Detection of KK-LC-1 Protein, a Cancer/Testis Antigen, in Patients with Breast Cancer

Abstract

Background: Kita-Kyushu lung cancer antigen-1 (KK-LC-1) is a cancer/testis antigen and predominant target for cancer immunotherapy. Its detection is only established based on gene expression. In this study, we established a monoclonal antibody against KK-LC-1 to detect its protein expression in formalin-fixed samples. Materials and Methods: The monoclonal antibody against KK-LC-1 was evaluated and the detection of KK-LC-1 between gene expression and protein expression was compared in patients with breast cancer. The monoclonal antibody clone 34B3, which we established, stained testicular germ cells positively. Results: The rates of detection of KK-LC-1 gene and protein expression were 11.8% and 52.9%, respectively. Protein expression was detected in all triple-negative breast cancer cases studied (n=8). Furthermore, KK-LC-1 was detected in all tumours without oestrogen receptor expression. Conclusion: This study indicated that KK-LC-1 expression was detected in breast cancer, especially in oestrogen receptor-negative subtypes.Breast cancer is the most frequently diagnosed cancer in women. It is also a predominant cause of mortality (1). However, standard therapies for breast cancer have not reduced mortality. New therapies against breast cancer, especially triple-negative breast cancer (TNBC), that cannot be applicable for hormone and HER2 therapy, are needed. A recent study indicated that inhibitors of immune checkpoints such as programmed death (PD)-1/PD ligand-1 interaction can restore the immune response of cytotoxic T-lymphocytes (CTLs) to tumour-associated antigens and have been successfully established as a new cancer therapy (2).Several tumour-associated antigens have been identified in various human cancer types (3). These antigens are classified into four categories, excluding extrinsic viral antigens, as follows: cancer/testis antigens (CTAs), differentiation antigens, amplification or overexpression antigens, and tumour-specific mutated antigens recently defined as neo-antigens. CTAs are especially attractive targets for immunotherapy because they are not at all, or minimally expressed in normal tissues except for the testis, but are aberrantly expressed in a range of human cancer types (4). Therefore, immune targeting of these antigens is thought to have negligible adverse side-effects.Kita-Kyushu lung cancer antigen-1 (KK-LC-1), also known as CT83 and CXORF61, is a CTA that has epitope peptides recognised by CTLs. When CTLs against KK-LC-1 accumulate predominantly among tumour-infiltrating lymphocytes, adaptive immunotherapy using such lymphocytes leads to a good response (5). KK-LC-1 maps to chromosome Xq23, and is not expressed in normal tissues except for the testis, but is expressed in 33% of non-small cell lung cancer (6, 7). Furthermore, KK-LC-1 was found to be expressed in 82% and 75% of patients with gastric cancer (10) and TNBC (8,9).Almost all studies about KK-LC-1 screening have evaluated its gene expression. Although some reports used polyclonal antibody (pAb) against KK-LC-1 (9, 10), we...

CAR T-Cell Cancer Therapy Targeting Surface Cancer/Testis Antigens

“…Further investigations must be performed to elucidate the potential of targeting SP17 by immunotherapy. CT83 is also expressed in multiple cancers, such as breast, gastric, and lung cancers, and the expression can be upregulated by DNMTis ( 62 – 67 ). CT83 as a target for TCR-based therapies has shown promising results ( 64 , 68 ), but the potential of the antigen as a target for CAR T-cell therapy remains unexplored.…”

Multiomics analysis reveals CT83 is the most specific gene for triple negative breast cancer and its hypomethylation is oncogenic in breast cancer

“…Interestingly, the aberrant expression of CT83 in the stomach is associated with Helicobacter pylori infection and atrophic status, and its expression in precancerous gastric lesions was considered as a potential predictor of gastric cancer 83 – 85 . Regarding CT83 in breast cancer, several studies have identified and emphasized its TNBC specificity but with a limited sample size 37 , 86 , 87 . Compared with previous findings, our data provided much stronger evidence to support this by analyzing its expression in 3617 breast cancer tissues and 71 breast cancer cell lines.…”

Cancer-Testis Antigens in Triple-Negative Breast Cancer: Role and Potential Utility in Clinical Practice

“…KK-LC-1/CT83/ CXorf6/MAMLD1 was found to be a critical gene in hypospadias and plays a less important role in testosterone production during the critical time for sex development [83,84]. KK-LC-1 was found in all TNBC tumours and all tumours without ER expression, with gene and protein expressions of 11.8% and 52.9%, respectively [68]. In another study, it was found that 53% of TNBC patients expressed CXorf61 in at least 30% of their tumour cells, whereas expression was strictly restricted to the testes in normal human tissues (Table 1) [67].…”