Naïve/Effector CD4 T cell ratio as a useful predictive marker of immune reconstitution in late presenter HIV patients: A multicenter study.

A significant proportion of HIV-infected patients experiencing a late diagnosis highlights the need to define immunological protocols able to help the clinicians in identifying patients at higher risk for immunological failure. The aim of the study was to evaluate the feasibility of easy cytometric tests in defining the effect of antiretroviral treatment (cART) on immunological homeostasis and in identifying predictive markers of early immune recovery. Chronic HIV infected patients (n = 202) were enrolled in a prospective multicentric study, and their immunological profile was studied before (w0) and after 24 weeks (w24) of antiretroviral treatment (cART) using a standardized flow cytometric panel. Based on CD4 T cell count before treatment, patients were divided in late (LP: CD4 <350/mmc), intermediate (IP: 350/mmc500/mmc) presenters. In all groups, cART introduction increased CD4 and CD4/CD8 T cell ratio, naïve T cell (CD4 and CD8) and CD127-expressing CD4 T cells. In parallel, cART significantly reduced effector memory T cells (CD4 and CD8) and T cell activation (CD38+CD8 and CD95+CD4 T cells). Moreover, the frequency of Naïve and Effector CD4 T cells before treatment correlated with several immune parameters key associated with the pathogenesis of HIV, thus mirroring the health of immune system. Interestingly, we identified the Naïve/Effector CD4 T cell ratio (N/EM) at w0 as a marker able to predict early immune recovery. Specifically, in LP, N/EM ratio was significantly higher in immunological responder patients (CD4>500/mmc at w24) when compared to immunological non responder (CD4 T cells <500/mmc at w24). Finally, a multivariate analysis indicates that after 24w patients with N/EM ratio higher than 1.86 at w0 recovered 96 CD4 T cells more than those with N/EM ratio lower than 0.46. Altogether, our data define an easy protocol able to define reliable immunological markers useful for the characterization of immune profile in viremic HIV patients and identify the naïve/effector CD4 T cell ratio as a new tool able to predict an early immune reconstitution potential.

Similarities and differences of innate immune responses elicited by smooth and rough LPS.

The lipopolysaccharide is the major component of Gram-negative bacteria outer membrane. LPS comprises three covalently linked regions: the lipid A, the rough core oligosaccharide, and the O-antigenic side chain determining serotype specificity. Wild-type LPS (sLPS) contains the O-antigenic side chain and is referred to as smooth. Rough LPS (rLPS) does not contain the O-side chain. Most wt bacteria and especially wt Enterobacteriaceae express prevalently the sLPS form although some truncated rLPS molecules always reach the external membrane. The two sLPS and rLPS forms are used almost indistinctly to study the effects on innate immune cells. Nevertheless, there is evidence that their mechanism of action may be different. For instance, while sLPS requires CD14 for the initiation of both MyD88-dependent and independent signal transduction pathways at least at low doses, rLPS leads to MyD88-dependent responses in the absence of CD14 even at low doses. Here we have identified additional differences in the signaling capacity of the two LPS species in the mouse. We have found that rLPS, diversely from sLPS, is capable of activating in dendritic cells (DCs) the Ca(2+)/calcineurin and NFAT pathway in a CD14-independent manner, moreover it is also capable per se of activating the inflammasome and eliciting IL-1ß secretion independent of the presence of additional stimuli required instead for sLPS. The ability of rLPS of activating the inflammasome in vitro has as a direct consequence a higher efficiency of rLPS-exposed DCs in activating natural killer (NK) cells compared to sLPS-exposed DCs. However, diversely from possible predictions, we found that the different efficiencies of the two LPS species in eliciting innate responses are almost nullified in vivo. Therefore, sLPS and rLPS induce nearly similar in vivo innate responses but with different mechanisms of signaling.

Modulators of arginine metabolism do not impact on peripheral T-cell tolerance and disease progression in a model of spontaneous prostate cancer.

PURPOSE: Chronic inflammation, recruitment of myeloid-derived cells, and perturbation of the arginine metabolism have been all proposed as mechanisms favoring prostate carcinogenesis and tumor immunoescape. Objective of this study was to evaluate whether accumulation of CD11b(+)Gr1(+) cells, also defined myeloid-derived suppressor cells, occur in mice affected by transplantable or spontaneous prostate cancer (PC). We also investigated whether N(G) nitro-L-arginine methyl ester (L-NAME) and sildenafil, both modulators of the arginine metabolism, restrain tumor growth and restore tumor-specific immunity. EXPERIMENTAL DESIGN: Wild-type C57BL/6 mice bearing TRAMP-C1 PC and transgenic adenocarcinoma of the mouse prostate (TRAMP) mice were treated with vehicle, L-NAME or sildenafil, and evaluated for CD11b(+) cells accumulation in the blood, several organs, and the tumor mass and for disease progression. RESULTS: CD11b(+)Gr1(high), CD11b(+)Gr1(int), and CD11b(+)Gr1(-) cells differently accumulated in different organs and especially in the tumor of the two mouse models. L-NAME and sildenafil impaired the immunosuppressive function of CD11b(+) cells in both models and restrained TRAMP-C1 growth, but they neither break tumor-specific immune tolerance nor limit tumor progression in TRAMP mice. CONCLUSIONS: Collectively, our results emphasize substantial differences in tumor-induced alteration of myelopoiesis and sensitivity to modulators of the arginine metabolism between a transplantable and a spontaneous model of PC. They also suggest that perturbation of the arginine metabolism is dispensable for PC progression and the associated T-cell tolerance.

