CD56(bright)CD16(-) natural killer cells as an important regulatory mechanism in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGvHD) is a major cause of morbidity after hematopoietic stem cell transplantation (HSCT). In large patient populations, we have shown a CD56(bright) natural killer (NK) population to strongly associate with a lack of cGvHD and we hypothesize that these cells function to suppress cGvHD. We aimed to isolate and define the characteristics of regulatory NK (NK(reg)) cells associated with suppression of cGvHD. Immunophenotypic evaluation of a large pediatric population found the CD56(bright) NK population associated with a lack of cGvHD to be perforin(-), Granzyme B(-), and CD335(+). Transcriptome analysis of a small patient cohort of CD56(bright) compared to CD56(dim) NK cells found the NK(reg) cells to also overexpress Granzyme K, IL-7R, GPR183, RANK, GM-CSFR, TCF7, and IL23A. Further analysis of this CD56(bright) NK(reg) population found a subpopulation that overexpressed IRF1, and TNF. We also found that viable NK(reg) cells may be isolated by sorting on CD56(+) and CD16(-) NK cells, and this population can suppress allogeneic CD4(+) T cells, but not T(reg) cells or CD8(+) T cells through a non-cytolytic, cell-cell contact dependent mechanism. Suppression was not reliant upon the NKp44, NKp46, or GPR183 receptors. Additionally, NK(reg) cells do not kill leukemic cells. Moreover, this is the first paper to clearly establish that a CD56(bright)CD3(-)CD16(-)perforin(-) NK(reg) population associates with a lack of cGvHD and has several unique characteristics, including the suppression of helper T-cell function in vitro. With further investigation we may decipher the mechanism of NK(reg) suppression and operationalize expansion of NK(reg) cells associated with cGvHD suppression.