Design Challenges for HIV-1 Vaccines Based on Humoral Immunity

Dr. Anthony Fauci Shares Insights on His Career and Leadership of the NIAID

In this interview, Dr. Anthony Fauci, who was, until recently, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, discusses the national response to the HIV/AIDS pandemic. He was the principal architect of the President's Emergency Plan for AIDS Relief, known as PEPFAR, that has saved millions of lives throughout the developing world by assuring access to life-saving antiretroviral therapies. In recent years, he's been the voice of our national response to SARS, Ebola, and COVID, and throughout this Dr. Fauci has led a large basic and translational immunology research laboratory, The Laboratory of Immunoregulation, which has revealed a trove of insights about HIV pathogenesis. 

HIV-Associated Interactions Between Oral Microbiota and Mucosal Immune Cells: Knowledge Gaps and Future Directions

Even with sustained use of antiretroviral therapy (ART), HIV-infected individuals have an increased risk of systemic comorbid conditions and oral pathologies, including opportunistic infections, oral mucosal inflammation, and gingival and periodontal diseases. The immune-mediated mechanisms that drive this increased risk, in the context of sustained viral suppression, are unclear. HIV infection, even when controlled, alters microbial communities contributing to a chronic low-grade inflammatory state that underlies these non-HIV co-morbidities. The higher prevalence of dental caries, and mucosal and periodontal inflammation reported in HIV-infected individuals on ART is often associated with differentially abundant oral microbial communities, possibly leading to a heightened susceptibility to inflammation. This mini-review highlights current gaps in knowledge regarding the microbe-mediated oral mucosal immunity with HIV infection while discussing opportunities for future research investigations and implementation of novel approaches to elucidate these gaps. Interventions targeting both inflammation and microbial diversity are needed to mitigate oral inflammation-related comorbidities, particularly in HIV-infected individuals. More broadly, additional research is needed to bolster general models of microbiome-mediated chronic immune activation and aid the development of precise microbiota-targeted interventions to reverse or mitigate adverse outcomes.

What does it mean to develop an HIV vaccine by rational design?

This review argues that the three popular concepts of design, rationality and reductionism, which guided vaccine research for many years, actually contributed to the inability of vaccinologists to develop an effective HIV vaccine. The strong goal-directed intentionality inherent in the concept of design together with excessive confidence in the power of rational thinking convinced investigators that the accumulated structural knowledge on HIV epitopes, derived from crystallographic studies of complexes of neutralizing antibodies bound to HIV Env epitopes, would allow them to rationally design complementary immunogens capable of inducing anti-HIV protective antibodies. This strategy failed because it was not appreciated that the structures observed in epitope-paratope crystallographic complexes result from mutually induced fit between the two partners and do not represent structures present in the free disordered molecules before they had interacted. In addition, reductionist thinking led investigators to accept that biology could be reduced to chemistry, and this made them neglect the fundamental difference between chemical antigenicity and biological immunogenicity. As a result, they did not investigate which inherent constituents of immune systems controlled the induction of protective antibodies and focused instead only on the steric complementarity that exists between bound epitopes and paratopes.

Development of a Preventive HIV Vaccine Requires Solving Inverse Problems Which Is Unattainable by Rational Vaccine Design

Hypotheses and theories are essential constituents of the scientific method. Many vaccinologists are unaware that the problems they try to solve are mostly inverse problems that consist in imagining what could bring about a desired outcome. An inverse problem starts with the result and tries to guess what are the multiple causes that could have produced it. Compared to the usual direct scientific problems that start with the causes and derive or calculate the results using deductive reasoning and known mechanisms, solving an inverse problem uses a less reliable inductive approach and requires the development of a theoretical model that may have different solutions or none at all. Unsuccessful attempts to solve inverse problems in HIV vaccinology by reductionist methods, systems biology and structure-based reverse vaccinology are described. The popular strategy known as rational vaccine design is unable to solve the multiple inverse problems faced by HIV vaccine developers. The term “rational” is derived from “rational drug design” which uses the 3D structure of a biological target for designing molecules that will selectively bind to it and inhibit its biological activity. In vaccine design, however, the word “rational” simply means that the investigator is concentrating on parts of the system for which molecular information is available. The economist and Nobel laureate Herbert Simon introduced the concept of “bounded rationality” to explain why the complexity of the world economic system makes it impossible, for instance, to predict an event like the financial crash of 2007–2008. Humans always operate under unavoidable constraints such as insufficient information, a limited capacity to process huge amounts of data and a limited amount of time available to reach a decision. Such limitations always prevent us from achieving the complete understanding and optimization of a complex system that would be needed to achieve a truly rational design process. This is why the complexity of the human immune system prevents us from rationally designing an HIV vaccine by solving inverse problems.

Structure-Based Reverse Vaccinology Failed in the Case of HIV Because it Disregarded Accepted Immunological Theory

Two types of reverse vaccinology (RV) should be distinguished: genome-based RV for bacterial vaccines and structure-based RV for viral vaccines. Structure-based RV consists in trying to generate a vaccine by first determining the crystallographic structure of a complex between a viral epitope and a neutralizing monoclonal antibody (nMab) and then reconstructing the epitope by reverse molecular engineering outside the context of the native viral protein. It is based on the unwarranted assumption that the epitope designed to fit the nMab will have acquired the immunogenic capacity to elicit a polyclonal antibody response with the same protective capacity as the nMab. After more than a decade of intensive research using this type of RV, this approach has failed to deliver an effective, preventive HIV-1 vaccine. The structure and dynamics of different types of HIV-1 epitopes and of paratopes are described. The rational design of an anti-HIV-1 vaccine is shown to be a misnomer since investigators who claim that they design a vaccine are actually only improving the antigenic binding capacity of one epitope with respect to only one paratope and not the immunogenic capacity of an epitope to elicit neutralizing antibodies. Because of the degeneracy of the immune system and the polyspecificity of antibodies, each epitope studied by the structure-based RV procedure is only one of the many epitopes that the particular nMab is able to recognize and there is no reason to assume that this nMab must have been elicited by this one epitope of known structure. Recent evidence is presented that the trimeric Env spikes of the virus possess such an enormous plasticity and intrinsic structural flexibility that it is it extremely difficult to determine which Env regions are the best candidate vaccine immunogens most likely to elicit protective antibodies.

Antiviral Vaccines: Challenges and Advances

Vaccination is the most effective means of preventing and controlling viral infections. The eradication of smallpox and the significant progress made toward polio eradication are clear examples of the great impact of antiviral vaccines. However, viral infections remain a major public health threat and a significant cause of death. Most of the antiviral vaccines introduced over the past century were empirically developed. Poliomyelitis, measles, mumps, and rubella are examples of diseases that are now largely controlled thanks to these empirically developed vaccines. However, there is a growing list of viral pathogens against which effective vaccines are yet to be developed. Recent technological advances will potentially provide us with new platforms that could be harnessed to develop vaccines against emerging and reemerging viral pathogens.