Figure 1.

The phenotypic memory of myeloid cells is not restricted to monocytes, and can be more pronounced in granulocytes. Macaques (n = 5) were immunized twice, subcutaneously, 2 months apart with a recombinant attenuated vaccinia virus encoding HIV clade B Ags, rec MVA HIV-B (MVA is for Modified Vaccinia Ankara). Blood myeloid cell subsets were analyzed overtime using mass cytometry and a multi-step clustering analysis. They were classified as prime signature (blue), boost signature (red), or non-discriminant “no signature” (green), after a Linear Discriminant Analysis (LDA) performed after Least Absolute Shrinkage and Selection Operator (LASSO). Cell subsets responding to the 2nd immunization differed for the intensity of expression of several markers from those responding to the 1st immunization. They were present prior to vaccine boost, and were induced long after the 1st immunization. They were “better equipped to respond” to restimulation. Most neutrophils were modified, in contrast to some monocytes and DCs (41).