To Ki or Not to Ki: Re-Evaluating the Use and Potentials of Ki-67 for T Cell Analysis

This study discusses substantive advances in T cell proliferation analysis, with the aim to provoke a re-evaluation of the generally-held view that Ki-67 is a reliable proliferation marker per se, and to offer a more sensitive and effective method for T cell cycle analysis, with informative examples in mouse and human settings. We summarize recent experimental work from our labs showing that, by Ki-67/DNA dual staining and refined flow cytometric methods, we were able to identify T cells in the S-G(2)/M phases of the cell-cycle in the peripheral blood (collectively termed T Double S for T cells in S-phase in Sanguine: in short T-DS cells). Without our refinement, such cells may be excluded from conventional lymphocyte analyses. Specifically, we analyzed clonal expansion of antigen-specific CD8 T cells in vaccinated mice, and demonstrated the potential of T-DS cells to reflect immune dynamics in human blood samples from healthy donors, and patients with type 1 diabetes, infectious mononucleosis, and COVID-19. The Ki-67/DNA dual staining, or T-DS assay, provides a reliable approach by which human peripheral blood can be used to reflect the dynamics of human lymphocytes, rather than providing mere steady-state phenotypic snapshots. The method does not require highly sophisticated -omics capabilities, so it should be widely-applicable to health care in diverse settings. Furthermore, our results argue that the T-DS assay can provide a window on immune dynamics in extra-lymphoid tissues, a long-sought potential of peripheral blood monitoring, for example in relation to organ-specific autoimmune diseases and infections, and cancer immunotherapy.

Automated summary

The study introduces a more sensitive and effective method for T cell cycle analysis - T-DS cells, identified by Ki-67/DNA dual staining and refined flow cytometric methods in experiments on mice and humans. This approach can reflect the dynamics of human lymphocytes in peripheral blood, while providing more than just a snapshot of static phenotypes.