Cancer vaccines have overall had a record of failure as an adjuvant therapy for malignancies that are treated with alkylating chemotherapy, and the contribution of standard treatment to that failure remains unclear. Vaccines aim to harness the proliferative potential of the immune system by expanding a small number of tumor-specific lymphocytes into a large number of anti-tumor effectors. Clinical trials are often conducted after treatment with alkylating chemotherapy, given either as standard therapy or for immunomodulatory effect. There is mounting evidence for synergy between chemotherapy and adoptive immunotherapy or vaccination against self-antigens; however, the impact of chemotherapy on lymphocytes primed against tumor neo-antigens remains poorly defined. We report here that clinically relevant dosages of standard alkylating chemotherapies such as temozolomide and cyclophosphamide significantly inhibit the proliferative abilities of lymphocytes in mice. This proliferative impairment was long lasting and led to quantitative and qualitative defects in B and T cell responses to neo-antigen vaccines. High affinity responder lymphocytes receiving the strongest proliferative signals from vaccines experienced the greatest DNA damage responses, skewing the response toward lower affinity responders with inferior functional characteristics. Together these defects lead to inferior efficacy and overall survival in murine tumor models treated by neo-antigen vaccines. These results suggest that clinical protocols for cancer vaccines should be designed to avoid exposing responder lymphocytes to alkylating chemotherapy.

The effect of alkylating chemotherapy on cancer vaccines is controversial, with numerous reports of immune stimulation via Treg depletion following cyclophosphamide and temozolomide treatment. Using a pre-clinical model of a cancer vaccine in both naïve and tumor bearing animals, we observed that the direct anti-proliferative effect of drugs such as temozolomide or cyclophosphamide reduced the quantity of vaccine induced immune responses in a dose dependent manner. Amounts of temozolomide exposure in mice that duplicated human pharmacokinetic exposure and lymphopenia led to lower numbers of CD8 T cells elicited by vaccination with the model antigen ovalbumin. In vitro experiments with purified OT-I CD8 T cells implicated activation of DNA damage responses within strongly proliferating cells as the cause of this diminished immunity. ATM phosphorylation was greater in temozolomide or cyclophosphamide exposed OT-I cells stimulated with the canonical SIINFEKL peptide relative to variant peptides that trigger weaker TCR signaling. In vaccinated mice, this activation of DNA damage response in lymphocytes receiving the highest intensity TCR signals lead to lower avidity of responder cells for cognate antigen and lower effector function. These quantitative and qualitative defects of vaccine driven responses lead to inferior efficacy and loss of survival benefit in murine models. Mice bearing ovalbumin peptide expressing glioma had faster tumor growth and shorter survival following temozolomide and vaccine relative to vaccine only treated mice. Similar defects of vaccine generated responses and a loss of survival benefit relative to controls were observed in response to a neo-antigen vaccine following cyclophosphamide pre-treatment in melanoma bearing mice. The clinical relevance of this finding is demonstrated by a phase II cancer vaccine trial in metastatic melanoma patients where vaccine only patients survived a median of 4.2 years versus less than 8 months in patients treated with low dose cyclophosphamide before vaccine. Citation Format: Adam J. Litterman, David M. Zellmer, Karen L. Grinnen, Arkadiusz Z. Dudek, David A. Largaespada, John R. Ohlfest. DNA damage response in responder lymphocytes reduces vaccine efficacy following alkylating chemotherapy. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B23.