Tag: lymphatic system

Expanding Lymph Nodes to Improve Vaccine Effectiveness

Swollen lymph nodes. Credit: Scientific Animations CC0

The human body has around 600 lymph nodes (LNs) scattered throughout it, small, bean-shaped organs that house various types of blood cells and filter lymph fluid which temporarily swell during infections with viruses or other pathogens. This LN expansion and subsequent contraction can also result from vaccines injected nearby, and in fact is thought to reflect the ongoing vaccine immune response. While researchers have studied the early expansion of LNs following vaccination, they have not investigated whether prolonged LN expansion could affect vaccine outcomes.

Now, for the first time, researchers from Harvard University and the company Genentech found a way to enhance and extend LN expansion, and study how this phenomenon affects both the immune system and efficacy of vaccinations against tumours.

Key to their approach was a biomaterial vaccine formulation that enabled greater and more persistent LN expansion than standard control vaccines. While the oversized LNs maintained a normal tissue organization, they displayed altered mechanical features and hosted higher numbers of various immune cell types that commonly are involved in immune responses against pathogens and cancers. Importantly, “jump-starting” lymph node expansion prior to administering a traditional vaccine against a melanoma-specific model antigen led to more effective and sustained anti-tumour responses in mice. The findings are published in Nature Biomedical Engineering.

“By enhancing the initial and sustained expansion of LNs with biomaterial scaffolds, non-invasively monitoring them individually over long time periods, and probing deeply into their tissue architecture and immune cell populations, we tightly correlate a persistent LN expansion with more robust immune and vaccination responses,” said Wyss Institute Founding Core Faculty member David Mooney, Ph.D., who led the study. “This opens a new front of investigation for immunologists, and could have far-reaching implications for future vaccine developments.” Mooney also is the Robert P. Pinkas Family Professor of Bioengineering at SEAS, and a co-principal investigator of the NIH-funded and Wyss-coordinated Immuno-Engineering to Improve Immunotherapy (i3) Center.

The research team had previously developed biomaterial vaccine formulations, but had not investigated how their vaccines and those developed by others could influence the response of LNs draining leaked tissue fluid at vaccine injection sites, and have an impact on the LNs tissue organisation, different cell types, and their gene expression, which could in turn affect vaccine efficacy. In their new study, they tested a previously developed vaccine formulation that is based on microscale mesoporous silica (MPS) rods that can be injected close to tumours and form a cell-permeable 3D scaffold structure under the skin. Engineered to release an immune cell-attracting cytokine (GM-CSF), and immune cell-activating adjuvant (CpG), and tumour-antigen molecules, MPS-vaccines are able to reprogram recruited so-called antigen-presenting cells that, upon migrating into nearby LNs, orchestrate complex tumour cell-killing immune responses. Their new study showed that there are more facets to that concept.

“As it turns out, the immune-boosting functions of basic MPS-vaccines actively change the state of LNs by persistently enlarging their whole organ structure, as well as changing their tissue mechanics and immune cell populations and functions,” said first-author Alexander Najibi, PhD, who performed his Ph.D. thesis with Mooney.

Probing LNs with ultra-sound and nano-devices

Using high-frequency ultrasound, the team traced individual LNs in MPS-vaccinated mice over 100 days. They identified an initial peak expansion period that lasted until day 20, in which LN volumes increased about 7-fold, significantly greater than in animals that received traditional vaccine formulations. Importantly, the LNs of MPS-vaccinated mice, while decreasing in volumes after this peak expansion, remained significantly more expanded than LNs from traditionally vaccinated mice throughout the 100-day time course.

When Najibi and the team investigated the mechanical responses of the LNs using a nanoindentation device, they found that LNs in MPS-vaccinated animals, although maintaining an overall normal structure, were less stiff and more viscous in certain locations. This was accompanied by a re-organisation of a protein that assembles and controls cells’ mechanically active cytoskeleton. Interestingly, Mooney’s group had shown in an earlier biomaterial study that changing mechanical features of immune cells’ environments, especially their viscoelasticity, affects immune cell development and functions. “It is very well-possible that in order to accommodate the significant growth induced by MPS-vaccines, LNs need to become softer and more viscous, and that this then further impacts immune cell recruitment, proliferation, and differentiation in a feed-forward process,” said Najibi.

