UAB Research Foundation

Memory B cells play a critical role to provide long-term immunity after a vaccination or infection. Researchers have now described a distinct and novel subset of memory B cells that predict long-lived antibody responses to influenza vaccination in humans. These effector memory B cells appear to be poised for a rapid serum antibody response upon secondary challenge one year later. Memory B cells play a critical role to provide long-term immunity after a vaccination or infection. In a study published in the journal Immunity, researchers describe a distinct and novel subset of memory B cells that predict long-lived antibody responses to influenza vaccination in humans. These effector memory B cells appear to be poised for a rapid serum antibody response upon secondary challenge one year later, Anoma Nellore, M.D., Fran Lund, Ph.D., and colleagues at the University of Alabama at Birmingham and Emory University report. Evidence from transcriptional and epigenetic profiling shows that the cells in this subset differ from all previously described memory B cell subsets. The UAB researchers identified the novel subset by the presence of FcRL5 receptor protein on the cell surface. In immunology, a profusion of different cell-surface markers is used to identify and separate immune-cell types. In the novel memory B cell subset, FcRL5 acts as a surrogate marker for positive expression of the T-bet transcription factor inside the cells. Various transcription factors act as master regulators to orchestrate the expression of many different gene sets as various cell types grow and differentiate. Nellore, Lund and colleagues found that the FcRL5+ T-bet+ memory B cells can be detected seven days after immunization, and the presence of these cells correlates with vaccine antibody responses months later. Thus, these cells may represent an early, easily monitored cellular compartment that can predict the development of a long-lived antibody response to vaccines. This could be a boon to the development of a more effective yearly influenza vaccine. "New annual influenza vaccines must be tested, and then manufactured, months in advance of the winter flu season," Lund said. "This means we must make an educated guess as to which flu strain will be circulating the next winter." Why are vaccine candidates made so far in advance? Pharmaceutical companies, Lund says, need to wait many weeks after vaccinating volunteers to learn whether the new vaccine elicits a durable immune response that will last for months. "One potential outcome of the current study is we may have identified a new way to predict influenza vaccine durability that would give us an answer in days, rather than weeks or months," Lund said. "If so, this type of early 'biomarker' could be used to test flu vaccines closer to flu season -- and moving that timeline might give us a better shot at predicting the right flu strain for the new annual vaccine." Seasonal flu kills 290,000 to 650,000 people each year, according to World Health Organization estimates. The global flu vaccine market was more than $5 billion in 2020. To understand the Immunity study, it is useful to remember what happens when a vaccinated person subsequently encounters a flu virus. Following exposure to previously encountered antigens, such as the hemagglutinin on inactivated influenza in flu vaccines, the immune system launches a recall response dominated by pre-existing memory B cells that can either produce new daughter cells or cells that can rapidly proliferate and differentiate into short-lived plasmablasts that produce antibodies to decrease morbidity and mortality. These latter B cells are called "effector" memory B cells. "The best vaccines induce the formation of long-lived plasma cells and memory B cells," said Lund, the Charles H. McCauley Professor in the UAB Department of Microbiology and director of the Immunology Institute. "Plasma cells live in your bone marrow and make protective antibodies that can be found in your blood, while memory B cells live for many years in your lymph nodes and in tissues like your lungs. "Although plasma cells can survive for decades after vaccines like the measles vaccine, other plasma cells wane much more quickly after vaccination, as is seen with COVID-19," Lund said. "If that happens, memory B cells become very important because these long-lived cells can rapidly respond to infection and can quickly begin making antibody." In the