Work

332: Effective graft-versus-leukemia responses are associated with the presence of nucleic acid-immunoglobulin complexes that stimulate toll-like receptors (TLR) 8 and 9

Year: 2007

Type: article

Abstract: In patients with chronic myeloid leukemia (CML) who demonstrated effective graft-versus-leukemia (GvL) responses after DLI without clinically significant GvHD, we previously identified a panel of CML-associated antigens that are targets of antibodies present in post-DLI sera. To gain insight into the possible mechanisms of immunogenicity of our GvL-associated target antigens, we surveyed previously known cellular functions of our entire panel of identified antigens, and observed that ∼70% are nucleic acid binding proteins, thus predicting that sera from DLI responders may contain nucleic-acid containing activities that stimulate immunity. Indeed, 5 of 6 post-DLI sera, but not pre-DLI sera, induced a 3 to 50-fold increase in the expression of MIP-1alpha, TNF-alpha, IP-10 and IFN-alpha transcripts in normal peripheral blood mononuclear cells (PBMC). Cytokines were also not induced by sera from 3 of 3 DLI non-responders or 3 of 3 CML patients who achieved molecular remission after imatinib treatment. This endogenous immunostimulatory factor required both nucleic acid and protein for its adjuvant activity as pretreatment of post-DLI sera with DNase, RNase, papain or pepsin resulted in marked decrease in cytokine induction. To test for the role of distinct TLRs in this response, HEK transfectants expressing TLR3, 4, 8 or 9 were exposed to sera collected 6-12 months after DLI. IL-8 expression increased only in the TLR8 and TLR9-expressing cell lines that are known to be responsive to RNA and DNA respectively. IL-8 expression was further induced by post-DLI sera in TLR9-expressing cell lines co-transfected with CD32, suggesting that internalization by FcR may enhance delivery of nucleic acids to endosomal TLR8/9. None of the transfectants could be activated by pre-DLI sera, nor by post-DLI sera from non-responders. Finally, sera from responders collected as early as 2 weeks after DLI consistently activated TLR8 and 9 suggesting that endogenous TLR8/9 activation may contribute to the early immunologic events involved in effective DLI responses. Taken together, these studies demonstrate for the first time that effective tumor immunity is correlated with the presence of endogenous adjuvant-like nucleic-acid-immunoglobulin complexes in patient sera. Ongoing studies are focused on studying the immunologic effects of this endogenous adjuvant and determining which of our previously identified CML antigens are bound to nucleic acids that activate TLR8 and TLR9.

Source: Transplantation and Cellular Therapy

DOI: 10.1016/j.bbmt.2006.12.337