Helping B Cells in the Tonsil See article p. 1359

Membrane-Associated Proteinase 3 Inhibits T Cell Proliferation See article p. 1389

Modeling Trm Dynamics during HSV-2 Infection See article p. 1522

ODN and IL-15 Synergy during B-CLL Growth See article p. 1570

B cell chronic lymphocytic leukemia (B-CLL) is characterized by malignant cell growth within lymphoid tissues, particularly lymph nodes (LN). Although recent studies have demonstrated that the TLR-9 ligand oligodeoxynucleotide (ODN) exhibits synergy with IL-15 to promote B-CLL clonal expansion, the mechanisms driving this relationship are not clear. In this issue, Gupta et al. (p. 1570) demonstrated that IL-15–producing cells are prominent in B-CLL–infiltrated LN. Time course studies using a B-CLL clone known to respond vigorously to ODN+IL-15 stimulation revealed that IL-15 is not critical until at least 24 h after ODN exposure to synergistically promote B-CLL growth. ODN stimulation of B-CLL cells significantly increased surface expression and mRNA levels of two IL-15 receptors, IL-15Rα and IL-2/15Rβ (CD122). Inhibition of NF-κB, which is activated by TLR9 signaling, abolished the ODN-induced rise in both IL-15 receptors at the protein and mRNA levels. Neutralization of IL-15 and CD122 in B-CLL cultures abrogated ODN+IL-15–induced growth when added at the initiation of culture. Interestingly, anti–IL-15 and anti-CD122 also reduced cellular division when added several days after ODN+IL-15 activation, indicating that clonal expansion requires continued IL-15/CD122 signaling. Finally, studies investigating the impact of cell density on ODN+IL-15–induced clonal expansion of B-CLL cells demonstrated that a reduction in cell density compromised ODN+IL-15–induced growth in some B-CLL clones, suggesting that trans IL-15 signaling may be an important factor for the growth of certain clones. Together, these findings demonstrate that NF-κB activation following ODN exposure fosters a rapid expression of IL-15Rα and CD122 to drive ODN+IL-15 clonal expansion of B-CLL cells. Furthermore, this study suggests that blockade of the IL-15/CD122 pathway could be an effective therapeutic target for treating B-CLL.

Tissue-resident memory CD8+ T cells (Trm) can rapidly eliminate virally infected cells in the mucosa and display spatial heterogeneity within the tissues. Although Trm are highly mobile at sites of viral replication, murine studies have demonstrated that Trm do not redistribute to adjacent sites to provide wider protection. In this issue, Schiffer et al. (p. 1522) performed mathematical modeling to analyze Trm-mediated responses after HSV-2 infection in the human genital tract. Although this model predicted that total Trm numbers are stable in the genital tract, their density within distinct spatial regions is highly dynamic, as Trm are either lost over time or proliferate in areas of active viral replication. Importantly, the model also demonstrated that interregional diffusion of Trm during infection is unlikely. To validate the modeling predictions, the authors performed spatial analysis of Trm distribution in paired biopsies from uninfected and infected individuals at 2 and 8 w following healing of lesions. The authors also used the model to predict the impact of therapeutic interventions on spatial Trm structure. The model predicted that daily treatment with pritelivir, an HSV-2 helicase inhibitor, would result in a dose-dependent decrease in Trm levels and variability across regions, which correlated with a reduction in viral shedding. However, the decline in Trm levels and cessation of antiviral therapy after 18 mo predicted viral shedding to a rate higher than pretreatment baseline, suggesting that many years of 100% suppressive therapy may possibly be required to control HSV-2 infection. Finally, the authors simulated the impact of vaccination and determined that a protective vaccine should aim to increase the total number of Trm rather than an increase in the density of Trm at different regions. In conclusion, this study offers important insights into Trm dynamics during active infection and effective vaccine design.

Follicular helper T (Tfh) cells, a specialized subset of CD4+ T cells, promote B cell maturation, but the subset of tonsillar CD4+ T cells that promotes maturation of memory B cells into Ab-forming cells remains to be characterized. In this issue, Kim et al. (p. 1359) characterized a novel human tonsillar CD4+ T cell subset that promotes humoral recall responses. CD4+ T cells expressing high levels of P-selectin glycoprotein ligand-1 (PSGL-1) resided only in the T cell zone of human tonsil sections and were not found within the follicular mantle and germinal centers. PSGL-1hi PD-1hi CXCR5hi CD4+ T cells were similar to Tfh cells in terms of expression of cell surface markers, including CD40L. However, gene expression profiling revealed that PSGL-1hi PD-1hi CXCR5hi T cells and Tfh cells were transcriptionally distinct. Compared with cocultures including Tfh cells, memory B cells produced more IgG when cocultured with PSGL-1hi PD-1hi CXCR5hi T cells. IL-10 was produced exclusively by PSGL-1hi PD-1hi CXCR5hi T cells. In the presence of anti–IL-10 Ab, Ig production in PSGL-1hi PD-1hi CXCR5hi T cell and memory B cell cocultures was reduced. Ab-mediated blockade of both IL-10 and IL-21 further inhibited Ig production in cocultures, indicating that the two cytokines work independently to promote Ig production by B cells. Furthermore, PSGL-1hi PD-1hi CXCR5hi T cells upregulated CD40L upon stimulation. Together, these data identify a population of extrafollicular CD4+ T cells in human tonsils that promote memory B cells to produce Abs via CD40L, IL-10, and IL-21.

Polymorphonuclear neutrophil (PMN)-derived serine proteases, such as proteinase 3 (P3), regulate the tumor microenvironment and inflammation. However, the effects of PMN-derived P3 on T cell proliferation are unknown. Thus, Yang et al. (p. 1389) examined the effects of membrane P3 (mP3)-expressing PMN and acute myeloid leukemia (AML) blasts on T cell proliferation. Coculture of healthy donor PMN and autologous PBMCs stimulated with anti-CD3/CD8 mAbs inhibited both CD4+ and CD8+ T cell proliferation in a PMN dose-dependent manner. PMN-mediated inhibition of T cell proliferation was largely abrogated when the cells were separated in a Transwell system, indicating that contact is required for maximal T cell inhibition by PMN. Addition of anti-P3 Ab to PMN–PBMC cocultures restored T cell proliferation. Moreover, the enzymatic function of P3 was required for the inhibition of T cell proliferation: addition of serine protease inhibitors reduced PMN-mediated inhibition of T cell proliferation. When PMN lacked mP3, inhibition of T cell proliferation was reduced. Proliferation of CD8+ and CD4+ T cells was significantly inhibited when cocultured with AML cells expressing high levels of mP3, whereas proliferation of T cells cocultured with AML expressing low levels of mP3 was comparable to PBMCs stimulated with anti-CD3/CD28 mAbs. Addition of anti-P3 Ab significantly restored T cells’ capacity to proliferate in the presence of mP3-expressing AML blasts. These data indicate that mP3 expression by PMN and AML cells inhibits T cell proliferation and suggest that targeting of P3 may be an effective immunotherapy for the treatment of AML and autoimmune diseases.