Abstract 1909: B cells present tumor antigen and mediate anti-tumor immunity induced by a combined immune-stimulatory/conditional cytotoxic therapy for glioblastoma
Authors: Candolfi Marianela , Curtin James F. , Yagiz Kader , Assi Hikmat , Wibowo Mia , Ahlzadeh Gabrielle , Foulad David , Kroeger Kurt M. , Tesarfreund Matthew , Alden Anderson , Liu Chunyan , Dunn Robert , Lowenstein Pedro , Castro Maria G. 
Published: February 2011

Abstract
Glioblastoma multiforme is a very invasive brain tumor of glial origin that bears a dismal prognosis. We have developed adenoviral vectors (Ads) expressing TK (Ad-TK; a conditional cytotoxic molecule) and Flt3L (Ad-Flt3L; an immune-stimulatory cytokine), which increase the survival of rodent models of glioblastoma. CD4+ and CD8+ T cells are necessary for Ad-TK+Ad-Flt3L-mediated tumor regression and immunological memory. Here we investigated whether B cells are also involved in GBM regression following Ad-TK+Ad-Flt3L treatment. While Ad-TK+Ad-Flt3L induced tumor regression and long term survival in 60% of the wild type (WT) mice, the treatment completely failed in B-cell deficient Igh6−/− mice. Similarly, in the treatment failed in WT mice depleted of total B cells (using anti-CD20 Abs), or marginal zone B cells (MZB, using anti-CD11a and anti-CD49d Abs). Although we did not find expansion of spleen CD19+ B cells, the number of MZB cells increased 7 days post-treatment. We did not find changes in the number of B cells within the tumor mass and we could not detect circulating Abs against tumor cells. Although B cells are well known by their role as producers of Ag specific immunoglobulins, they can also act as efficient antigen presenting cells (APCs). The clonal expression of BcR and the high specific avidity for Ag allow B cells to accumulate and concentrate low density extracellular Ag for presentation to T cells, lowering the threshold of Ag density required for triggering adaptive immune responses. Thus, we then studied whether B cells could be acting as tumor antigen presenting cells triggering the anti-tumoral immune response induced by Ad-TK+Ad-Flt3L. We found that treatment with Ad-TK+Ad-Flt3L led to an increase in the number of B cells in the cervical lymph nodes. B cells purified from the cervical lymph nodes of Ad-TK+Ad-Flt3L-treated mice, but not from control mice, significantly increased the proliferation of allogeneic T cells purified from spleen of naïve Balb/c mice. Tumor-specific T cell clonal expansion was studied in an ELISPOT using splenocytes from tumor-bearing WT or Igh6−/− mice treated with saline or Ad-TK+Ad-Flt3L, and stimulated with Trp2180–188, a MHCI-associated GL26 tumor antigen. Tumor-specific T cell precursors were detected only in Ad-TK+Ad-Flt3L-treated WT mice, but we did not observe any increase in the frequency of tumor antigen specific T cells in Igh6−/− mice. Our data indicate that B cells act as antigen presenting cells, facilitating the clonal expansion of tumor antigen specific T cells, which leads to brain tumor eradication and immunological memory.
Support: NIH/NINDS Grant 1R21-NS054143, 1UO1 NS052465 and 1RO1-NS057711 to M.G.C.; NIH/NINDS Grants 1 RO1 NS 054193, RO1 NS061107 and 1R21 NS047298 to P.R.L. M.C. is supported by NIH/NINDS 1F32 NS058156.
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 1909.