CD14 regulates the dendritic cell life cycle after LPS exposure through NFAT activation.

Toll-like receptors (TLRs) are the best characterized pattern recognition receptors. Individual TLRs recruit diverse combinations of adaptor proteins, triggering signal transduction pathways and leading to the activation of various transcription factors, including nuclear factor kappaB, activation protein 1 and interferon regulatory factors. Interleukin-2 is one of the molecules produced by mouse dendritic cells after stimulation by different pattern recognition receptor agonists. By analogy with the events after T-cell receptor engagement leading to interleukin-2 production, it is therefore plausible that the stimulation of TLRs on dendritic cells may lead to activation of the Ca(2+)/calcineurin and NFAT (nuclear factor of activated T cells) pathway. Here we show that mouse dendritic cell stimulation with lipopolysaccharide (LPS) induces Src-family kinase and phospholipase Cgamma2 activation, influx of extracellular Ca(2+) and calcineurin-dependent nuclear NFAT translocation. The initiation of this pathway is independent of TLR4 engagement, and dependent exclusively on CD14. We also show that LPS-induced NFAT activation via CD14 is necessary to cause the apoptotic death of terminally differentiated dendritic cells, an event that is essential for maintaining self-tolerance and preventing autoimmunity. Consequently, blocking this pathway in vivo causes prolonged dendritic cell survival and an increase in T-cell priming capability. Our findings reveal novel aspects of molecular signalling triggered by LPS in dendritic cells, and identify a new role for CD14: the regulation of the dendritic cell life cycle through NFAT activation. Given the involvement of CD14 in disease, including sepsis and chronic heart failure, the discovery of signal transduction pathways activated exclusively via CD14 is an important step towards the development of potential treatments involving interference with CD14 functions.

Modulators of arginine metabolism support cancer immunosurveillance.

BACKGROUND: Tumor-associated accrual of myeloid derived suppressor cells (MDSC) in the blood, lymphoid organs and tumor tissues may lead to perturbation of the arginine metabolism and impairment of the endogenous antitumor immunity. The objective of this study was to evaluate whether accumulation of MDSC occurred in Th2 prone BALB/c and Th1 biased C57BL/6 mice bearing the C26GM colon carcinoma and RMA T lymphoma, respectively, and to investigate whether N(G) nitro-L-arginine methyl ester (L-NAME) and sildenafil, both modulators of the arginine metabolism, restored antitumor immunity. RESULTS: We report here that MDSC accumulate in the spleen and blood of mice irrespective of the mouse and tumor model used. Treatment of tumor-bearing mice with either the phosphodiesterase-5 inhibitor sildenafil or the nitric-oxide synthase (NOS) inhibitor L-NAME significantly restrained tumor growth and expanded the tumor-specific immune response. CONCLUSION: Our data emphasize the role of MDSC in modulating the endogenous tumor-specific immune response and underline the anti-neoplastic therapeutic potential of arginine metabolism modulators.

Peripheral T-cell tolerance associated with prostate cancer is independent from CD4+CD25+ regulatory T cells.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) are thought to suppress the natural and vaccine-induced immune response against tumor-associated antigens (TAA). Here, we show that Treg accumulate in tumors and tumor-draining lymph nodes of aging transgenic adenocarcinoma of the mouse prostate (TRAMP) male mice, which spontaneously develop prostate cancer. TAA overexpression and disease progression associate also with induction of TAA-specific tolerance. TAA-specific T cells were found in the lymphoid organs of tumor-bearing mice. However, they had lost the ability to release IFN-gamma and kill relevant targets. Neither in vivo depletion of Treg by PC61 monoclonal antibody followed by repeated vaccinations with antigen-pulsed dendritic cells nor the combined treatment with 1-methyl-L-tryptophan inhibitor of the enzyme indoleamine 2,3-dyoxigenase, PC61 antibody, and dendritic cell vaccination restored the TAA-specific immune response. Treg did not seem to control the early phases of tolerance induction, as well. Indeed, depletion of Treg, starting at week 6, the age at which TRAMP mice are not yet tolerant, and prolonged up to week 12, did not avoid tolerance induction. A similar accumulation of Treg was found in the lymph nodes draining the site of dendritic cell vaccination both in TRAMP and wild-type animals. Hence, we conclude that Treg accrual is a phenomenon common to the sites of an ongoing immune response, and in TRAMP mice in particular, Treg are dispensable for induction of tumor-specific tolerance.

The regulatory role of dendritic cells in the immune response.

Dendritic cells (DCs) are key regulators of immune reactions. They control early innate responses, regulate long-lasting adaptive immunity and contribute to the maintenance of self-tolerance. DCs continuously monitor the environment through a multifaceted innate antigen receptor repertoire and, in response to perturbations, start a complex genetic reprogramming that leads to a complete activation of innate and, then, adaptive immune responses. This review discusses how DCs become efficient activators of NK and, subsequently, T cells following a microbial encounter.