24 mars 2026
Zimmerman et al. BioRxiv DOI: 10.64898/2026.02.05.704029
Keywords
Immunotherapy resistance
Inflammatory monocytes
Antigen presentation
Main Findings
Efficacy of immune checkpoint inhibitors, like anti-PD-1, remains one of the biggest challenges in cancer immunotherapy. These therapies are mostly aimed at restoring the function of exhausted T cells in the tumor microenvironment. However, tumor cells often downregulate MHC class I and therefore become resistant to T cell mediated cytotoxicity. An alternative strategy is to use CD40 agonists, which broadly activate many types of antigen presenting cells such as DCs, macrophages, and B cells and drives their maturation. Together, this is thought to induce a pro-inflammatory tumor microenvironment and aid in eradicating tumors that may escape T cell killing. This preprint aims to identify mechanisms involved in mediating immunotherapy resistance due loss of antigen presentation by tumor cells. The authors use B2m-null cancer cells lines in combination with various depletion antibodies and knock-out models to characterize the immune microenvironment of antigen presentation deficient tumors and observed that:
CD40 agonist therapy in their B16 B2m-null model can control tumor growth, an effect that was dependent on both CD8+ T cell and NK cells.
IFN-γ signalling is required in host cells, but is dispensable in tumor cells, for the efficacy of CD40 agonist treatment.
IFN-γ acts on tumor-infiltrating monocytes and repolarizes them toward a pro-inflammatory state which can be linked to a better prognosis in patients treated with anti-PD-1 therapy.
Limitations & Suggestions
The authors claim that inflammatory monocytes are strongly induced and related to the efficacy of CD40 agonist treatment. This claim could be significantly strengthened by trying to deplete monocytes (e.g. CCR2KO, Ms4a3KOmice) and assess efficacy in a model lacking monocytes. Additionally, the authors cannot exclude the possibility that these monocytes differentiate into monocyte-derived DCs and the effect is DC-mediated.
In their CD40 agonist treatment the authors seem to lose DCs in the tumors, which is a bit counterintuitive since CD40 agonist should activate these cells. This should be elaborated on. Additionally, the authors should check the tumor draining lymph nodes as they are essential for effective immunotherapy and CD40 agonist treatment might have a larger effect there (especially on DCs and subsequently T cells) than in the TME. Along the same line, it could be that CD40 agonist treatment mainly induces a bystander T cell response in the lymph node that is not related to the infiltration of inflammatory monocytes.
The finding that NK cells and T cells can kill tumor cells independently of MHC-I and independently of NKG2D is only briefly touched upon. To add mechanistic detail to the preprint, it would be important to stain for other NK receptors to identify an alternative effector mechanism to MHC-I/NKG2D and IFN-γ mediated cytotoxicity. Additionally, it might be helpful to characterize the baseline changes in expression of NK ligands on the B2m-null tumor cells.
Lastly, the scoring method used to group patients could be improved by dividing the scores for pro- and anti-inflammatory monocytes rather than subtracting. This would reduce noise due to patient heterogeneity by having a ratio rather than a random number and one could group easier than placing patient scores above and below a median in the hazard ratios.
Significance/Novelty
This preprint describes the tumor microenvironment in CD40 agonist treatment in the context of tumors lacking antigen presentation. As this is a major challenge in the clinics, it is important to assess potential treatment targets that could boost efficacy of immunotherapy. While CD40 agonist treatments have not been very successful in the clinics, the combination with anti-PD-1 may yield better results and based on the results presented in this preprint, it may also be a valuable strategy to boost NK and monocyte responses to overcome resistance in tumors with MHC class I loss.
Credit
Reviewed by Teresa Neuwirth as part of a cross-institutional journal club between the Max-Delbrück Center Berlin, the Ragon Institute Boston (Mass General, MIT, Harvard), the University of Virginia, the Medical University of Vienna and other life science institutes in Vienna.