Human antibodies reactive to NeuGcGM3 ganglioside have cytotoxic antitumor properties

Abstract

N-glycolylated gangliosides are not naturally expressed in healthy human tissues but are overexpressed in several tumors. We demonstrate the existence of antibodies that bind (N-glycolylneuraminyl)-lactosylceramide (NeuGcGM3) and are detectable in the sera of 65 from the 100 donors (65%) tested by ELISA. From those 65 NeuGcGM3 antibody-positive donors, 35 had antibodies that were able to recognize and kill NeuGcGM3-expressing tumor cells by a complement-mediated mechanism. After complement inactivation, 11 of the 35 positive sera showed a direct cytotoxic effect on the tumor cells. This complementindependent cytotoxicity was dependent on the presence of antigen on the membrane and resembles an oncotic necrosis cell death. Both the levels of anti-NeuGcGM3 antibodies in the sera as well as the percentage of healthy donors with this immunity decreased with the age of the donor. In contrast to age and gender-matched healthy donors, we could only detect low reactivity against NeuGcGM3 in the sera of six out of 53 non-small cell lung cancer patients. These results suggest the existence of antibodies against NeuGcGM3 with antitumor immune surveillance functions, reinforcing the importance of N-glycolylated gangliosides as antitumor targets.

A Randomized, Multicenter, Placebo-Controlled Clinical Trial of Racotumomab-Alum Vaccine as Switch Maintenance Therapy in Advanced Non–Small Cell Lung Cancer Patients

“…The selective expression of NeuGc-gangliosides in tumors appears to originate from exogenous sources (47,48), and various authors have proposed that tumor hypoxia induces the transcription of a sialin transporter that facilitates the incorporation of NeuGc units into tumor gangliosides (48). Recent reports described the unexpected presence of naturally occurring anti-NeuGcGM3 antibodies, with antitumor potential in healthy donors (39). However, the same team found reduced levels of circulating anti-NeuGcGM3 antibodies in nontreated patients with NSCLC, attributed to the inhibition of the specific antibody-secreting B-cell population, or the formation of immune complexes with the NeuGcGM3 released from tumor cells (39).…”

“…Recent reports described the unexpected presence of naturally occurring anti-NeuGcGM3 antibodies, with antitumor potential in healthy donors (39). However, the same team found reduced levels of circulating anti-NeuGcGM3 antibodies in nontreated patients with NSCLC, attributed to the inhibition of the specific antibody-secreting B-cell population, or the formation of immune complexes with the NeuGcGM3 released from tumor cells (39). It has been proposed that idiotypic vaccination is able to boost this natural immune response in patients with cancer.…”

“…The L1210 murine lymphocytic leukemia cell line, expressing high levels of NeuGcGM3 ganglioside (38,39), was obtained from the ATCC. L1210 cells deficient of NeuGc sialoconjugates (L1210 cmah-kd), were generated at CIM, as previously explained (40).…”

“…The lytic capacity of patients' sera was tested by incubating the 1:5 diluted sera with 10 5 tumor cells in DMEM/F12 medium supplemented with 1% FBS in 5% CO 2 atmosphere at 37 C, for 3 hours (33,39,41). Cell death percent was determined by flow cytometry after the addition of propidium iodide (PI; Sigma-Aldrich) at a final concentration of 10 mg/mL.…”

Cytolytic tests with hyperimmune patient sera is a good prognostic tool in racotumomab immunotherapy in advanced non-small cell lung cancer

“…In human healthy donors, it was found that naturally occurring antibodies against NeugcgM3 are able to recognize and kill tumor cells expressing this antigen [15] .…”