Abstract P029

A novel in vitro model to study the effect of PD1 inhibition in Hodgkin Lymphoma at a molecular level

PD1 inhibition in patients with relapsed/refractory Hodgkin Lymphoma (HL) achieves high overall response rates (ORR) ranging from 69-80%. While this result is promising, understanding the molecular mechanisms behind this therapy is crucial for maximizing its efficacy. Currently, there is no model that captures the heterogeneous HL microenvironment (TME) to study the effects of PD1 inhibitors on the immune response. Thus, we designed an in vitro model to study the impact of nivolumab (anti-PD1) on immune response by including key aspects of the HL TME. The model consists of two phases. In the initial phase, peripheral blood mononuclear cells (PBMCs) from healthy donors are co-cultured for 7 days with irradiated HL cell lines to upregulate PD1 expression. In the second part on day 7, the PBMCs are treated with nivolumab and co-cultured for 4 more days with newly irradiated HL cell lines. Two HL cell lines with opposite PDL1 expression were used, and each HL cell line was co-cultured with PBMCs from three HLA-II matched donors. Immune activation was assessed by measuring the production of IL-2 and IFNg and monitoring cell proliferation. Nivolumab significantly increased the production of activation cytokines and cell proliferation in co-cultures with PDL1+ HL cells. In untreated co-cultures, there was no IL-2 production, but nivolumab significantly increased IL-2 levels to 33-96 pg/mL. For IFNg, untreated co-cultures of two donors showed cytokine levels of 51 and 66 pg/mL, while nivolumab treatment increased levels to 276 and 390 pg/mL. The third donor's IFNg levels surged from 797 pg/mL to 2660 pg/mL with treatment. Additionally, PD1+CD4 T cell proliferation increased from an average of 11% (7-16% range) in untreated co-cultures to 21% (13-29% range) with nivolumab. In contrast, in co-cultures with PDL1-negative HL cells, cytokine levels and PD1+CD4 T cell proliferation varied among donors, without significant differences between treated and untreated groups. In short with our model we found that nivolumab enhances PD1+ CD4 T cell proliferation and stimulates the production of immune activation cytokines IL-2 and IFNg in the PDL1+ TME. This model allows for further investigation into which factors block the effect of nivolumab and can be used to test other checkpoint inhibitors prior to their use in clinical trials.