From immune cell engagement to vaccine responses

Interestingly, upon MPS-vaccination, the numbers of “innate immune cells,” including monocytes, neutrophils, macrophages, and other cell types that build up the first wave of immune defences against pathogens and unwanted cells, peaked first in expanding LNs. Peaking with a delay were dendritic cells (DCs), which normally transfer information in the form of antigens from invading pathogens and cancer cells to “adaptive immune cells” that then launch subsequent waves of highly specific immune responses against the antigen-producing invaders. In fact, along with DCs, also T and B cell types of the adaptive immune system started to reach their highest numbers. “It was fascinating to see how the distinct changes in immune cell populations that we detected in expanding LNs in response to the MPS-vaccine over time re-enacted a typical immune response to infectious pathogens,” commented Najibi.

Innate immune cells and DCs are also known as “myeloid cells,” which are known to interact with LN tissue during early expansion. To further define the impact of myeloid cells on LN expansion, Mooney’s team collaborated with the group of Shannon Turley, PhD, the VP of Immunology and Regenerative Medicine at Genentech, and an expert in lymph node biology and tumour immunology. “The MPS-vaccine led to extraordinary structural and cellular changes within the lymph node that supported potent antigen-specific immunity,” said Turley.

Using single cell RNA sequencing on myeloid cells from LNs, the groups were able to reconstruct distinct changes in myeloid cell populations during LN expansion, and identified distinct DC populations in durably expanded LNs whose changed gene expression was associated with LN expansion. In addition, the collaborators found that the number of monocytes was increased 80-fold upon MPS-vaccination – the highest increase among all myeloid cell types – and pinpointed subpopulations of “inflammatory and antigen-presenting monocytes” as promising candidates for facilitating LN expansion. In fact, when they depleted specific subpopulations of these types of monocytes from circulating blood of mice after vaccination, the maintenance of LN expansion, and timing of the T cell response to vaccination, was altered.

Finally, the team explored whether LN expansion could enhance the effectiveness of vaccination. “Jump-starting” the immune system in LNs with an antigen-free MPS-vaccine and subsequently administering the antigen in a traditional vaccine format significantly improved anti-tumour immunity and prolonged the survival of melanoma-bearing mice, compared to the traditional vaccine alone. “The priming of lymph nodes for subsequent vaccinations using various formulations could be a low-hanging fruit for future vaccine developments,” said Mooney.

Source: Wyss Institute for Biologically Inspired Engineering at Harvard

Bone Tissue has Lymphatic Vessels – and They Aid Healing

Doctor shows an X-ray of a foot
Photo by Tima Miroshnichenko on Pexels

To date, it has been assumed that bones lack lymphatic vessels, but new research published in the journal Cell not only mapped them within bone tissue, but demonstrated their role in bone and blood cell regeneration and reveals changes associated with ageing.

The network of vessels that form the lymphatic system plays an important role in draining excess fluid from tissues, clearing waste products and supporting immune responses.

The fine network of lymph vessels extends throughout the body, but a small number of sites such as the brain, eye and bone were previously assumed to lack lymph tissue. The hard tissue of bone in particular has traditionally made studying the distribution and role of blood and lymph more difficult.

Researchers used light-sheet imaging to identify and visualise the lymphatic vessels of bone in high-resolution 3D, revealing an active network of lymph vessels within bone. The researchers further identified some of the key signals happening between lymph vessels, blood stem cells and bone stem cells.

Dr Lincoln Biswas, co-first author of this study, said: ‘Interestingly after injury, lymphatic vessels in bone show dynamic crosstalk with blood stem cells and with specialised perivascular cells in order to accelerate bone healing. Such interactions between lymphatics and bone stem cells can harnessed to promote bone healing such as in fracture repair.’

The researchers found that lymphatic vessels in bone increase during injury via a signalling molecule called IL6, and trigger expansion of bone progenitor cells by secreting a different signal, called CXCL12. Dr Junyu Chen, a co-first author of the study now based at Sichuan University said: “Ageing is associated with diminished capacity for bone repair, and our findings show that lymphatic signalling is impaired in aged bones. Remarkably, the administration of young lymphatic endothelial cells restores healing of aged bones, thus providing a future direction to promote bone healing in elderly.”

