The
GD2 ganglioside expressed on
neuroectodermal tumor cells has been used as a target for passive and active immunotherapy in patients with
malignant melanoma and
neuroblastoma. We have reported that immunization of mice with a 47-LDA mimotope of GD2, isolated from a
phage display peptide library with anti-GD2 mAb 14G2a, induces MHC class I-restricted CD8(+) T cell responses to syngeneic
neuroblastoma tumor cells. The cytotoxic activity of the
vaccine-induced CTLs was independent of GD2 expression, suggesting recognition of a novel
tumor-associated Ag cross-reacting with 47-LDA.
Glycan microarray and immunoblotting studies using 14G2a mAb demonstrated that this Ab is highly specific for the entire
carbohydrate motif of GD2 but also cross-reacts with a 105 kDa
glycoprotein expressed by GD2(+) and GD2(-)
neuroblastoma and
melanoma cells. Functional studies of
tumor cells grown in three-dimensional
collagen cultures with 14G2a mAb showed decreases in
matrix metalloproteinase-2 activation, a process regulated by the 105 kDa-
activated leukocyte cell adhesion molecule (
ALCAM/CD166). A recombinant CD166
glycoprotein was shown to be recognized by 14G2a Ab and inhibition of CD166 expression by RNA interference ablated the cell sensitivity to lysis by 47-LDA-induced CD8(+) T cells in vitro and in vivo. The binding of 14G2a to CD166 was not disruptable by a variety of exo- and endo-
glycosidases, implying recognition of a non-
glycan epitope on CD166. These results suggest that the
vaccine-induced CTLs recognize a 47-LDA cross-reactive
epitope expressed by CD166, and reveal a novel mechanism of induction of potent
tumor-specific cellular responses by mimotopes of
tumor-associated
carbohydrate Ags.