We constructed the HIV-1 vaccine candidate MV1-F4, using an in vivo replication-competent MV vector (Combredet et al. 2003 ) derived from the Schwarz vaccine strain, to generate recombinant MV expressing the F4 antigen. F4 is a fusion protein comprising the clade B viral antigens p17, p24, reverse transcriptase and the regulatory protein Nef. Combined with AS01 (a liposome-based Adjuvant System containing 3-O-desacyl-4′-monophosphoryl lipid A (MPL) and QS21; Garçon et al. 2007 ), this F4 antigen was shown to induce potent polyfunctional CD4 + T cell responses in HIVseronegative volunteers (Van Braeckel et al. 2011 ).