HIV-1 causes lifelong infection and can lead to serious health complications in individuals living with the virus. Fortunately, antiretroviral therapies have been developed, and most people living with HIV live long, healthy lives. Pre-exposure prophylaxis can prevent infection while someone is taking the drug, but protection does not persist if they discontinue the medication. While both interventions have curbed HIV infection rates and improved HIV-1 care significantly, they can be expensive and not widely available in areas with high rates of infection. To address this problem, researchers have been trying to develop an effective vaccine against the virus.
HIV-1 uses a single protein, the envelop protein (Env), to attach to and enter host cells. Vaccines against HIV-1 have been challenging to develop because Envs are highly variable. Broadly neutralizing antibodies, which can recognize and target several HIV-1 Envs and prevent infection in healthy people, have been identified from multiple HIV-infected individuals. Patient-derived VRC01-class antibodies are among the most effective broadly neutralizing antibodies against HIV-1, and previous work has shown that introducing these antibodies into animals prevents experimental HIV-1 infection. Dr. Andy McGuire, a professor in the Vaccine and Infectious Disease Division at Fred Hutch, is interested in finding ways to elicit VRC01-class antibodies through vaccination in humans to prevent HIV-1 infection.
McGuire’s lab previously developed a molecule called iv4/iv9 that is designed to select for precursor B cells that will produce VRC01-class antibodies. All B cells have a unique B cell receptor composed of a heavy chain and a light chain that recognizes Env in a very specific way and will ultimately be used in antibodies produced by mature B cells. iv4/iv9 binds to VRC01-class B cell receptors (which have a VH1-2 heavy chain and 5AA CDRL3 light chain) and activates those B cells. The hope is immunization with iv4/iv9 could selectively activate VRC01-class B cells, eventually leading to the production of VRC01-class broadly neutralizing antibodies. McGuire’s group showed used flow cytometry to show iv4/iv9 could identify VRC01-class precursor B cells from human blood leading them to hypothesize that immunization with iv4/iv9 could prime VRC01-class precursor B cells to produce broadly neutralizing antibodies.
To investigate this potential, McGuire partnered with Alloy Therapeutics to use their specialized mouse model. “Mice and other small animals don't have the human VH1-2 heavy chain gene. The ATX-GK mice have most of the human antibody genes knocked in, including VH1-2, so that is why we used them,” explains McGuire. To start, they measured the frequency of B cells expressing either VH1-2 heavy chain or 5AA CDRL3 light chain in the ATX-GK mice. They found that the frequency of VH1-2 expression in the mice was very similar to that in humans, but mice expressed about eight times less 5AA CDRL3 than humans. Using these frequencies, they estimated that between 1 in 50,000 to 1 in 75,000 mouse B cells are VRC01-class precursors expressing both VH1-2 and 5AA CDRL3. Next, they wanted to know if iv4/iv9 could identify VRC01 precursors in mice, so they sorted and sequenced B-cells based on iv4/iv9 binding. They found that of the ~1500 B cells they analyzed, only one of them was a true VRC01-class precursor, leading them to conclude that while the VRC01-class precursors are rare in the ATX-GK mice, iv4/iv9 can identify them.
The team hypothesized that altering the affinity of iv4/iv9 could make them more selective for VRC01-class precursor cells, so they collaborated with Dr. Marie Pancera’s group to tweak the structure and produce an iv4/iv9mod immunogen that was more selective for VRC01-class precursors. From there, they immunized mice with either iv4/iv9 or iv4/iv9mod and measured which cells expressed VH1-2, 5AA CDRL3, or both. They analyzed spleens from these mice and found that immunized mice expressed more VH1-2 and 5AA CDRL3 compared to unimmunized controls, but only mice that received iv4/iv9mod had detectable VRC01-class precursor cells. Next, they sorted and sequenced lymph node B cells from iv4/iv9mod-immunized mice or unimmunized controls based on iv4/iv9mod binding and found that iv4/iv9mod immunization increased the frequency of VH1-2 and 5AA CDRL3 expressing cells and VRC01-class precursor cells that express both.
Excited by these results, they next tried to repeat the immunizations to identify more VRC01 precursors from other animals. Unfortunately, they were unsuccessful, likely due to the low frequency of these cells in the ATX-GK mice. Despite being unable to recapitulate their results in more animals, McGuire is still hopeful for the potential of iv4/iv9 as a vaccination strategy for HIV-1. “We found that the mice had the right genetic components, but the frequency of these cells was low compared to humans. So, the model probably isn't the best to test these idiotypes as immunogens,” he explained, “That being said, we did stimulate those rare B cells in a few animals so it suggests it might be possible to use these immunogens in a better animal model, or in humans.”
This work was supported by funding from the Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium and the National Institutes of Health.
Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium Member Dr. Andy McGuire contributed to this work.
Chhan CB, Wan Y, Wilcox-King A, Homad LJ, Aldridge NT, Iureniev R, Stamatatos L, McGuire AT. 2026. Evaluating an anti-idiotype derived germline-targeting immunogen designed to elicit VRC01-class precursors in human antibody transgenic mice. mSphere. 2026 Sep 29;11(9):e0031726. doi: 10.1128/msphere.00317-26.
Kelsey Woodruff is a PhD candidate in the Termini Lab at Fred Hutch Cancer Center. She studies how acute myeloid leukemia cells remodel the sugars on their membranes to reprogram cancer cell signaling. Originally from Indiana, she holds a bachelor's degree in Biochemistry from Ball State University. Outside of lab, you can find her crocheting and enjoying the Seattle summers.