CpG-ODN systemic administration before B16 melanoma cells inoculation increases tumor growth and decreases mice survival: analysis of the immune response elicited

LUCÍA BOFFELLI; JEREMÍAS DUTTO; CONSTANZA MARIN; FEDERICO RUIZ MORENO; BELKYS MALETTO; MARIANA MACCIONI

Congreso; Reunión Conjunta SAIC, SAI, AAFE, NANOMED.AR 2021; 2021

CpG-ODN immunostimulation has been extensively studied in animal models for the therapeutic treatment of solid tumors and as adjuvant for the development of cancer vaccines. However, the efficacy of CpG-ODN as a prophylactic agent in reducing metastatic dissemination has been less frequently studied. Recently, it was demonstrated that a single systemic prophylactic injection of class-C CpG-ODN, administered 24 h before tumor cell injection into the cerebral circulation, was sufficient to reduce brain tumor growth (Benbenishty, A. et al., 2019). In this work, we aimed to study the effect of prophylactic class-B CpG-ODN administration in B16 melanoma tumor growth. CpG-ODN (50ug/ml) was s.c. administered on days -8, -6,-4 and -2 before s.c inoculation of 5 x 105 B16 melanoma cells and then, tumor growth was measured every other day. Pre-treatment with CpG-ODN enhanced tumor growth and reduced mice survival in two separate experiments (n=6, per group; p≤0.05). As a control, therapeutic intratumoral inoculation of CpG-ODN reduced tumor size and prolonged survival, as expected. Flow cytometry analysis of immune populations in spleen and lymph nodes performed after 4 injections of CpG-ODN and 24 h before tumor cell inoculation showed in spleen a significant decrease in the percentage of T cells (CD45+ CD3+, p=0.0016), whereas dendritic cells (CD45+ CD3- CD19- Ly6G- Ly6C- CD11c+) show non-significant changes. In contrast, the frequency of B cells (CD45+ CD19+, p=0,0035) and neutrophils (CD45+ CD3- CD19- Ly6G+ CD11b+, p=0.0019) increases suggesting a possible tumor promoting role for these populations. When tumor infiltrating lymphocyte where studied at day 15 post inoculation, an important reshaping of the tumor infiltrate was observed. Further studies should be done to decipher the immune mechanisms underlying the tumor promoting role of CpG-ODN in this model.