Abstract 5341: Sensitivity of NHL to killing by anti-HLA-DR and anti-CD74 mAbs is increased by interferon-gamma

Abstract

Abstract Background: HLA-DR and CD74 are similarly, but not identically, expressed and induced by interferons on a variety of cells. Expression of both antigens on hematological malignancies led to their development as targets for antibody-based therapy. The humanized anti-CD74 monoclonal antibody (mAb), milatuzumab (Immunomedics Inc, Morris Plains, NJ), is in clinical evaluation for therapy of NHL, multiple myeloma (MM), and CLL after preclinical evidence of activity in these tumor types. A humanized anti-HLA-DR mAb, hL243γ4P (IMMU-114, Immunomedics) has demonstrated anti-tumor activity in vitro and in vivo, and clinical evaluation is planned. In addition to expression in hematologic cancers, these antigens are expressed on the surface of other tumor types, including melanoma and renal cell carcinoma, and in the cytoplasm of others, including pancreatic and colonic carcinomas, and glioblastomas (GBM). Methods: We examined whether the ability of anti-HLA-DR and anti-CD74 mAbs to kill cancer cells can be increased by using IFNγ as an inducer of antigen expression. Using a panel of diverse cancer cell lines (including NHL, MM, GBM, and pancreatic and colonic carcinomas), we examined IFNγ-induced changes in surface and cytoplasmic HLA-DR and CD74 expression. Sensitivity of malignant cells to milatuzumab and hL243γ4P was assessed with and without INFγ by cytotoxicity assays. Results: Without IFNγ surface expression of HLA-DR and CD74 were present on 2/2 NHL, 2/2 MM, and only weakly positive on 2/2 GBM cell lines. Surface CD74 and HLA-DR were weak or undetectable on 4/4 colon and 4/4 pancreatic carcinomas. Cytoplasmic CD74 and HLA-DR were seen in NHL, MM, GBM, and 1/4 colon and 1/4 pancreatic (CD74 only) carcinomas. Two-day incubation with IFNγ increased surface and cytoplasmic expression of both HLA-DR and CD74 in all the NHL and GBM, and 3/4 pancreatic cancer lines, but not MM cell lines. In all 4 colon lines, IFNγ increased cytoplasmic expression of both antigens, and surface expression of HLA-DR in 3/4 and CD74 in 2/4. Upregulation of HLA-DR and CD74 ranged from 23-3700%. Increased killing by both hL243γ4P (58%) and milatuzumab (33%) was seen in vitro after INFγ exposure in WSU-FSCCL NHL cells. No cell killing was observed using these mAbs in vitro on U118 (GBM), Capan-1 (pancreatic carcinoma), or LoVo (colon carcinoma), despite upregulation of the antigens in these cell lines. A CD74-transfected version of the U118 GBM cell line has been prepared for comparison of milatuzumab sensitivity based on antigen density only. Conclusions: Cell surface and cytoplasmic expression of CD74 and HLA-DR are increased on cell lines from a variety of cancer types after INFγ exposure. This increased expression correlates with increased toxicity of anti-HLA-DR and anti-CD74 mAbs in a NHL cell line, and is under evaluation in other cancer types. These studies could prove useful in predicting the potential benefit of combined INFγ and mAb therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5341.