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Alun R Barnard, Markus Groppe, Leonard Seymour, Robert E MacLaren; Immunological testing in choroideremia patients undergoing gene therapy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3296.
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Adeno-associated viral (AAV) vectors have been assessed for gene therapy in several diseases and have a good safety profile in clinical trials. Until now, the only retinal disease investigated for treatment using AAV-based gene therapy has been Leber congenital amaurosis type 2 (LCA2). Recently, a clinical trial of gene therapy for choroideremia (CHM) was initiated with the primary objective of assessing the safety and tolerability of AAV.REP1 vector administered at two different doses to the retina in 12 patients. As part of this, the immunological responses to the delivery vector were assessed.
Peripheral blood mononuclear cells (PBMCs) were isolated and cryopreserved from blood samples collected at pre-operative baseline, 1-2 weeks post-surgery and 1 month post-surgery. Ex vivo cell mediated immune responses were assessed using an Interferon-gamma (IFN-γ) Enzyme-linked immunosorbent spot (ELISpot) assay (Mabtech AB, Stockholm, Sweden). T-cell activation (spot formation) was assessed after exposure to AAV2 capsids and REP1 mimotopes (overlapping 15-mer peptides mimicking potential epitopes derived from REP1 protein coded by the therapeutic transgene). Responses were assessed relative to negative control wells (media) and positive control wells consisting of viral mimotopes (CEF peptide pool) and potent activators (CD3 mAb and PHA-M).
In five patients treated with low dose 10E+10 genome particles (gp) gene therapy, there was no significant reaction to REP1 peptide pools or AAV2 capsid protein when compared to appropriate negative and positive control wells. Furthermore, there was no change in the relative spot forming response to REP1 peptide pools or AAV2 capsid protein across the time points tested. In one patient treated with the low dose gene therapy, there was a non-significant increase in T-cell activity in response to REP1 peptides post-surgery, however, the CEF positive control response was very poor in this patient at baseline. Hence the results may represent a low and generally variable T-cell response, which cannot be confirmed.
Delivery of AAV.REP1 vector up to a dose of 10E+10 gp does not elicit significant systemic immune responses in six CHM patients treated consecutively. It will be important to assess whether immunological responses remain negative at higher doses that will be given in the CHM gene therapy trial.
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