LAG-3- and CXCR5-expressing CD4 T cells display progenitor-like properties during chronic visceral leishmaniasis.

Maintenance of CD4 T cells during chronic infections is vital for limiting pathogen burden and disease recrudescence. Although inhibitory receptor expression by CD4 T cells is commonly associated with immune suppression and exhaustion, such cell-intrinsic mechanisms that control activation are also associated with cell survival. Using a mouse model of visceral leishmaniasis (VL), we discovered a subset of lymphocyte activation gene 3 (LAG-3)-expressing CD4 T cells that co-express CXCR5. Although LAG3+CXCR5+ CD4 T cells are present in naive mice, they expand during VL. These cells express gene signatures associated with self-renewal capacity, suggesting progenitor-like properties. When transferred into Rag1-/- mice, these LAG3+CXCR5+ CD4 T cells differentiated into multiple effector types upon Leishmania donovani infection. The transcriptional repressor B cell lymphoma-6 was partially required for their maintenance. Altogether, we propose that the LAG3+CXCR5+ CD4 T cell subset could play a role in maintaining CD4 T cell responses during persistent infections.

Bcl-6 expression by CD4+ T cells determines concomitant immunity and host resistance across distinct parasitic infections.

Cluster of differentiation (CD4+) T cells consist of multiple subtypes, defined by expression of lineage-specific transcription factors, that contribute to the control of infectious diseases by providing help to immune and nonimmune target cells. In the current study, we examined the role of B cell lymphoma (Bcl)-6, a transcriptional repressor and master regulator of T follicular helper cell differentiation, in T cell-mediated host defense against intestinal and systemic parasitic infections. We demonstrate that while Bcl-6 expression by CD4+ T cells is critical for antibody-mediated protective immunity against secondary infection with the nematode Heligmosoides polygyrus bakeri, it paradoxically compromises worm expulsion during primary infection by limiting the generation of interleukin-10 (IL-10)-producing Gata3+ T helper 2 cells. Enhanced worm expulsion in the absence of Bcl-6 expressing T cells was associated with amplified intestinal goblet cell differentiation and increased generation of alternatively activated macrophages, effects that were reversed by neutralization of IL-10 signals. An increase in IL-10 production by Bcl-6-deficient CD4+ T cells was also evident in the context of systemic Leishmania donovani infection, but in contrast to Heligmosoides polygyrus bakeri infection, compromised T helper 1-mediated liver macrophage activation and increased susceptibility to this distinct parasitic challenge. Collectively, our studies suggest that host defense pathways that protect against parasite superinfection and lethal systemic protozoal infections can be engaged at the cost of compromised primary resistance to well-tolerated helminths.

Impact of in vitro HIV infection on human thymic regulatory T cell differentiation.

Background: The differentiation and function of immunosuppressive regulatory T cells (Tregs) is dictated by the master transcription factor FoxP3. During HIV infection, there is an increase in Treg frequencies in the peripheral blood and lymphoid tissues. This accentuates immune dysfunction and disease progression. Expression of FoxP3 by thymic Tregs (tTregs) is partially controlled by TGF-ß. This cytokine also contributes to Treg development in the peripheral blood and lymphoid tissues. Although TGF-ß mediates lymphoid tissue fibrosis and peripheral Treg differentiation in HIV-infected individuals, its role in the induction and maintenance of Tregs within the thymus during HIV infection remains unclear. Methods: Thymocytes were isolated from fresh human thymic tissues obtained from pediatric patients undergoing cardiac surgery. Infection by both R5- and X4-tropic HIV-1 strains and TGF-ß treatment of human thymocytes was performed in an in vitro co-culture model with OP9-DL1 cells expressing Notch ligand delta-like 1 without T cell receptor (TCR) activation. Results: Despite high expression of CCR5 and CXCR4 by tTregs, FoxP3 + CD3highCD8- thymocytes were much less prone to in vitro infection with R5- and X4-tropic HIV strains compared to FoxP3-CD3highCD8- thymocytes. As expected, CD3highCD4+ thymocytes, when treated with TGF-ß1, upregulated CD127 and this treatment resulted in increased FoxP3 expression and Treg differentiation, but did not affect the rate of HIV infection. FoxP3 expression and Treg frequencies remained unchanged following in vitro HIV infection alone or in combination with TGF-ß1. Conclusion: FoxP3 expression and tTreg differentiation is not affected by in vitro HIV infection alone or the combination of in vitro HIV infection and TGF-ß treatment.