Dr Anjali Kusumbe, who led the research said: “I am very excited as these findings not only demonstrate that lymphatic vessels do exist in bone but also reveal their critical interactions with blood stem cells and perivascular bone stem cells after injury to promote healing, thereby presenting lymphatics as a therapeutic avenue to stimulate bone and blood regeneration. Further, these findings are very fundamental, opening doors for understanding the impact of bone lymphatics on the immune system and their role in bone and blood diseases.”

Source: Oxford University

Completion Lymph Node Dissection Shows no Benefit in Advanced Melanoma

Melanoma cells. Source: National Cancer Institute.

A review of data, published in Annals of Surgical Oncology, shows that completion lymph node dissection surgery for patients with stage III melanoma confers no benefit. This is especially true given that immunotherapy has shown success in treating metastases.

For years, surgery for patients with stage III melanoma, where the cancer had metastasised into lymph nodes, involved removing them along with the primary tumour. Known as completion lymph node dissection (CLND), the surgery was meant to ensure that no cancer remained after surgery.

More recently, however, cancer surgeons have discovered that CLND has the potential to cause more problems than it solves. In most cases, patients do better on immunotherapy alone than they do when their surgery involves removal of the lymph nodes, due to potential complications from lymph node surgery.

To address this, researchers reviewed their patient data to determine if immunotherapy alone resulted in better outcomes than CLND.

“In the few years prior to immunotherapy being available, some surgical trials were done asking if regional node dissection by itself improves overall survival for the patients,” said Martin McCarter, MD, a professor of surgical oncology at the University of Colorado (CU). “And the answer came back: no, it did not improve survival. That had been the standard forever, because we didn’t have other effective therapies, but once the definitive trials were done, we learned that CLND wasn’t helping, it wasn’t improving survival. Subsequent trials demonstrated that immunotherapy can improve survival in metastatic melanoma.”

For the study, the researchers looked at data on 90 patients who underwent sentinel lymph node biopsy (a procedure to determine if a skin melanoma has spread microscopically) only for stage III melanoma but did not undergo CLND. Of those patients, 56 received immunotherapy and 34 did not. Those who received immunotherapy had better rates of distant metastasis-free survival, meaning their cancer was less likely to come back.

“As treatments for melanoma have evolved, the standard of care may be evolving as well,” Prof McCarter said. “This study took a look at the patients who had a sentinel lymph node biopsy, so we knew the patient had a positive melanoma metastasis to their regional node. Those folks historically used to go on and get the completion lymph node dissection, but recently, people started to forego doing that lymph node dissection, which did not improve survival, and instead moved directly to immunotherapy, which did improve survival in other clinical trials. We proved that this is acceptable, that we’re not causing more harm to patients by doing it, and that those who do go on to get the immunotherapy seem to benefit from it.”

Forgoing CLND is part of a recent movement in cancer treatment known as de-escalation (or de-implementation) — performing only absolutely needed surgery. It’s especially important when it comes to lymph node surgery, Prof McCarter said, as in addition to the usual surgical risks, CLND has a 20% to 30% risk of permanent lymphoedema.

“If you could avoid that complication and not compromise a patient’s survival, that would be beneficial,” McCarter said. “That’s what we guessed was happening outside of definitive clinical trial evidence, and that’s what we were able to show. We know that we often overtreat patients, and this fits in that paradigm of finding ways to de-escalate unnecessary therapies, which has been done in breast cancer and other cancers as well.”

The researchers hope the findings will sway surgeons for whom CLND is still routine, despite the earlier studies showing that the additional surgery was not improving survival.

“Previous clinical trials with the use of adjuvant immunotherapy for melanoma had required a CLND,” Prof McCarter explained. “This study used real-world data from our stage III melanoma patients who were treated with immunotherapy without having a prior CLND.

“It takes years to change people’s practice patterns. I still have conversations with community surgeons who treat melanoma, asking me, ‘Should I be doing these regional node dissections?’ even though this data has been out for five to 10 years now,” Prof McCarter continued. “They’re afraid to give up what they used to do, and they’re afraid that they are doing a disservice to the patients or not giving them the best chance, when in reality, our understanding of cancer biology has evolved. We now have effective immunotherapy, which is overcoming some of the limitations of surgery while improving outcomes.”

Source:  University of Colorado