CD4 and Crohn disease: However, the cells expressing the CD4+CD28−CCR7− phenotype, while also low in frequency in most PBMC samples (<1% of all CD4+ cells), was likely successfully clustered by HSNE because two of the 11 Crohn disease subjects in the dataset showed an unusually high frequency of this population (40.7% and 31.0% of all CD4+ cells), allowing it to be well represented in the kNN graph of the full dataset.