Defining the Cellular and Molecular Features of CD4 T Cell Reconstitution Post Allo-HCT

Introduction Immune reconstitution after allogeneic hematopoietic cell transplantation (allo-HCT) is required for protection from infection and response to vaccination. However, lymphocyte reconstitution can cause Graft versus Host Disease (GvHD), and conversely, GvHD can impact immune reconstitution. The longitudinal dynamics of the emerging adaptive immune cells and how they are remodelled in GvHD have not been fully explored.

Method: To capture features of emerging immune systems that were consistent across transplant contexts, we performed deep immunophenotyping on a cohort of 10 adults who received allo-HCT from peripheral blood stem cells (PBSCs) but for varying hematologic malignancies (ALL, CML, CMML, AML, MDS, HL, and myelofibrosis), from both haploidentical and matched unrelated donors, and with varying pre-transplant conditioning and post-transplant GvHD prophylaxis regimens. Of 10 individuals, 6 developed acute and chronic GvHD. Peripheral blood mononuclear cells (PBMCs) were drawn at 1, 2, 3, 6, and 12 months post-transplant. PBMCs from 8 age-approximated healthy individuals were included as normal immune controls. Samples were processed for high-parameter spectral flow cytometry, and viable lymphocytes were sorted for single cell RNA and immunoreceptor sequencing.

Result: CD4 T cells in individuals who developed acute and chronic GVHD demonstrated reduced T cell receptor clonal diversity by the second month after transplant. High-parameter flow cytometry demonstrated that GvHD was associated with a lower proportion of central memory CD4 T cells and an enrichment for T peripheral helper cells (Tph) as compared to individuals who did not develop GvHD and to healthy controls. These changes in CD4 T cell composition preceded clinical GvHD diagnosis and were reflected with greater detail in single cell sequencing studies, where GvHD was associated with early and sustained increases in Th1-like Tph, expressing PDCD1, TBX21, and GZMA. GvHD diagnosis was also associated with a delayed return of T follicular helper cells (Tfh) and increased expression of the transferrin receptor CD71 on both Tfh and regulatory T cells (Tregs). Of note, the proportion of Tregs, defined as CD127^negativeCD25^high by flow cytometry and FOXP3 expression in scRNAseq, was increased in all transplant recipients-with and without GvHD-as compared to healthy individuals. However, like conventional CD4 T cells, Tregs in GvHD displayed more PD-1 and were less likely to express the lymph node homing receptor CCR7.

Conclusion: Taken together, these data suggest that common features of immune dysregulation may define GvHD across transplant contexts, while other features of CD4 T cell reconstitution are found both with and without GvHD. Monitoring immunologic maturation post-transplant would provides crucial insights into potential therapeutic targets and surveillance markers and better informs our understanding of persistent immune dysfunction after allo-HCT

No relevant conflicts of interest to declare.