Immune checkpoint blockade: timing is everything.

Neoadjuvant immunotherapy effectively uses the in situ tumor as a reservoir of tumor antigens to promote systemic antitumor immunity. Studies indicate that intratumoral responses to immune checkpoint inhibitors (ICIs) are mediated by resident memory T cells cells that are sequestered in tumors and have specificity for a wide range of tumor antigens ICI treatment produces de novo priming of CD8 T cells in tumor and in tumor-draining lymph nodes, and can boost the antitumor immune response by blocking inhibitory checkpoint proteins that can turn off T cells within the tumor. Neoadjuvant ICI treatment can enhance both intratumoral and systemic antitumor immunity, including expansion of intratumoral T-cell clones which is strongly associated with pathological treatment response. Recent data have shown high rates of pathological response to neoadjuvant immunotherapy with prolongation of survival compared with adjuvant ICI therapy alone in patients with unresectable or advanced melanoma. These data suggest that removal of the reservoir of tumor-specific T cells in the tumor and draining nodes by surgical resection may remove a significant proportion of the patient's antitumor immunity with the potential to compromise ICI outcomes.