Chronic administration of protein therapeutics may elicit unacceptable immune responses to the specific protein. Our hypothesis is that the immunogenicity of protein drugs can be ascribed to a few immunodominant helper T lymphocyte (HTL) epitopes, and that reducing the MHC binding affinity of these HTL epitopes contained within these proteins can generate drugs with lower immunogenicity. To test this hypothesis, we studied the protein therapeutic erythropoietin (Epo). Two regions within Epo, designated Epo 91–120 and Epo 126–155, contained HTL epitopes that were recognized by individuals with numerous HLA-DR types, a property common to immunodominant HTL epitopes. We then engineered analog epitopes with reduced HLA binding affinity. These analog epitopes were associated with reduced in vitro immunogenicity. Two modified forms of Epo containing these substitutions were shown to be bioactive and nonimmunogenic in vitro. These findings support our hypothesis and demonstrate that immunogenicity of protein drugs can be reduced in a systematic and predictable manner.

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The AP-2 family of transcriptional regulator proteins has three members, alpha, beta and gamma. AP-2alpha and gamma are expressed in placenta and in the human trophoblast cell line JEG-3. AP-2 has been shown to regulate expression of the placental human chorionic gonado-tropin (hCG) alpha- and beta-subunit genes, however, previous work did not distinguish between the family members. Tryptic peptides of the AP-2 protein complexes purified from JEG-3 cells by oligo-affinity chromatography using the hCGalpha AP-2 site match the amino acid sequence of AP-2gamma. The fact that AP-2gamma is present at significant levels and binds the hCGalpha trophoblast-specific element suggests that AP-2gamma is at least part of the binding complex in vivo and plays a role in regulating hCG expression. We show that mutation of each of four AP-2 binding sites within the hCGbeta promoter decreases expression in transfection assays, demonstrating that all four sites are required for maximal expression in JEG-3 cells. Furthermore, we find differences in regulation of the family members: AP-2alpha mRNA levels increase in response to cAMP while AP-2gamma mRNA levels do not. The demonstrated importance of the AP-2 sites in controlling hCGalpha and beta expression and the likely involvement of more than one family member suggest that a balance in AP-2 proteins is involved in coordinate regulation of these genes. Moreover, many placenta-restricted genes are regulated by AP-2 proteins, thus members of this family may play an important overall role in placenta-specific expression.

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One challenge associated with the clinical use of protein therapeutics destined for chronic administration is the potential for the development of unwanted anti-drug immune reactions. The molecular basis for this reactivity is the binding of peptide fragments (epitopes) derived from the breakdown of the protein drug to the HLA receptors expressed by the patient's immune cells. If these epitopes are recognized as "foreign" by the immune system, specific helper T lymphocytes (HTL), are activated, which initiate and direct the formation of antibodies against the protein drug. These antibodies can bind and neutralize the protein drug, resulting in either decreased efficacy or total ineffectiveness of the drug. Moreover, various safety concerns, such as allergic reactions and other adverse events, are also frequently associated with the formation of anti-drug antibodies. Herein, we describe the development of "ImmunoStealth", an integrated bioinformatics, biochemical and cellular immunology approach that specifically addresses the issue of unwanted immune responses against protein therapeutics. Unwanted HTL epitopes are identified using in silico sequence analysis methods and high throughput in vitro biochemical evaluations and thereafter confirmed using cellular immunogenicity assays. The "offending" epitopes within the drug are then rationally modified to alter their HLA binding capacity, and thus render them non-recognizable by the immune system. This technology will ultimately facilitate the design of safer, more potent and more economical drugs.