Persistence of Increased Type-1 Alloeffector CD4+ T Cell Responses from ACR into CLAD in Lung Transplant Recipients

Purpose Chronic lung allograft dysfunction (CLAD) significantly limits long-term survival in lung transplant recipients (LTRs) and episodes of acute cellular rejection (ACR) are the major risk factor for CLAD. To study the immune mechanisms leading to ACR/CLAD, we have characterized donor-specific alloreactive effector lung T (bronchoalveolar lavage; BAL) cells and peripheral blood mononuclear cells (PBMC) via indirect/direct allorecognition responses in LTRs with/without histologic evidence of ACR and into those who developed CLAD. Understanding these mechanisms may lead to new therapies to prevent CLAD. Methods To assess alloeffector T cell responses from LTRs cells in BAL and PBMC, we used an ex vivo flow cytometric assay and donor alloantigen. LTRs with/without ACR (median 4 months), and a subset who developed CLAD (median 20 months) were studied. The effector responses (IFN-γ, TNF-α, CD107a, IL-17a, IL-13, IL-2 and the costimulation surface molecule, CD154) to donor alloantigen were measured using either donor lysate or irradiated cells in a 6 h in vitro re-stimulation assay. We also used single cell RNAseq analysis to analyze the transcriptome in response to alloantigen in isolated BAL T cells from LTRs with CLAD. Results The predominant BAL alloeffector responses during active ACR were similar between CD8+ and CD4+ T cells, with a Type-1 effector profile and IFN-γ responses predominant. The CD4+ T cells alloeffector responses were higher in BAL>PBMC (p Conclusion Type-1 alloeffector responses during ACR are similar between CD8+ and CD4+ T cells, with the latter predominant in BAL. Progression into CLAD is associated with persistently elevated CD4+ alloeffector responses with a potential cytotoxic CD4+ subset playing an important role.