Interleukin 15-mediated induction of cytotoxic effector cells capable of eliminating Epstein-Barr virus-transformed/immortalized lymphocytes in culture.
BACKGROUND
Interleukin 15 (IL-15) activates cytotoxic lymphocytes and drives the expansion of memory T cells. Its role in immune control of virus-transformed cells and other tumor cells remains to be elucidated. We investigated the role of IL-15 in controlling Epstein-Barr virus (EBV)-transformed/immortalized lymphocytes in culture. EBV is a highly potent lymphocyte-transforming and opportunistic oncogenic herpesvirus associated with several human tumors.


METHODS
Peripheral blood mononuclear cells (PBMCs) from healthy donors were infected with EBV and cultured with either IL-15 or IL-15 plus anti-IL-15 antibodies for 3-4 weeks. We monitored EBV-induced transformation by assessing the clearly visible cell clusters by microscopy and analyzing the expression of EBV-encoded latent membrane oncoprotein-1 (LMP-1) and the EBV nuclear antigen (EBNA) complex by immunoblotting and immunofluorescence techniques, respectively. We depleted EBV-infected cultures of PBMCs of specific effector cell populations to investigate the effector cells involved in mediating IL-15 effect.


RESULTS
The presence of IL-15 resulted in the complete elimination of EBV-transformed cells in PBMC cultures. Western blot and immunofluorescence analyses performed 3-4 weeks after infection showed no detectable levels of LMP-1 and EBNA in IL-15-treated EBV-infected cultures, whereas IL-15-untreated EBV-infected cultures and IL-15/anti-IL-15-treated cultures expressed both proteins. IL-15 mediated its anti-EBV effect through early and late response mechanisms, i.e., by first activating natural killer (NK) cells and subsequently inducing cytolytic NK-T cells. The presence of anti-IL-15 neutralizing antibodies abrogated IL-15's effect on both mechanisms.


CONCLUSIONS
In vitro, IL-15 mediated complete elimination of EBV-infected/transformed lymphocytes via successive activation of NK and NK-T cytotoxic effectors. If these in vitro findings reflect in vivo mechanisms, then IL-15 might be considered for cytokine-based immunotherapy in patients with EBV-associated lymphoproliferative disorders/malignancies.
Sharif-Askari
E
E
Laboratory of Immunovirology, Department of Microbiology and Immunology, and Pediatric Research Center, University of Montreal and Sainte-Justine Hospital, Montreal, PQ, Canada.
Fawaz
L M
LM
Tran
P
P
Ahmad
A
A
Menezes
J
J
D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral / Q000276:immunology*; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000187:drug effects* / Q000276:immunology*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000276:immunology / Q000378:metabolism; D004854:Herpesvirus 4, Human / Q000276:immunology*; D006801:Humans; D019409:Interleukin-15 / Q000276:immunology / Q000494:pharmacology*; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects; D016131:Lymphocyte Subsets / Q000187:drug effects / Q000276:immunology; D011994:Recombinant Proteins / Q000276:immunology / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D013997:Time Factors
D019309:Epstein-Barr Virus Nuclear Antigens; D019409:Interleukin-15; D011994:Recombinant Proteins