Background/Purpose:  Rheumatoid arthritis (RA) is an autoimmune disease leading to inflammatory destruction of the peripheral joints. Although pro-inflammatory T helper 1 (Th1) and/or Th17 cell responses play a central role in the immunopathology of RA, current therapies do not provide efficient inhibition of these pro-inflammatory T cells or their signature cytokines. In this study, we demonstrate that the peptide conjugate DerG-PG70 (CEL-4000) is able to inhibit Th1 and Th17 responses and can act as a therapeutic vaccine in an autoimmune mouse model of RA.

Methods:  Female BALB/c mice were immunized intraperitoneally (ip) with the recombinant G1 domain of human cartilage proteoglycan (PG) aggrecan in adjuvant. This G1-induced arthritis (GIA) model of RA can display Th1- or Th17-skewed cellular responses depending on the route of immunization (ip or id/sc, respectively). We elected to focus on the more aggressive ip-induced form with a Th1 signature phenotype (IFNg). Peptide conjugates composed of an immune cell binding motif (designated DerG or J) and the arthritogenic epitope of human PG (PG70) were constructed. DerG-PG70 (CEL-4000) or J-PG70 vaccine was administered with adjuvant twice (2 weeks apart) to the mice, beginning at the early phase of arthritis. Mice treated with adjuvant only served as controls. Disease severity was monitored by visual scoring of joint inflammation. Three weeks after the second vaccination limbs were processed for histopathology and serum was collected for measurement of pro- and anti-inflammatory cytokines. Spleen cell cultures were set up to examine binding of peptide conjugates to Th cells or antigen-presenting cells (APCs) and to determine Th cell cytokine profiles using flow cytometry and Millipore’s MagPix multiple cytokine assays.

Results:  The CEL-4000 vaccine significantly suppressed arthritis severity and limited joint damage in the ip-induced form of GIA. The other peptide conjugate (J-PG70) or single PG70 and DerG peptides were not therapeutically effective in the disease. Increased ratios of anti-inflammatory cytokines (IL-4 and IL-10) to pro-inflammatory IL-17 were found in the serum of mice vaccinated with CEL-4000 as compared to the other treatment groups. Spleen cells from mice with ip-induced GIA and vaccinated with either CEL-4000 or J-PG70 showed reduced production of Th1 and Th17 signature cytokines as well as other pro-inflammatory mediators in vitro as compared to controls. However, this inhibitory effect was found to be more potent in cell cultures of CEL-4000-treated than J-PG70 treated animals. In vitro cell binding experiments revealed preferential binding of the CEL-4000 peptide conjugate to Th cells whereas J-PG70 bound primarily to APCs.

Conclusion:  Our results suggest that while both peptide vaccines have an influence on the immune system, CEL-4000 powerfully down-modulates pro-inflammatory T-cell responses probably via direct binding to Th cells whereas J-PG70 does it indirectly, and less effectively, via binding to APCs. Robust inhibition of Th1, Th17, and pro-inflammatory pathways, as seen in mice with ip-induced GIA after receiving CEL-4000 vaccine, appears to be necessary for arthritis suppression.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-therapeutic-peptide-vaccine-reduces-pro-inflammatory-responses-and-suppresses-arthritis-in-the-cartilage-proteoglycan-g1-domain-induced-mouse-model-of-rheumatoid-arthritis/