Scientists have discovered a method to improve and prolong the expansion of LN (lymph node) and to study its impact on the immune system and the effectiveness of vaccines against tumors. The enlarged LNs maintained normal tissue organization but showed changes in mechanical features and contained higher numbers of different types of immune cells that are typically involved in immune responses against diseases and cancers. Interestingly, initiating lymph node expansion before administering a conventional vaccine for a specific antigen related to melanoma resulted in more potent and long-lasting anti-tumor responses in mice. <p id=”first” class=”lead” rnrnEach person has approximately 600 lymph nodes (LNs) distributed throughout their body. These small, bean-shaped organs contain various types of blood cells and filter lymph fluid. During infections with viruses or other pathogens, some of our lymph nodes may temporarily swell. This swelling can also occur as a result of vaccines injected nearby, and is believed to be a part of the ongoing vaccine immune response. While the early expansion of lymph nodes following vaccination has been studied, researchers have not looked into whether prolonged lymph node expansion could impact vaccine outcomes.id=”text”>
A team of researchers from the Wyss Institute for Biologically Inspired Engineering at Harvard University, Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Genentech, which is a member of the Roche Group, have made a groundbreaking discovery. They have found a way to improve and prolong the expansion of lymph nodes (LNs) and have studied how this process impacts both the immune system and the effectiveness of cancer vaccines. The key to their method was a vaccine formulation using biomaterial that allowed for greater and longer-lasting expansion of LNs compared to standard vaccines. Although the larger LNs maintained their normal tissue structure, they exhibited altered mechanics.The study found that using biomaterial scaffolds to enhance the expansion of lymph nodes led to more effective immune responses against pathogens and cancers. Administering a traditional vaccine against a melanoma-specific antigen after jump-starting lymph node expansion resulted in sustained anti-tumor responses in mice. The results were published in Nature Biomedical Engineering. The study also involved non-invasively monitoring lymph nodes over long periods and studying their tissue architecture and immune cell populations in depth.tions, we closely associate a persistent LN expansion with stronger immune and vaccination responses,” said David Mooney, Ph.D., a member of the Wyss Institute Founding Core Faculty who led the study. “This presents a new area of exploration for immunologists, and could have significant implications for future vaccine advancements.” Mooney also holds the position of the Robert P. Pinkas Family Professor of Bioengineering at SEAS and is a co-principal investigator of the NIH-funded and Wyss-coordinated Immuno-Engineering to Improve Immunotherapy (i3) Center.
Mooney’s team at the Wyss Institute and SEAS had previously created various biomaterial scafbiomaterial vaccine formulation in preclinical animal models and in a first clinical trial with cancer patients. In this study, they examined how their vaccines and others could affect the response of lymph nodes (LNs) that drain leaked tissue fluid at vaccine injection sites. They also looked at how the vaccines could impact the organization of LNs tissue, different cell types, and gene expression, which could ultimately affect vaccine efficacy. This research adds to the extensive body of work on biomaterial vaccine formulations and their potential to fight tumor growth and combat infections.The vaccine formulation previously developed is based on microscale mesoporous silica (MPS) rods, which can be injected near tumors to create a cell-permeable 3D scaffold structure under the skin. These rods are designed to release an immune cell-attracting cytokine (GM-CSF), an immune cell-activating adjuvant (CpG), and tumor-antigen molecules. MPS-vaccines can reprogram recruited antigen-presenting cells, which then migrate into nearby lymph nodes and orchestrate complex tumor cell-killing immune responses. A new study has revealed additional aspects of this concept.Vaccines actively alter the structure of LNs, as well as their tissue mechanics and immune cell populations and functions,” said first-author Alexander Najibi, Ph.D., who conducted his Ph.D. thesis with Mooney.
