HER-2/neu
oncoprotein is overexpressed in a variety of human
tumors and is associated with malignant transformation and aggressive disease. Due to its overexpression in
tumor cells and because it has been shown to be immunogenic, this
protein represents an excellent target for T-cell
immunotherapy.
Peptide extracts derived from primary
HLA-A*0201-positive (+) HER-2/neu+ human
tumors by
acid elution (
acid cell extracts (
ACEs)) were tested for their capacity to elicit in
HLA-A*0201 transgenic mice, cytotoxic T lymphocytes (CTLs) lysing
HLA-A*0201+ HER-2/neu+
tumor cells.
Injections of ACE in transgenic mice induced CTLs capable of specifically lysing HER-2/neu+ tumor cell lines (also including the original HER-2/neu+ primary
tumor cells from which the
ACEs were derived) in an
HLA-A*0201-restricted fashion. Adoptive transfer of ACE-induced CTLs was sufficient to significantly prolong survival of SCID mice inoculated with
HLA-A*0201+ HER-2/ neu+ human tumor cell lines. Cytotoxicity of such ACE-induced CTL lines was directed, at least as detected herein, also against the HER-2/ neu
peptides HER-2 (9(369)) and HER-2 (9(435)) demonstrating the immunodominance of these
epitopes. HER-2
peptide-specific CTLs generated in the
HLA-A*0201-transgenic mice, upon
peptide immunization, lysed in vitro HER-2/neu+ human tumor cell lines in an
HLA-A*0201-restricted manner and, when adoptively transferred, conferred sufficient protection in SCID mice inoculated with the same human tumor cell lines as above. However, CTLs induced by
ACEs displayed enhanced efficacy in the
therapy of xenografted SCID mice compared with the HER-2
peptide-specific CTLs (i.e., HER-2 [9(369)] or HER-2 [9(435)]). Even by administering mixtures of CTLs specific for each of these
peptides, the prolongation of survival achieved was still inferior compared with that obtained with ACE-induced CTLs. This suggested that additional
epitopes may contribute to the immunogenicity of such
tumor-derived
ACEs. Thus, immunization with
ACEs from HER-2/neu+ primary
tumor cells appears to be an effective approach to generate multiple and potent CTL-mediated immune responses against HER-2/neu+
tumors expressing the appropriate HLA allele(s). By screening ACE-induced CTL lines with synthetic
peptides encompassing the HER-2/neu sequence, it is feasible to identify
immunodominant epitopes which may be used in mixtures as
vaccines with enhanced efficacy in both the prevention and
therapy of HER-2/neu+
malignancies.