Abstract 5599: Novel mechanism of synergistic effect of cancer immunotherapy and chemotherapy
Authors: Ramakrishnan Rupal , Assudani Deepak , Celis Esteban , Gabrilovich Dmitry 
Published: February 2011

Despite advances in the development of new chemotherapeutic drugs and improvements in radiation therapy, conventional cancer therapy often falls short of the goal of controlling tumor progression. Emerging clinical and pre-clinical evidence suggests that an immune response elicited by using vaccines augments the anti-tumor effectiveness of subsequent chemotherapy. The main objectives of this study are to determine if combining vaccines with chemotherapeutic agents would render tumor cells more susceptible to T cell mediated killing and to identify the mechanisms involved.

In this study we used three drugs with different mechanisms of action- Paclitaxel (TAX), Doxorubicin (DOX) and Cisplatin (CIS). Using Cr51 release assays, we found that all three agents, at very low doses, accelerated killing of antigen specific tumor cells by Cytotoxic T lymphocytes (CTLs). This effect was observed with CTLs specific to different antigens.

Perforin-granzyme and Fas-FasL pathways are two major mechanisms by which CTLs destroy target cells. All three drugs did not affect the expression of either Fas or FasL on tumor cells but caused dramatic increase in permeability of cell membrane to granzyme B (GrB). Receptor studies revealed that TAX, DOX, and CIS induced substantial increase in the expression of mannose-6-phosphate receptor (MPR) on human and mouse tumor cells, but not in normal cells. MPR is considered an important factor that together with perforin mediates GrB entry into the cell.

Using CTLs from normal (WT) and Perforin Knockout (PKO) mice, we evaluated the levels of CTL mediated killing in chemotherapy treated, antigen specific tumor cells. Simultaneously, we examined CTL mediated killing after blocking MPR receptors on tumor cells. Our data demonstrated that chemotherapy regulates GrB uptake via up-regulation of MPR and bypasses the requirement for perforin. Adoptive transfer of T cells from WT and PKO mice, in tumor models, followed by chemotherapy confirmed the efficacy of combination therapy in delaying tumor growth, independent of perforin.

Our data suggests a mechanism for the combined effect of CTLs and chemotherapy. Chemotherapy, administered immediately after vaccination or T-cell transfer, causes disruption of tumor stroma that allows for better penetration of antigen-specific T cells. In addition, chemotherapy causes substantial increase in MPR expression on tumor cells. Small number of activated CTLs interacting with tumor cells expressing tumor antigen, release GrB that can penetrate into neighboring tumor cells without requirement for perforin, initiating localized bystander killing. Thus large number of tumor cells including those that do not express specific antigen would be susceptible to the effect of CTLs.

This provides a rationale for treatment of advanced stage cancer patients by combining standard of care chemotherapy with relatively non-toxic and highly specific immunotherapy

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 5599.