Current cancer immunotherapy strategies typically employ the two arms of the immune system: the humoral arm – systemic injection of high affinity monoclonal antibodies directed against cell surface tumor associated antigens, and the cellular arm of the immune system, mainly the CD8+ cytotoxic T-lymphocytes. A new immunotherapeutic approach takes advantage of two well-established areas: (i) the known effectiveness of CD8+ cytotoxic T-lymphocytes in the elimination of cells presenting highly immunogenic MHC/peptide complexes, and (ii) the tumor-specific cell surface antigens targeting via recombinant fragments of antibodies, mainly single chain Fv fragments (scFvs). This approach utilizes a recombinant fusion protein composed of two functionally distinct entities: (i) a single-chain MHC class I molecule that carries a highly immunogenic tumor or viral-derived peptide, and (ii) a tumor-specific, high-affinity scFv fragment. Several studies showed that a biotinylated MHC peptide multimerized on streptavidin or monomeric HLA-A2/influenza (Flu) matrix peptide complexes coupled via chemical conjugation to tumor-specific antibodies could induce in vitro T-lymphocyte-mediated lysis of coated tumor cells. However, stability and homogeneity, as well as tumor penetration capability are limited due to coupling strategy and large size of such molecules. To overcome the limitation of previous approaches, a recombinant molecule was constructed in which a single-chain MHC is specifically targeted to tumor cells through its fusion to cancer specific-recombinant antibody fragments or a ligand that binds to receptors expressed by tumor cells. The developed technology thus provides fusion proteins that include: (i) a cytomegalovirus human MHC-restricted peptide, (ii) a first peptide linker, (iii) a human β-2 microglobulin, (iv) a second peptide linker, (v) a HLA-A2 chain of a human MHC class I molecule, (vi) a third peptide linker, (vii) a variable region from a heavy chain of a scFv fragment of an antibody, and (viii) a variable region from a light chain of such scFv fragment, wherein the consecutive amino acids which correspond to (vii) and (viii) are bound together directly by a peptide bond or by consecutive amino acids which correspond to a fourth peptide linker, wherein the antibody from which the scFv fragment is derived specifically binds to mesothelin.
- Higher stability and homogeneity, as well as tumor penetration capability
Applications and Opportunities
- Cancer immunotherapy therapy