{
  "abstract": "Background GPRC5D is a G protein-coupled receptor that is expressed on multiple myeloma cells but absent from most healthy tissues. It is an attractive target for anti-tumor modalities including T cell-engaging multispecific antibodies. Antibodies that simultaneously engage GPRC5D and other molecules, including BCMA and CD3, to activate T cells are anticipated to provide excellent efficacy as monotherapies.Methods Multipass membrane proteins are valuable therapeutic targets but are largely inaccessible for antibody discovery due to structural complexity and high conservation. We developed an antibody discovery platform (MPS), tailored for membrane proteins, that utilizes advanced immunization strategies to deliver antibodies against native epitopes.We isolated antibodies against GPRC5D and engineered multispecific GPRC5DxCD3 and GPRC5DxBCMAxCD3 molecules using multiple formats and CD3 arms that encompass different geometries and binding stoichiometries. GPRC5D multispecific antibodies were tested for target specificity using Integral Molecular’s Membrane Proteome Array (MPA). They were also tested for in vitro potency and cytokine release using MM.1R and RPMI 8226 multiple myeloma cell lines. In vivo efficacy for a subset of antibodies was determined using xenograft models in humanized mice.In addition, we are engineering the GPRC5D moiety of our lead antibody to have increased species cross-reactivity and affinity with cynomolgus GPRC5D through the use of our Paratope-PLUS CDR-scanning platform. This involves comprehensive mutagenesis of each residue to all 19 other amino acid variants.Results We immunized chickens with GPRC5D, obtained high-titer immune responses, and configured the resulting antibodies as T cell-engaging multispecific molecules. These were configured with a CD3 binding arm, and for select molecules, an additional binding arm targeting BCMA. A subset of antibodies displayed potent T cell-mediated cytotoxicity with picomolar potency on multiple myeloma cell lines.Bispecific and trispecific antibodies demonstrated a large window between cell killing and cytokine release. GPRC5D multispecific antibodies also showed robust tumor control against multiple myeloma xenografts in a humanized mouse model. Antibody specificity profiling showed high specificity binding to the intended targets, but not to other proteins across the membrane proteome.Saturating mutagenesis of the CDR regions of the GPRC5D-specific moiety of the lead antibody identified variants with increased reactivity against the cynomolgus ortholog, enabling progress towards a preclinical candidate that can be tested in non-human primates.Conclusions GPRC5D multispecific antibodies hold promise as potent and safe therapeutics for multiple myeloma.",
  "authors": [
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Daniel Rogers"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Hayley Roth"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Ileine Sanchez"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Trevor Barnes"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Valerie Fiers"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Breanna Tyrell"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Amelia Snyder"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Kyle Doolan"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Benjamin Doranz"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Ross Chambers"
    },
    {
      "affiliations": [
        "Integral Molecular, Philadelphia, PA, USA"
      ],
      "name": "Joseph Rucker"
    }
  ],
  "title": "981 GPRC5D multispecific antibodies targeting multiple myeloma",
  "uid": "dbe58fa6-f14d-5ce5-8285-022d9e8f8da0"
}