LAUSR

Checkpoint inhibitors (CIs) are active in many types of cancer. However, only a minority of patients achieve complete and/or long-lasting responses. We studied the effects of 4 different doses of 3 widely-used, orally-active chemotherapeutics (vinorelbine, V, cyclophosphamide, C, and 5FU) over local and metastatic tumor growth, and over the landscape of circulating and tumor-infiltrating immune cells. V, C and 5-FU were given alone or with anti-PD-1 or anti-PD-L1 CIs. Immunocompetent Balb/c mice were used to generate orthotopic models of breast cancer (BC, 4T1 cells) and B-cell lymphoma (NHL, A20 cells). V, C and 5-FU were administered at low-dose metronomic, medium, or maximum tolerable dosages. V and and C increased circulating monocytes, 5-FU reduced circulating monocytes. C increased MDSC count. C and 5-FU reduced circulating APCs, V increased circulating APCs. V and C reduced circulating Tregs. C at low doses and 5-FU increased circulating Tregs. C reduced circulating CD3+CD4+ and CD3+CD8+ T cells. V slightly reduced CD3+CD4+ T cells. V, C, and 5-FU reduced circulating B cells, with C showing the most significant effect. V reduced NK cells, C and 5-FU increased circulating NKs. In both BC and NHL models, anti-PD-L1 was significantly more effective than anti-PD-1. In BC models V, C and 5-FU were effective in reducing local and metastatic tumor growth. The association of V, C and anti-PD-L1 was the most effective combinatorial regimen in terms of local and metastatic BC control. Anti-PD-L1 treatment alone increased BC-infiltrating immune cells, in particular B cells. Treatment with C alone was associated with the largest tumor infiltration by NK, CD3+CD4+ T cells and m-MDSC, and with the lowest B cell infiltration. Combinatorial treatment with C+V+anti-PD-L1 was associated with the largest intratumoral B cell count and the lowest number of CD3+CD8+PD-1+ T cells. In NHL models, the association of C and anti-PD-L1 was the most effective regimen. Anti-PD-L1 alone was associated with the largest increase in infiltrating immune cells, and in particular in B cells. C alone was associated with increased NK infiltration. V decreased the immune cell infiltrate. The addition of anti-PD-L1 to V and C increased B cell infiltrate. Taken together, our data indicate that chemotherapeutics have very complex effects on the circulating landscape of immune cells, with subtle but significant differences related to the dosage and duration of the administration of the drugs. Notably, these effects on circulating immune cells differ qualitatively and quantitatively from those observed in the intratumoral immune cell infiltrate. The present data also suggest that chemotherapy might add to the effect of CIs, even though different types and sites of cancer generate significantly different atlases of intratumoral infiltrates. Citation Format: Stefania Orecchioni, Giovanna Talarico, Valentina Labanca, Patrizia Mancuso, Francesco Bertolini. Vinorelbine, cyclophosphamide, and 5-FU effects on the circulating and intratumoral landscape of immune cells improve anti-PD-L1 efficacy in preclinical models of breast cancer and lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1017.