Key role of B cell as antigen presenting cells in the anti-tumor immunity induced by a combined immune-stimulatory/conditional cytotoxic therapy for glioblastoma

MARIANELA CANDOLFI; KADER YAGIZ; JAMES F CURTIN; HIKMAT ASSI; MIA WIBOWO; GABRIELLE E ALZADEH; DAVID FOULAD; KURT M KROEGER; ANDREW ALDEN; CHUNYAN LIU; ROBERT DUNN; PEDRO R LOWENSTEIN; MARIA G CASTRO

Washington DC, EEUU

Congreso; American Society of Cell and Gene Therapy 13 Annual Meeting; 2010

Glioblastoma multiforme is an invasive brain tumor of glial origin that bears a dismal prognosis. We developed adenoviral vectors (Ads) expressing TK (Ad-TK; a conditional cytotoxic molecule) and Flt3L (Ad- Flt3L; an immune-stimulatory cytokine), which when used in combination in large intracranial GBM models, elicit tumor regression, long term survival and immunological anti-GBM memory. 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 involved in GBM regression following Ad-TK+Ad-Flt3L treatment by eliciting anti-GBM antibodies or acting as tumor antigen presenting cells. 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, the treatment failed in WT mice depleted of total B cells (using anti-CD20 Abs), or marginal zone B cells (MZB, using anti-CD11a+anti-CD49d Abs). Although we did not find expansion of spleen CD19+ B cells, the number of MZB cells increased 7 d post-treatment. We also detected an increase in the number of B cells infiltrating the tumor mass, but 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). Clonal expression of BcR and high specific avidity for Ag allow B cells to concentrate low density extracellular Ag for presentation to T cells, lowering the amount of Ag required for triggering adaptive immune responses. Thus, we studied whether B cells could be acting as tumor antigen presenting cells in response to Ad-TK+Ad-Flt3L treatment in our model. 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 na ve 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.