AIDSWEEKLY Plus, 10 June 1996
Daniel J. DeNoon, Senior Editor

Long-lived peptide-grafted immunoglobulin molecules can induce tolerance in vivo.

These molecules could be used in future gene therapies that one day might:

* induce tolerance to autoantigens in autoimmune disease;

* prevent inhibitory antibodies that limit hemophilia treatment with recombinant factor VIII or IX; and

* stop ineffective or destructive immune responses in people with HIV disease.

Elias T. Zambidis of the American Red Cross, Rockville, Maryland, and David W. Scott of the University of Rochester, New York, reported their findings in the Proceedings of the National Academy of Sciences ("Epitope-Specific Tolerance Induction with an Engineered Immunoglobulin," PNAS, 1996;93(10):5019-5024).

"We show that peptide-grafted IgG molecules injected intravenously or expressed by transfected, autologous B cells, can efficiently modulate the cellular and humoral immune responses to immunodominant epitopes," they wrote.

"This model displays the feasibility of 'tailor-designing' immune responses to whole antigens by selecting epitopes for either tolerance or immunity."

Zambidis and Scott noted that while tolerance to self antigens arises in the early stages of development, this tolerance is incomplete and can often be disrupted by external factors. It would therefore be of enormous clinical utility to develop a means of specifically suppressing undesirable immune responses.

The researchers built on previous research showing that simple haptens (molecules incapable of inducing an immune response without a carrier molecule) such as nucleosides and peptides can induce unresponsiveness in immunocompetent adults.

They grafted an epitope to the N terminus of an IgG H chain. The 15-mer epitope they selected contained both a B- and T-cell epitope: the class II major histocompatibility complex (MHC)-restricted peptide sequence from the lambda cI repressor protein (p1-102), residues 12-26.

Mice tolerized with 12-26-IgG had diminished T-helper type 1 (Th1) and T-helper type 2 (Th2) responses to the parent antigen.

"Foreign immunogenic peptides genetically engrafted into Ig scaffolds can be very efficiently presented to the immune system in a tolerogenic manner when administered by the appropriate route and method," Zambidis and Scott wrote.

"These results show that pretreatment with peptide-Ig chimeras delivered either as single high doses or via slow release by transfected autologous B cells have promising potential to specifically manipulate undesirable T-cell responses in a very efficient manner."

The researchers then tested the ability of 12-26-IgG to induce B-cell unresponsiveness. For this purpose they constructed a 12-26 fusion protein with flagellin, a T- independent antigen.

Again, mouse experiments showed that mice pretreated with the fusion protein had diminished B-cell responses to the parent antigen.

"These studies show that, in addition to inducing potent T-helper tolerance, the chimeric IgG is also capable of independently inducing specific unresponsiveness in epitope- specific B cells," Zambidis and Scott wrote. "B-cell tolerance effects, however, appear to be more modest in vivo than T-cell effects and may reflect either the requirement for higher epitope multivalency than is provided by a bivalent structure or higher dosage requirements."

The researchers suggested that their approach would be even more effective if hematopoietic progenitor cells could be made to express an IgG chimera.

"Because this system consists of a 'genetic hapten- carrier', we propose that these tolerogenic fusion proteins can be used for the induction and long-term maintenance of tolerance if expressed as gene-transferred constructs in hematopoietic tissue," they wrote.

"We are currently analyzing the potential of this strategy in transgenic mice expressing engineered 12-26-IgG in the B- cell compartment, as well as in recipients of bone marrow stem cells that have been transduced with a retroviral vector for the long-term expression of peptide-IgG cDNA constructs."

This work was supported by National Institutes of Health Grant AI29691 and Red Cross funds. E.T. Zambidis was also supported by National Institute of Health Grants T32-GM07365 (MSTP) and T32-AI07285.

The corresponding author for this study is David W. Scott, Cancer Center and Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642.

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