Background: CD45RC is an isoform of CD45, a transmembrane tyrosine phosphatase, essential regulator of T and B cells antigen receptor signaling. CD45RC is expressed by most blood B cells while in T cells its high expression is restricted to Th1 precursor and Th1 cells, as well as TEMRA. We demonstrated that administration of an anti-CD45RC mAb in preclinical models of transplant rejection, graft versus host disease (GvHD), Duchene dystrophy or Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED) leads to prevention or control of the disease. RA is a chronic relapsing/remitting disease characterized by synovitis, joint deformity, loss of function and increased mortality. While T-cells are a major component in the pathogenesis, B-cells are also pathogenic.

Objectives: In this study, we deciphered the mechanism of action of the anti-human CD45RC mAb and assessed its effect in vitro and in vivo on human immune cell populations. We then assessed the potential of the anti-CD45RC mAb in an experimental model of rheumatoid arthritis.

Methods: Cells were isolated from peripheral blood. Apoptosis, antibody-Dependent Cellular Cytotoxicity (ADCC), antibody-Dependent Cellular Phagocytosis (ADCP) and Complement-Dependent Cytotoxicity (CDC) were assessed by Annexin V/DAPI staining. In vivo studies were performed in CD34+ immune-humanized NSG mice, in a model of xenogeneic GVHD in human PBMC-reconstituted immunodeficient NSG mice or in a model of collagen-induced arthritis (CIA) in rat.

Results: We demonstrated that the humanized anti-human CD45RC mAb induced CD45RC ^high T and B cell death mainly by direct apoptosis of CD45RC ^high cells expressing around 105 molecules per µm2 of membrane, inducing signaling but not cytokine release. We demonstrated contribution of ADCC and ADCP-mediated death of CD45RC ^high cells. Using in vivo studies in CD34+ immune-humanized NSG mice, we showed that a single iv administration of anti-CD45RC mAb induced an efficient killing of CD45RC ^high T and B cells as soon as day 1, this effect was dose and time-dependent and targeted cells recovered by day 24. We also showed a dose dependent efficacy in a model of xenogeneic GVHD in human PBMC-reconstituted immunodeficient NSG mice. Treatment with an anti-rat CD45RC mAb in a rat model of CIA efficiently prevented weight loss, mean arthritis severity, maximum score and AUC,in contrast to the isotype control mAb. Anti-CD45RC mAb completely inhibited anti-collagen antibody production, inflammation of the paws and GM-CSF secretion in the sera in contrast to controls. Efficacy of the anti-CD45RC mAb correlated with depletion of CD45RC ^high T and B cells by d3 (>94%) and until sacrifice with conserved Treg numbers. Analysis of RA patients showed in the blood presence of CD45RC ^high cells and a strong infiltration by CD45RC ^high cells of synovial tissues using IHC. Analysis of the potency of the anti-human CD45RC mAb demonstrated efficient apoptosis in vitro of CD45RC ^high T and B from blood cells from RA patients and HC.

Conclusion: Altogether our study demonstrates the mechanisms by which anti-human CD45RC mAb mediates CD45RC ^high T and B cell death to control immune responses. Our study demonstrates that anti-CD45RC mAb treatment is a potent immunomodulatory agent rebalancing the Treg/teff ratio to reduce joint inflammation and disease activity in RA and a potential alternative for first line DMARD. This highly specific targeting of cells involved in transplant rejection and autoimmune diseases could substantially improve the management of patients across a wide range of affections.

REFERENCES: [1] Besnard M. et al. Anti-CD45RC antibody immunotherapy prevents and treats experimental Autoimmune PolyEndocrinopathy Candidiasis Ectodermal Dystrophy syndrome. J Clin Invest. 2022. doi: 10.1172/JCI156507.

[2] Boucault L. et al.. Transient Antibody Targeting of CD45RC Inhibits the Development of Graft-versus-Host Disease. Blood Advances. 2020. doi: 10.1182/bloodadvances.2020001688.

[3] Picarda E. et al.. Transient antibody targeting of CD45RC induces transplant tolerance and potent antigen-specific regulatory T cells. JCI Insights. 2017 Feb 9;2(3):e90088.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: Cecile Bergua: None declared, Marine Besnard: None declared, Ghenima Ahmil: None declared, Laure-Helene Ouisse: None declared, Nadege Vimond: None declared, Apolline Salama: None declared, Berangere Evrard: None declared, Elise Brisebard: None declared, Alexis Collette AbolerIS Pharma, Frederic Blanchard: None declared, Thibaut Larcher: None declared, Ronald Van Brempt AbolerIS Pharma, Benoit Le Goff: None declared, Ignacio Anegon AbolerIS Pharma, AbolerIS Pharma, Carole Guillonneau AbolerIS Pharma, AbolerIS Pharma, AbolerIS Pharma.