Tumor Apoptotic Bodies Inhibit CTL Responses and Antitumor Immunity via Membrane-Bound Transforming Growth Factor-β1 Inducing CD8+ T-Cell Anergy and CD4+ Tr1 Cell Responses

Abstract

Tumor cell apoptosis induced by radiation therapy results in apoptotic tumor cells and apparition of membrane blebs termed apoptotic bodies (APB). The immune responses induced by apoptotic tumor cells have been extensively studied. However, the role of APB in modulation of tumor immune responses is elusive. In this study, we induced apoptosis in 90% ovabumin-expressing EG7 tumor cells by in vitro irradiation (9,000 rad) of tumor cells with a subsequent cell culture for 9 hours. APB purified from irradiation-induced apoptotic EG7 cell culture supernatant by differential ultracentrifugation were vesicles with 50 to 90 nm in diameter and expressed apoptosis-specific Annexin V, 14-3-3, and Histone H3. We then investigated its potential modulation in DC OVA -induced T-cell responses and antitumor immunity. We found that EG7-derived APB were tolerogenic and capable of suppressing DC OVA -stimulated CD8 + CTL responses and antitumor immunity via its induction of CD8 + T-cell anergy and type 1 regulatory CD4 + T-cell responses. Analysis of apoptotic tumor cells and APB revealed the expression of membrane-bound transforming growth factor (TGF)-B1 associated with irradiation-induced apoptosis formation, which is a result from activation of transcriptional factor NF-AT specific for TGF-B1 promoters. Our data further elucidate that it is the membrane-bound TGF-B1 expression on APB that contributes to its in vitro antiproliferative effect as shown by using neutralizing TGF-B1-specific antibody. Administration of anti-TGF-B1 antibody in vivo also blocked APB-mediated immune suppression of CD8 + CTL responses and antitumor immunity. Therefore, our study may have great impact in designing a combined radiation therapy with immunotherapy of cancer.

Apoptotic cells attenuate fulminant hepatitis by priming Kupffer cells to produce interleukin-10 through membrane-bound TGF-β

“…Previous reports showed the similar functional difference between membrane-bound TGF-b and recombinant TGFb 25,33,44,45 ; however, the mechanisms remain to be clarified. One hypothesis is that the membrane-bound TGF will have a kind of group effect, and a very high dose of soluble TGF may own the effect of membrane-bound TGF.…”

“…25,33,44,45 It is plausible that membrane-bound TGF-b on ACs can also directly inhibit immune responses via these processes. Nonetheless, in the current study we discovered that membrane-bound TGF-b on ACs could lead to hepatic immune hyporesponsiveness via induction of IL-10 from KCs.…”

TLR2-Mediated Expansion of MDSCs Is Dependent on the Source of Tumor Exosomes

“…In particular, tumor cells communicate with immune cells, leading to immune suppression. [1][2][3][4][5][6] One of the challenging issues is that the data generated from tumor cellderived exosomes released from in vitro cultured tumor cells may not represent the real effects caused by exosomes released from tumor cells being grown under immune pressure (a true physiological microenvironment). However, due to technical obstacles, it is difficult to isolate exosomes from solid tumor tissues.…”

CD4+ T cell-released exosomes inhibit CD8+ cytotoxic T-lymphocyte responses and antitumor immunity

“…12 The OVA-specific CD4 1 T cells were incubated with or without 0.5 mM carboxyfluorescein diacetate succinimidyl ester (CFSE) and then cultured in serum-free AIM-V medium (Invitrogen Corp., Carlsbad, CA, USA) with IL-2 (20 U/ ml) for 24 h. EXO were purified from the T-cell culture supernatants by differential ultracentrifugation, and protein content was quantified by Bradford assay. 13 DC OVA -activated OTII CD4 1 T cell-released EXO and CFSE-labeled OTII CD4…”

“…, CD11c, CD40, CD54, CD80, pMHC I, Fas and FasL and analyzed by flow cytometry as described previously. 13 EXO samples (10 g/100 ml PBS) were incubated with FITC-Abs (2 ml, 1 mg/ml) specific for CD4, Vb5.1, 5.2 TCR, LFA-1, CD25 and FasL on ice for 30 min and then analyzed by flow cytometry. 13 EXO were first gated using calibrated polystyrene latex microbeads (3.8 mm) bound to fluorescent dyes (Sigma, St Louis, MO, USA) and analyzed for expression of the above molecules by flow cytometry.…”