Impaired Interferon-Gamma Production as a Consequence of Profound STAT4 Deficiency in Lymphocytes of Lymphoma Patients after Autologous Hematopoietic Stem Cell Transplantation.

Production of IFN-gamma has been found to be critical for optimal antitumor immunotherapy in several preclinical animal models. IL-12-induced IFN-gamma production is markedly defective in patients with lymphoma who have undergone autologous hematopoietic stem cell transplantation (AHSCT). We have investigated the mechanism of defective IFN-gamma production after AHSCT. Increasing the number of CD4 T cells in IFN-gamma assays did not substantially improve IFN-gamma production by post-transplant patient peripheral blood mononuclear cells (PBMCs). Thus, the quantitative deficiency in CD4 T cells observed for up to a year after AHSCT was not the primary mechanism of defective IFN-gamma production. Post-transplant patient T cells and NK cells expressed the IL-12 receptor beta1 subunit at significantly higher levels than did control PBMCs. Moreover, IL-12 receptor beta2 was expressed by a higher proportion of NK cells from post-transplant patients as compared to control subjects. Thus, down-regulation of IL-12 receptor subunits did not account for defective IFN-gamma production by post-transplant patient PBMCs. Levels of Jak2 and Tyk2 were comparable in control and post-transplant patient PBMCs. In contrast, IL-12-induced tyrosine phosphorylation of STAT4 was undetectable or barely detectable in post-transplant patient PBMCs, whereas it was readily detectable in control PBMCs. The total levels of STAT4 protein were also markedly decreased (P<0.027) in post-transplant patient PBMCs (3275+/−1692; mean+/−SE by densitometric analysis) as compared to control PBMCs (8644+/−732). This profound STAT4 deficiency persists for at least 6 months following AHSCT. Incubation of post-transplant patient PBMCs with IL-12 and IL-18 in combination partially reversed the defective IFN-gamma production seen after stimulation with IL-12 alone. IFN-gamma production in response to IL-12 plus IL-18 was not associated with increased expression of STAT4 but was dependent on the activity of p38 MAP kinase. These results indicate that defective IFN-gamma production is due to an intrinsic deficiency in STAT4 expression by post-transplant patient lymphocytes and suggest strategies for circumventing this deficiency in post-transplant cancer immunotherapy.