New Approaches to in silico Design of Epitope-Based Vaccines
New Approaches to in silico Design of Epitope-Based Vaccines
New Approaches to in silico Design of Epitope-Based Vaccines
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7.1. OPTITOPE – A WEB SERVER FOR EPITOPE SELECTION 75<br />
converted <strong>in</strong><strong>to</strong> consensus sequences. From these sequences, all peptides <strong>of</strong> a given length<br />
will be derived and will be considered as candidate epi<strong>to</strong>pes. The user can adjust the<br />
peptide length <strong>to</strong> be applied via the advanced options.<br />
Step 2: Target population<br />
In the second step, <strong>in</strong>formation on the target population has <strong>to</strong> be entered. This step is<br />
subdivided <strong>in</strong><strong>to</strong> two queries. The user is queried (1) for the MHC alleles <strong>to</strong> consider (if<br />
they have not already been entered <strong>in</strong> the previous step) and (2) for their probabilities <strong>in</strong><br />
the target population.<br />
1. MHC alleles can be selected by population or geographic area based on data [122]<br />
retrieved from the NCBI dbMHC database [123]. The correspond<strong>in</strong>g probabilities<br />
will be employed for the next query. Alternatively, the MHC alleles can be selected<br />
manually from an expandable allele tree [124] or by past<strong>in</strong>g a list <strong>of</strong> alleles.<br />
2. In this step, a list <strong>of</strong> the selected MHC alleles along with probabilities (default values<br />
or values retrieved from the NCBI dbMHC database, respectively) is given. These<br />
probabilities can either be modified manually or they can be replaced by populationor<br />
geographic-area-specific probabilities from the NCBI dbMHC database via the<br />
advanced options. Individual MHC alleles can be excluded from further process<strong>in</strong>g.<br />
Furthermore, low probability MHC alleles can be excluded from the epi<strong>to</strong>pe selection<br />
process via a filter <strong>in</strong> the advanced options.<br />
If the user has not entered the immunogenicities <strong>of</strong> the candidate epi<strong>to</strong>pes <strong>to</strong>gether with<br />
the target sequences, OptiTope will employ a prediction method <strong>to</strong> determ<strong>in</strong>e the respective<br />
immunogenicities. The prediction method <strong>to</strong> be employed can be selected via the advanced<br />
options.<br />
Step 3: Constra<strong>in</strong>ts<br />
In the third step, the user is queried for the requirements on the epi<strong>to</strong>pe set <strong>to</strong> be selected.<br />
Depend<strong>in</strong>g on the data that have been entered <strong>in</strong> the previous steps – a summary <strong>of</strong> these<br />
data is given – a list <strong>of</strong> suitable constra<strong>in</strong>ts is displayed. The user can (de)select and modify<br />
these constra<strong>in</strong>ts. Potential constra<strong>in</strong>ts are:<br />
• Maximum number <strong>of</strong> epi<strong>to</strong>pes <strong>to</strong> select. This constra<strong>in</strong>t def<strong>in</strong>es the maximum number<br />
<strong>of</strong> epi<strong>to</strong>pes OptiTope should select. It is the only manda<strong>to</strong>ry constra<strong>in</strong>t.<br />
• M<strong>in</strong>imum epi<strong>to</strong>pe conservation. This constra<strong>in</strong>t ensures that only epi<strong>to</strong>pes that fulfill<br />
a user-def<strong>in</strong>ed conservation requirement will be considered.<br />
• M<strong>in</strong>imum number <strong>of</strong> alleles <strong>to</strong> cover. If this constra<strong>in</strong>t is selected, the optimal set <strong>of</strong><br />
epi<strong>to</strong>pes will be immunogenic with respect <strong>to</strong> the specified number <strong>of</strong> MHC alleles<br />
or more.<br />
• M<strong>in</strong>imum number <strong>of</strong> antigens <strong>to</strong> cover. This constra<strong>in</strong>t guarantees that the optimal<br />
epi<strong>to</strong>pe set will <strong>in</strong>clude epi<strong>to</strong>pes from a specified number <strong>of</strong> antigens or more.