The article is based on a paper written by Gendelman et al.. They write [1]:

"A potential therapeutic role for immune transformation in Parkinson’s disease evolves from more than a decade of animal investigations demonstrating regulatory T cell (Treg) nigrostriatal neuroprotection. To bridge these results to human disease, we conducted a randomized, placebo-controlled double-blind phase 1 trial with a well-studied immune modulator, sargramostim (granulocyte-macrophage colony-stimulating factor)."

The sample size is small: 10 active and 10 placebo. In Figure 4 there are two graphs, one showing the UPDRS III scores of the placebo group and the other the active group. To my eyes even before the treatment is started these groups have different properties.

Sargramostim has been used for, inter alia., fungal infections. I wonder if this is a confounding property.

Reference:

[1] "Evaluation of the safety and immunomodulatory effects of sargramostim in a randomized, double-blind phase 1 clinical Parkinson’s disease trial"
Howard E. Gendelman et al.
npj Parkinson's Disease 3, Article number: 10 (2017)
Evaluation of the safety and immunomodulatory effects of sargramostim in a randomized, double-blind phase 1 clinical Parkinson’s disease trial | npj Parkinson'''s Disease

John