99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA
Immune Modulation 1: Poster Presentations - Proffered Abstracts |
Abstract #2089
Prediction of outcome after anti-cancer immune stimulation by thermochemotherapy in a rat breast cancer model
Frederick Strebel,
Manisha Singh,
R. Wanda Rowe,
Dorothy Lewis and
Joan Bull
University of Texas Medical School, Houston, TX, Baylor College of Medicine, Houston, TX
BACKGROUND: Whole-body fever-range thermal therapy (FR-WB-TT), when optimally scheduled with chemotherapy, enhances the anti-cancer activity of many chemotherapy drugs. In the clinically relevant MTLn3 rat mammary adenocarcinoma model, oxaliplatin (Ox) given at sub-maximally tolerated doses 24h before FR-WB-TT reproducibly results in a 50% cure rate. Cured rats are immune to re-challenge with the same tumor. After initial growth inhibition tumors regrow in all rats, but starting around 10-12 days post-treatment partially responding and ultimately cured rats begin to regress both their primary tumors and lymph node metastases. Acute response during the first 4-5 days, however, is not predictive of long term outcome. Are there early markers of response to predict cure? Can additional treatment turn non-responders into responders? To begin answering these questions, we investigated the proliferative and activation responses of CD8+ T-cells to Ox + FR-WB-TT thermochemotherapy. METHODS: Female Fischer 344 rats bearing an orthotopically implanted syngeneic MTLn3 tumor were treated with Ox (10 mg/kg i.v.) 24 h before FR-WB-TT (40°C for 6 h). Peripheral blood mononuclear cells (PBMC), Ficoll-separated from whole blood, and labeled with carboxyfluorescein succinylester (CSFE) were examined by flow cytometry for cell proliferation 6 and 10 days after Ox treatment. Separated lymphocytes were stimulated in vitro with MTLn3 breast or syngeneic 9L glioma brain tumor cells and CD25 expression was examined after 2 days of restimulation. Anti-tumor effect was assessed by comparing tumor volume in treated and control animals. RESULTS: 50% of treated animals were cured and lived a normal life-span. The other 50% either partially responded or had no response at all. Cured animals were immune to re-challenge with MTLn3 cells but not to 9L glioma cells. CD8+ cell counts, determined by a bead counting method directly from whole blood, were significantly higher for the eventual responder animals on days 6 and 10 after treatment. Partial responders had CD8+ cell counts intermediate between non-responders and cured animals. Rats that later rejected their tumors showed a loss of CFSE label compared to non-responding rats with later tumor progression. There was 56% CFSE loss in the eventual responders compared to 34% CFSE loss in rats that did not reject tumor. Percent CD25 activation after in vitro stimulation was also higher in cured animals than in non-responders or partial responders. CONCLUSIONS: CD8+ cell proliferation (increased numbers of CD8+ cells) and functional activation (CD25 expression) may be predictive of curative therapy early after treatment. Further work is ongoing to improve assays of CD8+ T-cell quantity and function, and to understand the mechanisms of immune stimulation of chemotherapy by thermal therapy with a view to curative intervention for non-responders.
