Page 16 Adam • Evaluation of the Humoral/Fc-mediated Immune Responses… authors of this TRAVERSE study as well. Also like before, is the fact that the explicit goal of this study was to further determine what Ad26 viral vector-based vaccine regimen was optimal for progressing into later-stage, phase 2 clinical trials. What’s different, however, about the goals of this TRAVERSE study - and what makes this study, at the same time, intertwined with the APPROACH study - is that Baden et al. were essentially picking up their research where the Barouch-led team left off. For example, Baden et al. start their study already presuming that the Ad26/Ad26 HD gp140 regimen (the “winner” from the APPROACH study) was the best, most-promising regimen at the time of this TRAVERSE study. Yet, despite the Ad26/Ad26 HD gp140 regimen’s promise, Baden et al, for this APPROACH study, wanted to test a brand new replication-incompetent, tetravalent Ad26 vector vaccine (Ad26.Mos4.HIV - now containing an additional mosaic Env antigen-carrying Ad26 vector) against the Ad26 vector vaccine (Ad26.Mos.HIV) that was in the APPROACH study’s Ad26/Ad26 HD gp140 regimen. This new Mosaic Env antigen, called “Mosaic 2 Env” was designed to provide better coverage of Clade C HIV-1 strains in addition to the primarily Clade B HIV-1 strains covered by the Ad26.Mos.HIV vaccine’s single “Mosaic 1 Env” antigen (Baden et al., 2020; Barouch et al., 2018). Specifically, Baden et al. wanted to compare the safety and (more critical to this review) the immunogenicity of the new tetravalent vector against the older trivalent vector. With these goals in mind, it would be appropriate to briefly look at how Baden et al. set about accomplishing their study to further answer whether or not an Ad26 viral vector-based vaccine regimen can elicit sufficient immune correlates of protection against HIV-1 to warrant its further testing in clinical trials. Similar to Barouch et al.’s study, Baden et al., set their TRAVERSE study up as a randomized, parallel-group, placebo-controlled, double-blind study. Participants for this study were also required to be HIV-1-uninfected, as well as between the ages of 18 and 50 (ensuring that no immune responses measured were from pre-existing infection, as well as ensuring that differences in variables between the APPROACH and TRAVERSE studies were reduced.) Also, Baden et al., like Barouch et al., did “mask” both the participants and clinicians towards which group a particular participant was in during the study. Unlike previously, however, Baden et al. used only 198 participants from either 11 different medical centers in the United States or from one medical center in Rwanda. Thus, the sample group and variation in participants’ ethnicities/possible living conditions (no uniform distribution of ethnicities was mentioned for the United States participants) were significantly smaller, though Baden et al. did ensure to stratify the participants based on the two regions, ensuring a similar proportion of both region’s participants were randomly assigned to each group - of which there were only three in this TRAVERSE study. The three groups were the “tetravalent” group (110 people), the “trivalent” group (55 people), and the placebo group
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