Maraviroc is a drug designed to block the interaction between HIV attachment proteins and the host cell receptor protein CCR5, thus blocking the initial stages of viral infection. Although Maraviroc shows promise in clinical trials, one major concern is the long term physiological impact of blocking CCR5. Why is this a concern?

a) Long term blocking would cause the CCR5 protein to mutate and it would no longer be functional as a receptor.

b) Like all host cell receptor proteins, CCR5 has a normal role for the cell, and long term blocking by Maraviroc would also block this normal role

c)CCR5 cell receptors would habituate to the continued presence of Maraviroc and the drug would lose its effectiveness.