Antibody-mediated Recruitment of Viral-specific Effector Cells via Recombinant Antibody-MHC T cells Engagers

Our lab has developed a novel T cell engager (TCE) format whereby a Recombinant antibody fragment specific for a tumor-associated antigen of choice is genetically fused to HLA-A2/peptide complex that presents a viral T cell epitope. The HLA-A2/peptide complex is designed to engage the TCR of a CD8⁺ T cell while the scFV or Fab redirects specificity towards a tumor associated antigen (TAA), thus recruiting potent antiviral memory CTLs to attack tumor cells. We used the highly immunogenic cytomegalovirus (CMV) pp65-derived peptide as a target peptide for CTLs, taking into consideration the CMV prevalence of seropositive humans. Mesothelin was used as a TAA.

We monitored the binding of TCEs to target cells demonstrating that their binding is dependent exclusively on the interaction of the targeting domain (scFv/Fab) of the fusion molecule with mesothelin, and is dose-dependent. Potency of TCEs was determined in vitro using co-cultures of CMV-specific CTLs and mesothelin-expressing human tumor cell lines. The TCEs specifically and potently mediated the killing of mesothelin-positive cells in TCE-dose-dependent matter. Mesothelin-negative control cells were not affected. Moreover, a significant increase in CD25 expression and dose-dependent secretion of IL2 and IFNγ were observed in CTLs exposed to mesothelin-positive cells. In-vivo studies using mice models are planned.

The results represent a powerful new approach for immunotherapy. The MHC-based TCEs can mediate specific and efficient recruitment of viral-specific CTLs to kill tumor cells, adding an approach by which specific population of T cells can be engaged and recruited to the tumor site in a controllable manner in contrast to current CD3-based T cells engagers that cannot selectively target the specificity of interest. Such treatments can be very potent but with decreased toxicities involved, such as cytokine storm.