Microplates were read at 450 nm on a M3 SpectroMax plate reader (Molecular Devices, Sunnyvale, CA). == Robust Env protein expression was confirmed by western blot analysis and acknowledgement of cell surface Env gp160 by multiple bNAbs. Ad4Env vaccines induced humoral immune responses in rabbits that acknowledged Env 1086 gp140 and V1V2 polypeptide sequences derived from 1086 clade C, A244 clade AE, and gp70 V1V2 CASE A2 clade B fusion protein. The immune sera efficiently neutralized tier 1 clade C pseudovirus MW965. 26 and neutralized the homologous and heterologous tier 2 pseudoviruses to a lesser extent. Env-specific T cell responses were also induced in mice following Ad4Env160 vector immunization. == Conclusions == The Ad4Env vaccine vectors express high levels of Env glycoprotein and induce both Env-specific humoral and cellular immunity thus supporting further development of this new Ad4 HIV-1 Env vaccine platform in Phase 1 clinical trials. == Introduction == The development of an effective AIDS vaccine has encountered significant barriers including lack of predictive animal models and absence of well-defined correlates of protection [1,2]. Of major concern is the failure of four large efficacy trials, two based on the use of a recombinant HIV-1 Env gp120 (AIDSVAX), a third (Step study) based on the use of a replication-deficient Ad5 vaccine vectors [3-5], and a fourth, the HVTN 505 trial using a multiclade DNA prime immunization followed by a replication-deficient multiclade Ad5 boost immunization [6,7]. However, the results of the RV144 ALVAC/AIDSVAX Phase 2b efficacy trial in Thailand showed an estimated Pivmecillinam hydrochloride efficacy of 31.2% and suggested that a vaccine to prevent HIV-1 infection may be closer than previously thought [1,2,5,8]. However, efficacy was considered modest and insufficient for the vaccine to be implemented as a public health measure [9]. Furthermore, the vaccine had no effect on modifying viral load or CD4+T cell counts in Pivmecillinam hydrochloride vaccinated individuals who became infected. The vaccine components used in the RV144 trial were administered using a heterologous prime-boost approach. The priming vaccine was a recombinant canarypox vector virus (ALVAC), which is replication-incompetent in humans, expressing Gag, protease and clade E Env gp120 linked to the transmembrane anchoring portion of gp41. The boosting vaccine was the same AIDSVAX B/E gp120 used previously in the AIDSVAX trial in Thailand [5]. Cellular responses were tested in a subgroup of vaccinees with only minimal level of responses observed. Subsequent analyses have revealed potential immune correlates of protection including: 1) V1V2 binding antibodies and 2) CD4+T Pivmecillinam hydrochloride cell responses targeting epitopes within the V2 region [10,11]. Thus, vaccines Pivmecillinam hydrochloride designed to induce significant levels of Env gp120-specific V1V2 antibodies and T cell responses may have improved efficacy against HIV-1 infection. Additionally, several studies have suggested that a more robust induction of bNAbs may increase vaccine efficacy and duration. Many viral vaccines rely on the induction of bNAbs as the primary correlate of protection [12]. Specifically, for HIV-1, passive transfer of bNAbs can completely block infection by chimeric SHIV in non-human primates (NHP) studies [13-16]. The potential of bNAbs to protect against HIV-1 infections is also demonstrated by gene-based antibody delivery in humanized Pivmecillinam hydrochloride mice and NHPs [17,18]. The recent Phase 2b trials of HIV-1 vaccines support a prime-boost approach and the inclusion of a HIV-1 Env glycoprotein. The lack of efficacy in the AIDSVAX trials, VAX004 and VAX003, suggest a need for greater coverage of neutralizing antibody and T cell immunity [4,19-22]. The Step and HVTN 505 trials suggest a need for higher or WNT-12 qualitatively different T cell responses and a need for an Env.