Cancer immunotherapy employs two distinct approaches: (i) antibody therapy and
(ii) cell based therapeutic approaches. Herein, we present a new two strategies
for studying and targeting cancer and virus infected cells. First we developed
a process to isolate unique antibodies, termed T-Cell Receptor-like antibodies,
which recognize and bind tumor/viral-associated MHC-peptide complexes normally
recognized by cytotoxic T lymphocytes (CTLs). By using antibody phage display,
we isolated a panel of human recombinant Fab TCR-like antibodies directed
toward the HIV-1 epitope -SL9 (Gag 77-85) in complex with MHC-I molecule. We
characterized one of these antibodies, E5. The E5 antibody was used to
visualize, the specific HLA-A2/Gag epitope on antigen presenting cells (APCs)
that were pulsed with the Gag peptide, or on cells that have complexes formed
by naturally occurring active intracellular processing of the antigen as well
as on the surface of virus infected cells.
Moreover, we
constructed an immunotoxin molecule by using the E5 Ab. Specific cytotoxicity of
this molecule was achieved on APCs that were pulsed with the Gag peptide. Furthermore
we transformed the E5 Fab into a IgG1 molecule. The E5 IgG showed more
sensitive and specific binding to HLA-A2/Gag complexes, and is planed to be
tested for its ability to cause ADCC and CDC. Seconded we constructed a fusion
molecule that can bridge between antibody targeting against tumor cells, and recruiting cells with potent
killing activities from the immune system. We designed two fusion molecules: (i)
chemokine CCL21 was fused to a scFv antibody which targets EGFR (CCL21-scFv225).
The CCL21-scFv225 fusion molecule possess two functional domains, the scFv that
can specifically target tumor cells, and the CCL21 chemokine that can recruit
specific populations from the immune system. (ii) scHLA-A2/scFv225 fused via a
flexible linker to the CCL21 chemokine. The scHLA-A2/scFv225-CCL21 fusion
molecule possess three functional domains, the scFv that can specifically
target tumor cells, the MHC-peptide complex that can recruit specific
populations of CTLs depending on the antigenic peptide within the MHC groove,
and the CCL21 chemokine which can recruit different subpopulation from the
immune system. We show that the fusion molecules can bind the native antigen
expressed on the surface of tumor cells. The fusion molecules can chemoattract
PBMCs, and can mediate efficient lysis of EGFR positive HLA-A2 negative tumor
cells by PBMCs. These results suggest that our new fusion molecules could
represent a new approach for cancer immunotherapy, bridging antibody and immune
system attacks on cancer cells.
