  To study scattering amplitudes at high-energy, the T-product of two currents
can be expanded in terms of coefficient functions (impact factors) and matrix
elements of ``composite color dipoles'' made of Wilson line operators with
rapidity cutoff preserving conformal invariance. In the leading order, the
high-energy evolution of color dipoles is governed by the non-linear
Balitsky-Kovchegov (BK) equation. To describe the high-energy amplitudes in the
next-to-leading order (NLO) one needs to know the coefficient function
(``impact factor'') and the evolution of corresponding Wilson-line operators.
Using the high-energy OPE, we find the next-to-leading order (NLO) correction
to the BK equation and calculate the impact factor for virtual photons in deep
inelastic scattering.