Studying LNs with ultra-sound and nano-devices
To investigate the response of LNs to MPS-vaccines over time, the team used a high-frequency ultrasound (HFUS) imaging technique. Similar to monitoring the development of a fetus in a mother’s womb using clinical ultrasound, HFUS allows for non-invasive and detailed imaging of LNs.Non-invasively monitoring the anatomical details of tissues and organs in small animals like mice is achieved through HFUS. The research team used this method to track individual LNs in mice that were vaccinated with MPS for over 100 days. They observed a peak expansion period that lasted until day 20, during which the LN volumes increased approximately 7 times, which was significantly higher than the traditional vaccine formulations. Even after this peak expansion, the LNs of the MPS-vaccinated mice remained significantly more expanded than those of the traditionally vaccinated mice throughout the 100-day period.Najibi and the team used a nanoindentation device to study the mechanical responses of the LNs. They discovered that LNs in MPS-vaccinated animals, while maintaining an overall normal structure, were less rigid and more viscous in certain areas. This was accompanied by a re-organization of a protein that assembles and controls cells’ mechanically active cytoskeleton. Interestingly, previous research by Mooney’s group had demonstrated that altering the mechanical properties of immune cells’ environments, particularly their viscoelasticity, can impact immune cell development and functions. This suggests that in order to accommodate these changes, the immune system may need to adapt.According to Najibi, the growth of MPS-vaccines causes lymph nodes (LNs) to become softer and more viscous, which then affects immune cell recruitment, proliferation, and differentiation in a feed-forward process.
After MPS-vaccination, there is an increase in the numbers of “innate immune cells” such as monocytes, neutrophils, and macrophages in expanding LNs, which are the first line of defense against pathogens. Dendritic cells (DCs) also peak with a delay, as they usually transfer information related to vaccine responses.The body’s immune system works by sending signals in the form of antigens from invading pathogens and cancer cells to “adaptive immune cells” that then initiate specific immune responses against the invaders. Along with DCs, T and B cell types of the adaptive immune system also increased in number. These changes in immune cell populations in response to the MPS-vaccine mimic a typical immune response to infectious pathogens, according to Najibi.
Innate immune cells and DCs are also referred to as “myeloid cells,” which are recognized for their role in the immune system.The interaction with LN tissue during early expansion was studied by Mooney’s team. To better understand the impact of myeloid cells on LN expansion, they collaborated with Shannon Turley, Ph.D., the VP of Immunology and Regenerative Medicine at Genentech, and an expert in lymph node biology and tumor immunology. Turley stated, “The MPS-vaccine led to remarkable structural and cellular changes within the lymph node that supported potent antigen-specific immunity.” By isolating myeloid cells from LNs and analyzing the gene expression profiles of individual cells (single cell RNA-seq), the groups were able to identify specific changes in myeloid cells.The researchers observed changes in lymph node (LN) populations during LN expansion and identified different populations of dendritic cells (DC) in durably expanded LNs with altered gene expression associated with LN expansion. They also discovered that the number of monocytes increased 80-fold following MPS-vaccination, which was the highest increase among all myeloid cell types. They highlighted subpopulations of “inflammatory and antigen-presenting monocytes” as potential candidates for promoting LN expansion. Furthermore, when they removed specific subpopulations of these monocytes from the circulating blood of vaccinated mice, it affected the maintenance and timing of T cell activation in the LNs.The reaction to vaccination was changed. The researchers also looked into whether expanding the lymph nodes could improve the effectiveness of vaccination. By kickstarting the immune system in lymph nodes with an antigen-free MPS-vaccine and then giving the antigen in a regular vaccine format, the team saw a significant improvement in anti-tumor immunity and increased the survival of mice with melanoma, compared to just using the traditional vaccine. Mooney also mentioned that preparing the lymph nodes for future vaccinations using different formulations could be an easy way to improve future vaccine development.
The use of biomaterials in immunotherapy treatments could significantly improve the immune response in patients over longer periods of time. This innovative approach demonstrates how mechanics can play a crucial role in regulating living systems, including immune responses. These findings were shared by Donald Ingber, M.D., Ph.D., who is involved with various prestigious institutions such as Harvard Medical School, Boston Children’s Hospital, and SEAS.Other contributors to the research include Ryan Lane, Miguel Sobral, Giovanni Bovone, Shawn Kang, Benjamin Freedman, Joel Gutierrez Estupinan, Alberto Elosegui-Artola, Christina Tringides, Maxence Dellacherie, Katherine Williams, Hamza Ijaz, and Sören Müller. The National Institutes of Health/National Cancer Institute (award# U54 CA244726 and R01 CA223255) provided funding for the study.
Â
