Recruitment of Oligoclonal Viral-specific T-cells to Kill Human Tumor Cells Using Single-chain Antibody-peptide-HLA Fusion Molecules

Tumor progression is often associated with the development of diverse immune escape mechanisms. One of the main tumor escape mechanism is human leukocyte antigen (HLA) loss, in which human solid tumors exhibit alterations in HLA expression. Moreover, tumors that present immunogenic peptides via major histocompatibility complex class I (class I MHC) molecules are not susceptible to cytotoxic T lymphocytes (CTLs)-mediated lysis, because of the relatively low potency of the tumor- specific CLTs. Here, we present a novel cancer immunotherapy approach that overcomes these problems by utilizing the high affinity and specificity of anti-tumor antibodies to recruit potent anti-viral memory CTLs to attack tumor cells. We constructed a recombinant molecule by genetic fusion of a cytomegalovirus (CMV) derived peptide pp65 (NLVPMVATV) to scHLA-A2 molecules that were genetically fused to a single-chain Fv Ab fragment specific for the tumor cell surface antigen mesothelin. This fully covalent fusion molecule was expressed in E-coli as inclusion bodies and refolded in vitro. The fusion molecules could specifically bind mesothelin-expressing cells and mediate their lysis by NLVPMVATV-specific HLA-A2-restricted human CTLs. More importantly, these molecules exhibited very potent antitumor activity in vivo in a nude mice model bearing pre-established human tumor xenografts that were adoptively transferred along with human memory CTLs. These results represent a novel and powerful approach to immunotherapy for solid tumors, as demonstrated by the ability of the CMV/scHLA-A2/SS1(scFv) fusion molecule to mediate specific and efficient recruitment of CMV- specific CTLs to kill tumor cells.