Expression of alpha-fetoprotein and interleukin 2 receptors and impairment of membrane fluidity in peripheral blood mononuclear cells from AIDS and related syndromes

The adenocarcinoma cell surface mucin receptor for alpha-fetoprotein: is the same receptor present on circulating monocytes and macrophages? A commentary

The mucin family of proteins is largely expressed on sedentary epithelial cells lining the gastrointestinal, pulmonary, and reproductive tracts and their associated organs and malignant tumors. It is less well-known that mucins are also expressed on circulatory cells of the immune and inflammatory systems, such as monocytes, macrophages, leukemic, and lymphoma cells. The epithelial mucins function in (a) protection and lubrication of mucosal linings, (b) cell adhesion and cell-to-cell contact, (c) cell migration and metastasis, and (d) signal transduction. It would be logical to presume that mucins expressed on circulating mononuclear cells could perform similar functions. Recently, it was proposed that the alpha-fetoprotein (AFP) receptor, known to be present on solid epithelial-derived malignant tumor cells, can be identified as a mucin glycoprotein. Interestingly, it was also reported that AFP binds to a receptor on circulating cells and sedentary tumor cells of lymphoreticular origin, especially monocytes associated with lymphomas and leukemias. The primary objective of the present commentary is to present literature-based evidence that some of the cell surface mucins on sedentary epithelial tumor cells and certain mucins expressed on circulating monocytes/macrophages are identical to the AFP receptor. The secondary objective is to discuss the role of AFP and its derived peptides in the growth suppression of adenocarcinomas and lymphomas using the AFP-mucin receptor concept as a key to the mechanism of tumor growth inhibition.

Alpha-fetoprotein and other tumour-associated antigens for immunotherapy of hepatocellular cancer

BACKGROUND

Hepatocellular carcinoma (HCC) is a leading cause of cancer death, with few treatment options for advanced disease.

OBJECTIVES

Here, we review the aetiology of HCC and focus on recent data on tumour-associated antigens (TAA) for HCC, their functions and potential use as immunological targets for immune-based therapy for HCC. In addition, we examine some aspects of antigen presentation within the liver.

RESULTS/CONCLUSIONS

alpha-Fetoprotein (AFP) has been investigated for many years as a TAA, and has been tested in recent clinical trials. More recently, additional TAA have been identified and new therapeutic approaches have been investigated which may be testable clinically in this difficult disease setting.

AFP-specific CD4+ helper T-cell responses in healthy donors and HCC patients

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and is often diagnosed at an advanced stage. We have investigated alpha-fetoprotein (AFP) as a tumor-associated antigen for HCC. We identified major histocompatibility complex class I-restricted peptide epitopes derived from AFP and studied CD8 T-cell responses in vivo and in vitro in ongoing immunotherapy studies. Helper T cells are of critical importance in shaping the immune response; therefore, we investigated the frequency and function of AFP-specific CD4 T cells in the general population and among HCC patients. CD4 T-cell responses were assessed by direct ex vivo multicytokine enzyme-linked immunospot assay and by measurement of cytokine levels using a multicytokine assay. Our analysis indicates that healthy donors have very low frequencies of AFP-specific CD4 T-cell responses, which are of TH1 type, detectable ex vivo. In contrast, these T cells were either reduced or eliminated in HCC patients at advanced stages of disease. To better activate these cells, we compared the stimulatory capacity of both AFP protein-fed and AdVhAFP-engineered dendritic cells (DC). Healthy donors have CD4 T-cell responses, which were activated in response to AFP protein-fed DC whereas HCC patients do not demonstrate significant responses to AFP protein. AdVhAFP-transduced DC were capable of activating higher frequency TH1 CD4 responses to AFP in both healthy donors and AFP-positive HCC patients. Importantly, CD4 T-cell cytokine expression profiles were skewed towards interleukin-2 and interferon-gamma production when activated by adenovirally engineered DC, which has therapeutic implications for vaccination efforts.

Biological roles of alpha-fetoprotein during pregnancy and perinatal development

The use of alpha-fetoprotein (AFP) as a serum marker in cancer actually predates its employment in the detection of congenital defects; however, the latter use of AFP as a fetal defect marker has propelled its clinical utilization. Although the serum-marker capacity of AFP has long been exploited, less is known of the biological activities of this oncofetal protein during fetal and perinatal development. In the present review, the biological activities of AFP are discussed in light of this glycoprotein's presence in various biological fluid compartments: embryonic and fetal tissues, serum, urine, and reproductive fluids. After a review of the histochemical detection of AFP in various cells and tissues during development, AFP concentrations within various biological fluids were discussed in the context of gestational age and anatomic location. Discussion follows concerning the relationships and roles of AFP in developmental events such as erthyropoiesis, histogenesis/organogenesis, and ligand binding and in developmental disorders such as hypothyroidism, folate deficiencies, and acquired immunodeficiency disorder (AIDS). Based on its association with so many types of birth defects, malformations, and congenital anomalies, AFP can be viewed as a molecular "troubleshooter" until signal transduction pathways are established during pregnancy and prenatal development. The review concludes with a discussion of the place of AFP in the rapidly expanding field of proteomics.