In 2016, we pursued studies that can be broken down into three sections. 1) analysis of HIV-specific monoclonal antibodies (mAbs) derived from memory B cells of HIV-infected individuals; 2) assessment of HIV-specific B-cell responses in HIV-infected individuals who maintain undetectable viremia in the absence of antiretroviral therapy (ART); and 3) B-cell features and functions in immunodeficiencies unrelated to HIV infection. First, in a study published in JCI Insight, we investigated HIV-specific memory B cells at subset and single-cell levels in HIV-infected individuals with chronic viremia. In this study, we compared immunoglobulin (Ig) genes and mAbs derived from two subsets of circulating B cells: tissue-like memory B cells that are over-represented in chronically infected HIV-viremic individuals and have been associated with B cell exhaustion, and resting memory B cells that represent the majority of circulating memory B cells in healthy donors. We found that despite a higher number of cell divisions that should correlate with affinity maturation of the antibody response, Ig genes and HIV-specific mAbs isolated from the tissue-like memory B-cell compartment displayed reduced levels of somatic hypermutation when compared to their resting memory B-cell counterparts. HIV neutralizing activity was also reduced for mAbs derived from tissue-like compared to resting memory B cells. From a total of 167 clones isolated from three individuals, we identified several members of clonal families in each individual, some of which were present in both B-cell subsets, although there was evidence of segregation between the two subsets. The differences between subsets included Ig heavy chain usage, polyreactivity, and levels of Ig somatic hypermutation, which when combined explained the lower HIV neutralization activities observed among mAbs derived from tissue-like versus resting memory B cells. Collectively, these findings suggest that HIV-induced cellular exhaustion, as manifested by tissue-like memory B cells, is associated with a relatively inefficient memory response, which in turn, may help explain why humoral immunity in HIV-infected individuals does little to control viral replication. Second, in a study published in the Journal of Infectious Diseases, we designed a study to investigate humoral immunity in HIV-infected individuals who maintain undetectable viremia in the absence of antiretroviral therapy (ART) by evaluating their antigen-specific memory B-cell responses. Accordingly, we enrolled three groups of individuals: two HIV-infected groups, one whose viremia was controlled with ART and the other in the absence of ART, referred to as elite controllers; and, one group of HIV-uninfected individuals. In comparisons involving the two HIV groups, we found that despite a higher cellular HIV burden, which is generally associated with sustaining immune responses to the virus, in the ART group, the elite controller group had a stronger HIV-specific B-cell response. However, viral burden was nonetheless shown to be a determinant of HIV-specific B-cell responses in the elite controllers given that the B-cell responses decreased following a reduction of cellular levels of HIV by ART and returned to pre-ART levels upon cessation of ART. The longitudinal effect of suppressing residual viremia by ART in elite controllers was performed in a small subset of the group and is currently being repeated in much larger cohorts by the ACTG trials network. Finally, the frequency of B-cell responses to a non-HIV antigen that is infrequently encountered, namely tetanus, but not to one frequently encountered, namely influenza, was lower in the ART group when compared to the other two groups where responses were similar. Collectively, these findings suggest that the overall humoral immunity of elite controllers is superior to that of individuals whose viremia is controlled by ART, although the superior HIV response in elite controllers may also reflect distinct effects of residual viral replication on B-cell function. Third, we continue to pursue several collaborative efforts with colleagues in the LIR, as well as other laboratories at NIAID, other NIH institutes, and abroad. Over the past year, we have contributed to several lymphoid tissue-based studies as well as to B-cell related observations in various disease settings. Our contributions to studies that have been published over the past year include the analysis of HIV persistence in lymphoid tissues of infected individuals who control viremia without ART; the effect of dysregulated T follicular helper function on B cells of individuals whose viremia is controlled by ART; insight into peripheral B-cell reconstitution following gene-based stem cell therapy in patients with X-linked severe combined immunodeficiency (SCID-X1); and, delineating the effect of auto-inflammatory diseases with dysregulated cytokine pathways on B-cell populations that circulate in the peripheral blood. Based on our knowledge of human B-cell immunology accumulated over almost two decades of work on HIV-induced B-cell pathogenesis, we have been called upon to provide expertise in various disease settings that involve B cells. Some processes and affected pathways are common to different diseases, such as type I interferon dysregulation in both auto-inflammatory and HIV diseases and the appearance of immature/transitional B cells in individuals whose lymphopenia is caused by primary (SCID-X1) or acquired (HIV) immunodeficiencies. By collaborating with other investigators, we have gained a greater understanding of B cells and their role in the pathogenesis of various diseases than if we studied our respective diseases independently. Collectively, these collaborative efforts advance our understanding of human B-cell immunology, the dysregulation that occurs in various disease settings, and potential means of intervening to restore health.
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