14 A patient derived antibody targeting the tetraspanin CD9 inhibits tumour progression and metastasis

Abstract

IntroductionImmune reactions against cancer cells can be induced by immunotherapy. We investigated the possibility that an antibody response has contributed to the success of the immunotherapy of a cancer patient.Material and methodsA patient with metastatic melanoma was successfully treated by adoptive transfer of ex vivo expanded autologous tumour reactive T cells. This patient is still tumour free 11 years after treatment and had developed both CD4 and CD8 T cells specific for neoantigens. We isolated B cells from peripheral blood and generated clones following immortalization by forced expression of Bcl-6 and Bcl-xL.Results and discussionsA B-cell clone producing antibody AT1412 recognising a novel cell surface epitope on the tetraspanin CD9 was isolated. CD9 is widely expressed and plays a role in many phases of disease progression. AT1412 showed significant stronger binding to melanoma cells than to melanocytes indicating that the AT1412 epitope is overexpressed on tumour cells. In addition, AT1412 also strongly reacted with many solid tumours types including colon, pancreas and, breast cancer, as well as liquid tumours such as AML, B-ALL and multiple myeloma. Further analysis revealed that AT1412 favours binding to a clustered form of CD9. These clusters are dependent on the palmitoylation state of CD9 and known to be enriched on the surface of tumorigenic cells.Using immunodeficient mice harbouring a human immune system (HIS mice) we observed that AT1412 blocks tumour progression as a single agent and more strongly in combination with an anti-PD1 antibody. Highly significant, AT1412 strongly stimulated the influx of macrophages and CD8 +T cells into the tumour providing an explanation for the synergistic effects of anti PD1 and AT1412.In sharp contrast to previously described anti-CD9 antibodies AT1412 does not induce aggregation of platelets. This is in line with an absence of antibody-related adverse events, including thrombosis and colitis, in the patient during and after treatment. Altogether this indicates that the antibody is safe for use in humans.ConclusionThese data suggest that antibody AT1412 contributed to the success of the immunotherapy in this patient. This antibody could provide help to tumor-reactive immune cells in the eradication of tumour masses and is as such an attractive candidate drug for cancer treatment.Our results show that the B-cell repertoire of a patient who is cured after immunotherapy provides a highly attractive source of antibodies with clinical potential.