Background Immune checkpoint inhibitors (ICIs) are limited by the high incidence of immune-related adverse events (irAEs) occurring in up to 40% of solid tumor patients on anti-PD-1 monotherapy ^{1 2} and 72% in anti-CTLA-4/anti-PD-1 combination.^{3 4} These toxicities can cause treatment cessation, hospitalization and even death.^5–7 IrAEs are variable in severity, timing, onset, and remain poorly understood. Amongst the different toxicities, skin irAEs are most frequent, occur the earliest, and are correlated with a positive prognosis.^{4 8} However, there is a lack of preclinical models to study checkpoint toxicity. We evaluated a murine model of allergic contact dermatitis (contact hypersensitivity to 2,4-dinitrofluorobenzene) that is mediated by CD8+ T cells to gain a mechanistic understanding of skin checkpoint toxicity.

Methods C57BL/6 mice (n = 5 per group) were sensitized epicutaneously on shaved flank with hapten 0.5% DNFB on day -5 and elicited on their ears with DNFB on day 0. Starting four weeks later, mice were treated with either anti-programmed cell death protein (PD-1) or isotype. At the time of the first recall challenge only, mice were given either anti-PD-1 or isotype. Mice received subsequent rechallenges with DNFB to the ears and ear swelling was measured at various time points. Mice were depleted of circulating or skin CD8+ T cells by anti-CD8 mAbs from day 29 onwards, and maintained weekly, as in this model CD8+ T cells are the main hapten responder population. Samples were collected for histochemistry and analyzed by flow cytometry.

Results Our data indicate that despite the depletion of circulating T cells, anti-PD-1 recipients mount a higher initial recall response to contact agents. Higher ear swelling was observed with increased inflammation in these mice. Our data suggest anti-PD-1 can liberate local T cell responses in the absence of a contribution from blood, and may offer a model to test therapeutic interventions to alleviate peripheral immune toxicities.

Conclusions Our results suggest that this murine model of contact hypersensitivity represents a potential model for skin immune checkpoint toxicities. This model of locally-mediated inflammatory recall may advance the goal of uncoupling toxicity from efficacy in patients with immune-related adverse events.

Ethics Approval The animal study was approved by Weill Cornell Medicine’s IACUC; approval number D16-00186.

References

1. Naidoo J, Page DB, Li BT, et al. Toxicities of the anti-PD-1 and anti-PD-L1 immune checkpoint antibodies. Ann Oncol 2015;26(12):2375–91. doi: 10.1093/annonc/mdv383.

2. Belum VR, Benhuri B, Postow MA, et al. Characterisation and management of dermatologic adverse events to agents targeting the PD-1 receptor. Eur J Cancer 2016;60:12–25. doi: 10.1016/j.ejca.2016.02.010.

3. Postow MA, Sidlow R, Hellmann MD. Immune-Related Adverse Events Associated with Immune Checkpoint Blockade. N Engl J Med 2018;378(2):158–168. doi: 10.1056/NEJMra1703481.

4. Martins F, Sofiya L, Sykiotis GP, et al. Adverse effects of immune-checkpoint inhibitors: epidemiology, management and surveillance. Nat Rev Clin Oncol 2019;16(9):563–580. doi: 10.1038/s41571-019-0218-0.

5. Puzanov I, Diab A, Abdallah K, et al. Managing toxicities associated with immune checkpoint inhibitors: consensus recommendations from the society for immunotherapy of cancer (SITC) Toxicity Management Working Group. J Immunother Cancer 2017;5(1):95. doi: 10.1186/s40425-017-0300-z.

6. Wills B, Brahmer JR, Naidoo J. Treatment of complications from immune checkpoint inhibition in patients with lung cancer. Curr Treat Options Oncol 2018;19(9):46. doi: 10.1007/s11864-018-0562-9.

7. Michot JM, Bigenwald C, Champiat S, et al. Immune-related adverse events with immune checkpoint blockade: a comprehensive review. Eur J Cancer 2016;54:139–148. doi: 10.1016/j.ejca.2015.11.016.

8. Phillips GS, Wu J, Hellmann MD, et al. Treatment outcomes of immune-related cutaneous adverse events. J Clin Oncol 2019:JCO1802141. doi: 10.1200/JCO.18.02141.