The persistent spin helix (PSH) is a quantum phenomenon related to the relativistic effect of the spin-orbit interaction (SOI) in semiconductor quantum wells (QWs) with a specific regime of balanced terms of the bulk (Dresselhaus) and structural (Rashba) inversion asymmetries. The resulting effective magnetic field induces a unidirectional wave pattern of the electronic spin polarization (SZ) and substantially enhances the spin wave lifetime in comparison to the case of imbalanced SOI terms [1]. The PSH was first observed and thoroughly studied in GaAs QWs [2]. Here we report the first observation of the PSH in II-VI materials, namely in a [001]-grown CdTebased QW. The spatio-temporal evolution SZ(y,t) of the PSH is monitored by time-resolved Kerr-microscopy at cryogenic temperatures. The Dresselhaus and Rashba parameters are individually determined by modifying the PSH in external magnetic fields applied in two orthogonal directions (see Fig. 1). Spatially and temporally resolved measurements of the diffusive evolution SZ(y,t) reveal optical doping as an important tuning knob for the PSH. We relate this finding to the dependence of the SOI parameters and the spin diffusion coefficient on the resident (n0) and photoexcited carrier densities (nop), which is validated quantitatively by microscopic calculations. These results demonstrate that the effective SOI in QWs can be tailored by optical doping, which is an important step towards a more detailed understanding of the PSH [3].