Recombinant immunotargeting antigen, antibody fusions in vaccine design

by Cook, Jeremy K.

Recombinant Immunotargeting Antigen-Antibody Fusions in Vaccine Design @ 1997 by Ieremy K. Cook. Thesis submitted in confomiity with the requirements for the Degree of Doctor of Philosophy. Gnduate Department of Irnrnunology. University of Toronto Synthetic peptide vaccines offer the potential to elicit epitope-specific immune responses to the desired pathogen, without the normaliy attendant risk of infection or toxic side-effects possible with attenuated or inactivated whole organism vaccines. It is possible to choose the epitopes included in a synthetic peptide vaccine such that the immune response is focused on neutdiring epitopes, and epitopes which are not highly variable between viral suains. Thus, synthetic peptide vaccines have distinct advantages over current vaccine design approac hes. However. the successful development of synthetic peptide vaccines has been harnpered by two problerns: first. synthetic peptides are poorly immunogenic; second, antibodies directed against synthetic peptide antigens often do not cross-react with the intact protein frorn which the peptide was derived. due to poor conformational mimicry. Irnmunotargeting, in which a protein or peptide antigen is coupled to an antibody specific for celi surface molecules on professional antigen presenting cells. has been shown to be an effective way to induce adjuvant-independent antibody responses. In order to circumvrnt the shortcornings of synthetic peptide vaccine approaches, while taking advantage of their tàvounble charactenstics, a new approach to vaccine design was investigated. Recombinant immunotqeting antibody immunogens were created, in which a viral peptide antigen was inserted into the antibody . structure. Furthermore, the viral epitopes were in some instances inserted into loop regions of the antibody, in an attempt to retain the conformational characteristicsof the viral epitope. Studies using the influenza virus hemagglutinin A-loop epitope, a confomationally resvicted B ceii epitope, showed that it is possible to elicit conformation-specific antibody responses by inserting the epitope into a loop region of the antibody. This conformational epito~ insertion approach was subsequently extended to other epitopes from HIV- 1. Recombinant antibodies containing these epitopes were shown to be capable of eliciting high-titre anti-envelope HIV- 1 responses. Furthermore, the loop insertions were engineered into a V, framework region such that the immunotargeting capability of the recombinant antibody was preserved. In addition to the above constmcts, recombinant immunotargeting antibodies were constructed which possessed the potential to mediate immunotargeting to MHC class II molecules in outbred populations of many different species, using a pan-specific anti-KLA-DR antibody called 44H 1 O. HN- 1 cornbinecl T-B epitopes were hised ont0 the carboxy termini of the JJHlO heavy and light chains, and the resulting immunogens induced suong anti-HIV-1 gp 160 responses in both rabbits and macaque monkeys. Thus, the recombinant immunotargeting antibody approach to adjuvant-free immunhtion holds considenble promise as a new vaccine design option. Implications of this work are discussed.