B cells presentation of tumor antigen is required for therapeutic efficacy of an immunotherapeutic approach that combines immune-stimulatory and conditional cytotoxic adenoviral vectors for glioblastoma.

MARIANELA CANDOLFI; JAMES F CURTIN; KADER YAGIZ; HIKMAT ASSI; KURT M KROEGER; MATTHEW TESARFREUND; ANDREW ALDEN; CHUNYAN LIU; ROBERT DUNN; PEDRO R LOWENSTEIN; MARIA G CASTRO

New Orleans, LA, EEUU

Congreso; Society for Neuro-oncology 14 Annual Meeting; 2009

We have developed adenoviral vectors (Ads) expressing HSV1-TK (Ad-TK; a conditional cytotoxic molecule) and Flt3L (Ad-Flt3L; an immune-stimulatory cytokine), which increase the survival of rodent models of GBM. CD4+ and CD8+ T cells are necessary for Ad-TK+Ad-Flt3L-mediated tumor regression and immunological memory. Now we investigated whether B cells play a role in GBM regression following Ad-TK+Ad-Flt3L. METHODS We studied efficacy of Ad-TK+Ad-Flt3L in tumor-bearing B-cell-deficient Igh6-/- mice and in wild type mice depleted of B cells. B cells were collected and characterized from brain tumor, lymph nodes and spleen. RESULTS While Ad-TK+Ad-Flt3L induced tumor regression and long term survival in 60% of the wild type mice, the treatment failed in B-cell-deficient Igh6-/- mice. Similarly, Ad-TK+Ad-Flt3L treatment failed in wild type tumor-bearing mice depleted of total or marginal zone B cells. Ad-TK+Ad-Flt3L increased the number of MZB cells in the spleen, but did not change the B cell content in the tumor mass or draining lymph nodes. We could not detect circulating antibodies against tumor cells. Then, we studied whether B cells could present tumor antigen during the onset of the anti-tumoral immune response induced by Ad-TK+Ad-Flt3L. We found that B cells purified from the draining lymph nodes of Ad-TK+Ad-Flt3L-treated, but not from control tumor bearing mice increased allogeneic T cell proliferation. T cell clonal expansion was also studied by ELISPOT using splenocytes from tumor-bearing wild type or Igh6-/- mice treated with saline or Ad-TK+Ad-Flt3L, and stimulated with Trp2180-188, an MHCI associated GL26 tumor antigen. Trp2-specific T cell precursors were detected only in Ad-TK+Ad-Flt3L-treated wild type mice, but we did not observe any increase in the frequency of tumor antigen specific T cells in Igh6-/- mice. CONCLUSIONS Our results indicate that B cells play an important role in facilitating brain tumor regression, most likely by acting as antigen presenting cells, rather than antibody-producing cells.