Abstract: The present invention provides methods for lowering a viral load of a virus resistant to an antiviral drug by inducing cytotoxic T lymphocytes (CTL) to recognize a predetermined mutated epitope within a viral protein of the drug-resistant virus. CTLs are induced by immunizing a host with a peptide comprising the predetermined mutation. The immunostimulating peptide may be further improved by epitope-enhancement for inducing specific CTLs. The antiviral protection against drug-resistant virus shown by compositions of the present invention and mediated by human HLA-restricted CTL has not been previously achieved.