  We derive a resummation formula for a $k_T$-dependent parton distribution
function at threshold, where $k_T$ is a parton transverse momentum. The
derivation requires infrared cutoffs for both longitudinal and transverse loop
momenta as evaluating soft gluon emissions in the Collins-Soper resummation
framework. This unified resummation exhibits suppression at large $b$, $b$
being the conjugate variable of $k_T$, which is similar to the $k_T$
resummation, and exhibits enhancement at small $b$, similar to the threshold
resummation.
