A Phylogenetic Codon Substitution Model for Antibody Lineages.

Area of Science:

• Immunology
• Evolutionary Biology
• Computational Biology

Background:

• Phylogenetic methods are crucial for studying antibody lineage development.
• Somatic hypermutation, a key process in antibody evolution, is influenced by mutation-biased hotspot motifs.
• Existing phylogenetic substitution models often violate assumptions due to this context dependency.

Purpose of the Study:

• To develop a modified phylogenetic substitution model that addresses context-dependent mutation biases in antibody lineages.
• To improve the accuracy of phylogenetic analyses for broadly neutralizing antibody (bNAb) development.
• To provide a tool for testing hypotheses about the role of mutation hotspots and coldspots in B-cell evolution.

Main Methods:

• Development of a modified GY94-type substitution model incorporating context dependency.
• Application and comparison of the new model against the standard GY94 model using three well-characterized bNAb lineages.
• Exploration of the decay of hotspot motifs and mutation rates over time within bNAb lineages.

Main Results:

• The modified model demonstrates a substantially better fit to bNAb lineage data compared to the standard GY94 model.
• The model facilitates hypothesis testing regarding the influence of specific mutation motifs on B-cell lineage evolution.
• The study explores the potential decline of mutation hotspots and rates during bNAb lineage progression.

Conclusions:

• The developed phylogenetic model offers improved accuracy for analyzing antibody evolution, particularly for bNAb lineages.
• This approach enhances our understanding of somatic hypermutation's role and context dependency in shaping antibody diversity.
• The model provides a framework for investigating dynamic changes in mutation patterns during B-cell evolution.