Panchal, Neelam; (2020) Developing novel therapies for X-linked lymphoproliferative disease type 1. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

X-linked lymphoproliferative disease type 1 (XLP1) arises from mutations in the SH2D1A gene encoding SAP, an intracellular adaptor protein expressed in T, NK and NKT cells. SAP is a key regulator of immune function and deficiency leads to abnormalities of NK cell cytotoxicity, NKT cell development and T cell dependent humoral function. The absence of SAP in CD4+ T follicular helper (TFH) cells leads to defective long-term humoral immunity. Curative treatment is limited to allogeneic haematopoietic stem cell transplant with outcome reliant on a good donor match. Given that the majority of symptoms arise from defective T cell function, we investigated whether the infusion of gene corrected T cells could correct known effector cell defects associated with the condition. Proof of concept in vivo and in vitro experimental models demonstrated functional correction in both SAP mediated humoral immunity and cytotoxicity, recapitulating disease phenotypes seen in XLP1 patients. We achieved this by transferring CD3+ lymphocytes from SAP-/- donor mice that were transduced ex vivo with a gammaretroviral vector containing codon optimised human SAP cDNA before infusion into sub-lethally irradiated SAP-/- recipients. Reconstituted animals were then challenged 8-10 weeks post- infusion with the T cell dependent antigen NP-CGG and analysis performed after 10 days. Next, a SIN-lentiviral construct with codon optimised SAP transgene expression driven by the constitutive EFS promoter was employed to efficiently transduce XLP1 patient T cells resulting in improved cytotoxicity and TFH cell function in vitro. This work was then translated into an in vivo LCL lymphoma model in NSG mice to demonstrate that adoptive transfer of gene corrected patient CTLs reduces tumour burden upon restoration of SAP mediated cytotoxic function. In parallel to this we also investigated the use of alternative ‘bridging’ therapies such as small molecule inhibitors targeting SHP2, a key protein tyrosine phosphatase implicated in the SAP signalling pathway to determine if we can achieve similar restoration of cellular phenotypes with the inhibitor that may also hold clinical relevance. We show restoration of immunoglobulin and cytokine secretion through TFH: B cell co-culture assays, alongside rescue of cytotoxicity and re-stimulation induced cell death (RICD). Deep immunophenotyping and measurement of intracellular phosphorylation of signalling molecules (pSHP2, pERK, pAKT) are consistent with ablation of SHP2 mediated inhibitory signals and restoration of the key signalling events downstream of TCR/SLAM.

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