Early B-cell development and B-cell maturation are impaired in patients with active hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is characterized by hyperinflammation and multiorgan dysfunction. Infections, including the reactivation of viruses, contribute to significant disease mortality in HLH. Although T-cell and natural killer cell-driven immune activation and dysregulation are well described, limited data exist on the status of B-cell compartment and humoral immune function in HLH. We noted marked suppression of early B-cell development in patients with active HLH. In vitro B-cell differentiation studies after exposure to HLH-defining cytokines, such as interferon gamma (IFN-γ) and tumor necrosis factor, recapitulated B-cell development arrest. Messenger RNA sequencing of human CD34+ cells exposed to IFN-γ demonstrated changes in genes and pathways affecting B-cell development and maturation. In addition, patients with active HLH exhibited a marked decrease in class-switched memory B (CSMB) cells and a decrease in bone marrow plasmablast/plasma cell compartments. The decrease in CSMB cells was associated with a decrease in circulating T follicular helper (cTfh) cells. Finally, lymph node and spleen evaluation in a patient with HLH revealed absent germinal center formation and hemophagocytosis with associated lymphopenia. Reassuringly, the frequency of CSMB and cTfh improved with the control of T-cell activation. Taken together, in patients with active HLH, these changes in B cells may affect the humoral immune response; however, further immune studies are needed to determine its clinical significance.

Regulation of antigen-specific T cell infiltration and spatial architecture in multiple myeloma and premalignancy.

Entry of antigen-specific T cells into human tumors is critical for immunotherapy, but the underlying mechanisms are poorly understood. Here, we combined high-dimensional spatial analyses with in vitro and in vivo modeling to study the mechanisms underlying immune infiltration in human multiple myeloma (MM) and its precursor monoclonal gammopathy of undetermined significance (MGUS). Clustered tumor growth was a feature of MM but not MGUS biopsies, and this growth pattern was reproduced in humanized mouse models. MM biopsies exhibited intralesional as well as spatial heterogeneity, with coexistence of T cell-rich and T cell-sparse regions and the presence of areas of T cell exclusion. In vitro studies demonstrated that T cell entry into MM clusters was regulated by agonistic signals and CD2-CD58 interactions. Upon adoptive transfer, antigen-specific T cells localized to the tumor site but required in situ DC-mediated antigen presentation for tumor entry. C-type lectin domain family 9 member A-positive (CLEC9A+) DCs appeared to mark portals of entry for gradients of T cell infiltration in MM biopsies, and their proximity to T cell factor 1-positive (TCF1+) T cells correlated with disease state and risk status. These data illustrate a role for tumor-associated DCs and in situ activation in promoting the infiltration of antigen-specific T cells in MM and provide insights into spatial alterations in tumor/immune cells with malignant evolution.

Lassa Virus Targeting of Anterior Uvea and Endothelium of Cornea and Conjunctiva in Eye of Guinea Pig Model.

Lassa virus (LASV), a hemorrhagic fever virus endemic to West Africa, causes conjunctivitis in patients with acute disease. To examine ocular manifestations of LASV, we histologically examined eyes from infected guinea pigs. In fatal disease, LASV immunostaining was most prominent in the anterior uvea, especially in the filtration angle, ciliary body, and iris and in and around vessels in the bulbar conjunctiva and peripheral cornea, where it co-localized with an endothelial marker (platelet endothelial cell adhesion molecule). Antigen was primarily associated with infiltration of T-lymphocytes around vessels in the anterior uvea and with new vessel formation at the peripheral cornea. In animals that exhibited clinical signs but survived infection, eyes had little to no inflammation and no LASV immunostaining 6 weeks after infection. Overall, in this model, LASV antigen was restricted to the anterior uvea and was associated with mild chronic inflammation in animals with severe disease but was not detected in survivors.