IL-2, IL-3, AND IFN-GAMMA DIFFERENTLY AFFECT IN-VIVO FREQUENCIES OF CIRCULATING PRECURSORS OF CYTOTOXIC T-LYMPHOCYTES (CTL-P)

Experimental animal and human in vivo studies have previously demonstr ated the impact of exogenous administration of various cytokines on fr equencies of circulating myeloid and LAK precursor cells. For the firs t time we investigated whether exogenous cytokines, in the absence of antigeneic challenge, may also influence frequencies of circulating an tigen-specific cytotoxic T-lymphocyte precursor cells. We further aske d whether triggering of autoimmune pathways as has been reported for s everal cytokines can be confirmed on the cellular level by demonstrati on of induction of autoreactive CTL-p. Limiting dilution analysis was used to determine alloreactive CTL-p frequencies in 31 patients with n onhematologic diseases before and after short-term systemic treatment with either rIL-2 (4.8 x 10(6) IU/m2 bid), rIL-3 (2.5, 5.0 or 10.0 mug /kg qd), rGM-CSF (5 mug/kg qd), rIFN-gamma (200 or 400 mug qd), or IFN -alpha (3 or 5 x 10(6)IU qod). Simultaneously, autoreactive CTL-p freq uencies were determined by split-well analysis in 25 of these patients . We found that rIL-2 significantly expands the circulating precursor pool of alloreactive CTL (p < 0.05). rIL-3 affected CTL-p frequencies in a dose-dependent fashion. Low and intermediate doses of rIL-3 did n ot exhibit significant effects, whereas 10 mug/kg rIL-3 led to expansi on of alloreactive CTL-p in the same order of magnitude as did rIL-2. This effect was statistically significant when compared with rGM-CSF ( p < 0.02), which apparently had no influence on alloreactive CTL-p fre quencies. In contrast to rIL-2 and rIL-3, exogenous rIFN-gamma markedl y reduced the circulating precursor pool of CTL. This again was statis tically significant compared with rIFN-alpha (p < 0.03), which, like r GM-CSF, did not exhibit any effects on the level of alloreactive CTL-p . Frequencies of autoreactive CTL-p were invariably below the limit of detection in our system (<1/300000). In conclusion, these data demons trate that (a) short-term systemic administration of rIL-2, rIL-3, and rIFN-gamma differently affects the clone size of circulating precurso rs of alloreactive CTL in man, while rGM-CSF and rIFN-alpha do not exh ibit measurable effects, and (b) none of the cytokines administered is capable of uncovering detectable frequencies of autoreactive CTL-p.