New study reveals HIV pre-exposure prophylaxis (PrEP) alters immune cell function and metabolism

Posted on: 09 September 2026

Researchers from the Trinity Translational Medicine Institute (TTMI) and St James's Hospital have found that a widely used HIV prevention drug may also change how certain immune cells function.

The drug, known as PrEP (pre-exposure prophylaxis), is highly effective at preventing HIV infection. It consists of a combination of two antiretroviral drugs that are also used to treat of people living with HIV. While the development of PrEP has transformed HIV prevention, researchers have long been interested in understanding whether they may also have broader effects on the immune system.

More than 7,000 people in Ireland are living with HIV, and roughly half are cared for at St James's Hospital, which also provides PrEP to over 1,000 patients. In a new study published in the journal Frontiers in Immunology, the research team assessed the impact of PrEP on how immune cells function and use energy.

To explore these effects, the researchers recruited patients attending St James's Hospital for PrEP treatment. By analysing blood samples before and after treatment began, they were able to assess changes in immune cell activity linked to PrEP use. The team also studied immune cells from people who had been taking PrEP for more than a year.

The study focused on monocytes, a type of immune cell that acts as one of the body's first responders to infection. The researchers found clear differences between the monocytes of people taking PrEP and those of people who were not.

Specifically, monocytes from people on PrEP were more active, better able to respond to infection, and used glucose differently to generate energy. These findings offer new insight into how PrEP might affect the immune system beyond its role in preventing HIV. The researchers hope the work will help build a better understanding of inflammation and immune regulation, both in people living with HIV and in those taking PrEP.

Dr Dearbhla Murphy, Postdoctoral Research Fellow and co-lead author, said: “As PrEP use becomes more widespread, it's important to understand not just how well it prevents HIV, but also how it might affect the immune system more broadly.

"These findings reveal a previously unrecognised effect of antiretroviral drugs in people who are HIV-negative, offering new clues about how these medicines may influence the immune system's natural balance, even when HIV isn't present.”

Dr Liam Townsend, Consultant Physician in Infectious Diseases in St James’s Hospital and senior author, said: “This work highlights the impact medications can have on immune responses, even when no infection is present.

"This adds to our understanding of potential long-term changes in immune function in people taking these medications for long periods of time. It is a great example of translational research between patients and clinicians at St James's Hospital and researchers at Trinity Translational Medicine Institute.

"These findings will help us work out whether changes we see in the body are caused by the medication itself, or by the condition it's treating. That distinction matters because if it's the medication, it points to something that could potentially be managed, giving us a practical way to help people who take PrEP stay healthier over the long term."

The study was supported by research funding from Trinity College Dublin.