Jonathan P. McNally

HIV-1 envelope protein binds to and signals through integrin |[alpha]|4|[beta]|7, the gut mucosal homing receptor for peripheral T cells

Infection with human immunodeficiency virus 1 (HIV-1) results in the dissemination of virus to gut-associated lymphoid tissue. Subsequently, HIV-1 mediates massive depletion of gut CD4+ T cells, which contributes to HIV-1-induced immune dysfunction. The migration of lymphocytes to gut-associated lymphoid tissue is mediated by integrin α4β7. We demonstrate here that the HIV-1 envelope protein gp120 bound to an activated form of α4β7. This interaction was mediated by a tripeptide in the V2 loop of gp120, a peptide motif that mimics structures presented by the natural ligands of α4β7. On CD4+ T cells, engagement of α4β7 by gp120 resulted in rapid activation of LFA-1, the central integrin involved in the establishment of virological synapses, which facilitate efficient cell-to-cell spreading of HIV-1.

The Common γ-Chain Cytokines IL-2, IL-7, IL-15, and IL-21 Induce the Expression of Programmed Death-1 and Its Ligands

The programmed death (PD)-1 molecule and its ligands (PD-L1 and PD-L2), negative regulatory members of the B7 family, play an important role in peripheral tolerance. Previous studies have demonstrated that PD-1 is up-regulated on T cells following TCR-mediated activation; however, little is known regarding PD-1 and Ag-independent, cytokine-induced T cell activation. The common γ-chain (γc) cytokines IL-2, IL-7, IL-15, and IL-21, which play an important role in peripheral T cell expansion and survival, were found to up-regulate PD-1 and, with the exception of IL-21, PD-L1 on purified T cells in vitro. This effect was most prominent on memory T cells. Furthermore, these cytokines induced, indirectly, the expression of PD-L1 and PD-L2 on monocytes/macrophages in PBMC. The in vivo correlate of these observations was confirmed on PBMC isolated from HIV-infected individuals receiving IL-2 immunotherapy. Exposure of γc cytokine pretreated T cells to PD-1 ligand-IgG had no effect on STAT5 activation, T cell proliferation, or survival driven by γc cytokines. However, PD-1 ligand-IgG dramatically inhibited anti-CD3/CD28-driven proliferation and Lck activation. Furthermore, following restimulation with anti-CD3/CD28, cytokine secretion by both γc cytokine and anti-CD3/CD28 pretreated T cells was suppressed. These data suggest that γc cytokine-induced PD-1 does not interfere with cytokine-driven peripheral T cell expansion/survival, but may act to suppress certain effector functions of cytokine-stimulated cells upon TCR engagement, thereby minimizing immune-mediated damage to the host.

The integrin α4β7 forms a complex with cell-surface CD4 and defines a T-cell subset that is highly susceptible to infection by HIV-1

Both activated and resting CD4+ T cells in mucosal tissues play important roles in the earliest phases of infection after sexual transmission of HIV-1, a process that is inefficient. HIV-1 gp120 binds to integrin α4β7 (α4β7), the gut mucosal homing receptor. We find that α4β7high CD4+ T cells are more susceptible to productive infection than are α4β7low-neg CD4+ T cells in part because this cellular subset is enriched with metabolically active CD4+ T cells. α4β7high CD4+ T cells are CCR5high and CXCR4low; on these cells, α4β7 appears in a complex with CD4. The specific affinity of gp120 for α4β7 provides a mechanism for HIV-1 to target activated cells that are critical for efficient virus propagation and dissemination following sexual transmission.

Suppression of HIV-specific T cell activity by lymph node CD25+ regulatory T cells from HIV-infected individuals

CD25+ CD4+ FoxP3+ regulatory T (Treg) cells isolated from the peripheral blood of asymptomatic HIV-infected individuals have been demonstrated to significantly suppress HIV-specific immune responses in vitro. CD25+ Treg cell suppressor activity in the peripheral blood seems to diminish with progression of HIV disease, and it has been suggested that loss of Treg cells contributes to aberrant immune activation and disease progression. However, phenotypic studies suggest that Treg cells may migrate to, and be maintained or even expanded in, tissue sites of HIV replication. Currently, it is not known whether tissue-associated Treg cells maintain suppressive activity in the context of HIV infection, particularly in individuals with advanced disease. The present study demonstrates that CD25+ Treg cells isolated from lymph nodes and peripheral blood of HIV+ subjects, even those with high viral loads and/or low CD4+ T cell counts, maintain potent suppressive activity against HIV-specific cytolytic T cell function. This activity was better in lymph node as compared with peripheral blood, particularly in patients with high levels of plasma viremia. In addition, the expression of certain CD25+ Treg-associated markers on CD4+ T cells isolated from lymph nodes differed significantly from those on CD4+ T cell subsets isolated from the peripheral blood. These data suggest that CD25+ Treg cell-mediated suppression of HIV-specific responses continues throughout the course of HIV disease and, because of their particularly potent suppression of HIV-specific CTL activity in lymphoid tissue, may considerably impact the ability to control HIV replication in vivo.

