TLR9 engagement on CD4 T lymphocytes represses gamma-radiation-induced apoptosis through activation of checkpoint kinase response elements.
T cell-based therapies have much promise in cancer treatment. This approach may be enhanced if used in combination with radiotherapy provided that tumor-specific T cells can be protected against the effects of radiotherapy. Previously, we demonstrated that administration of TLR9 ligand into mice decreased activation- and serum deprivation-induced cell death in T cells. We hypothesized that TLR9 engagement on T lymphocytes decreased apoptosis after cellular stress. We show that TLR9 engagement on murine CD4 T cells reduces gamma-radiation-induced apoptosis as judged by decreased annexin-V/PI staining, caspase-3 activation, and PARP cleavage. TLR9-stimulated cells show heightened accumulation at the G2 cell-cycle phase and increased DNA repair rates. Irradiated, TLR9-engaged cells showed higher levels of phosphorylated Chk1 and Chk2. While the levels of activated ATM in response to IR did not differ between TLR9-stimulated and unstimulated cells, inhibition of ATM/ATR and Chk1/Chk2 kinases abolished the radioprotective effects in TLR9-stimulated cells. In vivo, TLR9-stimulated cells displayed higher radio resistance than TLR9-stimulated MyD88(-/-) T cells and responded to antigenic stimulation after total body irradiation. These findings show, for the first time, that TLR9 engagement on CD4 T cells reduces IR-induced apoptosis by influencing cell-cycle checkpoint activity, potentially allowing for combinatorial immunotherapy and radiotherapy.
Zheng
Liqin
L
Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, 533 Bolivar Street, New Orleans, LA 70112, USA.
Asprodites
Nicole
N
Keene
Angela H
AH
Rodriguez
Paulo
P
Brown
Kevin D
KD
Davila
Eduardo
E
D000818:Animals; D000941:Antigens / Q000276:immunology; D017209:Apoptosis / Q000528:radiation effects*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology* / Q000201:enzymology* / Q000276:immunology / Q000528:radiation effects; D002453:Cell Cycle / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects; D005720:Gamma Rays; D008024:Ligands; D008213:Lymphocyte Activation / Q000528:radiation effects; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000276:immunology; D011494:Protein Kinases / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D011836:Radiation Tolerance / Q000528:radiation effects; D020218:Response Elements / Q000235:genetics*; D015398:Signal Transduction / Q000528:radiation effects; D051217:Toll-Like Receptor 9 / Q000276:immunology*; D014916:Whole-Body Irradiation
D000941:Antigens; D008024:Ligands; D053594:Myeloid Differentiation Factor 88; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases