Topol explores advances in regulating immune responses, particularly in the context of autoimmune diseases. Over 10% of the population has autoimmune conditions such as lupus, Crohn’s disease, and rheumatoid arthritis. Current treatments rely on broad immunosuppressive drugs, which often lose effectiveness and increase infection risk. Emerging therapies instead aim to retrain the immune system not to attack the body’s own tissues.

Topol outlines the biology of immunity, which is divided into two systems. The innate system rapidly responds to threats, while the adaptive system develops long-lasting memory of past threats via B and T cells. Failures in distinguishing “self” from “other” can trigger autoimmunity, sometimes through molecular mimicry when viral antigens resemble the body’s proteins. Factors like caloric intake, obesity, environmental exposures, and genetics all influence immune tolerance. Women face higher rates of autoimmunity, partly linked to X chromosome behavior and sex hormones, though they also tend to display stronger immune resilience.

Research has revealed two layers of immune tolerance (guidelines for what the immune system views as a threat, which are disrupted in autoimmunity): central tolerance in the thymus and peripheral tolerance throughout the body. Novel treatments aim to reinforce both. Nanoparticles that generate regulatory T cells, glycosylated antigens processed in the liver, and tolerogenic vaccines are under development. Engineered immune cells have shown striking success, such as wiping out B cells and inducing long-term remission in lupus patients. Clinical trials are also underway for rheumatoid arthritis, multiple sclerosis, and celiac disease.

The gut microbiome plays a pivotal role in immune regulation. Differences in microbial composition have been linked to autoimmune conditions, so interventions such as probiotics, dietary changes, and fecal transplantation show promise. Long COVID, which shares autoimmune features, has been improved in trials using microbiome therapies.

Topol highlights recent breakthroughs such as teplizumab, the first FDA-approved drug to delay type 1 diabetes onset, as well as abatacept for rheumatoid arthritis prevention. Advances in T cell engineering, stem cell transplantation, and organ xenotransplantation underscore the potential of precisely controlling immune activity. Ultimately, the goal is to develop therapies that can dial immune responses up or down as needed, restoring balance, preventing disease, and extending health span.

Remarkable scientific advances have reshaped how we prevent and respond to infectious diseases. During the COVID-19 pandemic, there was fear and skepticism about developing a vaccine quickly. Historically, vaccine development took years or decades, yet the COVID-19 vaccines were achieved in just ten months with more than 90% efficacy. This breakthrough was enabled by decades of groundbreaking work in mRNA research, nanoparticle delivery systems, and structural biology techniques such as cryo-electron microscopy. Substitutions like pseudouridine in mRNA and proline modifications in spike proteins enhanced immune responses and reduced harmful inflammation. Operation Warp Speed further accelerated progress through large-scale funding and mass production risk-sharing.

The mRNA vaccine platform has since been extended to numerous infectious diseases, including influenza, malaria, tuberculosis, and HIV, though challenges remain, particularly with viral mutation and the durability of immune protection. Innovations such as self-amplifying RNA vaccines, nasal spray vaccines, and universal vaccine strategies targeting conserved viral features are under active development.

Other vaccine milestones include effective vaccines and antibodies for respiratory syncytial virus (RSV), which were finally approved after decades, and the human papillomavirus (HPV) vaccine, which has shown near-complete elimination of cervical cancer in highly vaccinated populations. Topol highlights the HPV vaccine as an example of “superhuman” immunity, where vaccine-induced protection surpasses that of natural infection.

The chapter also reviews the link between Epstein-Barr virus and multiple sclerosis, which has spurred vaccine trials aimed at prevention. Beyond vaccines, Topol emphasizes new strategies for combating antimicrobial resistance, including AI-driven drug discovery, structure-based drug design, and bacteriophage therapies. Sepsis, another major killer, may benefit from early detection through artificial intelligence, rapid metagenomic sequencing, and new biomarkers, all of which can speed accurate treatment.

Topol concludes by underscoring the profound role infectious disease prevention has played in extending human lifespan—from 48 years in 1900 to nearly 79 today. Yet he cautions that anti-vaccine and anti-science movements threaten this progress, as declining vaccination rates have already led to resurgences of polio and measles. Countering misinformation is crucial to safeguarding public health and longevity.

Topol focuses on the interdependence of mental and physical health, and their impact on health span. For example, chronic stress not only contributes to mental illness but also exacerbates conditions such as cancer and cardiovascular disease. The prevalence of mental health disorders in the United States is high, with more than 50 million Americans affected and a severe shortage of providers to meet demand.

There is evidence that lifestyle and environmental factors play critical roles in promoting mental well-being. Time spent in natural environments, even as little as two hours per week, has been linked to reduced depression, anxiety, and cardiovascular risk. Green space exposure also correlates with improved cognitive function and lower mortality. Nature prescriptions are emerging as a tool for clinicians, and bird song and natural sounds are highlighted as part of the benefit.

Music-based interventions have shown promise for reducing anxiety, depression, and even physical symptoms such as chronic pain. Studies suggest that music can activate reward and motor circuits in the brain, with potential applications for neurological conditions like Parkinson’s and Alzheimer’s disease. Sleep health is another major factor, with chronic deficiency linked to obesity, metabolic syndrome, and dementia. Digital cognitive behavioral therapy (dCBT) apps are being tested as scalable solutions to improve sleep and reduce mental health symptoms.

Exercise consistently demonstrates substantial benefits for depression and anxiety, outperforming medications like SSRIs in many studies. Even light activity, such as walking or gardening, has measurable effects. Social isolation and loneliness are identified as major threats to mental health and longevity, increasing risks for dementia, cancer, and premature death. Touch, whether through brief contact or therapeutic massage, is also shown to have significant mental and physical benefits.

The chapter also explores diet and the gut-brain axis, linking high-fiber, anti-inflammatory diets with reduced stress and depression, while ultra-processed foods correlate with worse outcomes. Advances in digital tools, including wearables, mental health apps, and chatbots, offer scalable but still limited solutions. Finally, pharmacologic approaches—from SSRIs to psychedelics—remain options but are framed as last resorts. Topol concludes that attention to mental health, through lifestyle, environment, and emerging technologies, is essential for extending health span.