W187 - Immunophenotypic Profiling Reveals Novel T Cell Subset Associated with “Tolerance” in Pediatric Transplant Recipients

Mahil Rao – Stanford University; Meelad Amouzgar – Stanford University; Andrea Reitsma – Stanford University; Josselyn Pena – Stanford University; Patricia Nova – Stanford University; Anika Shah – Stanford University; Sean Bendall – Stanford University; Carlos Esquivel – Stanford University; Olivia Martinez – Stanford University; Sheri Krams – Stanford University

Abstract Text: Achieving allograft health while minimizing chronic immunosuppression remains a challenge in pediatric solid organ transplantation. In a recent study we performed multilineage, single-cell analysis of the immune cell composition in pediatric solid-organ transplant recipients who received a heart, liver or kidney allograft (n=52); 24 children had stable graft function while 28 children experienced a rejection episode. Hierarchical clustering of the mean cell type proportion across allograft types and health states showed that a distinct subpopulation of CD4 T cells (CD45RA-,CD25+,CD5+,CD38-) was significantly (p < 0.05) associated with stable graft function, and were termed TOT cells.

The cosine similarity analysis of proteomics data from PBMC showed that TOT cells are phenotypically most similar to Tregs and least similar to CD4+ TEMRA. To further characterize the TOT cells, we developed an 8-marker flow cytometry panel (CD3, CD4, CD45RA, CD45RO, CD25, CD38, CD127, CCR7) to specifically sort Treg and TOT populations and performed 10x single-cell RNA-seq and TCR-seq with subsequent analysis in R and Loupe Browser.

Differentially expressed genes that were specifically associated with TOT cells included ANXA1, IL7R, TCF7, THEMIS, NELL2, KLRB1 and CD40LG while Treg expressed FOXP3, IKZF2, CTLA4, IL2RA, and RTKN2, consistent with their known function in immune suppression. TCR analysis indicates unique expansions of T cell clonotypes in TOT cells not seen in Treg. Further investigation into the immunoregulatory capacity of TOT cells could be instrumental in developing new strategies for enhancing graft survival.