Abstract
Allogeneic haematopoietic stem cell transplantation (HSCT) is a curative treatment for acute myeloid leukaemia (AML) in which donor-derived anti-leukaemia reactive T cells have an important role in disease control. However, relapse rates are high. AML is known to create an immunosuppressive microenvironment that likely limits the efficacy of allogeneic HSCT, and perhaps will also constrain other novel immunotherapeutic approaches being developed for the treatment of AML. Previous in vitro studies have investigated suppression of T cells by AML cells or supernatants from AML cell cultures. In this study, an in vitro model was established in which T cells were cultured in the presence of AML cells with the HS5 stromal cell line to better recapitulate the AML microenvironment.The expression of activation markers, proliferation and cytokine production by CD4+ and CD8+ T cells from healthy individuals stimulated non-specifically with αCD3/CD28 antibody coated-beads were significantly suppressed in the presence of AML cells with stromal cells. Inhibition was observed both in the context of immortalised AML cell lines and primary AML cells. A finding with therapeutic implications was that the AML microenvironment suppressed the activity of T cells from allogeneic HSCT patients and two types of leukaemia-reactive T cells that are being championed as potential novel immunotherapeutic strategies. The ability of Vδ2+ γδ T cells to lyse zoledronic acid sensitised AML cells was suppressed in the presence of stromal cells. Evaluation of αCD123 CAR T-cell recognition of AML cells in the presence of stromal cells showed that both cytolytic activity and cytokine production were significantly suppressed in the AML microenvironment. Investigation of the mechanistic basis for suppression indicated roles for both soluble factors and contact between T cells and AML cells. Neither immune checkpoint blockade with anti-PD-1 or anti-PD-L1 antibodies or the immunomodulatory drug lenalidomide counteracted suppression. Analysis of the gene expression profile of CD8+ T cells stimulated with αCD3/CD28 antibody coated-beads in the presence of AML cells with HS5 cells showed only subtle changes indicative of diminished overall activity. Of interest, responses to stimulation with αCD3 antibody coated-beads were not suppressed in the AML microenvironment, suggesting that inhibition may target the CD28 pathway. Consequently, naive and quiescent memory T cells that express CD28 might be more susceptible to suppression in the AML microenvironment.
In summary, an in-vitro co-culture model has been established that recapitulates inhibition of T-cell activity in the AML microenvironment. The platform can be used to investigate the important problem of how to circumvent suppression and thereby improve efficacy of current and new immunotherapeutic strategies that are being developed.
| Date of Award | 1 Mar 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Linda Barber (Supervisor) & Andrea Pepper née Buggins (Supervisor) |