Rousing the reservoir: Understanding more about where HIV hides in lymph nodes

Rousing the reservoir: Understanding more about where HIV hides in lymph nodes

December 12

Sydney researchers are leading a study to discover more about the HIV reservoir. The TRESAX study seeks to find out where HIV rebounds from during treatment interruption and what impact vaccination has on virus rebound. The work is led by Kirby Institute Director Professor Tony Kelleher and research fellow Dr Mee Ling Munier. The study is recruiting participants in Sydney now.

The T follicular helper REServoir in AXillary lymph nodes (TRESAX) study focusses on the role of a small family of lymph node CD4 T cells. CD4 T follicular helper cells (or TFH), are key players in the development of antibody responses. In people living with HIV, TFH increase in number and form one of the main reservoirs of replication-competent HIV. The importance of TFH cells in HIV infection is not well understood. The TRESAX study asks two main questions. The first is whether HIV rebound virus comes from TFH during a short treatment interruption. The second question is whether flu vaccination leads to more HIV rebound.

Describing the motivation for the study, Dr Munier says

We know that TFH in lymph nodes are infected and hang around for a long time. Next, we want to understand if the virus that rebounds if treatment stops comes from those TFH cells. Once we know where the virus comes from, we will be better positioned to target those cells with strategies to permanently block or eliminate HIV.

How is the study designed?
The study has two aims.

The first aim is to study how TFH contribute to HIV rebound during treatment interruption. To address this, the researchers will recruit a group of up to 30 adults living with well-controlled HIV infection. This group will undergo a short (28-day) treatment interruption.

The second aim is to understand how TFH contribute to HIV rebound after vaccination. To address this aim, the researchers will recruit a second group of adults with HIV. This group will receive the flu vaccine before a similar treatment interruption. The two groups can then be compared to understand the effect of vaccination on TFH in people living with HIV.

Why flu vaccination? What does that do?
Vaccination mimics natural infection by stimulating an immune response without causing disease. TFH reside in lymph nodes. Lymph nodes are critical co-ordinating centres of immune responses both after vaccination and infection. Vaccine components (antigens) activate TFH, leading to the production of effective antibody responses.

The seasonal flu vaccine is safe and routinely recommended for people living with HIV. The vaccine triggers an immune response involving numerous cell types in lymph nodes, including TFH cells. The researchers can then compare the TFH response in people living with HIV with or without prior vaccination. The effects of vaccination occur quickly – within days of vaccination. The study will therefore follow participants over the 2-4 weeks after vaccination.

What are the researchers looking for?
The researchers will take cells from lymph nodes and from blood. They will use a technique called flow cytometry to sort TFH cells from non-TFH cells. They will then study the HIV sequences found in each population. Studying the relationships between HIV sequences before and during treatment interruption will help the researchers understand where the rebound virus comes from.

What does the study involve for participants?
The TRESAX study is an intensive study requiring participants to have lymph node biopsies and a short treatment interruption (with or without a flu vaccination).

Participants will have biopsies of both left and right axillary lymph nodes performed by a highly experienced radiologist at two timepoints. One set of biopsies will occur at the beginning, and one at the end of the study. The biopsies involve application of a local anaesthetic and insertion of a fine needle into the lymph node to collect cells. The procedure takes about 30-45 minutes. The biopsy is guided by ultrasound to maximise the chance of getting a successful cell sample. The study team have performed nearly 100 of these biopsies without significant complication, although there may be short-term, mild local discomfort or occasional bruising.

Blood will also be collected at each study visit. Participants in the flu vaccine group will get the seasonal flu vaccine on the day the treatment interruption starts. During the treatment interruption, twice weekly monitoring will occur. Participants will restart treatment as soon as virus is detected (>200 copies/mL plasma). The treatment interruption will last for a maximum of 28 days. At that time, all participants will restart treatment regardless of whether HIV is detectable in their plasma or not. Participants undergoing a treatment interruption can opt to recommence treatment at any time.

What could this study contribute to the search for an HIV cure?
This study seeks to understand more about where HIV remains in lymph nodes during treatment. Even when HIV is undetectable in blood (and cannot be transmitted to sexual partners), virus remains in the body. Lymph nodes are a key virus hideout during treatment. In part, this is because the antiretroviral drugs are less effective at getting into tissue. It’s also because of the type of cells found in lymph nodes, including TFH cells.

The TRESAX study is one of the first studies in Australia to include treatment interruption in the undetectable=untransmittable (U=U) era. The study takes a cautious approach to treatment interruption, with a short and defined length, and bi-weekly monitoring. Community perception of this treatment interruption strategy may influence the design of future studies.

A clearer picture of the HIV reservoir will enable more specific strategies to eliminate HIV. The TRESAX study will help understand the role of TFH in viral rebound. The outcomes will provide further evidence for targeting these key lymph node players.