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What is expected from the HSV vaccine trial ?

  1. 122 Posts.
    There seems to be quite a lot of anticipation of the Phase 1 HSV-2 vaccine trial results - as a holder I hope the results are great, but I am not expecting something stunning and certainly not any hint of efficacy.  These are my reasons (please correct me if my facts are wrong – this is from memory):
    1)   The trial is a safety study, with a preliminary 'potency' study component - I don’t know the full details, but believe it comprises 5 groups of 4 subjects each, with each group receiving a different dose of the vaccine (please advise details if known).  Potency is to assess the strength and (depending on the study design) duration of immune responses - it does not assess efficacy since this can only be done via experimental challenge (not likely in humans) or environmental 'natural' infection (not part of this study design - would require much larger groups). All the subjects are (I believe) HSV seronegative i.e. have never been infected – this enables determination of the ‘naïve’ immune response to the vaccine; it means that the efficacy as a therapeutic (i.e. reduction of frequency/severity of HSV recurrence (genital herpes or cold sores)) is not part of the study.
    2)   Initial results demonstrated safety (i.e. no nasty reactions to the vaccine) and that a T cell response was activated (I don’t think the type of T cell response was specified). I don’t think the initial report commented on antibody responses.   Since this was primarily a safety study, it has already been reported to pass that test – what is left to be reported ?
    1.    Antibody responses ? (the vaccine is designed to induce both T cell and antibody responses) A strong neutralising antibody response (i.e. blocks the virus from infecting cells) would be good.
    2.   Broad MHC specificity of T cell response ? The MHC molecule displays virus peptides (target antigens) to T cells – there is substantial variation of MHC between different people (one reason why organ donations need to be ‘tissue type matched’) and different MHC molecules can present different virus peptides. Ideally, a vaccine would work with multiple different MHC types – potentially the study may have people with different MHC types and may have tested this.
    3.    ‘Potency’ of T cell responses ? This might be measured by looking at how much ‘weaponry’ the induced T cells are able to deploy against virus-infected cells, the frequency of virus-specific T cells circulating in the blood, or the ability of T cels recovered from the vaccinated volunteers to kill virus-infected cells in the lab.
    4.   Duration of immunity ? Perhaps the study was designed to take measurements at different times after vaccination, to see how well the antibody/ T cell responses persisted over time. Ideally, a vaccine would induce strong responses that remained at an effective level after several months (the duration is the key determinant of how often a vaccine booster is required).
    Now, without knowing the study details, the above is my speculation. The study may never have been designed to measure some/any of the above, so not reporting on eg. duration does not mean that the response didn’t last (it may just not have been tested). Hopefully, the final results may show some good results relating to some of the above ‘potency’ measures, but if there is no significant announcement that does not mean bad news, it may just be that the study was not designed to test additional ‘potency’ indicators.
    Sorry for such a long post – my sentiment is long term also.
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