The Genotype of Early-Transmitting HIV gp120s Promotes α4β7 –Reactivity, Revealing α4β7+/CD4+ T cells As Key Targets in Mucosal Transmission

Mucosal transmission of HIV is inefficient. The virus must breach physical barriers before it infects mucosal CD4+ T cells. Low-level viral replication occurs initially in mucosal CD4+ T cells, but within days high-level replication occurs in Peyers patches, the gut lamina propria and mesenteric lymph nodes. Understanding the early events in HIV transmission may provide valuable information relevant to the development of an HIV vaccine. The viral quasispecies in a donor contracts through a genetic bottleneck in the recipient, such that, in low-risk settings, infection is frequently established by a single founder virus. Early-transmitting viruses in subtypes A and C mucosal transmission tend to encode gp120s with reduced numbers of N-linked glycosylation sites at specific positions throughout the V1-V4 domains, relative to typical chronically replicating isolates in the donor quasispecies. The transmission advantage gained by the absence of these N-linked glycosylation sites is unknown. Using primary α4β7 +/CD4+ T cells and a flow-cytometry based steady-state binding assay we show that the removal of transmission-associated N-linked glycosylation sites results in large increases in the specific reactivity of gp120 for integrin- α4β7. High-affinity for integrin α4β7, although not found in many gp120s, was observed in early-transmitting gp120s that we analyzed. Increased α4β7 affinity is mediated by sequences encoded in gp120 V1/V2. α4β7-reactivity was also influenced by N-linked glycosylation sites located in C3/V4. These results suggest that the genetic bottleneck that occurs after transmission may frequently involve a relative requirement for the productive infection of α4β7 +/CD4+ T cells. Early-transmitting gp120s were further distinguished by their dependence on avidity-effects to interact with CD4, suggesting that these gp120s bear unusual structural features not present in many well-characterized gp120s derived from chronically replicating viruses. Understanding the structural features that characterize early-transmitting gp120s may aid in the design of an effective gp120-based subunit vaccine.

Eliminating Encephalitogenic T Cells without Undermining Protective Immunity

The current clinical approach for treating autoimmune diseases is to broadly blunt immune responses as a means of preventing autoimmune pathology. Among the major side effects of this strategy are depressed beneficial immunity and increased rates of infections and tumors. Using the experimental autoimmune encephalomyelitis model for human multiple sclerosis, we report a novel alternative approach for purging autoreactive T cells that spares beneficial immunity. The moderate and temporally limited use of etoposide, a topoisomerase inhibitor, to eliminate encephalitogenic T cells significantly reduces the onset and severity of experimental autoimmune encephalomyelitis, dampens cytokine production and overall pathology, while dramatically limiting the off-target effects on naive and memory adaptive immunity. Etoposide-treated mice show no or significantly ameliorated pathology with reduced antigenic spread, yet have normal T cell and T-dependent B cell responses to de novo antigenic challenges as well as unimpaired memory T cell responses to viral rechallenge. Thus, etoposide therapy can selectively ablate effector T cells and limit pathology in an animal model of autoimmunity while sparing protective immune responses. This strategy could lead to novel approaches for the treatment of autoimmune diseases with both enhanced efficacy and decreased treatment-associated morbidities.

Correction: Eliminating Encephalitogenic T Cells without Undermining Protective Immunity

McNally, J. P., E. E. Elfers, C. E. Terrell, E. Grunblatt, D. A. Hildeman, M. B. Jordan, and J. D. Katz. 2014. Eliminating encephalitogenic T cells without undermining protective immunity. J. Immunol . 192: [73–83][1]. The e-mail address for Dr. Michael B. Jordan in the correspondence footnote

P07-01. The gut mucosal homing receptor integrin α4β7 forms a complex with CD4 and defines a T cell subset that is highly susceptible to infection by HIV-1

Background In the acute phase of HIV infection, following mucosal transmission, the bulk of HIV replication occurs in Peyers patches and mesenteric lymph nodes. Concurrently, HIV mediates a massive depletion of lamina propria CD4+ T cells. Integrin α4β7 (α4β7) facilitates the migration of lymphocytes from gut inductive sites (Peyers patches and mesenteric lymph nodes) to the lamina propria. Thus α4β7 is functionally linked to the major sites of HIV replication and CD4+ T cell depletion during acute infection. It is in this context that we described a specific biochemical interaction between the HIV-1 envelope protein gp120 and α4β7 on CD4+ T cells. The explicit linkage between α4β7 and the major sites of HIV replication following mucosal transmission suggests that this interaction plays an important role at an early phase in the HIV infection cycle during sexual transmission.