Leishmania donovani Exploits Tunneling Nanotubes for Dissemination and Propagation of B Cell Activation.

Polyclonal B cell activation and the resulting hypergammaglobulinemia are a detrimental consequence of visceral leishmaniasis (VL); however, the mechanisms underlying this excessive production of nonprotective antibodies are still poorly understood. Here, we show that a causative agent of VL, Leishmania donovani, induces CD21-dependent formation of tunneling nanotubule (TNT)-like protrusions in B cells. These intercellular connections are used by the parasite to disseminate among cells and propagate B cell activation, and close contact both among the cells and between B cells and parasites is required to achieve this activation. Direct contact between cells and parasites is also observed in vivo, as L. donovani can be detected in the splenic B cell area as early as 14 days postinfection. Interestingly, Leishmania parasites can also glide from macrophages to B cells via TNT-like protrusions. Taken together, our results suggest that, during in vivo infection, B cells may acquire L. donovani from macrophages via TNT-like protrusions, and these connections are subsequently exploited by the parasite to disseminate among B cells, thus propagating B cell activation and ultimately leading to polyclonal B cell activation. IMPORTANCE Leishmania donovani is a causative agent of visceral leishmaniasis, a potentially lethal disease characterized by strong B cell activation and the subsequent excessive production of nonprotective antibodies, which are known to worsen the disease. How Leishmania activates B cells is still unknown, particularly because this parasite mostly resides inside macrophages and would not have access to B cells during infection. In this study, we describe for the first time how the protozoan parasite Leishmania donovani induces and exploits the formation of protrusions that connect B lymphocytes with each other or with macrophages and glides on these structures from one cell to another. In this way, B cells can acquire Leishmania from macrophages and become activated upon contact with the parasites. This activation will then lead to antibody production. These findings provide an explanation for how the parasite may propagate B cell activation during infection.

Characterization and use of HapT1-derived homologous tumors as a preclinical model to evaluate therapeutic efficacy of drugs against pancreatic tumor desmoplasia.

Desmoplasia in human pancreatic cancer (PC) promotes cancer progression and hinders effective drug delivery. The objectives of this study were to characterize a homologous orthotopic model of PC in Syrian golden hamster and investigate the effect of anti-fibrotic (pirfenidone), antioxidant (N-acetyl cysteine, NAC) and anti-addiction (disulfiram, DSF) drugs on desmoplasia and tumor growth in this model. The HapT1 PC cells when implanted orthotopically into hamsters formed tumors with morphological, cellular and molecular similarities to human PC. Protein profiling of activated hamster pancreatic stellate cells (ha-PSCs) revealed expression of proteins involved in fibrosis, cancer cells growth and metastasis. Pirfenidone, suppressed growth of HapT1 cells and the desmoplastic response in vivo; these effects were enhanced by co-administration of NAC. Disulfiram alone or in combination with copper (Cu) was toxic to HapT1 cells and PSCs in vitro; but co-administration of DSF and Cu accelerated growth of HapT1 cells in vivo. Moreover, DSF had no effect on tumor-associated desmoplasia. Overall, this study identifies HapT1-derived orthotopic tumors as a useful model to study desmoplasia and tumor-directed therapeutics in PC. Pirfenidone in combination with NAC could be a novel combination therapy for PC and warrants investigation in human subjects.