Natural and induced immunity against the tumour-associated antigen, Ep-CAM

The tumour-associated antigen (TAA), Ep-CAM is overexpressed on various human carcinomas, including colorectal carcinoma (CRC). TAAs or their immunodominant epitopes that are spontaneously recognised by the immune system might constitute a suitable target for immunotherapy. Fifteen % of sera of CRC patients with no previous immunotherapy elicited IgG antibodies against Ep-CAM. No Ep-CAM specific antibodies were detected in healthy controls or patients with Crohn's disease or colitis ulcerosa. Further analyses revelaed that 50% of the Ep-CAM-reactive sera bound to peptide residues 29-46 of Ep-CAM. The results provide evidence for spontaneous immune recognition of Ep-CAM in CRC patients and identify an immunodominant B cell epitope of human Ep-CAM.

Anti-idiotypic antibodies (anti-Id) may serve as surrogate TAAs for vaccination. The optimal design of an anti-Id vaccine, however remains unclear. Moreover, whether vaccination with anti-Id or the original antigen is superior is controversial.

SM262 is a human anti-Id raised against mAb 17-1A that recognises Ep-CAM. Vaccination of mice with anti-Id induced antibodies that shared idiotopes with mAb 17-1A and recognised Ep-CAM. Fusion of GM-CSF to anti-Id enhanced the magnitude of the antibody responses, while xenogeneic Fc domain had no significant modulatory effect. Recombinant anti-Id protein vaccine evoked a more potent humoral immunity as compared to DNA delivered by gene gun. Our study provides the fist evidence that immune tolerance in mice expressing the transgene for human Ep-CAM can be circumvented by anti-Id vaccination. The results may have implications for future anti-Id vaccine design.

Vaccination of CRC patients with recombinant Ep-CAM protein, in combination with GM-CSF, induced Ep-CAM specific T and NK-like T cells producing cytotoxic cytokines. In addition, a long-lasting Th1 biased humoral and proliferative T cell response was elicited against Ep-CAM.

The original antigen, Ep-CAM induced a more potent overall immune response as compared to anti-Id mimicking Ep-CAM. Analysis of TCR BV gene repertoire revealed that BV19+ CD8+ T cells might be involved in the vaccine induced anti-Ep-CAM immune response. The results collectively suggest that immunisation with Ep-CAM protein may serve as a novel approach to CRC immunotherapy. Furthermore, immunogenic MHC class I and II restricted Ep-CAM epitopes were identified that may provide new opportunities for developing effective multiepitope cancer vaccines targeting Ep-CAM.

Vaccination with a recombinant canarypox virus (ALVAC) encoding human Ep-CAM in combination with GM-CSF induced a potent Ep-CAM specific, type 1 cellular immune response in CRC patients. However, no anti-Ep-CAM antibody or proliferative T cell responses were elicited. Combining ALVAC-Ep-CAM and recombinant Ep-CAM in a prime-boost vaccination approach may represent an effective strategy to induce a coordinated antigen specific cellular and humoral immune response.

In conclusion, the results suggest that Ep-CAM is a promising target structure for immunotherapy. The present studies may form a basis for further enlarged clinical trials targeting Ep-CAM by active specific vaccination.

List of scientific papers

I. Mosolits S, Harmenberg U, Ruden U, Ohman L, Nilsson B, Wahren B, Fagerberg J, Mellstedt H (1999). Autoantibodies against the tumour-associated antigen GA733-2 in patients with colorectal carcinoma. Cancer Immunol Immunother. 47(6): 315-20.
https://pubmed.ncbi.nlm.nih.gov/10203061

II. Mosolits S, Steinitz M, Harmenberg U, Ruden U, Eriksson E, Mellstedt H, Fagerberg J (2002). Immunogenic regions of the GA733-2 tumour-associated antigen recognised by autoantibodies of patients with colorectal carcinoma. Cancer Immunol Immunother. 51(4): 209-18. Epub 2002 Apr 10
https://pubmed.ncbi.nlm.nih.gov/12012108

III. Mosolits S, Campbell F, Litvinov SV, Fagerberg J, Crowe JS, Mellstedt H, Ellis JH (2003). Targeting human Ep-CAM in transgenic mice by anti-idiotype and antigen based vaccines. [Submitted]

IV. Mosolits S, Markovic K, Frodin JE, Virving L, Magnusson CG, Steinitz M, Fagerberg J, Mellstedt H (2003). Vaccination with recombinant Ep-CAM protein or anti-idiotypic antibody induced Th1-biased response against MHC class I and II restricted Ep-CAM epitopes in colorectal carcinoma patients. [Manuscript]

V. Mosolits S, Markovic K, Fagerberg J, Frodin JE, Rezvany MR, Kiaii S, Mellstedt H, Tehrani MJ (2003). TCR BV gene usage in colorectal carcinoma patients immunised with recombinant Ep-CAM protein or anti-idiotypic antibody. [Manuscript]

VI. Ullenhag GJ, Frodin JE, Mosolits S, Kiaii S, Hassan M, Bonnet MC, Moingeon P, Mellstedt H, Rabbani H (2003). Immunization of colorectal carcinoma patients with a recombinant canarypox virus expressing the tumor antigen Ep-CAM/KSA (ALVAC-KSA) and granulocyte macrophage colony- stimulating factor induced a tumor-specific cellular immune response. Clin Cancer Res. 9(7): 2447-56.
https://pubmed.ncbi.nlm.nih.gov/12855617