Combined Gemcitabine and Immune-Checkpoint Inhibition Conquers Anti-PD-L1 Resistance in Low-Immunogenic Mismatch Repair-Deficient Tumors

Abstract

Tumors arising in the context of Lynch Syndrome or constitutional mismatch repair deficiency are hypermutated and have a good response towards immune-checkpoint inhibitors (ICIs), including α-PD-L1 antibodies. However, in most cases, resistance mechanisms evolve. To improve outcomes and prevent resistance development, combination approaches are warranted. Herein, we applied a combined regimen with an α-PD-L1 antibody and gemcitabine in a preclinical tumor model to activate endogenous antitumor immune responses. Mlh1−/− mice with established gastrointestinal tumors received the α-PD-L1 antibody (clone 6E11; 2.5 mg/kg bw, i.v., q2wx3) and gemcitabine (100 mg/kg bw, i.p., q4wx3) in mono- or combination therapy. Survival and tumor growth were recorded. Immunological changes in the blood were routinely examined via multi-color flow cytometry and complemented by ex vivo frameshift mutation analysis to identify alterations in Mlh1−/−-tumor-associated target genes. The combined therapy of α-PD-L1 and gemcitabine prolonged median overall survival of Mlh1−/− mice from four weeks in the untreated control group to 12 weeks, accompanied by therapy-induced tumor growth inhibition, as measured by [18F]-FDG PET/CT. Plasma cytokine levels of IL13, TNFα, and MIP1β were increased and also higher than in mice receiving either monotherapy. Circulating splenic and intratumoral myeloid-derived suppressor cells (MDSCs), as well as M2 macrophages, were markedly reduced. Besides, residual tumor specimens from combi-treated mice had increased numbers of infiltrating cytotoxic T-cells. Frameshift mutations in APC, Tmem60, and Casc3 were no longer detectable upon treatment, likely because of the successful eradication of single mutated cell clones. By contrast, novel mutations appeared. Collectively, we herein confirm the safe application of combined chemo-immunotherapy by long-term tumor growth control to prevent the development of resistance mechanisms.

Targeting myeloid-derived suppressor cells to attenuate vasculogenic mimicry and synergistically enhance the anti-tumor effect of PD-1 inhibitor

“…MDSC is one of the important factors in the tumor immunosuppressive microenvironment. An increase in MDSCs count is related to PD-1 or PD-L1 inhibitor resistance (Li et al, 2021;Olivares-Herna ´ndez et al, 2021;Salewski et al, 2021;Shi et al, 2021;Uckun, 2021). Therefore, MDSC inhibitors combined with PD-1/PD-L1 inhibitors can achieve better antitumor effects than PD-1/PD-L1 inhibitors alone.…”

Current status and advances of immunotherapy in nasopharyngeal carcinoma

“…Apart from PD-1/PD-L1 pathway, there are other co-inhibitory pathways, such as CTLA4, LAG-3, TIGIT, and TIM3, which suppress immune cell activation and avoid immune surveillance in TME, and co-stimulatory pathways including CD27/CD70, CD40/CD40 L, 4-1BB/4-1BBL, and OX40/OX4, which regulate T-cell function. 52 – 55 …”

“…[50][51][52] The immunosuppression states could be unleashed by chemotherapy (including gemcitabine, platinum, and 5-fluorouracil) by promoting antigen presentation, enhancing T-cell responses, and relieving immunosuppression in TME. 41,50,[53][54][55][56][57][58][59] Given the promising results of ICI monotherapy and preclinical evidence of the synergy between chemotherapy and ICIs, clinical exploration of the combination of ICIs with chemotherapy is required to promote the management of R/M NPC (Table 1).…”

Combination of Low-Dose Gemcitabine and PD-1 Inhibitors for Treatment in Patients With Advanced Malignancies

“…Gemcitabine also enhances CD8 + T cell and natural killer (NK) cell-mediated anti-tumor immunity through depletion of myeloid-derived suppressor cells and regulatory T cells ( 11 ). Some preclinical data provide a rationale for combining gemcitabine with ICIs ( 12 , 13 ); however, the clinical efficacy of gemcitabine combined with ICIs for treating solid tumors is not as expected. For example, in the first-line treatment of advanced non-small-cell lung cancer, progression-free survival (PFS) and overall survival (OS) in patients treated with gemcitabine combined with nivolumab did not increase compared with single drug use ( 14 ).…”