Exploring the Prognostic Significance of Graft CD161-Expressing T Cells in Allo-HSCT
Authors: Mengge Gao , Chang Ying-Jun , Huang Xiao Jun , Zhao Xiaosu 
Published: December 2024

Background:
CD161 (NKR-P1A) is known for its role in inhibiting natural killer (NK) cell-mediated tumor cytotoxicity, with CLEC2D (also known as lectin-like transcript 1, LLT1) identified as its ligand. Unlike the widely studied T cell inhibitory receptors PD-1 and CTLA-4, CD161 and its ligand CLEC2D exhibit high expression levels in hematologic malignancies, including B-cell and T-cell lymphomas, as well as lymphocytic and myeloid leukemias. This suggests potential for targeting CD161 as a novel immunotherapeutic strategy for these blood cancers. Recent study by Alvarez Calderon et al. develops a fully human CD161 monoclonal antibody (mAb) that blocks CLEC2D binding, enhancing T cell-mediated immunity against hematologic malignancies, and resulting in significant survival benefits.
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a promising treatment for various malignant hematologic diseases. However, post-transplant immune deficiencies remain a major clinical obstacle, significantly limiting the broader use of this therapy and negatively impacting patient survival and overall prognosis. A recent study has shown that high frequencies of CD161-expressing CD4 T cells are associated with the relapse of acute myeloid leukemia (AML) following bone marrow transplantation. This finding provides new insights into the reconstruction of the immune landscape post-HSCT. Despite these advances, the role of CD161 in T cell immune recovery and its impact on the outcomes of allo-HSCT are not well understood. This study aims to explore the expression of CD161 in T cells from bone marrow (BM) and peripheral blood stem cells (PBSCs) grafts, and its influence on early post-transplant adverse clinical events, including acute graft-versus-host disease (aGVHD) and infections.
Methods：
A total of 142 patients underwent non-myeloablative allo-HSCT. Peripheral blood samples were collected on days 30, 60, 90, and 180 post-transplant. The frequency and functional cytokines of CD161-expressing cells were assessed using multiparameter flow cytometry (FCM).
Results：
Among the 142 patients and their respective donors, 110 underwent haplo-HSCT, and 32 had sibling-identical HSCT. A combination of PBSCs and BM was used for 114 patients, while 28 received only PBSCs. CD161+ lymphocytes in the grafts were predominantly CD3+ T cells, with a higher frequency in PBSCs (Median:71.7%, range 37.1-91.3%) compared to BM (Median: 61.5%, range 22.3-89.1%) (P&lt;0.001). Hence, further analysis focused on CD161+ T cells. Subgroup analysis based on CD4 and CD8 expression revealed a higher proportion of CD4+CD161+ T cells in PBSCs (11.1%) compared to BM (8.5%) (P&lt;0.001), while BM had a higher proportion of CD8+CD161+ T cells (5.2%) compared to PBSCs (3.1%) (P&lt;0.001).Further examination showed that most CD4+CD161+ T cells were CD4+CD161+CCR6+ cells (PBSCs: 68.2%, BM: 63.6%) (P&lt;0.001), and the CD8+CD161+ T cells were predominantly mucosal-associated invariant T (MAIT) cells (CD8+CD161+Vα7.2+) (PBSCs: 80.7%, BM: 76.0%) (P&lt;0.005).
Early post-transplant reconstitution of CD161+ T cells depended on the graft's CD161+ T cell content. Univariate analysis of early post-transplant adverse events (post-transplant days 0-100) revealed that a lower proportion of CD161+ T cells was significantly associated with EBV infection (P=0.011). Further analysis indicated that a higher proportion of CD4+CD161+CCR6+ T cells in PBSC grafts was significantly correlated with lower rates of CMV and pneumonia infections (P&lt;0.05) but higher incidence of aGVHD. Conversely, a higher proportion of CD8+CD161+ MAIT cells was associated with a lower incidence of gut aGVHD (P&lt;0.05).
Conclusions:
Our preliminary results indicate that CD161+ T cells in the graft play a crucial immunoregulatory role in early EBV infection following allo-HSCT. The CD4+CD161+CCR6+ T cell subset is associated with early post-transplant CMV and pneumonia, while the CD8+CD161+Vα7.2+ T cells are closely linked to gut aGVHD. These findings underscore the importance of different CD161+ T cell subsets in predicting and managing post-transplant complications.