Clinical significance of pre‐transplant circulating CD3+CD4+CD161+ cell frequency on the occurrence of neutropenic infections after allogeneic stem cell transplantation

Background Few studies have been performed to identify factors that are associated with an increased risk of infections during the neutropenic period in patients undergoing allogeneic stem cell transplantation (allo‐SCT). The aim of this study was to identify the host immune cells responsible for infections before engraftment. Methods A total of 282 patients who underwent allo‐SCT were enrolled. Peripheral blood samples were collected before conditioning therapy. Expression of CD161‐expressing T cells, natural killer cells, and immature myeloid cells was analyzed by flow cytometry. Microbially and clinically defined infections and fevers of unknown origin as proposed by the Immunocompromised Host Society were included in this study. Results The median age was 45 years (range, 16‐68 years). Patients had various hematologic disorders and were transplanted from human leukocyte antigen (HLA)‐matched siblings, unrelated donors, and familial HLA‐mismatched donors. In univariate analysis, younger age and a familial HLA‐mismatched donor were risk factors for the occurrence of infections. After adjusting for potential variables in univariate analysis, multivariate analyses revealed that a lower frequency of CD3+CD4+CD161+ cells was significantly associated with the occurrence of neutropenic infections. An age of 35 years or younger and allografting from familial HLA‐mismatched donors showed a trend toward higher infection rates. Conclusion Our data indicated that a lower frequency of CD3+CD4+CD161+ T cells in peripheral blood before conditioning therapy was associated with a higher incidence of infection during the neutropenic period. These results suggest that recipient innate T cells with expression of C‐type lectin CD161 can guard against infections before engraftment.