Antibodies against Tumor Cell Glycolipids and Proteins, but Not Mucins, Mediate Complement-Dependent Cytotoxicity

Abstract

One of several effector mechanisms thought to contribute to Ab efficacy against cancer is complement-dependent cytotoxicity (CDC). Serological analysis of a series of clinical trials conducted over a 10-year period suggested that six vaccines containing different glycolipids induced Abs mediating CDC whereas four vaccines containing carbohydrate or peptide epitopes carried almost exclusively by mucin molecules induced Abs that did not mediate CDC. To explore this further, we have now compared cell surface reactivity using flow cytometry assays (FACS), complement-fixing ability, and CDC activity of a panel of mAbs and immune sera from these trials on the same two tumor cell lines. Abs against glycolipids GM2, globo H and Lewis Y, protein KSA (epithelial cell adhesion molecule, also known as EpCAM) and mucin Ags Tn, sialylated Tn, Thomsen Friedenreich (TF), and MUC1 all reacted comparably by FACS with tumor cells expressing these Ags. Compared with the strong complement binding and CDC with Abs against glycolipids and KSA, complement binding was diminished with Abs against mucin Ags and no CDC was detected. A major difference between these two groups of Ags is proximity to the cell membrane. Glycolipids and globular glycoproteins extend less than 100 Å from the cell membrane while mucins extend up to 5000 Å. Although complement activation at sites remote from the cell membrane has long been known as a mechanism for resistance from complement lysis in bacteria, it is identified here for the first time as a factor which may contribute to resistance from CDC against cancer cells.

Hypoxic Culture Induces Expression of Sialin, a Sialic Acid Transporter, and Cancer-Associated Gangliosides Containing Non–Human Sialic Acid on Human Cancer Cells

“…Among the cancer-associated gangliosides, G M2 is known to have a particularly high ability to elicit humoral immune response in humans, when conjugated with KLH and introduced with appropriate adjuvants (15,16). G M2 has been applied in clinical trials for vaccine therapy of cancers (11)(12)(13)(14). The main component of the hitherto applied G M2 vaccines is conventional NeuAc-containing G M2 .…”

“…15,16) and humanized anti-G M2 antibodies (17)(18)(19)(20) are now under clinical trial. Preliminary results on G M2 vaccine therapy trial indicated that it would be beneficial, if the immune reaction directed to the determinant is elicited (11,12,21,22). G M2 ganglioside, as well as other monosialogangliosides in humans, contains one N-acetyl sialic acid (NeuAc) residue.…”

Retargeting of Human T Cells to Tumor-Associated MUC1: The Evolution of a Chimeric Antigen Receptor

“…Second, pronounced structural diversity results from alternative splicing, variability in VNTR number, and altered glycosylation. Third, steric inhibition by MUC1 may compromise Ab binding and recruitment of effector function (13). Finally, tumor-derived MUC1 can impair T cell growth (14) and shield transformed cells from killing by NK and T cells (15).…”

Antibody Targeting of Cell-Bound MUC1 SEA Domain Kills Tumor Cells

“…Antibodies against the tandem repeat part of MUC1 fail to induce complement lysis despite appreciable binding by flow cytometry. This has been attributed to the great distance from the cell surface that complement is activated (43). In this regard, it is pertinent to note that all DMB mAbs bind MUC1-SEA domain epitopes that are located close by to the cell membrane making CDC a distinct possibility for DMB mAbs.…”