Carbohydrate-associated Immunodominant Epitope(s) of CA215

Abstract

RP215 monoclonal antibody (Mab) was initially generated against OC-3-VGH ovarian cancer cells and was shown to react with a cancer-associated carbohydrate epitope in glycoproteins designated as CA215. Additional five high affinity Mabs, designated as RCA-10, -100, -104, -110 and -111, respectively, were generated by using affinity-purified CA215 as the immunogen in this study. All RCA Mabs were found to recognize periodate-sensitive carbohydrate-associated epitope(s) and to pair with RP215 in typical sandwich enzyme immunoassays for the quantification of CA215. When compared with those of RP215, the amino acid sequence homology of the Fab regions ranged from 100% for RCA-100 to 65% for RCA-110, based on which 3 distinct Mab groups were categorized. In vitro TUNEL apoptosis and complement-dependent cytotoxicity assays were performed with these Mabs and found to have comparable inhibitory efficacy to cancer cells. Results of biochemical and immunological assays revealed that RP215, RCA-100 and RCA-10 react with the linear carbohydrate-associated epitope, whereas the others recognize the conformational form of the epitope in CA215. This study has suggested that the unique carbohydrate-associated epitope(s) is immunodominant in mice when immunized with CA215. It remains to be demonstrated if the differential anti-cancer efficacy exists among the distinct groups of these anti-CA215 Mabs.

Cancerous Immunoglobulins and Ca215: Implications in Cancer Immunology

“…Unexpectedly, all of the new generation monoclonal antibodies (RCA-related mAbs) recovered were found to react with epitope(s) related to the one recognized by RP215 mAb (Lee et al, 2012d). This indicated the existence of an immunodominant carbohydrate-associated epitope recognized originally by RP215 mAb in mice.…”

“…RP215 and its RCA related mAbs were shown to react with the same linear or conformational carbohydrate associated epitope(s). This could be demonstrated either by self-pairing or mutual pairing of any of these mAbs in enzyme immunoassays for quantitative determinations for CA215 (Lee et al, 2012d). The reason for the existence of immunodominant epitope(s) recognized by RP215 and other CA215-derived mAbs in mice remains to be explained (Lee et al, 2012d).…”

“…In addition to RP215, apoptosis could also be induced in OC-3-VGH ovarian cancer cells by other RP215-epitope-related monoclonal antibodies (RCA10, RCA100, RCA104, RCA110 and RCA111 to be described later) (Lee et al, 2012d). By comparison, goat anti-human IgG also induced apoptosis to a similar extent to that of RP215 mAb, indicating that cancer cell expressed surface bound immunoglobulins are effectively blocked by antibodies against cancerous immunoglobulins Lee et al, 2012d). The results of the apoptosis assay are summarized in Table 3 for comparison.…”

Roles of antigen receptors and CA215 in the innate immunity of cancer cells

“…Due to the lack of sufficient experimental evidence, the majority of these reviews only reported the summary of available research results with little definite conclusion regarding the roles and mechanisms of action of these cancerous immunoglobulins. The situation was somewhat improved, when RP215 was identified as a unique probe for further studies of cancerous immunoglobulins [21][22][23][24][25]. However, it later became apparent that CA215 glycoproteins, each of which contained the RP215-specific epitope, consisted of more protein molecules than immunoglobulins.…”

“…Following the discovery of RP215 and its cognate antigen, CA215, many biological and immunological studies were performed [22,[24][25][26]. The major emphasis of these studies has been placed on the roles of cancer cellexpressed antigen receptors and/or CA215 in the growth regulations of cancer cells, as well as the possible mechanisms of action of these antigen receptors and CA215 [22,27].…”