HIV's Evolution is Constrained by Fitness Valleys

What is it about?

When adaptation requires changes at more than one genetic locus, some changes may be deleterious on their own but beneficial in combination with other changes. HIV experiences such fitness valleys when adapting to its alternative target cells. This study represents the first analysis of the evolutionary dynamics of crossing empirical fitness valleys. We show that these fitness valleys constrain the evolutionary paths that the virus may take in evolving to infect its alternative target cells.

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Why is it important?

This study represents the first analysis of the evolutionary dynamics of crossing empirical fitness valleys. The result that the probability of HIV crossing the fitness valleys analysed is very low helps explain why the virus evolves to infect its alternative target cells only in half of patients and only late in infection. This result may help direct efforts to block the virus's evolution within a patient.