study, the UAB researchers looked at B cells isolated from blood of human volunteers who received flu vaccines over a span of three years, as well as B cells from tonsil tissue obtained after tonsillectomies. They compared naïve B cells, FcRL5+ T-bet+ hemagglutinin-specific memory B cells, FcRL5neg T-betneg hemagglutinin-specific memory B cells and antibody secreting B cells, using standard phenotype profiling and single-cell RNA sequencing. They found that the FcRL5+ T-bet+ hemagglutinin-specific memory B cells were transcriptionally similar to effector-like memory cells, while the FcRL5neg T-betneg hemagglutinin-specific memory B cells exhibited stem-like central memory properties. Antibody-secreting B cells need to produce a lot of energy to churn out antibody production, and they also must turn on processes that protect the cells from some of the detrimental side effects of that intense metabolism, including controlling the dangerous reactive oxygen species and boosting the unfolded protein response. The FcRL5+ T-bet+ hemagglutinin-specific memory B cells did not express the plasma cell commitment factor, but did express transcriptional, epigenetic and metabolic functional programs that poised these cells for antibody production. These included upregulated genes for energy-intensive metabolic processes and cellular stress responses. Accordingly, FcRL5+ T-bet+ hemagglutinin-specific memory B cells at Day 7 post-vaccination expressed intracellular immunoglobulin, a sign of early transition to antibody-secreting cells. Furthermore, human tonsil-derived FcRL5+ T-bet+ memory B differentiated more rapidly into antibody-secreting cells in vitro than did FcRL5neg T-betneg hemagglutinin-specific memory B cells. Lund and Nellore, an associate professor in the UAB Department of Medicine Division of Infectious Diseases, are co-corresponding authors of the study, "A transcriptionally distinct subset of influenza-specific effector memory B cells predicts long-lived antibody responses to vaccination in humans." Co-authors with Lund and Nellore are Esther Zumaquero, R. Glenn King, Betty Mousseau, Fen Zhou and Alexander F. Rosenberg, UAB Department of Microbiology; Christopher D. Scharer, Tian Mi, Jeremy M. Boss, Christopher M. Tipton and Ignacio Sanz, Emory University School of Medicine, Atlanta, Georgia; Christopher F. Fucile, UAB Informatics Institute; John E. Bradley and Troy D. Randall, UAB Department of Medicine, Division of Clinical Immunology and Rheumatology; and Stuti Mutneja and Paul A. Goepfert, UAB Department of Medicine Division of Infectious Diseases. Funding for the work came from National Institutes of Health grants AI125180, AI109962 and AI142737 and from the UAB Center for Clinical and Translational Science.

While lower vertebrates can repair their adult hearts after a heart attack, mammals -- including humans -- cannot. The ability to regenerate dead muscle tissue in mammalian hearts disappears just a few days after birth because the heart muscle cells, called cardiomyocytes, exit the cell cycle. In 2020, researchers reported that surgery to remove the left ventricle apex of the heart of pigs, one day after birth, somehow extended the replication ability of heart muscle cells. To better understand the underlying gene expression changes in this extended regeneration window, researchers now report nuclear RNA-sequencing of heart muscle cells, using this porcine model. From such knowledge, and much further research yet to come, clinicians may potentially learn how to regenerate adult heart cardiomyocytes after a heart attack. While lower vertebrates can repair their adult hearts after a heart attack, mammals -- including humans -- cannot. The ability to regenerate dead muscle tissue in mammalian hearts disappears just a few days after birth because the heart muscle cells, called cardiomyocytes, exit the cell cycle. After that, all growth of the heart comes from enlargement of existing cells, not from creation of new muscle cells. In an adult heart attack, heart failure results when the lost cardiomyocytes are replaced by fibrous scar tissue, instead of new muscle cells. This starts a vicious cycle of heart enlargement, loss of pumping function and eventual death. In 2020, University of Alabama at Birmingham researchers reported that surgery to remove the left ventricle apex of the heart of pigs, one day after birth, somehow extended the replication ability of heart muscle cells. In fact, after such