Report 11 from Dallas, 50th AASLD Meeting, Nov 5-9

IFN & T-Cell Mediated Immunity: differences between interferons
Jules Levin, NATAP

EFFECTS OF INTERFERON AND RIBAVIRIN ON T CELL MEDIATED IMMUNOLOGIC FUNCTION: 
DIFFERENCES BETWEEN INTERFERONS AND EVIDENCE FOR THE IMPROVED CLINICAL 
RESPONSE TO COMBINATION THERAPY
abstract 806

Pamela M Kimball, Scott Verbeke, Mitchell L Shiffman, Med Coll of Virginia Commonwealth Univ, Richmond, VA

Interferon (INF) with or without ribavirin (RBV) represents the only effective therapy for pts with chronic HCV. These agents exert their effects, in part, via immune modulation. However, the specific immunologic effects of IFN and RBV and how these agents interact to enhance virologic response remains undefined. Aims: To evaluate the effect of two types of IFNs (INF-a-2b(INTRON), INF-a-con-1 (CIFN)), RBV and combinations of IFN/RBV on T cell proliferation and cytokine release.

Methods: Proliferation assays were conducted on T lymphocytes obtained from healthy volunteers. The clonal expansion of T lymphocytes was assessed by incorporation of H3-thymidine following stimulation with the mitogen PHA both with and without INTRON (105-107 IU/ml), CIFN (1.5-150 ng/ml) or RVN (0.5-50 mg/ml). Interactions between IFN and RBV, when utilized in combination, were assessed by mathematical isobologram analysis which identifies whether interations are additive, synergistic or antagonistic. The density of IFN-receptors (INFr) on T cells was assessed by flow cytometry. The secretion of IL-2, IL-10, TNF and g-INF was assessed by EIA. Results: Incubation with varying doses of INTRON, CIFN or RBV led to a dose dependent suppression in T cell proliferation. Cultivation with 1.5, 15 and 150 ng/ml of CIFN reduced cpm (x103) from a baseline of 160 to 100, 64 and 42 respectively (P<.001). Similar results were observed with titrations of INTRON and RBV. Isobologram analysis indicated that the effects of INTRON/RBV were additive (the effect of INTRON/RBV was equal to the sum of either agent alone). In contrast, the combination of CIFN/RBV was weakly antagonistic (there was less inhibition of T cell proliferation with CIFN/RBV than with either agent alone). Supression of proliferative by both INFs was cell cycle restricted; IFN did not reduce T cell proliferation if added 24 hrs after stimulation (after T cells had converted from G1 to S phase). This loss in IFN sensitivity correlated with a 50% decline in INFr density during S phase. In contrast, RBV inhibited proliferation at all times throughout the cell cycle. Incubation of cells with INTRON increased IL-2, TNF and g-IFN release 4.5, 4.1 and 8.3 fold above control values (p<.005). CIFN increased release of these cytokines by only 1.0, 1.9 and 1.9 fold (p<0.05). This was significantly less than with INTRON (p<0.05). Neither IFN effected IL-10 secretion. The secretion of these cytokines was unaffected by RBV when utilized as either a single agent or in combination with either IFN. 

Conclusions: Inhibition of T cell proliferation and enhanced TH1 cytokine production by IFN may explain the reduction in hepatic inflammation and viral levels observed during treatment of chronic HCV. Since IFNr is downregulated during proliferation, the effects of IFNs are cell cycle restricted. In contrast, the effects of RBV are cell cycle independent. These observations may explain the enhanced clinical response observed with INTRON/RBV combination therapy compared with IFN alone in pts with chronic HCV. Given the observation that RBV antagonizes the antiproliferative effects of CIFN and that TH1 cytokine release is reduced with CIFN in vitro, it is quite possible that the combination of CIFN/RVN will not be as clinically effective as INTRON/RBV.