Characterization of Donor-Specific Alloreactive CD4+ and CD8+ Cellular Immune T Cell Responses in the Lung Allograft and Blood in Lung Transplant Recipients

Purpose Lung transplantation remains the only therapeutic option for select patients with end-stage lung diseases, however chronic lung allograft dysfunction (CLAD) significantly limits long-term survival in lung transplant recipients (LTRs). Episodes of acute cellular rejection (ACR) are common and the major risk factor for developing CLAD, however little is known about donor-specific cellular T cell responses, as these have not been previously characterized in LTRs. Methods We used a novel ex vivo flow cytometric assay to assess donor-specific alloimmune responses from LTRs cells in lung allograft resident effector T cells (BAL-derived) and PBMC. Using a 6h in vitro re-stimulation protocol with either irradiated donor cells or donor lysate, we measured the frequencies of effector responses (IFN-γ, TNF-α, the cytotoxic marker CD107a, IL-17a, IL-13, IL-2 and the costimulation surface molecule, CD154) from CD4+ and CD8+ lung resident or blood compartment T cells. Results Overall the predominant alloreactive effector responses were donor-specific CD154 surface expression following in vitro re-stimulation with donor lysate in lung resident CD4+ T cells compared to the PBMC compartment, with minimal to absent expression on CD8+ T cells. Expression of surface CD154 was highly co-expressed with allospecific CD4+ T cells producing the Type-1 cytokines IFN-γ, TNF-α and CD107a suggesting CD154 as a marker for Type-1 effector function, but not Type-2 or Type-17 responses. In fact, donor-specific IL-13 and IL-17 responses were detectable in some patients but at significantly lower frequencies compared to Type-1 effector responses, suggesting a hierarchy of alloeffector immune responses. Comparison between the lung resident T cells and blood T cells revealed consistently increased donor-specific alloreactive frequencies in the lung allograft versus the periphery. Ongoing experiments are assessing the proliferative capacities of donor-specific alloreactive T cell populations in the blood compartment. Conclusion Together, these data indicate donor-specific alloreactive effector CD4+CD154+ lung resident T cells activated via the indirect allorecognition pathway are present in high frequencies in LTRs with histologic evidence or history of ACR and segregate to Type-1 effector cytokine responses.