The FDA has suggested that protein therapeutic developers assess and manage unwanted immunogenicity. DeFT™ is cost effective and highly accurate in establishing and eliminating the immunogenic risks hidden within your protein therapeutic or biologic. Our deimmunization strategy is focused on the identification and elimination of T-cell epitopes contained within your candidate sequence.
Established leaders, skilled team. EpiVax has developed and validated a streamlined approach to the deimmunization of therapeutic proteins, coupling advance computational analysis with high throughput in vitro and in vivo assays. The team of scientists at EpiVax are recognized experts in immunogenicity, setting the pace in the deimmunization field, with their unique mix of immunoinformatics and immunology expertise.
Tools for deimmunization: the EpiMatrix system
Searching for Putative T-cell Epitopes
EpiMatrix predicts the binding potential with respect to each of a panel of eight common Class II super-type alleles, covering the majority of the human population (>90%).
Searching for Epitope “Clusters”
We and others have found that potential immunogenicity is not randomly distributed throughout protein sequences but instead tends to “cluster” in immunogenic regions (which are often also immunodominant, see below), facilitating the process of deimmunization. The statistical algorithm ClustiMer allows us to screen EpiMatrix results sets and identify putative T-cell epitope clusters.
Evaluating Overall Immunogenic Potential
The ability to compare peptide scores across multiple alleles, a feature unique to the EpiMatrix system, is the key to evaluating the overall immunogenic potential of proteins. For a given protein, the frequency and number of observed hits, compared to expected hits is a good indicator of overall immunogenic potential. Our expectation is based on an EpiMatrix analysis of a large sample of randomly generated sequences with normal amino acid frequencies; the expectation is expressed as hits per 1000 amino acids to account for the variable sizes of target proteins. Examples of autologous proteins that score low on the scale include albumin and insulin.
Evaluating Regional Immunogenic Potential
Within proteins, regional immunogenic potential (T cell epitope clusters) can be quickly assessed. We have also noted a characteristic pattern that we call the “EpiBar” (Figure 1). This band-like pattern, in which a single 9-mer frame scores well among four or more of our eight ‘super-type’ alleles, is characteristic of promiscuous epitopes. Immunodominant sequences that contain EpiBars include Tetanus Toxin 825-850 (deviation +16), Flu HA 306-318 (deviation +18) and GAD65 557-567 (deviation +19). In our selection of regions for deimmunization, we give preference to immunodominant epitopes that also contain this EpiBar pattern.
Designing Deimmunized Sequences
To identify amino acids within clusters that are suitable for modification, we first create a “logo report” (Figure 3) for each of the immunogenic regions using OptiMatrix. These reports identify “critical” residues, which contribute most to MHC binding.
OptiMatrix offers the mutation with the most impact. Also, one can independently choose mutaions. In making our selections, we generally consider common mutations, changes tolerated in other species or variants of the target protein, published information describing residues important to structure and/or function and, if structural models are available, predicted impacts on tertiary structure. We then focus on the “key” amino acids, as illustrated by a larger font size (and higher OptiMatrix score) in the logo report. Given this list of targeted amino acids and viable alternatives we then evaluate all possible alternative sequences and compile a list of the best single amino acid changes, the best double changes, the best triple changes, and, if necessary, even more complex changes, using OptiMatrix. The de-immunized sequences are then validated (in vitro) before being integrated into the protein and tested for functionality (in-vivo).
Watch this video to see a live demo of OptiMatrix:
Limiting Modifications to Immunodominant Regions
The connection between immunodominance and promiscuous binding has been illustrated in several proteins. EpiVax thus focuses on modifying immunodominant determinants, not on modifying all peptides capable of binding to class II HLA. Furthermore, in contrast to methods others have pursued, our proprietary technology allows us to limit the modifications to one to two amino acids per immunodominant region thus further reducing the impact on protein function. EpiVax has previously demonstrated that modification of a few immunodominant epitopes with promiscuous binding reduces immunogenicity of protein therapeutics (this is known as the “threshold effect”). This has also been demonstrated in a study of erythropoietin where reduced immunogenicity was observed when modifications were made to only two regions of the protein. In that case the sequence changes reduced both HLA binding affinity and human T cell responses while having no significant effect on bioactivity.
Target Validation and Deimmunization
Each of the identified epitopes and corresponding variants are tested as peptides in-vitro for binding affinity with respect to a panel of MHC Class II alleles. The HLA cell free binding assay serves as a “first pass” screen for confirming epitopes and de-immunized peptides. Any cluster that is not confirmed to bind is not in need of deimmunizing modifications.
In a binding assay screen, an unmodified peptide and its modified counterparts are compared in their binding affinity for five HLA alleles. The unmodified (gold bars) peptide binds with high affinity across three of four tested HLA alleles. As intended, strategic modifications to this sequence confer disruption of binding (blue bars). Failure to bind to HLA is usually indicative of lower immunogenicity in T cell assays.
Modification, Re-synthesis, Expression. The next step in the deimmunization process is to integrate the modifications present in the de-immunized T-cell epitope clusters into the full-length protein. Expressed proteins are purified, tested for function in vitro and for immunogenicity in HLA transgenic mice. Over the past years, we have been engaged in a number of protein re-engineering projects using the DeFT approach. We have successfully accomplished each step in the process.
Information about our successful DeFT programs will be provided upon request.
Tregitopes, a proprietary tool for DeFT:
Tregitopes are a set of peptides that EpiVax discovered using our EpiMatrix platform while screening large libraries of IgG antibodies. They have the ability to call off the body’s immune response and can induce tolerance to co-administered antigens. When appropriate, Tregitopes can be incorporated into the DeFT process. Tregitopes are a set of peptides that specifically activate CD4+CD25+FoxP3+ natural regulatory T cells (nTregs). Tregitopes are promiscuous MHC Class II T cell epitopes located in the Fc and framework regions of Fab from IgG. In vitro, co-incubation of antigens with Tregitopes leads to suppression of effector cytokine and chemokine secretion, reduced proliferation of effector T cells, and expansion of antigen-specific adaptive Tregs (aTregs). In vivo, co-administration of Tregitopes with a wide range of proteins (such as FVIII, thyroid stimulating hormone receptor, ovalbumin, and autoantigens) leads to suppression of T cell and antibody responses to test antigens.Full list of Tregitope publications with links to full PDF’s – http://bit.ly/TregPubList
For more information on DeFT and Tregitope please Email Us Here.