Proinflammatory and cytotoxic CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells are peripherally expanded in human...

T cell mediated immunity is reported to play a pathogenic role in cardiac allograft vasculopathy (CAV) in heart transplant (HTx) patients. However, peripheral blood CD8 ⁺ T cells have not been previously characterized in CAV. This study aimed to identify potentially pathogenic circulating CD8 ⁺ T cell populations in high grade CAV patients using cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq).

Peripheral blood mononuclear cells (PBMC) collected from International Society for Heart and Lung Transplant (ISHLT) grade 2 or 3 CAV (high grade CAV; n=6) and normal HTx (n=12) patients were analyzed using CITE-seq and VDJ-seq. Key findings were validated by flow cytometry in an independent patient cohort of age-matched CAV (n=11) patients, normal HTx (n=12) patients and healthy donor subjects (n=11).

Among the seven peripheral CD8 ⁺ T cell clusters, high grade CAV patients demonstrated a significantly higher proportion of the CD38 ⁺ HLA-DR ⁺ CD8 ⁺ effector memory T (Tem) cell cluster compared to normal HTx patients (median 6.2% vs 2.9%, p=0.01). CD38 ⁺ HLA-DR ⁺ CD8 ⁺ Tem cells showed clonal expansion, activated interferon-γ (IFNG) signaling and enhanced cytotoxicity with granzyme B (GZMB) and perforin (PRF) overexpression. Significantly higher proportion of the proinflammatory and cytotoxic CD38 ⁺ HLA-DR ⁺ CD8 ⁺ Tem cell cluster in high grade CAV compared to normal HTx patients was validated by flow cytometry. There was significantly increased clonal expansion of peripheral CD8 ⁺ T cells in high grade CAV compared to normal HTx patients (median Shannon index = 4.4 vs 6.1, p=0.03). CITE-seq identified LAIR2 as a potential biomarker for identifying high grade CAV patients as increased expression was found in CD38 ⁺ HLA-DR ⁺ CD8 ⁺ Tem cells. Plasma LAIR2 was significantly elevated in the high grade CAV (n=20) compared to normal HTx patients (n=20; 16.0 pg/mL vs 70.3 pg/mL, p=0.02).

We discovered and validated circulating CD38 ⁺ HLA-DR ⁺ CD8 ⁺ Tem cells to be significantly increased in high grade CAV compared to normal HTx patients. The proinflammatory and cytotoxic phenotype of this CD8 ⁺ T cell cluster suggest its potential pathogenic role in human CAV.

What is new?: This is the first study to identify clonal expansion of circulating CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells in human cardiac allograft vasculopathy. CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells possess both proinflammatory and cytotoxic characteristics, suggesting their potential pathogenic role in human cardiac allograft vasculopathy. LAIR2 is a potential signature gene of CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells. What are the clinical implications?: Circulating CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells and plasma LAIR2 protein are potential early biomarkers of cardiac allograft vasculopathy. Evaluation of CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells in longitudinal studies may reveal how this T cell cluster contributes to the development of human cardiac allograft vasculopathy. Inhibiting the expansion of CD38 ⁺ HLA-DR ⁺ effector memory CD8 ⁺ T cells and/or the LAIR2 pathway may become important therapeutic targets for prevention and treatment of human cardiac allograft vasculopathy.