Role of a conditioned melanoma cell lysate inthe promotion of a cd8+ t cell mediated anti-tumor response

Abstract

In the tumor microenvironment, high and sustained antigen stimulation can lead to al- tered CD8 + T cell differentiation inducing a dysfunctional state so-called exhaustion. This phenomenon impedes the elimination of tumor cells, therefore impeding an effective anti-tumor response. Hence, hindering this process is key to obtain an optimal clinical response. In Chile, our laboratory developed an immunotherapy based on heat conditioned mel- anoma cell lysate loaded dendritic cells, which has had successful clinical results. Recently, we have optimized this therapy using an innovative approach through the direct inoculation of a heat-conditioned melanoma cell lysate, in conjunction with the hemocyanin derived from the Chilean mollusk concholepas concholepas as an adjuvant, called TRIMELvax vaccine. Our preclinical data showed that mice immunized with TRIMELvax show a marked decrease in the tumor growth rate using the B16-F10 murine melanoma model which was CD8+ T cell dependent. In this work, we characterized the CD8+ T cell population within the tumor site, expect- ing to understand possible mechanisms behind TRIMELvax antitumor effect. Further analysis of this CD8+ T cell population using flow cytometry showed that immunotherapy based on tumor cell lysates induced an important decrease in the expression and frequency of tumor infiltrating CD8+ T cells expressing exhaustion associated receptors such as PD-1, Lag-3 and ICOS in addition to preliminary data indicating lower levels of expression of exhaustion- associated TOX transcription factor. Unfortunately, no differences between treatments were determined when analyzing effector cytokine production (IL-2, IFN-γ and TNF-α). Remarkably, TRIMELvax vaccination not only reduced the exhaustion-associated phenotype of CD8+ tumor infiltrating lymphocytes but also increased the frequency of central memory T cells rather than effector memory T cells as observed on control mice. Interestingly, TRIMELvax promoted an increase on a naive-like phenotype on tumor infiltrating CD8+ T cells, which might have progenitor-like features which is currently being further studied. Additionally, we analyzed TRIMELvax effect modulating the tumor myeloid compartment since it’s complex interaction with tumor infiltrating CD8+ T cell population. As expected, TRIMELvax vaccination strongly increased tumor infiltrating conventional dendritic cells and in vitro promoted maturation markers expression and IL-12 production, inducing an anti-tumoral DC associated phenotype (DC3 state). Overall, this new knowledge will help elucidating possible mechanisms by which TRIMELvax boosts the antitumor response improving the development of a TRIMELvax clinical trial phase I that is currently taking place.