Low-Dose Immunotherapy: Is It Just an Illusion?

Performance of Low-Dose Immunotherapy and Standard-Dose Immunotherapy in Microsatellite Instability-High Metastatic Colorectal Cancer: Real-World Data (CLouD-High Study)

PURPOSE

Standard-dose immune checkpoint inhibitors (SD-ICIs) are the standard of care as initial therapy in microsatellite instable-high (MSI-H) advanced/metastatic colorectal adenocarcinomas (mCRC), but there are preclinical data to suggest that low-dose ICIs (LD-ICI) might also have similar efficacy.

MATERIALS AND METHODS

A retrospective study of patients with MSI-H mCRC receiving ICIs between June 2017 and January 2023 was conducted. The primary end point of the study was 12-month progression-free survival (PFS), which was computed using the Kaplan-Meier method.

RESULTS

A total of 65 patients were available for analysis during the study period. Sixty patients (92%) received nivolumab, whereas the remaining received pembrolizumab. First-line ICIs were received by 18 patients (28%), whereas 47 patients (72%) received ICIs during later lines. Thirty patients (47%) received LD-ICIs (all received nivolumab), with the remaining receiving SD-ICIs (53%). At a median follow-up of 16.5 (95% CI, 11.8 to 21.2) months, median PFS was not reached in the entire cohort. The 12-month PFS rate in the LD-ICI cohort was 90%, whereas it was 75.8% in the SD-ICI cohort. There were no statistical differences in patients receiving ICIs as first-line therapy (12 months PFS-94.4%) or during later lines of therapy (12-month PFS-77.9%; P = .56).

CONCLUSION

ICIs in the current study show survivals which are similar to those seen in seminal trials in patients with MSI-H mCRC. Low-dose ICIs appear to work in MSI-H mCRC and should be explored prospectively in clinical trials. Patients with MSI-H status should be exposed to ICIs, whether initially or later during treatment, whenever feasible.

Mitigating non-genetic resistance to checkpoint inhibition based on multiple states of immune exhaustion

Despite the revolutionary impact of immune checkpoint inhibition on cancer therapy, the lack of response in a subset of patients, as well as the emergence of resistance, remain significant challenges. Here we explore the theoretical consequences of the existence of multiple states of immune cell exhaustion on response to checkpoint inhibition therapy. In particular, we consider the emerging understanding that T cells can exist in various states: fully functioning cytotoxic cells, reversibly exhausted cells with minimal cytotoxicity, and terminally exhausted cells. We hypothesize that inflammation augmented by drug activity triggers transitions between these phenotypes, which can lead to non-genetic resistance to checkpoint inhibitors. We introduce a conceptual mathematical model, coupled with a standard 2-compartment pharmacometric (PK) model, that incorporates these mechanisms. Simulations of the model reveal that, within this framework, the emergence of resistance to checkpoint inhibitors can be mitigated through altering the dose and the frequency of administration. Our analysis also reveals that standard PK metrics do not correlate with treatment outcome. However, we do find that levels of inflammation that we assume trigger the transition from the reversibly to terminally exhausted states play a critical role in therapeutic outcome. A simulation of a population that has different values of this transition threshold reveals that while the standard high-dose, low-frequency dosing strategy can be an effective therapeutic design for some, it is likely to fail a significant fraction of the population. Conversely, a metronomic-like strategy that distributes a fixed amount of drug over many doses given close together is predicted to be effective across the entire simulated population, even at a relatively low cumulative drug dose. We also demonstrate that these predictions hold if the transitions between different states of immune cell exhaustion are triggered by prolonged antigen exposure, an alternative mechanism that has been implicated in this process. Our theoretical analyses demonstrate the potential of mitigating resistance to checkpoint inhibitors via dose modulation.