Featured Poster Abstract 84: CD8 T cell-mediated immune responses are critical to the increased efficacy of Doxil in BRCA1 deficient tumors Gina Mantia-Smaldone, Victoria Gamerman, Phyllis Gimotty, Regina Loomis, Lukas Ronner, Christopher Morse, Sandra Orsulic, Stephen Rubin, George Coukos, Sarah Adams
BRCA-deficient tumors are vulnerable to the immunomodulatory effects of Doxil • 56% of women with recurrent BRCA-associated ovarian cancer demonstrated a response to Doxil1 • In addition to causing DNA damage, Doxil increases the vulnerability of ovarian cancer cells to T cell attack • Immunophenotypic changes in response to Doxil are more pronounced in BRCA-/- cells • BRCA-/- tumors recruit higher numbers of T cells after Doxil exposure • We hypothesized that the immunogenicity of BRCA-/- tumors contributes to the improved clinical response to Doxil among women with hereditary ovarian cancer • The role of T cells in tumor clearance following exposure to Doxil was tested using a murine BRCA1-/- ovarian cancer model Expression of Fas is associated with increased Fas-FasL mediated T cell cytotoxicity; MHC I expression, which is higher in BRCA-/- cells, is required for a CD8 T cell response Evaluated in a cohort of 23 women with BRCA mutations and 41 women with sporadic cancer treated at three institutions between 2000-2010 for recurrent cancer. The response to Doxil was associated with a significant improval in overall survival 1Adams SF et al, Gynecol Oncol 2011
Doxil increased intratumoral T cell recruitment and overall survival in mice with BRCA1- tumors Both CD4 and CD8 T cell populations were present in BRCA1- tumors and ascites Doxil exposure increased cytotoxic CD8 T cells and reduced suppressive FoxP3 T cells Doxil therapy significantly prolonged the survival of animals with BRCA1- tumors P=0.0407 Survival Distribution Function Doxil Control Survival (Days) Survival measured from the time of tumor inoculation until animals reached 30g due to ascites accumulation Flow cytometry was performed on tumor, ascites, spleen and peripheral blood mononuclear cells (PBMCs). Illustrated are the portion of CD45+/CD3+ T cells present in representative tumor or ascites samples for placebo or Doxil treated mice.
The survival advantage associated with Doxil treatment persisted in the absence of CD4 T cells An immunodepleting antibody successfully eliminated CD4 T cells from BRCA1- tumors and ascites In the absence of CD4 T cells, the proportion of CD8 T cells was higher in Doxil-treated animals Doxil significantly prolonged the survival of CD4-depleted animals with BRCA1- tumors P=0.0079 Survival Distribution Function Doxil Control * p< 0.05 Survival (Days) After treatment with anti-CD4 antibody, a population of CD4-/CD8- cells persisted Survival measured from the time of tumor inoculation until animals reached 30g due to ascites accumulation *
There was no statistically significant difference in survival after Doxil treatment in the absence of CD8 T cells An immunodepleting antibody successfully eliminated all CD8 T cells from BRCA1- tumors and ascites In mice lacking CD8 T cells, the proportion of mature CD4 T cells, but not suppressive FoxP3 T cells, was higher after Doxil treatment The survival among animals depleted of CD8 cells was not improved with Doxil treatment * p< 0.05 P=0.0952 Doxil Survival Distribution Function Control Survival (Days) After treatment with anti-CD8 antibody, a population of CD4-/CD8- cells persisted Survival measured from the time of tumor inoculation until animals reached 30g due to ascites accumulation *
Conclusions Limitations: These results represent a small pilot study and need to be confirmed in larger cohorts Unfortunately the national Doxil shortage has limited our ability to conduct planned experiments • Doxil improved survival in a BRCA1- model of ovarian cancer • This effect persisted in the absence of CD4 T cells but is diminished in the absence of CD8 T cells • Cytotoxic CD8 T cells are necessary for the enhanced response to Doxil observed in BRCA1- tumor bearing mice • BRCA1- deficient ovarian cancers may be more susceptible to immunotherapeutic strategies This work was supported by a grant from the