CD8 Cells of Patients with Diffuse Cutaneous Leishmaniasis Display Functional Exhaustion: The Latter Is Reversed, In Vitro, by TLR2 Agonists

Abstract

Leishmania mexicana (Lm) causes localized (LCL) and diffuse (DCL) cutaneous leishmaniasis. DCL patients have a poor cellular immune response leading to chronicity. It has been proposed that CD8 T lymphocytes (CD8) play a crucial role in infection clearance, although the role of CD8 cytotoxicity in disease control has not been elucidated. Lesions of DCL patients have been shown to harbor low numbers of CD8, as compared to patients with LCL, and leishmanicidal treatment restores CD8 numbers. The marked response of CD8 towards Leishmania parasites led us to analyze possible functional differences between CD8 from patients with LCL and DCL. We compared IFNγ production, antigen-specific proliferation, and cytotoxicity of CD8 purified from PBMC against autologous macrophages (MO) infected with Leishmania mexicana (MOi). Additionally, we analyzed tissue biopsies from both groups of patients for evidence of cytotoxicity associated with apoptotic cells in the lesions. We found that CD8 cell of DCL patients exhibited low cytotoxicity, low antigen-specific proliferation and low IFNγ production when stimulated with MOi, as compared to LCL patients. Additionally, DCL patients had significantly less TUNEL+ cells in their lesions. These characteristics are similar to cellular “exhaustion” described in chronic infections. We intended to restore the functional capacity of CD8 cells of DCL patients by preincubating them with TLR2 agonists: Lm lipophosphoglycan (LPG) or Pam3Cys. Cytotoxicity against MOi, antigen-specific proliferation and IFNγ production were restored with both stimuli, whereas PD-1 (a molecule associated with cellular exhaustion) expression, was reduced. Our work suggests that CD8 response is associated with control of Lm infection in LCL patients and that chronic infection in DCL patients leads to a state of CD8 functional exhaustion, which could facilitate disease spread. This is the first report that shows the presence of functionally exhausted CD8 T lymphocytes in DCL patients and, additionally, that pre-stimulation with TLR2 ligands can restore the effector mechanisms of CD8 T lymphocytes from DCL patients against Leishmania mexicana-infected macrophages.

HIV-specific CD8+ T cells and HIV eradication

“…IL-15 agonists are of particular interest in this regard, having been shown to enhance CD8 + T cell and NK cell activity in a number of preclinical models (135)(136)(137)(138)(139), and the IL-15 superagonist ALT-803 is moving into a clinical trial in cART-treated HIV-infected subjects (ClinicalTrials.gov identifier: NCT02191098). Other immunostimulatory agents include TLR-2 agonists, which reverse CD8 + T cell exhaustion and enhance both tumor-and pathogen-specific T cell responses in vivo (140)(141)(142), and agonistic Abs against 41BB or CD40 (143-145), among others.…”

Protective and Pathological Functions of CD8+T Cells in Leishmania braziliensis Infection

“…These data indicate that CD8 ϩ T cells are able to induce apoptosis in both groups but suggest that CD8 ϩ T cells from SC individuals are less cytotoxic than CD8 ϩ T cells from CL patients. To determine the specific cytotoxic effects exerted by CD8 ϩ T cells, the cytotoxicity index (CI) was calculated as previously described (25,26). CL patients had a CI of 8.3 Ϯ 5.3, which was higher than those for SC individuals (4.8 Ϯ 3.6) and the HC group (4.5 Ϯ 3.6) (P Ͻ 0.05) (Fig.…”

Dysfunctional Adaptive Immunity During Parasitic Infections

“…Cutaneous leishmaniasis in humans has been linked to exhaustion of PD-1+ parasite-specific CD8 T cells, which could be functionally improved in vitro through the addition of toll like receptor 2 (TLR2) agonists [50]. Exhausted CD4 T cells have also been described in the context of experimental Leishmania infection [51].…”