Investigation of factors influencing the immunogenicity of hCG as a potential cancer vaccine

Abstract

Human chorionic gonadotrophin (hCG) and its β-subunit (hCGβ) are tumour autocrine growth factors whose presence in the serum of cancer patients has been linked to poorer prognosis. Previous studies have shown that vaccines which target these molecules and/or the 37 amino acid C-terminal hCGβ peptide (hCGβCTP) induce antibody responses in a majority of human recipients. Here we explored whether the immunogenicity of vaccines containing an hCGβ mutant (hCGβR68E, designed to eliminate cross-reactivity with luteinizing hormone) or hCGβCTP could be enhanced by coupling the immunogen to different carriers [keyhole limpet haemocyanin (KLH) or heat shock protein 70 (Hsp70)] using different cross-linkers [1-ethyl-3(3-dimethylaminopropyl)carboiimide (EDC) or glutaraldehyde (GAD)] and formulated with different adjuvants (RIBI or Montanide ISA720). While there was little to choose between KLH and Hsp70 as carriers, their influence on the effectiveness of a vaccine containing the BAChCGβR68E mutant was less marked, presumably because, being a foreign species, this mutant protein itself might provide T helper epitopes. The mutant provided a significantly better vaccine than the hCGβCTP peptide irrespective of the carrier used, how it was cross-linked to the carrier or which adjuvant was used when hCG was the target. Nonetheless, for use in humans where hCG is a tolerated self-protein, the need for a carrier is of fundamental importance. Highest antibody titres were obtained by linking the BAChCGβR68E to Hsp70 as a carrier by GAD and using RIBI as the adjuvant, which also resulted in antibodies with significantly higher affinity than those elicited by hCGβCTP peptide vaccine. This makes this mutant vaccine a promising candidate for therapeutic studies in hCGβ-positive cancer patients.

Prevalence of high affinity naturally occurring IgG2 antibodies against human chorionic gonadotropin and its subunits in patients with ovarian cyst

“…For the assessment of the titres of naturally-occurring autoantibodies of various IgG isotypes to hCGαβ, hCGβ, hCGα, hCGβ carboxy-terminal peptide (hCGβCTP) and hCGβ core fragment (hCGβCF), a standard enzyme linked immunosorbent assay (ELISA) method was used as we have previously described (Chikadze et al, 2010;Kvirkvelia et al, 2018;Porakishvili et al, 2002). Briefly, Nunc MaxisorpC 96-well flat-bottomed microtitre plates were coated with 50µl of hCGαβ (Sigma, USA), hCGβ (Sigma, USA), hCGα (Fitzgerald, USA), hCGβCTP (Sigma, USA) or hCGβCF (National Institute for Biological Standards and Control (NIBSC), UK) at the concentration 1µg/ml in 0.05M carbonate-bicarbonate buffer (CBB, pH9.6; Sigma, USA.).…”

“…Recently we have demonstrated, that it is possible to develop a potential cancer vaccine, with high immunogenicity, which selectively targets hCG and its β subunit (Kvirkvelia et al, 2018). We have also reported that naturally occurring anti-hCG antibodies can be used as a predictive biomarker for nonmalignant ovarian cysts and hypothesized that they might play a protective role against them becoming malignant (Chikadze et al, 2010).…”

Human Chorionic Gonadotrophin: New Pleiotropic Functions for an “Old” Hormone During Pregnancy

“…In contrast, hCG production by cancers, aside from these two types, is generally associated with a worsening of the prognosis, like in lung, liver, or ovary cancers (41,42). Immunization to hCG in experimental models has been shown to have antitumor effects (43)(44)(45).…”

Modulation of Gonadotropins Activity by Antibodies

“…As far as we know, the product has not reached the market yet. Recently, another group proposed another vaccine, where one residue in the amino-acid sequence of hCG beta-subunit is substituted (hCGβR68E) to eliminate cross reactivity with LH and conjugated to heat shock protein (Hsp70) as carrier to increase its immunogenicity (131). This vaccine has not been tested in humans yet.…”