surgery, pigs can completely recover from a heart attack four weeks after birth, without scarring or decline in heart function. To better understand the underlying gene expression changes in this extended regeneration window, UAB researchers now report nuclear RNA-sequencing of heart muscle cells, using this porcine model. From such knowledge, and much further research yet to come, clinicians may potentially learn how to regenerate adult heart cardiomyocytes after a heart attack. This study, led by Jianyi "Jay" Zhang, M.D., Ph.D., chair of the UAB Department of Biomedical Engineering, is published as a Circulation research letter. The researchers compared nuclei from heart tissue of five groups of pigs. Two groups were regeneration models that had left ventricle apical resections, or AR, at postnatal day one, or P1. One of those two groups then had ligation of the left anterior descending coronary artery four weeks after birth, or P28, to induce a myocardial infarction, or MI; this group is called ARP1MIP28. The other group, called ARP1, did not have ligation. Two non-regenerative controls did not have the P1 apical resection, but one of those did have the induced heart attack at P28. Those two groups were called Control and MIP28. Hearts were removed for single-nucleus RNA-sequencing at P30 through P56 for the ARP1MIP28 animals, and hearts from all other groups were explanted for sequencing on P1, P28 or P56. The fifth group were fetal hearts, or FH, at embryonic day 80. A total of 218,945 high-quality nuclei were captured, and a network biology clustering analysis identified all eight major heart cell types. Complete gene nucleus data were available for 94,844 cardiomyocytes. The cardiomyocytes were distributed among six clusters, named cardiomyocyte 1 through cardiomyocyte 6. Three clusters were almost entirely composed of cardiomyocytes from a single experimental group: cardiomyocyte 2 from control-P56, cardiomyocyte 3 from control-P1, and cardiomyocyte 6 from FH. The cardiomyocyte 4 and 5 clusters contained primarily ARP1MIP28-P35 cardiomyocytes. The cardiomyocyte 1 cluster included cardiomyocytes from all other animal groups and time points and a small number of ARP1MIP28-P35 cardiomyocytes, but few fetal or control-P56 cardiomyocytes. The cardiomyocyte 4 and 5 clusters that contained primarily ARP1MIP28-P35 cardiomyocytes showed increased cell cycle activity and proliferation, changes that helped remuscularize the left ventricle after experimental heart attack, without scarring. The researchers also found 506 genes that were positively correlated with the highly proliferative ARP1MIP28-P30 and ARP1MIP28-P35 cardiomyocytes; these genes participated in pathways that regulated heart development, cell proliferation and cardiomyocyte proliferation. "It will be interesting to examine these two distinct cell populations from the ARP1MIP28 injury in future studies," Zhang said. "The findings are highly impactful because they show, for the first time, that the left ventricle can remuscularize the myocardial infarct beyond postnatal day seven, or P7, in large mammals. These observations provide a foundation for future investigations of the molecular mechanisms and signaling molecules that regulate the injury-induced preservation of cardiomyocyte cell cycle activity in newborn large mammals, and ultimately to remuscularize the heart muscle in patients suffering from heart attacks, thus preventing heart failure." The study is titled "Single nucleus transcriptomics: Apical resection in newborn pigs extends the time window of cardiomyocyte proliferation and myocardial regeneration." Co-authors with Zhang are Yuji Nakada, Yang Zhou, Eric Y. Zhang, Yuhua Wei, Meng Zhao, Wangping Chen, Jiacheng Sun and S. Naqi Raza, UAB Department of Biomedical Engineering; Thanh Nguyen and Jake Y. Chen, UAB Informatics Institute; Gregory P. Walcott, UAB Department of Medicine, Division of Cardiovascular Disease; and Wuming Gong, Erik Skie and Daniel J. Garry, School of Medicine, University of Minnesota, Minneapolis. Support came from National Institutes of Health grants HL114120, HL131017, HL149137 and HL134764. At UAB, Zhang holds the T. Michael and Gillian Goodrich Endowed Chair of Engineering Leadership. Biomedical Engineering is a joint department of the UAB Marnix E. Heersink School of Medicine and the UAB School of Engineering. The Informatics Institute and the Department of Medicine are part of the Heersink School of Medicine.