Functional and in situ evidence for nitric oxide production driven by CD40-CD40L interactions in graft-versus-leukemia reactivity

In a murine tumor model, complete tumor remission is achievable at even adv anced metastasized stages by transfer of immune T cells from donor B10.D2 ( H-2(d), Mls(b)) into tumor-bearing DBA/2 (H-2(d), Mls(a)) mice, We showed p reviously that this graft-versus-leukemia (GvL) effect is dependent on syne rgistic interactions of transferred CD4+ and CD8+ T cells with host siaload hesin (SER)-positive macrophages, We now show that the CD40-CD40L (CD154) i nteraction is involved in the induction of inducible nitric oxide synthase (iNOS) expression during adoptive immunotherapy (ADI). We demonstrate that during ADI, the level of CD40 expression in the liver becomes significantly augmented in comparison to livers of tumor-bearing, untreated animals, CD4 0 expression is found mostly on SER+ macrophages and to a lesser extent on dendritic cells (DCs). In GvL animals, more SER+ macrophages express iNOS t han untreated animals. iNOS expressing cells are found in close proximity t o apoptotic cells, at early time points of the therapy in areas of metastas is, and at late stages around portal veins, where CD4+ and CD8+ T lymphocyt es form clusters with SER+ macrophages, Blocking of CD40L in ciao at days 5 and 20, when all iNOS+ cells express CD40, leads to significantly reduced CD40 and iNOS expression as well as to a marked inhibition of the therapeut ic effect, These data provide functional and ill situ evidence that the inc reased CD40 and iNOS expression observed during ADI contribute to the eradi cation of liver metastases and to the clearance of donor lymphocytes from t he liver.