Antigenic cooperation in viral populations: Transformation of functions of intra-host viral variants.

In this paper, we study intra-host viral adaptation by antigenic cooperation - a mechanism of immune escape that serves as an alternative to the standard mechanism of escape by continuous genomic diversification and allows to explain a number of experimental observations associated with the establishment of chronic infections by highly mutable viruses. Within this mechanism, the topology of a cross-immunoreactivity network forces intra-host viral variants to specialize for complementary roles and adapt to the host's immune response as a quasi-social ecosystem. Here we study dynamical changes in immune adaptation caused by evolutionary and epidemiological events. First, we show that the emergence of a viral variant with altered antigenic features may result in a rapid re-arrangement of the viral ecosystem and a change in the roles played by existing viral variants. In particular, it may push the population under immune escape by genomic diversification towards the stable state of adaptation by antigenic cooperation. Next, we study the effect of a viral transmission between two chronically infected hosts, which results in the merging of two intra-host viral populations in the state of stable immune-adapted equilibrium. In this case, we also describe how the newly formed viral population adapts to the host's environment by changing the functions of its members. The results are obtained analytically for minimal cross-immunoreactivity networks and numerically for larger populations. • Antigenic cooperation is a mechanism of immune escape which provides an alternative to immune escape by continuous genomic diversification. • Intra-host viral variants create a network of cross-immunoreactivity, with each variant performing a different role to escape the host immune system. • Emergence of a new viral variant with altered antigenic features may result in a rapid rearrangement of the viral ecosystem and a change in the roles played by existing viral variants. • Emergence of a new viral variant with altered antigenic features may push the viral population into a stable state of immune escape by antigenic cooperation. • Viral transmission between two infected hosts results in the merging of two intra-host viral populations and results in changes in the functions of its members to adapt to the new host environment. [ABSTRACT FROM AUTHOR]