Autologous Tolerogenic Dendritic Cells for Rheumatoid Arthritis-2 (AuToDeCRA-2) Study: Protocol for a single-centre, experimental medicine study investigating the route of delivery and potential efficacy of autologous tolerogenic dendritic cell (TolDC) therapy for Rheumatoid Arthritis

Background: Dendritic cells are professional antigen presenting cells with the ability, in their immature state, to induce tolerance in T-cells. A protocol to develop phenotypically stable tolerogenic dendritic cells (TolDC) was developed in Newcastle and cells administered to participants in the phase I AuToDeCRA study, demonstrating that TolDC were safe and well tolerated. More knowledge of the TolDC product is now needed, such as optimal dose, route of administration and antigen loading. Establishing this and developing a biomarker profile to demonstrate favourable immunomodulation is the focus of AuToDeCRA-2. Methods: AuToDeCRA-2 is a non-commercial, phase IIa, 5-arm, randomised, unblinded, single centre study. It is designed to demonstrate and compare immunomodulation achieved by TolDC administered via three distinct routes: intra-nodal, intra-articular, intra-dermal and, in the case of intra-nodal administration, at 2 doses. Participants will be randomised to one of these four active intervention arms or standard care. Participants in intervention arms will receive a single dose of TolDC loaded with synthetic citrullinated peptides (TolDC _CitPep ) representing disease relevant autoantigens. 20 Anti-Citrullinated Peptide Antibody (ACPA) positive, shared epitope positive Rheumatoid Arthritis patients with nil-to-moderate disease activity will be randomised in an allocation ratio of 1:1:1:1:1. Participants will be followed up with immune state monitoring performed on peripheral blood samples at baseline, 1, 3 and 6 weeks and lymph node aspirates at baseline and 1 week, alongside clinical assessment performed throughout and additionally at 12 weeks. Discussion: TolDC therapy is an emerging cellular therapy aimed at reversing the underlying abnormality in autoimmune disease by inducing tolerance to autoantigen. Expected challenges to this study include recruitment of potentially asymptomatic participants to a complex and intensive experimental medicine study. Limitations include the relatively small number of participants although adequate to address the aims of the study. Establishing acceptable route(s) of administration as well as demonstrating favourable immunomodulation via the development of a biomarker profile is the focus of AuToDeCRA-2, which aims to address some of the existing scientific gaps necessary for the development of TolDC therapy in autoimmune disease. Trial registration: ISRCTN, ISRCTN14999554. Registered on 27 ^th September 2023, https://doi.org/10.1186/ISRCTN14999554