Immunomonitoring in a phase II/III trial of therapeutic vaccination with CSF-470 plus BCG plus GM-CSF versus IFNa in patients with cutaneous melanoma

PAMPENA, MARÍA BETINA; LEVY, ESTRELLA MARIEL; BLANCO, PAULA; BARRIO, MARÍA MARCELA; MORDOH, JOSÉ

Conferencia; Tumor Immunology and Immunotherapy: A New Chapter.; 2014

Melanoma is the deadliest form of skin cancer. Once it has metastasized, treatment options are limited and prognosis is bleak. Immunotherapy is one of the current promising treatments for patients (pts) after surgery, but markers for prediction of immune response are still lacking. In a phase II/III randomized clinical trial (CASVAC-0401, NCT01729663), cutaneous melanoma pts with Stages IIB, IIC and III were randomized to receive CSF-470 versus medium-dose IFN-alpha in a 2:1 ratio. The duration of the study is two years, during which the vaccinated pts would receive 13 vaccinations. CSF-470 vaccine is a mini-allograft consisting of four lethally-irradiated allogeneic cutaneous melanoma cell lines, combined with BCG and rhGM-CSF as adjuvants with the goal of stimulating adaptive and innate immunity. Thirty one pts have been included so far in the study; 20 pts have been randomized to the vaccine arm and 11 to the IFN-alfa arm. The DMFS (distant-metastases-free-survival) is significantly longer for pts in the CSF-470 arm than in those of the IFN alfa arm (p=0.034, Gehan-Breslow-Wilcoxon Test); besides, quality of life is significantly better in the CSF 470 arm. Looking for parameters involved in the immune system stimulation in vaccinated pts, DTH (Delayed-Type Hypersensitivity) and lymphocyte subsets were periodically evaluated. A significant increase in the DTH response between NED (non evident disease) and PRO (progressed) was observed in vaccinated pts (p=0.0362, unpaired t test with Welch?s correction). In order to investigate if the increase in DTH was accompanied by changes in lymphocyte peripheral populations, we investigated changes between pre-and post-treatment samples from 24 enrolled pts, 16 from the vaccine arm and 8 from the IFN alfa arm. We did not observe significant differences between PRE and POST1 samples (6 months; five vaccinations) in T CD4+, CD8+ or regulatory cells, neither in vaccinated nor in IFN alfa treated pts. Furthermore, we did not detect any changes in the frequencies of T CD8+ specific clones against MART-1 or gp100 Ags after treatment in HLA*0201 pts. Instead, we observed that only vaccinated pts increased the percentage of Natural Killer (NK) in the POST1 sample (PRE 16.6±8.0% vs POST1 22±12.4% p=0.0106, paired t test). Given these observations, we investigated, using a degranulation assay after challenge with live melanoma cell lines or K562 cells, if NK cells functionality was also augmented. Nevertheless, we did not see significant differences in NK cell activity after vaccination or IFN alfa treatment. In contrast, we observed significant increases in antibody (Ab) responses against melanoma cells in vaccinated pts sera, that was not observed in IFN alfa treated pts, as determined by ELISA (vaccine arm: PRE 0.3±0.2 vs POST1 0.8±0.3; p0.05, paired t test). Anti-melanoma Abs increased both in NED and in PRO vaccinated pts. In conclusion, we suggest that the increase in circulating NK cells that coexist with anti-melanoma Abs could contribute to eliminate circulating tumor cells, thus hampering further metastatic dissemination. Also, since DTH was clearly increased in responding vaccinated pts, we suggest that lymphocyte subsets located in peripheral tissues, which give rise to DTH reactivity, would more closely reflect clinical responses and should receive closer examination than circulating lymphocytes populations. Efforts to understand the impact of CSF-470 in the pts´ immune system are needed to identify the effectors involved in clinical responses.