chimeric protein in Sf9 insect cells in our previous SPP research [13]. The aim of the present study was to evaluate the immunogenicity of hCG-oLH expressed inPichia pastoris, as well as the effect of its antibody on the SPP growth of hCG-positive tumor cells both in vitro and in vivo. == Materials and methods == == Cell lines and animals == Human.