Do adjuvants have any medical use outside of vaccines?

Submitted by Accelerator231 t3_102yk48 in askscience

I know about aluminium hydroxide and how it's used to increase the immune response when putting in vaccines. The virus protein interacts with the immune system , leading to an acquired immunity. Aluminium hydroxide increases this effect.

But here's the thing. In the case that there's already a virus or pathogen there, and there's already an immune response in the body (albeit a weak one), can aluminium adjuvants alone serve to boost immune response and increase chances of recovery? Or is it's effectiveness dependent on an already weakened antigen?

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Smokey_Katt t1_j2wf8b7 wrote

I’d like to know too. I remember reading about a clinical trial where they had just the adjuvant as a control, and they had a response rate similar to the actual drug. So I’d guess “yes, needs more research” and probably applies to some diseases more than others.

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pansveil t1_j2wifjx wrote

tl;dr: Adjuvants may increase the response of the immune system if given without an antigen, but that immune response would not be directed towards the existing pathogen.

The reason behind this is tied to how the immune system targets a pathogen in the first place. The initial step is chopping up the pathogen/virus and creating antigens by the first line responders (known as antigen presenting cells, or APCs). These cells then give two signals to other white blood cells to induce the immune response: the antigen and the biochemical signals (cytokines) to teach the WBCs how to break down the pathogen. Without both signals, the antigen AND the cytokines, there is no further immune response.

Some adjuvants (aluminum/M59) increase antigen processing while other adjuvants artificially provide instructions on how to combat the pathogen. Without an antigen associated with the adjuvant, the immune system would fail to create any immune response to target the pathogen even if it's already in the body. Failure in this two-signal process is mirrored in some inherited auto-immune deficiencies as well as immune evasion of cancer cells.

If you're interested in a relatively recent update on how adjuvants work, this literature review go over recent advancements.

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daywalkker t1_j3042ig wrote

I can give you a bit of a more frank, less technical and comprehensive answer that may help. If this helps add to the other answers, great. If not, ignore me.

Adjuvants work locally as well as systemically, but not both in equal measure. They are especially active at the site of the injection. A vital part of the desired vaccine-induced immune response relies on the adjuvant and vaccine antigens being in relatively high concentrations in the same place in the body.

If you just injected a person with an adjuvant only and they already had the virus on-board, you may see a very mild increase in overall immune response in the form of a slight elevation in body temp and very, very mild systemic inflammation, but it wouldn't be nearly enough to affect the course of the infection. You would also have a local inflammatory response at the site of the injection but without the vaccine along with it, you just get a sore arm with no benefit.

The adjuvant triggers local inflammation which calls white blood cells to come running, or rolling and oozing as the case may be. These white blood cells (macrophages/dendritic cells/Antigen presenting cells) are stimulated by the adjuvant to grab the vaccine antigen particles that are highly concentrated in that area and (long story short) present those viral particles to the immune system so they can pump out new lymphocytes (another kind of white blood cell) to target and kill specifically the strain of virus that was in the vaccine.

I don't know if that clarifies or obfuscates things!

Edit: typos, clarification

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