Characterization of Molecular Correlates of the Chronic Humoral Immune Response: Clues towards Eliciting Broadly Neutralizing Antibodies against HIV

A central focus in the pursuit of an effective vaccine against HIV-1 is the induction of broadly neutralizing (bNt) antibodies (Abs). However, these Abs are rarely elicited in natural infection and the immunological processes that drive this occurrence are not clearly defined. Modulation of the immunological environment during the chronic phase of infection provides a plausible mechanism by which bNt Abs are elicited and also advances the possibility that vaccine design should account for the immune response specific to this phase. Thus, the work presented here seeks to characterize the chronic phase of the humoral immune response to gain insight into the immunological mechanisms that generate bNt-Ab responses. First, disturbances in B-cell distribution in HIV+ individuals were evaluated using a computational algorithm, flowType, compared to a manual-analysis tool. In addition to yielding similar results to manual analysis, flowType revealed dysregulation of novel B-cell subsets in HIV, providing a representation of the global extent of HIV-associated B-cell dysregulation. Second, changes in B-cell distribution and serum reactivity were compared between HIV+ individuals who followed different clinical courses and individuals with the autoimmune disease, systemic lupus erythematosus (SLE). B-cell dysregulation was evident in both cohorts, though more extensive in HIV. Sera from HIV+ individuals with increased viral load, as well as SLE patients, displayed significant polyreactivity as compared to HIV+ sera from those controlling their infections. These results illustrate that despite similarities in cellular perturbations, the Ab response against HIV is antigen driven rather than autoimmune. In addition, immunogenetic analyses of B-cell repertoires of HIV+ individuals demonstrated perturbations within antigen-inexperienced naïve B cells as well as increased somatic-mutation levels, which were observed in the effector B-cell subpopulations. Finally, a murine model for chronic infection was developed using immunization with filamentous bacteriophage as a model virus-like particle. Functional analyses of CD138+ plasma cells showed that a single immunization elicited innate-like and type-1 T-cell independent (TI-1) B-cell responses, and prolonged immunization resulted in perturbations reminiscent of those observed in chronic infections (i.e., plasma-cell exhaustion). Preliminary data from transcriptomic analyses of plasma cells from different time points after immunization suggests immunophenotypic differences within the population, indicating either developmental changes, or selection from different precursor populations. Collectively, the data provide deeper insight into changes occurring in short-term and chronic humoral immune responses, as well as establishing a functional animal model that may be used to probe these features further.